Static Version

Node.js and Redis Pub-Sub

This is the 7th in a series of posts leading up to Node.js Knockout on how to use node.js. This post, cross-posted from GitHub, was written by James Bracy, founder of Redis To Go. Redis To Go is a dead simple solution for managed Redis instances.

Node.js is a perfect platform for creating event driven applications. Redis and WebSockets are great companions to Node.js. The following tutorial will walk through the steps to build a web application that streams real time flight information using Node.js, Redis, and WebSockets.

Dependencies

Node.js, Redis, and a WebSocket enabled browser (Firefox 4, Google Chrome 4, or Safari 5) are required. A tutorial covering the installation of Node.js can be found here.

The easiest way to get a Redis instance would be to use Redis To Go. The free plan is all that is needed for this tutorial. If you wish to install locally run the following commands:

$ git clone http://github.com/antirez/redis.git
$ cd redis
/src
$ make
$ sudo make install
$ cd
../..
$ rm
-rf redis

Now you can start a Redis instance locally using the redis-server command.

Create the Project

Create a directory for the project. We will name the project "Flight Stream".

$ mkdir flight-stream
$ cd flight
-stream

The project will require the Node.js Redis client redis-client, the WebSocket library node-websocket-server, and the MIME library node-mime. Create a lib directory and copy the libraries to this directory.

$ mkdir lib
$ cd lib
$ curl
-O http://github.com/fictorial/redis-node-client/raw/master/lib/redis-client.js \
       
-O http://github.com/bentomas/node-mime/raw/master/mime.js \
       
-O http://github.com/miksago/node-websocket-server/raw/master/lib/ws.js
$ mkdir ws
$ cd ws
$ curl
-O http://github.com/miksago/node-websocket-server/raw/master/lib/ws/connection.js \
       
-O http://github.com/miksago/node-websocket-server/raw/master/lib/ws/manager.js
$ cd
../..

Create the Server

Initially the Node.js server will simply server the static index.html file that will be create. Create the server.js file and add the following code:

server.js
require.paths.unshift(__dirname + '/lib');

var fs = require('fs'),
    ws
= require('ws'),
    sys
= require('sys'),
    url
= require('url'),
    http
= require('http'),
    path
= require('path'),
    mime
= require('mime'),
    redis
= require('redis-client');

var httpServer = http.createServer( function(request, response) {
   
var pathname = url.parse(request.url).pathname;
   
if (pathname == "/") pathname = "index.html";
   
var filename = path.join(process.cwd(), 'public', pathname);

    path
.exists(filename, function(exists) {
       
if (!exists) {
            response
.writeHead(404, {"Content-Type": "text/plain"});
            response
.write("404 Not Found");
            response
.end();
           
return;
       
}

        response
.writeHead(200, {'Content-Type': mime.lookup(filename)});
        fs
.createReadStream(filename, {
           
'flags': 'r',
           
'encoding': 'binary',
           
'mode': 0666,
           
'bufferSize': 4 * 1024
       
}).addListener("data", function(chunk) {
            response
.write(chunk, 'binary');
       
}).addListener("close",function() {
            response
.end();
       
});
   
});
});


var server = ws.createServer({}, httpServer);

server
.listen(8000);

The httpServer serves the static files in the public directory. The server is what will be handling the WebSocket connections.

Create the public directory:

$ mkdir public

Now copy the source for the index and stylesheets from github.

$ cd public
$ curl
-O http://github.com/waratuman/flight-stream/raw/master/public/application.css \
       
-O http://github.com/waratuman/flight-stream/raw/master/public/reset.css \
       
-O http://github.com/waratuman/flight-stream/raw/master/public/jquery.js \
       
-O http://github.com/waratuman/flight-stream/raw/master/public/text.css \
       
-O http://github.com/waratuman/flight-stream/raw/master/public/index.html
$ mkdir images
$ cd images
$ curl
-O http://github.com/waratuman/flight-stream/raw/master/public/images/background.png \
       
-O http://github.com/waratuman/flight-stream/raw/master/public/images/red.png \
       
-O http://github.com/waratuman/flight-stream/raw/master/public/images/orange.png \
       
-O http://github.com/waratuman/flight-stream/raw/master/public/images/green.png \
       
-O http://github.com/waratuman/flight-stream/raw/master/public/images/blue.png

At this point you should be able to run node server.js and see the index page when you got to localhost:8000.

