From a48c4ef2b3a79aca2edaea240a7ed973ea4ab094 Mon Sep 17 00:00:00 2001
From: Neel Somani <neel@berkeley.edu>
Date: Mon, 27 Apr 2020 18:07:10 -0700
Subject: [PATCH] Implement PING/PONG for WebSockets to keep Heroku alive (#15)

---
 backend.py                  | 17 ++++++++++++++---
 constants.py                |  1 +
 src/components/Constants.js |  2 ++
 src/views/Game.js           | 16 +++++++++++++++-
 test_backend.py             | 11 ++++++++++-
 5 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/backend.py b/backend.py
index 031d1c4..2f1bc5e 100644
--- a/backend.py
+++ b/backend.py
@@ -174,6 +174,8 @@ def register_with_uuid(self, player_uuid):
         """
         Send the client the info for the specified `player_uuid`.
         The `player_uuid` must already be present in `self.players`.
+
+        Send the player names if they have updated.
         """
         player_n = self.users[player_uuid].player_n
         payload = {
@@ -191,7 +193,8 @@ def register_with_uuid(self, player_uuid):
         self.logger.info('Sent registration to user {}'.format(player_uuid))
         username = self.users[player_uuid].username
         if self.player_names.get(player_n) != username:
-            self.player_names[player_n] = username
+            if player_n != VISITOR_PLAYER_ID:
+                self.player_names[player_n] = username
             self._send_player_names()
 
         if self.current_players == self.n_players:
@@ -224,7 +227,8 @@ def _send(self, client, data):
                         self.logger.info(
                             'Player {} is disconnected from game {}'
                             .format(player_uuid, self.uuid))
-                        self.player_names[u.player_n] = u.username
+                        if u.player_n != VISITOR_PLAYER_ID:
+                            self.player_names[u.player_n] = u.username
                         self._send_player_names()
 
     def _send_all(self, message):
@@ -250,12 +254,19 @@ def _fill_bots(self, message):
                 util.BotClient(),
                 'Bot {}'.format(self.current_players + i))
 
+    def _ping_pong(self, payload):
+        user = self.users[payload['key']]
+        gevent.spawn(self._send, user.socket, {
+            'action': PING_PONG
+        })
+
     def handle_message(self, message):
         action_map = {
             CLAIM: self._claim,
             MOVE: self._move,
             SWITCH_TEAM: self._switch_team,
-            START_GAME: self._fill_bots
+            START_GAME: self._fill_bots,
+            PING_PONG: self._ping_pong
         }
         fn = action_map.get(message['action'])
         if fn is None:
diff --git a/constants.py b/constants.py
index 5094f99..901e155 100644
--- a/constants.py
+++ b/constants.py
@@ -10,3 +10,4 @@
 SWITCH_TEAM = 'switch_team'
 START_GAME = 'start_game'
 PLAYER_NAMES = 'player_names'
+PING_PONG = 'ping_pong'
diff --git a/src/components/Constants.js b/src/components/Constants.js
index ba99066..77da41c 100644
--- a/src/components/Constants.js
+++ b/src/components/Constants.js
@@ -35,3 +35,5 @@ export const UNCLAIMED = 'unclaimed';
 
 export const PLAYER_UUID = 'player_uuid';
 export const PLAYER_NAME = 'player_name';
+
+export const PING_PONG_INTERVAL_MS = 5000
diff --git a/src/views/Game.js b/src/views/Game.js
index bd28b7e..0b77c42 100644
--- a/src/views/Game.js
+++ b/src/views/Game.js
@@ -14,7 +14,8 @@ import {
   UNCLAIMED,
   SET_NAME_MAP,
   PLAYER_UUID,
-  PLAYER_NAME
+  PLAYER_NAME,
+  PING_PONG_INTERVAL_MS
 } from '../components/Constants';
 import './Game.css';
 
@@ -40,6 +41,17 @@ class Game extends Component {
     };
     const audioUrl = process.env.PUBLIC_URL + '/bell.mp3';
     this.bell = new Audio(audioUrl);
+    setInterval(this.pingPong.bind(this), PING_PONG_INTERVAL_MS)
+  }
+
+  pingPong() {
+    this.sendMessage({
+      'action': 'ping_pong',
+      'game_uuid': this.state.gameUuid,
+      'payload': {
+        'key': this.state.uuid
+      }
+    })
   }
 
   defaultNames() {
@@ -246,6 +258,8 @@ class Game extends Component {
       case 'player_names':
         this.playerNames(data.payload)
         break;
+      case 'ping_pong':
+        break;
       default:
         throw new Error('Unhandled action: ' + data.action);
     }
diff --git a/test_backend.py b/test_backend.py
index 72a71f0..0973ff5 100644
--- a/test_backend.py
+++ b/test_backend.py
@@ -104,11 +104,20 @@ def test_registration(api):
     assert len(c.messages) == 2
     msg = _action_from_messages(c.messages, REGISTER)
     assert msg['player_n'] != VISITOR_PLAYER_ID
-    assert 'player_uuid' in msg
+    player_uuid = msg['player_uuid']
+    game_uuid = msg['game_uuid']
     assert msg['time_limit'] == TIME_LIMIT
     assert msg['n_players'] == N_PLAYERS
     msg = _action_from_messages(c.messages, PLAYER_NAMES)
     assert msg['names']['0'] == MOCK_NAME
+    api.handle_message({
+        'action': PING_PONG,
+        'game_uuid': game_uuid,
+        'payload': {
+            'key': player_uuid
+        }
+    })
+    assert c.messages[-1]['action'] == PING_PONG
 
 
 def _action_from_messages(messages, action):