Optimize client nested streams in McpClientSession (modelcontextprotocol#33)

Signed-off-by: JermaineHua <[email protected]>

Author: CrazyHZM

mcp/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java

@@ -122,7 +122,12 @@ public McpClientSession(Duration requestTimeout, McpClientTransport transport,
 		// Observation associated with the individual message - it can be used to
 		// create child Observation and emit it together with the message to the
 		// consumer
-		this.connection = this.transport.connect(mono -> mono.doOnNext(message -> {
+		this.connection = this.transport.connect(mono -> mono.doOnNext(message -> handle(message).subscribe()))
+			.subscribe();
+	}
+
+	public Mono<Void> handle(McpSchema.JSONRPCMessage message) {
+		return Mono.defer(() -> {
 			if (message instanceof McpSchema.JSONRPCResponse response) {
 				logger.debug("Received Response: {}", response);
 				var sink = pendingResponses.remove(response.id());
@@ -132,23 +137,27 @@ public McpClientSession(Duration requestTimeout, McpClientTransport transport,
 				else {
 					sink.success(response);
 				}
+				return Mono.empty();
 			}
 			else if (message instanceof McpSchema.JSONRPCRequest request) {
 				logger.debug("Received request: {}", request);
-				handleIncomingRequest(request).subscribe(response -> transport.sendMessage(response).subscribe(),
-						error -> {
-							var errorResponse = new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
-									null, new McpSchema.JSONRPCResponse.JSONRPCError(
-											McpSchema.ErrorCodes.INTERNAL_ERROR, error.getMessage(), null));
-							transport.sendMessage(errorResponse).subscribe();
-						});
+				return handleIncomingRequest(request).onErrorResume(error -> {
+					var errorResponse = new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(), null,
+							new McpSchema.JSONRPCResponse.JSONRPCError(McpSchema.ErrorCodes.INTERNAL_ERROR,
+									error.getMessage(), null));
+					return this.transport.sendMessage(errorResponse).then(Mono.empty());
+				}).flatMap(this.transport::sendMessage);
 			}
 			else if (message instanceof McpSchema.JSONRPCNotification notification) {
 				logger.debug("Received notification: {}", notification);
-				handleIncomingNotification(notification).subscribe(null,
-						error -> logger.error("Error handling notification: {}", error.getMessage()));
+				return handleIncomingNotification(notification)
+					.doOnError(error -> logger.error("Error handling notification: {}", error.getMessage()));
 			}
-		})).subscribe();
+			else {
+				logger.warn("Received unknown message type: {}", message);
+				return Mono.empty();
+			}
+		});
 	}
 
 	/**