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feat: implement MCP protocol version per transport support (#404)

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- Add protocolVersion() method to transport and transport provider interfaces and implementations
- Replace hardcoded HTTP header strings with HttpHeaders constants
- Update protocol versions to be transport-specific rather than global
- Deprecate McpSchema.LATEST_PROTOCOL_VERSION in favor of transport-specific versions
- Standardize header names: MCP-Protocol-Version, mcp-session-id, last-event-id
- Update clients and servers to use transport.protocolVersion() for initialization
- Refactor tests to use transport-specific protocol versions
- Include MCP-Protocol-Version header in all GET/POST/DELETE requests
- Update WebClientStreamableHttpTransport, WebFluxSseClientTransport,
  HttpClientSseClientTransport, and HttpClientStreamableHttpTransport

Related to #398 , #363 , #250

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>
This commit is contained in:
Christian Tzolov 2025-07-30 23:54:28 +02:00 • committed by GitHub
commit 9d58621918
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GPG key ID: B5690EEEBB952194
27 changed files with 169 additions and 34 deletions
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38
mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/client/transport/WebClientStreamableHttpTransport.java
View file

@ -23,6 +23,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
import io.modelcontextprotocol.spec.DefaultMcpTransportSession;
import io.modelcontextprotocol.spec.DefaultMcpTransportStream;
import io.modelcontextprotocol.spec.HttpHeaders;
import io.modelcontextprotocol.spec.McpClientTransport;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
@ -66,6 +67,8 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
private static final Logger logger = LoggerFactory.getLogger(WebClientStreamableHttpTransport.class);
private static final String MCP_PROTOCOL_VERSION = "2025-03-26";
private static final String DEFAULT_ENDPOINT = "/mcp";
/**
@ -103,6 +106,11 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
this.activeSession.set(createTransportSession());
}
@Override
public String protocolVersion() {
return MCP_PROTOCOL_VERSION;
}
/**
* Create a stateful builder for creating {@link WebClientStreamableHttpTransport}
* instances.
@ -128,12 +136,20 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
private DefaultMcpTransportSession createTransportSession() {
Function<String, Publisher<Void>> onClose = sessionId -> sessionId == null ? Mono.empty()
: webClient.delete().uri(this.endpoint).headers(httpHeaders -> {
httpHeaders.add("mcp-session-id", sessionId);
}).retrieve().toBodilessEntity().onErrorComplete(e -> {
logger.warn("Got error when closing transport", e);
return true;
}).then();
: webClient.delete()
.uri(this.endpoint)
.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
.headers(httpHeaders -> {
httpHeaders.add(HttpHeaders.MCP_SESSION_ID, sessionId);
httpHeaders.add(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION);
})
.retrieve()
.toBodilessEntity()
.onErrorComplete(e -> {
logger.warn("Got error when closing transport", e);
return true;
})
.then();
return new DefaultMcpTransportSession(onClose);
}
@ -186,10 +202,11 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
Disposable connection = webClient.get()
.uri(this.endpoint)
.accept(MediaType.TEXT_EVENT_STREAM)
.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
.headers(httpHeaders -> {
transportSession.sessionId().ifPresent(id -> httpHeaders.add("mcp-session-id", id));
transportSession.sessionId().ifPresent(id -> httpHeaders.add(HttpHeaders.MCP_SESSION_ID, id));
if (stream != null) {
stream.lastId().ifPresent(id -> httpHeaders.add("last-event-id", id));
stream.lastId().ifPresent(id -> httpHeaders.add(HttpHeaders.LAST_EVENT_ID, id));
}
})
.exchangeToFlux(response -> {
@ -246,13 +263,14 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
Disposable connection = webClient.post()
.uri(this.endpoint)
.accept(MediaType.APPLICATION_JSON, MediaType.TEXT_EVENT_STREAM)
.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
.headers(httpHeaders -> {
transportSession.sessionId().ifPresent(id -> httpHeaders.add("mcp-session-id", id));
transportSession.sessionId().ifPresent(id -> httpHeaders.add(HttpHeaders.MCP_SESSION_ID, id));
})
.bodyValue(message)
.exchangeToFlux(response -> {
if (transportSession
.markInitialized(response.headers().asHttpHeaders().getFirst("mcp-session-id"))) {
.markInitialized(response.headers().asHttpHeaders().getFirst(HttpHeaders.MCP_SESSION_ID))) {
// Once we have a session, we try to open an async stream for
// the server to send notifications and requests out-of-band.
reconnect(null).contextWrite(sink.contextView()).subscribe();

