Support resource subscriptions (#839)
Clients can now subscribe to specific resources and receive targeted notifications when those resources change. Previously, calling `notifyResourceUpdated` on the server would broadcast the notification to every connected client regardless of interest — now only sessions that have explicitly subscribed to a given resource URI receive the update, making resource change propagation both correct and efficient. The subscription lifecycle is fully handled: clients can subscribe and unsubscribe at any time, and the server cleans up subscription state when a session closes. Supersedes #838. Resolves #837, #776. --------- Signed-off-by: Dariusz Jędrzejczyk <dariusz.jedrzejczyk@broadcom.com>
This commit is contained in:
Dariusz Jędrzejczyk
GitHub
parent
ce2c747c92
commit
7f68ea5bc0
4 changed files with 506 additions and 60 deletions
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@ -1746,6 +1746,95 @@ public abstract class AbstractMcpClientServerIntegrationTests {
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}
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}
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// ---------------------------------------
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// Resource Subscription Tests
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// ---------------------------------------
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@ParameterizedTest(name = "{0} : {displayName} ")
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@MethodSource("clientsForTesting")
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void testResourceSubscription(String clientType) throws InterruptedException {
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var clientBuilder = clientBuilders.get(clientType);
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String resourceUri = "test://subscribable-resource";
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var receivedContents = new AtomicReference<List<McpSchema.ResourceContents>>();
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var latch = new CountDownLatch(1);
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McpServerFeatures.SyncResourceSpecification resourceSpec = new McpServerFeatures.SyncResourceSpecification(
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McpSchema.Resource.builder()
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.uri(resourceUri)
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.name("Subscribable Resource")
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.mimeType("text/plain")
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.build(),
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(exchange, req) -> new McpSchema.ReadResourceResult(
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List.of(new McpSchema.TextResourceContents(resourceUri, "text/plain", "initial content"))));
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McpSyncServer mcpServer = prepareSyncServerBuilder().serverInfo("test-server", "1.0.0")
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.capabilities(McpSchema.ServerCapabilities.builder().resources(true, false).build())
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.resources(resourceSpec)
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.build();
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try (var mcpClient = clientBuilder.resourcesUpdateConsumer(contents -> {
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receivedContents.set(contents);
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latch.countDown();
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}).build()) {
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mcpClient.initialize();
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mcpClient.subscribeResource(new McpSchema.SubscribeRequest(resourceUri));
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mcpServer.notifyResourcesUpdated(new McpSchema.ResourcesUpdatedNotification(resourceUri));
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assertThat(latch.await(5, TimeUnit.SECONDS))
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.as("client should receive the resources/updated notification within 5 seconds")
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.isTrue();
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assertThat(receivedContents.get()).isNotEmpty();
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}
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finally {
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mcpServer.closeGracefully();
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}
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}
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@ParameterizedTest(name = "{0} : {displayName} ")
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@MethodSource("clientsForTesting")
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void testResourceSubscription_afterUnsubscribe_noNotification(String clientType) throws InterruptedException {
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var clientBuilder = clientBuilders.get(clientType);
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String resourceUri = "test://subscribable-resource-unsub";
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var notificationCount = new java.util.concurrent.atomic.AtomicInteger(0);
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McpServerFeatures.SyncResourceSpecification resourceSpec = new McpServerFeatures.SyncResourceSpecification(
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McpSchema.Resource.builder()
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.uri(resourceUri)
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.name("Subscribable Resource")
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.mimeType("text/plain")
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.build(),
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(exchange, req) -> new McpSchema.ReadResourceResult(
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List.of(new McpSchema.TextResourceContents(resourceUri, "text/plain", "content"))));
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McpSyncServer mcpServer = prepareSyncServerBuilder().serverInfo("test-server", "1.0.0")
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.capabilities(McpSchema.ServerCapabilities.builder().resources(true, false).build())
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.resources(resourceSpec)
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.build();
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try (var mcpClient = clientBuilder.resourcesUpdateConsumer(contents -> notificationCount.incrementAndGet())
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.build()) {
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mcpClient.initialize();
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mcpClient.subscribeResource(new McpSchema.SubscribeRequest(resourceUri));
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mcpClient.unsubscribeResource(new McpSchema.UnsubscribeRequest(resourceUri));
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mcpServer.notifyResourcesUpdated(new McpSchema.ResourcesUpdatedNotification(resourceUri));
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assertThat(notificationCount.get()).as("no notification should be received after unsubscribing").isZero();
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}
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finally {
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mcpServer.closeGracefully();
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}
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}
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private double evaluateExpression(String expression) {
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// Simple expression evaluator for testing
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return switch (expression) {
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@ -6,6 +6,7 @@ package io.modelcontextprotocol;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.concurrent.CountDownLatch;
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import java.util.function.BiConsumer;
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import io.modelcontextprotocol.json.McpJsonDefaults;
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@ -38,6 +38,14 @@ public class MockMcpServerTransportProvider implements McpServerTransportProvide
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return session.sendNotification(method, params);
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}
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@Override
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public Mono<Void> notifyClient(String sessionId, String method, Object params) {
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if (session != null && session.getId().equals(sessionId)) {
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return session.sendNotification(method, params);
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}
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return Mono.empty();
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}
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@Override
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public Mono<Void> closeGracefully() {
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return session.closeGracefully();
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@ -0,0 +1,166 @@
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/*
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* Copyright 2025-2025 the original author or authors.
