Merge branch 'main' into fix/header

Author: cliffhall

README.md

@@ -10,6 +10,16 @@ The MCP inspector is a developer tool for testing and debugging MCP servers.
 
 - Node.js: ^22.7.5
 
+### Quick Start (UI mode)
+
+To get up and running right away with the UI, just execute the following:
+
+```bash
+npx @modelcontextprotocol/inspector
+```
+
+The server will start up and the UI will be accessible at `http://localhost:6274`.
+
 ### From an MCP server repository
 
 To inspect an MCP server implementation, there's no need to clone this repo. Instead, use `npx`. For example, if your server is built at `build/index.js`:

server/src/index.ts

@@ -86,7 +86,8 @@ app.use((req, res, next) => {
   next();
 });
 
-const webAppTransports: Map<string, Transport> = new Map<string, Transport>(); // Transports by sessionId
+const webAppTransports: Map<string, Transport> = new Map<string, Transport>(); // Web app transports by web app sessionId
+const serverTransports: Map<string, Transport> = new Map<string, Transport>(); // Server Transports by web app sessionId
 
 const createTransport = async (req: express.Request): Promise<Transport> => {
   const query = req.query;
@@ -154,8 +155,6 @@ const createTransport = async (req: express.Request): Promise<Transport> => {
   }
 };
 
-let backingServerTransport: Transport | undefined;
-
 app.get("/mcp", async (req, res) => {
   const sessionId = req.headers["mcp-session-id"] as string;
   console.log(`Received GET message for sessionId ${sessionId}`);
@@ -178,12 +177,12 @@ app.get("/mcp", async (req, res) => {
 app.post("/mcp", async (req, res) => {
   const sessionId = req.headers["mcp-session-id"] as string | undefined;
   console.log(`Received POST message for sessionId ${sessionId}`);
+  let serverTransport: Transport | undefined;
   if (!sessionId) {
     try {
       console.log("New streamable-http connection");
       try {
-        await backingServerTransport?.close();
-        backingServerTransport = await createTransport(req);
+        serverTransport = await createTransport(req);
       } catch (error) {
         if (error instanceof SseError && error.code === 401) {
           console.error(
@@ -197,12 +196,13 @@ app.post("/mcp", async (req, res) => {
         throw error;
       }
 
-      console.log("Connected MCP client to backing server transport");
+      console.log("Connected MCP client to server transport");
 
       const webAppTransport = new StreamableHTTPServerTransport({
         sessionIdGenerator: randomUUID,
         onsessioninitialized: (sessionId) => {
           webAppTransports.set(sessionId, webAppTransport);
+          serverTransports.set(sessionId, serverTransport!);
           console.log("Created streamable web app transport " + sessionId);
         },
       });
@@ -211,7 +211,7 @@ app.post("/mcp", async (req, res) => {
 
       mcpProxy({
         transportToClient: webAppTransport,
-        transportToServer: backingServerTransport,
+        transportToServer: serverTransport,
       });
 
       await (webAppTransport as StreamableHTTPServerTransport).handleRequest(
@@ -246,10 +246,9 @@ app.post("/mcp", async (req, res) => {
 app.get("/stdio", async (req, res) => {
   try {
     console.log("New connection");
-
+    let serverTransport: Transport | undefined;
     try {
-      await backingServerTransport?.close();
-      backingServerTransport = await createTransport(req);
+      serverTransport = await createTransport(req);
     } catch (error) {
       if (error instanceof SseError && error.code === 401) {
         console.error(
@@ -267,26 +266,24 @@ app.get("/stdio", async (req, res) => {
 
     const webAppTransport = new SSEServerTransport("/message", res);
     webAppTransports.set(webAppTransport.sessionId, webAppTransport);
-
-    console.log("Created web app transport");
+    serverTransports.set(webAppTransport.sessionId, serverTransport);
+    console.log("Created client/server transports");
 
     await webAppTransport.start();
-    (backingServerTransport as StdioClientTransport).stderr!.on(
-      "data",
-      (chunk) => {
-        webAppTransport.send({
-          jsonrpc: "2.0",
-          method: "notifications/stderr",
-          params: {
-            content: chunk.toString(),
-          },
-        });
-      },
-    );
+
+    (serverTransport as StdioClientTransport).stderr!.on("data", (chunk) => {
+      webAppTransport.send({
+        jsonrpc: "2.0",
+        method: "notifications/stderr",
+        params: {
+          content: chunk.toString(),
+        },
+      });
+    });
 
     mcpProxy({
       transportToClient: webAppTransport,
-      transportToServer: backingServerTransport,
+      transportToServer: serverTransport,
     });
 
     console.log("Set up MCP proxy");
@@ -301,10 +298,9 @@ app.get("/sse", async (req, res) => {
     console.log(
       "New SSE connection. NOTE: The sse transport is deprecated and has been replaced by streamable-http",
     );
-
+    let serverTransport: Transport | undefined;
     try {
-      await backingServerTransport?.close();
-      backingServerTransport = await createTransport(req);
+      serverTransport = await createTransport(req);
     } catch (error) {
       if (error instanceof SseError && error.code === 401) {
         console.error(
@@ -322,13 +318,15 @@ app.get("/sse", async (req, res) => {
 
     const webAppTransport = new SSEServerTransport("/message", res);
     webAppTransports.set(webAppTransport.sessionId, webAppTransport);
-    console.log("Created web app transport");
+    console.log("Created client transport");
+    serverTransports.set(webAppTransport.sessionId, serverTransport);
+    console.log("Created server transport");
 
     await webAppTransport.start();
 
     mcpProxy({
       transportToClient: webAppTransport,
-      transportToServer: backingServerTransport,
+      transportToServer: serverTransport,
     });
 
     console.log("Set up MCP proxy");