11
mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/client/transport/WebFluxSseClientTransport.java
View file

@ -9,6 +9,8 @@ import java.util.function.Function;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import io.modelcontextprotocol.spec.HttpHeaders;
import io.modelcontextprotocol.spec.McpClientTransport;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
@ -62,6 +64,8 @@ public class WebFluxSseClientTransport implements McpClientTransport {
private static final Logger logger = LoggerFactory.getLogger(WebFluxSseClientTransport.class);
private static final String MCP_PROTOCOL_VERSION = "2024-11-05";
/**
* Event type for JSON-RPC messages received through the SSE connection. The server
* sends messages with this event type to transmit JSON-RPC protocol data.
@ -166,6 +170,11 @@ public class WebFluxSseClientTransport implements McpClientTransport {
this.sseEndpoint = sseEndpoint;
}
@Override
public String protocolVersion() {
return MCP_PROTOCOL_VERSION;
}
/**
* Establishes a connection to the MCP server using Server-Sent Events (SSE). This
* method initiates the SSE connection and sets up the message processing pipeline.
@ -250,6 +259,7 @@ public class WebFluxSseClientTransport implements McpClientTransport {
return webClient.post()
.uri(messageEndpointUri)
.contentType(MediaType.APPLICATION_JSON)
.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
.bodyValue(jsonText)
.retrieve()
.toBodilessEntity()
@ -282,6 +292,7 @@ public class WebFluxSseClientTransport implements McpClientTransport {
.get()
.uri(this.sseEndpoint)
.accept(MediaType.TEXT_EVENT_STREAM)
.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
.retrieve()
.bodyToFlux(SSE_TYPE)
.retryWhen(Retry.from(retrySignal -> retrySignal.handle(inboundRetryHandler)));

7
mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxSseServerTransportProvider.java
View file

@ -79,6 +79,8 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
*/
public static final String ENDPOINT_EVENT_TYPE = "endpoint";
private static final String MCP_PROTOCOL_VERSION = "2025-06-18";
/**
* Default SSE endpoint path as specified by the MCP transport specification.
*/
@ -212,6 +214,11 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
}
}
@Override
public String protocolVersion() {
return "2024-11-05";
}
@Override
public void setSessionFactory(McpServerSession.Factory sessionFactory) {
this.sessionFactory = sessionFactory;

1
mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxStatelessServerTransport.java
View file

@ -21,7 +21,6 @@ import reactor.core.publisher.Mono;
import java.io.IOException;
import java.util.List;
import java.util.function.Function;
/**
* Implementation of a WebFlux based {@link McpStatelessServerTransport}.

5
mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxStreamableServerTransportProvider.java
View file

@ -95,6 +95,11 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
}
@Override
public String protocolVersion() {
return "2025-03-26";
}
@Override
public void setSessionFactory(McpStreamableServerSession.Factory sessionFactory) {
this.sessionFactory = sessionFactory;

5
mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransportProvider.java
View file

@ -209,6 +209,11 @@ public class WebMvcSseServerTransportProvider implements McpServerTransportProvi
}
}
@Override
public String protocolVersion() {
return "2024-11-05";
}
@Override
public void setSessionFactory(McpServerSession.Factory sessionFactory) {
this.sessionFactory = sessionFactory;

5
mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcStreamableServerTransportProvider.java
View file

@ -147,6 +147,11 @@ public class WebMvcStreamableServerTransportProvider implements McpStreamableSer
}
}
@Override
public String protocolVersion() {
return "2025-03-26";
}
@Override
public void setSessionFactory(McpStreamableServerSession.Factory sessionFactory) {
this.sessionFactory = sessionFactory;

11
mcp-spring/mcp-spring-webmvc/src/test/java/io/modelcontextprotocol/server/WebMvcSseCustomContextPathTests.java
View file

