nodejs webserver

Node.js allows you to use Javascript as a scripting language on the host instead of just on the client in the browser. It's very commonly used to build things like web servers, apps that use sockets to communicate, and generally things that work between a computer and the internet.
https://nodejs.org/en/
https://en.wikipedia.org/wiki/Node.js
It's an ideal way to develop a web server that runs on Dexter, serves a web page that interacts with the robot and allows you to directly control it without anything but a browser.

Installing Node.js on Dexter

Because we need to download files, your Dexter must be connected to your router and the internet. Check Dexter Networking for more information on that.

SSH into Dexter.

To ensure you have enough space check that df -h shows more than 4.0G available.

To install Node.js, you can use the method outlined at:
https://www.liquidweb.com/kb/how-to-install-node-js-via-nvm-node-version-manager-on-ubuntu-12-04-lts/
which uses NVM (Node Version Manager). And the procedure for installing that is described at:
https://www.liquidweb.com/kb/how-to-install-nvm-node-version-manager-for-node-js-on-ubuntu-12-04-lts/
Everything is up to date, so you can start at:
apt-get install build-essential libssl-dev
that is 29 Megs, so we should have space for it. You can approve it. That takes quite a while.

To actually install NVM, you need curl, so you have to install that:
sudo apt-get install curl

The current version of NVM is 0.33.11 so I did
curl https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh | bash
but you can probably use whatever the latest version is. It should complete quickly, and advise you to close and re-open your terminal, so log off and back on. And now we should have nvm. You can check with nvm --help

Now you can use NVM to install different versions of Node.js. The latest LTR (Long Term Release) version which is compatible with Ubuntu 12 is version 4.9. So install that with:
nvm install 4.9

Once that finishes, you should be able to run node:
node --help

Notes:

• If you install more than one version of node, you must select the default each time. To avoid this, use nvm alias default 4.9.1 to set the default to e.g. 4.9.1 (use whatever version you have working)

A Node.js Web / socket server.

To setup a simple web server / Socket interface to the Dexter Firmware first create a sub folder under the share:
mkdir /srv/samba/share/www
This folder will hold all the files your server will serve when a user connects.

Next, make a file called httpd.js using nano:
nano httpd.js
and then copy in the following text (to paste into PuTTY just right click the window)

var http = require('http'); 
var url = require('url'); //url parsing
var fs = require('fs'); //file system
var net = require('net'); //network
const ws = require('ws'); //websocket
//https://github.com/websockets/ws
//install with:
//npm install --save ws

//standard web server on port 8080 to serve files
http.createServer(function (req, res) {
  var q = url.parse(req.url, true)
  if ("/"==q.pathname) q.pathname="index.html"
  var filename = "/srv/samba/share/www/" + q.pathname
  console.log("serving"+q.pathname)
  fs.readFile(filename, function(err, data) {
    if (err) {
      res.writeHead(404, {'Content-Type': 'text/html'})
      return res.end("404 Not Found")
    }  
    res.writeHead(200, {'Content-Type': 'text/html'})
    res.write(data)
    return res.end()
  });
}).listen(80)

//socket server to accept websockets from the browser on port 3000
//and forward them out to DexRun as a raw socket
var browser = new ws.Server({ port:3000 })

browser.on('connection', function connection(socket) {
    console.log("connected");
    socket.on('message', function (data) {
        console.log(data.toString());
        dexter.write(data.toString());
        });
    });


//Now as a client, open a raw socket to DexRun on localhost
var dexter = new net.Socket()
dexter.connect(50000,"127.0.0.1")
dexter.on("data", function(data){
	console.log("dexter:", data)
	})

//test to see if we can get a status update from DexRun
dexter.write("1 1 1 undefined g ;")

That last line tests the socket interface by sending a status update request to Dexter and then writing out the returned value to the console. when you run the script by entering
node httpd.js
you should see:
dexter: <Buffer 01 00 00 00 01 00 00 00 1f 18 1a 5b 41 e9 04 00 67 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 ... >

You can see the returned little endian integer values (4 bytes each) which are 1, 1, then the two times, and the 67 is the 'g'. The rest of the data (not shown) includes all the status values. See Dexter - DDE communications for more on how to talk to Dexter via the socket interface.

To stop the server, press Ctrl+C

To run your web server in the background while you continue to work, use
node httpd.js &
The & or and sign at the end places the server in the background. You can check on it with job or take it back to the foreground with fg and then press Ctrl+C to stop it.

But as long as it's running in the background, you can edit files for it to serve in the /srv/samba/share/www folder. For example, if you place a file called "index.html" in that folder, with something like:

<html>
<body>
<h1>HELLO WORLD!</h1>
</body>
</html>

and then go to http://dexers-ip-address/index.html you should see "HELLO WORLD!"

Now you can make a file with some Javascript in it that makes a websocket connection to the Node.JS server on port 3000, which will then make a raw socket connection to Dexter on port 50000, and pass on your request, and log the result. Like this:

<html>
<body>
<script type="text/javascript">
let port = 3000
let ip_address = "192.168.0.137"
	let ws = new WebSocket('ws://'+ip_address+":"+port)
	ws.onopen =  function(){
		document.write("open")
		ws.send("2 1 1 undefined g")
		}
	ws.onerror = function(error) {
		document.write("error"+error)
		}
	ws.onmessage = function(msg) {
		document.write("message:"+msg.data)
		}
</script>
</body>
</html>