fiberflow-mcp-gateway/src/index.ts

Run Fiberflow MCP SSE Server over stdio.

#!/usr/bin/env node
import express from "express";
import bodyParser from "body-parser";
import cors from "cors";
import { spawn, ChildProcessWithoutNullStreams } from "child_process";
import yargs from "yargs";
import { hideBin } from "yargs/helpers";
import { z } from "zod";
import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";
import { SSEClientTransport } from "@modelcontextprotocol/sdk/client/sse.js";
import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import {
  JSONRPCMessage,
  JSONRPCRequest,
} from "@modelcontextprotocol/sdk/types.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { fileURLToPath } from "url";
import { join, dirname } from "path";
import { readFileSync } from "fs";

const __filename = fileURLToPath(import.meta.url);
const __dirname = dirname(__filename);

function getVersion(): string {
  try {
    const packageJsonPath = join(__dirname, "../package.json");
    const packageJson = JSON.parse(readFileSync(packageJsonPath, "utf-8"));
    return packageJson.version || "1.0.0";
  } catch (err) {
    console.error("[fiberflow]", "Unable to retrieve version:", err);
    return "unknown";
  }
}

const log = (...args: any[]) => console.log("[fiberflow]", ...args);
const logStderr = (...args: any[]) => console.error("[fiberflow]", ...args);

interface Logger {
  info: (...args: any[]) => void;
  error: (...args: any[]) => void;
}

const noneLogger: Logger = {
  info: () => {},
  error: () => {},
};

interface StdioToSseArgs {
  stdioCmd: string;
  port: number;
  baseUrl: string;
  ssePath: string;
  messagePath: string;
  logger: Logger;
  enableCors: boolean;
  healthEndpoints: string[];
}

const onSignals = ({ logger }: { logger: Logger }) => {
  process.on("SIGINT", () => {
    logger.info("Caught SIGINT. Exiting...");
    process.exit(0);
  });

  process.on("SIGTERM", () => {
    logger.info("Caught SIGTERM. Exiting...");
    process.exit(0);
  });

  process.on("SIGHUP", () => {
    logger.info("Caught SIGHUP. Exiting...");
    process.exit(0);
  });

  process.stdin.on("close", () => {
    logger.info("stdin closed. Exiting...");
    process.exit(0);
  });
};

async function stdioToSse(args: StdioToSseArgs) {
  const {
    stdioCmd,
    port,
    baseUrl,
    ssePath,
    messagePath,
    logger,
    enableCors,
    healthEndpoints,
  } = args;

  logger.info("Starting...");
  logger.info(`  - port: ${port}`);
  logger.info(`  - stdio: ${stdioCmd}`);
  if (baseUrl) {
    logger.info(`  - baseUrl: ${baseUrl}`);
  }
  logger.info(`  - ssePath: ${ssePath}`);
  logger.info(`  - messagePath: ${messagePath}`);

  logger.info(`  - CORS enabled: ${enableCors}`);
  logger.info(
    `  - Health endpoints: ${
      healthEndpoints.length ? healthEndpoints.join(", ") : "(none)"
    }`
  );

  onSignals({ logger });

  const child: ChildProcessWithoutNullStreams = spawn(stdioCmd, {
    shell: true,
  });
  child.on("exit", (code, signal) => {
    logger.error(`Child exited: code=${code}, signal=${signal}`);
    process.exit(code ?? 1);
  });

  const server = new Server(
    { name: "fiberflow", version: getVersion() },
    { capabilities: {} }
  );

  const sessions: Record<
    string,
    { transport: SSEServerTransport; response: express.Response }
  > = {};

  const app = express();

  if (enableCors) {
    app.use(cors());
  }

  app.use((req, res, next) => {
    if (req.path === messagePath) return next();
    return bodyParser.json()(req, res, next);
  });

  for (const ep of healthEndpoints) {
    app.get(ep, (_req, res) => {
      res.send("ok");
    });
  }

