Sample Implementation of a ZeroMQ Echo Server and Client

ZeroMQ is a messaging library that provides sockets on steroids. The private npm package in this repository implements an echo server and a client that illustrate some of the features gained by using ZeroMQ sockets.

Prerequisites

First make sure ZeroMQ is installed. Both the ZeroMQ library and its header files are required. The installation instructions vary from platform to platform. In the Debian and Ubuntu distributions, it's enough to run the following command:

sudo apt-get install libzmq-dev

Perhaps needless to say: git and npm should also be installed in your system to be able to run the commands in the next section.

Installation

git clone https://github.com/n-riesco/zmq-echo.git
npm install zmq-echo

Usage

To start the echo server up, we type in the terminal:

zmq-echo-server tcp://127.0.0.1:7777

where tcp://127.0.0.1:7777 is the address the echo server will bind. The server will keep running until CTRL-C is pressed.

And to start the echo client up, we type in another terminal:

zmq-echo-client tcp://127.0.0.1:7777

where tcp://127.0.0.1:7777 must be the address used to bind the server.

The client sends every typed line to the address. If the server is bound to that address, it will reply back with the same content sent by the client. When the client receives the response back, it will print it out. E.g.:

$ zmq-echo-client tcp://127.0.0.1:7777
Hello, World!
Hello, World!

The server and client can be killed with a simple CTRL-C. Ensure they've been killed before proceeding into the next section.

The Steroids

What if the server isn't running when the client sends its message? Here's where the steroids come into action. ZMQ will ensure the message doesn't get lost.

Let's see with an example how this works. This time, first, we run the client and type the message:

$ zmq-echo-client tcp://127.0.0.1:7777
Hello, World!

Then, we run the server:

zmq-echo-server tcp://127.0.0.1:7777

And just after that, we will see the reply in the client's terminal:

$ zmq-echo-client tcp://127.0.0.1:7777
Hello, World!
Hello, World!