@ -91,8 +91,15 @@ class WebMvcSseCustomContextPathTests {
@Bean
public WebMvcSseServerTransportProvider webMvcSseServerTransportProvider() {
return new WebMvcSseServerTransportProvider(new ObjectMapper(), CUSTOM_CONTEXT_PATH, MESSAGE_ENDPOINT,
WebMvcSseServerTransportProvider.DEFAULT_SSE_ENDPOINT);
return WebMvcSseServerTransportProvider.builder()
.objectMapper(new ObjectMapper())
.baseUrl(CUSTOM_CONTEXT_PATH)
.messageEndpoint(MESSAGE_ENDPOINT)
.sseEndpoint(WebMvcSseServerTransportProvider.DEFAULT_SSE_ENDPOINT)
.build();
// return new WebMvcSseServerTransportProvider(new ObjectMapper(),
// CUSTOM_CONTEXT_PATH, MESSAGE_ENDPOINT,
// WebMvcSseServerTransportProvider.DEFAULT_SSE_ENDPOINT);
}
@Bean

5
mcp/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java
View file

@ -272,9 +272,8 @@ public class McpAsyncClient {
asyncProgressNotificationHandler(progressConsumersFinal));
this.initializer = new LifecycleInitializer(clientCapabilities, clientInfo,
List.of(McpSchema.LATEST_PROTOCOL_VERSION), initializationTimeout,
ctx -> new McpClientSession(requestTimeout, transport, requestHandlers, notificationHandlers,
con -> con.contextWrite(ctx)));
List.of(transport.protocolVersion()), initializationTimeout, ctx -> new McpClientSession(requestTimeout,
transport, requestHandlers, notificationHandlers, con -> con.contextWrite(ctx)));
this.transport.setExceptionHandler(this.initializer::handleException);
}

15
mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransport.java
View file

@ -61,6 +61,10 @@ import reactor.core.publisher.Sinks;
*/
public class HttpClientSseClientTransport implements McpClientTransport {
private static final String MCP_PROTOCOL_VERSION = "2024-11-05";
private static final String MCP_PROTOCOL_VERSION_HEADER_NAME = "MCP-Protocol-Version";
private static final Logger logger = LoggerFactory.getLogger(HttpClientSseClientTransport.class);
/** SSE event type for JSON-RPC messages */
@ -211,6 +215,11 @@ public class HttpClientSseClientTransport implements McpClientTransport {
this.httpRequestCustomizer = httpRequestCustomizer;
}
@Override
public String protocolVersion() {
return MCP_PROTOCOL_VERSION;
}
/**
* Creates a new builder for {@link HttpClientSseClientTransport}.
* @param baseUri the base URI of the MCP server
@ -391,6 +400,7 @@ public class HttpClientSseClientTransport implements McpClientTransport {
.uri(uri)
.header("Accept", "text/event-stream")
.header("Cache-Control", "no-cache")
.header(MCP_PROTOCOL_VERSION_HEADER_NAME, MCP_PROTOCOL_VERSION)
.GET();
return Mono.from(this.httpRequestCustomizer.customize(builder, "GET", uri, null));
}).flatMap(requestBuilder -> Mono.create(sink -> {
@ -516,7 +526,10 @@ public class HttpClientSseClientTransport implements McpClientTransport {
private Mono<HttpResponse<String>> sendHttpPost(final String endpoint, final String body) {
final URI requestUri = Utils.resolveUri(baseUri, endpoint);
return Mono.defer(() -> {
var builder = this.requestBuilder.copy().uri(requestUri).POST(HttpRequest.BodyPublishers.ofString(body));
var builder = this.requestBuilder.copy()
.uri(requestUri)
.header(MCP_PROTOCOL_VERSION_HEADER_NAME, MCP_PROTOCOL_VERSION)
.POST(HttpRequest.BodyPublishers.ofString(body));
return Mono.from(this.httpRequestCustomizer.customize(builder, "POST", requestUri, body));
}).flatMap(customizedBuilder -> {
var request = customizedBuilder.build();

