feat(webflux): Add configurable SSE endpoints to WebFlux transport (#41, #67)

Enhances WebFlux SSE transport implementation with customizable endpoint paths:
- Add configurable SSE endpoint support in both client and server transports
- Update tests to verify custom SSE endpoint functionality
- Implement builder pattern to support the new configuration options

Co-authored-by: haidao <wwulfric@gmail.com>
Co-authored-by: Harry <34418180+HarryFQG@users.noreply.github.com>
Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

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

@@ -79,7 +79,7 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 	 * Default SSE endpoint path as specified by the MCP transport specification. This
 	 * endpoint is used to establish the SSE connection with the server.
 	 */
-	private static final String SSE_ENDPOINT = "/sse";
+	private static final String DEFAULT_SSE_ENDPOINT = "/sse";
 
 	/**
 	 * Type reference for parsing SSE events containing string data.
@@ -117,6 +117,12 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 	 */
 	protected final Sinks.One<String> messageEndpointSink = Sinks.one();
 
+	/**
+	 * The SSE endpoint URI provided by the server. Used for sending outbound messages via
+	 * HTTP POST requests.
+	 */
+	private String sseEndpoint;
+
 	/**
 	 * Constructs a new SseClientTransport with the specified WebClient builder. Uses a
 	 * default ObjectMapper instance for JSON processing.
@@ -137,11 +143,27 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 	 * @throws IllegalArgumentException if either parameter is null
 	 */
 	public WebFluxSseClientTransport(WebClient.Builder webClientBuilder, ObjectMapper objectMapper) {
+		this(webClientBuilder, objectMapper, DEFAULT_SSE_ENDPOINT);
+	}
+
+	/**
+	 * Constructs a new SseClientTransport with the specified WebClient builder and
+	 * ObjectMapper. Initializes both inbound and outbound message processing pipelines.
+	 * @param webClientBuilder the WebClient.Builder to use for creating the WebClient
+	 * instance
+	 * @param objectMapper the ObjectMapper to use for JSON processing
+	 * @param sseEndpoint the SSE endpoint URI to use for establishing the connection
+	 * @throws IllegalArgumentException if either parameter is null
+	 */
+	public WebFluxSseClientTransport(WebClient.Builder webClientBuilder, ObjectMapper objectMapper,
+			String sseEndpoint) {
 		Assert.notNull(objectMapper, "ObjectMapper must not be null");
 		Assert.notNull(webClientBuilder, "WebClient.Builder must not be null");
+		Assert.hasText(sseEndpoint, "SSE endpoint must not be null or empty");
 
 		this.objectMapper = objectMapper;
 		this.webClient = webClientBuilder.build();
+		this.sseEndpoint = sseEndpoint;
 	}
 
 	/**
@@ -254,7 +276,7 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 	protected Flux<ServerSentEvent<String>> eventStream() {// @formatter:off
 		return this.webClient
 			.get()
-			.uri(SSE_ENDPOINT)
+			.uri(this.sseEndpoint)
 			.accept(MediaType.TEXT_EVENT_STREAM)
 			.retrieve()
 			.bodyToFlux(SSE_TYPE)
@@ -321,4 +343,66 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 		return this.objectMapper.convertValue(data, typeRef);
 	}
 
