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     var lastUpdated  = 0;
  13     var rowCount = 0;
  14     while (true) {
  15         try {
  16             var res = await db.getMaxUpdatedState(session_id);
  17             var newRowCount = res[0].num_rows;
  18             var updatedAt = res[0].last_updated;
  19
  20             // update board state of client if more moves
  21             // have been added since max last timestamp
  22             // If more moves have been added in <1 sec,
  23             // use the row count for the max last updated timestamp
  24             if (updatedAt > lastUpdated || rowCount < newRowCount) {
  25                 lastUpdated = updatedAt;
  26                 rowCount = newRowCount;
  27                 ws.send(JSON.stringify({
  28                     "type": "board",
  29                     "data": await db.getBoardState(session_id)
  30                 }));
  31             }
  32         } catch(err) {
  33             console.log(`websocket poll error: ${err}`);
  34         }
  35         await sleep(1000);
  36     }
  37 }
  38
  39 app.ws('/ws', async function(ws, req) {
  40     // poll for stateful change and notify clients to update their boards
  41     var session_id = 0;
  42     db.initBoard();
  43
  44     // get session ID
  45     ws.send(JSON.stringify({
  46         "type": "session"
  47     }));
  48
  49     ws.on('message', async function(msg) {
  50         let parsed;
  51         try {
  52             parsed = JSON.parse(msg);
  53             switch (parsed.type) {
  54                 case "session":
  55                     session_id = parsed.data.session
  56
  57                     // send initial message to draw session client board
  58                     ws.send(JSON.stringify({
  59                         "type": "board",
  60                         "data": await db.getBoardState(session_id)
  61                     }));
  62                     break;
  63                 case "new":
  64                     ws.send(JSON.stringify({
  65                         "type": "new",
  66                         "data": await db.deleteSession(parsed.data.session)
  67                     }));
  68                     break;
  69                 case "move":
  70                     await db.addMove(
  71                         parsed.data.session,
  72                         parsed.data.x,
  73                         parsed.data.y,
  74                         parsed.data.state,
  75                         );
  76                     // fall through and return new board state
  77                 case "board":
  78                     ws.send(JSON.stringify({
  79                         "type": "board",
  80                         "data": await db.getBoardState(parsed.data.session)
  81                     }));
  82                     break;
  83                 default:
  84                     console.log("ws message: Unknown message type: " + type);
  85             }
  86         } catch(err) {
  87             console.log(`ws message error: ${err}`);
  88         }
  89     });
  90
  91     pollStatefulChange(ws, session_id);
  92 });
  93
  94 app.listen(3000);