Now lets get redis-client working in the server. The following lines establish a connection to Redis. The connected and reconnected listeners authenticate the connection after it has been established.

redis-client.js
var db = redis.createClient(9281, 'goosefish.redistogo.com');
var dbAuth = function() { db.auth('dc64f7b818f4e3ec2e3d3d033e3e5ff4'); }
db
.addListener('connected', dbAuth);
db
.addListener('reconnected', dbAuth);
dbAuth
();

View the full source here

Now subscribe to the flight_stream channel on Redis.

redis-subscribe.js
db.subscribeTo("flight_stream", function(channel, message, pattern) {
   
try { var flight = JSON.parse(message); }
   
catch (SyntaxError) { return false; }

   
if ( flight.origin.iata == "BOS" || flight.destination.iata == "BOS") {
        server
.broadcast(message);
   
}
});

View the full source here

Whenever a message is published the function passed to the subscribeTo method will get called. In this case we try to parse the message as JSON then publish it to all of the clients if the flight is leaving Boston or arriving at Boston.

Client

Next the client will need to be coded. I previously created the HTML for this app, so all that we need to do is set up the WebSockets.

Open public/application.js and insert the following code. This code will create a WebSocket if the browser supports it and if it does, create a connection with the server. When a message is received, another row will be inserted on the page displaying the flight.

application.js
function delay_color(mins) {
   
var min = parseInt(mins);
   
if (min <= -15) return 'green';
   
else if (min <= 0) return 'green';
   
else if (min <= 15) return 'orange';
   
else return 'red';
}

function delay_name(mins) {
   
var min = parseInt(mins);
   
if (min <= 0) return 'On-Time';
   
else return 'Delayed';
}

var ws;
var connect = function() {
   
if (!window['WebSocket']) {
        alert
("No WebSocket support.");
       
return;
   
}

    ws
= new WebSocket('ws://' + window.location.host);
    ws
.onmessage = function(evt) {
       
try { var flight = JSON.parse(evt.data); }
       
catch (SyntaxError) { return false; }

        $
('table.flight-updates > tbody').prepend(
           
'<tr>' +
               
'<td>' + flight.airline.icao + ' ' + flight.number + '</td>' +
               
'<td>' + flight.origin.iata + '</td>' +
               
'<td>' + flight.destination.iata + '</td>' +
               
'<td>' +
                   
'<div class="tag ' + delay_color(flight.destination.gate_delay) + '">' +
                        delay_name
(flight.destination.gate_delay) +
                       
'<span>' + flight.destination.gate_delay + ' min</span>' +
                   
'</div>'+
               
'</td>'+
               
'<td>' + flight.destination.gate + '</td>' +
           
'</tr>');
   
};
};

$
(document).ready( function() {
    connect
();
});

The functions delay_color and delay_name are helper functions for displaying text and selecting the right class for styling.

Now you can start the server, go to http://localhost:8000/ and you should start seeing updates roll in. If you are using your own Redis, you are going to need to publish something to the flight_stream. Here is a sample message that you can use:

{
   
"number": "482",
   
"status": "Scheduled",
   
"origin": {
       
"gate_delay": 0,
       
"icao": "KSFO",
       
"name": "San Francisco International Airport",
       
"iata": "SFO",
       
"gate": "3-88"
   
},
   
"destination": {
       
"gate_delay": 0,
       
"icao": "KBOS",
       
"name": "Denver International Airport",
       
"iata": "BOS",
       
"gate": "-"
   
},
   
"airline": {
       
"icao": "UAL",
       
"name": "United Airlines",
       
"iata": "UA"
   
}
}

If you are using the Redis instance used throughout the tutorial, you will start seeing flight come up. I will be publishing some data every few seconds to the instance for the coming days.

Basic Operations

Basic operations were not really covered in this tutorial, so here are some examples to get you started.

basic-operations.js
db.set("foo", 1)
db
.get("foo", function(err, value) { sys.puts(value); });
db
.randomkey(function(err, key) { sys.puts(key); });
db
.hset("bar", "hi", "world");
db
.hget("bar", "hi", function(err, value) { sys.puts(value); });
db
.hgetall("bar", function(err, data) { sys.puts(data["hi"]); });

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