fix the baseUrl is configured with a trailing slash

Signed-off-by: lance <leehaut@gmail.com>
Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>

mcp-core/src/main/java/io/modelcontextprotocol/server/transport/HttpServletSseServerTransportProvider.java

@@ -14,9 +14,9 @@ import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import io.modelcontextprotocol.common.McpTransportContext;
 import io.modelcontextprotocol.json.McpJsonMapper;
 import io.modelcontextprotocol.json.TypeRef;
-import io.modelcontextprotocol.common.McpTransportContext;
 import io.modelcontextprotocol.server.McpTransportContextExtractor;
 import io.modelcontextprotocol.spec.McpError;
 import io.modelcontextprotocol.spec.McpSchema;
@@ -69,7 +69,9 @@ import reactor.core.publisher.Mono;
 @WebServlet(asyncSupported = true)
 public class HttpServletSseServerTransportProvider extends HttpServlet implements McpServerTransportProvider {
 
-	/** Logger for this class */
+	/**
+	 * Logger for this class
+	 */
 	private static final Logger logger = LoggerFactory.getLogger(HttpServletSseServerTransportProvider.class);
 
 	public static final String UTF_8 = "UTF-8";
@@ -78,38 +80,60 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 
 	public static final String FAILED_TO_SEND_ERROR_RESPONSE = "Failed to send error response: {}";
 
-	/** Default endpoint path for SSE connections */
+	/**
+	 * Default endpoint path for SSE connections
+	 */
 	public static final String DEFAULT_SSE_ENDPOINT = "/sse";
 
-	/** Event type for regular messages */
+	/**
+	 * Event type for regular messages
+	 */
 	public static final String MESSAGE_EVENT_TYPE = "message";
 
-	/** Event type for endpoint information */
+	/**
+	 * Event type for endpoint information
+	 */
 	public static final String ENDPOINT_EVENT_TYPE = "endpoint";
 
+	public static final String SESSION_ID = "sessionId";
+
 	public static final String DEFAULT_BASE_URL = "";
 
-	/** JSON mapper for serialization/deserialization */
+	/**
+	 * JSON mapper for serialization/deserialization
+	 */
 	private final McpJsonMapper jsonMapper;
 
-	/** Base URL for the server transport */
+	/**
+	 * Base URL for the server transport
+	 */
 	private final String baseUrl;
 
-	/** The endpoint path for handling client messages */
+	/**
+	 * The endpoint path for handling client messages
+	 */
 	private final String messageEndpoint;
 
-	/** The endpoint path for handling SSE connections */
+	/**
+	 * The endpoint path for handling SSE connections
+	 */
 	private final String sseEndpoint;
 
-	/** Map of active client sessions, keyed by session ID */
+	/**
+	 * Map of active client sessions, keyed by session ID
+	 */
 	private final Map<String, McpServerSession> sessions = new ConcurrentHashMap<>();
 
 	private McpTransportContextExtractor<HttpServletRequest> contextExtractor;
 
-	/** Flag indicating if the transport is in the process of shutting down */
+	/**
+	 * Flag indicating if the transport is in the process of shutting down
+	 */
 	private final AtomicBoolean isClosing = new AtomicBoolean(false);
 
-	/** Session factory for creating new sessions */
+	/**
+	 * Session factory for creating new sessions
+	 */
 	private McpServerSession.Factory sessionFactory;
 
 	/**
@@ -243,7 +267,22 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 		this.sessions.put(sessionId, session);
 
 		// Send initial endpoint event
-		this.sendEvent(writer, ENDPOINT_EVENT_TYPE, this.baseUrl + this.messageEndpoint + "?sessionId=" + sessionId);
+		this.sendEvent(writer, ENDPOINT_EVENT_TYPE, buildEndpointUrl(sessionId));
+	}
+
+	/**
+	 * Constructs the full message endpoint URL by combining the base URL, message path,
+	 * and the required session_id query parameter.
+	 * @param sessionId the unique session identifier
+	 * @return the fully qualified endpoint URL as a string
+	 */
+	private String buildEndpointUrl(String sessionId) {
+		// for WebMVC compatibility
+		if (this.baseUrl.endsWith("/")) {
+			return this.baseUrl.substring(0, this.baseUrl.length() - 1) + this.messageEndpoint + "?sessionId="
+					+ sessionId;
+		}
+		return this.baseUrl + this.messageEndpoint + "?sessionId=" + sessionId;
 	}
 
