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Christian Tzolov 2025-01-28 17:23:07 +01:00 • committed by Christian Tzolov
commit 181e1f25ab
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mcp/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java Normal file
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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.client;
import java.time.Duration;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Consumer;
import java.util.function.Function;
import com.fasterxml.jackson.core.type.TypeReference;
import io.modelcontextprotocol.spec.ClientMcpTransport;
import io.modelcontextprotocol.spec.DefaultMcpSession;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpTransport;
import io.modelcontextprotocol.spec.DefaultMcpSession.NotificationHandler;
import io.modelcontextprotocol.spec.DefaultMcpSession.RequestHandler;
import io.modelcontextprotocol.spec.McpSchema.ClientCapabilities;
import io.modelcontextprotocol.spec.McpSchema.CreateMessageRequest;
import io.modelcontextprotocol.spec.McpSchema.CreateMessageResult;
import io.modelcontextprotocol.spec.McpSchema.GetPromptRequest;
import io.modelcontextprotocol.spec.McpSchema.GetPromptResult;
import io.modelcontextprotocol.spec.McpSchema.ListPromptsResult;
import io.modelcontextprotocol.spec.McpSchema.LoggingLevel;
import io.modelcontextprotocol.spec.McpSchema.LoggingMessageNotification;
import io.modelcontextprotocol.spec.McpSchema.PaginatedRequest;
import io.modelcontextprotocol.spec.McpSchema.Root;
import io.modelcontextprotocol.util.Assert;
import io.modelcontextprotocol.util.Utils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;
/**
* The Model Context Protocol (MCP) client implementation that provides asynchronous
* communication with MCP servers using Project Reactor's Mono and Flux types.
*
* <p>
* This client implements the MCP specification, enabling AI models to interact with
* external tools and resources through a standardized interface. Key features include:
* <ul>
* <li>Asynchronous communication using reactive programming patterns
* <li>Tool discovery and invocation for server-provided functionality
* <li>Resource access and management with URI-based addressing
* <li>Prompt template handling for standardized AI interactions
* <li>Real-time notifications for tools, resources, and prompts changes
* <li>Structured logging with configurable severity levels
* <li>Message sampling for AI model interactions
* </ul>
*
* <p>
* The client follows a lifecycle:
* <ol>
* <li>Initialization - Establishes connection and negotiates capabilities
* <li>Normal Operation - Handles requests and notifications
* <li>Graceful Shutdown - Ensures clean connection termination
* </ol>
*
* <p>
* This implementation uses Project Reactor for non-blocking operations, making it
* suitable for high-throughput scenarios and reactive applications. All operations return
* Mono or Flux types that can be composed into reactive pipelines.
*
* @author Dariusz Jędrzejczyk
* @author Christian Tzolov
* @see McpClient
* @see McpSchema
* @see DefaultMcpSession
*/
public class McpAsyncClient {
private static final Logger logger = LoggerFactory.getLogger(McpAsyncClient.class);
private static TypeReference<Void> VOID_TYPE_REFERENCE = new TypeReference<>() {
};
/**
* The MCP session implementation that manages bidirectional JSON-RPC communication
* between clients and servers.
*/
private final DefaultMcpSession mcpSession;
/**
* Client capabilities.
*/
private final McpSchema.ClientCapabilities clientCapabilities;
/**
* Client implementation information.
*/
private final McpSchema.Implementation clientInfo;
/**
* Server capabilities.
*/
private McpSchema.ServerCapabilities serverCapabilities;
/**
* Server implementation information.
*/
private McpSchema.Implementation serverInfo;
/**
* Roots define the boundaries of where servers can operate within the filesystem,
* allowing them to understand which directories and files they have access to.
* Servers can request the list of roots from supporting clients and receive
* notifications when that list changes.
*/
private final ConcurrentHashMap<String, Root> roots;
/**
* MCP provides a standardized way for servers to request LLM sampling ("completions"
* or "generations") from language models via clients. This flow allows clients to
* maintain control over model access, selection, and permissions while enabling
* servers to leverage AI capabilities—with no server API keys necessary. Servers can
* request text or image-based interactions and optionally include context from MCP
* servers in their prompts.
*/
private Function<CreateMessageRequest, Mono<CreateMessageResult>> samplingHandler;
/**
* Client transport implementation.
*/
private final McpTransport transport;
/**
* Supported protocol versions.
*/
private List<String> protocolVersions = List.of(McpSchema.LATEST_PROTOCOL_VERSION);
/**
* Create a new McpAsyncClient with the given transport and session request-response
* timeout.
* @param transport the transport to use.
* @param requestTimeout the session request-response timeout.
* @param features the MCP Client supported features.
*/
McpAsyncClient(ClientMcpTransport transport, Duration requestTimeout, McpClientFeatures.Async features) {
Assert.notNull(transport, "Transport must not be null");
Assert.notNull(requestTimeout, "Request timeout must not be null");
this.clientInfo = features.clientInfo();
this.clientCapabilities = features.clientCapabilities();
this.transport = transport;
this.roots = new ConcurrentHashMap<>(features.roots());
// Request Handlers
Map<String, RequestHandler<?>> requestHandlers = new HashMap<>();
// Roots List Request Handler
if (this.clientCapabilities.roots() != null) {
requestHandlers.put(McpSchema.METHOD_ROOTS_LIST, rootsListRequestHandler());
}
// Sampling Handler
if (this.clientCapabilities.sampling() != null) {
if (features.samplingHandler() == null) {
throw new McpError("Sampling handler must not be null when client capabilities include sampling");
}
this.samplingHandler = features.samplingHandler();
requestHandlers.put(McpSchema.METHOD_SAMPLING_CREATE_MESSAGE, samplingCreateMessageHandler());
}
// Notification Handlers
Map<String, NotificationHandler> notificationHandlers = new HashMap<>();
// Tools Change Notification
List<Function<List<McpSchema.Tool>, Mono<Void>>> toolsChangeConsumersFinal = new ArrayList<>();
toolsChangeConsumersFinal
.add((notification) -> Mono.fromRunnable(() -> logger.info("Tools changed: {}", notification)));
if (!Utils.isEmpty(features.toolsChangeConsumers())) {
toolsChangeConsumersFinal.addAll(features.toolsChangeConsumers());
}
notificationHandlers.put(McpSchema.METHOD_NOTIFICATION_TOOLS_LIST_CHANGED,
asyncToolsChangeNotificationHandler(toolsChangeConsumersFinal));
// Resources Change Notification
List<Function<List<McpSchema.Resource>, Mono<Void>>> resourcesChangeConsumersFinal = new ArrayList<>();
resourcesChangeConsumersFinal
.add((notification) -> Mono.fromRunnable(() -> logger.info("Resources changed: {}", notification)));
if (!Utils.isEmpty(features.resourcesChangeConsumers())) {
resourcesChangeConsumersFinal.addAll(features.resourcesChangeConsumers());
}
notificationHandlers.put(McpSchema.METHOD_NOTIFICATION_RESOURCES_LIST_CHANGED,
asyncResourcesChangeNotificationHandler(resourcesChangeConsumersFinal));
// Prompts Change Notification
List<Function<List<McpSchema.Prompt>, Mono<Void>>> promptsChangeConsumersFinal = new ArrayList<>();
promptsChangeConsumersFinal
.add((notification) -> Mono.fromRunnable(() -> logger.info("Prompts changed: {}", notification)));
if (!Utils.isEmpty(features.promptsChangeConsumers())) {
promptsChangeConsumersFinal.addAll(features.promptsChangeConsumers());
}
notificationHandlers.put(McpSchema.METHOD_NOTIFICATION_PROMPTS_LIST_CHANGED,
asyncPromptsChangeNotificationHandler(promptsChangeConsumersFinal));
// Utility Logging Notification
List<Function<LoggingMessageNotification, Mono<Void>>> loggingConsumersFinal = new ArrayList<>();
loggingConsumersFinal.add((notification) -> Mono.fromRunnable(() -> logger.info("Logging: {}", notification)));
if (!Utils.isEmpty(features.loggingConsumers())) {
loggingConsumersFinal.addAll(features.loggingConsumers());
}
notificationHandlers.put(McpSchema.METHOD_NOTIFICATION_MESSAGE,
asyncLoggingNotificationHandler(loggingConsumersFinal));
this.mcpSession = new DefaultMcpSession(requestTimeout, transport, requestHandlers, notificationHandlers);
}
// --------------------------
// Lifecycle
// --------------------------
/**
* The initialization phase MUST be the first interaction between client and server.
* During this phase, the client and server:
* <ul>
* <li>Establish protocol version compatibility</li>
* <li>Exchange and negotiate capabilities</li>
* <li>Share implementation details</li>
* </ul>
* <br/>
* The client MUST initiate this phase by sending an initialize request containing:
* <ul>
* <li>The protocol version the client supports</li>
* <li>The client's capabilities</li>
* <li>Client implementation information</li>
* </ul>
*
* The server MUST respond with its own capabilities and information:
* {@link McpSchema.ServerCapabilities}. <br/>
* After successful initialization, the client MUST send an initialized notification
* to indicate it is ready to begin normal operations.
*
* <br/>
*
* <a href=
* "https://github.com/modelcontextprotocol/specification/blob/main/docs/specification/basic/lifecycle.md#initialization">Initialization
* Spec</a>
* @return the initialize result.
*/
public Mono<McpSchema.InitializeResult> initialize() {
String latestVersion = this.protocolVersions.get(this.protocolVersions.size() - 1);
McpSchema.InitializeRequest initializeRequest = new McpSchema.InitializeRequest(// @formatter:off
latestVersion,
this.clientCapabilities,
this.clientInfo); // @formatter:on
Mono<McpSchema.InitializeResult> result = this.mcpSession.sendRequest(McpSchema.METHOD_INITIALIZE,
initializeRequest, new TypeReference<McpSchema.InitializeResult>() {
});
return result.flatMap(initializeResult -> {
this.serverCapabilities = initializeResult.capabilities();
this.serverInfo = initializeResult.serverInfo();
logger.info("Server response with Protocol: {}, Capabilities: {}, Info: {} and Instructions {}",
initializeResult.protocolVersion(), initializeResult.capabilities(), initializeResult.serverInfo(),
initializeResult.instructions());
if (!this.protocolVersions.contains(initializeResult.protocolVersion())) {
return Mono.error(new McpError(
"Unsupported protocol version from the server: " + initializeResult.protocolVersion()));
}
else {
return this.mcpSession.sendNotification(McpSchema.METHOD_NOTIFICATION_INITIALIZED, null)
.thenReturn(initializeResult);
}
});
}
/**
* Get the server capabilities that define the supported features and functionality.
* @return The server capabilities
*/
public McpSchema.ServerCapabilities getServerCapabilities() {
return this.serverCapabilities;
}
/**
* Get the server implementation information.
* @return The server implementation details
*/
public McpSchema.Implementation getServerInfo() {
return this.serverInfo;
}
/**
* Get the client capabilities that define the supported features and functionality.
* @return The client capabilities
*/
public ClientCapabilities getClientCapabilities() {
return this.clientCapabilities;
}
/**
* Get the client implementation information.
* @return The client implementation details
*/
public McpSchema.Implementation getClientInfo() {
return this.clientInfo;
}
/**
* Closes the client connection immediately.
*/
public void close() {
this.mcpSession.close();
}
/**
* Gracefully closes the client connection.
* @return A Mono that completes when the connection is closed
*/
public Mono<Void> closeGracefully() {
return this.mcpSession.closeGracefully();
}
// --------------------------
// Basic Utilites
// --------------------------
/**
* Sends a ping request to the server.
* @return A Mono that completes with the server's ping response
*/
public Mono<Object> ping() {
return this.mcpSession.sendRequest(McpSchema.METHOD_PING, null, new TypeReference<Object>() {
});
}
// --------------------------
// Roots
// --------------------------
/**
* Adds a new root to the client's root list.
* @param root The root to add
* @return A Mono that completes when the root is added and notifications are sent
*/
public Mono<Void> addRoot(Root root) {
if (root == null) {
return Mono.error(new McpError("Root must not be null"));
}
if (this.clientCapabilities.roots() == null) {
return Mono.error(new McpError("Client must be configured with roots capabilities"));
}
if (this.roots.containsKey(root.uri())) {
return Mono.error(new McpError("Root with uri '" + root.uri() + "' already exists"));
}
this.roots.put(root.uri(), root);
logger.info("Added root: {}", root);
if (this.clientCapabilities.roots().listChanged()) {
return this.rootsListChangedNotification();
}
return Mono.empty();
}
/**
* Removes a root from the client's root list.
* @param rootUri The URI of the root to remove
* @return A Mono that completes when the root is removed and notifications are sent
*/
public Mono<Void> removeRoot(String rootUri) {
if (rootUri == null) {
return Mono.error(new McpError("Root uri must not be null"));
}
if (this.clientCapabilities.roots() == null) {
return Mono.error(new McpError("Client must be configured with roots capabilities"));
}
Root removed = this.roots.remove(rootUri);
if (removed != null) {
logger.info("Removed Root: {}", rootUri);
if (this.clientCapabilities.roots().listChanged()) {
return this.rootsListChangedNotification();
}
return Mono.empty();
}
return Mono.error(new McpError("Root with uri '" + rootUri + "' not found"));
}
/**
* Manually sends a roots/list_changed notification. The addRoot and removeRoot
* methods automatically send the roots/list_changed notification.
* @return A Mono that completes when the notification is sent
*/
public Mono<Void> rootsListChangedNotification() {
return this.mcpSession.sendNotification(McpSchema.METHOD_NOTIFICATION_ROOTS_LIST_CHANGED);
}
private RequestHandler<McpSchema.ListRootsResult> rootsListRequestHandler() {
return params -> {
@SuppressWarnings("unused")
McpSchema.PaginatedRequest request = transport.unmarshalFrom(params,
new TypeReference<McpSchema.PaginatedRequest>() {
});
List<Root> roots = this.roots.values().stream().toList();
return Mono.just(new McpSchema.ListRootsResult(roots));
};
}
// --------------------------
// Sampling
// --------------------------
private RequestHandler<CreateMessageResult> samplingCreateMessageHandler() {
return params -> {
McpSchema.CreateMessageRequest request = transport.unmarshalFrom(params,
new TypeReference<McpSchema.CreateMessageRequest>() {
});
return this.samplingHandler.apply(request);
};
}
// --------------------------
// Tools
// --------------------------
private static final TypeReference<McpSchema.CallToolResult> CALL_TOOL_RESULT_TYPE_REF = new TypeReference<>() {
};
private static final TypeReference<McpSchema.ListToolsResult> LIST_TOOLS_RESULT_TYPE_REF = new TypeReference<>() {
};
/**
* Calls a tool provided by the server. Tools enable servers to expose executable
* functionality that can interact with external systems, perform computations, and
* take actions in the real world.
* @param callToolRequest The request containing: - name: The name of the tool to call
* (must match a tool name from tools/list) - arguments: Arguments that conform to the
* tool's input schema
* @return A Mono that emits the tool execution result containing: - content: List of
* content items (text, images, or embedded resources) representing the tool's output
* - isError: Boolean indicating if the execution failed (true) or succeeded
* (false/absent)
*/
public Mono<McpSchema.CallToolResult> callTool(McpSchema.CallToolRequest callToolRequest) {
return this.mcpSession.sendRequest(McpSchema.METHOD_TOOLS_CALL, callToolRequest, CALL_TOOL_RESULT_TYPE_REF);
}
/**
* Retrieves the list of all tools provided by the server.
* @return A Mono that emits the list of tools result containing: - tools: List of
* available tools, each with a name, description, and input schema - nextCursor:
* Optional cursor for pagination if more tools are available
*/
public Mono<McpSchema.ListToolsResult> listTools() {
return this.listTools(null);
}
/**
* Retrieves a paginated list of tools provided by the server.
* @param cursor Optional pagination cursor from a previous list request
* @return A Mono that emits the list of tools result containing: - tools: List of
* available tools, each with a name, description, and input schema - nextCursor:
* Optional cursor for pagination if more tools are available
*/
public Mono<McpSchema.ListToolsResult> listTools(String cursor) {
return this.mcpSession.sendRequest(McpSchema.METHOD_TOOLS_LIST, new McpSchema.PaginatedRequest(cursor),
LIST_TOOLS_RESULT_TYPE_REF);
}
/**
* Creates a notification handler for tools/list_changed notifications from the
* server. When the server's available tools change, it sends a notification to inform
* connected clients. This handler automatically fetches the updated tool list and
* distributes it to all registered consumers.
* @param toolsChangeConsumers List of consumers that will be notified when the tools
* list changes. Each consumer receives the complete updated list of tools.
* @return A NotificationHandler that processes tools/list_changed notifications by:
* 1. Fetching the current list of tools from the server 2. Distributing the updated
* list to all registered consumers 3. Handling any errors that occur during this
* process
*/
private NotificationHandler asyncToolsChangeNotificationHandler(
List<Function<List<McpSchema.Tool>, Mono<Void>>> toolsChangeConsumers) {
// TODO: params are not used yet
return params -> listTools().flatMap(listToolsResult -> Flux.fromIterable(toolsChangeConsumers)
.flatMap(consumer -> consumer.apply(listToolsResult.tools()))
.onErrorResume(error -> {
logger.error("Error handling tools list change notification", error);
return Mono.empty();
})
.then());
}
// --------------------------
// Resources
// --------------------------
private static final TypeReference<McpSchema.ListResourcesResult> LIST_RESOURCES_RESULT_TYPE_REF = new TypeReference<>() {
};
private static final TypeReference<McpSchema.ReadResourceResult> READ_RESOURCE_RESULT_TYPE_REF = new TypeReference<>() {
};
private static final TypeReference<McpSchema.ListResourceTemplatesResult> LIST_RESOURCE_TEMPLATES_RESULT_TYPE_REF = new TypeReference<>() {
};
/**
* Send a resources/list request.
* @return A Mono that completes with the list of resources result
*/
public Mono<McpSchema.ListResourcesResult> listResources() {
return this.listResources(null);
}
/**
* Send a resources/list request.
* @param cursor the cursor for pagination
* @return A Mono that completes with the list of resources result
*/
public Mono<McpSchema.ListResourcesResult> listResources(String cursor) {
return this.mcpSession.sendRequest(McpSchema.METHOD_RESOURCES_LIST, new McpSchema.PaginatedRequest(cursor),
LIST_RESOURCES_RESULT_TYPE_REF);
}
/**
* Send a resources/read request.
* @param resource the resource to read
* @return A Mono that completes with the resource content
*/
public Mono<McpSchema.ReadResourceResult> readResource(McpSchema.Resource resource) {
return this.readResource(new McpSchema.ReadResourceRequest(resource.uri()));
}
/**
* Send a resources/read request.
* @param readResourceRequest the read resource request
* @return A Mono that completes with the resource content
*/
public Mono<McpSchema.ReadResourceResult> readResource(McpSchema.ReadResourceRequest readResourceRequest) {
return this.mcpSession.sendRequest(McpSchema.METHOD_RESOURCES_READ, readResourceRequest,
READ_RESOURCE_RESULT_TYPE_REF);
}
/**
* Resource templates allow servers to expose parameterized resources using URI
* templates. Arguments may be auto-completed through the completion API.
*
* Request a list of resource templates the server has.
* @return A Mono that completes with the list of resource templates result
*/
public Mono<McpSchema.ListResourceTemplatesResult> listResourceTemplates() {
return this.listResourceTemplates(null);
}
/**
* Resource templates allow servers to expose parameterized resources using URI
* templates. Arguments may be auto-completed through the completion API.
*
* Request a list of resource templates the server has.
* @param cursor the cursor for pagination
* @return A Mono that completes with the list of resource templates result
*/
public Mono<McpSchema.ListResourceTemplatesResult> listResourceTemplates(String cursor) {
return this.mcpSession.sendRequest(McpSchema.METHOD_RESOURCES_TEMPLATES_LIST,
new McpSchema.PaginatedRequest(cursor), LIST_RESOURCE_TEMPLATES_RESULT_TYPE_REF);
}
/**
* List Changed Notification. When the list of available resources changes, servers
* that declared the listChanged capability SHOULD send a notification.
* @return A Mono that completes when the notification is sent
*/
public Mono<Void> sendResourcesListChanged() {
return this.mcpSession.sendNotification(McpSchema.METHOD_NOTIFICATION_RESOURCES_LIST_CHANGED);
}
/**
* Subscriptions. The protocol supports optional subscriptions to resource changes.
* Clients can subscribe to specific resources and receive notifications when they
* change.
*
* Send a resources/subscribe request.
* @param subscribeRequest the subscribe request contains the uri of the resource to
* subscribe to
* @return A Mono that completes when the subscription is complete
*/
public Mono<Void> subscribeResource(McpSchema.SubscribeRequest subscribeRequest) {
return this.mcpSession.sendRequest(McpSchema.METHOD_RESOURCES_SUBSCRIBE, subscribeRequest, VOID_TYPE_REFERENCE);
}
/**
* Send a resources/unsubscribe request.
* @param unsubscribeRequest the unsubscribe request contains the uri of the resource
* to unsubscribe from
* @return A Mono that completes when the unsubscription is complete
*/
public Mono<Void> unsubscribeResource(McpSchema.UnsubscribeRequest unsubscribeRequest) {
return this.mcpSession.sendRequest(McpSchema.METHOD_RESOURCES_UNSUBSCRIBE, unsubscribeRequest,
VOID_TYPE_REFERENCE);
}
private NotificationHandler asyncResourcesChangeNotificationHandler(
List<Function<List<McpSchema.Resource>, Mono<Void>>> resourcesChangeConsumers) {
return params -> listResources().flatMap(listResourcesResult -> Flux.fromIterable(resourcesChangeConsumers)
.flatMap(consumer -> consumer.apply(listResourcesResult.resources()))
.onErrorResume(error -> {
logger.error("Error handling resources list change notification", error);
return Mono.empty();
})
.then());
}
// --------------------------
// Prompts
// --------------------------
private static final TypeReference<McpSchema.ListPromptsResult> LIST_PROMPTS_RESULT_TYPE_REF = new TypeReference<>() {
};
private static final TypeReference<McpSchema.GetPromptResult> GET_PROMPT_RESULT_TYPE_REF = new TypeReference<>() {
};
/**
* List all available prompts.
* @return A Mono that completes with the list of prompts result
*/
public Mono<ListPromptsResult> listPrompts() {
return this.listPrompts(null);
}
/**
* List all available prompts.
* @param cursor the cursor for pagination
* @return A Mono that completes with the list of prompts result
*/
public Mono<ListPromptsResult> listPrompts(String cursor) {
return this.mcpSession.sendRequest(McpSchema.METHOD_PROMPT_LIST, new PaginatedRequest(cursor),
LIST_PROMPTS_RESULT_TYPE_REF);
}
/**
* Get a prompt by its id.
* @param getPromptRequest the get prompt request
* @return A Mono that completes with the get prompt result
*/
public Mono<GetPromptResult> getPrompt(GetPromptRequest getPromptRequest) {
return this.mcpSession.sendRequest(McpSchema.METHOD_PROMPT_GET, getPromptRequest, GET_PROMPT_RESULT_TYPE_REF);
}
/**
* (Server) An optional notification from the server to the client, informing it that
* the list of prompts it offers has changed. This may be issued by servers without
* any previous subscription from the client.
* @return A Mono that completes when the notification is sent
*/
public Mono<Void> promptListChangedNotification() {
return this.mcpSession.sendNotification(McpSchema.METHOD_NOTIFICATION_PROMPTS_LIST_CHANGED);
}
private NotificationHandler asyncPromptsChangeNotificationHandler(
List<Function<List<McpSchema.Prompt>, Mono<Void>>> promptsChangeConsumers) {
return params -> listPrompts().flatMap(listPromptsResult -> Flux.fromIterable(promptsChangeConsumers)
.flatMap(consumer -> consumer.apply(listPromptsResult.prompts()))
.onErrorResume(error -> {
logger.error("Error handling prompts list change notification", error);
return Mono.empty();
})
.then());
}
// --------------------------
// Logging
// --------------------------
/**
* Create a notification handler for logging notifications from the server. This
* handler automatically distributes logging messages to all registered consumers.
* @param loggingConsumers List of consumers that will be notified when a logging
* message is received. Each consumer receives the logging message notification.
