socket/server.js

   1 var express = require('express');
   2 var app = express();
   3 var expressWs = require('express-ws')(app);
   4
   5 var db = require('./db');
   6
   7 function sleep(ms) {
   8   return new Promise(resolve => setTimeout(resolve, ms));
   9 }
  10
  11 async function pollStatefulChange(ws, session_id) {
  12     let conn;
  13     try {
  14         conn = await db.pool.getConnection();
  15         var lastUpdated = 0;
  16         while(true) {
  17             var res = await conn.query(`
  18 select UNIX_TIMESTAMP(MAX(updated_at)) as last_updated
  19 from go.state
  20 where session_id = ?;
  21             `, [session_id]);
  22             console.log(res);
  23             let updatedAt = res[0].last_updated;
  24             if ( updatedAt > lastUpdated) {
  25                 console.log("websocket poll: board updated!");
  26                 lastUpdated = updatedAt;
  27                 res = await db.getBoardState(session_id);
  28                 ws.send(JSON.stringify({
  29                     "type": "board",
  30                     "data": res
  31                 }));
  32             }
  33             await sleep(1000);
  34         }
  35     } catch(err) {
  36         console.log(`websocket poll error: ${err}`);
  37     } finally {
  38         if (conn) conn.end();
  39     }
  40 }
  41
  42 app.ws('/ws', async function(ws, req) {
  43     // poll for stateful change and notify clients to update their boards
  44     var session_id = 0;
  45     pollStatefulChange(ws, 0);
  46
  47     ws.on('message', async function(msg) {
  48         console.log(`ws message: ${msg}`);
  49
  50         var parsed = JSON.parse(msg);
  51         switch (parsed.type) {
  52             case "move":
  53                 await db.addMove(
  54                     parsed.data.session,
  55                     parsed.data.x,
  56                     parsed.data.y,
  57                     parsed.data.state,
  58                     );
  59                 // fall through and return new board state
  60             case "board":
  61                 var res = await db.getBoardState(
  62                     parsed.data.session
  63                     );
  64                 ws.send(JSON.stringify({
  65                     "type": "board",
  66                     "data": res
  67                 }));
  68                 break;
  69             default:
  70                 console.log("ws message: Unknown message type: " + type);
  71         }
  72     });
  73 });
  74
  75 app.listen(3000);