Hono | Cap'n Web

If your app is built on Hono, on any runtime it supports, check out @hono/capnweb.

npm i @hono/capnweb

The middleware mounts a Cap’n Web endpoint on a route in your existing Hono app, so your RPC API can live alongside your regular HTTP routes and share the same middleware stack for logging, CORS, and so on.

Refer to the @hono/capnweb README for current usage and options; it is maintained in the Hono middleware repository, not here.

Rolling your own

If you’d rather not add a dependency, Hono handlers receive standard Request objects and return standard Response objects, so the generic Fetch-API helpers work directly:

import { Hono } from 'hono';
import { RpcTarget, newHttpBatchRpcResponse } from 'capnweb';

class MyApiImpl extends RpcTarget {
  greet(name: string) {
    return `Hello, ${name}!`;
  }
}

const app = new Hono();

app.post('/api', (c) => newHttpBatchRpcResponse(c.req.raw, new MyApiImpl()));

export default app;

WebSocket support depends on the runtime you deploy Hono to. See Cloudflare Workers, Node.js, Deno, or Bun.