* @return A NotificationHandler that processes log notifications by distributing the
* message to all registered consumers
*/
private NotificationHandler loggingNotificationHandler(
List<Consumer<LoggingMessageNotification>> loggingConsumers) {
return params -> {
McpSchema.LoggingMessageNotification loggingMessageNotification = transport.unmarshalFrom(params,
new TypeReference<McpSchema.LoggingMessageNotification>() {
});
return Mono.fromRunnable(() -> {
for (Consumer<LoggingMessageNotification> loggingConsumer : loggingConsumers) {
loggingConsumer.accept(loggingMessageNotification);
}
}).subscribeOn(Schedulers.boundedElastic()).then();
};
}
/**
* Create a notification handler for logging notifications from the server. This
* handler automatically distributes logging messages to all registered consumers.
* @param loggingConsumers List of consumers that will be notified when a logging
* message is received. Each consumer receives the logging message notification.
* @return A NotificationHandler that processes log notifications by distributing the
* message to all registered consumers
*/
private NotificationHandler asyncLoggingNotificationHandler(
List<Function<LoggingMessageNotification, Mono<Void>>> loggingConsumers) {
return params -> {
McpSchema.LoggingMessageNotification loggingMessageNotification = transport.unmarshalFrom(params,
new TypeReference<McpSchema.LoggingMessageNotification>() {
});
return Flux.fromIterable(loggingConsumers)
.flatMap(consumer -> consumer.apply(loggingMessageNotification))
.then();
};
}
/**
* Client can set the minimum logging level it wants to receive from the server.
* @param loggingLevel the min logging level
*/
public Mono<Void> setLoggingLevel(LoggingLevel loggingLevel) {
Assert.notNull(loggingLevel, "Logging level must not be null");
String levelName = this.transport.unmarshalFrom(loggingLevel, new TypeReference<String>() {
});
Map<String, Object> params = Map.of("level", levelName);
return this.mcpSession.sendNotification(McpSchema.METHOD_LOGGING_SET_LEVEL, params);
}
/**
* This method is package-private and used for test only. Should not be called by user
* code.
* @param protocolVersions the Client supported protocol versions.
*/
void setProtocolVersions(List<String> protocolVersions) {
this.protocolVersions = protocolVersions;
}
}

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mcp/src/main/java/io/modelcontextprotocol/client/McpClient.java Normal file
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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.client;
import java.time.Duration;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;
import java.util.function.Function;
import io.modelcontextprotocol.spec.ClientMcpTransport;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpTransport;
import io.modelcontextprotocol.spec.McpSchema.ClientCapabilities;
import io.modelcontextprotocol.spec.McpSchema.CreateMessageRequest;
import io.modelcontextprotocol.spec.McpSchema.CreateMessageResult;
import io.modelcontextprotocol.spec.McpSchema.Implementation;
import io.modelcontextprotocol.spec.McpSchema.Root;
import io.modelcontextprotocol.util.Assert;
import reactor.core.publisher.Mono;
/**
* Factory class for creating Model Context Protocol (MCP) clients. MCP is a protocol that
* enables AI models to interact with external tools and resources through a standardized
* interface.
*
* <p>
* This class serves as the main entry point for establishing connections with MCP
* servers, implementing the client-side of the MCP specification. The protocol follows a
* client-server architecture where:
* <ul>
* <li>The client (this implementation) initiates connections and sends requests
* <li>The server responds to requests and provides access to tools and resources
* <li>Communication occurs through a transport layer (e.g., stdio, SSE) using JSON-RPC
* 2.0
* </ul>
*
* <p>
* The class provides factory methods to create either:
* <ul>
* <li>{@link McpAsyncClient} for non-blocking operations with CompletableFuture responses
* <li>{@link McpSyncClient} for blocking operations with direct responses
* </ul>
*
* <p>
* Example of creating a basic synchronous client: <pre>{@code
* McpClient.sync(transport)
* .requestTimeout(Duration.ofSeconds(5))
* .build();
* }</pre>
*
* Example of creating a basic asynchronous client: <pre>{@code
* McpClient.async(transport)
* .requestTimeout(Duration.ofSeconds(5))
* .build();
* }</pre>
*
* <p>
* Example with advanced asynchronous configuration: <pre>{@code
* McpClient.async(transport)
* .requestTimeout(Duration.ofSeconds(10))
* .capabilities(new ClientCapabilities(...))
* .clientInfo(new Implementation("My Client", "1.0.0"))
* .roots(new Root("file://workspace", "Workspace Files"))
* .toolsChangeConsumer(tools -> Mono.fromRunnable(() -> System.out.println("Tools updated: " + tools)))
* .resourcesChangeConsumer(resources -> Mono.fromRunnable(() -> System.out.println("Resources updated: " + resources)))
* .promptsChangeConsumer(prompts -> Mono.fromRunnable(() -> System.out.println("Prompts updated: " + prompts)))
* .loggingConsumer(message -> Mono.fromRunnable(() -> System.out.println("Log message: " + message)))
* .build();
* }</pre>
*
* <p>
* The client supports:
* <ul>
* <li>Tool discovery and invocation
* <li>Resource access and management
* <li>Prompt template handling
* <li>Real-time updates through change consumers
* <li>Custom sampling strategies
* <li>Structured logging with severity levels
* </ul>
*
* <p>
* The client supports structured logging through the MCP logging utility:
* <ul>
* <li>Eight severity levels from DEBUG to EMERGENCY
* <li>Optional logger name categorization
* <li>Configurable logging consumers
* <li>Server-controlled minimum log level
* </ul>
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
* @see McpAsyncClient
* @see McpSyncClient
* @see McpTransport
*/
public interface McpClient {
/**
* Start building a synchronous MCP client with the specified transport layer. The
* synchronous MCP client provides blocking operations. Synchronous clients wait for
* each operation to complete before returning, making them simpler to use but
* potentially less performant for concurrent operations. The transport layer handles
* the low-level communication between client and server using protocols like stdio or
* Server-Sent Events (SSE).
* @param transport The transport layer implementation for MCP communication. Common
* implementations include {@code StdioClientTransport} for stdio-based communication
* and {@code SseClientTransport} for SSE-based communication.
* @return A new builder instance for configuring the client
* @throws IllegalArgumentException if transport is null
*/
static SyncSpec sync(ClientMcpTransport transport) {
return new SyncSpec(transport);
}
/**
* Start building an asynchronous MCP client with the specified transport layer. The
* asynchronous MCP client provides non-blocking operations. Asynchronous clients
* return reactive primitives (Mono/Flux) immediately, allowing for concurrent
* operations and reactive programming patterns. The transport layer handles the
* low-level communication between client and server using protocols like stdio or
* Server-Sent Events (SSE).
* @param transport The transport layer implementation for MCP communication. Common
* implementations include {@code StdioClientTransport} for stdio-based communication
* and {@code SseClientTransport} for SSE-based communication.
* @return A new builder instance for configuring the client
* @throws IllegalArgumentException if transport is null
*/
static AsyncSpec async(ClientMcpTransport transport) {
return new AsyncSpec(transport);
}
/**
* Synchronous client specification. This class follows the builder pattern to provide
* a fluent API for setting up clients with custom configurations.
*
* <p>
* The builder supports configuration of:
* <ul>
* <li>Transport layer for client-server communication
* <li>Request timeouts for operation boundaries
* <li>Client capabilities for feature negotiation
* <li>Client implementation details for version tracking
* <li>Root URIs for resource access
* <li>Change notification handlers for tools, resources, and prompts
* <li>Custom message sampling logic
* </ul>
*/
class SyncSpec {
private final ClientMcpTransport transport;
private Duration requestTimeout = Duration.ofSeconds(20); // Default timeout
private ClientCapabilities capabilities;
private Implementation clientInfo = new Implementation("Java SDK MCP Client", "1.0.0");
private final Map<String, Root> roots = new HashMap<>();
private final List<Consumer<List<McpSchema.Tool>>> toolsChangeConsumers = new ArrayList<>();
private final List<Consumer<List<McpSchema.Resource>>> resourcesChangeConsumers = new ArrayList<>();
private final List<Consumer<List<McpSchema.Prompt>>> promptsChangeConsumers = new ArrayList<>();
private final List<Consumer<McpSchema.LoggingMessageNotification>> loggingConsumers = new ArrayList<>();
private Function<CreateMessageRequest, CreateMessageResult> samplingHandler;
private SyncSpec(ClientMcpTransport transport) {
Assert.notNull(transport, "Transport must not be null");
this.transport = transport;
}
/**
* Sets the duration to wait for server responses before timing out requests. This
* timeout applies to all requests made through the client, including tool calls,
* resource access, and prompt operations.
* @param requestTimeout The duration to wait before timing out requests. Must not
* be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if requestTimeout is null
*/
public SyncSpec requestTimeout(Duration requestTimeout) {
Assert.notNull(requestTimeout, "Request timeout must not be null");
this.requestTimeout = requestTimeout;
return this;
}
/**
* Sets the client capabilities that will be advertised to the server during
* connection initialization. Capabilities define what features the client
* supports, such as tool execution, resource access, and prompt handling.
* @param capabilities The client capabilities configuration. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if capabilities is null
*/
public SyncSpec capabilities(ClientCapabilities capabilities) {
Assert.notNull(capabilities, "Capabilities must not be null");
this.capabilities = capabilities;
return this;
}
/**
* Sets the client implementation information that will be shared with the server
* during connection initialization. This helps with version compatibility and
* debugging.
* @param clientInfo The client implementation details including name and version.
* Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if clientInfo is null
*/
public SyncSpec clientInfo(Implementation clientInfo) {
Assert.notNull(clientInfo, "Client info must not be null");
this.clientInfo = clientInfo;
return this;
}
/**
* Sets the root URIs that this client can access. Roots define the base URIs for
* resources that the client can request from the server. For example, a root
* might be "file://workspace" for accessing workspace files.
* @param roots A list of root definitions. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if roots is null
*/
public SyncSpec roots(List<Root> roots) {
Assert.notNull(roots, "Roots must not be null");
for (Root root : roots) {
this.roots.put(root.uri(), root);
}
return this;
}
/**
* Sets the root URIs that this client can access, using a varargs parameter for
* convenience. This is an alternative to {@link #roots(List)}.
* @param roots An array of root definitions. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if roots is null
* @see #roots(List)
*/
public SyncSpec roots(Root... roots) {
Assert.notNull(roots, "Roots must not be null");
for (Root root : roots) {
this.roots.put(root.uri(), root);
}
return this;
}
/**
* Sets a custom sampling handler for processing message creation requests. The
* sampling handler can modify or validate messages before they are sent to the
* server, enabling custom processing logic.
* @param samplingHandler A function that processes message requests and returns
* results. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if samplingHandler is null
*/
public SyncSpec sampling(Function<CreateMessageRequest, CreateMessageResult> samplingHandler) {
Assert.notNull(samplingHandler, "Sampling handler must not be null");
this.samplingHandler = samplingHandler;
return this;
}
/**
* Adds a consumer to be notified when the available tools change. This allows the
* client to react to changes in the server's tool capabilities, such as tools
* being added or removed.
* @param toolsChangeConsumer A consumer that receives the updated list of
* available tools. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if toolsChangeConsumer is null
*/
public SyncSpec toolsChangeConsumer(Consumer<List<McpSchema.Tool>> toolsChangeConsumer) {
Assert.notNull(toolsChangeConsumer, "Tools change consumer must not be null");
this.toolsChangeConsumers.add(toolsChangeConsumer);
return this;
}
/**
* Adds a consumer to be notified when the available resources change. This allows
* the client to react to changes in the server's resource availability, such as
* files being added or removed.
* @param resourcesChangeConsumer A consumer that receives the updated list of
* available resources. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if resourcesChangeConsumer is null
*/
public SyncSpec resourcesChangeConsumer(Consumer<List<McpSchema.Resource>> resourcesChangeConsumer) {
Assert.notNull(resourcesChangeConsumer, "Resources change consumer must not be null");
this.resourcesChangeConsumers.add(resourcesChangeConsumer);
return this;
}
/**
* Adds a consumer to be notified when the available prompts change. This allows
* the client to react to changes in the server's prompt templates, such as new
* templates being added or existing ones being modified.
* @param promptsChangeConsumer A consumer that receives the updated list of
* available prompts. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if promptsChangeConsumer is null
*/
public SyncSpec promptsChangeConsumer(Consumer<List<McpSchema.Prompt>> promptsChangeConsumer) {
Assert.notNull(promptsChangeConsumer, "Prompts change consumer must not be null");
this.promptsChangeConsumers.add(promptsChangeConsumer);
return this;
}
/**
* Adds a consumer to be notified when logging messages are received from the
* server. This allows the client to react to log messages, such as warnings or
* errors, that are sent by the server.
* @param loggingConsumer A consumer that receives logging messages. Must not be
* null.
* @return This builder instance for method chaining
*/
public SyncSpec loggingConsumer(Consumer<McpSchema.LoggingMessageNotification> loggingConsumer) {
Assert.notNull(loggingConsumer, "Logging consumer must not be null");
this.loggingConsumers.add(loggingConsumer);
return this;
}
/**
* Adds multiple consumers to be notified when logging messages are received from
* the server. This allows the client to react to log messages, such as warnings
* or errors, that are sent by the server.
* @param loggingConsumers A list of consumers that receive logging messages. Must
* not be null.
* @return This builder instance for method chaining
*/
public SyncSpec loggingConsumers(List<Consumer<McpSchema.LoggingMessageNotification>> loggingConsumers) {
Assert.notNull(loggingConsumers, "Logging consumers must not be null");
this.loggingConsumers.addAll(loggingConsumers);
return this;
}
/**
* Create an instance of {@link McpSyncClient} with the provided configurations or
* sensible defaults.
* @return a new instance of {@link McpSyncClient}.
*/
public McpSyncClient build() {
McpClientFeatures.Sync syncFeatures = new McpClientFeatures.Sync(this.clientInfo, this.capabilities,
this.roots, this.toolsChangeConsumers, this.resourcesChangeConsumers, this.promptsChangeConsumers,
this.loggingConsumers, this.samplingHandler);
McpClientFeatures.Async asyncFeatures = McpClientFeatures.Async.fromSync(syncFeatures);
return new McpSyncClient(new McpAsyncClient(transport, this.requestTimeout, asyncFeatures));
}
}
/**
* Asynchronous client specification. This class follows the builder pattern to
* provide a fluent API for setting up clients with custom configurations.
*
* <p>
* The builder supports configuration of:
* <ul>
* <li>Transport layer for client-server communication
* <li>Request timeouts for operation boundaries
* <li>Client capabilities for feature negotiation
* <li>Client implementation details for version tracking
* <li>Root URIs for resource access
* <li>Change notification handlers for tools, resources, and prompts
* <li>Custom message sampling logic
* </ul>
*/
class AsyncSpec {
private final ClientMcpTransport transport;
private Duration requestTimeout = Duration.ofSeconds(20); // Default timeout
private ClientCapabilities capabilities;
private Implementation clientInfo = new Implementation("Spring AI MCP Client", "0.3.1");
private final Map<String, Root> roots = new HashMap<>();
private final List<Function<List<McpSchema.Tool>, Mono<Void>>> toolsChangeConsumers = new ArrayList<>();
private final List<Function<List<McpSchema.Resource>, Mono<Void>>> resourcesChangeConsumers = new ArrayList<>();
private final List<Function<List<McpSchema.Prompt>, Mono<Void>>> promptsChangeConsumers = new ArrayList<>();
private final List<Function<McpSchema.LoggingMessageNotification, Mono<Void>>> loggingConsumers = new ArrayList<>();
private Function<CreateMessageRequest, Mono<CreateMessageResult>> samplingHandler;
private AsyncSpec(ClientMcpTransport transport) {
Assert.notNull(transport, "Transport must not be null");
this.transport = transport;
}
/**
* Sets the duration to wait for server responses before timing out requests. This
* timeout applies to all requests made through the client, including tool calls,
* resource access, and prompt operations.
* @param requestTimeout The duration to wait before timing out requests. Must not
* be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if requestTimeout is null
*/
public AsyncSpec requestTimeout(Duration requestTimeout) {
Assert.notNull(requestTimeout, "Request timeout must not be null");
this.requestTimeout = requestTimeout;
return this;
}
/**
* Sets the client capabilities that will be advertised to the server during
* connection initialization. Capabilities define what features the client
* supports, such as tool execution, resource access, and prompt handling.
* @param capabilities The client capabilities configuration. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if capabilities is null
*/
public AsyncSpec capabilities(ClientCapabilities capabilities) {
Assert.notNull(capabilities, "Capabilities must not be null");
this.capabilities = capabilities;
return this;
}
/**
* Sets the client implementation information that will be shared with the server
* during connection initialization. This helps with version compatibility and
* debugging.
* @param clientInfo The client implementation details including name and version.
* Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if clientInfo is null
*/
public AsyncSpec clientInfo(Implementation clientInfo) {
Assert.notNull(clientInfo, "Client info must not be null");
this.clientInfo = clientInfo;
return this;
}
/**
* Sets the root URIs that this client can access. Roots define the base URIs for
* resources that the client can request from the server. For example, a root
* might be "file://workspace" for accessing workspace files.
* @param roots A list of root definitions. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if roots is null
*/
public AsyncSpec roots(List<Root> roots) {
Assert.notNull(roots, "Roots must not be null");
for (Root root : roots) {
this.roots.put(root.uri(), root);
}
return this;
}
/**
* Sets the root URIs that this client can access, using a varargs parameter for
* convenience. This is an alternative to {@link #roots(List)}.
* @param roots An array of root definitions. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if roots is null
* @see #roots(List)
*/
public AsyncSpec roots(Root... roots) {
Assert.notNull(roots, "Roots must not be null");
for (Root root : roots) {
this.roots.put(root.uri(), root);
}
return this;
}
/**
* Sets a custom sampling handler for processing message creation requests. The
* sampling handler can modify or validate messages before they are sent to the
* server, enabling custom processing logic.
* @param samplingHandler A function that processes message requests and returns
* results. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if samplingHandler is null
*/
public AsyncSpec sampling(Function<CreateMessageRequest, Mono<CreateMessageResult>> samplingHandler) {
Assert.notNull(samplingHandler, "Sampling handler must not be null");
this.samplingHandler = samplingHandler;
return this;
}
/**
* Adds a consumer to be notified when the available tools change. This allows the
* client to react to changes in the server's tool capabilities, such as tools
* being added or removed.
* @param toolsChangeConsumer A consumer that receives the updated list of
* available tools. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if toolsChangeConsumer is null
*/
public AsyncSpec toolsChangeConsumer(Function<List<McpSchema.Tool>, Mono<Void>> toolsChangeConsumer) {
Assert.notNull(toolsChangeConsumer, "Tools change consumer must not be null");
this.toolsChangeConsumers.add(toolsChangeConsumer);
return this;
}
/**
* Adds a consumer to be notified when the available resources change. This allows
* the client to react to changes in the server's resource availability, such as
* files being added or removed.
* @param resourcesChangeConsumer A consumer that receives the updated list of
* available resources. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if resourcesChangeConsumer is null
*/
public AsyncSpec resourcesChangeConsumer(
Function<List<McpSchema.Resource>, Mono<Void>> resourcesChangeConsumer) {
Assert.notNull(resourcesChangeConsumer, "Resources change consumer must not be null");
this.resourcesChangeConsumers.add(resourcesChangeConsumer);
return this;
}
/**
* Adds a consumer to be notified when the available prompts change. This allows
* the client to react to changes in the server's prompt templates, such as new
* templates being added or existing ones being modified.
* @param promptsChangeConsumer A consumer that receives the updated list of
* available prompts. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if promptsChangeConsumer is null
*/
public AsyncSpec promptsChangeConsumer(Function<List<McpSchema.Prompt>, Mono<Void>> promptsChangeConsumer) {
Assert.notNull(promptsChangeConsumer, "Prompts change consumer must not be null");
this.promptsChangeConsumers.add(promptsChangeConsumer);
return this;
}
/**
* Adds a consumer to be notified when logging messages are received from the
* server. This allows the client to react to log messages, such as warnings or
* errors, that are sent by the server.
* @param loggingConsumer A consumer that receives logging messages. Must not be
* null.
* @return This builder instance for method chaining
*/
public AsyncSpec loggingConsumer(Function<McpSchema.LoggingMessageNotification, Mono<Void>> loggingConsumer) {
Assert.notNull(loggingConsumer, "Logging consumer must not be null");
this.loggingConsumers.add(loggingConsumer);
return this;
}
/**
* Adds multiple consumers to be notified when logging messages are received from
* the server. This allows the client to react to log messages, such as warnings
* or errors, that are sent by the server.
* @param loggingConsumers A list of consumers that receive logging messages. Must
* not be null.
* @return This builder instance for method chaining
*/
public AsyncSpec loggingConsumers(
List<Function<McpSchema.LoggingMessageNotification, Mono<Void>>> loggingConsumers) {
Assert.notNull(loggingConsumers, "Logging consumers must not be null");
this.loggingConsumers.addAll(loggingConsumers);
return this;
}
/**
* Create an instance of {@link McpAsyncClient} with the provided configurations
* or sensible defaults.
* @return a new instance of {@link McpAsyncClient}.
*/
public McpAsyncClient build() {
return new McpAsyncClient(this.transport, this.requestTimeout,
new McpClientFeatures.Async(this.clientInfo, this.capabilities, this.roots,
this.toolsChangeConsumers, this.resourcesChangeConsumers, this.promptsChangeConsumers,
this.loggingConsumers, this.samplingHandler));
}
}
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.client;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Consumer;
import java.util.function.Function;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.util.Assert;
import io.modelcontextprotocol.util.Utils;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;
/**
* Representation of features and capabilities for Model Context Protocol (MCP) clients.
* This class provides two record types for managing client features:
* <ul>
* <li>{@link Async} for non-blocking operations with Project Reactor's Mono responses
* <li>{@link Sync} for blocking operations with direct responses
* </ul>
*
* <p>
* Each feature specification includes:
* <ul>
* <li>Client implementation information and capabilities
* <li>Root URI mappings for resource access
* <li>Change notification handlers for tools, resources, and prompts
* <li>Logging message consumers
* <li>Message sampling handlers for request processing
* </ul>
*
* <p>
* The class supports conversion between synchronous and asynchronous specifications
* through the {@link Async#fromSync} method, which ensures proper handling of blocking
* operations in non-blocking contexts by scheduling them on a bounded elastic scheduler.
*
* @author Dariusz Jędrzejczyk
* @see McpClient
* @see McpSchema.Implementation
* @see McpSchema.ClientCapabilities
*/
class McpClientFeatures {
/**
* Asynchronous client features specification providing the capabilities and request
* and notification handlers.
*
* @param clientInfo the client implementation information.
* @param clientCapabilities the client capabilities.
* @param roots the roots.
* @param toolsChangeConsumers the tools change consumers.
* @param resourcesChangeConsumers the resources change consumers.
* @param promptsChangeConsumers the prompts change consumers.
* @param loggingConsumers the logging consumers.
* @param samplingHandler the sampling handler.
*/
record Async(McpSchema.Implementation clientInfo, McpSchema.ClientCapabilities clientCapabilities,
Map<String, McpSchema.Root> roots, List<Function<List<McpSchema.Tool>, Mono<Void>>> toolsChangeConsumers,
List<Function<List<McpSchema.Resource>, Mono<Void>>> resourcesChangeConsumers,
List<Function<List<McpSchema.Prompt>, Mono<Void>>> promptsChangeConsumers,
List<Function<McpSchema.LoggingMessageNotification, Mono<Void>>> loggingConsumers,
Function<McpSchema.CreateMessageRequest, Mono<McpSchema.CreateMessageResult>> samplingHandler) {
/**
* Create an instance and validate the arguments.
* @param clientCapabilities the client capabilities.
* @param roots the roots.
* @param toolsChangeConsumers the tools change consumers.
* @param resourcesChangeConsumers the resources change consumers.
* @param promptsChangeConsumers the prompts change consumers.
* @param loggingConsumers the logging consumers.
* @param samplingHandler the sampling handler.
