From: Carl Worth <cworth@cworth.org>
Date: Sun, 3 May 2020 22:05:23 +0000 (-0700)
Subject: Add an API for server-sent events at `/events`
X-Git-Url: https://git.cworth.org/git?a=commitdiff_plain;h=a7af56552e2a36e0a069f0aec5c1a9e9b0407e6e;p=empires-server

Add an API for server-sent events at `/events`

So far there are two event types being sent here:

  players: An event reporting the complete list of registered players

  player-register: An event reporting a new player has registered

I'm not 100% sure these are all formatted correctly yet. I'll need to
implement a client to listen to these events and then check that.
---

diff --git a/server.js b/server.js
index f0bc78e..bbc5d8a 100644
--- a/server.js
+++ b/server.js
@@ -9,15 +9,23 @@ class Game {
   constructor() {
     this._players = [];
     this.next_player_id = 1;
+    this.clients = [];
+    this.next_client_id = 1;
   }
 
   add_player(name, character) {
-    this._players.push({id: this.next_player_id,
+    const new_player = {id: this.next_player_id,
                        name: name,
                        character: character,
                        captures: [],
-                      })
+                       };
+    this._players.push(new_player);
     this.next_player_id++;
+    /* The syntax here is using an anonymous function to create a new
+      object from new_player with just the subset of fields that we
+      want. */
+    const player_string = JSON.stringify((({id, name}) => ({id, name}))(new_player));
+    this.broadcast("player-register", player_string);
   }
 
   remove_player(id) {
@@ -60,6 +68,24 @@ class Game {
   get players() {
     return this._players.map(player => ({id: player.id, name: player.name }));
   }
+
+  add_client(response) {
+    const id = this.next_client_id;
+    this.clients.push({id: id,
+                       response: response});
+    this.next_client_id++;
+
+    return id;
+  }
+
+  remove_client(id) {
+    this.clients = this.clients.filter(client => client.id !== id);
+  }
+
+  /* Send an event to all clients */
+  broadcast(type, data) {
+    this.clients.forEach(client => client.response.write(`event: ${type}\ndata: ${data}\n\n`));
+  }
 }
 
 const game = new Game();
@@ -67,6 +93,32 @@ const game = new Game();
 app.use(body_parser.urlencoded({ extended: false }));
 app.use(body_parser.json());
 
+function handle_events(request, response) {
+  /* These headers will keep the connection open so we can stream events. */
+  const headers = {
+    "Content-type": "text/event-stream",
+    "Connection": "keep-alive",
+    "Cache-Control": "no-cache"
+  };
+  response.writeHead(200, headers);
+
+  /* Now that a client has connected, first we need to stream all of
+   * the existing players (if any). */
+  if (game._players.length > 0) {
+    const players_json = JSON.stringify(game.players);
+    const players_data = `event: players\ndata: ${players_json}\n\n`;
+    response.write(players_data);
+  }
+
+  /* Add this new client to our list of clients. */
+  const id = game.add_client(response);
+
+  /* And queue up cleanup to be tirggered on client close. */
+  request.on('close', () => {
+    game.remove_client(id);
+  });
+}
+
 app.get('/', (request, response) => {
   response.send('Hello World!');
 });
@@ -113,6 +165,8 @@ app.get('/players', (request, response) => {
   response.send(game.players);
 });
 
+app.get('/events', handle_events);
+
 app.listen(3000, function () {
   console.log('Example app listening on port 3000!');
 });