From 3733664ed3cf4a12b59c141b442327615ccb417f Mon Sep 17 00:00:00 2001
From: Pham Khanh Hoa <frank@wisami.com>
Date: Wed, 15 Apr 2026 21:49:35 +0700
Subject: [PATCH] fix: resolve ERR_HTTP_HEADERS_SENT and transport reuse errors

- Remove redundant response send in DELETE /mcp handler (StreamableHTTPServerTransport handles headers internally)
- Remove manual flushHeaders/hijack in GET /mcp handler (transport manages headers)
- Convert mcp-server singleton to factory pattern (creates fresh Server instance per transport connection)

This fixes two recurring Chrome MCP bridge errors:
1. ERR_HTTP_HEADERS_SENT - double header send from transport + reply.send()
2. "Already connected to a transport" - singleton Server instance reuse across connections

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 dist/mcp/mcp-server.js | 19 ++++++++++---------
 dist/server/index.js   | 16 ++--------------
 2 files changed, 12 insertions(+), 23 deletions(-)

diff --git a/dist/mcp/mcp-server.js b/dist/mcp/mcp-server.js
index 1e646b8..c9e2633 100644
--- a/dist/mcp/mcp-server.js
+++ b/dist/mcp/mcp-server.js
@@ -1,14 +1,12 @@
 "use strict";
 Object.defineProperty(exports, "__esModule", { value: true });
-exports.getMcpServer = exports.mcpServer = void 0;
+exports.createMcpServer = void 0;
 const index_js_1 = require("@modelcontextprotocol/sdk/server/index.js");
 const register_tools_1 = require("./register-tools");
-exports.mcpServer = null;
-const getMcpServer = () => {
-    if (exports.mcpServer) {
-        return exports.mcpServer;
-    }
-    exports.mcpServer = new index_js_1.Server({
+// Factory function - creates a new MCP Server instance per transport connection
+// This fixes "Already connected to a transport" error from singleton reuse
+const createMcpServer = () => {
+    const server = new index_js_1.Server({
         name: 'ChromeMcpServer',
         version: '1.0.0',
     }, {
@@ -16,8 +14,11 @@ const getMcpServer = () => {
             tools: {},
         },
     });
-    (0, register_tools_1.setupTools)(exports.mcpServer);
-    return exports.mcpServer;
+    (0, register_tools_1.setupTools)(server);
+    return server;
 };
+exports.createMcpServer = createMcpServer;
+// Backwards compatibility - still works but creates new instance each time
+const getMcpServer = () => createMcpServer();
 exports.getMcpServer = getMcpServer;
 //# sourceMappingURL=mcp-server.js.map
\ No newline at end of file
diff --git a/dist/server/index.js b/dist/server/index.js
index 5cc6f07..7e1972b 100644
--- a/dist/server/index.js
+++ b/dist/server/index.js
@@ -157,17 +157,9 @@ class Server {
                 reply.code(constant_1.HTTP_STATUS.BAD_REQUEST).send({ error: constant_1.ERROR_MESSAGES.INVALID_SSE_SESSION });
                 return;
             }
-            reply.raw.setHeader('Content-Type', 'text/event-stream');
-            reply.raw.setHeader('Cache-Control', 'no-cache');
-            reply.raw.setHeader('Connection', 'keep-alive');
-            reply.raw.flushHeaders(); // Ensure headers are sent immediately
             try {
-                // transport.handleRequest will take over the response stream
+                // transport.handleRequest will take over the response stream and send headers
                 await transport.handleRequest(request.raw, reply.raw);
-                if (!reply.sent) {
-                    // If transport didn't send anything (unlikely for SSE initial handshake)
-                    reply.hijack(); // Prevent Fastify from automatically sending response
-                }
             }
             catch (error) {
                 if (!reply.raw.writableEnded) {
@@ -176,7 +168,6 @@ class Server {
             }
             request.socket.on('close', () => {
                 request.log.info(`SSE client disconnected for session: ${sessionId}`);
-                // transport's onclose should handle its own cleanup
             });
         });
         this.fastify.delete('/mcp', async (request, reply) => {
@@ -189,11 +180,8 @@ class Server {
                 return;
             }
             try {
+                // Let transport handleRequest close the session - do NOT send additional response
                 await transport.handleRequest(request.raw, reply.raw);
-                // Assume transport.handleRequest will send response or transport.onclose will cleanup
-                if (!reply.sent) {
-                    reply.code(constant_1.HTTP_STATUS.NO_CONTENT).send();
-                }
             }
             catch (error) {
                 if (!reply.sent) {