*/
public Async(McpSchema.Implementation clientInfo, McpSchema.ClientCapabilities clientCapabilities,
Map<String, McpSchema.Root> roots,
List<Function<List<McpSchema.Tool>, Mono<Void>>> toolsChangeConsumers,
List<Function<List<McpSchema.Resource>, Mono<Void>>> resourcesChangeConsumers,
List<Function<List<McpSchema.Prompt>, Mono<Void>>> promptsChangeConsumers,
List<Function<McpSchema.LoggingMessageNotification, Mono<Void>>> loggingConsumers,
Function<McpSchema.CreateMessageRequest, Mono<McpSchema.CreateMessageResult>> samplingHandler) {
Assert.notNull(clientInfo, "Client info must not be null");
this.clientInfo = clientInfo;
this.clientCapabilities = (clientCapabilities != null) ? clientCapabilities
: new McpSchema.ClientCapabilities(null,
!Utils.isEmpty(roots) ? new McpSchema.ClientCapabilities.RootCapabilities(false) : null,
samplingHandler != null ? new McpSchema.ClientCapabilities.Sampling() : null);
this.roots = roots != null ? new ConcurrentHashMap<>(roots) : new ConcurrentHashMap<>();
this.toolsChangeConsumers = toolsChangeConsumers != null ? toolsChangeConsumers : List.of();
this.resourcesChangeConsumers = resourcesChangeConsumers != null ? resourcesChangeConsumers : List.of();
this.promptsChangeConsumers = promptsChangeConsumers != null ? promptsChangeConsumers : List.of();
this.loggingConsumers = loggingConsumers != null ? loggingConsumers : List.of();
this.samplingHandler = samplingHandler;
}
/**
* Convert a synchronous specification into an asynchronous one and provide
* blocking code offloading to prevent accidental blocking of the non-blocking
* transport.
* @param syncSpec a potentially blocking, synchronous specification.
* @return a specification which is protected from blocking calls specified by the
* user.
*/
public static Async fromSync(Sync syncSpec) {
List<Function<List<McpSchema.Tool>, Mono<Void>>> toolsChangeConsumers = new ArrayList<>();
for (Consumer<List<McpSchema.Tool>> consumer : syncSpec.toolsChangeConsumers()) {
toolsChangeConsumers.add(t -> Mono.<Void>fromRunnable(() -> consumer.accept(t))
.subscribeOn(Schedulers.boundedElastic()));
}
List<Function<List<McpSchema.Resource>, Mono<Void>>> resourcesChangeConsumers = new ArrayList<>();
for (Consumer<List<McpSchema.Resource>> consumer : syncSpec.resourcesChangeConsumers()) {
resourcesChangeConsumers.add(r -> Mono.<Void>fromRunnable(() -> consumer.accept(r))
.subscribeOn(Schedulers.boundedElastic()));
}
List<Function<List<McpSchema.Prompt>, Mono<Void>>> promptsChangeConsumers = new ArrayList<>();
for (Consumer<List<McpSchema.Prompt>> consumer : syncSpec.promptsChangeConsumers()) {
promptsChangeConsumers.add(p -> Mono.<Void>fromRunnable(() -> consumer.accept(p))
.subscribeOn(Schedulers.boundedElastic()));
}
List<Function<McpSchema.LoggingMessageNotification, Mono<Void>>> loggingConsumers = new ArrayList<>();
for (Consumer<McpSchema.LoggingMessageNotification> consumer : syncSpec.loggingConsumers()) {
loggingConsumers.add(l -> Mono.<Void>fromRunnable(() -> consumer.accept(l))
.subscribeOn(Schedulers.boundedElastic()));
}
Function<McpSchema.CreateMessageRequest, Mono<McpSchema.CreateMessageResult>> samplingHandler = r -> Mono
.fromCallable(() -> syncSpec.samplingHandler().apply(r))
.subscribeOn(Schedulers.boundedElastic());
return new Async(syncSpec.clientInfo(), syncSpec.clientCapabilities(), syncSpec.roots(),
toolsChangeConsumers, resourcesChangeConsumers, promptsChangeConsumers, loggingConsumers,
samplingHandler);
}
}
/**
* Synchronous client features specification providing the capabilities and request
* and notification handlers.
*
* @param clientInfo the client implementation information.
* @param clientCapabilities the client capabilities.
* @param roots the roots.
* @param toolsChangeConsumers the tools change consumers.
* @param resourcesChangeConsumers the resources change consumers.
* @param promptsChangeConsumers the prompts change consumers.
* @param loggingConsumers the logging consumers.
* @param samplingHandler the sampling handler.
*/
public record Sync(McpSchema.Implementation clientInfo, McpSchema.ClientCapabilities clientCapabilities,
Map<String, McpSchema.Root> roots, List<Consumer<List<McpSchema.Tool>>> toolsChangeConsumers,
List<Consumer<List<McpSchema.Resource>>> resourcesChangeConsumers,
List<Consumer<List<McpSchema.Prompt>>> promptsChangeConsumers,
List<Consumer<McpSchema.LoggingMessageNotification>> loggingConsumers,
Function<McpSchema.CreateMessageRequest, McpSchema.CreateMessageResult> samplingHandler) {
/**
* Create an instance and validate the arguments.
* @param clientInfo the client implementation information.
* @param clientCapabilities the client capabilities.
* @param roots the roots.
* @param toolsChangeConsumers the tools change consumers.
* @param resourcesChangeConsumers the resources change consumers.
* @param promptsChangeConsumers the prompts change consumers.
* @param loggingConsumers the logging consumers.
* @param samplingHandler the sampling handler.
*/
public Sync(McpSchema.Implementation clientInfo, McpSchema.ClientCapabilities clientCapabilities,
Map<String, McpSchema.Root> roots, List<Consumer<List<McpSchema.Tool>>> toolsChangeConsumers,
List<Consumer<List<McpSchema.Resource>>> resourcesChangeConsumers,
List<Consumer<List<McpSchema.Prompt>>> promptsChangeConsumers,
List<Consumer<McpSchema.LoggingMessageNotification>> loggingConsumers,
Function<McpSchema.CreateMessageRequest, McpSchema.CreateMessageResult> samplingHandler) {
Assert.notNull(clientInfo, "Client info must not be null");
this.clientInfo = clientInfo;
this.clientCapabilities = (clientCapabilities != null) ? clientCapabilities
: new McpSchema.ClientCapabilities(null,
!Utils.isEmpty(roots) ? new McpSchema.ClientCapabilities.RootCapabilities(false) : null,
samplingHandler != null ? new McpSchema.ClientCapabilities.Sampling() : null);
this.roots = roots != null ? new HashMap<>(roots) : new HashMap<>();
this.toolsChangeConsumers = toolsChangeConsumers != null ? toolsChangeConsumers : List.of();
this.resourcesChangeConsumers = resourcesChangeConsumers != null ? resourcesChangeConsumers : List.of();
this.promptsChangeConsumers = promptsChangeConsumers != null ? promptsChangeConsumers : List.of();
this.loggingConsumers = loggingConsumers != null ? loggingConsumers : List.of();
this.samplingHandler = samplingHandler;
}
}
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.client;
import java.time.Duration;
import io.modelcontextprotocol.spec.ClientMcpTransport;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.ClientCapabilities;
import io.modelcontextprotocol.spec.McpSchema.GetPromptRequest;
import io.modelcontextprotocol.spec.McpSchema.GetPromptResult;
import io.modelcontextprotocol.spec.McpSchema.ListPromptsResult;
import io.modelcontextprotocol.util.Assert;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A synchronous client implementation for the Model Context Protocol (MCP) that wraps an
* {@link McpAsyncClient} to provide blocking operations.
*
* <p>
* This client implements the MCP specification by delegating to an asynchronous client
* and blocking on the results. Key features include:
* <ul>
* <li>Synchronous, blocking API for simpler integration in non-reactive applications
* <li>Tool discovery and invocation for server-provided functionality
* <li>Resource access and management with URI-based addressing
* <li>Prompt template handling for standardized AI interactions
* <li>Real-time notifications for tools, resources, and prompts changes
* <li>Structured logging with configurable severity levels
* </ul>
*
* <p>
* The client follows the same lifecycle as its async counterpart:
* <ol>
* <li>Initialization - Establishes connection and negotiates capabilities
* <li>Normal Operation - Handles requests and notifications
* <li>Graceful Shutdown - Ensures clean connection termination
* </ol>
*
* <p>
* This implementation implements {@link AutoCloseable} for resource cleanup and provides
* both immediate and graceful shutdown options. All operations block until completion or
* timeout, making it suitable for traditional synchronous programming models.
*
* @author Dariusz Jędrzejczyk
* @author Christian Tzolov
* @see McpClient
* @see McpAsyncClient
* @see McpSchema
*/
public class McpSyncClient implements AutoCloseable {
private static final Logger logger = LoggerFactory.getLogger(McpSyncClient.class);
// TODO: Consider providing a client config to set this properly
// this is currently a concern only because AutoCloseable is used - perhaps it
// is not a requirement?
private static final long DEFAULT_CLOSE_TIMEOUT_MS = 10_000L;
private final McpAsyncClient delegate;
/**
* Create a new McpSyncClient with the given delegate.
* @param delegate the asynchronous kernel on top of which this synchronous client
* provides a blocking API.
* @deprecated Use {@link McpClient#sync(ClientMcpTransport)} to obtain an instance.
*/
@Deprecated
// TODO make the constructor package private post-deprecation
public McpSyncClient(McpAsyncClient delegate) {
Assert.notNull(delegate, "The delegate can not be null");
this.delegate = delegate;
}
/**
* Get the server capabilities that define the supported features and functionality.
* @return The server capabilities
*/
public McpSchema.ServerCapabilities getServerCapabilities() {
return this.delegate.getServerCapabilities();
}
/**
* Get the server implementation information.
* @return The server implementation details
*/
public McpSchema.Implementation getServerInfo() {
return this.delegate.getServerInfo();
}
/**
* Get the client capabilities that define the supported features and functionality.
* @return The client capabilities
*/
public ClientCapabilities getClientCapabilities() {
return this.delegate.getClientCapabilities();
}
/**
* Get the client implementation information.
* @return The client implementation details
*/
public McpSchema.Implementation getClientInfo() {
return this.delegate.getClientInfo();
}
@Override
public void close() {
this.delegate.close();
}
public boolean closeGracefully() {
try {
this.delegate.closeGracefully().block(Duration.ofMillis(DEFAULT_CLOSE_TIMEOUT_MS));
}
catch (RuntimeException e) {
logger.warn("Client didn't close within timeout of {} ms.", DEFAULT_CLOSE_TIMEOUT_MS, e);
return false;
}
return true;
}
/**
* The initialization phase MUST be the first interaction between client and server.
* During this phase, the client and server:
* <ul>
* <li>Establish protocol version compatibility</li>
* <li>Exchange and negotiate capabilities</li>
* <li>Share implementation details</li>
* </ul>
* <br/>
* The client MUST initiate this phase by sending an initialize request containing:
* <ul>
* <li>The protocol version the client supports</li>
* <li>The client's capabilities</li>
* <li>Client implementation information</li>
* </ul>
*
* The server MUST respond with its own capabilities and information:
* {@link McpSchema.ServerCapabilities}. <br/>
* After successful initialization, the client MUST send an initialized notification
* to indicate it is ready to begin normal operations.
*
* <br/>
*
* <a href=
* "https://github.com/modelcontextprotocol/specification/blob/main/docs/specification/basic/lifecycle.md#initialization">Initialization
* Spec</a>
* @return the initialize result.
*/
public McpSchema.InitializeResult initialize() {
// TODO: block takes no argument here as we assume the async client is
// configured with a requestTimeout at all times
return this.delegate.initialize().block();
}
/**
* Send a roots/list_changed notification.
*/
public void rootsListChangedNotification() {
this.delegate.rootsListChangedNotification().block();
}
/**
* Add a roots dynamically.
*/
public void addRoot(McpSchema.Root root) {
this.delegate.addRoot(root).block();
}
/**
* Remove a root dynamically.
*/
public void removeRoot(String rootUri) {
this.delegate.removeRoot(rootUri).block();
}
/**
* Send a synchronous ping request.
* @return
*/
public Object ping() {
return this.delegate.ping().block();
}
// --------------------------
// Tools
// --------------------------
/**
* Calls a tool provided by the server. Tools enable servers to expose executable
* functionality that can interact with external systems, perform computations, and
* take actions in the real world.
* @param callToolRequest The request containing: - name: The name of the tool to call
* (must match a tool name from tools/list) - arguments: Arguments that conform to the
* tool's input schema
* @return The tool execution result containing: - content: List of content items
* (text, images, or embedded resources) representing the tool's output - isError:
* Boolean indicating if the execution failed (true) or succeeded (false/absent)
*/
public McpSchema.CallToolResult callTool(McpSchema.CallToolRequest callToolRequest) {
return this.delegate.callTool(callToolRequest).block();
}
/**
* Retrieves the list of all tools provided by the server.
* @return The list of tools result containing: - tools: List of available tools, each
* with a name, description, and input schema - nextCursor: Optional cursor for
* pagination if more tools are available
*/
public McpSchema.ListToolsResult listTools() {
return this.delegate.listTools().block();
}
/**
* Retrieves a paginated list of tools provided by the server.
* @param cursor Optional pagination cursor from a previous list request
* @return The list of tools result containing: - tools: List of available tools, each
* with a name, description, and input schema - nextCursor: Optional cursor for
* pagination if more tools are available
*/
public McpSchema.ListToolsResult listTools(String cursor) {
return this.delegate.listTools(cursor).block();
}
// --------------------------
// Resources
// --------------------------
/**
* Send a resources/list request.
* @param cursor the cursor
* @return the list of resources result.
*/
public McpSchema.ListResourcesResult listResources(String cursor) {
return this.delegate.listResources(cursor).block();
}
/**
* Send a resources/list request.
* @return the list of resources result.
*/
public McpSchema.ListResourcesResult listResources() {
return this.delegate.listResources().block();
}
/**
* Send a resources/read request.
* @param resource the resource to read
* @return the resource content.
*/
public McpSchema.ReadResourceResult readResource(McpSchema.Resource resource) {
return this.delegate.readResource(resource).block();
}
/**
* Send a resources/read request.
* @param readResourceRequest the read resource request.
* @return the resource content.
*/
public McpSchema.ReadResourceResult readResource(McpSchema.ReadResourceRequest readResourceRequest) {
return this.delegate.readResource(readResourceRequest).block();
}
/**
* Resource templates allow servers to expose parameterized resources using URI
* templates. Arguments may be auto-completed through the completion API.
*
* Request a list of resource templates the server has.
* @param cursor the cursor
* @return the list of resource templates result.
*/
public McpSchema.ListResourceTemplatesResult listResourceTemplates(String cursor) {
return this.delegate.listResourceTemplates(cursor).block();
}
/**
* Request a list of resource templates the server has.
* @return the list of resource templates result.
*/
public McpSchema.ListResourceTemplatesResult listResourceTemplates() {
return this.delegate.listResourceTemplates().block();
}
/**
* List Changed Notification. When the list of available resources changes, servers
* that declared the listChanged capability SHOULD send a notification:
*/
public void sendResourcesListChanged() {
this.delegate.sendResourcesListChanged().block();
}
/**
* Subscriptions. The protocol supports optional subscriptions to resource changes.
* Clients can subscribe to specific resources and receive notifications when they
* change.
*
* Send a resources/subscribe request.
* @param subscribeRequest the subscribe request contains the uri of the resource to
* subscribe to.
*/
public void subscribeResource(McpSchema.SubscribeRequest subscribeRequest) {
this.delegate.subscribeResource(subscribeRequest).block();
}
/**
* Send a resources/unsubscribe request.
* @param unsubscribeRequest the unsubscribe request contains the uri of the resource
* to unsubscribe from.
*/
public void unsubscribeResource(McpSchema.UnsubscribeRequest unsubscribeRequest) {
this.delegate.unsubscribeResource(unsubscribeRequest).block();
}
// --------------------------
// Prompts
// --------------------------
public ListPromptsResult listPrompts(String cursor) {
return this.delegate.listPrompts(cursor).block();
}
public ListPromptsResult listPrompts() {
return this.delegate.listPrompts().block();
}
public GetPromptResult getPrompt(GetPromptRequest getPromptRequest) {
return this.delegate.getPrompt(getPromptRequest).block();
}
/**
* (Server) An optional notification from the server to the client, informing it that
* the list of prompts it offers has changed. This may be issued by servers without
* any previous subscription from the client.
*/
public void promptListChangedNotification() {
this.delegate.promptListChangedNotification().block();
}
/**
* Client can set the minimum logging level it wants to receive from the server.
* @param loggingLevel the min logging level
*/
public void setLoggingLevel(McpSchema.LoggingLevel loggingLevel) {
this.delegate.setLoggingLevel(loggingLevel).block();
}
}

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/*
* Copyright 2024 - 2024 the original author or authors.
*/
package io.modelcontextprotocol.client.transport;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Flow;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Function;
import java.util.regex.Pattern;
/**
* A Server-Sent Events (SSE) client implementation using Java's Flow API for reactive
* stream processing. This client establishes a connection to an SSE endpoint and
* processes the incoming event stream, parsing SSE-formatted messages into structured
* events.
*
* <p>
* The client supports standard SSE event fields including:
* <ul>
* <li>event - The event type (defaults to "message" if not specified)</li>
* <li>id - The event ID</li>
* <li>data - The event payload data</li>
* </ul>
*
* <p>
* Events are delivered to a provided {@link SseEventHandler} which can process events and
* handle any errors that occur during the connection.
*
* @author Christian Tzolov
* @see SseEventHandler
* @see SseEvent
*/
public class FlowSseClient {
private final HttpClient httpClient;
/**
* Pattern to extract the data content from SSE data field lines. Matches lines
* starting with "data:" and captures the remaining content.
*/
private static final Pattern EVENT_DATA_PATTERN = Pattern.compile("^data:(.+)$", Pattern.MULTILINE);
/**
* Pattern to extract the event ID from SSE id field lines. Matches lines starting
* with "id:" and captures the ID value.
*/
private static final Pattern EVENT_ID_PATTERN = Pattern.compile("^id:(.+)$", Pattern.MULTILINE);
/**
* Pattern to extract the event type from SSE event field lines. Matches lines
* starting with "event:" and captures the event type.
*/
private static final Pattern EVENT_TYPE_PATTERN = Pattern.compile("^event:(.+)$", Pattern.MULTILINE);
/**
* Record class representing a Server-Sent Event with its standard fields.
*
* @param id the event ID (may be null)
* @param type the event type (defaults to "message" if not specified in the stream)
* @param data the event payload data
*/
public static record SseEvent(String id, String type, String data) {
}
/**
* Interface for handling SSE events and errors. Implementations can process received
* events and handle any errors that occur during the SSE connection.
*/
public interface SseEventHandler {
/**
* Called when an SSE event is received.
* @param event the received SSE event containing id, type, and data
*/
void onEvent(SseEvent event);
/**
* Called when an error occurs during the SSE connection.
* @param error the error that occurred
*/
void onError(Throwable error);
}
/**
* Creates a new FlowSseClient with the specified HTTP client.
* @param httpClient the {@link HttpClient} instance to use for SSE connections
*/
public FlowSseClient(HttpClient httpClient) {
this.httpClient = httpClient;
}
/**
* Subscribes to an SSE endpoint and processes the event stream.
*
* <p>
* This method establishes a connection to the specified URL and begins processing the
* SSE stream. Events are parsed and delivered to the provided event handler. The
* connection remains active until either an error occurs or the server closes the
* connection.
* @param url the SSE endpoint URL to connect to
* @param eventHandler the handler that will receive SSE events and error
* notifications
* @throws RuntimeException if the connection fails with a non-200 status code
*/
public void subscribe(String url, SseEventHandler eventHandler) {
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create(url))
.header("Accept", "text/event-stream")
.header("Cache-Control", "no-cache")
.GET()
.build();
StringBuilder eventBuilder = new StringBuilder();
AtomicReference<String> currentEventId = new AtomicReference<>();
AtomicReference<String> currentEventType = new AtomicReference<>("message");
Flow.Subscriber<String> lineSubscriber = new Flow.Subscriber<>() {
private Flow.Subscription subscription;
@Override
public void onSubscribe(Flow.Subscription subscription) {
this.subscription = subscription;
subscription.request(Long.MAX_VALUE);
}
@Override
public void onNext(String line) {
if (line.isEmpty()) {
// Empty line means end of event
if (eventBuilder.length() > 0) {
String eventData = eventBuilder.toString();
SseEvent event = new SseEvent(currentEventId.get(), currentEventType.get(), eventData.trim());
eventHandler.onEvent(event);
eventBuilder.setLength(0);
}
}
else {
if (line.startsWith("data:")) {
var matcher = EVENT_DATA_PATTERN.matcher(line);
if (matcher.find()) {
eventBuilder.append(matcher.group(1).trim()).append("\n");
}
}
else if (line.startsWith("id:")) {
var matcher = EVENT_ID_PATTERN.matcher(line);
if (matcher.find()) {
currentEventId.set(matcher.group(1).trim());
}
}
else if (line.startsWith("event:")) {
var matcher = EVENT_TYPE_PATTERN.matcher(line);
if (matcher.find()) {
currentEventType.set(matcher.group(1).trim());
}
}
}
subscription.request(1);
}
@Override
public void onError(Throwable throwable) {
eventHandler.onError(throwable);
}
@Override
public void onComplete() {
// Handle any remaining event data
if (eventBuilder.length() > 0) {
String eventData = eventBuilder.toString();
SseEvent event = new SseEvent(currentEventId.get(), currentEventType.get(), eventData.trim());
eventHandler.onEvent(event);
}
}
};
Function<Flow.Subscriber<String>, HttpResponse.BodySubscriber<Void>> subscriberFactory = subscriber -> HttpResponse.BodySubscribers
.fromLineSubscriber(subscriber);
CompletableFuture<HttpResponse<Void>> future = this.httpClient.sendAsync(request,
info -> subscriberFactory.apply(lineSubscriber));
future.thenAccept(response -> {
int status = response.statusCode();
if (status != 200 && status != 201 && status != 202 && status != 206) {
throw new RuntimeException("Failed to connect to SSE stream. Unexpected status code: " + status);
}
}).exceptionally(throwable -> {
eventHandler.onError(throwable);
return null;
});
}
}

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/*
* Copyright 2024 - 2024 the original author or authors.
*/
package io.modelcontextprotocol.client.transport;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import io.modelcontextprotocol.client.transport.FlowSseClient.SseEvent;
import io.modelcontextprotocol.spec.ClientMcpTransport;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.JSONRPCMessage;
import io.modelcontextprotocol.util.Assert;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Mono;
import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.time.Duration;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Function;
/**
* Server-Sent Events (SSE) implementation of the
* {@link io.modelcontextprotocol.spec.McpTransport} that follows the MCP HTTP with SSE
* transport specification, using Java's HttpClient.
*
* <p>
* This transport implementation establishes a bidirectional communication channel between
* client and server using SSE for server-to-client messages and HTTP POST requests for
* client-to-server messages. The transport:
* <ul>
* <li>Establishes an SSE connection to receive server messages</li>
* <li>Handles endpoint discovery through SSE events</li>
* <li>Manages message serialization/deserialization using Jackson</li>
* <li>Provides graceful connection termination</li>
* </ul>
*
* <p>
* The transport supports two types of SSE events:
* <ul>
* <li>'endpoint' - Contains the URL for sending client messages</li>
* <li>'message' - Contains JSON-RPC message payload</li>
* </ul>
*
* @author Christian Tzolov
* @see io.modelcontextprotocol.spec.McpTransport
* @see io.modelcontextprotocol.spec.ClientMcpTransport
*/
public class HttpClientSseClientTransport implements ClientMcpTransport {
private static final Logger logger = LoggerFactory.getLogger(HttpClientSseClientTransport.class);
/** SSE event type for JSON-RPC messages */
private static final String MESSAGE_EVENT_TYPE = "message";
/** SSE event type for endpoint discovery */
private static final String ENDPOINT_EVENT_TYPE = "endpoint";
/** Default SSE endpoint path */
private static final String SSE_ENDPOINT = "/sse";
/** Base URI for the MCP server */
private final String baseUri;
/** SSE client for handling server-sent events. Uses the /sse endpoint */
private final FlowSseClient sseClient;
/**
* HTTP client for sending messages to the server. Uses HTTP POST over the message
* endpoint
*/
private final HttpClient httpClient;
/** JSON object mapper for message serialization/deserialization */
protected ObjectMapper objectMapper;
/** Flag indicating if the transport is in closing state */
private volatile boolean isClosing = false;
/** Latch for coordinating endpoint discovery */
private CountDownLatch closeLatch = new CountDownLatch(1);
/** Holds the discovered message endpoint URL */
private final AtomicReference<String> messageEndpoint = new AtomicReference<>();
/** Holds the SSE connection future */
private final AtomicReference<CompletableFuture<Void>> connectionFuture = new AtomicReference<>();
/**
* Creates a new transport instance with default HTTP client and object mapper.
* @param baseUri the base URI of the MCP server
*/
public HttpClientSseClientTransport(String baseUri) {
this(HttpClient.newBuilder(), baseUri, new ObjectMapper());
}
/**
* Creates a new transport instance with custom HTTP client builder and object mapper.
