RPC client does not pass extra arguments, like headers, when using a websocket

[NuroDev]

What version of Hono are you using?

4.4.3

What runtime/platform is your app running on?

Bun

What steps can reproduce the bug?

import { Hono } from 'hono';
import { createBunWebSocket } from 'hono/bun';
import { hc } from 'hono/client';

const { upgradeWebSocket, websocket } = createBunWebSocket();

const app = new Hono()
  .use('*', async (c, next) => {
    console.log({
      Authorization: c.req.header('Authorization'), // undefined
    });

    await next();
  })
  .get(
    '/ws',
    upgradeWebSocket(() => ({
      onMessage(event, ws) {
        console.log(`Message from client: ${event.data}`);
        ws.send('Hello from server!');
      },
      onClose: () => {
        console.log('Connection closed');
      },
    })),
  );

const server = Bun.serve({
  fetch: app.fetch,
  websocket,
});

const client = hc<typeof app>(server.url.href, {
  headers: {
    Authorization: 'Bearer 123',
  },
});

const socket = client.ws.$ws();

await new Promise((resolve) => setTimeout(resolve, 500));

socket.close();
server.stop();

What is the expected behavior?

Based on the example above: c.req.header('Authorization') should return 'Bearer 123'.

What do you see instead?

Based on the example above: c.req.header('Authorization') instead returns undefined.

Additional information

I of course did a quick look into this and this line seems to be the cause. We just need to pass args as a 2nd argument when creating the new websocket instance.

At a basic level the const args = ... could just be moved up & used for both req.fetch(...) and new WebSocket(...) but I don't know if there is any issue with exposing all arguments when creating the new websocket instance, or if it should be limited to just headers?

[nakasyou]

Hello @NuroDev

Currently, WebSocket API in JavaScript doesn't support sending headers. WebSocket constructor supports only URL and protocol.
RPC Client uses WebSocket API, so I think we can't resolve it. However writing about it to docs is good idea.

Reference:

• https://stackoverflow.com/questions/4361173/http-headers-in-websockets-client-api

[nakasyou]

Oh, sorry, I missed a fact.
WebSocket in Bun accepts headers.

[NuroDev]

Interesting, good point @nakasyou. After a bit more digging I found this issue created 7 years asking for this to become a standard. However Bun seems to have gone ahead and added support for it anyway.