Allow passing in a custom `createConnection` function

[connor4312]

• I've searched for any related issues and avoided creating a duplicate issue.

Description

We have a kind of exotic use case where we want to instantiate a websocket off an existing stream that's not from an HTTP or unix socket source. Currently the createConnection method is hardcoded to either create a TLS or standard net connection:

ws/lib/websocket.js

Line 654 in f871195

opts.createConnection = isSecure ? tlsConnect : netConnect;

I suggest allowing a custom createConnection function to be passed in the websocket options and, if present, it should take precedence over the existing default logic.

I'm happy to put together a PR for this if it's something you'd accept 🙂

ws version

8.2.2

Node.js Version

v16.6.1

System

System:
OS: Windows 10 10.0.19043
CPU: (24) x64 AMD Ryzen 9 5900X 12-Core Processor
Memory: 23.22 GB / 63.89 GB

Expected result

N/A

Actual result

N/A

Attachments

No response

[lpinca]

You can use the agent option and provide a custom Agent to do that.

import { Agent } from 'https';
import { WebSocket } from 'ws';
import { connect } from 'tls';

const agent = new Agent();

agent.createConnection = function (options) {
  return connect(options);
};

const ws = new WebSocket('wss://ws.ifelse.io', { agent });

ws.on('open', function () {
  console.log('open');
});

[connor4312]

Ah, cool, I didn't realize that that was also an option on the agent. I'll try that out and close this issue if it works.

[connor4312]

It turns out that it's not enough to just return the stream, it also needs to be wrapped to look at least a bit like a network socket. Here's the conversion function, with TypeScript typings, in case anyone else stumbles upon the need for this:

import { Socket } from 'net';
import { Duplex } from 'stream';

export const makeNetSocketFromDuplexStream = (stream: Duplex) => {
	const cast = stream as Socket;
	const patched: { [K in keyof Omit<Socket, keyof Duplex>]: Socket[K] } = {
		bufferSize: 0,
		bytesRead: 0,
		bytesWritten: 0,
		connecting: false,
		localAddress: '127.0.0.1',
		localPort: 1,
		remoteAddress: '127.0.0.1',
		remoteFamily: 'tcp',
		remotePort: 1,
		address: () => ({ address: '127.0.0.1', family: 'tcp', port: 1 }),
		unref: () => cast,
		ref: () => cast,
		connect: (_port: unknown, _host?: unknown, connectionListener?: () => void) => {
			if (connectionListener) {
				setImmediate(connectionListener);
			}
			return cast;
		},
		setKeepAlive: () => cast,
		setNoDelay: () => cast,
		setTimeout: (_timeout: number, callback?: () => void) => {
			callback?.();
			return cast;
		},
	};

	return Object.assign(stream, patched) as Socket;
};

[lpinca]

If the opening handshake can be skipped, then a generic duplex stream can be used by calling the "private" WebSocket#setSocket() method.

function noop() {}

const duplex = new Duplex({
  read() {},
  write() {}
});

duplex.setTimeout = noop;
duplex.setNoDelay = noop;

const ws = new WebSocket(null);

ws.setSocket(duplex, Buffer.alloc(0));

// ...

Anyway this is not recommended as it makes use of a private API.