* @param clientBuilder the HTTP client builder to use
* @param baseUri the base URI of the MCP server
* @param objectMapper the object mapper for JSON serialization/deserialization
* @throws IllegalArgumentException if objectMapper or clientBuilder is null
*/
public HttpClientSseClientTransport(HttpClient.Builder clientBuilder, String baseUri, ObjectMapper objectMapper) {
Assert.notNull(objectMapper, "ObjectMapper must not be null");
Assert.hasText(baseUri, "baseUri must not be empty");
Assert.notNull(clientBuilder, "clientBuilder must not be null");
this.baseUri = baseUri;
this.objectMapper = objectMapper;
this.httpClient = clientBuilder.connectTimeout(Duration.ofSeconds(10)).build();
this.sseClient = new FlowSseClient(this.httpClient);
}
/**
* Establishes the SSE connection with the server and sets up message handling.
*
* <p>
* This method:
* <ul>
* <li>Initiates the SSE connection</li>
* <li>Handles endpoint discovery events</li>
* <li>Processes incoming JSON-RPC messages</li>
* </ul>
* @param handler the function to process received JSON-RPC messages
* @return a Mono that completes when the connection is established
*/
@Override
public Mono<Void> connect(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> handler) {
CompletableFuture<Void> future = new CompletableFuture<>();
connectionFuture.set(future);
sseClient.subscribe(this.baseUri + SSE_ENDPOINT, new FlowSseClient.SseEventHandler() {
@Override
public void onEvent(SseEvent event) {
if (isClosing) {
return;
}
try {
if (ENDPOINT_EVENT_TYPE.equals(event.type())) {
String endpoint = event.data();
messageEndpoint.set(endpoint);
closeLatch.countDown();
future.complete(null);
}
else if (MESSAGE_EVENT_TYPE.equals(event.type())) {
JSONRPCMessage message = McpSchema.deserializeJsonRpcMessage(objectMapper, event.data());
handler.apply(Mono.just(message)).subscribe();
}
else {
logger.error("Received unrecognized SSE event type: {}", event.type());
}
}
catch (IOException e) {
logger.error("Error processing SSE event", e);
future.completeExceptionally(e);
}
}
@Override
public void onError(Throwable error) {
if (!isClosing) {
logger.error("SSE connection error", error);
future.completeExceptionally(error);
}
}
});
return Mono.fromFuture(future);
}
/**
* Sends a JSON-RPC message to the server.
*
* <p>
* This method waits for the message endpoint to be discovered before sending the
* message. The message is serialized to JSON and sent as an HTTP POST request.
* @param message the JSON-RPC message to send
* @return a Mono that completes when the message is sent
* @throws McpError if the message endpoint is not available or the wait times out
*/
@Override
public Mono<Void> sendMessage(JSONRPCMessage message) {
if (isClosing) {
return Mono.empty();
}
try {
if (!closeLatch.await(10, TimeUnit.SECONDS)) {
return Mono.error(new McpError("Failed to wait for the message endpoint"));
}
}
catch (InterruptedException e) {
return Mono.error(new McpError("Failed to wait for the message endpoint"));
}
String endpoint = messageEndpoint.get();
if (endpoint == null) {
return Mono.error(new McpError("No message endpoint available"));
}
try {
String jsonText = this.objectMapper.writeValueAsString(message);
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create(this.baseUri + endpoint))
.header("Content-Type", "application/json")
.POST(HttpRequest.BodyPublishers.ofString(jsonText))
.build();
return Mono.fromFuture(
httpClient.sendAsync(request, HttpResponse.BodyHandlers.discarding()).thenAccept(response -> {
if (response.statusCode() != 200 && response.statusCode() != 201 && response.statusCode() != 202
&& response.statusCode() != 206) {
logger.error("Error sending message: {}", response.statusCode());
}
}));
}
catch (IOException e) {
if (!isClosing) {
return Mono.error(new RuntimeException("Failed to serialize message", e));
}
return Mono.empty();
}
}
/**
* Gracefully closes the transport connection.
*
* <p>
* Sets the closing flag and cancels any pending connection future. This prevents new
* messages from being sent and allows ongoing operations to complete.
* @return a Mono that completes when the closing process is initiated
*/
@Override
public Mono<Void> closeGracefully() {
return Mono.fromRunnable(() -> {
isClosing = true;
CompletableFuture<Void> future = connectionFuture.get();
if (future != null && !future.isDone()) {
future.cancel(true);
}
});
}
/**
* Unmarshals data to the specified type using the configured object mapper.
* @param data the data to unmarshal
* @param typeRef the type reference for the target type
* @param <T> the target type
* @return the unmarshalled object
*/
@Override
public <T> T unmarshalFrom(Object data, TypeReference<T> typeRef) {
return this.objectMapper.convertValue(data, typeRef);
}
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.client.transport;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import io.modelcontextprotocol.util.Assert;
/**
* Server parameters for stdio client.
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
*/
@JsonInclude(JsonInclude.Include.NON_ABSENT)
public class ServerParameters {
// Environment variables to inherit by default
private static final List<String> DEFAULT_INHERITED_ENV_VARS = System.getProperty("os.name")
.toLowerCase()
.contains("win")
? Arrays.asList("APPDATA", "HOMEDRIVE", "HOMEPATH", "LOCALAPPDATA", "PATH", "PROCESSOR_ARCHITECTURE",
"SYSTEMDRIVE", "SYSTEMROOT", "TEMP", "USERNAME", "USERPROFILE")
: Arrays.asList("HOME", "LOGNAME", "PATH", "SHELL", "TERM", "USER");
@JsonProperty("command")
private String command;
@JsonProperty("args")
private List<String> args = new ArrayList<>();
@JsonProperty("env")
private Map<String, String> env;
private ServerParameters(String command, List<String> args, Map<String, String> env) {
Assert.notNull(command, "The command can not be null");
Assert.notNull(args, "The args can not be null");
this.command = command;
this.args = args;
this.env = new HashMap<>(getDefaultEnvironment());
if (env != null && !env.isEmpty()) {
this.env.putAll(env);
}
}
public String getCommand() {
return this.command;
}
public List<String> getArgs() {
return this.args;
}
public Map<String, String> getEnv() {
return this.env;
}
public static Builder builder(String command) {
return new Builder(command);
}
public static class Builder {
private String command;
private List<String> args = new ArrayList<>();
private Map<String, String> env = new HashMap<>();
public Builder(String command) {
Assert.notNull(command, "The command can not be null");
this.command = command;
}
public Builder args(String... args) {
Assert.notNull(args, "The args can not be null");
this.args = Arrays.asList(args);
return this;
}
public Builder args(List<String> args) {
Assert.notNull(args, "The args can not be null");
this.args = new ArrayList<>(args);
return this;
}
public Builder arg(String arg) {
Assert.notNull(arg, "The arg can not be null");
this.args.add(arg);
return this;
}
public Builder env(Map<String, String> env) {
if (env != null && !env.isEmpty()) {
this.env.putAll(env);
}
return this;
}
public Builder addEnvVar(String key, String value) {
Assert.notNull(key, "The key can not be null");
Assert.notNull(value, "The value can not be null");
this.env.put(key, value);
return this;
}
public ServerParameters build() {
return new ServerParameters(command, args, env);
}
}
/**
* Returns a default environment object including only environment variables deemed
* safe to inherit.
*/
private static Map<String, String> getDefaultEnvironment() {
return System.getenv()
.entrySet()
.stream()
.filter(entry -> DEFAULT_INHERITED_ENV_VARS.contains(entry.getKey()))
.filter(entry -> entry.getValue() != null)
.filter(entry -> !entry.getValue().startsWith("()"))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
}
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.client.transport;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Executors;
import java.util.function.Consumer;
import java.util.function.Function;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import io.modelcontextprotocol.spec.ClientMcpTransport;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.JSONRPCMessage;
import io.modelcontextprotocol.util.Assert;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.core.publisher.Sinks;
import reactor.core.scheduler.Scheduler;
import reactor.core.scheduler.Schedulers;
/**
* Implementation of the MCP Stdio transport that communicates with a server process using
* standard input/output streams. Messages are exchanged as newline-delimited JSON-RPC
* messages over stdin/stdout, with errors and debug information sent to stderr.
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
*/
public class StdioClientTransport implements ClientMcpTransport {
private static final Logger logger = LoggerFactory.getLogger(StdioClientTransport.class);
private final Sinks.Many<JSONRPCMessage> inboundSink;
private final Sinks.Many<JSONRPCMessage> outboundSink;
/** The server process being communicated with */
private Process process;
private ObjectMapper objectMapper;
/** Scheduler for handling inbound messages from the server process */
private Scheduler inboundScheduler;
/** Scheduler for handling outbound messages to the server process */
private Scheduler outboundScheduler;
/** Scheduler for handling error messages from the server process */
private Scheduler errorScheduler;
/** Parameters for configuring and starting the server process */
private final ServerParameters params;
private final Sinks.Many<String> errorSink;
private volatile boolean isClosing = false;
// visible for tests
private Consumer<String> errorHandler = error -> logger.error("Error received: {}", error);
/**
* Creates a new StdioClientTransport with the specified parameters and default
* ObjectMapper.
* @param params The parameters for configuring the server process
*/
public StdioClientTransport(ServerParameters params) {
this(params, new ObjectMapper());
}
/**
* Creates a new StdioClientTransport with the specified parameters and ObjectMapper.
* @param params The parameters for configuring the server process
* @param objectMapper The ObjectMapper to use for JSON serialization/deserialization
*/
public StdioClientTransport(ServerParameters params, ObjectMapper objectMapper) {
Assert.notNull(params, "The params can not be null");
Assert.notNull(objectMapper, "The ObjectMapper can not be null");
this.inboundSink = Sinks.many().unicast().onBackpressureBuffer();
this.outboundSink = Sinks.many().unicast().onBackpressureBuffer();
this.params = params;
this.objectMapper = objectMapper;
this.errorSink = Sinks.many().unicast().onBackpressureBuffer();
// Start threads
this.inboundScheduler = Schedulers.fromExecutorService(Executors.newSingleThreadExecutor(), "inbound");
this.outboundScheduler = Schedulers.fromExecutorService(Executors.newSingleThreadExecutor(), "outbound");
this.errorScheduler = Schedulers.fromExecutorService(Executors.newSingleThreadExecutor(), "error");
}
/**
* Starts the server process and initializes the message processing streams. This
* method sets up the process with the configured command, arguments, and environment,
* then starts the inbound, outbound, and error processing threads.
* @throws RuntimeException if the process fails to start or if the process streams
* are null
*/
@Override
public Mono<Void> connect(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> handler) {
return Mono.<Void>fromRunnable(() -> {
handleIncomingMessages(handler);
handleIncomingErrors();
// Prepare command and environment
List<String> fullCommand = new ArrayList<>();
fullCommand.add(params.getCommand());
fullCommand.addAll(params.getArgs());
ProcessBuilder processBuilder = this.getProcessBuilder();
processBuilder.command(fullCommand);
processBuilder.environment().putAll(params.getEnv());
// Start the process
try {
this.process = processBuilder.start();
}
catch (IOException e) {
throw new RuntimeException("Failed to start process with command: " + fullCommand, e);
}
// Validate process streams
if (this.process.getInputStream() == null || process.getOutputStream() == null) {
this.process.destroy();
throw new RuntimeException("Process input or output stream is null");
}
// Start threads
startInboundProcessing();
startOutboundProcessing();
startErrorProcessing();
}).subscribeOn(Schedulers.boundedElastic());
}
/**
* Creates and returns a new ProcessBuilder instance. Protected to allow overriding in
* tests.
* @return A new ProcessBuilder instance
*/
protected ProcessBuilder getProcessBuilder() {
return new ProcessBuilder();
}
/**
* Sets the handler for processing transport-level errors.
*
* <p>
* The provided handler will be called when errors occur during transport operations,
* such as connection failures or protocol violations.
* </p>
* @param errorHandler a consumer that processes error messages
*/
public void setErrorHandler(Consumer<String> errorHandler) {
this.errorHandler = errorHandler;
}
/**
* Waits for the server process to exit.
* @throws RuntimeException if the process is interrupted while waiting
*/
public void awaitForExit() {
try {
this.process.waitFor();
}
catch (InterruptedException e) {
throw new RuntimeException("Process interrupted", e);
}
}
/**
* Starts the error processing thread that reads from the process's error stream.
* Error messages are logged and emitted to the error sink.
*/
private void startErrorProcessing() {
this.errorScheduler.schedule(() -> {
try (BufferedReader processErrorReader = new BufferedReader(
new InputStreamReader(process.getErrorStream()))) {
String line;
while (!isClosing && (line = processErrorReader.readLine()) != null) {
try {
logger.error("Received error line: {}", line);
if (!this.errorSink.tryEmitNext(line).isSuccess()) {
if (!isClosing) {
logger.error("Failed to emit error message");
}
break;
}
}
catch (Exception e) {
if (!isClosing) {
logger.error("Error processing error message", e);
}
break;
}
}
}
catch (IOException e) {
if (!isClosing) {
logger.error("Error reading from error stream", e);
}
}
finally {
isClosing = true;
errorSink.tryEmitComplete();
}
});
}
private void handleIncomingMessages(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> inboundMessageHandler) {
this.inboundSink.asFlux()
.flatMap(message -> Mono.just(message)
.transform(inboundMessageHandler)
.contextWrite(ctx -> ctx.put("observation", "myObservation")))
.subscribe();
}
private void handleIncomingErrors() {
this.errorSink.asFlux().subscribe(e -> {
this.errorHandler.accept(e);
});
}
@Override
public Mono<Void> sendMessage(JSONRPCMessage message) {
if (this.outboundSink.tryEmitNext(message).isSuccess()) {
// TODO: essentially we could reschedule ourselves in some time and make
// another attempt with the already read data but pause reading until
// success
// In this approach we delegate the retry and the backpressure onto the
// caller. This might be enough for most cases.
return Mono.empty();
}
else {
return Mono.error(new RuntimeException("Failed to enqueue message"));
}
}
/**
* Starts the inbound processing thread that reads JSON-RPC messages from the
* process's input stream. Messages are deserialized and emitted to the inbound sink.
*/
private void startInboundProcessing() {
this.inboundScheduler.schedule(() -> {
try (BufferedReader processReader = new BufferedReader(new InputStreamReader(process.getInputStream()))) {
String line;
while (!isClosing && (line = processReader.readLine()) != null) {
try {
JSONRPCMessage message = McpSchema.deserializeJsonRpcMessage(this.objectMapper, line);
if (!this.inboundSink.tryEmitNext(message).isSuccess()) {
if (!isClosing) {
logger.error("Failed to enqueue inbound message: {}", message);
}
break;
}
}
catch (Exception e) {
if (!isClosing) {
logger.error("Error processing inbound message for line: " + line, e);
}
break;
}
}
}
catch (IOException e) {
if (!isClosing) {
logger.error("Error reading from input stream", e);
}
}
finally {
isClosing = true;
inboundSink.tryEmitComplete();
}
});
}
/**
* Starts the outbound processing thread that writes JSON-RPC messages to the
* process's output stream. Messages are serialized to JSON and written with a newline
* delimiter.
*/
private void startOutboundProcessing() {
this.handleOutbound(messages -> messages
// this bit is important since writes come from user threads and we
// want to ensure that the actual writing happens on a dedicated thread
.publishOn(outboundScheduler)
.handle((message, s) -> {
if (message != null && !isClosing) {
try {
String jsonMessage = objectMapper.writeValueAsString(message);
// Escape any embedded newlines in the JSON message as per spec:
// https://spec.modelcontextprotocol.io/specification/basic/transports/#stdio
// - Messages are delimited by newlines, and MUST NOT contain
// embedded newlines.
jsonMessage = jsonMessage.replace("\r\n", "\\n").replace("\n", "\\n").replace("\r", "\\n");
var os = this.process.getOutputStream();
synchronized (os) {
os.write(jsonMessage.getBytes(StandardCharsets.UTF_8));
os.write("\n".getBytes(StandardCharsets.UTF_8));
os.flush();
}
s.next(message);
}
catch (IOException e) {
s.error(new RuntimeException(e));
}
}
}));
}
protected void handleOutbound(Function<Flux<JSONRPCMessage>, Flux<JSONRPCMessage>> outboundConsumer) {
outboundConsumer.apply(outboundSink.asFlux()).doOnComplete(() -> {
isClosing = true;
outboundSink.tryEmitComplete();
}).doOnError(e -> {
if (!isClosing) {
logger.error("Error in outbound processing", e);
isClosing = true;
outboundSink.tryEmitComplete();
}
}).subscribe();
}
/**
* Gracefully closes the transport by destroying the process and disposing of the
* schedulers. This method sends a TERM signal to the process and waits for it to exit
* before cleaning up resources.
* @return A Mono that completes when the transport is closed
*/
@Override
public Mono<Void> closeGracefully() {
return Mono.fromRunnable(() -> {
isClosing = true;
logger.debug("Initiating graceful shutdown");
}).then(Mono.defer(() -> {
// First complete all sinks to stop accepting new messages
inboundSink.tryEmitComplete();
outboundSink.tryEmitComplete();
errorSink.tryEmitComplete();
// Give a short time for any pending messages to be processed
return Mono.delay(Duration.ofMillis(100));
})).then(Mono.fromFuture(() -> {
logger.info("Sending TERM to process");
if (this.process != null) {
this.process.destroy();
return process.onExit();
}
else {
return CompletableFuture.failedFuture(new RuntimeException("Process not started"));
}
})).doOnNext(process -> {
if (process.exitValue() != 0) {
logger.warn("Process terminated with code " + process.exitValue());
}
}).then(Mono.fromRunnable(() -> {
try {
// The Threads are blocked on readLine so disposeGracefully would not
// interrupt them, therefore we issue an async hard dispose.
inboundScheduler.dispose();
errorScheduler.dispose();
outboundScheduler.dispose();
logger.info("Graceful shutdown completed");
}
catch (Exception e) {
logger.error("Error during graceful shutdown", e);
}
})).then().subscribeOn(Schedulers.boundedElastic());
}
public Sinks.Many<String> getErrorSink() {
return this.errorSink;
}
@Override
public <T> T unmarshalFrom(Object data, TypeReference<T> typeRef) {
return this.objectMapper.convertValue(data, typeRef);
}
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.server;
import java.time.Duration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.function.Function;
import com.fasterxml.jackson.core.type.TypeReference;
import io.modelcontextprotocol.spec.DefaultMcpSession;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.ServerMcpTransport;
import io.modelcontextprotocol.spec.DefaultMcpSession.NotificationHandler;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import io.modelcontextprotocol.spec.McpSchema.ClientCapabilities;
import io.modelcontextprotocol.spec.McpSchema.LoggingLevel;
import io.modelcontextprotocol.spec.McpSchema.LoggingMessageNotification;
import io.modelcontextprotocol.spec.McpSchema.Tool;
import io.modelcontextprotocol.util.Utils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
/**
* The Model Context Protocol (MCP) server implementation that provides asynchronous
* communication using Project Reactor's Mono and Flux types.
*
* <p>
* This server implements the MCP specification, enabling AI models to expose tools,
* resources, and prompts through a standardized interface. Key features include:
* <ul>
* <li>Asynchronous communication using reactive programming patterns
* <li>Dynamic tool registration and management
* <li>Resource handling with URI-based addressing
* <li>Prompt template management
* <li>Real-time client notifications for state changes
* <li>Structured logging with configurable severity levels
* <li>Support for client-side AI model sampling
* </ul>
*
* <p>
* The server follows a lifecycle:
* <ol>
* <li>Initialization - Accepts client connections and negotiates capabilities
* <li>Normal Operation - Handles client requests and sends notifications
* <li>Graceful Shutdown - Ensures clean connection termination
* </ol>
*
* <p>
* This implementation uses Project Reactor for non-blocking operations, making it
* suitable for high-throughput scenarios and reactive applications. All operations return
* Mono or Flux types that can be composed into reactive pipelines.
*
* <p>
* The server supports runtime modification of its capabilities through methods like
* {@link #addTool}, {@link #addResource}, and {@link #addPrompt}, automatically notifying
* connected clients of changes when configured to do so.
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
* @see McpServer
* @see McpSchema
* @see DefaultMcpSession
*/
public class McpAsyncServer {
private static final Logger logger = LoggerFactory.getLogger(McpAsyncServer.class);
/**
* The MCP session implementation that manages bidirectional JSON-RPC communication
* between clients and servers.
*/
private final DefaultMcpSession mcpSession;
private final ServerMcpTransport transport;
private final McpSchema.ServerCapabilities serverCapabilities;
private final McpSchema.Implementation serverInfo;
private McpSchema.ClientCapabilities clientCapabilities;
private McpSchema.Implementation clientInfo;
/**
* Thread-safe list of tool handlers that can be modified at runtime.
*/
private final CopyOnWriteArrayList<McpServerFeatures.AsyncToolRegistration> tools = new CopyOnWriteArrayList<>();
private final CopyOnWriteArrayList<McpSchema.ResourceTemplate> resourceTemplates = new CopyOnWriteArrayList<>();
private final ConcurrentHashMap<String, McpServerFeatures.AsyncResourceRegistration> resources = new ConcurrentHashMap<>();
private final ConcurrentHashMap<String, McpServerFeatures.AsyncPromptRegistration> prompts = new ConcurrentHashMap<>();
private LoggingLevel minLoggingLevel = LoggingLevel.DEBUG;
/**
* Supported protocol versions.
*/
private List<String> protocolVersions = List.of(McpSchema.LATEST_PROTOCOL_VERSION);
/**
* Create a new McpAsyncServer with the given transport and capabilities.
* @param mcpTransport The transport layer implementation for MCP communication.
* @param features The MCP server supported features.
*/
McpAsyncServer(ServerMcpTransport mcpTransport, McpServerFeatures.Async features) {
this.serverInfo = features.serverInfo();
this.serverCapabilities = features.serverCapabilities();
this.tools.addAll(features.tools());
this.resources.putAll(features.resources());
this.resourceTemplates.addAll(features.resourceTemplates());
this.prompts.putAll(features.prompts());
Map<String, DefaultMcpSession.RequestHandler<?>> requestHandlers = new HashMap<>();
// Initialize request handlers for standard MCP methods
requestHandlers.put(McpSchema.METHOD_INITIALIZE, asyncInitializeRequestHandler());
// Ping MUST respond with an empty data, but not NULL response.
requestHandlers.put(McpSchema.METHOD_PING, (params) -> Mono.just(""));
// Add tools API handlers if the tool capability is enabled
if (this.serverCapabilities.tools() != null) {
requestHandlers.put(McpSchema.METHOD_TOOLS_LIST, toolsListRequestHandler());
requestHandlers.put(McpSchema.METHOD_TOOLS_CALL, toolsCallRequestHandler());
}
// Add resources API handlers if provided
if (!Utils.isEmpty(this.resources)) {
requestHandlers.put(McpSchema.METHOD_RESOURCES_LIST, resourcesListRequestHandler());
requestHandlers.put(McpSchema.METHOD_RESOURCES_READ, resourcesReadRequestHandler());
}
// Add resource templates API handlers if provided.
if (!Utils.isEmpty(this.resourceTemplates)) {
requestHandlers.put(McpSchema.METHOD_RESOURCES_TEMPLATES_LIST, resourceTemplateListRequestHandler());
}
// Add prompts API handlers if provider exists
if (!Utils.isEmpty(this.prompts)) {
requestHandlers.put(McpSchema.METHOD_PROMPT_LIST, promptsListRequestHandler());
requestHandlers.put(McpSchema.METHOD_PROMPT_GET, promptsGetRequestHandler());
}
// Add logging API handlers if the logging capability is enabled
if (this.serverCapabilities.logging() != null) {
requestHandlers.put(McpSchema.METHOD_LOGGING_SET_LEVEL, setLoggerRequestHandler());
}
Map<String, NotificationHandler> notificationHandlers = new HashMap<>();
notificationHandlers.put(McpSchema.METHOD_NOTIFICATION_INITIALIZED, (params) -> Mono.empty());
List<Function<List<McpSchema.Root>, Mono<Void>>> rootsChangeConsumers = features.rootsChangeConsumers();
if (Utils.isEmpty(rootsChangeConsumers)) {
rootsChangeConsumers = List.of((roots) -> Mono.fromRunnable(() -> logger
.warn("Roots list changed notification, but no consumers provided. Roots list changed: {}", roots)));
}
notificationHandlers.put(McpSchema.METHOD_NOTIFICATION_ROOTS_LIST_CHANGED,
asyncRootsListChangedNotificationHandler(rootsChangeConsumers));
this.transport = mcpTransport;
this.mcpSession = new DefaultMcpSession(Duration.ofSeconds(10), mcpTransport, requestHandlers,
notificationHandlers);
}
// ---------------------------------------
// Lifecycle Management
// ---------------------------------------
private DefaultMcpSession.RequestHandler<McpSchema.InitializeResult> asyncInitializeRequestHandler() {
return params -> {
McpSchema.InitializeRequest initializeRequest = transport.unmarshalFrom(params,
new TypeReference<McpSchema.InitializeRequest>() {
});
this.clientCapabilities = initializeRequest.capabilities();
this.clientInfo = initializeRequest.clientInfo();
logger.info("Client initialize request - Protocol: {}, Capabilities: {}, Info: {}",
initializeRequest.protocolVersion(), initializeRequest.capabilities(),
initializeRequest.clientInfo());
String serverProtocolVersion = this.protocolVersions.get(this.protocolVersions.size() - 1);
if (this.protocolVersions.contains(initializeRequest.protocolVersion())) {
serverProtocolVersion = initializeRequest.protocolVersion();
}
else {
logger.warn(
"Client requested unsupported protocol version: {}, so the server will sugggest the {} version instead",
initializeRequest.protocolVersion(), serverProtocolVersion);
}
return Mono.just(new McpSchema.InitializeResult(serverProtocolVersion, this.serverCapabilities,
this.serverInfo, null));
};
}
/**
* Get the server capabilities that define the supported features and functionality.