 	/**
@@ -434,8 +473,8 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 		 * Converts data from one type to another using the configured JsonMapper.
 		 * @param data The source data object to convert
 		 * @param typeRef The target type reference
-		 * @return The converted object of type T
 		 * @param <T> The target type
+		 * @return The converted object of type T
 		 */
 		@Override
 		public <T> T unmarshalFrom(Object data, TypeRef<T> typeRef) {

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

@@ -9,10 +9,9 @@ import java.time.Duration;
 import java.util.List;
 import java.util.concurrent.ConcurrentHashMap;
 
+import io.modelcontextprotocol.common.McpTransportContext;
 import io.modelcontextprotocol.json.McpJsonMapper;
 import io.modelcontextprotocol.json.TypeRef;
-
-import io.modelcontextprotocol.common.McpTransportContext;
 import io.modelcontextprotocol.server.McpTransportContextExtractor;
 import io.modelcontextprotocol.spec.McpError;
 import io.modelcontextprotocol.spec.McpSchema;
@@ -22,7 +21,6 @@ import io.modelcontextprotocol.spec.McpServerTransportProvider;
 import io.modelcontextprotocol.spec.ProtocolVersions;
 import io.modelcontextprotocol.util.Assert;
 import io.modelcontextprotocol.util.KeepAliveScheduler;
-
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import reactor.core.Exceptions;
@@ -37,6 +35,7 @@ import org.springframework.web.reactive.function.server.RouterFunction;
 import org.springframework.web.reactive.function.server.RouterFunctions;
 import org.springframework.web.reactive.function.server.ServerRequest;
 import org.springframework.web.reactive.function.server.ServerResponse;
+import org.springframework.web.util.UriComponentsBuilder;
 
 /**
  * Server-side implementation of the MCP (Model Context Protocol) HTTP transport using
@@ -95,6 +94,8 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 	 */
 	public static final String DEFAULT_SSE_ENDPOINT = "/sse";
 
+	public static final String SESSION_ID = "sessionId";
+
 	public static final String DEFAULT_BASE_URL = "";
 
 	private final McpJsonMapper jsonMapper;
@@ -224,6 +225,7 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 	// FIXME: This javadoc makes claims about using isClosing flag but it's not
 	// actually
 	// doing that.
+
 	/**
 	 * Initiates a graceful shutdown of all the sessions. This method ensures all active
 	 * sessions are properly closed and cleaned up.
@@ -286,10 +288,8 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 
 				// Send initial endpoint event
 				logger.debug("Sending initial endpoint event to session: {}", sessionId);
-				sink.next(ServerSentEvent.builder()
+				sink.next(
-					.event(ENDPOINT_EVENT_TYPE)
+						ServerSentEvent.builder().event(ENDPOINT_EVENT_TYPE).data(buildEndpointUrl(sessionId)).build());
-					.data(this.baseUrl + this.messageEndpoint + "?sessionId=" + sessionId)
-					.build());
 				sink.onCancel(() -> {
 					logger.debug("Session {} cancelled", sessionId);
 					sessions.remove(sessionId);
@@ -297,6 +297,21 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 			}).contextWrite(ctx -> ctx.put(McpTransportContext.KEY, transportContext)), ServerSentEvent.class);
 	}
 
+	/**
+	 * Constructs the full message endpoint URL by combining the base URL, message path,
+	 * and the required session_id query parameter.
+	 * @param sessionId the unique session identifier
+	 * @return the fully qualified endpoint URL as a string
+	 */
+	private String buildEndpointUrl(String sessionId) {
+		// for WebMVC compatibility
+		return UriComponentsBuilder.fromUriString(this.baseUrl)
+			.path(this.messageEndpoint)
+			.queryParam(SESSION_ID, sessionId)
+			.build()
+			.toUriString();
+	}
+
 	/**
 	 * Handles incoming JSON-RPC messages from clients. Deserializes the message and
 	 * processes it through the configured message handler.

