From f5aab36a2fc0abf836cb3e956920e6d8023d4f42 Mon Sep 17 00:00:00 2001 From: jiajingda Date: Fri, 7 Aug 2026 23:48:03 +0800 Subject: [PATCH 1/3] Fix SSE event classification to follow spec for missing event field (#913) Per the SSE specification (WHATWG HTML Living Standard 9.2.6), an event with no explicit event field MUST be dispatched as a message event. HttpClientStreamableHttpTransport previously used strict equality and silently dropped such frames in the reconnect/GET stream path, causing server-initiated notifications to never reach the handler. Extract classification into a package-private isMessageEvent helper and cover with parameterized unit tests. Closes gh-885 --- .../HttpClientStreamableHttpTransport.java | 25 ++++++++- ...reamableHttpTransportSseEventTypeTest.java | 51 +++++++++++++++++++ 2 files changed, 75 insertions(+), 1 deletion(-) create mode 100644 mcp-core/src/test/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransportSseEventTypeTest.java diff --git a/mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java b/mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java index 48462c0db..d8cbe2f0b 100644 --- a/mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java +++ b/mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java @@ -114,6 +114,29 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport { public static int BAD_REQUEST = 400; + /** + * Determines whether an SSE event should be treated as a "message" event carrying a + * JSON-RPC payload. + * + *

+ * Per the + * SSE specification (WHATWG HTML Living Standard §9.2.6), an event with no + * explicit {@code event:} field MUST be dispatched as a {@code message} event by + * default. This method applies that rule by treating {@code null} or empty event + * names as equivalent to {@link #MESSAGE_EVENT_TYPE}. + * + *

+ * This alignment ensures interoperability with MCP servers that emit bare + * {@code data:} frames without an accompanying {@code event:} line, which are valid + * per the SSE spec. + * @param eventName the SSE event name, which may be {@code null} or empty + * @return {@code true} if the event should be parsed as a JSON-RPC message + */ + static boolean isMessageEvent(String eventName) { + return eventName == null || eventName.isEmpty() || MESSAGE_EVENT_TYPE.equals(eventName); + } + private final McpJsonMapper jsonMapper; private final URI baseUri; @@ -323,7 +346,7 @@ else if (statusCode == METHOD_NOT_ALLOWED) { + statusCode)); } else if (statusCode >= 200 && statusCode < 300) { - if (MESSAGE_EVENT_TYPE.equals(sseResponseEvent.sseEvent().event())) { + if (isMessageEvent(sseResponseEvent.sseEvent().event())) { String data = sseResponseEvent.sseEvent().data(); // Per 2025-11-25 spec (SEP-1699), servers may // send SSE events diff --git a/mcp-core/src/test/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransportSseEventTypeTest.java b/mcp-core/src/test/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransportSseEventTypeTest.java new file mode 100644 index 000000000..d5f7196bd --- /dev/null +++ b/mcp-core/src/test/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransportSseEventTypeTest.java @@ -0,0 +1,51 @@ +/* + * Copyright 2024-2026 the original author or authors. + */ + +package io.modelcontextprotocol.client.transport; + +import org.junit.jupiter.api.Test; +import org.junit.jupiter.params.ParameterizedTest; +import org.junit.jupiter.params.provider.NullAndEmptySource; +import org.junit.jupiter.params.provider.ValueSource; + +import static org.assertj.core.api.Assertions.assertThat; + +/** + * Unit tests for {@link HttpClientStreamableHttpTransport#isMessageEvent(String)}. + * + *

+ * Verifies that SSE event classification follows the + * WHATWG HTML Living Standard §9.2.6: an event without an explicit {@code event:} + * field must be dispatched as a {@code message} event. + * + * @author jiajingda + * @see #885 + */ +class HttpClientStreamableHttpTransportSseEventTypeTest { + + @ParameterizedTest + @NullAndEmptySource + void shouldTreatNullOrEmptyEventAsMessage(String eventName) { + assertThat(HttpClientStreamableHttpTransport.isMessageEvent(eventName)) + .as("SSE frame with null/empty event field must be treated as a 'message' event per SSE spec") + .isTrue(); + } + + @Test + void shouldTreatExplicitMessageEventAsMessage() { + assertThat(HttpClientStreamableHttpTransport.isMessageEvent("message")) + .as("Explicit 