* @return The server capabilities
*/
public McpSchema.ServerCapabilities getServerCapabilities() {
return this.serverCapabilities;
}
/**
* Get the server implementation information.
* @return The server implementation details
*/
public McpSchema.Implementation getServerInfo() {
return this.serverInfo;
}
/**
* Get the client capabilities that define the supported features and functionality.
* @return The client capabilities
*/
public ClientCapabilities getClientCapabilities() {
return this.clientCapabilities;
}
/**
* Get the client implementation information.
* @return The client implementation details
*/
public McpSchema.Implementation getClientInfo() {
return this.clientInfo;
}
/**
* Gracefully closes the server, allowing any in-progress operations to complete.
* @return A Mono that completes when the server has been closed
*/
public Mono<Void> closeGracefully() {
return this.mcpSession.closeGracefully();
}
/**
* Close the server immediately.
*/
public void close() {
this.mcpSession.close();
}
private static final TypeReference<McpSchema.ListRootsResult> LIST_ROOTS_RESULT_TYPE_REF = new TypeReference<>() {
};
/**
* Retrieves the list of all roots provided by the client.
* @return A Mono that emits the list of roots result.
*/
public Mono<McpSchema.ListRootsResult> listRoots() {
return this.listRoots(null);
}
/**
* Retrieves a paginated list of roots provided by the server.
* @param cursor Optional pagination cursor from a previous list request
* @return A Mono that emits the list of roots result containing
*/
public Mono<McpSchema.ListRootsResult> listRoots(String cursor) {
return this.mcpSession.sendRequest(McpSchema.METHOD_ROOTS_LIST, new McpSchema.PaginatedRequest(cursor),
LIST_ROOTS_RESULT_TYPE_REF);
}
private NotificationHandler asyncRootsListChangedNotificationHandler(
List<Function<List<McpSchema.Root>, Mono<Void>>> rootsChangeConsumers) {
return params -> listRoots().flatMap(listRootsResult -> Flux.fromIterable(rootsChangeConsumers)
.flatMap(consumer -> consumer.apply(listRootsResult.roots()))
.onErrorResume(error -> {
logger.error("Error handling roots list change notification", error);
return Mono.empty();
})
.then());
}
// ---------------------------------------
// Tool Management
// ---------------------------------------
/**
* Add a new tool registration at runtime.
* @param toolRegistration The tool registration to add
* @return Mono that completes when clients have been notified of the change
*/
public Mono<Void> addTool(McpServerFeatures.AsyncToolRegistration toolRegistration) {
if (toolRegistration == null) {
return Mono.error(new McpError("Tool registration must not be null"));
}
if (toolRegistration.tool() == null) {
return Mono.error(new McpError("Tool must not be null"));
}
if (toolRegistration.call() == null) {
return Mono.error(new McpError("Tool call handler must not be null"));
}
if (this.serverCapabilities.tools() == null) {
return Mono.error(new McpError("Server must be configured with tool capabilities"));
}
return Mono.defer(() -> {
// Check for duplicate tool names
if (this.tools.stream().anyMatch(th -> th.tool().name().equals(toolRegistration.tool().name()))) {
return Mono
.error(new McpError("Tool with name '" + toolRegistration.tool().name() + "' already exists"));
}
this.tools.add(toolRegistration);
logger.info("Added tool handler: {}", toolRegistration.tool().name());
if (this.serverCapabilities.tools().listChanged()) {
return notifyToolsListChanged();
}
return Mono.empty();
});
}
/**
* Remove a tool handler at runtime.
* @param toolName The name of the tool handler to remove
* @return Mono that completes when clients have been notified of the change
*/
public Mono<Void> removeTool(String toolName) {
if (toolName == null) {
return Mono.error(new McpError("Tool name must not be null"));
}
if (this.serverCapabilities.tools() == null) {
return Mono.error(new McpError("Server must be configured with tool capabilities"));
}
return Mono.defer(() -> {
boolean removed = this.tools.removeIf(toolRegistration -> toolRegistration.tool().name().equals(toolName));
if (removed) {
logger.info("Removed tool handler: {}", toolName);
if (this.serverCapabilities.tools().listChanged()) {
return notifyToolsListChanged();
}
return Mono.empty();
}
return Mono.error(new McpError("Tool with name '" + toolName + "' not found"));
});
}
/**
* Notifies clients that the list of available tools has changed.
* @return A Mono that completes when all clients have been notified
*/
public Mono<Void> notifyToolsListChanged() {
return this.mcpSession.sendNotification(McpSchema.METHOD_NOTIFICATION_TOOLS_LIST_CHANGED, null);
}
private DefaultMcpSession.RequestHandler<McpSchema.ListToolsResult> toolsListRequestHandler() {
return params -> {
List<Tool> tools = this.tools.stream().map(McpServerFeatures.AsyncToolRegistration::tool).toList();
return Mono.just(new McpSchema.ListToolsResult(tools, null));
};
}
private DefaultMcpSession.RequestHandler<CallToolResult> toolsCallRequestHandler() {
return params -> {
McpSchema.CallToolRequest callToolRequest = transport.unmarshalFrom(params,
new TypeReference<McpSchema.CallToolRequest>() {
});
Optional<McpServerFeatures.AsyncToolRegistration> toolRegistration = this.tools.stream()
.filter(tr -> callToolRequest.name().equals(tr.tool().name()))
.findAny();
if (toolRegistration.isEmpty()) {
return Mono.error(new McpError("Tool not found: " + callToolRequest.name()));
}
return toolRegistration.map(tool -> tool.call().apply(callToolRequest.arguments()))
.orElse(Mono.error(new McpError("Tool not found: " + callToolRequest.name())));
};
}
// ---------------------------------------
// Resource Management
// ---------------------------------------
/**
* Add a new resource handler at runtime.
* @param resourceHandler The resource handler to add
* @return Mono that completes when clients have been notified of the change
*/
public Mono<Void> addResource(McpServerFeatures.AsyncResourceRegistration resourceHandler) {
if (resourceHandler == null || resourceHandler.resource() == null) {
return Mono.error(new McpError("Resource must not be null"));
}
if (this.serverCapabilities.resources() == null) {
return Mono.error(new McpError("Server must be configured with resource capabilities"));
}
return Mono.defer(() -> {
if (this.resources.putIfAbsent(resourceHandler.resource().uri(), resourceHandler) != null) {
return Mono
.error(new McpError("Resource with URI '" + resourceHandler.resource().uri() + "' already exists"));
}
logger.info("Added resource handler: {}", resourceHandler.resource().uri());
if (this.serverCapabilities.resources().listChanged()) {
return notifyResourcesListChanged();
}
return Mono.empty();
});
}
/**
* Remove a resource handler at runtime.
* @param resourceUri The URI of the resource handler to remove
* @return Mono that completes when clients have been notified of the change
*/
public Mono<Void> removeResource(String resourceUri) {
if (resourceUri == null) {
return Mono.error(new McpError("Resource URI must not be null"));
}
if (this.serverCapabilities.resources() == null) {
return Mono.error(new McpError("Server must be configured with resource capabilities"));
}
return Mono.defer(() -> {
McpServerFeatures.AsyncResourceRegistration removed = this.resources.remove(resourceUri);
if (removed != null) {
logger.info("Removed resource handler: {}", resourceUri);
if (this.serverCapabilities.resources().listChanged()) {
return notifyResourcesListChanged();
}
return Mono.empty();
}
return Mono.error(new McpError("Resource with URI '" + resourceUri + "' not found"));
});
}
/**
* Notifies clients that the list of available resources has changed.
* @return A Mono that completes when all clients have been notified
*/
public Mono<Void> notifyResourcesListChanged() {
return this.mcpSession.sendNotification(McpSchema.METHOD_NOTIFICATION_RESOURCES_LIST_CHANGED, null);
}
private DefaultMcpSession.RequestHandler<McpSchema.ListResourcesResult> resourcesListRequestHandler() {
return params -> {
var resourceList = this.resources.values()
.stream()
.map(McpServerFeatures.AsyncResourceRegistration::resource)
.toList();
return Mono.just(new McpSchema.ListResourcesResult(resourceList, null));
};
}
private DefaultMcpSession.RequestHandler<McpSchema.ListResourceTemplatesResult> resourceTemplateListRequestHandler() {
return params -> Mono.just(new McpSchema.ListResourceTemplatesResult(this.resourceTemplates, null));
}
private DefaultMcpSession.RequestHandler<McpSchema.ReadResourceResult> resourcesReadRequestHandler() {
return params -> {
McpSchema.ReadResourceRequest resourceRequest = transport.unmarshalFrom(params,
new TypeReference<McpSchema.ReadResourceRequest>() {
});
var resourceUri = resourceRequest.uri();
McpServerFeatures.AsyncResourceRegistration registration = this.resources.get(resourceUri);
if (registration != null) {
return registration.readHandler().apply(resourceRequest);
}
return Mono.error(new McpError("Resource not found: " + resourceUri));
};
}
// ---------------------------------------
// Prompt Management
// ---------------------------------------
/**
* Add a new prompt handler at runtime.
* @param promptRegistration The prompt handler to add
* @return Mono that completes when clients have been notified of the change
*/
public Mono<Void> addPrompt(McpServerFeatures.AsyncPromptRegistration promptRegistration) {
if (promptRegistration == null) {
return Mono.error(new McpError("Prompt registration must not be null"));
}
if (this.serverCapabilities.prompts() == null) {
return Mono.error(new McpError("Server must be configured with prompt capabilities"));
}
return Mono.defer(() -> {
McpServerFeatures.AsyncPromptRegistration registration = this.prompts
.putIfAbsent(promptRegistration.prompt().name(), promptRegistration);
if (registration != null) {
return Mono.error(
new McpError("Prompt with name '" + promptRegistration.prompt().name() + "' already exists"));
}
logger.info("Added prompt handler: {}", promptRegistration.prompt().name());
// Servers that declared the listChanged capability SHOULD send a
// notification,
// when the list of available prompts changes
if (this.serverCapabilities.prompts().listChanged()) {
return notifyPromptsListChanged();
}
return Mono.empty();
});
}
/**
* Remove a prompt handler at runtime.
* @param promptName The name of the prompt handler to remove
* @return Mono that completes when clients have been notified of the change
*/
public Mono<Void> removePrompt(String promptName) {
if (promptName == null) {
return Mono.error(new McpError("Prompt name must not be null"));
}
if (this.serverCapabilities.prompts() == null) {
return Mono.error(new McpError("Server must be configured with prompt capabilities"));
}
return Mono.defer(() -> {
McpServerFeatures.AsyncPromptRegistration removed = this.prompts.remove(promptName);
if (removed != null) {
logger.info("Removed prompt handler: {}", promptName);
// Servers that declared the listChanged capability SHOULD send a
// notification, when the list of available prompts changes
if (this.serverCapabilities.prompts().listChanged()) {
return this.notifyPromptsListChanged();
}
return Mono.empty();
}
return Mono.error(new McpError("Prompt with name '" + promptName + "' not found"));
});
}
/**
* Notifies clients that the list of available prompts has changed.
* @return A Mono that completes when all clients have been notified
*/
public Mono<Void> notifyPromptsListChanged() {
return this.mcpSession.sendNotification(McpSchema.METHOD_NOTIFICATION_PROMPTS_LIST_CHANGED, null);
}
private DefaultMcpSession.RequestHandler<McpSchema.ListPromptsResult> promptsListRequestHandler() {
return params -> {
// TODO: Implement pagination
// McpSchema.PaginatedRequest request = transport.unmarshalFrom(params,
// new TypeReference<McpSchema.PaginatedRequest>() {
// });
var promptList = this.prompts.values()
.stream()
.map(McpServerFeatures.AsyncPromptRegistration::prompt)
.toList();
return Mono.just(new McpSchema.ListPromptsResult(promptList, null));
};
}
private DefaultMcpSession.RequestHandler<McpSchema.GetPromptResult> promptsGetRequestHandler() {
return params -> {
McpSchema.GetPromptRequest promptRequest = transport.unmarshalFrom(params,
new TypeReference<McpSchema.GetPromptRequest>() {
});
// Implement prompt retrieval logic here
McpServerFeatures.AsyncPromptRegistration registration = this.prompts.get(promptRequest.name());
if (registration == null) {
return Mono.error(new McpError("Prompt not found: " + promptRequest.name()));
}
return registration.promptHandler().apply(promptRequest);
};
}
// ---------------------------------------
// Logging Management
// ---------------------------------------
/**
* Send a logging message notification to all connected clients. Messages below the
* current minimum logging level will be filtered out.
* @param loggingMessageNotification The logging message to send
* @return A Mono that completes when the notification has been sent
*/
public Mono<Void> loggingNotification(LoggingMessageNotification loggingMessageNotification) {
if (loggingMessageNotification == null) {
return Mono.error(new McpError("Logging message must not be null"));
}
Map<String, Object> params = this.transport.unmarshalFrom(loggingMessageNotification,
new TypeReference<Map<String, Object>>() {
});
if (loggingMessageNotification.level().level() < minLoggingLevel.level()) {
return Mono.empty();
}
return this.mcpSession.sendNotification(McpSchema.METHOD_NOTIFICATION_MESSAGE, params);
}
/**
* Handles requests to set the minimum logging level. Messages below this level will
* not be sent.
* @return A handler that processes logging level change requests
*/
private DefaultMcpSession.RequestHandler<Void> setLoggerRequestHandler() {
return params -> {
this.minLoggingLevel = transport.unmarshalFrom(params, new TypeReference<LoggingLevel>() {
});
return Mono.empty();
};
}
// ---------------------------------------
// Sampling
// ---------------------------------------
private static final TypeReference<McpSchema.CreateMessageResult> CREATE_MESSAGE_RESULT_TYPE_REF = new TypeReference<>() {
};
/**
* Create a new message using the sampling capabilities of the client. The Model
* Context Protocol (MCP) provides a standardized way for servers to request LLM
* sampling (“completions” or “generations”) from language models via clients. This
* flow allows clients to maintain control over model access, selection, and
* permissions while enabling servers to leverage AI capabilities—with no server API
* keys necessary. Servers can request text or image-based interactions and optionally
* include context from MCP servers in their prompts.
* @param createMessageRequest The request to create a new message
* @return A Mono that completes when the message has been created
* @throws McpError if the client has not been initialized or does not support
* sampling capabilities
* @throws McpError if the client does not support the createMessage method
* @see McpSchema.CreateMessageRequest
* @see McpSchema.CreateMessageResult
* @see <a href=
* "https://spec.modelcontextprotocol.io/specification/client/sampling/">Sampling
* Specification</a>
*/
public Mono<McpSchema.CreateMessageResult> createMessage(McpSchema.CreateMessageRequest createMessageRequest) {
if (this.clientCapabilities == null) {
return Mono.error(new McpError("Client must be initialized. Call the initialize method first!"));
}
if (this.clientCapabilities.sampling() == null) {
return Mono.error(new McpError("Client must be configured with sampling capabilities"));
}
return this.mcpSession.sendRequest(McpSchema.METHOD_SAMPLING_CREATE_MESSAGE, createMessageRequest,
CREATE_MESSAGE_RESULT_TYPE_REF);
}
/**
* This method is package-private and used for test only. Should not be called by user
* code.
* @param protocolVersions the Client supported protocol versions.
*/
void setProtocolVersions(List<String> protocolVersions) {
this.protocolVersions = protocolVersions;
}
}

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@ -0,0 +1,897 @@
/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.server;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;
import java.util.function.Function;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpTransport;
import io.modelcontextprotocol.spec.ServerMcpTransport;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import io.modelcontextprotocol.spec.McpSchema.ResourceTemplate;
import io.modelcontextprotocol.util.Assert;
import reactor.core.publisher.Mono;
/**
* Factory class for creating Model Context Protocol (MCP) servers. MCP servers expose
* tools, resources, and prompts to AI models through a standardized interface.
*
* <p>
* This class serves as the main entry point for implementing the server-side of the MCP
* specification. The server's responsibilities include:
* <ul>
* <li>Exposing tools that models can invoke to perform actions
* <li>Providing access to resources that give models context
* <li>Managing prompt templates for structured model interactions
* <li>Handling client connections and requests
* <li>Implementing capability negotiation
* </ul>
*
* <p>
* Thread Safety: Both synchronous and asynchronous server implementations are
* thread-safe. The synchronous server processes requests sequentially, while the
* asynchronous server can handle concurrent requests safely through its reactive
* programming model.
*
* <p>
* Error Handling: The server implementations provide robust error handling through the
* McpError class. Errors are properly propagated to clients while maintaining the
* server's stability. Server implementations should use appropriate error codes and
* provide meaningful error messages to help diagnose issues.
*
* <p>
* The class provides factory methods to create either:
* <ul>
* <li>{@link McpAsyncServer} for non-blocking operations with CompletableFuture responses
* <li>{@link McpSyncServer} for blocking operations with direct responses
* </ul>
*
* <p>
* Example of creating a basic synchronous server: <pre>{@code
* McpServer.sync(transport)
* .serverInfo("my-server", "1.0.0")
* .tool(new Tool("calculator", "Performs calculations", schema),
* args -> new CallToolResult("Result: " + calculate(args)))
* .build();
* }</pre>
*
* Example of creating a basic asynchronous server: <pre>{@code
* McpServer.async(transport)
* .serverInfo("my-server", "1.0.0")
* .tool(new Tool("calculator", "Performs calculations", schema),
* args -> Mono.just(new CallToolResult("Result: " + calculate(args))))
* .build();
* }</pre>
*
* <p>
* Example with comprehensive asynchronous configuration: <pre>{@code
* McpServer.async(transport)
* .serverInfo("advanced-server", "2.0.0")
* .capabilities(new ServerCapabilities(...))
* // Register tools
* .tools(
* new McpServerFeatures.AsyncToolRegistration(calculatorTool,
* args -> Mono.just(new CallToolResult("Result: " + calculate(args)))),
* new McpServerFeatures.AsyncToolRegistration(weatherTool,
* args -> Mono.just(new CallToolResult("Weather: " + getWeather(args))))
* )
* // Register resources
* .resources(
* new McpServerFeatures.AsyncResourceRegistration(fileResource,
* req -> Mono.just(new ReadResourceResult(readFile(req)))),
* new McpServerFeatures.AsyncResourceRegistration(dbResource,
* req -> Mono.just(new ReadResourceResult(queryDb(req))))
* )
* // Add resource templates
* .resourceTemplates(
* new ResourceTemplate("file://{path}", "Access files"),
* new ResourceTemplate("db://{table}", "Access database")
* )
* // Register prompts
* .prompts(
* new McpServerFeatures.AsyncPromptRegistration(analysisPrompt,
* req -> Mono.just(new GetPromptResult(generateAnalysisPrompt(req)))),
* new McpServerFeatures.AsyncPromptRegistration(summaryPrompt,
* req -> Mono.just(new GetPromptResult(generateSummaryPrompt(req))))
* )
* .build();
* }</pre>
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
* @see McpAsyncServer
* @see McpSyncServer
* @see McpTransport
*/
public interface McpServer {
/**
* Starts building a synchronous MCP server that provides blocking operations.
* Synchronous servers process each request to completion before handling the next
* one, making them simpler to implement but potentially less performant for
* concurrent operations.
* @param transport The transport layer implementation for MCP communication
* @return A new instance of {@link SyncSpec} for configuring the server.
*/
static SyncSpec sync(ServerMcpTransport transport) {
return new SyncSpec(transport);
}
/**
* Starts building an asynchronous MCP server that provides blocking operations.
* Asynchronous servers can handle multiple requests concurrently using a functional
* paradigm with non-blocking server transports, making them more efficient for
* high-concurrency scenarios but more complex to implement.
* @param transport The transport layer implementation for MCP communication
* @return A new instance of {@link SyncSpec} for configuring the server.
*/
static AsyncSpec async(ServerMcpTransport transport) {
return new AsyncSpec(transport);
}
/**
* Asynchronous server specification.
*/
class AsyncSpec {
private static final McpSchema.Implementation DEFAULT_SERVER_INFO = new McpSchema.Implementation("mcp-server",
"1.0.0");
private final ServerMcpTransport transport;
private McpSchema.Implementation serverInfo = DEFAULT_SERVER_INFO;
private McpSchema.ServerCapabilities serverCapabilities;
/**
* The Model Context Protocol (MCP) allows servers to expose tools that can be
* invoked by language models. Tools enable models to interact with external
* systems, such as querying databases, calling APIs, or performing computations.
* Each tool is uniquely identified by a name and includes metadata describing its
* schema.
*/
private final List<McpServerFeatures.AsyncToolRegistration> tools = new ArrayList<>();
/**
* The Model Context Protocol (MCP) provides a standardized way for servers to
* expose resources to clients. Resources allow servers to share data that
* provides context to language models, such as files, database schemas, or
* application-specific information. Each resource is uniquely identified by a
* URI.
*/
private final Map<String, McpServerFeatures.AsyncResourceRegistration> resources = new HashMap<>();
private final List<ResourceTemplate> resourceTemplates = new ArrayList<>();
/**
* The Model Context Protocol (MCP) provides a standardized way for servers to
* expose prompt templates to clients. Prompts allow servers to provide structured
* messages and instructions for interacting with language models. Clients can
* discover available prompts, retrieve their contents, and provide arguments to
* customize them.
*/
private final Map<String, McpServerFeatures.AsyncPromptRegistration> prompts = new HashMap<>();
private final List<Function<List<McpSchema.Root>, Mono<Void>>> rootsChangeConsumers = new ArrayList<>();
private AsyncSpec(ServerMcpTransport transport) {
Assert.notNull(transport, "Transport must not be null");
this.transport = transport;
}
/**
* Sets the server implementation information that will be shared with clients
* during connection initialization. This helps with version compatibility,
* debugging, and server identification.
* @param serverInfo The server implementation details including name and version.
* Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if serverInfo is null
*/
public AsyncSpec serverInfo(McpSchema.Implementation serverInfo) {
Assert.notNull(serverInfo, "Server info must not be null");
this.serverInfo = serverInfo;
return this;
}
/**
* Sets the server implementation information using name and version strings. This
* is a convenience method alternative to
* {@link #serverInfo(McpSchema.Implementation)}.
* @param name The server name. Must not be null or empty.
* @param version The server version. Must not be null or empty.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if name or version is null or empty
* @see #serverInfo(McpSchema.Implementation)
*/
public AsyncSpec serverInfo(String name, String version) {
Assert.hasText(name, "Name must not be null or empty");
Assert.hasText(version, "Version must not be null or empty");
this.serverInfo = new McpSchema.Implementation(name, version);
return this;
}
/**
* Sets the server capabilities that will be advertised to clients during
* connection initialization. Capabilities define what features the server
* supports, such as:
* <ul>
* <li>Tool execution
* <li>Resource access
* <li>Prompt handling
* <li>Streaming responses
* <li>Batch operations
* </ul>
* @param serverCapabilities The server capabilities configuration. Must not be
* null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if serverCapabilities is null
*/
public AsyncSpec capabilities(McpSchema.ServerCapabilities serverCapabilities) {
this.serverCapabilities = serverCapabilities;
return this;
}
/**
* Adds a single tool with its implementation handler to the server. This is a
* convenience method for registering individual tools without creating a
* {@link McpServerFeatures.AsyncToolRegistration} explicitly.