22
mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java
View file

@ -28,6 +28,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
import io.modelcontextprotocol.client.transport.ResponseSubscribers.ResponseEvent;
import io.modelcontextprotocol.spec.DefaultMcpTransportSession;
import io.modelcontextprotocol.spec.DefaultMcpTransportStream;
import io.modelcontextprotocol.spec.HttpHeaders;
import io.modelcontextprotocol.spec.McpClientTransport;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
@ -72,6 +73,8 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
private static final Logger logger = LoggerFactory.getLogger(HttpClientStreamableHttpTransport.class);
private static final String MCP_PROTOCOL_VERSION = "2025-03-26";
private static final String DEFAULT_ENDPOINT = "/mcp";
/**
@ -131,6 +134,11 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
this.httpRequestCustomizer = httpRequestCustomizer;
}
@Override
public String protocolVersion() {
return MCP_PROTOCOL_VERSION;
}
public static Builder builder(String baseUri) {
return new Builder(baseUri);
}
@ -157,12 +165,14 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
}
private Publisher<Void> createDelete(String sessionId) {
var uri = Utils.resolveUri(this.baseUri, this.endpoint);
return Mono.defer(() -> {
var builder = this.requestBuilder.copy()
.uri(uri)
.header("Cache-Control", "no-cache")
.header("mcp-session-id", sessionId)
.header(HttpHeaders.MCP_SESSION_ID, sessionId)
.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
.DELETE();
return Mono.from(this.httpRequestCustomizer.customize(builder, "DELETE", uri, null));
}).flatMap(requestBuilder -> {
@ -221,16 +231,18 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
HttpRequest.Builder requestBuilder = this.requestBuilder.copy();
if (transportSession != null && transportSession.sessionId().isPresent()) {
requestBuilder = requestBuilder.header("mcp-session-id", transportSession.sessionId().get());
requestBuilder = requestBuilder.header(HttpHeaders.MCP_SESSION_ID,
transportSession.sessionId().get());
}
if (stream != null && stream.lastId().isPresent()) {
requestBuilder = requestBuilder.header("last-event-id", stream.lastId().get());
requestBuilder = requestBuilder.header(HttpHeaders.LAST_EVENT_ID, stream.lastId().get());
}
var builder = requestBuilder.uri(uri)
.header("Accept", TEXT_EVENT_STREAM)
.header("Cache-Control", "no-cache")
.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
.GET();
return Mono.from(this.httpRequestCustomizer.customize(builder, "GET", uri, null));
})
@ -377,13 +389,15 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
HttpRequest.Builder requestBuilder = this.requestBuilder.copy();
if (transportSession != null && transportSession.sessionId().isPresent()) {
requestBuilder = requestBuilder.header("mcp-session-id", transportSession.sessionId().get());
requestBuilder = requestBuilder.header(HttpHeaders.MCP_SESSION_ID,
transportSession.sessionId().get());
}
var builder = requestBuilder.uri(uri)
.header("Accept", APPLICATION_JSON + ", " + TEXT_EVENT_STREAM)
.header("Content-Type", APPLICATION_JSON)
.header("Cache-Control", "no-cache")
.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
.POST(HttpRequest.BodyPublishers.ofString(jsonBody));
return Mono.from(this.httpRequestCustomizer.customize(builder, "GET", uri, jsonBody));
}).flatMapMany(requestBuilder -> Flux.<ResponseEvent>create(responseEventSink -> {

6
mcp/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java
View file

@ -115,7 +115,7 @@ public class McpAsyncServer {
private final ConcurrentHashMap<McpSchema.CompleteReference, McpServerFeatures.AsyncCompletionSpecification> completions = new ConcurrentHashMap<>();
private List<String> protocolVersions = List.of(McpSchema.LATEST_PROTOCOL_VERSION);
private List<String> protocolVersions;
private McpUriTemplateManagerFactory uriTemplateManagerFactory = new DeafaultMcpUriTemplateManagerFactory();
@ -145,6 +145,8 @@ public class McpAsyncServer {
Map<String, McpRequestHandler<?>> requestHandlers = prepareRequestHandlers();
Map<String, McpNotificationHandler> notificationHandlers = prepareNotificationHandlers(features);
this.protocolVersions = List.of(mcpTransportProvider.protocolVersion());
mcpTransportProvider.setSessionFactory(transport -> new McpServerSession(UUID.randomUUID().toString(),
requestTimeout, transport, this::asyncInitializeRequestHandler, requestHandlers, notificationHandlers));
}
@ -168,6 +170,8 @@ public class McpAsyncServer {
Map<String, McpRequestHandler<?>> requestHandlers = prepareRequestHandlers();
Map<String, McpNotificationHandler> notificationHandlers = prepareNotificationHandlers(features);
this.protocolVersions = List.of(mcpTransportProvider.protocolVersion());
mcpTransportProvider.setSessionFactory(new DefaultMcpStreamableServerSessionFactory(requestTimeout,
this::asyncInitializeRequestHandler, requestHandlers, notificationHandlers));
}