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

@@ -11,20 +11,18 @@ import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.locks.ReentrantLock;
 
+import io.modelcontextprotocol.common.McpTransportContext;
 import io.modelcontextprotocol.json.McpJsonMapper;
 import io.modelcontextprotocol.json.TypeRef;
-
-import io.modelcontextprotocol.common.McpTransportContext;
 import io.modelcontextprotocol.server.McpTransportContextExtractor;
 import io.modelcontextprotocol.spec.McpError;
 import io.modelcontextprotocol.spec.McpSchema;
+import io.modelcontextprotocol.spec.McpServerSession;
 import io.modelcontextprotocol.spec.McpServerTransport;
 import io.modelcontextprotocol.spec.McpServerTransportProvider;
 import io.modelcontextprotocol.spec.ProtocolVersions;
-import io.modelcontextprotocol.spec.McpServerSession;
 import io.modelcontextprotocol.util.Assert;
 import io.modelcontextprotocol.util.KeepAliveScheduler;
-
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import reactor.core.publisher.Flux;
@@ -36,6 +34,7 @@ import org.springframework.web.servlet.function.RouterFunctions;
 import org.springframework.web.servlet.function.ServerRequest;
 import org.springframework.web.servlet.function.ServerResponse;
 import org.springframework.web.servlet.function.ServerResponse.SseBuilder;
+import org.springframework.web.util.UriComponentsBuilder;
 
 /**
  * Server-side implementation of the Model Context Protocol (MCP) transport layer using
@@ -87,6 +86,8 @@ public class WebMvcSseServerTransportProvider implements McpServerTransportProvi
 	 */
 	public static final String ENDPOINT_EVENT_TYPE = "endpoint";
 
+	public static final String SESSION_ID = "sessionId";
+
 	/**
 	 * Default SSE endpoint path as specified by the MCP transport specification.
 	 */
@@ -275,9 +276,7 @@ public class WebMvcSseServerTransportProvider implements McpServerTransportProvi
 				this.sessions.put(sessionId, session);
 
 				try {
-					sseBuilder.id(sessionId)
+					sseBuilder.id(sessionId).event(ENDPOINT_EVENT_TYPE).data(buildEndpointUrl(sessionId));
-						.event(ENDPOINT_EVENT_TYPE)
-						.data(this.baseUrl + this.messageEndpoint + "?sessionId=" + sessionId);
 				}
 				catch (Exception e) {
 					logger.error("Failed to send initial endpoint event: {}", e.getMessage());
@@ -292,6 +291,21 @@ public class WebMvcSseServerTransportProvider implements McpServerTransportProvi
 		}
 	}
 
+	/**
+	 * Constructs the full message endpoint URL by combining the base URL, message path,
+	 * and the required session_id query parameter.
+	 * @param sessionId the unique session identifier
+	 * @return the fully qualified endpoint URL as a string
+	 */
+	private String buildEndpointUrl(String sessionId) {
+		// for WebMVC compatibility
+		return UriComponentsBuilder.fromUriString(this.baseUrl)
+			.path(this.messageEndpoint)
+			.queryParam(SESSION_ID, sessionId)
+			.build()
+			.toUriString();
+	}
+
 	/**
 	 * Handles incoming JSON-RPC messages from clients. This method:
 	 * <ul>
@@ -308,11 +322,11 @@ public class WebMvcSseServerTransportProvider implements McpServerTransportProvi
 			return ServerResponse.status(HttpStatus.SERVICE_UNAVAILABLE).body("Server is shutting down");
 		}
 
-		if (request.param("sessionId").isEmpty()) {
+		if (request.param(SESSION_ID).isEmpty()) {
 			return ServerResponse.badRequest().body(new McpError("Session ID missing in message endpoint"));
 		}
 
-		String sessionId = request.param("sessionId").get();
+		String sessionId = request.param(SESSION_ID).get();
 		McpServerSession session = sessions.get(sessionId);
 
 		if (session == null) {
@@ -327,9 +341,9 @@ public class WebMvcSseServerTransportProvider implements McpServerTransportProvi
 
 			// Process the message through the session's handle method
 			session.handle(message).contextWrite(ctx -> ctx.put(McpTransportContext.KEY, transportContext)).block(); // Block
-																														// for
+			// for
-																														// WebMVC
+			// WebMVC
-																														// compatibility
+			// compatibility
 
 			return ServerResponse.ok().build();
 		}
@@ -398,8 +412,8 @@ public class WebMvcSseServerTransportProvider implements McpServerTransportProvi
 		 * Converts data from one type to another using the configured McpJsonMapper.
 		 * @param data The source data object to convert
 		 * @param typeRef The target type reference
-		 * @return The converted object of type T
 		 * @param <T> The target type
+		 * @return The converted object of type T
 		 */
 		@Override
 		public <T> T unmarshalFrom(Object data, TypeRef<T> typeRef) {

