ExpressJS MCP

import type { Application } from "express"; import type { InMemoryDispatcher } from "./inMemoryDispatcher"; import type { RouteInfo } from "./index"; import type { SchemaResolver } from "./schemaResolver"; type Logger = { info: (...a: unknown[]) => void; error: (...a: unknown[]) => void; }; export class McpServer { private routes: RouteInfo[] = []; private tools: unknown[] = []; constructor( private dispatcher: InMemoryDispatcher, private schemas: SchemaResolver, private log: Logger = console, ) {} async loadRoutes(routes: RouteInfo[]) { this.routes = routes; this.tools = routes.map((r) => this.schemas.toTool(r)); } listTools() { return this.tools; } mount(app: Application, basePath: string) { app.get(`${basePath}/tools`, (_req, res) => res.json({ tools: this.tools }), ); app.post(`${basePath}/invoke`, async (req, res) => { const { toolName, args, streaming, timeout } = req.body ?? {}; const route = this.routes.find( (r) => this.schemas.toolName(r) === toolName || this.schemas.safeName(r) === toolName, ); if (!route) return res.status(404).json({ error: "Tool not found" }); try { if (streaming) { // Handle streaming response res.setHeader("Content-Type", "application/json"); res.setHeader("Transfer-Encoding", "chunked"); res.setHeader("Cache-Control", "no-cache"); res.setHeader("Connection", "keep-alive"); const stream = await this.dispatcher.dispatchStream( route.method, route.path, args, {}, timeout, ); stream.on("data", (chunk) => { const data = { type: "chunk", data: chunk.toString() }; res.write(`${JSON.stringify(data)}\n`); }); stream.on("end", () => { res.write(`${JSON.stringify({ type: "end" })}\n`); res.end(); }); stream.on("error", (error) => { const data = { type: "error", error: error.message }; res.write(`${JSON.stringify(data)}\n`); res.end(); }); } else { // Regular non-streaming response const rsp = await this.dispatcher.dispatch( route.method, route.path, args, {}, { timeout }, ); if (rsp.isStreaming && rsp.stream) { // Handle unexpected streaming response const chunks: Buffer[] = []; rsp.stream.on("data", (chunk) => chunks.push(chunk)); rsp.stream.on("end", () => { const body = Buffer.concat(chunks).toString(); res.status(200).json({ ok: true, result: body, status: rsp.status, streaming: true, }); }); rsp.stream.on("error", (error) => { this.log.error("Stream error:", error); res.status(500).json({ ok: false, error: error.message, }); }); } else { res.status(200).json({ ok: true, result: rsp.body, status: rsp.status, }); } } } catch (e: unknown) { this.log.error("MCP invoke error", e); res.status(500).json({ ok: false, error: e && typeof e === "object" && "message" in e ? (e as { message: string }).message : "Unknown error", }); } }); } async listen(port: number) { const express = (await import("express")).default; const app = express(); app.use(express.json()); this.mount(app as Application, "/mcp"); await new Promise<void>((r) => app.listen(port, () => r())); this.log.info( `MCP HTTP gateway listening on :${port} (paths: /mcp/tools, /mcp/invoke)`, ); } }