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*/
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package io.modelcontextprotocol.server;
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import java.util.UUID;
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import io.modelcontextprotocol.MockMcpServerTransport;
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import io.modelcontextprotocol.MockMcpServerTransportProvider;
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import io.modelcontextprotocol.spec.McpSchema;
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import io.modelcontextprotocol.spec.ProtocolVersions;
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import org.junit.jupiter.api.Test;
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import reactor.test.StepVerifier;
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import static org.assertj.core.api.Assertions.assertThat;
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/**
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* Unit tests for resource subscription logic in {@link McpAsyncServer}. Uses
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* {@link MockMcpServerTransportProvider} to drive sessions directly without a real
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* network stack.
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*/
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class ResourceSubscriptionTests {
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private static final String RESOURCE_URI = "test://resource/1";
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private static final McpSchema.Implementation SERVER_INFO = new McpSchema.Implementation("test-server", "1.0.0");
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private static final McpSchema.Implementation CLIENT_INFO = new McpSchema.Implementation("test-client", "1.0.0");
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private static McpAsyncServer buildServer(MockMcpServerTransportProvider transportProvider) {
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return McpServer.async(transportProvider)
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.serverInfo(SERVER_INFO)
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.capabilities(McpSchema.ServerCapabilities.builder().resources(true, false).build())
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.build();
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}
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private static McpSchema.JSONRPCRequest initRequest() {
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return new McpSchema.JSONRPCRequest(McpSchema.JSONRPC_VERSION, McpSchema.METHOD_INITIALIZE,
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UUID.randomUUID().toString(),
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new McpSchema.InitializeRequest(ProtocolVersions.MCP_2025_11_25, null, CLIENT_INFO));
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}
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private static McpSchema.JSONRPCNotification initializedNotification() {
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return new McpSchema.JSONRPCNotification(McpSchema.JSONRPC_VERSION, McpSchema.METHOD_NOTIFICATION_INITIALIZED,
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null);
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}
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private static McpSchema.JSONRPCRequest subscribeRequest(String uri) {
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return new McpSchema.JSONRPCRequest(McpSchema.JSONRPC_VERSION, McpSchema.METHOD_RESOURCES_SUBSCRIBE,
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UUID.randomUUID().toString(), new McpSchema.SubscribeRequest(uri));
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}
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private static McpSchema.JSONRPCRequest unsubscribeRequest(String uri) {
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return new McpSchema.JSONRPCRequest(McpSchema.JSONRPC_VERSION, McpSchema.METHOD_RESOURCES_UNSUBSCRIBE,
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UUID.randomUUID().toString(), new McpSchema.UnsubscribeRequest(uri));
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}
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@Test
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void notifyResourcesUpdated_noSubscribers_completesEmpty() {
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MockMcpServerTransport transport = new MockMcpServerTransport();
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MockMcpServerTransportProvider transportProvider = new MockMcpServerTransportProvider(transport);
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McpAsyncServer server = buildServer(transportProvider);
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transportProvider.simulateIncomingMessage(initRequest());
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transportProvider.simulateIncomingMessage(initializedNotification());
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transport.clearSentMessages();
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StepVerifier.create(server.notifyResourcesUpdated(new McpSchema.ResourcesUpdatedNotification(RESOURCE_URI)))
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.verifyComplete();
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assertThat(transport.getAllSentMessages()).as("no notification should be sent when nobody is subscribed")
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.isEmpty();
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server.closeGracefully().block();
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}
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@Test
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void notifyResourcesUpdated_afterSubscribe_notifiesSession() {
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MockMcpServerTransport transport = new MockMcpServerTransport();
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MockMcpServerTransportProvider transportProvider = new MockMcpServerTransportProvider(transport);
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McpAsyncServer server = buildServer(transportProvider);
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transportProvider.simulateIncomingMessage(initRequest());
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transportProvider.simulateIncomingMessage(initializedNotification());
