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

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] you can 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');
var fs = require('fs');
var net = require('net');

//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
  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(8080)

//socket server to accept websockets from the browser on port 3000
//and forward them out to DexRun as a raw socket
require('net').createServer(function (socket) {
    console.log("connected");
    socket.on('data', function (data) {
        console.log(data.toString());
        dexter.write(data);
    });
}).listen(3000);

//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.