feat: reconnect websocket on disconnection

This is a port of this PR: #2235

(But it was easier to copy-paste than rebase, given the split of umap.js
and co.)

Co-authored-by: Alexis Métaireau <alexis@notmyidea.org>
Co-authored-by: David Larlet <david@larlet.fr>

umap/static/umap/css/bar.css

@@ -32,6 +32,10 @@
     background-color: var(--color-lightCyan);
     color: var(--color-dark);
 }
+.dark .off.connected-peers {
+    background-color: var(--color-lightGray);
+    color: var(--color-darkGray);
+}
 
 .leaflet-container .edit-cancel,
 .leaflet-container .edit-disable,

umap/static/umap/js/modules/data/features.js

@@ -20,7 +20,7 @@ import loadPopup from '../rendering/popup.js'
 class Feature {
   constructor(umap, datalayer, geojson = {}, id = null) {
     this._umap = umap
-    this.sync = umap.sync_engine.proxy(this)
+    this.sync = umap.syncEngine.proxy(this)
     this._marked_for_deletion = false
     this._isDirty = false
     this._ui = null

umap/static/umap/js/modules/data/layer.js

@@ -41,7 +41,7 @@ export class DataLayer extends ServerStored {
   constructor(umap, leafletMap, data = {}) {
     super()
     this._umap = umap
-    this.sync = umap.sync_engine.proxy(this)
+    this.sync = umap.syncEngine.proxy(this)
     this._index = Array()
     this._features = {}
     this._geojson = null

umap/static/umap/js/modules/sync/engine.js

@@ -3,6 +3,12 @@ import { HybridLogicalClock } from './hlc.js'
 import { DataLayerUpdater, FeatureUpdater, MapUpdater } from './updaters.js'
 import { WebSocketTransport } from './websocket.js'
 
