Practical XMPP

XMPP is used to solve many real-world problems and has made its way into many large services, often without users realizing. Some large examples of deployments or XMPP-based services include:

Additionally, many services also allow users to connect via an XMPP gateway, meaning that users can connect with their preferred clients rather than with those supplied by a company, such as Slack and Skype.

XMPP is deployed in many industries where its uses go beyond simple chat applications to include diverse purposes such as the following:

With the continuing rise of the real-time web and WebRTC applications, XMPP is becoming more relevant on the web than ever before. Its push architecture means that lightweight real-time applications can be built without continuously polling the server, making for more scalable web applications. Its mature standards mean that developers are quickly able to build real-world applications without having to design their own proprietary standards and benefit from the thought and problem solving that has gone into XMPP.

With all its advantages, one area that WebRTC hasn't solved (nor was it designed to solve) is the issue of session negotiation. Not only was a standard called Jingle available in XMPP before WebRTC arrived in the browser, but also it turns out that it's a great way of transferring session data to form peer-to-peer sessions. This means that users are now able to use WebRTC clients of their choice without having to visit and reply upon a meet me type URL or a proprietary signaling method.

Node.js was released in 2009, and since its release, it has quickly become a nearly indispensable tool for server side development using JavaScript. Node.js allows developers to create fast and scalable applications (especially when asynchronous IO libraries are used) in a single language throughout an application's stack, with JavaScript running on both the back-end and front-end.

While Node.js is not required for working with XMPP, all examples in this book will utilize libraries written in Node.js, some of which can also run on the browser.

Using Ubuntu 16.04 as a base, we're now going to install Node.js and some core dependencies for the libraries we'll be using.

First we'll install libicu-dev and libexpat-dev. These libraries allow us to perform case transformations on international characters and process XML, respectively:

$ sudo apt-get install libicu libexpat1-dev

Next, we'll work on installing Node.js itself. My preferred method of achieving this is to use nvm by Tim Caswell, which is available from this GitHub repository: https://github.com/creationix/nvm . Please check out the readme for the current installation instructions, but at the time of writing this book, the procedure is as follows:

$ curl https://raw.githubusercontent.com/creationix/nvm/v0.32.0
    /install.sh | bash
$ source ~/.bashrc
$ nvm install 6
$ node -v

This will install the latest version of the Node.js 6 release for you. The advantage of using nvm over the operating system packages is that it is easy to switch between different versions of Node.js with a simple command.

Installing Prosody on an Ubuntu system is very easy since it is included in the main package repositories. In order to install Prosody, run the following command at the command line:

$ sudo apt-get install prosody

Prosody can then be started and stopped using the following standard methods:

$ sudo service prosody start
$ sudo service prosody stop

If you are not using Ubuntu, then Prosody may be available via your respective package manager. The best installation instructions for Prosody can be found at http://prosody.im/doc/install.

Prosody also produces Docker images of their releases, which are available from the official Docker hub: https://registry.hub.docker.com/u/prosody/prosody/ .

By default, Prosody will store its configuration file at /etc/prosody/prosody.cfg.lua. The configuration file itself is rather simple and is written in the Lua language, which is the same language in which the Prosody server is written.

Shown here is the configuration file we are going to use throughout this book. Following the configuration example is an explanation of each part of these settings. As always, for the most up-to-date and detailed information, please visit the Prosody website (http://prosody.im):

modules_enabled = { 
        "roster"; 
        "saslauth"; 
        "tls"; 
        "dialback"; 
        "disco"; 
        "version"; 
        "uptime"; 
        "time"; 
        "ping", 
        "register"; 
        "posix"; 
        "bosh"; 
}; 
allow_registration = true; 
daemonize = true; 
consider_bosh_secure = true; 
cross_domain_bosh = true; 
pidfile = "/var/run/prosody/prosody.pid"; 
c2s_require_encryption = false 
authentication = "internal_plain" 
 
log = { 
        debug = "/var/log/prosody/prosody.log"; 
        error = "/var/log/prosody/prosody.err"; 
        { levels = { "error" }; to = "syslog";  }; 
} 
 
VirtualHost "localhost" 
    enabled = true 
    ssl = { 
        key = "/etc/prosody/certs/example.com.key"; 
        certificate = "/etc/prosody/certs/example.com.crt"; 
    } 
 
VirtualHost "anon.localhost" 
   authentication = "anonymous" 
 
Component "component.localhost" 
    component_secret = "mysecretcomponentpassword" 

Now, let's discuss each of the sections of the configuration file:

Then we save this configuration file to /etc/prosody/prosody.cfg.lua and restart the server:

$ sudo service prosody restart

Next, we're going to test our Prosody setup. First, we will test whether Prosody is listening to the client-to-server (C2S) and server-to-server (S2S) ports. By default, with XMPP, the C2S port is 5222 and the S2S port is 5269. We can perform a quick and easy test using telnet. If your server is running as expected, you will see an output similar to the following screenshot:

Testing Prosody connections using telnet

Next, we will also verify whether we have set up our BOSH endpoint correctly by visiting the endpoint in a browser, by visiting http://localhost:5280/http-bind/, port number 5280 being the default BOSH port, we should see the following screenshot:

Testing Prosody's BOSH endpoint from a browser

Prosody has a great command-line utility, prosodyctl, which allows us to create and update user accounts as well as command the server. Here, we're going to use it to create our first XMPP account on the server. Type the following command in the command line:

$ sudo prosodyctl adduser test@localhost

You will then be prompted to enter a password. Let's use the Password password for now. Once this is complete, we have our XMPP account. We'll test this with a client in a moment.

Lastly, we'll install a standard desktop XMPP client, which will allow us to interact with our code. A list of XMPP clients is held on the XMPP website (http://xmpp.org/xmpp-software/clients/). Find one suitable for your platform and follow the installation instructions.

In this book, we're going to use Empathy (https://live.gnome.org/Empathy) since it comes installed as standard in the Ubuntu desktop: