Fix NPE caused by response without id

Close GH-506

Signed-off-by: Yanming Zhou <zhouyanming@gmail.com>

Author: quaff

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

@@ -35,6 +35,7 @@
  *
  * @author Christian Tzolov
  * @author Dariusz Jędrzejczyk
+ * @author Yanming Zhou
  */
 public class McpClientSession implements McpSession {
 
@@ -146,13 +147,18 @@ private void dismissPendingResponses() {
 
 	private void handle(McpSchema.JSONRPCMessage message) {
 		if (message instanceof McpSchema.JSONRPCResponse response) {
-			logger.debug("Received Response: {}", response);
-			var sink = pendingResponses.remove(response.id());
-			if (sink == null) {
-				logger.warn("Unexpected response for unknown id {}", response.id());
+			logger.debug("Received response: {}", response);
+			if (response.id() != null) {
+				var sink = pendingResponses.remove(response.id());
+				if (sink == null) {
+					logger.warn("Unexpected response for unknown id {}", response.id());
+				}
+				else {
+					sink.success(response);
+				}
 			}
 			else {
-				sink.success(response);
+				logger.debug("Discarded response without id");
 			}
 		}
 		else if (message instanceof McpSchema.JSONRPCRequest request) {

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

@@ -25,6 +25,7 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 
 import io.modelcontextprotocol.util.Assert;
+import reactor.util.annotation.Nullable;
 
 /**
  * Based on the <a href="http://www.jsonrpc.org/specification">JSON-RPC 2.0
@@ -36,6 +37,7 @@
  * @author Luca Chang
  * @author Surbhi Bansal
  * @author Anurag Pant
+ * @author Yanming Zhou
  */
 public final class McpSchema {
 
@@ -281,7 +283,7 @@ public record JSONRPCNotification( // @formatter:off
 	// @JsonFormat(with = JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
 	public record JSONRPCResponse( // @formatter:off
 		@JsonProperty("jsonrpc") String jsonrpc,
-		@JsonProperty("id") Object id,
+		@JsonProperty("id") @Nullable Object id,
 		@JsonProperty("result") Object result,
 		@JsonProperty("error") JSONRPCError error) implements JSONRPCMessage { // @formatter:on
 

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

@@ -202,13 +202,18 @@ public Mono<Void> handle(McpSchema.JSONRPCMessage message) {
 			// TODO handle errors for communication to without initialization happening
 			// first
 			if (message instanceof McpSchema.JSONRPCResponse response) {
-				logger.debug("Received Response: {}", response);
-				var sink = pendingResponses.remove(response.id());
-				if (sink == null) {
-					logger.warn("Unexpected response for unknown id {}", response.id());
+				logger.debug("Received response: {}", response);
+				if (response.id() != null) {
+					var sink = pendingResponses.remove(response.id());
+					if (sink == null) {
+						logger.warn("Unexpected response for unknown id {}", response.id());
+					}
+					else {
+						sink.success(response);
+					}
 				}
 				else {
-					sink.success(response);
+					logger.debug("Discarded response without id");
 				}
 				return Mono.empty();
 			}

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

@@ -33,6 +33,7 @@
  * capability without the insight into the transport-specific details of HTTP handling.
  *
  * @author Dariusz Jędrzejczyk
+ * @author Yanming Zhou
  */
 public class McpStreamableServerSession implements McpLoggableSession {
 
@@ -214,19 +215,25 @@ public Mono<Void> accept(McpSchema.JSONRPCNotification notification) {
 	 */
 	public Mono<Void> accept(McpSchema.JSONRPCResponse response) {
 		return Mono.defer(() -> {
-			var stream = this.requestIdToStream.get(response.id());
-			if (stream == null) {
-				return Mono.error(new McpError("Unexpected response for unknown id " + response.id())); // TODO
-																										// JSONize
-			}
-			// TODO: encapsulate this inside the stream itself
-			var sink = stream.pendingResponses.remove(response.id());
-			if (sink == null) {
-				return Mono.error(new McpError("Unexpected response for unknown id " + response.id())); // TODO
-																										// JSONize
+			logger.debug("Received response: {}", response);
+			if (response.id() != null) {
+				var stream = this.requestIdToStream.get(response.id());
+				if (stream == null) {
+					return Mono.error(new McpError("Unexpected response for unknown id " + response.id())); // TODO
+					// JSONize
+				}
+				// TODO: encapsulate this inside the stream itself
+				var sink = stream.pendingResponses.remove(response.id());
+				if (sink == null) {
+					return Mono.error(new McpError("Unexpected response for unknown id " + response.id())); // TODO
+					// JSONize
+				}
+				else {
+					sink.success(response);
+				}
 			}
 			else {
-				sink.success(response);
+				logger.debug("Discarded response without id");
 			}
 			return Mono.empty();
 		});