'message' event must be parsed as a JSON-RPC message") + .isTrue(); + } + + @ParameterizedTest + @ValueSource(strings = { "ping", "error", "notification", "MESSAGE", "Message", "custom-event" }) + void shouldNotTreatOtherEventsAsMessage(String eventName) { + assertThat(HttpClientStreamableHttpTransport.isMessageEvent(eventName)) + .as("Non-'message' SSE event '%s' must not be parsed as a JSON-RPC message", eventName) + .isFalse(); + } + +} \ No newline at end of file From 27b91521c0f7b9b10a688d389fe59802c2f24149 Mon Sep 17 00:00:00 2001 From: nanookclaw Date: Fri, 7 Aug 2026 16:25:39 +0000 Subject: [PATCH 2/3] fix: stop pagination on empty cursors (#954) Signed-off-by: Nanook Co-authored-by: Nanook --- .../client/McpAsyncClient.java | 43 +++--- .../client/McpAsyncClientTests.java | 123 ++++++++++++++++++ 2 files changed, 144 insertions(+), 22 deletions(-) diff --git a/mcp-core/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java b/mcp-core/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java index 945221bd0..3509b760b 100644 --- a/mcp-core/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java +++ b/mcp-core/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java @@ -818,13 +818,13 @@ private NotificationHandler asyncToolsChangeNotificationHandler( * @see #readResource(McpSchema.Resource) */ public Mono listResources() { - return this.listResources(McpSchema.FIRST_PAGE) - .expand(result -> (result.nextCursor() != null) ? this.listResources(result.nextCursor()) : Mono.empty()) - .reduce(new ArrayList(), (accumulated, result) -> { - accumulated.addAll(result.resources()); - return accumulated; - }) - .map(all -> McpSchema.ListResourcesResult.builder(Collections.unmodifiableList(all)).build()); + return this.listResources(McpSchema.FIRST_PAGE).expand(result -> { + String next = result.nextCursor(); + return (next != null && !next.isEmpty()) ? this.listResources(next) : Mono.empty(); + }).reduce(new ArrayList(), (accumulated, result) -> { + accumulated.addAll(result.resources()); + return accumulated; + }).map(all -> McpSchema.ListResourcesResult.builder(Collections.unmodifiableList(all)).build()); } /** @@ -904,14 +904,13 @@ public Mono readResource(McpSchema.ReadResourceReq * @see McpSchema.ListResourceTemplatesResult */ public Mono listResourceTemplates() { - return this.listResourceTemplates(McpSchema.FIRST_PAGE) - .expand(result -> (result.nextCursor() != null) ? this.listResourceTemplates(result.nextCursor()) - : Mono.empty()) - .reduce(new ArrayList(), (accumulated, result) -> { - accumulated.addAll(result.resourceTemplates()); - return accumulated; - }) - .map(all -> McpSchema.ListResourceTemplatesResult.builder(Collections.unmodifiableList(all)).build()); + return this.listResourceTemplates(McpSchema.FIRST_PAGE).expand(result -> { + String next = result.nextCursor(); + return (next != null && !next.isEmpty()) ? this.listResourceTemplates(next) : Mono.empty(); + }).reduce(new ArrayList(), (accumulated, result) -> { + accumulated.addAll(result.resourceTemplates()); + return accumulated; + }).map(all -> McpSchema.ListResourceTemplatesResult.builder(Collections.unmodifiableList(all)).build()); } /** @@ -1024,13 +1023,13 @@ private NotificationHandler asyncResourcesUpdatedNotificationHandler( * @see #getPrompt(GetPromptRequest) */ public Mono listPrompts() { - return this.listPrompts(McpSchema.FIRST_PAGE) - .expand(result -> (result.nextCursor() != null) ? this.listPrompts(result.nextCursor()) : Mono.empty()) - .reduce(new ArrayList(), (accumulated, result) -> { - accumulated.addAll(result.prompts()); - return accumulated; - }) - .map(all -> McpSchema.ListPromptsResult.builder(Collections.unmodifiableList(all)).build()); + return this.listPrompts(McpSchema.FIRST_PAGE).expand(result -> { + String next = result.nextCursor(); + return (next != null && !next.isEmpty()) ? this.listPrompts(next) : Mono.empty(); + }).reduce(new ArrayList(), (accumulated, result) -> { + accumulated.addAll(result.prompts()); + return accumulated; + }).map(all -> McpSchema.ListPromptsResult.builder(Collections.unmodifiableList(all)).build()); } /** diff --git a/mcp-test/src/test/java/io/modelcontextprotocol/client/McpAsyncClientTests.java b/mcp-test/src/test/java/io/modelcontextprotocol/client/McpAsyncClientTests.java index 493b5812a..c2496e204 100644 --- a/mcp-test/src/test/java/io/modelcontextprotocol/client/McpAsyncClientTests.java +++ b/mcp-test/src/test/java/io/modelcontextprotocol/client/McpAsyncClientTests.java @@ -8,6 +8,7 @@ import java.util.Map; import java.util.Objects; import java.util.Set; +import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.atomic.AtomicReference; import java.util.function.Function; import java.util.stream.Collectors; @@ -298,6 +299,42 @@ void testListPromptsWithCursorAndMeta() { } + @Test + void listResourcesStopsOnEmptyNextCursor() { + var transport = new EmptyCursorTestMcpClientTransport(McpSchema.METHOD_RESOURCES_LIST); + McpAsyncClient client = McpClient.async(transport).build(); + + McpSchema.ListResourcesResult result = client.listResources().block(); + + assertThat(result).isNotNull(); + assertThat(result.resources()).extracting(McpSchema.Resource::name).containsExactly("test.txt"); + assertThat(transport.getRequestCount()).isEqualTo(1); + } + + @Test + void listResourceTemplatesStopsOnEmptyNextCursor() { + var transport = new EmptyCursorTestMcpClientTransport(McpSchema.METHOD_RESOURCES_TEMPLATES_LIST); + McpAsyncClient client = McpClient.async(transport).build(); + + McpSchema.ListResourceTemplatesResult result = client.listResourceTemplates().block(); + + assertThat(result).isNotNull(); + assertThat(result.resourceTemplates()).extracting(McpSchema.ResourceTemplate::name).containsExactly("template"); + assertThat(transport.getRequestCount()).isEqualTo(1); + } + + @Test + void listPromptsStopsOnEmptyNextCursor() { + var transport = new EmptyCursorTestMcpClientTransport(McpSchema.METHOD_PROMPT_LIST); + McpAsyncClient client = McpClient.async(transport).build(); + + McpSchema.ListPromptsResult result = client.listPrompts().block(); + + assertThat(result).isNotNull(); + assertThat(result.prompts()).extracting(McpSchema.Prompt::name).containsExactly("test-prompt"); + assertThat(transport.getRequestCount()).isEqualTo(1); + } + static class TestMcpClientTransport implements McpClientTransport { private Function, Mono> handler; @@ -397,4 +434,90 @@ public McpSchema.PaginatedRequest getCapturedRequest() { } + static class EmptyCursorTestMcpClientTransport implements McpClientTransport { + + private final String listMethod; + + private final AtomicInteger requestCount = new AtomicInteger(); + + private Function, Mono> handler; + + EmptyCursorTestMcpClientTransport(String listMethod) { + this.listMethod = listMethod; + } + + @Override + public Mono connect(Function, Mono> handler) { + this.handler = handler; + return Mono.empty(); + } + + @Override + public Mono closeGracefully() { + return Mono.empty(); + } + + @Override + public Mono sendMessage(McpSchema.JSONRPCMessage message) { + if (!(message instanceof McpSchema.JSONRPCRequest request)) { + return Mono.empty(); + } + + McpSchema.JSONRPCResponse response; + if (McpSchema.METHOD_INITIALIZE.equals(request.method())) { + McpSchema.ServerCapabilities caps = McpSchema.ServerCapabilities.builder() + .prompts(false) + .resources(false, false) + .tools(false) + .build(); + + McpSchema.InitializeResult initResult = McpSchema.InitializeResult + .builder(ProtocolVersions.MCP_2024_11_05, caps, MOCK_SERVER_INFO) + .build(); + response = McpSchema.JSONRPCResponse.result(request.id(), initResult); + } + else if (this.listMethod.equals(request.method())) { + this.requestCount.incrementAndGet(); + response = McpSchema.JSONRPCResponse.result(request.id(), resultForMethod(request.method())); + } + else { + return Mono.empty(); + } + + return this.handler.apply(Mono.just(response)).then(); + } + + private Object resultForMethod(String method) { + if (McpSchema.METHOD_RESOURCES_LIST.equals(method)) { + McpSchema.Resource resource = McpSchema.Resource.builder("file:///test.txt", "test.txt").build(); + return McpSchema.ListResourcesResult.builder(List.of(resource)).nextCursor("").build(); + } + if (McpSchema.METHOD_RESOURCES_TEMPLATES_LIST.equals(method)) { + McpSchema.ResourceTemplate template = McpSchema.ResourceTemplate.builder("file:///{name}", "template") + .build(); + return McpSchema.ListResourceTemplatesResult.builder(List.of(template)).nextCursor("").build(); + } + if (McpSchema.METHOD_PROMPT_LIST.equals(method)) { + McpSchema.Prompt prompt = McpSchema.Prompt.builder("test-prompt").build(); + return McpSchema.ListPromptsResult.builder(List.of(prompt)).nextCursor("").build(); + } + throw