xTeVe/ts/network.ts

// Websocket transport between the web UI and xTeVe.
//
// One socket stays open for the life of the page. Requests are queued and
// sent one at a time; each carries an id that the server echoes back, and
// the response is matched on it (or, for older servers that close after a
// single reply, to the oldest in-flight request). Connection loss triggers
// a reconnect with exponential backoff, and queued requests survive it.

interface PendingRequest {
  id: string
  payload: Object
  resolve: (response: any) => void
  reject: (err: Error) => void
  timer: number
  sent: boolean
}

class WSClient {
  private socket: WebSocket = null
  private queue: PendingRequest[] = []
  private inFlight: PendingRequest = null
  private nextID: number = 1
  private reconnectDelay: number = 500
  private reconnectTimer: number = 0
  private closedByUs: boolean = false

  readonly requestTimeoutMs: number = 12000

  private url(): string {
    var protocol = window.location.protocol == "https:" ? "wss://" : "ws://"
    var host = window.location.host
    if (host == undefined || host.length < 1) {
      host = window.location.hostname
    }
    return protocol + host + "/data/"
  }

  // send queues a command and resolves with the parsed response.
  send(payload: Object): Promise<any> {
    var client = this
    return new Promise(function(resolve, reject) {
      var req: PendingRequest = {
        id: String(client.nextID++),
        payload: payload,
        resolve: resolve,
        reject: reject,
        timer: 0,
        sent: false
      }
      client.queue.push(req)
      client.pump()
    })
  }

  // hasQueued reports whether a command of this kind is already waiting.
  hasQueued(cmd: string): boolean {
    if (this.inFlight != null && this.inFlight.payload["cmd"] == cmd) {
      return true
    }
    for (var i = 0; i < this.queue.length; i++) {
      if (this.queue[i].payload["cmd"] == cmd) {
        return true
      }
    }
    return false
  }

  private connect(): void {
    if (this.socket != null && (this.socket.readyState == WebSocket.OPEN || this.socket.readyState == WebSocket.CONNECTING)) {
      return
    }

    var client = this
    var socket = new WebSocket(this.url())
    this.socket = socket

    socket.onopen = function() {
      WS_AVAILABLE = true
      client.reconnectDelay = 500
      client.pump()
    }

    socket.onmessage = function(e: MessageEvent) {
      client.handleMessage(e.data)
    }

    socket.onerror = function() {
      // onclose follows; nothing to do here.
    }

    socket.onclose = function() {
      if (client.socket == socket) {
        client.socket = null
      }
      // An in-flight request that never got its answer goes back to the
      // front of the queue and is retried on the next connection.
      if (client.inFlight != null) {
        var req = client.inFlight
        client.inFlight = null
        req.sent = false
        client.queue.unshift(req)
      }
      client.scheduleReconnect()
    }
  }

  private scheduleReconnect(): void {
    if (this.closedByUs || this.reconnectTimer != 0) {
      return
    }
    if (this.queue.length == 0) {
      // Idle: reconnect lazily on the next request.
      return
    }
    var client = this
    this.reconnectTimer = window.setTimeout(function() {
      client.reconnectTimer = 0
      client.connect()
    }, this.reconnectDelay)
    this.reconnectDelay = Math.min(this.reconnectDelay * 2, 10000)
  }

  // pump sends the next queued request if the socket is open and idle.
  private pump(): void {
    if (this.inFlight != null || this.queue.length == 0) {
      return
    }
    if (this.socket == null || this.socket.readyState != WebSocket.OPEN) {
      this.connect()
      return
    }

    var req = this.queue.shift()
    this.inFlight = req
    req.sent = true
    req.payload["id"] = req.id

    var client = this
    req.timer = window.setTimeout(function() {
      if (client.inFlight == req) {
        client.inFlight = null
        req.reject(new Error("timeout"))
        // A socket that stopped answering is not trusted any more.
        client.resetSocket()
        client.pump()
      }
    }, this.requestTimeoutMs)

    try {
      this.socket.send(JSON.stringify(req.payload))
    } catch (err) {
      window.clearTimeout(req.timer)
      this.inFlight = null
      req.sent = false
      this.queue.unshift(req)
      this.resetSocket()
    }
  }

  private resetSocket(): void {
    var socket = this.socket
    this.socket = null
    if (socket != null) {
      socket.onclose = null
      try { socket.close() } catch (err) { /* ignore */ }
    }
    this.scheduleReconnect()
  }

  private handleMessage(raw: string): void {
    var response: any
    try {
      response = JSON.parse(raw)
    } catch (err) {
      return
    }

    var req = this.inFlight
    if (req == null) {
      return
    }
    // Servers that echo the id let us drop stray late answers.
    if (response.hasOwnProperty("id") && response["id"] != req.id) {
      return
    }

    window.clearTimeout(req.timer)
    this.inFlight = null
    req.resolve(response)
    this.pump()
  }
}

var WS = new WSClient()

class Server {
  cmd: string

  constructor(cmd: string) {
    this.cmd = cmd
  }

  request(data: Object): any {

    var isLogUpdate: boolean = this.cmd == "updateLog"

    // Log polling must never pile up behind a stalled connection.
    if (isLogUpdate && WS.hasQueued("updateLog")) {
      return
    }

    if (!isLogUpdate) {
      showElement("loading", true)
      UNDO = new Object()
      setConnectionState("busy")
    }

    data["cmd"] = this.cmd
    var requestCmd: string = this.cmd

    WS.send(data).then(function(response) {

      WS_FAILURE_COUNT = 0
      if (!isLogUpdate) {
        showElement("loading", false)
      }
      setConnectionState("online")

      if (response["status"] == false) {
        setConnectionState("offline")
        alert(response["err"])
        if (response.hasOwnProperty("reload")) {
          location.reload()
        }
        return
      }

      if (response.hasOwnProperty("logoURL")) {
        var div = (document.getElementById("channel-icon") as HTMLInputElement)
        div.value = response["logoURL"]
        div.className = "changed"
        return
      }

      switch (requestCmd) {
        case "updateLog":
          SERVER["log"] = response["log"]
          if (document.getElementById("content_log")) {
            showLogs(false)
          }
          return

        default:
          SERVER = response
          break
      }

      if (response.hasOwnProperty("openMenu")) {
        var menu = document.getElementById(response["openMenu"])
        menu.click()
        showElement("popup", false)
      }

      if (response.hasOwnProperty("openLink")) {
        window.location = response["openLink"]
      }

      if (response.hasOwnProperty("alert")) {
        alert(response["alert"])
      }

      if (response.hasOwnProperty("reload")) {
        location.reload()
      }

      if (response.hasOwnProperty("wizard")) {
        createLayout()
        configurationWizard[response["wizard"]].createWizard()
        return
      }

      createLayout()

    }, function(err) {

      WS_FAILURE_COUNT++
      if (!isLogUpdate) {
        showElement("loading", false)
      }

      var state: string = "offline"
      if (isLogUpdate && WS_FAILURE_COUNT < 2) {
        state = "idle"
      }
      setConnectionState(state)

      if (WS_AVAILABLE == false && !isLogUpdate && requestCmd != "getServerConfig") {
        alert("No websocket connection to xTeVe could be established. Check your network configuration.")
      }

    })
  }
}

var WS_FAILURE_COUNT: number = 0