TCP Server in Node.js

TCP Server

Server is an EventEmitter. It can be TCP or IPC based on what it listens to.
TCP Server has a connectionListener callback that lets you access a socket connection, which is a Subclass of Duplex Stream.
We can define the on "data", "end", "error", etc. events on it, whenever something is written in the internal write buffer - A packet is sent through the socket carrying that buffer as data.
Once a server with a connectionListener is created - We call the listen method, which is basically an endless loop in which your node.js TCP server is constantly listening.
We define a hostName(IP Address) and a Port number on which the server listens. In this case we define a default LoopBack IP Address - 127.0.0.1*
Running the listening method basically means running your server on hostName:PORT, and now it can talk to the world!

All routes, switches, devices know that 127.0.0.1 is the LoopBack IP address. What it means that any traffic which is coming from 127.0.0.1 os looped back to 127.0.0.1. Its also known as the infamous localHost.`

A simple sender/ Socket is a Subclass of Duplex Stream, which is connecting to that same host and port.
The createConnection method of net module returns a Socket that inherits from Duplex Stream.
It returns us a Socket Connection which has a stream to pass data through and an endpoint.
First parameter in net.createConnection is options in which we can define hostName(LoopBack Address in this case) and PORT to create a connection to.
Second parameter is connectionListener which access the top level socket connection and can write buffers to it.
We create a buffer and write it to the socket.

On the hostName and PORT our socket is connected to, we just wrote a buffer in the stream of it.
The socket sends a packet which along with many things(like headers, src address, dst address, etc.) contains the "data". The buffer we wrote.
The TCP Server is already running/ listening on the hostName:PORT. It listens to the "data" event on the socket it receives.
As of now, we are just printing that data or buffer we get from the write event on the socket.