The following steps will show you how to run the example Websocket (ws) server using Node.JS, however any ws server will work.

You can find some wonderful documentation on how to set up websocket servers using Node.JS here, and you can see the example that I built off of here.

1. Open your CLI (Command Line Interface, For windows this is PowerShell or Command Prompt and for Unix users its terminal) and change directories into .../ws_server/.
2. If Node.JS is not installed, install it.
3. Type npm install to install the packages we will use.
4. Type node ws.js to start the server.

1. Make sure that you have unity beta >= 2017.2.0b4 installed.
2. Open edit -> project settings -> player then scroll down to Scripting Runtime Version and change it to Experimental (.NET 4.6) and when prompted click re-start.
3. Click Assets -> import new asset... and then select .../Librarys/* and click import.
4. Create the client script that will connect, send and receive messages using the How-To, or use the example one in .../Scripts/ws_script.cs.
5. Add your script to an empty Game Object.
6. Thats it! If you used the example script you should see that it is sending/receiving data in the console.

The npm ws docs cover this very well. If you have any questions feel free to submit an issue and I will try my best to answer it.

This is the trickier part. If you looked over the example script (which I suggest you do) you will notice that we use IEnumerator Start () instead of void Start (). For those of you who do not know, IEnumerator is used to run a function in another thread. The reason for this is to be able to yield things (like connecting to a server) that might take some time. RampantStudios sums it up pretty well here:

The IEnumerator allows the program to yield things like the WaitForSeconds function, which lets you tell the script to wait without hogging the CPU

Basically after you have created your C# script in unity, change void to IEnumerator before Start. And we can actually delete the Update function because we will not be using that.

Instead of update you will use an always true while loop. The reason for this is because if you put your connection code inside of the Update function you would have to reconnect every time, and as you can imagine this would be problematic. So you can go ahead and add this inside of your Start function:

while (true) {

}

Now for the fun part; connecting to the server. Above the while loop place WebSocket w = new WebSocket (new Uri ("ws://<ip>:<port>"));. This creates a WebSocket variable using the libraries you imported above. You can then connect to it with yield return StartCoroutine (w.Connect ()); (StartCoroutine runs your connecting code in another thread). Then you can send your first message to the server with w.SendString ("START");. After you have done everything you want to, you can close the connection like so w.Close ();.

Right now our script looks like this:

IEnumerator Start ()
{
  WebSocket w = new WebSocket (new Uri ("ws://localhost:8000"));
  yield return StartCoroutine (w.Connect ());
  w.SendString ("START");

  while (true) {

  }

  w.Close ();
}

Currently your script can send the word "START" to our server. If you want, try it out! (It is very satisfying to watch your unity project send something to a server and see it pop up in the terminal). But we will want our project to do more than just send "START", so lets add some code that allows your project to receive messages. Inside of your while loop add the following:

string reply = w.RecvString ();
if (reply != null) {
	Debug.Log (reply);
}
yield return 0;

The first line here creates a variable of the response that our server might have sent to us. Then there is an if statement that checks if anything was actually sent to us, and if so it prints it to the console. Lastly we return 0 so that we do not create an infinite loop for our processor.

Next you need to have some way to log the errors that we will inevitably get. You can do this with the following:

if (w.error != null) {
	Debug.LogError ("Error: " + w.error);
	break;
}

Now you can go ahead an try the program, click play in unity and you should see the word "START" in the console.

Thats it! Here is the full script for TL; DR

IEnumerator Start ()
{
	WebSocket w = new WebSocket (new Uri ("ws://" + ip + ":" + port));
	yield return StartCoroutine (w.Connect ());
	w.SendString ("START");

	while (true) {
		string reply = w.RecvString ();
		if (reply != null) {
			Debug.Log (reply);
		}
		if (w.error != null) {
			Debug.LogError ("Error: " + w.error);
			break;
		}
		yield return 0;
	}
	w.Close ();
}

The libraries I am using are from Simple Web Sockets For Unity WebGL.