*
* <p>
* Example usage: <pre>{@code
* .tool(
* new Tool("calculator", "Performs calculations", schema),
* args -> Mono.just(new CallToolResult("Result: " + calculate(args)))
* )
* }</pre>
* @param tool The tool definition including name, description, and schema. Must
* not be null.
* @param handler The function that implements the tool's logic. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if tool or handler is null
*/
public AsyncSpec tool(McpSchema.Tool tool, Function<Map<String, Object>, Mono<CallToolResult>> handler) {
Assert.notNull(tool, "Tool must not be null");
Assert.notNull(handler, "Handler must not be null");
this.tools.add(new McpServerFeatures.AsyncToolRegistration(tool, handler));
return this;
}
/**
* Adds multiple tools with their handlers to the server using a List. This method
* is useful when tools are dynamically generated or loaded from a configuration
* source.
* @param toolRegistrations The list of tool registrations to add. Must not be
* null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if toolRegistrations is null
* @see #tools(McpServerFeatures.AsyncToolRegistration...)
*/
public AsyncSpec tools(List<McpServerFeatures.AsyncToolRegistration> toolRegistrations) {
Assert.notNull(toolRegistrations, "Tool handlers list must not be null");
this.tools.addAll(toolRegistrations);
return this;
}
/**
* Adds multiple tools with their handlers to the server using varargs. This
* method provides a convenient way to register multiple tools inline.
*
* <p>
* Example usage: <pre>{@code
* .tools(
* new McpServerFeatures.AsyncToolRegistration(calculatorTool, calculatorHandler),
* new McpServerFeatures.AsyncToolRegistration(weatherTool, weatherHandler),
* new McpServerFeatures.AsyncToolRegistration(fileManagerTool, fileManagerHandler)
* )
* }</pre>
* @param toolRegistrations The tool registrations to add. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if toolRegistrations is null
* @see #tools(List)
*/
public AsyncSpec tools(McpServerFeatures.AsyncToolRegistration... toolRegistrations) {
for (McpServerFeatures.AsyncToolRegistration tool : toolRegistrations) {
this.tools.add(tool);
}
return this;
}
/**
* Registers multiple resources with their handlers using a Map. This method is
* useful when resources are dynamically generated or loaded from a configuration
* source.
* @param resourceRegsitrations Map of resource name to registration. Must not be
* null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if resourceRegsitrations is null
* @see #resources(McpServerFeatures.AsyncResourceRegistration...)
*/
public AsyncSpec resources(Map<String, McpServerFeatures.AsyncResourceRegistration> resourceRegsitrations) {
Assert.notNull(resourceRegsitrations, "Resource handlers map must not be null");
this.resources.putAll(resourceRegsitrations);
return this;
}
/**
* Registers multiple resources with their handlers using a List. This method is
* useful when resources need to be added in bulk from a collection.
* @param resourceRegsitrations List of resource registrations. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if resourceRegsitrations is null
* @see #resources(McpServerFeatures.AsyncResourceRegistration...)
*/
public AsyncSpec resources(List<McpServerFeatures.AsyncResourceRegistration> resourceRegsitrations) {
Assert.notNull(resourceRegsitrations, "Resource handlers list must not be null");
for (McpServerFeatures.AsyncResourceRegistration resource : resourceRegsitrations) {
this.resources.put(resource.resource().uri(), resource);
}
return this;
}
/**
* Registers multiple resources with their handlers using varargs. This method
* provides a convenient way to register multiple resources inline.
*
* <p>
* Example usage: <pre>{@code
* .resources(
* new McpServerFeatures.AsyncResourceRegistration(fileResource, fileHandler),
* new McpServerFeatures.AsyncResourceRegistration(dbResource, dbHandler),
* new McpServerFeatures.AsyncResourceRegistration(apiResource, apiHandler)
* )
* }</pre>
* @param resourceRegistrations The resource registrations to add. Must not be
* null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if resourceRegistrations is null
*/
public AsyncSpec resources(McpServerFeatures.AsyncResourceRegistration... resourceRegistrations) {
Assert.notNull(resourceRegistrations, "Resource handlers list must not be null");
for (McpServerFeatures.AsyncResourceRegistration resource : resourceRegistrations) {
this.resources.put(resource.resource().uri(), resource);
}
return this;
}
/**
* Sets the resource templates that define patterns for dynamic resource access.
* Templates use URI patterns with placeholders that can be filled at runtime.
*
* <p>
* Example usage: <pre>{@code
* .resourceTemplates(
* new ResourceTemplate("file://{path}", "Access files by path"),
* new ResourceTemplate("db://{table}/{id}", "Access database records")
* )
* }</pre>
* @param resourceTemplates List of resource templates. If null, clears existing
* templates.
* @return This builder instance for method chaining
* @see #resourceTemplates(ResourceTemplate...)
*/
public AsyncSpec resourceTemplates(List<ResourceTemplate> resourceTemplates) {
this.resourceTemplates.addAll(resourceTemplates);
return this;
}
/**
* Sets the resource templates using varargs for convenience. This is an
* alternative to {@link #resourceTemplates(List)}.
* @param resourceTemplates The resource templates to set.
* @return This builder instance for method chaining
* @see #resourceTemplates(List)
*/
public AsyncSpec resourceTemplates(ResourceTemplate... resourceTemplates) {
for (ResourceTemplate resourceTemplate : resourceTemplates) {
this.resourceTemplates.add(resourceTemplate);
}
return this;
}
/**
* Registers multiple prompts with their handlers using a Map. This method is
* useful when prompts are dynamically generated or loaded from a configuration
* source.
*
* <p>
* Example usage: <pre>{@code
* .prompts(Map.of("analysis", new McpServerFeatures.AsyncPromptRegistration(
* new Prompt("analysis", "Code analysis template"),
* request -> Mono.just(new GetPromptResult(generateAnalysisPrompt(request)))
* )));
* }</pre>
* @param prompts Map of prompt name to registration. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if prompts is null
*/
public AsyncSpec prompts(Map<String, McpServerFeatures.AsyncPromptRegistration> prompts) {
this.prompts.putAll(prompts);
return this;
}
/**
* Registers multiple prompts with their handlers using a List. This method is
* useful when prompts need to be added in bulk from a collection.
* @param prompts List of prompt registrations. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if prompts is null
* @see #prompts(McpServerFeatures.AsyncPromptRegistration...)
*/
public AsyncSpec prompts(List<McpServerFeatures.AsyncPromptRegistration> prompts) {
for (McpServerFeatures.AsyncPromptRegistration prompt : prompts) {
this.prompts.put(prompt.prompt().name(), prompt);
}
return this;
}
/**
* Registers multiple prompts with their handlers using varargs. This method
* provides a convenient way to register multiple prompts inline.
*
* <p>
* Example usage: <pre>{@code
* .prompts(
* new McpServerFeatures.AsyncPromptRegistration(analysisPrompt, analysisHandler),
* new McpServerFeatures.AsyncPromptRegistration(summaryPrompt, summaryHandler),
* new McpServerFeatures.AsyncPromptRegistration(reviewPrompt, reviewHandler)
* )
* }</pre>
* @param prompts The prompt registrations to add. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if prompts is null
*/
public AsyncSpec prompts(McpServerFeatures.AsyncPromptRegistration... prompts) {
for (McpServerFeatures.AsyncPromptRegistration prompt : prompts) {
this.prompts.put(prompt.prompt().name(), prompt);
}
return this;
}
/**
* Registers a consumer that will be notified when the list of roots changes. This
* is useful for updating resource availability dynamically, such as when new
* files are added or removed.
* @param consumer The consumer to register. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if consumer is null
*/
public AsyncSpec rootsChangeConsumer(Function<List<McpSchema.Root>, Mono<Void>> consumer) {
Assert.notNull(consumer, "Consumer must not be null");
this.rootsChangeConsumers.add(consumer);
return this;
}
/**
* Registers multiple consumers that will be notified when the list of roots
* changes. This method is useful when multiple consumers need to be registered at
* once.
* @param consumers The list of consumers to register. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if consumers is null
*/
public AsyncSpec rootsChangeConsumers(List<Function<List<McpSchema.Root>, Mono<Void>>> consumers) {
Assert.notNull(consumers, "Consumers list must not be null");
this.rootsChangeConsumers.addAll(consumers);
return this;
}
/**
* Registers multiple consumers that will be notified when the list of roots
* changes using varargs. This method provides a convenient way to register
* multiple consumers inline.
* @param consumers The consumers to register. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if consumers is null
*/
public AsyncSpec rootsChangeConsumers(
@SuppressWarnings("unchecked") Function<List<McpSchema.Root>, Mono<Void>>... consumers) {
for (Function<List<McpSchema.Root>, Mono<Void>> consumer : consumers) {
this.rootsChangeConsumers.add(consumer);
}
return this;
}
/**
* Builds an asynchronous MCP server that provides non-blocking operations.
* @return A new instance of {@link McpAsyncServer} configured with this builder's
* settings
*/
public McpAsyncServer build() {
return new McpAsyncServer(this.transport,
new McpServerFeatures.Async(this.serverInfo, this.serverCapabilities, this.tools, this.resources,
this.resourceTemplates, this.prompts, this.rootsChangeConsumers));
}
}
/**
* Synchronous server specification.
*/
class SyncSpec {
private static final McpSchema.Implementation DEFAULT_SERVER_INFO = new McpSchema.Implementation("mcp-server",
"1.0.0");
private final ServerMcpTransport transport;
private McpSchema.Implementation serverInfo = DEFAULT_SERVER_INFO;
private McpSchema.ServerCapabilities serverCapabilities;
/**
* The Model Context Protocol (MCP) allows servers to expose tools that can be
* invoked by language models. Tools enable models to interact with external
* systems, such as querying databases, calling APIs, or performing computations.
* Each tool is uniquely identified by a name and includes metadata describing its
* schema.
*/
private final List<McpServerFeatures.SyncToolRegistration> tools = new ArrayList<>();
/**
* The Model Context Protocol (MCP) provides a standardized way for servers to
* expose resources to clients. Resources allow servers to share data that
* provides context to language models, such as files, database schemas, or
* application-specific information. Each resource is uniquely identified by a
* URI.
*/
private final Map<String, McpServerFeatures.SyncResourceRegistration> resources = new HashMap<>();
private final List<ResourceTemplate> resourceTemplates = new ArrayList<>();
/**
* The Model Context Protocol (MCP) provides a standardized way for servers to
* expose prompt templates to clients. Prompts allow servers to provide structured
* messages and instructions for interacting with language models. Clients can
* discover available prompts, retrieve their contents, and provide arguments to
* customize them.
*/
private final Map<String, McpServerFeatures.SyncPromptRegistration> prompts = new HashMap<>();
private final List<Consumer<List<McpSchema.Root>>> rootsChangeConsumers = new ArrayList<>();
private SyncSpec(ServerMcpTransport transport) {
Assert.notNull(transport, "Transport must not be null");
this.transport = transport;
}
/**
* Sets the server implementation information that will be shared with clients
* during connection initialization. This helps with version compatibility,
* debugging, and server identification.
* @param serverInfo The server implementation details including name and version.
* Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if serverInfo is null
*/
public SyncSpec serverInfo(McpSchema.Implementation serverInfo) {
Assert.notNull(serverInfo, "Server info must not be null");
this.serverInfo = serverInfo;
return this;
}
/**
* Sets the server implementation information using name and version strings. This
* is a convenience method alternative to
* {@link #serverInfo(McpSchema.Implementation)}.
* @param name The server name. Must not be null or empty.
* @param version The server version. Must not be null or empty.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if name or version is null or empty
* @see #serverInfo(McpSchema.Implementation)
*/
public SyncSpec serverInfo(String name, String version) {
Assert.hasText(name, "Name must not be null or empty");
Assert.hasText(version, "Version must not be null or empty");
this.serverInfo = new McpSchema.Implementation(name, version);
return this;
}
/**
* Sets the server capabilities that will be advertised to clients during
* connection initialization. Capabilities define what features the server
* supports, such as:
* <ul>
* <li>Tool execution
* <li>Resource access
* <li>Prompt handling
* <li>Streaming responses
* <li>Batch operations
* </ul>
* @param serverCapabilities The server capabilities configuration. Must not be
* null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if serverCapabilities is null
*/
public SyncSpec capabilities(McpSchema.ServerCapabilities serverCapabilities) {
this.serverCapabilities = serverCapabilities;
return this;
}
/**
* Adds a single tool with its implementation handler to the server. This is a
* convenience method for registering individual tools without creating a
* {@link ToolRegistration} explicitly.
*
* <p>
* Example usage: <pre>{@code
* .tool(
* new Tool("calculator", "Performs calculations", schema),
* args -> new CallToolResult("Result: " + calculate(args))
* )
* }</pre>
* @param tool The tool definition including name, description, and schema. Must
* not be null.
* @param handler The function that implements the tool's logic. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if tool or handler is null
*/
public SyncSpec tool(McpSchema.Tool tool, Function<Map<String, Object>, McpSchema.CallToolResult> handler) {
Assert.notNull(tool, "Tool must not be null");
Assert.notNull(handler, "Handler must not be null");
this.tools.add(new McpServerFeatures.SyncToolRegistration(tool, handler));
return this;
}
/**
* Adds multiple tools with their handlers to the server using a List. This method
* is useful when tools are dynamically generated or loaded from a configuration
* source.
* @param toolRegistrations The list of tool registrations to add. Must not be
* null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if toolRegistrations is null
* @see #tools(McpServerFeatures.SyncToolRegistration...)
*/
public SyncSpec tools(List<McpServerFeatures.SyncToolRegistration> toolRegistrations) {
Assert.notNull(toolRegistrations, "Tool handlers list must not be null");
this.tools.addAll(toolRegistrations);
return this;
}
/**
* Adds multiple tools with their handlers to the server using varargs. This
* method provides a convenient way to register multiple tools inline.
*
* <p>
* Example usage: <pre>{@code
* .tools(
* new ToolRegistration(calculatorTool, calculatorHandler),
* new ToolRegistration(weatherTool, weatherHandler),
* new ToolRegistration(fileManagerTool, fileManagerHandler)
* )
* }</pre>
* @param toolRegistrations The tool registrations to add. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if toolRegistrations is null
* @see #tools(List)
*/
public SyncSpec tools(McpServerFeatures.SyncToolRegistration... toolRegistrations) {
for (McpServerFeatures.SyncToolRegistration tool : toolRegistrations) {
this.tools.add(tool);
}
return this;
}
/**
* Registers multiple resources with their handlers using a Map. This method is
* useful when resources are dynamically generated or loaded from a configuration
* source.
* @param resourceRegsitrations Map of resource name to registration. Must not be
* null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if resourceRegsitrations is null
* @see #resources(McpServerFeatures.SyncResourceRegistration...)
*/
public SyncSpec resources(Map<String, McpServerFeatures.SyncResourceRegistration> resourceRegsitrations) {
Assert.notNull(resourceRegsitrations, "Resource handlers map must not be null");
this.resources.putAll(resourceRegsitrations);
return this;
}
/**
* Registers multiple resources with their handlers using a List. This method is
* useful when resources need to be added in bulk from a collection.
* @param resourceRegsitrations List of resource registrations. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if resourceRegsitrations is null
* @see #resources(McpServerFeatures.SyncResourceRegistration...)
*/
public SyncSpec resources(List<McpServerFeatures.SyncResourceRegistration> resourceRegsitrations) {
Assert.notNull(resourceRegsitrations, "Resource handlers list must not be null");
for (McpServerFeatures.SyncResourceRegistration resource : resourceRegsitrations) {
this.resources.put(resource.resource().uri(), resource);
}
return this;
}
/**
* Registers multiple resources with their handlers using varargs. This method
* provides a convenient way to register multiple resources inline.
*
* <p>
* Example usage: <pre>{@code
* .resources(
* new ResourceRegistration(fileResource, fileHandler),
* new ResourceRegistration(dbResource, dbHandler),
* new ResourceRegistration(apiResource, apiHandler)
* )
* }</pre>
* @param resourceRegistrations The resource registrations to add. Must not be
* null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if resourceRegistrations is null
*/
public SyncSpec resources(McpServerFeatures.SyncResourceRegistration... resourceRegistrations) {
Assert.notNull(resourceRegistrations, "Resource handlers list must not be null");
for (McpServerFeatures.SyncResourceRegistration resource : resourceRegistrations) {
this.resources.put(resource.resource().uri(), resource);
}
return this;
}
/**
* Sets the resource templates that define patterns for dynamic resource access.
* Templates use URI patterns with placeholders that can be filled at runtime.
*
* <p>
* Example usage: <pre>{@code
* .resourceTemplates(
* new ResourceTemplate("file://{path}", "Access files by path"),
* new ResourceTemplate("db://{table}/{id}", "Access database records")
* )
* }</pre>
* @param resourceTemplates List of resource templates. If null, clears existing
* templates.
* @return This builder instance for method chaining
* @see #resourceTemplates(ResourceTemplate...)
*/
public SyncSpec resourceTemplates(List<ResourceTemplate> resourceTemplates) {
this.resourceTemplates.addAll(resourceTemplates);
return this;
}
/**
* Sets the resource templates using varargs for convenience. This is an
* alternative to {@link #resourceTemplates(List)}.
* @param resourceTemplates The resource templates to set.
* @return This builder instance for method chaining
* @see #resourceTemplates(List)
*/
public SyncSpec resourceTemplates(ResourceTemplate... resourceTemplates) {
for (ResourceTemplate resourceTemplate : resourceTemplates) {
this.resourceTemplates.add(resourceTemplate);
}
return this;
}
/**
* Registers multiple prompts with their handlers using a Map. This method is
* useful when prompts are dynamically generated or loaded from a configuration
* source.
*
* <p>
* Example usage: <pre>{@code
* Map<String, PromptRegistration> prompts = new HashMap<>();
* prompts.put("analysis", new PromptRegistration(
* new Prompt("analysis", "Code analysis template"),
* request -> new GetPromptResult(generateAnalysisPrompt(request))
* ));
* .prompts(prompts)
* }</pre>
* @param prompts Map of prompt name to registration. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if prompts is null
*/
public SyncSpec prompts(Map<String, McpServerFeatures.SyncPromptRegistration> prompts) {
this.prompts.putAll(prompts);
return this;
}
/**
* Registers multiple prompts with their handlers using a List. This method is
* useful when prompts need to be added in bulk from a collection.
* @param prompts List of prompt registrations. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if prompts is null
* @see #prompts(McpServerFeatures.SyncPromptRegistration...)
*/
public SyncSpec prompts(List<McpServerFeatures.SyncPromptRegistration> prompts) {
for (McpServerFeatures.SyncPromptRegistration prompt : prompts) {
this.prompts.put(prompt.prompt().name(), prompt);
}
return this;
}
/**
* Registers multiple prompts with their handlers using varargs. This method
* provides a convenient way to register multiple prompts inline.
*
* <p>
* Example usage: <pre>{@code
* .prompts(
* new PromptRegistration(analysisPrompt, analysisHandler),
* new PromptRegistration(summaryPrompt, summaryHandler),
* new PromptRegistration(reviewPrompt, reviewHandler)
* )
* }</pre>
* @param prompts The prompt registrations to add. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if prompts is null
*/
public SyncSpec prompts(McpServerFeatures.SyncPromptRegistration... prompts) {
for (McpServerFeatures.SyncPromptRegistration prompt : prompts) {
this.prompts.put(prompt.prompt().name(), prompt);
}
return this;
}
/**
* Registers a consumer that will be notified when the list of roots changes. This
* is useful for updating resource availability dynamically, such as when new
* files are added or removed.
* @param consumer The consumer to register. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if consumer is null
*/
public SyncSpec rootsChangeConsumer(Consumer<List<McpSchema.Root>> consumer) {
Assert.notNull(consumer, "Consumer must not be null");
this.rootsChangeConsumers.add(consumer);
return this;
}
/**
* Registers multiple consumers that will be notified when the list of roots
* changes. This method is useful when multiple consumers need to be registered at
* once.
* @param consumers The list of consumers to register. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if consumers is null
*/
public SyncSpec rootsChangeConsumers(List<Consumer<List<McpSchema.Root>>> consumers) {
Assert.notNull(consumers, "Consumers list must not be null");
this.rootsChangeConsumers.addAll(consumers);
return this;
}
/**
* Registers multiple consumers that will be notified when the list of roots
* changes using varargs. This method provides a convenient way to register
* multiple consumers inline.
* @param consumers The consumers to register. Must not be null.
* @return This builder instance for method chaining
* @throws IllegalArgumentException if consumers is null
*/
public SyncSpec rootsChangeConsumers(Consumer<List<McpSchema.Root>>... consumers) {
for (Consumer<List<McpSchema.Root>> consumer : consumers) {
this.rootsChangeConsumers.add(consumer);
}
return this;
}
/**
* Builds a synchronous MCP server that provides blocking operations.
* @return A new instance of {@link McpSyncServer} configured with this builder's
* settings
*/
public McpSyncServer build() {
McpServerFeatures.Sync syncFeatures = new McpServerFeatures.Sync(this.serverInfo, this.serverCapabilities,
this.tools, this.resources, this.resourceTemplates, this.prompts, this.rootsChangeConsumers);
return new McpSyncServer(
new McpAsyncServer(this.transport, McpServerFeatures.Async.fromSync(syncFeatures)));
}
}
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.server;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;
import java.util.function.Function;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.util.Assert;
import io.modelcontextprotocol.util.Utils;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;
/**
* MCP server features specification that a particular server can choose to support.
*
* @author Dariusz Jędrzejczyk
*/
public class McpServerFeatures {
/**
* Asynchronous server features specification.
*
* @param serverInfo The server implementation details
* @param serverCapabilities The server capabilities
* @param tools The list of tool registrations
* @param resources The map of resource registrations
* @param resourceTemplates The list of resource templates
* @param prompts The map of prompt registrations
* @param rootsChangeConsumers The list of consumers that will be notified when the
* roots list changes
*/
record Async(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
List<McpServerFeatures.AsyncToolRegistration> tools, Map<String, AsyncResourceRegistration> resources,
List<McpSchema.ResourceTemplate> resourceTemplates,
Map<String, McpServerFeatures.AsyncPromptRegistration> prompts,
List<Function<List<McpSchema.Root>, Mono<Void>>> rootsChangeConsumers) {
/**
* Create an instance and validate the arguments.
* @param serverInfo The server implementation details
* @param serverCapabilities The server capabilities
* @param tools The list of tool registrations
* @param resources The map of resource registrations
* @param resourceTemplates The list of resource templates
* @param prompts The map of prompt registrations
* @param rootsChangeConsumers The list of consumers that will be notified when
* the roots list changes
*/
Async(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
List<McpServerFeatures.AsyncToolRegistration> tools, Map<String, AsyncResourceRegistration> resources,
List<McpSchema.ResourceTemplate> resourceTemplates,
Map<String, McpServerFeatures.AsyncPromptRegistration> prompts,
List<Function<List<McpSchema.Root>, Mono<Void>>> rootsChangeConsumers) {
Assert.notNull(serverInfo, "Server info must not be null");
this.serverInfo = serverInfo;
this.serverCapabilities = (serverCapabilities != null) ? serverCapabilities
: new McpSchema.ServerCapabilities(null, // experimental
new McpSchema.ServerCapabilities.LoggingCapabilities(), // Enable
// logging
// by
// default
!Utils.isEmpty(prompts) ? new McpSchema.ServerCapabilities.PromptCapabilities(false) : null,
!Utils.isEmpty(resources)
? new McpSchema.ServerCapabilities.ResourceCapabilities(false, false) : null,
!Utils.isEmpty(tools) ? new McpSchema.ServerCapabilities.ToolCapabilities(false) : null);
this.tools = (tools != null) ? tools : List.of();
this.resources = (resources != null) ? resources : Map.of();
this.resourceTemplates = (resourceTemplates != null) ? resourceTemplates : List.of();
this.prompts = (prompts != null) ? prompts : Map.of();
this.rootsChangeConsumers = (rootsChangeConsumers != null) ? rootsChangeConsumers : List.of();
}
/**
* Convert a synchronous specification into an asynchronous one and provide
* blocking code offloading to prevent accidental blocking of the non-blocking
* transport.
* @param syncSpec a potentially blocking, synchronous specification.
* @return a specification which is protected from blocking calls specified by the
* user.
