Cloudflare Workers

For connecting your MCP with a LLM, you will need to pressists the transport instance. On a server it is quite easy, but on a worker you will need to use Durable Objects to achieve that. Here is an example of how to do that:

const server = new Hono<{ Bindings: { transport: SSEHonoTransport } }>();
 
server.get("/sse", (c) => {
  return streamSSE(c, async (stream) => {
    c.env.transport.connectWithStream(stream);
 
    await bridge({
      mcp,
      transport: c.env.transport,
    });
  });
});
 
server.post("/messages", async (c) => {
  const transport = c.env.transport;
 
  if (!transport) {
    throw new Error("Transport not initialized");
  }
 
  await transport.handlePostMessage(c);
  return c.text("ok");
});
 
server.onError((err, c) => {
  console.error(err);
  return c.body(err.message, 500);
});
 
export class MyDurableObject extends DurableObject<Env> {
  transport?: SSEHonoTransport;
 
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
    this.transport = new SSEHonoTransport("/messages", ctx.id.toString());
  }
 
  async fetch(request: Request) {
    return server.fetch(request, {
      ...this.env,
      transport: this.transport,
    });
  }
}
 
export default {
  async fetch(
    request: Request,
    env: { MY_DO: DurableObjectNamespace<MyDurableObject> },
    ctx: ExecutionContext,
  ): Promise<Response> {
    const url = new URL(request.url);
    const sessionId = url.searchParams.get("sessionId");
 
    const namespace = env.MY_DO;
 
    let stub: DurableObjectStub<MyDurableObject>;
 
    if (sessionId) stub = namespace.get(namespace.idFromString(sessionId));
    else stub = namespace.get(namespace.newUniqueId());
 
    return stub.fetch(request);
  },
};

Over here we are creating a proxy server that will handle the SSE connection. The MyDurableObject class is a Durable Object that will handle the transport instance. The fetch method will handle the incoming requests and pass them to the Durable Object.

To identify the session, we are using the sessionId query parameter. If it is not present, we will create a new Durable Object instance. If it is present, we will use the existing instance.