The screen websocket now sends ping messages every now and then, so that it won't get caught by nginx's proxy_read_timeout if the screen is off or not moving. Previously, nginx may have decided to kill the connection after a period of no activity.

lib/cli/device/index.js

@@ -85,6 +85,12 @@ module.exports.builder = function(yargs) {
     , type: 'number'
     , default: process.env.SCREEN_JPEG_QUALITY || 80
     })
+    .option('screen-ping-interval', {
+      describe: 'The interval at which to send ping messages to keep the ' +
+        'screen WebSocket alive.'
+    , type: 'number'
+    , default: 30000
+    })
     .option('screen-port', {
       describe: 'Port allocated to the screen WebSocket.'
     , type: 'number'
@@ -129,9 +135,10 @@ module.exports.handler = function(argv) {
   , storageUrl: argv.storageUrl
   , adbHost: argv.adbHost
   , adbPort: argv.adbPort
-  , screenWsUrlPattern: argv.screenWsUrlPattern
   , screenJpegQuality: argv.screenJpegQuality
+  , screenPingInterval: argv.screenPingInterval
   , screenPort: argv.screenPort
+  , screenWsUrlPattern: argv.screenWsUrlPattern
   , connectUrlPattern: argv.connectUrlPattern
   , connectPort: argv.connectPort
   , vncPort: argv.vncPort

lib/cli/provider/index.js

@@ -104,6 +104,12 @@ module.exports.builder = function(yargs) {
     , type: 'number'
     , default: process.env.SCREEN_JPEG_QUALITY || 80
     })
+    .option('screen-ping-interval', {
+      describe: 'The interval at which to send ping messages to keep the ' +
+        'screen WebSocket alive.'
+    , type: 'number'
+    , default: 30000
+    })
     .option('screen-ws-url-pattern', {
       describe: 'The URL pattern to use for the screen WebSocket.'
     , type: 'string'
@@ -163,8 +169,9 @@ module.exports.handler = function(argv) {
       , '--storage-url', argv.storageUrl
       , '--adb-host', argv.adbHost
       , '--adb-port', argv.adbPort
-      , '--screen-ws-url-pattern', argv.screenWsUrlPattern
       , '--screen-jpeg-quality', argv.screenJpegQuality
+      , '--screen-ping-interval', argv.screenPingInterval
+      , '--screen-ws-url-pattern', argv.screenWsUrlPattern
       , '--connect-url-pattern', argv.connectUrlPattern
       , '--heartbeat-interval', argv.heartbeatInterval
       , '--boot-complete-timeout', argv.bootCompleteTimeout

lib/units/device/plugins/screen/stream.js

@@ -502,22 +502,18 @@ module.exports = syrup.serial()
 
         wss.on('connection', function(ws) {
           var id = uuid.v4()
+          var pingTimer
 
-          function wsStartNotifier() {
+          function send(message, options) {
             return new Promise(function(resolve, reject) {
-              var message = util.format(
-                'start %s'
-              , JSON.stringify(frameProducer.banner)
-              )
-
               switch (ws.readyState) {
               case WebSocket.OPENING:
                 // This should never happen.
-                log.warn('Unable to send banner to OPENING client "%s"', id)
+                log.warn('Unable to send to OPENING client "%s"', id)
                 break
               case WebSocket.OPEN:
                 // This is what SHOULD happen.
-                ws.send(message, function(err) {
+                ws.send(message, options, function(err) {
                   return err ? reject(err) : resolve()
                 })
                 break
@@ -527,41 +523,37 @@ module.exports = syrup.serial()
                 break
               case WebSocket.CLOSED:
                 // This should never happen.
-                log.warn('Unable to send banner to CLOSED client "%s"', id)
+                log.warn('Unable to send to CLOSED client "%s"', id)
+                clearInterval(pingTimer)
                 broadcastSet.remove(id)
                 break
               }
             })
           }
 
+          function wsStartNotifier() {
+            return send(util.format(
+              'start %s'
+            , JSON.stringify(frameProducer.banner)
+            ))
+          }
+
+          function wsPingNotifier() {
+            return send('ping')
+          }
+
           function wsFrameNotifier(frame) {
-            return new Promise(function(resolve, reject) {
+            return send(frame, {
-              switch (ws.readyState) {
-              case WebSocket.OPENING:
-                // This should never happen.
-                return reject(new Error(util.format(
-                  'Unable to send frame to OPENING client "%s"', id)))
-              case WebSocket.OPEN:
-                // This is what SHOULD happen.
-                ws.send(frame, {
               binary: true
-                }, function(err) {
-                  return err ? reject(err) : resolve()
-                })
-                return
-              case WebSocket.CLOSING:
-                // Ok, a 'close' event should remove the client from the set
-                // soon.
-                return
-              case WebSocket.CLOSED:
-                // This should never happen.
-                broadcastSet.remove(id)
-                return reject(new Error(util.format(
-                  'Unable to send frame to CLOSED client "%s"', id)))
-              }
             })
           }
 
+          // Sending a ping message every now and then makes sure that
+          // reverse proxies like nginx don't time out the connection [1].
+          //
+          // [1] http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_read_timeout
+          pingTimer = setInterval(wsPingNotifier, options.screenPingInterval)
+
           ws.on('message', function(data) {
             var match = /^(on|off|(size) ([0-9]+)x([0-9]+))$/.exec(data)
             if (match) {
@@ -574,6 +566,7 @@ module.exports = syrup.serial()
                 break
               case 'off':
                 broadcastSet.remove(id)
+                // Keep pinging even when the screen is off.
                 break
               case 'size':
                 frameProducer.updateProjection(
@@ -584,6 +577,7 @@ module.exports = syrup.serial()
           })
 
           ws.on('close', function() {
+            clearInterval(pingTimer)
             broadcastSet.remove(id)
           })
         })