  app.get(ssePath, async (req, res) => {
    logger.info(`New SSE connection from ${req.ip}`);

    const sseTransport = new SSEServerTransport(
      `${baseUrl}${messagePath}`,
      res
    );
    await server.connect(sseTransport);

    const sessionId = sseTransport.sessionId;
    if (sessionId) {
      sessions[sessionId] = { transport: sseTransport, response: res };
    }

    sseTransport.onmessage = (msg: JSONRPCMessage) => {
      logger.info(`SSE → Child (session ${sessionId}): ${JSON.stringify(msg)}`);
      child.stdin.write(JSON.stringify(msg) + "\n");
    };

    sseTransport.onclose = () => {
      logger.info(`SSE connection closed (session ${sessionId})`);
      delete sessions[sessionId];
    };

    sseTransport.onerror = (err) => {
      logger.error(`SSE error (session ${sessionId}):`, err);
      delete sessions[sessionId];
    };

    req.on("close", () => {
      logger.info(`Client disconnected (session ${sessionId})`);
      delete sessions[sessionId];
    });
  });

  // @ts-ignore
  app.post(messagePath, async (req, res) => {
    const sessionId = req.query.sessionId as string;
    if (!sessionId) {
      return res.status(400).send("Missing sessionId parameter");
    }

    const session = sessions[sessionId];
    if (session?.transport?.handlePostMessage) {
      logger.info(`POST to SSE transport (session ${sessionId})`);
      await session.transport.handlePostMessage(req, res);
    } else {
      res.status(503).send(`No active SSE connection for session ${sessionId}`);
    }
  });

  app.listen(port, () => {
    logger.info(`Listening on port ${port}`);
    logger.info(`SSE endpoint: http://localhost:${port}${ssePath}`);
    logger.info(`POST messages: http://localhost:${port}${messagePath}`);
  });

  let buffer = "";
  child.stdout.on("data", (chunk: Buffer) => {
    buffer += chunk.toString("utf8");
    const lines = buffer.split(/\r?\n/);
    buffer = lines.pop() ?? "";
    lines.forEach((line) => {
      if (!line.trim()) return;
      try {
        const jsonMsg = JSON.parse(line);
        logger.info("Child → SSE:", jsonMsg);
        for (const [sid, session] of Object.entries(sessions)) {
          try {
            session.transport.send(jsonMsg);
          } catch (err) {
            logger.error(`Failed to send to session ${sid}:`, err);
            delete sessions[sid];
          }
        }
      } catch {
        logger.error(`Child non-JSON: ${line}`);
      }
    });
  });

  child.stderr.on("data", (chunk: Buffer) => {
    logger.error(`Child stderr: ${chunk.toString("utf8")}`);
  });
}

interface SseToStdioArgs {
  sseUrl: string;
  logger: Logger;
}

async function sseToStdio(args: SseToStdioArgs) {
  const { sseUrl, logger } = args;

  logger.info("Starting...");
  logger.info(`  - sse: ${sseUrl}`);
  logger.info("Connecting to SSE...");

  onSignals({ logger });

  const sseTransport = new SSEClientTransport(new URL(sseUrl));
  const sseClient = new Client(
    { name: "fiberflow", version: getVersion() },
    { capabilities: {} }
  );

  sseTransport.onerror = (err) => {
    logger.error("SSE error:", err);
  };
  sseTransport.onclose = () => {
    logger.error("SSE connection closed");
    process.exit(1);
  };

  await sseClient.connect(sseTransport);
  logger.info("SSE connected");

  const stdioServer = new Server(
    sseClient.getServerVersion() ?? {
      name: "fiberflow",
      version: getVersion(),
    },
    { capabilities: sseClient.getServerCapabilities() }
  );
  const stdioTransport = new StdioServerTransport();
  await stdioServer.connect(stdioTransport);

