Writing header in upgrade handler

[mirpo]

Hi.

Setup:

• macOS 10.15.5
• uWebSockets.js v18.1.0

Official server example:

/* A quite detailed WebSockets example */

const uWS = require('uWebSockets.js')
const port = 9001;

const app = uWS./*SSL*/App({
  key_file_name: 'misc/key.pem',
  cert_file_name: 'misc/cert.pem',
  passphrase: '1234'
}).ws('/*', {
  /* Options */
  compression: uWS.SHARED_COMPRESSOR,
  maxPayloadLength: 16 * 1024 * 1024,
  idleTimeout: 10,
  /* Handlers */
  upgrade: (res, req, context) => {
    console.log('An Http connection wants to become WebSocket, URL: ' + req.getUrl() + '!');

    // THIS DOESN'T WORK
    res.writeHeader('test-header', 'header-value')

    // THIS WORKS
    // res.writeStatus("101 Switching Protocols\ntest-header: header-value")

    /* This immediately calls open handler, you must not use res after this call */
    res.upgrade({
        url: req.getUrl()
      },
      /* Spell these correctly */
      req.getHeader('sec-websocket-key'),
      req.getHeader('sec-websocket-protocol'),
      req.getHeader('sec-websocket-extensions'),
      context);

  },
  open: (ws) => {
    console.log('A WebSocket connected with URL: ' + ws.url);
  },
  message: (ws, message, isBinary) => {
    /* Ok is false if backpressure was built up, wait for drain */
    let ok = ws.send(message, isBinary);
  },
  drain: (ws) => {
    console.log('WebSocket backpressure: ' + ws.getBufferedAmount());
  },
  close: (ws, code, message) => {
    console.log('WebSocket closed');
  }
}).any('/*', (res, req) => {
  res.end('Nothing to see here!');
}).listen(port, (token) => {
  if (token) {
    console.log('Listening to port ' + port);
  } else {
    console.log('Failed to listen to port ' + port);
  }
});

Client code:

const WebSocket = require('ws')

const ws = new WebSocket('ws://127.0.0.1:9001/ws1')

ws.on('upgrade', (res) => {
    console.log('upgrade event')
    console.log(`test-header: ${res.headers['test-header']}`)
})

ws.on('open', () => {
    console.log('upgrade event')
})

ws.on('error', (err) => {
    console.log(err)
})

When I add in upgrade res.writeHeader('test-header', 'header-value'), I get in client error:

Error: Unexpected server response: 200
    at ClientRequest.<anonymous> (/Users/user/Downloads/uws/node_modules/ws/lib/websocket.js:579:7)
    at ClientRequest.emit (events.js:315:20)
    at HTTPParser.parserOnIncomingClient [as onIncoming] (_http_client.js:639:27)
    at HTTPParser.parserOnHeadersComplete (_http_common.js:117:17)
    at Socket.socketOnData (_http_client.js:507:22)
    at Socket.emit (events.js:315:20)
    at addChunk (_stream_readable.js:302:12)
    at readableAddChunk (_stream_readable.js:278:9)
    at Socket.Readable.push (_stream_readable.js:217:10)
    at TCP.onStreamRead (internal/stream_base_commons.js:186:23)

If I use res.writeStatus("101 Switching Protocols\ntest-header: header-value") no problems

➜  node client.js
upgrade event
test-header: header-value
open event

I know it's not correct way of using writeStatus, I used just to show idea.

[ghost]

It should work if you do

res.writeStatus("101 Switching Protocols").writeHeader("asdasd", "asdasda") before calling upgrade, right?

[mirpo]

Yep, this res.writeStatus("101 Switching Protocols").writeHeader("test-header", "header-value") works fine.
Anyway It's just not clear that writeHeader changes/resets status to 200.

[ghost]

This could be documented better. What happens is, you have to call writeStatus before writeHeader but writeHeader will automatically call writeStatus(200 ok) otherwise.

Headers are written in a linear buffer, not to a tree, so order matters

[ghost]

This is now covered in the docs