From 9ca242e2d8f46327ffaebb7b48a53b40e6d36010 Mon Sep 17 00:00:00 2001
From: Ryan Buchmayer <ryan.buchmayer@perplexity.ai>
Date: Wed, 22 Jul 2026 15:24:18 -0700
Subject: [PATCH] fix(http): create a server instance per request in stateless
 HTTP mode

The stateless streamable HTTP path reused a single McpServer across
requests, but a Protocol instance only supports one transport. The second
POST in any session failed with "Already connected to a transport"
(HTTP 500), which breaks initialize -> tools/list for every client.

Follow the SDK's stateless pattern: build a fresh server + transport pair
per request and close both when the response closes.
---
 src/http.config.test.ts | 43 +++++++++++++++++++++++++++++++++++++++++
 src/http.ts             |  6 ++++--
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/src/http.config.test.ts b/src/http.config.test.ts
index c899821..a0d6205 100644
--- a/src/http.config.test.ts
+++ b/src/http.config.test.ts
@@ -350,4 +350,47 @@ describe("HTTP transport configuration", () => {
       expect(status).toBe(200);
     });
   });
+
+  describe("stateless request handling", () => {
+    it("serves multiple sequential requests on one app instance", async () => {
+      await start();
+
+      const listTools = () =>
+        fetch(`${baseUrl}/mcp`, {
+          method: "POST",
+          headers: {
+            "Content-Type": "application/json",
+            Accept: "application/json, text/event-stream",
+          },
+          body: JSON.stringify({
+            jsonrpc: "2.0",
+            id: 1,
+            method: "tools/list",
+            params: {},
+          }),
+        });
+
+      // A single server instance can only bind one transport, so the app must
+      // build a fresh pair per request; before that fix the second request
+      // failed with a 500 "Already connected to a transport".
+      const first = await listTools();
+      expect(first.status).toBe(200);
+
+      const second = await listTools();
+      expect(second.status).toBe(200);
+      const data = await second.json();
+      expect(data.result.tools).toHaveLength(4);
+    });
+
+    it("serves the health endpoint", async () => {
+      await start();
+
+      const response = await fetch(`${baseUrl}/health`);
+      expect(response.ok).toBe(true);
+      expect(await response.json()).toEqual({
+        status: "ok",
+        service: "perplexity-mcp-server",
+      });
+    });
+  });
 });
diff --git a/src/http.ts b/src/http.ts
index e9923ad..8c96715 100644
--- a/src/http.ts
+++ b/src/http.ts
@@ -124,17 +124,19 @@ export function createHttpApp(options: HttpAppOptions): Express {
 
   app.use(express.json());
 
-  const mcpServer = createPerplexityServer();
-
   app.all("/mcp", async (req, res) => {
     try {
+      // Stateless mode: a Protocol instance supports one transport, so build
+      // a fresh server + transport pair per request.
       const transport = new StreamableHTTPServerTransport({
         sessionIdGenerator: undefined,
         enableJsonResponse: true,
       });
+      const mcpServer = createPerplexityServer();
 
       res.on("close", () => {
         transport.close();
+        mcpServer.close();
       });
 
       await mcpServer.connect(transport);