Itsdone

Uses - Quick project demonstrating how to use Socket.io / Redis / and Ionic to have a simple chat applications with expiring messages

Screenshots

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<img src="http://i.imgur.com/5dmJ9RG.gif" title="source: imgur.com" width="300px": />

Requirements

• Redis brew install redis
• Node.js & npm
• MongoDB
• Ionic Framework
• Phonegap

See the app repo ItsDone

This is just the backend service, the main app is there

Requirements for Mobile

• Cordova npm install -g cordova
• Ionic npm install -g ionic
• iOS SDK
• Android SDK

Getting started

• Clone the repo and ensure redis is running
• run npm install to get all packages required to run the server.
• run node server to run the server
• visit VaniChat in your browser

Running the iOS Application

• Change directories to client/RedisChat
• run cordova run ios

Running the Android Application

• Change directories to client/RedisChat
• run cordova run android

Technology details

DISCLAIMER: I know using Redis as a data store for large scale users is not the best use case for Redis. I wanted to play more with Redis and get some more experience using it and the expires functionality.

The messages are stored in Redis as a sorted set in the messages:channel:channelname key where channelname is the channel they are in. The value stored is a simple JSON encoded object with information about the message (message, user, expires time) with its score set as it's UNIX time of posting.

There is a method in the server.js file - removeKeys that will remove messages from channels if they exceed the expire time stored in the set.

//Channels are populated before this call
var channelWatchList = ['Lobby', 'Redis', 'Ionic', 'Socket.io'];
function removeKeys() {
  console.log('We are removing old messages');

  for(var channelIndex in channelWatchList) {
    var channel = channelWatchList[channelIndex];
    var timeToRemove = moment().subtract('m', 2).unix(); //Two minutes ago
    var messageChannel = 'messages:' + channel;

    redisClient.zrangebyscore(messageChannel, 0, timeToRemove, function(err, result) {
      if(result && result.length > 0) {
        console.log('Emitting information to client to remove: ', result);
        for (var resultIndex in result) {
          var message = JSON.parse(result[resultIndex]);
          console.log('emitting: ', message);
          //Signal to all of our connected clients to remove the message.
          io.emit('message:remove:channel:' + channel, { message: message, channel: channel });
        }
      }
    });

    redisClient.zremrangebyscore(messageChannel, 0, timeToRemove, function(err, result) {
      console.log('Removed ', result, ' records');
    });
  }
}

var cleanUpMesssagesInterval = setInterval(removeKeys, 6000);

Interesting tidbits

After failing miserably at trying to make keys that expire, I spoke to Michael Gorsuch and he had found an easier way to manage that using sorted sets and expire times as scores.

The idea is, you have a sorted set with a key. Then you add a score with a JSON encoded string. The score itself is the unix timestamp. Then, have a timer that passes over and checks for a unix timestamp with some time in the past (2 minutes) and remove using zremrangebyscore with 0 to the timestamp - time past.

NOTES

• All ports / hostnames are hardcoded. In later versions these will be put into a configuration file.
• Channels need to be expired - and users then removed from channels as well as messages