What is Hono Mcp Server Sse Transport

hono-mcp-server-sse-transport is a transport layer designed for Hono applications to connect with the MCP Server, facilitating communication between them.

Use cases

Use cases include real-time data updates in web applications, IoT device communication, and scenarios where multiple clients need to receive updates from a central server simultaneously.

How to use

To use hono-mcp-server-sse-transport, install it via ‘pnpm add -D hono-mcp-server-sse-transport’. Then, import it into your Hono application and create an SSETransport instance to manage connections to the MCP Server.

Key features

Key features include support for Server-Sent Events (SSE), the ability to handle multiple simultaneous connections, and integration with the MCP Server using the official TypeScript SDK.

Where to use

hono-mcp-server-sse-transport is suitable for applications that require real-time communication and data streaming capabilities, particularly in IoT, web applications, and microservices architectures.

MCP Server transport for Hono applications

Overview

This project provides a transport for Hono application that needs to connect to MCP Server. An official TypeScript SDK is designed to be used with express.
If you try and follow their instructions but change express with hono, you will find that it’s not going to work. Even if you set HttpBinding as an env (see an example from @hono/node-server),
it still doesn’t work as some headers are being added to a response after it’s sent.

This implementation is inspired by the following pull request

You can use this transport until there is a proper support for Hono in the official SDK.

Getting started

Installation

pnpm add -D hono-mcp-server-sse-transport

Usage

import { Hono } from 'hono';
import { serve } from '@hono/node-server';
import { streamSSE } from 'hono/streaming';
import { SSETransport } from 'hono-mcp-server-sse-transport';
import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';

const mcpServer = new McpServer(
  {
    name: 'your-mcp-server-name',
    version: '1.0.0',
  },
  {
    capabilities: {
      tools: {},
    },
  },
);

// here you add your tools
// ...

const app = new Hono();

// to support multiple simultaneous connections we have a lookup object from
// sessionId to transport
const transports: { [sessionId: string]: SSETransport } = {};

app.get('/sse', (c) => {
  return streamSSE(c, async (stream) => {
    const transport = new SSETransport('/messages', stream);

    transports[transport.sessionId] = transport;

    stream.onAbort(() => {
      delete transports[transport.sessionId];
    });

    await mcpServer.connect(transport);

    while (true) {
      // This will keep the connection alive
      // You can also await for a promise that never resolves
      await stream.sleep(60_000);
    }
  });
});

app.post('/messages', async (c) => {
  const sessionId = c.req.query('sessionId');
  const transport = transports[sessionId];

  if (transport == null) {
    return c.text('No transport found for sessionId', 400);
  }

  return await transport.handlePostMessage(c);
});

serve(
  {
    fetch: app.fetch,
    port: 3000,
  },
);