+	/**
+	 * Creates a new builder for {@link WebFluxSseClientTransport}.
+	 * @param webClientBuilder the WebClient.Builder to use for creating the WebClient
+	 * instance
+	 * @return a new builder instance
+	 */
+	public static Builder builder(WebClient.Builder webClientBuilder) {
+		return new Builder(webClientBuilder);
+	}
+
+	/**
+	 * Builder for {@link WebFluxSseClientTransport}.
+	 */
+	public static class Builder {
+
+		private final WebClient.Builder webClientBuilder;
+
+		private String sseEndpoint = DEFAULT_SSE_ENDPOINT;
+
+		private ObjectMapper objectMapper = new ObjectMapper();
+
+		/**
+		 * Creates a new builder with the specified WebClient.Builder.
+		 * @param webClientBuilder the WebClient.Builder to use
+		 */
+		public Builder(WebClient.Builder webClientBuilder) {
+			Assert.notNull(webClientBuilder, "WebClient.Builder must not be null");
+			this.webClientBuilder = webClientBuilder;
+		}
+
+		/**
+		 * Sets the SSE endpoint path.
+		 * @param sseEndpoint the SSE endpoint path
+		 * @return this builder
+		 */
+		public Builder sseEndpoint(String sseEndpoint) {
+			Assert.hasText(sseEndpoint, "sseEndpoint must not be empty");
+			this.sseEndpoint = sseEndpoint;
+			return this;
+		}
+
+		/**
+		 * Sets the object mapper for JSON serialization/deserialization.
+		 * @param objectMapper the object mapper
+		 * @return this builder
+		 */
+		public Builder objectMapper(ObjectMapper objectMapper) {
+			Assert.notNull(objectMapper, "objectMapper must not be null");
+			this.objectMapper = objectMapper;
+			return this;
+		}
+
+		/**
+		 * Builds a new {@link WebFluxSseClientTransport} instance.
+		 * @return a new transport instance
+		 */
+		public WebFluxSseClientTransport build() {
+			return new WebFluxSseClientTransport(webClientBuilder, objectMapper, sseEndpoint);
+		}
+
+	}
+
 }

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

@@ -346,4 +346,74 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 
 	}
 
+	public static Builder builder() {
+		return new Builder();
+	}
+
+	/**
+	 * Builder for creating instances of {@link WebFluxSseServerTransportProvider}.
+	 * <p>
+	 * This builder provides a fluent API for configuring and creating instances of
+	 * WebFluxSseServerTransportProvider with custom settings.
+	 */
+	public static class Builder {
+
+		private ObjectMapper objectMapper;
+
+		private String messageEndpoint;
+
+		private String sseEndpoint = DEFAULT_SSE_ENDPOINT;
+
+		/**
+		 * Sets the ObjectMapper to use for JSON serialization/deserialization of MCP
+		 * messages.
+		 * @param objectMapper The ObjectMapper instance. Must not be null.
+		 * @return this builder instance
+		 * @throws IllegalArgumentException if objectMapper is null
+		 */
+		public Builder objectMapper(ObjectMapper objectMapper) {
+			Assert.notNull(objectMapper, "ObjectMapper must not be null");
+			this.objectMapper = objectMapper;
+			return this;
+		}
+
+		/**
+		 * Sets the endpoint URI where clients should send their JSON-RPC messages.
+		 * @param messageEndpoint The message endpoint URI. Must not be null.
+		 * @return this builder instance
+		 * @throws IllegalArgumentException if messageEndpoint is null
+		 */
+		public Builder messageEndpoint(String messageEndpoint) {
+			Assert.notNull(messageEndpoint, "Message endpoint must not be null");
+			this.messageEndpoint = messageEndpoint;
+			return this;
+		}
+
+		/**
+		 * Sets the SSE endpoint path.
+		 * @param sseEndpoint The SSE endpoint path. Must not be null.
+		 * @return this builder instance
+		 * @throws IllegalArgumentException if sseEndpoint is null
+		 */
+		public Builder sseEndpoint(String sseEndpoint) {
+			Assert.notNull(sseEndpoint, "SSE endpoint must not be null");
+			this.sseEndpoint = sseEndpoint;
+			return this;
+		}
+
+		/**
+		 * Builds a new instance of {@link WebFluxSseServerTransportProvider} with the
+		 * configured settings.
+		 * @return A new WebFluxSseServerTransportProvider instance
+		 * @throws IllegalStateException if required parameters are not set
+		 */
+		public WebFluxSseServerTransportProvider build() {
+			Assert.notNull(objectMapper, "ObjectMapper must be set");
+			Assert.notNull(messageEndpoint, "Message endpoint must be set");
+
+			return new WebFluxSseServerTransportProvider(objectMapper, messageEndpoint, sseEndpoint);
+		}
+
+	}
+
 }