mcp-spring/mcp-spring-webmvc/src/test/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransportProviderTests.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2025 - 2025 the original author or authors.
+ */
+
+package io.modelcontextprotocol.server.transport;
+
+import io.modelcontextprotocol.client.McpClient;
+import io.modelcontextprotocol.client.transport.HttpClientSseClientTransport;
+import io.modelcontextprotocol.common.McpTransportContext;
+import io.modelcontextprotocol.json.McpJsonMapper;
+import io.modelcontextprotocol.server.McpServer;
+import io.modelcontextprotocol.server.TestUtil;
+import io.modelcontextprotocol.server.TomcatTestUtil;
+import io.modelcontextprotocol.spec.McpSchema;
+import org.apache.catalina.LifecycleException;
+import org.apache.catalina.LifecycleState;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.servlet.config.annotation.EnableWebMvc;
+import org.springframework.web.servlet.function.RouterFunction;
+import org.springframework.web.servlet.function.ServerResponse;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for WebMvcSseServerTransportProvider
+ *
+ * @author lance
+ */
+class WebMvcSseServerTransportProviderTests {
+
+	private static final int PORT = TestUtil.findAvailablePort();
+
+	private static final String CUSTOM_CONTEXT_PATH = "";
+
+	private static final String MESSAGE_ENDPOINT = "/mcp/message";
+
+	private WebMvcSseServerTransportProvider mcpServerTransportProvider;
+
+	McpClient.SyncSpec clientBuilder;
+
+	private TomcatTestUtil.TomcatServer tomcatServer;
+
+	@BeforeEach
+	public void before() {
+		tomcatServer = TomcatTestUtil.createTomcatServer(CUSTOM_CONTEXT_PATH, PORT, TestConfig.class);
+
+		try {
+			tomcatServer.tomcat().start();
+			assertThat(tomcatServer.tomcat().getServer().getState()).isEqualTo(LifecycleState.STARTED);
+		}
+		catch (Exception e) {
+			throw new RuntimeException("Failed to start Tomcat", e);
+		}
+
+		HttpClientSseClientTransport transport = HttpClientSseClientTransport.builder("http://localhost:" + PORT)
+			.sseEndpoint(WebMvcSseServerTransportProvider.DEFAULT_SSE_ENDPOINT)
+			.build();
+
+		clientBuilder = McpClient.sync(transport);
+		mcpServerTransportProvider = tomcatServer.appContext().getBean(WebMvcSseServerTransportProvider.class);
+	}
+
+	@Test
+	void validBaseUrl() {
+		McpServer.async(mcpServerTransportProvider).serverInfo("test-server", "1.0.0").build();
+		try (var client = clientBuilder.clientInfo(new McpSchema.Implementation("Sample " + "client", "0.0.0"))
+			.build()) {
+			assertThat(client.initialize()).isNotNull();
+		}
+	}
+
+	@AfterEach
+	public void after() {
+		if (mcpServerTransportProvider != null) {
+			mcpServerTransportProvider.closeGracefully().block();
+		}
+		if (tomcatServer.appContext() != null) {
+			tomcatServer.appContext().close();
+		}
+		if (tomcatServer.tomcat() != null) {
+			try {
+				tomcatServer.tomcat().stop();
+				tomcatServer.tomcat().destroy();
+			}
+			catch (LifecycleException e) {
+				throw new RuntimeException("Failed to stop Tomcat", e);
+			}
+		}
+	}
+
+	@Configuration
+	@EnableWebMvc
+	static class TestConfig {
+
+		@Bean
+		public WebMvcSseServerTransportProvider webMvcSseServerTransportProvider() {
+
+			return WebMvcSseServerTransportProvider.builder()
+				.baseUrl("http://localhost:" + PORT + "/")
+				.messageEndpoint(MESSAGE_ENDPOINT)
+				.sseEndpoint(WebMvcSseServerTransportProvider.DEFAULT_SSE_ENDPOINT)
+				.jsonMapper(McpJsonMapper.getDefault())
+				.contextExtractor(req -> McpTransportContext.EMPTY)
+				.build();
+		}
+
+		@Bean
+		public RouterFunction<ServerResponse> routerFunction(WebMvcSseServerTransportProvider transportProvider) {
+			return transportProvider.getRouterFunction();
+		}
+
+	}
+
+}