4
mcp/src/main/java/io/modelcontextprotocol/server/McpStatelessAsyncServer.java
View file

@ -63,7 +63,7 @@ public class McpStatelessAsyncServer {
private final ConcurrentHashMap<McpSchema.CompleteReference, McpStatelessServerFeatures.AsyncCompletionSpecification> completions = new ConcurrentHashMap<>();
private List<String> protocolVersions = List.of(McpSchema.LATEST_PROTOCOL_VERSION);
private List<String> protocolVersions;
private McpUriTemplateManagerFactory uriTemplateManagerFactory = new DeafaultMcpUriTemplateManagerFactory();
@ -118,6 +118,8 @@ public class McpStatelessAsyncServer {
requestHandlers.put(McpSchema.METHOD_COMPLETION_COMPLETE, completionCompleteRequestHandler());
}
this.protocolVersions = List.of(mcpTransport.protocolVersion());
McpStatelessServerHandler handler = new DefaultMcpStatelessServerHandler(requestHandlers, Map.of());
mcpTransport.setMcpHandler(handler);
}

5
mcp/src/main/java/io/modelcontextprotocol/server/transport/HttpServletSseServerTransportProvider.java
View file

@ -178,6 +178,11 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
}
}
@Override
public String protocolVersion() {
return "2024-11-05";
}
/**
* Creates a new HttpServletSseServerTransportProvider instance with the default SSE
* endpoint.

5
mcp/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java
View file

@ -154,6 +154,11 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
}
@Override
public String protocolVersion() {
return "2025-03-26";
}
@Override
public void setSessionFactory(McpStreamableServerSession.Factory sessionFactory) {
this.sessionFactory = sessionFactory;

5
mcp/src/main/java/io/modelcontextprotocol/server/transport/StdioServerTransportProvider.java
View file

@ -88,6 +88,11 @@ public class StdioServerTransportProvider implements McpServerTransportProvider
this.outputStream = outputStream;
}
@Override
public String protocolVersion() {
return "2024-11-05";
}
@Override
public void setSessionFactory(McpServerSession.Factory sessionFactory) {
// Create a single session for the stdio connection

5
mcp/src/main/java/io/modelcontextprotocol/spec/HttpHeaders.java
View file

@ -17,4 +17,9 @@ public interface HttpHeaders {
*/
String LAST_EVENT_ID = "last-event-id";
/**
* Identifies the MCP protocol version.
*/
String PROTOCOL_VERSION = "MCP-Protocol-Version";
}

1
mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java
View file

@ -44,6 +44,7 @@ public final class McpSchema {
private McpSchema() {
}
@Deprecated
public static final String LATEST_PROTOCOL_VERSION = "2025-03-26";
public static final String JSONRPC_VERSION = "2.0";

8
mcp/src/main/java/io/modelcontextprotocol/spec/McpServerTransportProviderBase.java
View file

@ -55,4 +55,12 @@ public interface McpServerTransportProviderBase {
*/
Mono<Void> closeGracefully();
/**
* Returns the protocol version supported by this transport provider.
* @return the protocol version as a string
*/
default String protocolVersion() {
return "2024-11-05";
}
}

4
mcp/src/main/java/io/modelcontextprotocol/spec/McpStatelessServerTransport.java
View file

@ -22,4 +22,8 @@ public interface McpStatelessServerTransport {
*/
Mono<Void> closeGracefully();
default String protocolVersion() {
return "2025-03-26";
}
}

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