MCP Background Task Server

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js"; import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js"; import { z } from "zod"; import childProcess from "node:child_process"; class Child { process: childProcess.ChildProcess; state: "running" | "stopped" = "running"; stopCode: number | null = null; stdout: string = ""; stderr: string = ""; constructor(shell: string) { const child = childProcess.spawn(shell, { shell: true, }); child.stdout?.on("data", (data) => { this.stdout += data.toString(); }); child.stderr?.on("data", (data) => { this.stderr += data.toString(); }); child.on("exit", (code) => { this.state = "stopped"; this.stopCode = code; }); this.process = child; } public getStdout(): string { return this.stdout; } public getStderr(): string { return this.stderr; } public getState(): "running" | "stopped" { return this.state; } public getStopCode(): number | null { return this.stopCode; } public getPid(): number { return this.process.pid || -1; } public writeToStdin(data: string): void { if (this.process.stdin) { this.process.stdin.write(data); } else { throw new Error("Child process stdin is not available."); } } public kill(): void { if (this.process.killed) { return; } this.process.kill(); this.state = "stopped"; } } // Create an MCP server const server = new McpServer({ name: "bgtask-server", version: "1.0.0", }); const processes = new Map<string, Child>(); // Add an addition tool server.registerTool( "run-background-task", { title: "Run Background Task", description: "Runs a long-running command (like 'npm run dev') in background. When the command is running, you can interact with it using other tools.", inputSchema: { name: z.string().describe("Unique name of the task"), shell: z.string().describe("Shell command to run in background"), }, }, async ({ name, shell }) => { if (processes.has(name)) { throw new Error(`Task with name "${name}" is already running.`); } const child = new Child(shell); processes.set(name, child); return { content: [ { type: "text", text: `Task "${name}" started with PID ${child.getPid()}.`, }, ], }; } ); server.registerTool( "stop-background-task", { title: "Stop Background Task", description: "Stops a running background task by its name.", inputSchema: { name: z.string().describe("Unique name of the task to stop"), }, }, async ({ name }) => { const child = processes.get(name); if (!child) { return { content: [ { type: "text", text: `No task found with name "${name}".`, }, ], }; } child.kill(); processes.delete(name); return { content: [ { type: "text", text: `Task "${name}" has been stopped.`, }, ], }; } ); server.registerTool( "list-background-tasks", { title: "List Background Tasks", description: "Lists all currently running background tasks.", inputSchema: {}, }, async () => { if (processes.size === 0) { return { content: [ { type: "text", text: "No background tasks are currently running.", }, ], }; } else { const tasks = Array.from(processes.entries()).map(([name, child]) => ({ name, pid: child.getPid(), state: child.getState(), })); return { content: [ { type: "text", text: `Currently running tasks:\n${tasks .map( (task) => `- ${task.name} (PID: ${task.pid}, State: ${task.state})` ) .join("\n")}`, }, ], }; } } ); server.registerTool( "get-task-stdout", { title: "Get Task Stdout", description: "Retrieves the stdout of a running background task.", inputSchema: { name: z.string().describe("Unique name of the task"), }, }, async ({ name }) => { const child = processes.get(name); if (!child) { return { content: [ { type: "text", text: `No task found with name "${name}".`, }, ], }; } return { content: [ { type: "text", text: `Stdout of task "${name}":\n${ child.stdout || "No output yet." }`, }, ], }; } ); server.registerTool( "get-task-stderr", { title: "Get Task Stderr", description: "Retrieves the stderr of a running background task.", inputSchema: { name: z.string().describe("Unique name of the task"), }, }, async ({ name }) => { const child = processes.get(name); if (!child) { return { content: [ { type: "text", text: `No task found with name "${name}".`, }, ], }; } return { content: [ { type: "text", text: `Stderr of task "${name}":\n${ child.stderr || "No error output yet." }`, }, ], }; } ); server.registerTool( "send-to-task-stdin", { title: "Send to Task Stdin", description: "Sends data to the stdin of a running background task.", inputSchema: { name: z.string().describe("Unique name of the task"), data: z.string().describe("Data to send to the task's stdin"), }, }, async ({ name, data }) => { const child = processes.get(name); if (!child) { return { content: [ { type: "text", text: `No task found with name "${name}".`, }, ], }; } try { child.writeToStdin(data); return { content: [ { type: "text", text: `Data sent to task "${name}" stdin.`, }, ], }; } catch (error) { return { content: [ { type: "text", text: `Failed to send data to task "${name}" stdin: ${ error instanceof Error ? error.message : String(error) }`, }, ], }; } } ); // Exit child processes when the server is stopped for (const signal of ["SIGINT", "SIGTERM"]) { process.on(signal, () => { // console.log(`Received ${signal}, stopping all background tasks...`); for (const [name, child] of processes.entries()) { // console.log(`Stopping task "${name}" with PID ${child.pid}...`); child.kill(); } // console.log("All background tasks stopped."); process.exit(0); }); } // Start receiving messages on stdin and sending messages on stdout const transport = new StdioServerTransport(); await server.connect(transport);