+// Start reconnecting after 2 seconds, then double the delay each time
+// maxing out at 32 seconds.
+const RECONNECT_DELAY = 2000
+const RECONNECT_DELAY_FACTOR = 2
+const MAX_RECONNECT_DELAY = 32000
+
 /**
  * The syncEngine exposes an API to sync messages between peers over the network.
  *
@@ -42,32 +48,65 @@ import { WebSocketTransport } from './websocket.js'
  * ```
  */
 export class SyncEngine {
-  constructor(map) {
+  constructor(umap) {
+    this._umap = umap
     this.updaters = {
-      map: new MapUpdater(map),
-      feature: new FeatureUpdater(map),
-      datalayer: new DataLayerUpdater(map),
+      map: new MapUpdater(umap),
+      feature: new FeatureUpdater(umap),
+      datalayer: new DataLayerUpdater(umap),
     }
     this.transport = undefined
     this._operations = new Operations()
+
+    this._reconnectTimeout = null
+    this._reconnectDelay = RECONNECT_DELAY
+    this.websocketConnected = false
   }
 
-  async authenticate(tokenURI, webSocketURI, server) {
-    const [response, _, error] = await server.get(tokenURI)
+  async authenticate() {
+    const websocketTokenURI = this._umap.urls.get('map_websocket_auth_token', {
+      map_id: this._umap.id,
+    })
+
+    const [response, _, error] = await this._umap.server.get(websocketTokenURI)
     if (!error) {
-      this.start(webSocketURI, response.token)
+      this.start(response.token)
     }
   }
 
-  start(webSocketURI, authToken) {
-    this.transport = new WebSocketTransport(webSocketURI, authToken, this)
+  start(authToken) {
+    this.transport = new WebSocketTransport(
+      this._umap.properties.websocketURI,
+      authToken,
+      this
+    )
   }
 
   stop() {
-    if (this.transport) this.transport.close()
+    if (this.transport) {
+      this.transport.close()
+    }
     this.transport = undefined
   }
 
+  onConnection() {
+    this._reconnectTimeout = null
+    this._reconnectDelay = RECONNECT_DELAY
+    this.websocketConnected = true
+    this.updaters.map.update({ key: 'numberOfConnectedPeers' })
+  }
+
+  reconnect() {
+    this.websocketConnected = false
+    this.updaters.map.update({ key: 'numberOfConnectedPeers' })
+
+    this._reconnectTimeout = setTimeout(() => {
+      if (this._reconnectDelay < MAX_RECONNECT_DELAY) {
+        this._reconnectDelay = this._reconnectDelay * RECONNECT_DELAY_FACTOR
+      }
+      this.authenticate()
+    }, this._reconnectDelay)
+  }
   upsert(subject, metadata, value) {
     this._send({ verb: 'upsert', subject, metadata, value })
   }

umap/static/umap/js/modules/sync/websocket.js

@@ -1,15 +1,59 @@
+const PONG_TIMEOUT = 5000
+const PING_INTERVAL = 30000
+const FIRST_CONNECTION_TIMEOUT = 2000
+
 export class WebSocketTransport {
   constructor(webSocketURI, authToken, messagesReceiver) {
+    this.receiver = messagesReceiver
+    this.closeRequested = false
+
     this.websocket = new WebSocket(webSocketURI)
+
     this.websocket.onopen = () => {
       this.send('JoinRequest', { token: authToken })
+      this.receiver.onConnection()
     }
     this.websocket.addEventListener('message', this.onMessage.bind(this))
-    this.receiver = messagesReceiver
+    this.websocket.onclose = () => {
+      console.log('websocket closed')
+      if (!this.closeRequested) {
+        console.log('Not requested, reconnecting...')
+        this.receiver.reconnect()
+      }
+    }
+
+    this.ensureOpen = setInterval(() => {
+      if (this.websocket.readyState !== WebSocket.OPEN) {
+        this.websocket.close()
+        clearInterval(this.ensureOpen)
+      }
+    }, FIRST_CONNECTION_TIMEOUT)
+
+    // To ensure the connection is still alive, we send ping and expect pong back.
+    // Websocket provides a `ping` method to keep the connection alive, but it's
+    // unfortunately not possible to access it from the WebSocket object.
+    // See https://making.close.com/posts/reliable-websockets/ for more details.
+    this.pingInterval = setInterval(() => {
+      if (this.websocket.readyState === WebSocket.OPEN) {
+        this.websocket.send('ping')
+        this.pongReceived = false
+        setTimeout(() => {
+          if (!this.pongReceived) {
+            console.warn('No pong received, reconnecting...')
+            this.websocket.close()
+            clearInterval(this.pingInterval)
+          }
+        }, PONG_TIMEOUT)
+      }
+    }, PING_INTERVAL)
   }
 
   onMessage(wsMessage) {
-    this.receiver.receive(JSON.parse(wsMessage.data))
+    if (wsMessage.data === 'pong') {
+      this.pongReceived = true
+    } else {
+      this.receiver.receive(JSON.parse(wsMessage.data))
+    }
   }
 
   send(kind, payload) {
@@ -20,6 +64,7 @@ export class WebSocketTransport {
   }
 
   close() {
+    this.closeRequested = true
     this.websocket.close()
   }
 }

umap/static/umap/js/modules/umap.js

@@ -61,8 +61,6 @@ export default class Umap extends ServerStored {
     )
     this.searchParams = new URLSearchParams(window.location.search)
 
-    this.sync_engine = new SyncEngine(this)
-    this.sync = this.sync_engine.proxy(this)
     // Locale name (pt_PT, en_US…)
     // To be used for Django localization
     if (geojson.properties.locale) setLocale(geojson.properties.locale)
@@ -124,6 +122,9 @@ export default class Umap extends ServerStored {
     this.share = new Share(this)
     this.rules = new Rules(this)
 
+    this.syncEngine = new SyncEngine(this)
+    this.sync = this.syncEngine.proxy(this)
+
     if (this.hasEditMode()) {
       this.editPanel = new EditPanel(this, this._leafletMap)
       this.fullPanel = new FullPanel(this, this._leafletMap)
@@ -1257,18 +1258,13 @@ export default class Umap extends ServerStored {
   }
 
   async initSyncEngine() {
+    // this.properties.websocketEnabled is set by the server admin
     if (this.properties.websocketEnabled === false) return
+    // this.properties.syncEnabled is set by the user in the map settings
     if (this.properties.syncEnabled !== true) {
       this.sync.stop()
     } else {
-      const ws_token_uri = this.urls.get('map_websocket_auth_token', {
-        map_id: this.id,
-      })
-      await this.sync.authenticate(
-        ws_token_uri,
-        this.properties.websocketURI,
-        this.server
-      )
+      await this.sync.authenticate()
     }
   }
 
@@ -1343,7 +1339,12 @@ export default class Umap extends ServerStored {
       },
       numberOfConnectedPeers: () => {
         Utils.eachElement('.connected-peers span', (el) => {
-          el.textContent = this.sync.getNumberOfConnectedPeers()
+          if (this.sync.websocketConnected) {
+            el.textContent = this.sync.getNumberOfConnectedPeers()
+          } else {
+            el.textContent = translate('Disconnected')
+          }
+          el.parentElement.classList.toggle('off', !this.sync.websocketConnected)
         })
       },
     }

umap/static/umap/unittests/sync.js

@@ -8,8 +8,11 @@ import { MapUpdater } from '../js/modules/sync/updaters.js'
 import { SyncEngine, Operations } from '../js/modules/sync/engine.js'
 
 describe('SyncEngine', () => {
+  const websocketTokenURI = 'http://localhost:8000/api/v1/maps/1/websocket_auth_token/'
+  const websocketURI = 'ws://localhost:8000/ws/maps/1/'
+
   it('should initialize methods even before start', () => {
-    const engine = new SyncEngine({})
+    const engine = new SyncEngine({}, websocketTokenURI, websocketURI)
     engine.upsert()
     engine.update()
     engine.delete()

umap/websocket_server.py

@@ -126,6 +126,10 @@ async def join_and_listen(
 
     try:
         async for raw_message in websocket:
+            if raw_message == "ping":
+                await websocket.send("pong")
+                continue
+
             # recompute the peers list at the time of message-sending.
             # as doing so beforehand would miss new connections
             other_peers = connections.get_other_peers(websocket)
@@ -192,4 +196,7 @@ def run(host: str, port: int):
             logging.debug(f"Waiting for connections on {host}:{port}")
             await asyncio.Future()  # run forever
 
-    asyncio.run(_serve())
+    try:
+        asyncio.run(_serve())
+    except KeyboardInterrupt:
+        print("Closing WebSocket server")