#!/usr/bin/env node
/**
* YouTube Subtitle MCP Server - Streamable HTTP mode (for server deployment)
* Using latest MCP Protocol 2025-06-18
*/
import express, { Request, Response } from "express";
import cors from "cors";
import { randomUUID } from "node:crypto";
import "dotenv/config";
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import { isInitializeRequest } from "@modelcontextprotocol/sdk/types.js";
import { z } from "zod";
// Import business tools
import { fetchYoutubeSubtitles } from "./tools/fetchYoutubeSubtitles.js";
// Create MCP server instance (reusable across requests)
function createMCPServer(): McpServer {
const server = new McpServer({
name: "youtube-subtitle-mcp",
version: "1.0.0",
});
// Register YouTube subtitle fetching tool using new API
server.registerTool(
fetchYoutubeSubtitles.name,
{
title: "Fetch YouTube Subtitles",
description: fetchYoutubeSubtitles.description,
inputSchema: {
url: z
.string()
.describe(
"YouTube video URL or video ID. Supported formats: https://www.youtube.com/watch?v=xxx, https://youtu.be/xxx, or direct video ID"
),
format: z
.enum(["SRT", "VTT", "TXT", "JSON"])
.default("JSON")
.optional()
.describe(
"Output format. SRT: subtitle file format (with sequence numbers), VTT: WebVTT format, TXT: plain text (text only), JSON: structured JSON (with timestamps)"
),
lang: z
.string()
.optional()
.describe(
"Subtitle language code (optional). Examples: zh-Hans (Simplified Chinese), zh-Hant (Traditional Chinese), en (English). Auto-detect if not specified"
),
},
},
async (args) => {
const result = await fetchYoutubeSubtitles.run(args);
return result;
}
);
return server;
}
const app = express();
const PORT = Number(process.env.PORT) || 3000;
// Configure CORS
app.use(
cors({
origin: "*",
methods: ["GET", "POST", "DELETE", "OPTIONS"],
allowedHeaders: [
"Content-Type",
"Accept",
"Authorization",
"Mcp-Session-Id",
"X-Api-Key",
],
exposedHeaders: ["Content-Type", "Mcp-Session-Id"],
})
);
app.use(express.json({ limit: "10mb" }));
// Store transports by session ID for stateful mode
const transports: Record<string, StreamableHTTPServerTransport> = {};
// Health check endpoint
app.get("/health", (_req: Request, res: Response) => {
res.json({
status: "healthy",
transport: "streamable-http",
protocol: "2025-06-18",
activeSessions: Object.keys(transports).length,
name: "youtube-subtitle-mcp",
version: "1.0.0",
timestamp: new Date().toISOString(),
});
});
// Main MCP endpoint using new Streamable HTTP transport
app.post("/mcp", async (req: Request, res: Response) => {
try {
const sessionId = req.headers["mcp-session-id"] as string | undefined;
let transport: StreamableHTTPServerTransport;
if (sessionId && transports[sessionId]) {
// Reuse existing transport for this session
transport = transports[sessionId];
} else if (!sessionId && isInitializeRequest(req.body)) {
// New session initialization
transport = new StreamableHTTPServerTransport({
sessionIdGenerator: () => randomUUID(),
onsessioninitialized: (id) => {
transports[id] = transport;
console.log(`✅ Session initialized: ${id}`);
},
onsessionclosed: (id) => {
delete transports[id];
console.log(`❌ Session closed: ${id}`);
},
enableJsonResponse: true,
// Disable DNS rebinding protection for local development
// If deploying to production, enable it and configure allowedHosts properly
enableDnsRebindingProtection: false,
});
// Clean up transport when closed
transport.onclose = () => {
if (transport.sessionId) {
delete transports[transport.sessionId];
}
};
const server = createMCPServer();
await server.connect(transport);
} else {
// Invalid request
return res.status(400).json({
jsonrpc: "2.0",
error: {
code: -32000,
message: "Bad Request: No valid session ID provided",
},
id: null,
});
}
// Handle the request using new transport API
await transport.handleRequest(req, res, req.body);
} catch (error) {
console.error("❌ Error handling MCP request:", error);
if (!res.headersSent) {
res.status(500).json({
jsonrpc: "2.0",
error: {
code: -32603,
message: "Internal server error",
},
id: null,
});
}
}
});
// Reusable handler for GET and DELETE requests (session management)
const handleSessionRequest = async (req: Request, res: Response) => {
const sessionId = req.headers["mcp-session-id"] as string | undefined;
if (!sessionId || !transports[sessionId]) {
return res.status(400).send("Invalid or missing session ID");
}
const transport = transports[sessionId];
await transport.handleRequest(req, res);
};
// Handle GET requests for server-to-client notifications via SSE
app.get("/mcp", handleSessionRequest);
// Handle DELETE requests for session termination
app.delete("/mcp", handleSessionRequest);
// Start Streamable HTTP server
app.listen(PORT, () => {
console.log(`\n🚀 YouTube Subtitle MCP Server (Streamable HTTP)`);
console.log(`📋 Protocol Version: 2025-06-18 (Latest)`);
console.log(`📡 Listening on: http://localhost:${PORT}`);
console.log(`🔗 MCP endpoint: http://localhost:${PORT}/mcp`);
console.log(`💚 Health check: http://localhost:${PORT}/health`);
console.log(`\n⚡ Using new McpServer API with registerTool`);
console.log(`✨ Features: Session management, DNS rebinding protection`);
console.log(`\nPress Ctrl+C to stop the server\n`);
}).on("error", (error) => {
console.error("❌ Server error:", error);
process.exit(1);
});
