fix: 1 transport per request

Author: tonxxd

packages/mcp-use/src/server/mcp-server.ts

@@ -296,7 +296,8 @@ export class McpServer {
    * 
    * Sets up the HTTP transport layer for the MCP server, creating endpoints for
    * Server-Sent Events (SSE) streaming, POST message handling, and DELETE session cleanup.
-   * Uses stateless mode for session management, making it suitable for stateless deployments.
+   * Each request gets its own transport instance to prevent state conflicts between
+   * concurrent client connections.
    * 
    * This method is called automatically when the server starts listening and ensures
    * that MCP clients can communicate with the server over HTTP.
@@ -314,34 +315,53 @@ export class McpServer {
     if (this.mcpMounted) return
 
     const { StreamableHTTPServerTransport } = await import('@modelcontextprotocol/sdk/server/streamableHttp.js')
-    
-    // Create StreamableHTTPServerTransport in stateless mode
-    // Note: Stateless mode means one active connection at a time
-    // For multiple concurrent inspectors, use the built-in proxy or same-origin connections
-    const httpTransport = new StreamableHTTPServerTransport({
-      sessionIdGenerator: undefined, // Stateless mode
-      enableJsonResponse: true
-    })
 
+    const endpoint = '/mcp'
+
+    // POST endpoint for messages
+    // Create a new transport for each request to support multiple concurrent clients
+    this.app.post(endpoint, express.json(), async (req, res) => {
+      const transport = new StreamableHTTPServerTransport({
+        sessionIdGenerator: undefined,
+        enableJsonResponse: true
+      })
 
-    // Connect the MCP server to the transport
-    await this.server.connect(httpTransport)
+      res.on('close', () => {
+        transport.close()
+      })
 
-    const endpoint = '/mcp'
+      await this.server.connect(transport)
+      await transport.handleRequest(req, res, req.body)
+    })
 
     // GET endpoint for SSE streaming
     this.app.get(endpoint, async (req, res) => {
-      await httpTransport.handleRequest(req, res)
-    })
+      const transport = new StreamableHTTPServerTransport({
+        sessionIdGenerator: undefined,
+        enableJsonResponse: true
+      })
 
-    // POST endpoint for messages
-    this.app.post(endpoint, express.json(), async (req, res) => {
-      await httpTransport.handleRequest(req, res, req.body)
+      res.on('close', () => {
+        transport.close()
+      })
+
+      await this.server.connect(transport)
+      await transport.handleRequest(req, res)
     })
 
     // DELETE endpoint for session cleanup
     this.app.delete(endpoint, async (req, res) => {
-      await httpTransport.handleRequest(req, res)
+      const transport = new StreamableHTTPServerTransport({
+        sessionIdGenerator: undefined,
+        enableJsonResponse: true
+      })
+
+      res.on('close', () => {
+        transport.close()
+      })
+
+      await this.server.connect(transport)
+      await transport.handleRequest(req, res)
     })
 
     this.mcpMounted = true