Redirect HTTP traffic on Internet Sharing to a local Charles proxy

proxy.js

#!/usr/bin/env node
var options = require('minimist')(process.argv.slice(2), { default: {
    cport: 8888
}});

var disable = options.disable || options.d;
var enable = options.enable || options.e;
var status = options.s || options.status;

var child = require('child_process');

// -s or --status to list active rules
if (status) {
    child.exec('sudo pfctl -s nat -i bridge100', function (error, stdout, stderror) {
        console.log(stdout || stderror);
    });

    return;
}

if (enable) {
    var pfrules = [
        'rdr pass on bridge100 inet proto tcp from any to any port 80 -> 127.0.0.1 port {charles_port}',
    ];

    pfrules.forEach(function (pfrule) {
        pfrule = pfrule.replace(/{charles_port}/g, options.cport);
        child.exec('echo "' + pfrule + '" | sudo pfctl -ef -');
    });

    console.log('HTTP & HTTPS traffic on Internet Sharing network now redirecting to 127.0.0.1:' + options.cport);
    return;
} else if (disable) {
    console.log('Cleared all rules on the Internet Sharing network');
    child.exec('sudo pfctl -F nat -i bridge100');
    return;
}

console.log('Usage: -e to enable, -d to disable or -s for status');