import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import { InMemoryEventStore } from "@modelcontextprotocol/sdk/examples/shared/inMemoryEventStore.js";
import express, { Request, Response } from "express";
import { createServer } from "../server/index.js";
import { randomUUID } from "node:crypto";
import cors from "cors";
console.log("Starting Streamable HTTP server...");
// Express app with permissive CORS for testing with Inspector direct connect mode
const app = express();
app.use(
cors({
origin: "*", // use "*" with caution in production
methods: "GET,POST,DELETE",
preflightContinue: false,
optionsSuccessStatus: 204,
exposedHeaders: ["mcp-session-id", "last-event-id", "mcp-protocol-version"],
})
);
// Map sessionId to server transport for each client
const transports: Map<string, StreamableHTTPServerTransport> = new Map<
string,
StreamableHTTPServerTransport
>();
// Handle POST requests for client messages
app.post("/mcp", async (req: Request, res: Response) => {
console.log("Received MCP POST request");
try {
// Check for existing session ID
const sessionId = req.headers["mcp-session-id"] as string | undefined;
let transport: StreamableHTTPServerTransport;
if (sessionId && transports.has(sessionId)) {
// Reuse existing transport
transport = transports.get(sessionId)!;
} else if (!sessionId) {
const { server, cleanup } = createServer();
// New initialization request
const eventStore = new InMemoryEventStore();
transport = new StreamableHTTPServerTransport({
sessionIdGenerator: () => randomUUID(),
eventStore, // Enable resumability
onsessioninitialized: (sessionId: string) => {
// Store the transport by session ID when a session is initialized
// This avoids race conditions where requests might come in before the session is stored
console.log(`Session initialized with ID: ${sessionId}`);
transports.set(sessionId, transport);
},
});
// Set up onclose handler to clean up transport when closed
server.server.onclose = async () => {
const sid = transport.sessionId;
if (sid && transports.has(sid)) {
console.log(
`Transport closed for session ${sid}, removing from transports map`
);
transports.delete(sid);
cleanup(sid);
}
};
// Connect the transport to the MCP server BEFORE handling the request
// so responses can flow back through the same transport
await server.connect(transport);
await transport.handleRequest(req, res);
return;
} else {
// Invalid request - no session ID or not initialization request
res.status(400).json({
jsonrpc: "2.0",
error: {
code: -32000,
message: "Bad Request: No valid session ID provided",
},
id: req?.body?.id,
});
return;
}
// Handle the request with existing transport - no need to reconnect
// The existing transport is already connected to the server
await transport.handleRequest(req, res);
} catch (error) {
console.log("Error handling MCP request:", error);
if (!res.headersSent) {
res.status(500).json({
jsonrpc: "2.0",
error: {
code: -32603,
message: "Internal server error",
},
id: req?.body?.id,
});
return;
}
}
});
// Handle GET requests for SSE streams
app.get("/mcp", async (req: Request, res: Response) => {
console.log("Received MCP GET request");
const sessionId = req.headers["mcp-session-id"] as string | undefined;
if (!sessionId || !transports.has(sessionId)) {
res.status(400).json({
jsonrpc: "2.0",
error: {
code: -32000,
message: "Bad Request: No valid session ID provided",
},
id: req?.body?.id,
});
return;
}
// Check for Last-Event-ID header for resumability
const lastEventId = req.headers["last-event-id"] as string | undefined;
if (lastEventId) {
console.log(`Client reconnecting with Last-Event-ID: ${lastEventId}`);
} else {
console.log(`Establishing new SSE stream for session ${sessionId}`);
}
const transport = transports.get(sessionId);
await transport!.handleRequest(req, res);
});
// Handle DELETE requests for session termination
app.delete("/mcp", async (req: Request, res: Response) => {
const sessionId = req.headers["mcp-session-id"] as string | undefined;
if (!sessionId || !transports.has(sessionId)) {
res.status(400).json({
jsonrpc: "2.0",
error: {
code: -32000,
message: "Bad Request: No valid session ID provided",
},
id: req?.body?.id,
});
return;
}
console.log(`Received session termination request for session ${sessionId}`);
try {
const transport = transports.get(sessionId);
await transport!.handleRequest(req, res);
} catch (error) {
console.log("Error handling session termination:", error);
if (!res.headersSent) {
res.status(500).json({
jsonrpc: "2.0",
error: {
code: -32603,
message: "Error handling session termination",
},
id: req?.body?.id,
});
return;
}
}
});
// Start the server
const PORT = process.env.PORT || 3001;
const server = app.listen(PORT, () => {
console.error(`MCP Streamable HTTP Server listening on port ${PORT}`);
});
// Handle server errors
server.on("error", (err: unknown) => {
const code =
typeof err === "object" && err !== null && "code" in err
? (err as { code?: unknown }).code
: undefined;
if (code === "EADDRINUSE") {
console.error(
`Failed to start: Port ${PORT} is already in use. Set PORT to a free port or stop the conflicting process.`
);
} else {
console.error("HTTP server encountered an error while starting:", err);
}
// Ensure a non-zero exit so npm reports the failure instead of silently exiting
process.exit(1);
});
// Handle server shutdown
process.on("SIGINT", async () => {
console.log("Shutting down server...");
// Close all active transports to properly clean up resources
for (const sessionId in transports) {
try {
console.log(`Closing transport for session ${sessionId}`);
await transports.get(sessionId)!.close();
transports.delete(sessionId);
} catch (error) {
console.log(`Error closing transport for session ${sessionId}:`, error);
}
}
console.log("Server shutdown complete");
process.exit(0);
});
