node WebSocket server

README.md

WebSocket server in node

server.js

import { createServer } from 'node:http'
import { makeHandshake, readMessage, generateMessage } from './wss.js'

const server = createServer(async (req, res) => {
	//
})

server.on('upgrade', (req, socket) => {
	socket.write(makeHandshake(req))
	const { host } = new URL(req.headers.origin)
	console.log(`connected from`, host)
	socket.on('readable', () => {
		console.log('message', readMessage((n) => socket.read(n)))
	})
	const send = (s) => socket.write(generateMessage(s))
})

wss.js

import { createHash } from 'node:crypto'

/** @import { IncomingMessage } from 'node:http' */

const WS_MAGIC = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11'
const WS_HEAD = [
	'HTTP/1.1 101 Switching Protocols',
	'Upgrade: websocket',
	'Connection: Upgrade',
]

const MAX_MSG_LEN = 2 ** 16 - 1

const encoder = new TextEncoder()
const decoder = new TextDecoder()

/** @param {IncomingMessage} req */
export function makeHandshake(req) {
	const key = `${req.headers['sec-websocket-key']}${WS_MAGIC}`
	const dg = createHash('sha1').update(key).digest('base64')
	return [...WS_HEAD, `Sec-WebSocket-Accept: ${dg}`, '', ''].join('\r\n')
}

/** @param {string} message */
export function generateMessage(message) {
	const msg = encoder.encode(message)
	const len = msg.length
	if (len > MAX_MSG_LEN) throw new Error(`too long (${len})`)

	const head = len < 126 ? [0x81, len] : [0x81, 0x7e, len >> 8, len & 0xff]
	const out = new Uint8Array(head.length + len)
	out.set(head)
	out.set(msg, head.length)
	return out
}

/** @param {(n: number) => Buffer} read */
export function readMessage(read) {
	read(1)
	const lenB = read(1)[0] - 128
	const msgLen =
		lenB < 126
			? lenB
			: lenB === 126
			? read(2).readUint16BE(0)
			: Number(read(8).readBigUInt64BE(0))

	const mask = read(4)
	const msg = read(msgLen)
	if (!msg) return ''
	const encoded = msg.map((v, i) => v ^ mask[i % 4])
	return decoder.decode(encoded)
}