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/WebFluxSseIntegrationTests.java

@@ -46,14 +46,17 @@ import org.springframework.web.reactive.function.server.RouterFunctions;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.awaitility.Awaitility.await;
-import static org.junit.Assert.assertThat;
 import static org.mockito.Mockito.mock;
 
 public class WebFluxSseIntegrationTests {
 
 	private static final int PORT = 8182;
 
-	private static final String MESSAGE_ENDPOINT = "/mcp/message";
+	// private static final String MESSAGE_ENDPOINT = "/mcp/message";
+
+	private static final String CUSTOM_SSE_ENDPOINT = "/somePath/sse";
+
+	private static final String CUSTOM_MESSAGE_ENDPOINT = "/otherPath/mcp/message";
 
 	private DisposableServer httpServer;
 
@@ -64,15 +67,25 @@ public class WebFluxSseIntegrationTests {
 	@BeforeEach
 	public void before() {
 
-		this.mcpServerTransportProvider = new WebFluxSseServerTransportProvider(new ObjectMapper(), MESSAGE_ENDPOINT);
+		this.mcpServerTransportProvider = new WebFluxSseServerTransportProvider.Builder()
+			.objectMapper(new ObjectMapper())
+			.messageEndpoint(CUSTOM_MESSAGE_ENDPOINT)
+			.sseEndpoint(CUSTOM_SSE_ENDPOINT)
+			.build();
 
 		HttpHandler httpHandler = RouterFunctions.toHttpHandler(mcpServerTransportProvider.getRouterFunction());
 		ReactorHttpHandlerAdapter adapter = new ReactorHttpHandlerAdapter(httpHandler);
 		this.httpServer = HttpServer.create().port(PORT).handle(adapter).bindNow();
 
-		clientBulders.put("httpclient", McpClient.sync(new HttpClientSseClientTransport("http://localhost:" + PORT)));
+		clientBulders.put("httpclient",
+				McpClient.sync(HttpClientSseClientTransport.builder("http://localhost:" + PORT)
+					.sseEndpoint(CUSTOM_SSE_ENDPOINT)
+					.build()));
 		clientBulders.put("webflux",
-				McpClient.sync(new WebFluxSseClientTransport(WebClient.builder().baseUrl("http://localhost:" + PORT))));
+				McpClient
+					.sync(WebFluxSseClientTransport.builder(WebClient.builder().baseUrl("http://localhost:" + PORT))
+						.sseEndpoint(CUSTOM_SSE_ENDPOINT)
+						.build()));
 
 	}
 

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/client/WebFluxSseMcpAsyncClientTests.java

@@ -33,7 +33,7 @@ class WebFluxSseMcpAsyncClientTests extends AbstractMcpAsyncClientTests {
 
 	@Override
 	protected McpClientTransport createMcpTransport() {
-		return new WebFluxSseClientTransport(WebClient.builder().baseUrl(host));
+		return WebFluxSseClientTransport.builder(WebClient.builder().baseUrl(host)).build();
 	}
 
 	@Override

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/client/WebFluxSseMcpSyncClientTests.java

@@ -33,7 +33,7 @@ class WebFluxSseMcpSyncClientTests extends AbstractMcpSyncClientTests {
 
 	@Override
 	protected McpClientTransport createMcpTransport() {
-		return new WebFluxSseClientTransport(WebClient.builder().baseUrl(host));
+		return WebFluxSseClientTransport.builder(WebClient.builder().baseUrl(host)).build();
 	}
 
 	@Override

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/client/transport/WebFluxSseClientTransportTests.java

@@ -63,13 +63,6 @@ class WebFluxSseClientTransportTests {
 			super(webClientBuilder, objectMapper);
 		}
 
