fix: connect error when sse with multiple clients (#233)

* fix: connect error when sse with multiple clients

* chore: lock zod-to-json-schema version

* fix: typo of connect

Author: hustcc

__tests__/server.spec.ts

@@ -75,7 +75,7 @@ describe("MCP Server", () => {
     const transport = new SSEClientTransport(new URL(url), {});
 
     const client = new Client(
-      { name: "stress-client", version: "1.0.0" },
+      { name: "sse-client", version: "1.0.0" },
       { capabilities: {} },
     );
 
@@ -159,4 +159,66 @@ describe("MCP Server", () => {
 
     await killAsync(child);
   });
+
+  it("sse with multiple clients", async () => {
+    const child = await spawnAsync("ts-node", ["./src/index.ts", "-t", "sse"]);
+
+    const url = "http://localhost:1122/sse";
+
+    const transport1 = new SSEClientTransport(new URL(url), {});
+    const client1 = new Client(
+      { name: "sse-client-1", version: "1.0.0" },
+      { capabilities: {} },
+    );
+
+    const transport2 = new SSEClientTransport(new URL(url), {});
+    const client2 = new Client(
+      { name: "sse-client-2", version: "1.0.0" },
+      { capabilities: {} },
+    );
+
+    await Promise.all([
+      client1.connect(transport1),
+      client2.connect(transport2),
+    ]);
+
+    expect((await client1.listTools()).tools.length).toBe(
+      (await client2.listTools()).tools.length,
+    );
+
+    await killAsync(child);
+  });
+
+  it("streamable with multiple clients", async () => {
+    const child = await spawnAsync("ts-node", [
+      "./src/index.ts",
+      "-t",
+      "streamable",
+    ]);
+
+    const url = "http://localhost:1122/mcp";
+
+    const transport1 = new StreamableHTTPClientTransport(new URL(url), {});
+    const client1 = new Client(
+      { name: "streamable-client-1", version: "1.0.0" },
+      { capabilities: {} },
+    );
+
+    const transport2 = new StreamableHTTPClientTransport(new URL(url), {});
+    const client2 = new Client(
+      { name: "streamable-client-2", version: "1.0.0" },
+      { capabilities: {} },
+    );
+
+    await Promise.all([
+      client1.connect(transport1),
+      client2.connect(transport2),
+    ]);
+
+    expect((await client1.listTools()).tools.length).toBe(
+      (await client2.listTools()).tools.length,
+    );
+
+    await killAsync(child);
+  });
 });

package.json

@@ -47,7 +47,7 @@
     "cors": "^2.8.5",
     "express": "^5.1.0",
     "zod": "^3.25.16",
-    "zod-to-json-schema": "^3.24.5"
+    "zod-to-json-schema": "3.24.6"
   },
   "devDependencies": {
     "@biomejs/biome": "1.9.4",

src/server.ts

@@ -92,8 +92,7 @@ export async function runSSEServer(
   port = 1122,
   endpoint = "/sse",
 ): Promise<void> {
-  const server = createServer();
-  await startSSEMcpServer(server, endpoint, port, host);
+  await startSSEMcpServer(createServer, endpoint, port, host);
 }
 
 /**

src/services/sse.ts

@@ -4,22 +4,24 @@ import express, { type Request, type Response } from "express";
 import { logger } from "../utils/logger";
 
 export const startSSEMcpServer = async (
-  server: Server,
+  createServer: () => Server,
   endpoint = "/sse",
   port = 1122,
   host = "localhost",
 ): Promise<void> => {
   const app = express();
   app.use(express.json());
 
-  const transports: Record<string, SSEServerTransport> = {};
+  const connections: Record<string, SSEServerTransport> = {};
 
   app.get(endpoint, async (req: Request, res: Response) => {
+    const server = createServer();
+
     const transport = new SSEServerTransport("/messages", res);
-    transports[transport.sessionId] = transport;
+    connections[transport.sessionId] = transport;
 
     transport.onclose = () => {
-      delete transports[transport.sessionId];
+      delete connections[transport.sessionId];
       logger.info(`SSE Server disconnected: sessionId=${transport.sessionId}`);
     };
 
@@ -34,7 +36,7 @@ export const startSSEMcpServer = async (
       return res.status(400).send("Missing sessionId parameter");
     }
 
-    const transport = transports[sessionId];
+    const transport = connections[sessionId];
     if (!transport) {
       logger.warn(`SSE Server session not found: sessionId=${sessionId}`);
       return res.status(404).send("Session not found");

vitest.config.ts

@@ -5,8 +5,8 @@ const enableCoverage = process.argv.includes("--coverage");
 export default defineConfig({
   resolve: {},
   test: {
-    testTimeout: 20_000,
-    hookTimeout: 20_000,
+    testTimeout: 60_000,
+    hookTimeout: 60_000,
     include: ["__tests__/**/*.{test,spec}.?(c|m)[jt]s?(x)"],
     ...(enableCoverage
       ? {