lib0/websocket.js

/* eslint-env browser */

/**
 * Tiny websocket connection handler.
 *
 * Implements exponential backoff reconnects, ping/pong, and a nice event system using [lib0/observable].
 *
 * @module websocket
 */

import { Observable } from './observable.js'
import * as time from './time.js'
import * as math from './math.js'

const reconnectTimeoutBase = 1200
const maxReconnectTimeout = 2500
// @todo - this should depend on awareness.outdatedTime
const messageReconnectTimeout = 30000

/**
 * @param {WebsocketClient} wsclient
 */
const setupWS = (wsclient) => {
  if (wsclient.shouldConnect && wsclient.ws === null) {
    const websocket = new WebSocket(wsclient.url)
    const binaryType = wsclient.binaryType
    /**
     * @type {any}
     */
    let pingTimeout = null
    if (binaryType) {
      websocket.binaryType = binaryType
    }
    wsclient.ws = websocket
    wsclient.connecting = true
    wsclient.connected = false
    websocket.onmessage = event => {
      wsclient.lastMessageReceived = time.getUnixTime()
      const data = event.data
      const message = typeof data === 'string' ? JSON.parse(data) : data
      if (message && message.type === 'pong') {
        clearTimeout(pingTimeout)
        pingTimeout = setTimeout(sendPing, messageReconnectTimeout / 2)
      }
      wsclient.emit('message', [message, wsclient])
    }
    /**
     * @param {any} error
     */
    const onclose = error => {
      if (wsclient.ws !== null) {
        wsclient.ws = null
        wsclient.connecting = false
        if (wsclient.connected) {
          wsclient.connected = false
          wsclient.emit('disconnect', [{ type: 'disconnect', error }, wsclient])
        } else {
          wsclient.unsuccessfulReconnects++
        }
        // Start with no reconnect timeout and increase timeout by
        // log10(wsUnsuccessfulReconnects).
        // The idea is to increase reconnect timeout slowly and have no reconnect
        // timeout at the beginning (log(1) = 0)
        setTimeout(setupWS, math.min(math.log10(wsclient.unsuccessfulReconnects + 1) * reconnectTimeoutBase, maxReconnectTimeout), wsclient)
      }
      clearTimeout(pingTimeout)
    }
    const sendPing = () => {
      if (wsclient.ws === websocket) {
        wsclient.send({
          type: 'ping'
        })
      }
    }
    websocket.onclose = () => onclose(null)
    websocket.onerror = error => onclose(error)
    websocket.onopen = () => {
      wsclient.lastMessageReceived = time.getUnixTime()
      wsclient.connecting = false
      wsclient.connected = true
      wsclient.unsuccessfulReconnects = 0
      wsclient.emit('connect', [{ type: 'connect' }, wsclient])
      // set ping
      pingTimeout = setTimeout(sendPing, messageReconnectTimeout / 2)
    }
  }
}

/**
 * @extends Observable<string>
 */
export class WebsocketClient extends Observable {
  /**
   * @param {string} url
   * @param {object} [opts]
   * @param {'arraybuffer' | 'blob' | null} [opts.binaryType] Set `ws.binaryType`
   */
  constructor (url, { binaryType } = {}) {
    super()
    this.url = url
    /**
     * @type {WebSocket?}
     */
    this.ws = null
    this.binaryType = binaryType || null
    this.connected = false
    this.connecting = false
    this.unsuccessfulReconnects = 0
    this.lastMessageReceived = 0
    /**
     * Whether to connect to other peers or not
     * @type {boolean}
     */
    this.shouldConnect = true
    this._checkInterval = setInterval(() => {
      if (this.connected && messageReconnectTimeout < time.getUnixTime() - this.lastMessageReceived) {
        // no message received in a long time - not even your own awareness
        // updates (which are updated every 15 seconds)
        /** @type {WebSocket} */ (this.ws).close()
      }
    }, messageReconnectTimeout / 2)
    setupWS(this)
  }

  /**
   * @param {any} message
   */
  send (message) {
    if (this.ws) {
      this.ws.send(JSON.stringify(message))
    }
  }

  destroy () {
    clearInterval(this._checkInterval)
    this.disconnect()
    super.destroy()
  }

  disconnect () {
    this.shouldConnect = false
    if (this.ws !== null) {
      this.ws.close()
    }
  }

  connect () {
    this.shouldConnect = true
    if (!this.connected && this.ws === null) {
      setupWS(this)
    }
  }
}