wswatch

#!/usr/bin/env node

// server for wswatch, serves the output of another program via WebSockets etc.

"use strict";

var argparse = require('argparse');
var connect = require('connect');
var socket = require('socket.io');
var child = require('child_process');

var parser = new argparse.ArgumentParser({
        version: '0.1.0',
        description: "Unix watch(1) in the browser"
    });
parser.addArgument([ '-p', '--port' ], { type: parseInt, required: true, help: "HTTP port to serve the view" });
parser.addArgument([ '-n', '--interval' ], { defaultValue: 2, help: "Update interval in seconds (default: 2)" });
parser.addArgument([ 'command' ], { help: "Program to run" });
parser.addArgument([ 'args' ], { nargs: '...', help: "Arguments for program to run" });
var args = parser.parseArgs();

var app = connect();
app.use(connect.static('public'));
var server = app.listen(args.port);
var io = socket.listen(server);

io.set('log level', 1); // reduce logging

var command = args.command;
if (args.args) {
    command += ' ' + args.args.join(' ');
}

var screen; // cache of last screen to speed up initial paint when new clients connect
function run() {
    // exec rather than spawn to handle shell syntax within command
    child.exec(command, function (error, stdout, stderr) {
            screen = stdout.toString();
            io.sockets.emit('screen', screen);
            if (stderr) {
                console.error("error: " + stderr);
            }
            if (error !== null) {
                console.error("exec error: " + error);
            }
        });
}

run(); // initial run to populate cache
setInterval(run, args.interval * 1000);

io.sockets.on('connection', function (socket) {
        socket.emit('title', command);
        socket.emit('screen', screen); // initial paint from cache
    });