*/
static Async fromSync(Sync syncSpec) {
List<McpServerFeatures.AsyncToolRegistration> tools = new ArrayList<>();
for (var tool : syncSpec.tools()) {
tools.add(AsyncToolRegistration.fromSync(tool));
}
Map<String, AsyncResourceRegistration> resources = new HashMap<>();
syncSpec.resources().forEach((key, resource) -> {
resources.put(key, AsyncResourceRegistration.fromSync(resource));
});
Map<String, AsyncPromptRegistration> prompts = new HashMap<>();
syncSpec.prompts().forEach((key, prompt) -> {
prompts.put(key, AsyncPromptRegistration.fromSync(prompt));
});
List<Function<List<McpSchema.Root>, Mono<Void>>> rootChangeConsumers = new ArrayList<>();
for (var rootChangeConsumer : syncSpec.rootsChangeConsumers()) {
rootChangeConsumers.add(list -> Mono.<Void>fromRunnable(() -> rootChangeConsumer.accept(list))
.subscribeOn(Schedulers.boundedElastic()));
}
return new Async(syncSpec.serverInfo(), syncSpec.serverCapabilities(), tools, resources,
syncSpec.resourceTemplates(), prompts, rootChangeConsumers);
}
}
/**
* Synchronous server features specification.
*
* @param serverInfo The server implementation details
* @param serverCapabilities The server capabilities
* @param tools The list of tool registrations
* @param resources The map of resource registrations
* @param resourceTemplates The list of resource templates
* @param prompts The map of prompt registrations
* @param rootsChangeConsumers The list of consumers that will be notified when the
* roots list changes
*/
record Sync(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
List<McpServerFeatures.SyncToolRegistration> tools,
Map<String, McpServerFeatures.SyncResourceRegistration> resources,
List<McpSchema.ResourceTemplate> resourceTemplates,
Map<String, McpServerFeatures.SyncPromptRegistration> prompts,
List<Consumer<List<McpSchema.Root>>> rootsChangeConsumers) {
/**
* Create an instance and validate the arguments.
* @param serverInfo The server implementation details
* @param serverCapabilities The server capabilities
* @param tools The list of tool registrations
* @param resources The map of resource registrations
* @param resourceTemplates The list of resource templates
* @param prompts The map of prompt registrations
* @param rootsChangeConsumers The list of consumers that will be notified when
* the roots list changes
*/
Sync(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
List<McpServerFeatures.SyncToolRegistration> tools,
Map<String, McpServerFeatures.SyncResourceRegistration> resources,
List<McpSchema.ResourceTemplate> resourceTemplates,
Map<String, McpServerFeatures.SyncPromptRegistration> prompts,
List<Consumer<List<McpSchema.Root>>> rootsChangeConsumers) {
Assert.notNull(serverInfo, "Server info must not be null");
this.serverInfo = serverInfo;
this.serverCapabilities = (serverCapabilities != null) ? serverCapabilities
: new McpSchema.ServerCapabilities(null, // experimental
new McpSchema.ServerCapabilities.LoggingCapabilities(), // Enable
// logging
// by
// default
!Utils.isEmpty(prompts) ? new McpSchema.ServerCapabilities.PromptCapabilities(false) : null,
!Utils.isEmpty(resources)
? new McpSchema.ServerCapabilities.ResourceCapabilities(false, false) : null,
!Utils.isEmpty(tools) ? new McpSchema.ServerCapabilities.ToolCapabilities(false) : null);
this.tools = (tools != null) ? tools : new ArrayList<>();
this.resources = (resources != null) ? resources : new HashMap<>();
this.resourceTemplates = (resourceTemplates != null) ? resourceTemplates : new ArrayList<>();
this.prompts = (prompts != null) ? prompts : new HashMap<>();
this.rootsChangeConsumers = (rootsChangeConsumers != null) ? rootsChangeConsumers : new ArrayList<>();
}
}
/**
* Registration of a tool with its asynchronous handler function. Tools are the
* primary way for MCP servers to expose functionality to AI models. Each tool
* represents a specific capability, such as:
* <ul>
* <li>Performing calculations
* <li>Accessing external APIs
* <li>Querying databases
* <li>Manipulating files
* <li>Executing system commands
* </ul>
*
* <p>
* Example tool registration: <pre>{@code
* new McpServerFeatures.AsyncToolRegistration(
* new Tool(
* "calculator",
* "Performs mathematical calculations",
* new JsonSchemaObject()
* .required("expression")
* .property("expression", JsonSchemaType.STRING)
* ),
* args -> {
* String expr = (String) args.get("expression");
* return Mono.just(new CallToolResult("Result: " + evaluate(expr)));
* }
* )
* }</pre>
*
* @param tool The tool definition including name, description, and parameter schema
* @param call The function that implements the tool's logic, receiving arguments and
* returning results
*/
public record AsyncToolRegistration(McpSchema.Tool tool,
Function<Map<String, Object>, Mono<McpSchema.CallToolResult>> call) {
static AsyncToolRegistration fromSync(SyncToolRegistration tool) {
// FIXME: This is temporary, proper validation should be implemented
if (tool == null) {
return null;
}
return new AsyncToolRegistration(tool.tool(),
map -> Mono.fromCallable(() -> tool.call().apply(map)).subscribeOn(Schedulers.boundedElastic()));
}
}
/**
* Registration of a resource with its asynchronous handler function. Resources
* provide context to AI models by exposing data such as:
* <ul>
* <li>File contents
* <li>Database records
* <li>API responses
* <li>System information
* <li>Application state
* </ul>
*
* <p>
* Example resource registration: <pre>{@code
* new McpServerFeatures.AsyncResourceRegistration(
* new Resource("docs", "Documentation files", "text/markdown"),
* request -> {
* String content = readFile(request.getPath());
* return Mono.just(new ReadResourceResult(content));
* }
* )
* }</pre>
*
* @param resource The resource definition including name, description, and MIME type
* @param readHandler The function that handles resource read requests
*/
public record AsyncResourceRegistration(McpSchema.Resource resource,
Function<McpSchema.ReadResourceRequest, Mono<McpSchema.ReadResourceResult>> readHandler) {
static AsyncResourceRegistration fromSync(SyncResourceRegistration resource) {
// FIXME: This is temporary, proper validation should be implemented
if (resource == null) {
return null;
}
return new AsyncResourceRegistration(resource.resource(),
req -> Mono.fromCallable(() -> resource.readHandler().apply(req))
.subscribeOn(Schedulers.boundedElastic()));
}
}
/**
* Registration of a prompt template with its asynchronous handler function. Prompts
* provide structured templates for AI model interactions, supporting:
* <ul>
* <li>Consistent message formatting
* <li>Parameter substitution
* <li>Context injection
* <li>Response formatting
* <li>Instruction templating
* </ul>
*
* <p>
* Example prompt registration: <pre>{@code
* new McpServerFeatures.AsyncPromptRegistration(
* new Prompt("analyze", "Code analysis template"),
* request -> {
* String code = request.getArguments().get("code");
* return Mono.just(new GetPromptResult(
* "Analyze this code:\n\n" + code + "\n\nProvide feedback on:"
* ));
* }
* )
* }</pre>
*
* @param prompt The prompt definition including name and description
* @param promptHandler The function that processes prompt requests and returns
* formatted templates
*/
public record AsyncPromptRegistration(McpSchema.Prompt prompt,
Function<McpSchema.GetPromptRequest, Mono<McpSchema.GetPromptResult>> promptHandler) {
static AsyncPromptRegistration fromSync(SyncPromptRegistration prompt) {
// FIXME: This is temporary, proper validation should be implemented
if (prompt == null) {
return null;
}
return new AsyncPromptRegistration(prompt.prompt(),
req -> Mono.fromCallable(() -> prompt.promptHandler().apply(req))
.subscribeOn(Schedulers.boundedElastic()));
}
}
/**
* Registration of a tool with its synchronous handler function. Tools are the primary
* way for MCP servers to expose functionality to AI models. Each tool represents a
* specific capability, such as:
* <ul>
* <li>Performing calculations
* <li>Accessing external APIs
* <li>Querying databases
* <li>Manipulating files
* <li>Executing system commands
* </ul>
*
* <p>
* Example tool registration: <pre>{@code
* new McpServerFeatures.SyncToolRegistration(
* new Tool(
* "calculator",
* "Performs mathematical calculations",
* new JsonSchemaObject()
* .required("expression")
* .property("expression", JsonSchemaType.STRING)
* ),
* args -> {
* String expr = (String) args.get("expression");
* return new CallToolResult("Result: " + evaluate(expr));
* }
* )
* }</pre>
*
* @param tool The tool definition including name, description, and parameter schema
* @param call The function that implements the tool's logic, receiving arguments and
* returning results
*/
public record SyncToolRegistration(McpSchema.Tool tool,
Function<Map<String, Object>, McpSchema.CallToolResult> call) {
}
/**
* Registration of a resource with its synchronous handler function. Resources provide
* context to AI models by exposing data such as:
* <ul>
* <li>File contents
* <li>Database records
* <li>API responses
* <li>System information
* <li>Application state
* </ul>
*
* <p>
* Example resource registration: <pre>{@code
* new McpServerFeatures.SyncResourceRegistration(
* new Resource("docs", "Documentation files", "text/markdown"),
* request -> {
* String content = readFile(request.getPath());
* return new ReadResourceResult(content);
* }
* )
* }</pre>
*
* @param resource The resource definition including name, description, and MIME type
* @param readHandler The function that handles resource read requests
*/
public record SyncResourceRegistration(McpSchema.Resource resource,
Function<McpSchema.ReadResourceRequest, McpSchema.ReadResourceResult> readHandler) {
}
/**
* Registration of a prompt template with its synchronous handler function. Prompts
* provide structured templates for AI model interactions, supporting:
* <ul>
* <li>Consistent message formatting
* <li>Parameter substitution
* <li>Context injection
* <li>Response formatting
* <li>Instruction templating
* </ul>
*
* <p>
* Example prompt registration: <pre>{@code
* new McpServerFeatures.SyncPromptRegistration(
* new Prompt("analyze", "Code analysis template"),
* request -> {
* String code = request.getArguments().get("code");
* return new GetPromptResult(
* "Analyze this code:\n\n" + code + "\n\nProvide feedback on:"
* );
* }
* )
* }</pre>
*
* @param prompt The prompt definition including name and description
* @param promptHandler The function that processes prompt requests and returns
* formatted templates
*/
public record SyncPromptRegistration(McpSchema.Prompt prompt,
Function<McpSchema.GetPromptRequest, McpSchema.GetPromptResult> promptHandler) {
}
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.server;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.ClientCapabilities;
import io.modelcontextprotocol.spec.McpSchema.LoggingMessageNotification;
import io.modelcontextprotocol.util.Assert;
/**
* A synchronous implementation of the Model Context Protocol (MCP) server that wraps
* {@link McpAsyncServer} to provide blocking operations. This class delegates all
* operations to an underlying async server instance while providing a simpler,
* synchronous API for scenarios where reactive programming is not required.
*
* <p>
* The MCP server enables AI models to expose tools, resources, and prompts through a
* standardized interface. Key features available through this synchronous API include:
* <ul>
* <li>Tool registration and management for extending AI model capabilities
* <li>Resource handling with URI-based addressing for providing context
* <li>Prompt template management for standardized interactions
* <li>Real-time client notifications for state changes
* <li>Structured logging with configurable severity levels
* <li>Support for client-side AI model sampling
* </ul>
*
* <p>
* While {@link McpAsyncServer} uses Project Reactor's Mono and Flux types for
* non-blocking operations, this class converts those into blocking calls, making it more
* suitable for:
* <ul>
* <li>Traditional synchronous applications
* <li>Simple scripting scenarios
* <li>Testing and debugging
* <li>Cases where reactive programming adds unnecessary complexity
* </ul>
*
* <p>
* The server supports runtime modification of its capabilities through methods like
* {@link #addTool}, {@link #addResource}, and {@link #addPrompt}, automatically notifying
* connected clients of changes when configured to do so.
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
* @see McpAsyncServer
* @see McpSchema
*/
public class McpSyncServer {
/**
* The async server to wrap.
*/
private final McpAsyncServer asyncServer;
/**
* Creates a new synchronous server that wraps the provided async server.
* @param asyncServer The async server to wrap
*/
public McpSyncServer(McpAsyncServer asyncServer) {
Assert.notNull(asyncServer, "Async server must not be null");
this.asyncServer = asyncServer;
}
/**
* Retrieves the list of all roots provided by the client.
* @return The list of roots
*/
public McpSchema.ListRootsResult listRoots() {
return this.listRoots(null);
}
/**
* Retrieves a paginated list of roots provided by the server.
* @param cursor Optional pagination cursor from a previous list request
* @return The list of roots
*/
public McpSchema.ListRootsResult listRoots(String cursor) {
return this.asyncServer.listRoots(cursor).block();
}
/**
* Add a new tool handler.
* @param toolHandler The tool handler to add
*/
public void addTool(McpServerFeatures.SyncToolRegistration toolHandler) {
this.asyncServer.addTool(McpServerFeatures.AsyncToolRegistration.fromSync(toolHandler)).block();
}
/**
* Remove a tool handler.
* @param toolName The name of the tool handler to remove
*/
public void removeTool(String toolName) {
this.asyncServer.removeTool(toolName).block();
}
/**
* Add a new resource handler.
* @param resourceHandler The resource handler to add
*/
public void addResource(McpServerFeatures.SyncResourceRegistration resourceHandler) {
this.asyncServer.addResource(McpServerFeatures.AsyncResourceRegistration.fromSync(resourceHandler)).block();
}
/**
* Remove a resource handler.
* @param resourceUri The URI of the resource handler to remove
*/
public void removeResource(String resourceUri) {
this.asyncServer.removeResource(resourceUri).block();
}
/**
* Add a new prompt handler.
* @param promptRegistration The prompt registration to add
*/
public void addPrompt(McpServerFeatures.SyncPromptRegistration promptRegistration) {
this.asyncServer.addPrompt(McpServerFeatures.AsyncPromptRegistration.fromSync(promptRegistration)).block();
}
/**
* Remove a prompt handler.
* @param promptName The name of the prompt handler to remove
*/
public void removePrompt(String promptName) {
this.asyncServer.removePrompt(promptName).block();
}
/**
* Notify clients that the list of available tools has changed.
*/
public void notifyToolsListChanged() {
this.asyncServer.notifyToolsListChanged().block();
}
/**
* Get the server capabilities that define the supported features and functionality.
* @return The server capabilities
*/
public McpSchema.ServerCapabilities getServerCapabilities() {
return this.asyncServer.getServerCapabilities();
}
/**
* Get the server implementation information.
* @return The server implementation details
*/
public McpSchema.Implementation getServerInfo() {
return this.asyncServer.getServerInfo();
}
/**
* Get the client capabilities that define the supported features and functionality.
* @return The client capabilities
*/
public ClientCapabilities getClientCapabilities() {
return this.asyncServer.getClientCapabilities();
}
/**
* Get the client implementation information.
* @return The client implementation details
*/
public McpSchema.Implementation getClientInfo() {
return this.asyncServer.getClientInfo();
}
/**
* Notify clients that the list of available resources has changed.
*/
public void notifyResourcesListChanged() {
this.asyncServer.notifyResourcesListChanged().block();
}
/**
* Notify clients that the list of available prompts has changed.
*/
public void notifyPromptsListChanged() {
this.asyncServer.notifyPromptsListChanged().block();
}
/**
* Send a logging message notification to all clients.
* @param loggingMessageNotification The logging message notification to send
*/
public void loggingNotification(LoggingMessageNotification loggingMessageNotification) {
this.asyncServer.loggingNotification(loggingMessageNotification).block();
}
/**
* Close the server gracefully.
*/
public void closeGracefully() {
this.asyncServer.closeGracefully().block();
}
/**
* Close the server immediately.
*/
public void close() {
this.asyncServer.close();
}
/**
* Get the underlying async server instance.
* @return The wrapped async server
*/
public McpAsyncServer getAsyncServer() {
return this.asyncServer;
}
/**
* Create a new message using the sampling capabilities of the client. The Model
* Context Protocol (MCP) provides a standardized way for servers to request LLM
* sampling ("completions" or "generations") from language models via clients.
*
* <p>
* This flow allows clients to maintain control over model access, selection, and
* permissions while enabling servers to leverage AI capabilities—with no server API
* keys necessary. Servers can request text or image-based interactions and optionally
* include context from MCP servers in their prompts.
*
* <p>
* Unlike its async counterpart, this method blocks until the message creation is
* complete, making it easier to use in synchronous code paths.
* @param createMessageRequest The request to create a new message
* @return The result of the message creation
* @throws McpError if the client has not been initialized or does not support
* sampling capabilities
* @throws McpError if the client does not support the createMessage method
* @see McpSchema.CreateMessageRequest
* @see McpSchema.CreateMessageResult
* @see <a href=
* "https://spec.modelcontextprotocol.io/specification/client/sampling/">Sampling
* Specification</a>
*/
public McpSchema.CreateMessageResult createMessage(McpSchema.CreateMessageRequest createMessageRequest) {
return this.asyncServer.createMessage(createMessageRequest).block();
}
}

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/*
* Copyright 2024 - 2024 the original author or authors.
*/
package io.modelcontextprotocol.server.transport;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.Function;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.ServerMcpTransport;
import jakarta.servlet.AsyncContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Mono;
/**
* A Servlet-based implementation of the MCP HTTP with Server-Sent Events (SSE) transport
* specification. This implementation provides similar functionality to
* WebFluxSseServerTransport but uses the traditional Servlet API instead of WebFlux.
*
* <p>
* The transport handles two types of endpoints:
* <ul>
* <li>SSE endpoint (/sse) - Establishes a long-lived connection for server-to-client
* events</li>
* <li>Message endpoint (configurable) - Handles client-to-server message requests</li>
* </ul>
*
* <p>
* Features:
* <ul>
* <li>Asynchronous message handling using Servlet 6.0 async support</li>
* <li>Session management for multiple client connections</li>
* <li>Graceful shutdown support</li>
* <li>Error handling and response formatting</li>
* </ul>
*
* @author Christian Tzolov
* @author Alexandros Pappas
* @see ServerMcpTransport
* @see HttpServlet
*/
@WebServlet(asyncSupported = true)
public class HttpServletSseServerTransport extends HttpServlet implements ServerMcpTransport {
/** Logger for this class */
private static final Logger logger = LoggerFactory.getLogger(HttpServletSseServerTransport.class);
public static final String UTF_8 = "UTF-8";
public static final String APPLICATION_JSON = "application/json";
public static final String FAILED_TO_SEND_ERROR_RESPONSE = "Failed to send error response: {}";
/** Default endpoint path for SSE connections */
public static final String DEFAULT_SSE_ENDPOINT = "/sse";
/** Event type for regular messages */
public static final String MESSAGE_EVENT_TYPE = "message";
/** Event type for endpoint information */
public static final String ENDPOINT_EVENT_TYPE = "endpoint";
/** JSON object mapper for serialization/deserialization */
private final ObjectMapper objectMapper;
/** The endpoint path for handling client messages */
private final String messageEndpoint;
/** The endpoint path for handling SSE connections */
private final String sseEndpoint;
/** Map of active client sessions, keyed by session ID */
private final Map<String, ClientSession> sessions = new ConcurrentHashMap<>();
/** Flag indicating if the transport is in the process of shutting down */
private final AtomicBoolean isClosing = new AtomicBoolean(false);
/** Handler for processing incoming messages */
private Function<Mono<McpSchema.JSONRPCMessage>, Mono<McpSchema.JSONRPCMessage>> connectHandler;
/**
* Creates a new HttpServletSseServerTransport instance with a custom SSE endpoint.
* @param objectMapper The JSON object mapper to use for message
* serialization/deserialization
* @param messageEndpoint The endpoint path where clients will send their messages
* @param sseEndpoint The endpoint path where clients will establish SSE connections
*/
public HttpServletSseServerTransport(ObjectMapper objectMapper, String messageEndpoint, String sseEndpoint) {
this.objectMapper = objectMapper;
this.messageEndpoint = messageEndpoint;
this.sseEndpoint = sseEndpoint;
}
/**
* Creates a new HttpServletSseServerTransport instance with the default SSE endpoint.
* @param objectMapper The JSON object mapper to use for message
* serialization/deserialization
* @param messageEndpoint The endpoint path where clients will send their messages
*/
public HttpServletSseServerTransport(ObjectMapper objectMapper, String messageEndpoint) {
this(objectMapper, messageEndpoint, DEFAULT_SSE_ENDPOINT);
}
/**
* Handles GET requests to establish SSE connections.
* <p>
* This method sets up a new SSE connection when a client connects to the SSE
* endpoint. It configures the response headers for SSE, creates a new session, and
* sends the initial endpoint information to the client.
* @param request The HTTP servlet request
* @param response The HTTP servlet response
* @throws ServletException If a servlet-specific error occurs
* @throws IOException If an I/O error occurs
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String pathInfo = request.getPathInfo();
if (!sseEndpoint.equals(pathInfo)) {
response.sendError(HttpServletResponse.SC_NOT_FOUND);
return;
}
if (isClosing.get()) {
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, "Server is shutting down");
return;
}
response.setContentType("text/event-stream");
response.setCharacterEncoding(UTF_8);
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Connection", "keep-alive");
response.setHeader("Access-Control-Allow-Origin", "*");
String sessionId = UUID.randomUUID().toString();
AsyncContext asyncContext = request.startAsync();
asyncContext.setTimeout(0);
PrintWriter writer = response.getWriter();
ClientSession session = new ClientSession(sessionId, asyncContext, writer);
this.sessions.put(sessionId, session);
// Send initial endpoint event
this.sendEvent(writer, ENDPOINT_EVENT_TYPE, messageEndpoint);
}
/**
* Handles POST requests for client messages.
* <p>
* This method processes incoming messages from clients, routes them through the
* connect handler if configured, and sends back the appropriate response. It handles
* error cases and formats error responses according to the MCP specification.
* @param request The HTTP servlet request
* @param response The HTTP servlet response
* @throws ServletException If a servlet-specific error occurs
* @throws IOException If an I/O error occurs
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
if (isClosing.get()) {
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, "Server is shutting down");
return;
}
String pathInfo = request.getPathInfo();
if (!messageEndpoint.equals(pathInfo)) {
response.sendError(HttpServletResponse.SC_NOT_FOUND);
return;
}
try {
BufferedReader reader = request.getReader();
StringBuilder body = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
body.append(line);
}
McpSchema.JSONRPCMessage message = McpSchema.deserializeJsonRpcMessage(objectMapper, body.toString());
if (connectHandler != null) {
connectHandler.apply(Mono.just(message)).subscribe(responseMessage -> {
try {
response.setContentType(APPLICATION_JSON);
response.setCharacterEncoding(UTF_8);
String jsonResponse = objectMapper.writeValueAsString(responseMessage);
PrintWriter writer = response.getWriter();
writer.write(jsonResponse);
writer.flush();
}
catch (Exception e) {
logger.error("Error sending response: {}", e.getMessage());
try {
response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
"Error processing response: " + e.getMessage());
}
catch (IOException ex) {
logger.error(FAILED_TO_SEND_ERROR_RESPONSE, ex.getMessage());
}
}
}, error -> {
try {
logger.error("Error processing message: {}", error.getMessage());
McpError mcpError = new McpError(error.getMessage());
response.setContentType(APPLICATION_JSON);
response.setCharacterEncoding(UTF_8);
response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
String jsonError = objectMapper.writeValueAsString(mcpError);
PrintWriter writer = response.getWriter();
writer.write(jsonError);
writer.flush();
}
catch (IOException e) {
logger.error(FAILED_TO_SEND_ERROR_RESPONSE, e.getMessage());
try {
response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
"Error sending error response: " + e.getMessage());
}
catch (IOException ex) {
logger.error(FAILED_TO_SEND_ERROR_RESPONSE, ex.getMessage());
}
}
});
}
else {
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, "No message handler configured");
}
}
catch (Exception e) {
logger.error("Invalid message format: {}", e.getMessage());
try {
McpError mcpError = new McpError("Invalid message format: " + e.getMessage());
response.setContentType(APPLICATION_JSON);
response.setCharacterEncoding(UTF_8);
response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
String jsonError = objectMapper.writeValueAsString(mcpError);
PrintWriter writer = response.getWriter();
writer.write(jsonError);
writer.flush();
}
catch (IOException ex) {
logger.error(FAILED_TO_SEND_ERROR_RESPONSE, ex.getMessage());
response.sendError(HttpServletResponse.SC_BAD_REQUEST, "Invalid message format");
}
}
}
/**
* Sets up the message handler for processing client requests.
