Add WebSocket heartbeat (#16)

* add heartbeat.

* rename.

src/component/internal/websocket.ts

@@ -1,5 +1,5 @@
 import EventEmitter from 'eventemitter3'
-import { SYSTEM_LOGS } from '../types/events'
+import { SYSTEM_HEARTBEAT, SYSTEM_LOGS } from '../types/events'
 import { Logger } from '../utils/logger'
 
 export interface NekoWebSocketEvents {
@@ -8,7 +8,13 @@ export interface NekoWebSocketEvents {
   message: (event: string, payload: any) => void
 }
 
-const statusCodeMap = {
+// how long can connection be idle before closing
+const STALE_TIMEOUT_MS = 12_500 // 12.5 seconds
+
+// how often should stale check be evaluated
+const STALE_INTERVAL_MS = 7_000 // 7 seconds
+
+const STATUS_CODE_MAP = {
   1000: 'Normal Closure',
   1001: 'Going Away',
   1002: 'Protocol Error',
@@ -29,6 +35,8 @@ const statusCodeMap = {
 
 export class NekoWebSocket extends EventEmitter<NekoWebSocketEvents> {
   private _ws?: WebSocket
+  private _stale_interval?: number
+  private _last_received?: Date
 
   // eslint-disable-next-line
   constructor(
@@ -67,8 +75,8 @@ export class NekoWebSocket extends EventEmitter<NekoWebSocketEvents> {
     this._ws.onclose = (e: CloseEvent) => {
       let reason = 'close'
 
-      if (e.code in statusCodeMap) {
+      if (e.code in STATUS_CODE_MAP) {
-        reason = statusCodeMap[e.code]
+        reason = STATUS_CODE_MAP[e.code]
       }
 
       this.onDisconnected(reason)
@@ -78,6 +86,13 @@ export class NekoWebSocket extends EventEmitter<NekoWebSocketEvents> {
   }
 
   public disconnect(reason: string) {
+    this._last_received = undefined
+
+    if (this._stale_interval) {
+      window.clearInterval(this._stale_interval)
+      this._stale_interval = undefined
+    }
+
     if (typeof this._ws !== 'undefined') {
       // unmount all events
       this._ws.onopen = () => {}
@@ -106,6 +121,10 @@ export class NekoWebSocket extends EventEmitter<NekoWebSocketEvents> {
   private onMessage(e: MessageEvent) {
     const { event, payload } = JSON.parse(e.data)
 
+    this._last_received = new Date()
+    // heartbeat only updates last_received
+    if (event == SYSTEM_HEARTBEAT) return
+
     this._log.debug(`received websocket event`, { event, payload })
     this.emit('message', event, payload)
   }
@@ -116,6 +135,10 @@ export class NekoWebSocket extends EventEmitter<NekoWebSocketEvents> {
       return
     }
 
+    // periodically check if connection is stale
+    if (this._stale_interval) window.clearInterval(this._stale_interval)
+    this._stale_interval = window.setInterval(this.onStaleCheck.bind(this), STALE_INTERVAL_MS)
+
     this._log.info(`connected`)
     this.emit('connected')
   }
@@ -126,4 +149,16 @@ export class NekoWebSocket extends EventEmitter<NekoWebSocketEvents> {
     this._log.info(`disconnected`, { reason })
     this.emit('disconnected', new Error(`connection ${reason}`))
   }
+
+  private onStaleCheck() {
+    if (!this._last_received) return
+
+    // if we haven't received a message in specified time,
+    // assume the connection is dead
+    const diff = new Date().getTime() - this._last_received.getTime()
+    if (diff < STALE_TIMEOUT_MS) return
+
+    this._log.warn(`websocket connection is stale, disconnecting`)
+    this.onDisconnected('stale')
+  }
 }

src/component/types/events.ts

@@ -3,6 +3,7 @@ export const SYSTEM_ADMIN = 'system/admin'
 export const SYSTEM_SETTINGS = 'system/settings'
 export const SYSTEM_LOGS = 'system/logs'
 export const SYSTEM_DISCONNECT = 'system/disconnect'
+export const SYSTEM_HEARTBEAT = 'system/heartbeat'
 
 export const SIGNAL_REQUEST = 'signal/request'
 export const SIGNAL_RESTART = 'signal/restart'