new IllegalArgumentException("Unsupported method: " + method); + } + + @Override + public T unmarshalFrom(Object data, TypeRef typeRef) { + return JSON_MAPPER.convertValue(data, new TypeRef<>() { + @Override + public java.lang.reflect.Type getType() { + return typeRef.getType(); + } + }); + } + + int getRequestCount() { + return this.requestCount.get(); + } + + } + } From 8ee8ccbc1772b1382dcc28c11b5190822d8ef222 Mon Sep 17 00:00:00 2001 From: Iuliia Sobolevska Date: Fri, 7 Aug 2026 18:36:22 +0200 Subject: [PATCH 3/3] Make McpTransportContext.metadata immutable (#1076) Signed-off-by: Daniel Garnier-Moiroux --- .../common/DefaultMcpTransportContext.java | 2 +- .../common/McpTransportContextTests.java | 89 +++++++++++++++++++ 2 files changed, 90 insertions(+), 1 deletion(-) create mode 100644 mcp-core/src/test/java/io/modelcontextprotocol/common/McpTransportContextTests.java diff --git a/mcp-core/src/main/java/io/modelcontextprotocol/common/DefaultMcpTransportContext.java b/mcp-core/src/main/java/io/modelcontextprotocol/common/DefaultMcpTransportContext.java index cde637b15..322aa3a07 100644 --- a/mcp-core/src/main/java/io/modelcontextprotocol/common/DefaultMcpTransportContext.java +++ b/mcp-core/src/main/java/io/modelcontextprotocol/common/DefaultMcpTransportContext.java @@ -20,7 +20,7 @@ class DefaultMcpTransportContext implements McpTransportContext { DefaultMcpTransportContext(Map metadata) { Assert.notNull(metadata, "The metadata cannot be null"); - this.metadata = metadata; + this.metadata = Map.copyOf(metadata); } @Override diff --git a/mcp-core/src/test/java/io/modelcontextprotocol/common/McpTransportContextTests.java b/mcp-core/src/test/java/io/modelcontextprotocol/common/McpTransportContextTests.java new file mode 100644 index 000000000..a19b1015d --- /dev/null +++ b/mcp-core/src/test/java/io/modelcontextprotocol/common/McpTransportContextTests.java @@ -0,0 +1,89 @@ +/* + * Copyright 2026-2026 the original author or authors. + */ + +package io.modelcontextprotocol.common; + +import java.util.HashMap; +import java.util.Map; + +import org.junit.jupiter.api.Test; + +import static org.assertj.core.api.Assertions.assertThat; + +/** + * Tests for {@link McpTransportContext#create(Map)}, which is documented to return an + * unmodifiable context. + */ +class McpTransportContextTests { + + @Test + void createdContextShouldNotSeeLaterWritesToTheSourceMap() { + Map metadata = new HashMap<>(); + metadata.put("tenant", "acme"); + + McpTransportContext context = McpTransportContext.create(metadata); + metadata.put("tenant", "other"); + + assertThat(context.get("tenant")).isEqualTo("acme"); + } + + @Test + void createdContextShouldNotSeeLaterAdditionsToTheSourceMap() { + Map metadata = new HashMap<>(); + metadata.put("tenant", "acme"); + + McpTransportContext context = McpTransportContext.create(metadata); + metadata.put("added-after-the-fact", "surprise"); + + assertThat(context.get("added-after-the-fact")).isNull(); + } + + @Test + void createdContextShouldNotBeEmptiedByClearingTheSourceMap() { + Map metadata = new HashMap<>(); + metadata.put("tenant", "acme"); + + McpTransportContext context = McpTransportContext.create(metadata); + metadata.clear(); + + assertThat(context.get("tenant")).isEqualTo("acme"); + } + + @Test + void createdContextShouldRemainUsableAsAMapKey() { + Map metadata = new HashMap<>(); + metadata.put("tenant", "acme"); + McpTransportContext context = McpTransportContext.create(metadata); + + Map byContext = new HashMap<>(); + byContext.put(context, "value"); + metadata.put("tenant", "other"); + + assertThat(byContext.get(context)).isEqualTo("value"); + } + + @Test + void twoContextsCreatedFromEqualMapsShouldStayEqual() { + Map first = new HashMap<>(); + first.put("tenant", "acme"); + Map second = new HashMap<>(); + second.put("tenant", "acme"); + + McpTransportContext firstContext = McpTransportContext.create(first); + McpTransportContext secondContext = McpTransportContext.create(second); + assertThat(firstContext).isEqualTo(secondContext); + + first.put("tenant", "other"); + + assertThat(firstContext).isEqualTo(secondContext); + } + + @Test + void createdContextFromAnImmutableMapIsAlreadyCorrect() { + McpTransportContext context = McpTransportContext.create(Map.of("tenant", "acme")); + + assertThat(context.get("tenant")).isEqualTo("acme"); + } + +}