* @param handler The function to process incoming messages and produce responses
* @return A Mono that completes when the handler is set up
*/
@Override
public Mono<Void> connect(Function<Mono<McpSchema.JSONRPCMessage>, Mono<McpSchema.JSONRPCMessage>> handler) {
this.connectHandler = handler;
return Mono.empty();
}
/**
* Broadcasts a message to all connected clients.
* <p>
* This method serializes the message and sends it to all active client sessions. If a
* client is disconnected, its session is removed.
* @param message The message to broadcast
* @return A Mono that completes when the message has been sent to all clients
*/
@Override
public Mono<Void> sendMessage(McpSchema.JSONRPCMessage message) {
if (sessions.isEmpty()) {
logger.debug("No active sessions to broadcast message to");
return Mono.empty();
}
return Mono.create(sink -> {
try {
String jsonText = objectMapper.writeValueAsString(message);
sessions.values().forEach(session -> {
try {
this.sendEvent(session.writer, MESSAGE_EVENT_TYPE, jsonText);
}
catch (IOException e) {
logger.error("Failed to send message to session {}: {}", session.id, e.getMessage());
removeSession(session);
}
});
sink.success();
}
catch (Exception e) {
logger.error("Failed to process message: {}", e.getMessage());
sink.error(new McpError("Failed to process message: " + e.getMessage()));
}
});
}
/**
* Closes the transport.
* <p>
* This implementation delegates to the super class's close method.
*/
@Override
public void close() {
ServerMcpTransport.super.close();
}
/**
* Unmarshals data from one type to another using the object mapper.
* @param <T> The target type
* @param data The source data
* @param typeRef The type reference for the target type
* @return The unmarshaled data
*/
@Override
public <T> T unmarshalFrom(Object data, TypeReference<T> typeRef) {
return objectMapper.convertValue(data, typeRef);
}
/**
* Initiates a graceful shutdown of the transport.
* <p>
* This method marks the transport as closing and closes all active client sessions.
* New connection attempts will be rejected during shutdown.
* @return A Mono that completes when all sessions have been closed
*/
@Override
public Mono<Void> closeGracefully() {
isClosing.set(true);
logger.debug("Initiating graceful shutdown with {} active sessions", sessions.size());
return Mono.create(sink -> {
sessions.values().forEach(this::removeSession);
sink.success();
});
}
/**
* Sends an SSE event to a client.
* @param writer The writer to send the event through
* @param eventType The type of event (message or endpoint)
* @param data The event data
* @throws IOException If an error occurs while writing the event
*/
private void sendEvent(PrintWriter writer, String eventType, String data) throws IOException {
writer.write("event: " + eventType + "\n");
writer.write("data: " + data + "\n\n");
writer.flush();
if (writer.checkError()) {
throw new IOException("Client disconnected");
}
}
/**
* Removes a client session and completes its async context.
* @param session The session to remove
*/
private void removeSession(ClientSession session) {
sessions.remove(session.id);
session.asyncContext.complete();
}
/**
* Represents a client connection session.
* <p>
* This class holds the necessary information about a client's SSE connection,
* including its ID, async context, and output writer.
*/
private static class ClientSession {
private final String id;
private final AsyncContext asyncContext;
private final PrintWriter writer;
ClientSession(String id, AsyncContext asyncContext, PrintWriter writer) {
this.id = id;
this.asyncContext = asyncContext;
this.writer = writer;
}
}
/**
* Cleans up resources when the servlet is being destroyed.
* <p>
* This method ensures a graceful shutdown by closing all client connections before
* calling the parent's destroy method.
*/
@Override
public void destroy() {
closeGracefully().block();
super.destroy();
}
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.server.transport;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.util.concurrent.Executors;
import java.util.function.Function;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.ServerMcpTransport;
import io.modelcontextprotocol.spec.McpSchema.JSONRPCMessage;
import io.modelcontextprotocol.util.Assert;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.core.publisher.Sinks;
import reactor.core.scheduler.Scheduler;
import reactor.core.scheduler.Schedulers;
/**
* Implementation of the MCP Stdio transport for servers that communicates using standard
* input/output streams. Messages are exchanged as newline-delimited JSON-RPC messages
* over stdin/stdout, with errors and debug information sent to stderr.
*
* @author Christian Tzolov
*/
public class StdioServerTransport implements ServerMcpTransport {
private static final Logger logger = LoggerFactory.getLogger(StdioServerTransport.class);
private final Sinks.Many<JSONRPCMessage> inboundSink;
private final Sinks.Many<JSONRPCMessage> outboundSink;
private ObjectMapper objectMapper;
/** Scheduler for handling inbound messages */
private Scheduler inboundScheduler;
/** Scheduler for handling outbound messages */
private Scheduler outboundScheduler;
private volatile boolean isClosing = false;
private final InputStream inputStream;
private final OutputStream outputStream;
private final Sinks.One<Void> inboundReady = Sinks.one();
private final Sinks.One<Void> outboundReady = Sinks.one();
/**
* Creates a new StdioServerTransport with a default ObjectMapper and System streams.
*/
public StdioServerTransport() {
this(new ObjectMapper());
}
/**
* Creates a new StdioServerTransport with the specified ObjectMapper and System
* streams.
* @param objectMapper The ObjectMapper to use for JSON serialization/deserialization
*/
public StdioServerTransport(ObjectMapper objectMapper) {
Assert.notNull(objectMapper, "The ObjectMapper can not be null");
this.inboundSink = Sinks.many().unicast().onBackpressureBuffer();
this.outboundSink = Sinks.many().unicast().onBackpressureBuffer();
this.objectMapper = objectMapper;
this.inputStream = System.in;
this.outputStream = System.out;
// Use bounded schedulers for better resource management
this.inboundScheduler = Schedulers.fromExecutorService(Executors.newSingleThreadExecutor(), "inbound");
this.outboundScheduler = Schedulers.fromExecutorService(Executors.newSingleThreadExecutor(), "outbound");
}
@Override
public Mono<Void> connect(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> handler) {
return Mono.<Void>fromRunnable(() -> {
handleIncomingMessages(handler);
// Start threads
startInboundProcessing();
startOutboundProcessing();
}).subscribeOn(Schedulers.boundedElastic());
}
private void handleIncomingMessages(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> inboundMessageHandler) {
this.inboundSink.asFlux()
.flatMap(message -> Mono.just(message)
.transform(inboundMessageHandler)
.contextWrite(ctx -> ctx.put("observation", "myObservation")))
.doOnTerminate(() -> {
// The outbound processing will dispose its scheduler upon completion
this.outboundSink.tryEmitComplete();
this.inboundScheduler.dispose();
})
.subscribe();
}
@Override
public Mono<Void> sendMessage(JSONRPCMessage message) {
return Mono.zip(inboundReady.asMono(), outboundReady.asMono()).then(Mono.defer(() -> {
if (this.outboundSink.tryEmitNext(message).isSuccess()) {
return Mono.empty();
}
else {
return Mono.error(new RuntimeException("Failed to enqueue message"));
}
}));
}
/**
* Starts the inbound processing thread that reads JSON-RPC messages from stdin.
* Messages are deserialized and emitted to the inbound sink.
*/
private void startInboundProcessing() {
this.inboundScheduler.schedule(() -> {
inboundReady.tryEmitValue(null);
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(inputStream));
while (!isClosing) {
try {
String line = reader.readLine();
if (line == null || isClosing) {
break;
}
try {
JSONRPCMessage message = McpSchema.deserializeJsonRpcMessage(this.objectMapper, line);
if (!this.inboundSink.tryEmitNext(message).isSuccess()) {
logIfNotClosing("Failed to enqueue message");
break;
}
}
catch (Exception e) {
logIfNotClosing("Error processing inbound message", e);
break;
}
}
catch (IOException e) {
logIfNotClosing("Error reading from stdin", e);
break;
}
}
}
catch (Exception e) {
logIfNotClosing("Error in inbound processing", e);
}
finally {
isClosing = true;
inboundSink.tryEmitComplete();
}
});
}
/**
* Starts the outbound processing thread that writes JSON-RPC messages to stdout.
* Messages are serialized to JSON and written with a newline delimiter.
*/
private void startOutboundProcessing() {
Function<Flux<JSONRPCMessage>, Flux<JSONRPCMessage>> outboundConsumer = messages -> messages // @formatter:off
.doOnSubscribe(subscription -> outboundReady.tryEmitValue(null))
.publishOn(outboundScheduler)
.handle((message, sink) -> {
if (message != null && !isClosing) {
try {
String jsonMessage = objectMapper.writeValueAsString(message);
// Escape any embedded newlines in the JSON message as per spec
jsonMessage = jsonMessage.replace("\r\n", "\\n").replace("\n", "\\n").replace("\r", "\\n");
synchronized (outputStream) {
outputStream.write(jsonMessage.getBytes(StandardCharsets.UTF_8));
outputStream.write("\n".getBytes(StandardCharsets.UTF_8));
outputStream.flush();
}
sink.next(message);
}
catch (IOException e) {
if (!isClosing) {
logger.error("Error writing message", e);
sink.error(new RuntimeException(e));
}
else {
logger.debug("Stream closed during shutdown", e);
}
}
}
else if (isClosing) {
sink.complete();
}
})
.doOnComplete(() -> {
isClosing = true;
outboundScheduler.dispose();
})
.doOnError(e -> {
if (!isClosing) {
logger.error("Error in outbound processing", e);
isClosing = true;
outboundScheduler.dispose();
}
})
.map(msg -> (JSONRPCMessage) msg);
outboundConsumer.apply(outboundSink.asFlux()).subscribe();
} // @formatter:on
@Override
public Mono<Void> closeGracefully() {
return Mono.<Void>defer(() -> {
isClosing = true;
logger.debug("Initiating graceful shutdown");
// Completing the inbound causes the outbound to be completed as well, so
// we only close the inbound.
inboundSink.tryEmitComplete();
logger.info("Graceful shutdown complete");
return Mono.empty();
}).subscribeOn(Schedulers.boundedElastic());
}
@Override
public <T> T unmarshalFrom(Object data, TypeReference<T> typeRef) {
return this.objectMapper.convertValue(data, typeRef);
}
private void logIfNotClosing(String message, Exception e) {
if (!this.isClosing) {
logger.error(message, e);
}
}
private void logIfNotClosing(String message) {
if (!this.isClosing) {
logger.error(message);
}
}
}

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/*
* Copyright 2024 - 2024 the original author or authors.
*/
package io.modelcontextprotocol.spec;
/**
* Marker interface for the client-side MCP transport.
*
* @author Christian Tzolov
*/
public interface ClientMcpTransport extends McpTransport {
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.spec;
import java.time.Duration;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicLong;
import com.fasterxml.jackson.core.type.TypeReference;
import io.modelcontextprotocol.util.Assert;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.Disposable;
import reactor.core.publisher.Mono;
import reactor.core.publisher.MonoSink;
/**
* Default implementation of the MCP (Model Context Protocol) session that manages
* bidirectional JSON-RPC communication between clients and servers. This implementation
* follows the MCP specification for message exchange and transport handling.
*
* <p>
* The session manages:
* <ul>
* <li>Request/response handling with unique message IDs</li>
* <li>Notification processing</li>
* <li>Message timeout management</li>
* <li>Transport layer abstraction</li>
* </ul>
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
*/
public class DefaultMcpSession implements McpSession {
/** Logger for this class */
private static final Logger logger = LoggerFactory.getLogger(DefaultMcpSession.class);
/** Duration to wait for request responses before timing out */
private final Duration requestTimeout;
/** Transport layer implementation for message exchange */
private final McpTransport transport;
/** Map of pending responses keyed by request ID */
private final ConcurrentHashMap<Object, MonoSink<McpSchema.JSONRPCResponse>> pendingResponses = new ConcurrentHashMap<>();
/** Map of request handlers keyed by method name */
private final ConcurrentHashMap<String, RequestHandler<?>> requestHandlers = new ConcurrentHashMap<>();
/** Map of notification handlers keyed by method name */
private final ConcurrentHashMap<String, NotificationHandler> notificationHandlers = new ConcurrentHashMap<>();
/** Session-specific prefix for request IDs */
private final String sessionPrefix = UUID.randomUUID().toString().substring(0, 8);
/** Atomic counter for generating unique request IDs */
private final AtomicLong requestCounter = new AtomicLong(0);
private final Disposable connection;
/**
* Functional interface for handling incoming JSON-RPC requests. Implementations
* should process the request parameters and return a response.
*
* @param <T> Response type
*/
@FunctionalInterface
public interface RequestHandler<T> {
/**
* Handles an incoming request with the given parameters.
* @param params The request parameters
* @return A Mono containing the response object
*/
Mono<T> handle(Object params);
}
/**
* Functional interface for handling incoming JSON-RPC notifications. Implementations
* should process the notification parameters without returning a response.
*/
@FunctionalInterface
public interface NotificationHandler {
/**
* Handles an incoming notification with the given parameters.
* @param params The notification parameters
* @return A Mono that completes when the notification is processed
*/
Mono<Void> handle(Object params);
}
/**
* Creates a new DefaultMcpSession with the specified configuration and handlers.
* @param requestTimeout Duration to wait for responses
* @param transport Transport implementation for message exchange
* @param requestHandlers Map of method names to request handlers
* @param notificationHandlers Map of method names to notification handlers
*/
public DefaultMcpSession(Duration requestTimeout, McpTransport transport,
Map<String, RequestHandler<?>> requestHandlers, Map<String, NotificationHandler> notificationHandlers) {
Assert.notNull(requestTimeout, "The requstTimeout can not be null");
Assert.notNull(transport, "The transport can not be null");
Assert.notNull(requestHandlers, "The requestHandlers can not be null");
Assert.notNull(notificationHandlers, "The notificationHandlers can not be null");
this.requestTimeout = requestTimeout;
this.transport = transport;
this.requestHandlers.putAll(requestHandlers);
this.notificationHandlers.putAll(notificationHandlers);
// TODO: consider mono.transformDeferredContextual where the Context contains
// the
// Observation associated with the individual message - it can be used to
// create child Observation and emit it together with the message to the
// consumer
this.connection = this.transport.connect(mono -> mono.doOnNext(message -> {
if (message instanceof McpSchema.JSONRPCResponse response) {
logger.info("Received Response: {}", response);
var sink = pendingResponses.remove(response.id());
if (sink == null) {
logger.warn("Unexpected response for unkown id {}", response.id());
}
else {
sink.success(response);
}
}
else if (message instanceof McpSchema.JSONRPCRequest request) {
logger.info("Received request: {}", request);
handleIncomingRequest(request).subscribe(response -> transport.sendMessage(response).subscribe(),
error -> {
var errorResponse = new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
null, new McpSchema.JSONRPCResponse.JSONRPCError(
McpSchema.ErrorCodes.INTERNAL_ERROR, error.getMessage(), null));
transport.sendMessage(errorResponse).subscribe();
});
}
else if (message instanceof McpSchema.JSONRPCNotification notification) {
logger.info("Received notification: {}", notification);
handleIncomingNotification(notification).subscribe(null,
error -> logger.error("Error handling notification: {}", error.getMessage()));
}
})).subscribe();
}
/**
* Handles an incoming JSON-RPC request by routing it to the appropriate handler.
* @param request The incoming JSON-RPC request
* @return A Mono containing the JSON-RPC response
*/
private Mono<McpSchema.JSONRPCResponse> handleIncomingRequest(McpSchema.JSONRPCRequest request) {
return Mono.defer(() -> {
var handler = this.requestHandlers.get(request.method());
if (handler == null) {
MethodNotFoundError error = getMethodNotFoundError(request.method());
return Mono.just(new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(), null,
new McpSchema.JSONRPCResponse.JSONRPCError(McpSchema.ErrorCodes.METHOD_NOT_FOUND,
error.message(), error.data())));
}
return handler.handle(request.params())
.map(result -> new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(), result, null))
.onErrorResume(error -> Mono.just(new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
null, new McpSchema.JSONRPCResponse.JSONRPCError(McpSchema.ErrorCodes.INTERNAL_ERROR,
error.getMessage(), null)))); // TODO: add error message
// through the data field
});
}
record MethodNotFoundError(String method, String message, Object data) {
}
public static MethodNotFoundError getMethodNotFoundError(String method) {
switch (method) {
case McpSchema.METHOD_ROOTS_LIST:
return new MethodNotFoundError(method, "Roots not supported",
Map.of("reason", "Client does not have roots capability"));
default:
return new MethodNotFoundError(method, "Method not found: " + method, null);
}
}
/**
* Handles an incoming JSON-RPC notification by routing it to the appropriate handler.
* @param notification The incoming JSON-RPC notification
* @return A Mono that completes when the notification is processed
*/
private Mono<Void> handleIncomingNotification(McpSchema.JSONRPCNotification notification) {
return Mono.defer(() -> {
var handler = notificationHandlers.get(notification.method());
if (handler == null) {
logger.error("No handler registered for notification method: {}", notification.method());
return Mono.empty();
}
return handler.handle(notification.params());
});
}
/**
* Generates a unique request ID in a non-blocking way. Combines a session-specific
* prefix with an atomic counter to ensure uniqueness.
* @return A unique request ID string
*/
private String generateRequestId() {
return this.sessionPrefix + "-" + this.requestCounter.getAndIncrement();
}
/**
* Sends a JSON-RPC request and returns the response.
* @param <T> The expected response type
* @param method The method name to call
* @param requestParams The request parameters
* @param typeRef Type reference for response deserialization
* @return A Mono containing the response
*/
@Override
public <T> Mono<T> sendRequest(String method, Object requestParams, TypeReference<T> typeRef) {
String requestId = this.generateRequestId();
return Mono.<McpSchema.JSONRPCResponse>create(sink -> {
this.pendingResponses.put(requestId, sink);
McpSchema.JSONRPCRequest jsonrpcRequest = new McpSchema.JSONRPCRequest(McpSchema.JSONRPC_VERSION, method,
requestId, requestParams);
this.transport.sendMessage(jsonrpcRequest)
// TODO: It's most efficient to create a dedicated Subscriber here
.subscribe(v -> {
}, error -> {
this.pendingResponses.remove(requestId);
sink.error(error);
});
}).timeout(this.requestTimeout).handle((jsonRpcResponse, sink) -> {
if (jsonRpcResponse.error() != null) {
sink.error(new McpError(jsonRpcResponse.error()));
}
else {
if (typeRef.getType().equals(Void.class)) {
sink.complete();
}
else {
sink.next(this.transport.unmarshalFrom(jsonRpcResponse.result(), typeRef));
}
}
});
}
/**
* Sends a JSON-RPC notification.
* @param method The method name for the notification
* @param params The notification parameters
* @return A Mono that completes when the notification is sent
*/
@Override
public Mono<Void> sendNotification(String method, Map<String, Object> params) {
McpSchema.JSONRPCNotification jsonrpcNotification = new McpSchema.JSONRPCNotification(McpSchema.JSONRPC_VERSION,
method, params);
return this.transport.sendMessage(jsonrpcNotification);
}
/**
* Closes the session gracefully, allowing pending operations to complete.
* @return A Mono that completes when the session is closed
*/
@Override
public Mono<Void> closeGracefully() {
this.connection.dispose();
return transport.closeGracefully();
}
/**
* Closes the session immediately, potentially interrupting pending operations.
*/
@Override
public void close() {
this.connection.dispose();
transport.close();
}
}

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/*
* Copyright 2024 - 2024 the original author or authors.
*/
package io.modelcontextprotocol.spec;
import io.modelcontextprotocol.spec.McpSchema.JSONRPCResponse.JSONRPCError;
public class McpError extends RuntimeException {
private JSONRPCError jsonRpcError;
public McpError(JSONRPCError jsonRpcError) {
super(jsonRpcError.message());
this.jsonRpcError = jsonRpcError;
}
public McpError(Object error) {
super(error.toString());
}
public JSONRPCError getJsonRpcError() {
return jsonRpcError;
}
}

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mcp/src/main/java/io/modelcontextprotocol/spec/McpSession.java Normal file
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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.spec;
import java.util.Map;
import com.fasterxml.jackson.core.type.TypeReference;
import reactor.core.publisher.Mono;
/**
* Represents a Model Control Protocol (MCP) session that handles communication between
* clients and the server. This interface provides methods for sending requests and
* notifications, as well as managing the session lifecycle.
*
* <p>
* The session operates asynchronously using Project Reactor's {@link Mono} type for
* non-blocking operations. It supports both request-response patterns and one-way
* notifications.
* </p>
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
*/
public interface McpSession {
/**
* Sends a request to the model server and expects a response of type T.
*
* <p>
* This method handles the request-response pattern where a response is expected from
* the server. The response type is determined by the provided TypeReference.
* </p>
* @param <T> the type of the expected response
* @param method the name of the method to be called on the server
* @param requestParams the parameters to be sent with the request
* @param typeRef the TypeReference describing the expected response type
* @return a Mono that will emit the response when received
*/
<T> Mono<T> sendRequest(String method, Object requestParams, TypeReference<T> typeRef);
/**
* Sends a notification to the model server without parameters.
*
* <p>
* This method implements the notification pattern where no response is expected from
* the server. It's useful for fire-and-forget scenarios.
* </p>
* @param method the name of the notification method to be called on the server
* @return a Mono that completes when the notification has been sent
*/
default Mono<Void> sendNotification(String method) {
return sendNotification(method, null);
}
/**
* Sends a notification to the model server with parameters.
*
* <p>
* Similar to {@link #sendNotification(String)} but allows sending additional
* parameters with the notification.
* </p>
* @param method the name of the notification method to be called on the server
* @param params a map of parameters to be sent with the notification
* @return a Mono that completes when the notification has been sent
*/
Mono<Void> sendNotification(String method, Map<String, Object> params);
/**
* Closes the session and releases any associated resources asynchronously.
* @return a {@link Mono<Void>} that completes when the session has been closed.
*/
Mono<Void> closeGracefully();
/**
* Closes the session and releases any associated resources.
*/
void close();
}

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/*
* Copyright 2024-2024 the original author or authors.
*/
package io.modelcontextprotocol.spec;
import java.util.function.Function;
import com.fasterxml.jackson.core.type.TypeReference;
import io.modelcontextprotocol.spec.McpSchema.JSONRPCMessage;
import reactor.core.publisher.Mono;
/**
* Defines the asynchronous transport layer for the Model Context Protocol (MCP).
*
* <p>
* The McpTransport interface provides the foundation for implementing custom transport
* mechanisms in the Model Context Protocol. It handles the bidirectional communication
* between the client and server components, supporting asynchronous message exchange
* using JSON-RPC format.
* </p>
*
* <p>
* Implementations of this interface are responsible for:
* </p>
* <ul>
* <li>Managing the lifecycle of the transport connection</li>
* <li>Handling incoming messages and errors from the server</li>
* <li>Sending outbound messages to the server</li>
* </ul>
*
* <p>
* The transport layer is designed to be protocol-agnostic, allowing for various
* implementations such as WebSocket, HTTP, or custom protocols.
* </p>
*
* @author Christian Tzolov
* @author Dariusz Jędrzejczyk
*/
public interface McpTransport {
/**
* Initializes and starts the transport connection.
*
* <p>
* This method should be called before any message exchange can occur. It sets up the
* necessary resources and establishes the connection to the server.
* </p>
*/
Mono<Void> connect(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> handler);
/**
* Closes the transport connection and releases any associated resources.
*
* <p>
* This method ensures proper cleanup of resources when the transport is no longer
* needed. It should handle the graceful shutdown of any active connections.
* </p>
*/
default void close() {
this.closeGracefully().subscribe();
}
/**
* Closes the transport connection and releases any associated resources
* asynchronously.
* @return a {@link Mono<Void>} that completes when the connection has been closed.
*/
Mono<Void> closeGracefully();
/**
* Sends a message to the server asynchronously.
*
* <p>
* This method handles the transmission of messages to the server in an asynchronous
* manner. Messages are sent in JSON-RPC format as specified by the MCP protocol.
* </p>
* @param message the {@link JSONRPCMessage} to be sent to the server
* @return a {@link Mono<Void>} that completes when the message has been sent
*/
Mono<Void> sendMessage(JSONRPCMessage message);
/**
* Unmarshals the given data into an object of the specified type.
* @param <T> the type of the object to unmarshal
* @param data the data to unmarshal
* @param typeRef the type reference for the object to unmarshal
* @return the unmarshalled object
*/
<T> T unmarshalFrom(Object data, TypeReference<T> typeRef);
}

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