  const wrapResponse = (req: JSONRPCRequest, payload: object) => ({
    jsonrpc: req.jsonrpc || "2.0",
    id: req.id,
    ...payload,
  });

  stdioServer.transport!.onmessage = async (message: JSONRPCMessage) => {
    const isRequest = "method" in message && "id" in message;
    if (isRequest) {
      logger.info("Stdio → SSE:", message);
      const req = message as JSONRPCRequest;
      let result;
      try {
        result = await sseClient.request(req, z.any());
      } catch (err) {
        logger.error("Request error:", err);
        const errorCode =
          err && typeof err === "object" && "code" in err
            ? (err as any).code
            : -32000;
        let errorMsg =
          err && typeof err === "object" && "message" in err
            ? (err as any).message
            : "Internal error";
        const prefix = `MCP error ${errorCode}:`;
        if (errorMsg.startsWith(prefix)) {
          errorMsg = errorMsg.slice(prefix.length).trim();
        }
        const errorResp = wrapResponse(req, {
          error: {
            code: errorCode,
            message: errorMsg,
          },
        });
        process.stdout.write(JSON.stringify(errorResp) + "\n");
        return;
      }
      const response = wrapResponse(
        req,
        result.hasOwnProperty("error")
          ? { error: { ...result.error } }
          : { result: { ...result } }
      );
      logger.info("Response:", response);
      process.stdout.write(JSON.stringify(response) + "\n");
    } else {
      logger.info("SSE → Stdio:", message);
      process.stdout.write(JSON.stringify(message) + "\n");
    }
  };

  logger.info("Stdio server listening");
}

async function main() {
  const argv = yargs(hideBin(process.argv))
    .option("stdio", {
      type: "string",
      description: "Command to run an MCP server over Stdio",
    })
    .option("sse", {
      type: "string",
      description: "SSE URL to connect to",
    })
    .option("port", {
      type: "number",
      default: 8000,
      description: "(stdio→SSE) Port to run on",
    })
    .option("baseUrl", {
      type: "string",
      default: "",
      description: "(stdio→SSE) Base URL for SSE clients",
    })
    .option("ssePath", {
      type: "string",
      default: "/sse",
      description: "(stdio→SSE) Path for SSE subscriptions",
    })
    .option("messagePath", {
      type: "string",
      default: "/message",
      description: "(stdio→SSE) Path for SSE messages",
    })
    .option("logLevel", {
      choices: ["info", "none"] as const,
      default: "info",
      description: 'Set logging level: "info" or "none"',
    })
    .option("cors", {
      type: "boolean",
      default: false,
      description: "Enable CORS",
    })
    .option("healthEndpoint", {
      type: "array",
      default: [],
      description:
        'One or more endpoints returning "ok", e.g. --healthEndpoint /healthz --healthEndpoint /readyz',
    })
    .help()
    .parseSync();

  const hasStdio = Boolean(argv.stdio);
  const hasSse = Boolean(argv.sse);

  if (hasStdio && hasSse) {
    logStderr("Error: Specify only one of --stdio or --sse, not both");
    process.exit(1);
  } else if (!hasStdio && !hasSse) {
    logStderr("Error: You must specify one of --stdio or --sse");
    process.exit(1);
  }

  try {
    if (hasStdio) {
      await stdioToSse({
        stdioCmd: argv.stdio!,
        port: argv.port,
        baseUrl: argv.baseUrl,
        ssePath: argv.ssePath,
        messagePath: argv.messagePath,
        logger:
          argv.logLevel === "none"
            ? noneLogger
            : { info: log, error: logStderr },
        enableCors: argv.cors,
        healthEndpoints: argv.healthEndpoint as string[],
      });
    } else {
      await sseToStdio({
        sseUrl: argv.sse!,
        logger:
          argv.logLevel === "none"
            ? noneLogger
            : { info: logStderr, error: logStderr },
      });
    }
  } catch (err) {
    logStderr("Fatal error:", err);
    process.exit(1);
  }
}

main();