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transportProvider.simulateIncomingMessage(subscribeRequest(RESOURCE_URI));
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transport.clearSentMessages();
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StepVerifier.create(server.notifyResourcesUpdated(new McpSchema.ResourcesUpdatedNotification(RESOURCE_URI)))
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.verifyComplete();
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McpSchema.JSONRPCMessage sent = transport.getLastSentMessage();
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assertThat(sent).isInstanceOf(McpSchema.JSONRPCNotification.class);
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McpSchema.JSONRPCNotification notification = (McpSchema.JSONRPCNotification) sent;
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assertThat(notification.method()).isEqualTo(McpSchema.METHOD_NOTIFICATION_RESOURCES_UPDATED);
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server.closeGracefully().block();
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}
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@Test
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void notifyResourcesUpdated_differentUri_doesNotNotifySession() {
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MockMcpServerTransport transport = new MockMcpServerTransport();
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MockMcpServerTransportProvider transportProvider = new MockMcpServerTransportProvider(transport);
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McpAsyncServer server = buildServer(transportProvider);
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transportProvider.simulateIncomingMessage(initRequest());
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transportProvider.simulateIncomingMessage(initializedNotification());
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transportProvider.simulateIncomingMessage(subscribeRequest(RESOURCE_URI));
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transport.clearSentMessages();
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StepVerifier
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.create(server.notifyResourcesUpdated(new McpSchema.ResourcesUpdatedNotification("test://other/resource")))
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.verifyComplete();
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assertThat(transport.getAllSentMessages())
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.as("notification for a different URI should not reach a session subscribed to a different URI")
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.isEmpty();
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server.closeGracefully().block();
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}
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@Test
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void notifyResourcesUpdated_afterUnsubscribe_doesNotNotifySession() {
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MockMcpServerTransport transport = new MockMcpServerTransport();
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MockMcpServerTransportProvider transportProvider = new MockMcpServerTransportProvider(transport);
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McpAsyncServer server = buildServer(transportProvider);
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transportProvider.simulateIncomingMessage(initRequest());
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transportProvider.simulateIncomingMessage(initializedNotification());
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transportProvider.simulateIncomingMessage(subscribeRequest(RESOURCE_URI));
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transportProvider.simulateIncomingMessage(unsubscribeRequest(RESOURCE_URI));
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transport.clearSentMessages();
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StepVerifier.create(server.notifyResourcesUpdated(new McpSchema.ResourcesUpdatedNotification(RESOURCE_URI)))
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.verifyComplete();
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assertThat(transport.getAllSentMessages()).as("no notification should be sent after the session unsubscribed")
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.isEmpty();
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server.closeGracefully().block();
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}
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@Test
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void notifyResourcesUpdated_afterSessionClose_doesNotNotifySession() {
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MockMcpServerTransport transport = new MockMcpServerTransport();
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MockMcpServerTransportProvider transportProvider = new MockMcpServerTransportProvider(transport);
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McpAsyncServer server = buildServer(transportProvider);
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transportProvider.simulateIncomingMessage(initRequest());
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transportProvider.simulateIncomingMessage(initializedNotification());
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transportProvider.simulateIncomingMessage(subscribeRequest(RESOURCE_URI));
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// Close the session; onClose must fire and remove the subscription
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transportProvider.closeGracefully().block();
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transport.clearSentMessages();
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StepVerifier.create(server.notifyResourcesUpdated(new McpSchema.ResourcesUpdatedNotification(RESOURCE_URI)))
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.verifyComplete();
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assertThat(transport.getAllSentMessages()).as("no notification should be sent after the session has closed")
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.isEmpty();
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server.closeGracefully().block();
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}
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}
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