Use an error handler to process a response received on the HTTP connection.

Signed-off-by: Santiago Pericas-Geertsen <[email protected]>

Author: spericas

integrations/mcp/server/src/main/java/io/helidon/integrations/mcp/server/McpHttpFeature.java

@@ -102,6 +102,8 @@ public McpHttpFeature(McpHttpFeatureConfig config) {
         builder.method(McpJsonRPC.METHOD_NOTIFICATION_INITIALIZED, this::notificationInitRpc);
         builder.method(McpJsonRPC.METHOD_NOTIFICATION_CANCELED, this::notificationCancelRpc);
 
+        builder.error(this::handleErrorRequest);
+
         jsonRpcHandlers = builder.build();
     }
 
@@ -169,6 +171,30 @@ private McpSession findSession(JsonRpcRequest req) {
         }
     }
 
+    /**
+     * If we receive what looks like a response on the error handler,
+     * pass it to the session.
+     *
+     * @param req the HTTP request
+     * @param object the invalid JSON-RPC request
+     * @return whether error was handled or not
+     */
+    private boolean handleErrorRequest(ServerRequest req, JsonObject object) {
+        try {
+            if (object.containsKey("result") || object.containsKey("error")) {
+                String sessionId = req.query().get("sessionId");
+                McpSession session = sessions.get(sessionId);
+                if (session != null) {
+                    session.handleResponse(object);
+                    return true;
+                }
+            }
+        } catch (Exception e) {
+            // falls through
+        }
+        return false;
+    }
+
     private void notificationInitRpc(JsonRpcRequest req, JsonRpcResponse res) {
         McpSession session = findSession(req);
         if (session == null) {
@@ -284,7 +310,7 @@ private void resourcesListRpc(JsonRpcRequest req, JsonRpcResponse res) {
         this.config.resources().stream()
                 .map(Jsonable::json)
                 .forEach(builder::add);
-        JsonObject result =  Json.createObjectBuilder()
+        JsonObject result = Json.createObjectBuilder()
                 .add("resources", builder.build())
                 .build();
 
@@ -351,7 +377,7 @@ private void promptsListRpc(JsonRpcRequest req, JsonRpcResponse res) {
         this.config.prompts().stream()
                 .map(Jsonable::json)
                 .forEach(builder::add);
-        JsonObject result =  Json.createObjectBuilder()
+        JsonObject result = Json.createObjectBuilder()
                 .add("prompts", builder.build())
                 .build();
 
@@ -370,7 +396,7 @@ private void promptsGetRpc(JsonRpcRequest req, JsonRpcResponse res) {
                 .filter(p -> Objects.equals(p.name(), params.getString("name")))
                 .findFirst();
         McpParameters parameters = new McpParameters(params.getJsonObject("arguments"), "arguments");
-        JsonObject result =  prompt.map(value -> Json.createObjectBuilder()
+        JsonObject result = prompt.map(value -> Json.createObjectBuilder()
                         .add("description", value.description())
                         .add("messages", Json.createArrayBuilder()
                                 .add(value.prompt(parameters).json()))
@@ -395,7 +421,7 @@ private void completionRpc(JsonRpcRequest req, JsonRpcResponse res) {
         JsonObject reference = params.getJsonObject("ref");
         Optional<String> search = parseCompletionName(reference);
         if (search.isEmpty()) {
-            JsonObject result =  Json.createObjectBuilder()
+            JsonObject result = Json.createObjectBuilder()
                     .add("error", Json.createObjectBuilder()
                             .add("code", McpJsonRPC.INVALID_REQUEST)
                             .add("message", "Completion reference not found"))

integrations/mcp/server/src/main/java/io/helidon/integrations/mcp/server/McpSession.java

@@ -83,7 +83,7 @@ void disconnect() {
     }
 
     // TODO: Response to server notifications?
-    private void handleResponse(JsonObject response) {
+    void handleResponse(JsonObject response) {
         pendingResponses.remove(response.getString("id"));
     }