-		// @Override
-		// public Mono<Void> connect(Function<Mono<McpSchema.JSONRPCMessage>,
-		// Mono<McpSchema.JSONRPCMessage>> handler) {
-		// simulateEndpointEvent("https://localhost:3001");
-		// return super.connect(handler);
-		// }
-
 		@Override
 		protected Flux<ServerSentEvent<String>> eventStream() {
 			return super.eventStream().mergeWith(events.asFlux());
@@ -137,6 +130,33 @@ class WebFluxSseClientTransportTests {
 			.hasMessageContaining("ObjectMapper must not be null");
 	}
 
+	@Test
+	void testBuilderPattern() {
+		// Test default builder
+		WebFluxSseClientTransport transport1 = WebFluxSseClientTransport.builder(webClientBuilder).build();
+		assertThatCode(() -> transport1.closeGracefully().block()).doesNotThrowAnyException();
+
+		// Test builder with custom ObjectMapper
+		ObjectMapper customMapper = new ObjectMapper();
+		WebFluxSseClientTransport transport2 = WebFluxSseClientTransport.builder(webClientBuilder)
+			.objectMapper(customMapper)
+			.build();
+		assertThatCode(() -> transport2.closeGracefully().block()).doesNotThrowAnyException();
+
+		// Test builder with custom SSE endpoint
+		WebFluxSseClientTransport transport3 = WebFluxSseClientTransport.builder(webClientBuilder)
+			.sseEndpoint("/custom-sse")
+			.build();
+		assertThatCode(() -> transport3.closeGracefully().block()).doesNotThrowAnyException();
+
+		// Test builder with all custom parameters
+		WebFluxSseClientTransport transport4 = WebFluxSseClientTransport.builder(webClientBuilder)
+			.objectMapper(customMapper)
+			.sseEndpoint("/custom-sse")
+			.build();
+		assertThatCode(() -> transport4.closeGracefully().block()).doesNotThrowAnyException();
+	}
+
 	@Test
 	void testMessageProcessing() {
 		// Create a test message
@@ -240,7 +260,7 @@ class WebFluxSseClientTransportTests {
 		// Create a WebClient that simulates connection failures
 		WebClient.Builder failingWebClientBuilder = WebClient.builder().baseUrl("http://non-existent-host");
 
-		WebFluxSseClientTransport failingTransport = new WebFluxSseClientTransport(failingWebClientBuilder);
+		WebFluxSseClientTransport failingTransport = WebFluxSseClientTransport.builder(failingWebClientBuilder).build();
 
 		// Verify that the transport attempts to reconnect
 		StepVerifier.create(Mono.delay(Duration.ofSeconds(2))).expectNextCount(1).verifyComplete();

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/server/WebFluxSseMcpAsyncServerTests.java

@@ -31,7 +31,9 @@ class WebFluxSseMcpAsyncServerTests extends AbstractMcpAsyncServerTests {
 
 	@Override
 	protected McpServerTransportProvider createMcpTransportProvider() {
-		var transportProvider = new WebFluxSseServerTransportProvider(new ObjectMapper(), MESSAGE_ENDPOINT);
+		var transportProvider = new WebFluxSseServerTransportProvider.Builder().objectMapper(new ObjectMapper())
+			.messageEndpoint(MESSAGE_ENDPOINT)
+			.build();
 
 		HttpHandler httpHandler = RouterFunctions.toHttpHandler(transportProvider.getRouterFunction());
 		ReactorHttpHandlerAdapter adapter = new ReactorHttpHandlerAdapter(httpHandler);

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/server/WebFluxSseMcpSyncServerTests.java

@@ -33,7 +33,9 @@ class WebFluxSseMcpSyncServerTests extends AbstractMcpSyncServerTests {
 
 	@Override
 	protected McpServerTransportProvider createMcpTransportProvider() {
-		transportProvider = new WebFluxSseServerTransportProvider(new ObjectMapper(), MESSAGE_ENDPOINT);
+		transportProvider = new WebFluxSseServerTransportProvider.Builder().objectMapper(new ObjectMapper())
+			.messageEndpoint(MESSAGE_ENDPOINT)
+			.build();
 		return transportProvider;
 	}