Drunken Coder

Making a Safari Extension to handle torrent clicks

Posted 04/04/2013

Earlier I talked about my awesome media/storage server named “stooge”. I want stooge to handle all the torrents on my network. I saw some good extensions for Firefox & Chrome, but not Safari. Since my new housemate prefers Mac Safari, I set out to make it awesome.

I just need one for Transmission WebUI, but the principle is the same for any other web-based torrent-thing. Basically, I want to trigger a callback for the configured back-end (only transmission implemented) and send it a torrent when the user clicks on a torrent file or magnet link.

If you just want to download and use it, click here. If you are curious how I made it, continue reading. This is a simple example to get get you started making Safari extensions.

You can checkout my github project, here.

Step 1: RTFM

I needed to figure out the Safari API. Go read it! It’s a piece of cake.

Enable your tools

First, you will need a developer certificate. Do that here

If you have not done any development on Safari, you may need to enable some stuff. Here is what I did:

Go to Safari/Preferences/Advanced, and enable the developer menu.

develop menu

Under new “Develop” menu in toolbar, go to “Show Extension Builder” and add a new extension.

add extension

Global Page

Safari extensions load most of their stuff in the global page file. I added a file to the extension dir called global.html. Mine looked like this:

<!DOCTYPE html>
      <script type="text/javascript" charset="utf-8">
        // generic cross-origin AJAX function
        function ajax(method, url, data, cb, headers){
            var xhr = new XMLHttpRequest();
            xhr.onreadystatechange = readystatechange;
            xhr.open(method, url);
            xhr.setRequestHeader("Content-Type", "application/json");
            if (headers){
                for(i in headers){
                    xhr.setRequestHeader(i, headers[i]);

            if (data){
                data = JSON.stringify(data);

            function readystatechange(){
                if(this.readyState === this.DONE) {
                    if (this.status == 200){
                        if(this.getResponseHeader("Content-Type").split(";")[0] === "application/json"){
                            return cb(null, JSON.parse(this.response), this);
                            return cb(null, this.response, this);
                        return cb(this.status, this.response, this);

        // pass console.log() to current window/tab end-script
        var console = {log: function(){
            safari.application.activeBrowserWindow.activeTab.page.dispatchMessage("log", arguments);

        var settings={};

        // global settings
        function settingsChanged(){
            settings = {
                client: safari.extension.settings.getItem('client'),
                host: safari.extension.settings.getItem('host'),
                port: safari.extension.settings.getItem('port'),
                username: safari.extension.secureSettings.getItem('username'),
                password: safari.extension.secureSettings.getItem('password')
        safari.extension.settings.addEventListener("change", settingsChanged, false);

        // callbacks, keyed by client
        var add = {};

        add["Transmission WebUI"] = function(torrent){
            var url = 'http://' + settings.username + ':' + settings.password + '@' + settings.host + ':' + settings.port + '/transmission/rpc';
            ajax('POST', url, {"method": "torrent-add", arguments:{"filename": torrent}}, function(err, res, req){
                if (err){
                    if (err == 409){
                        add["Transmission WebUI"].token = req.getResponseHeader('X-Transmission-Session-Id');
                        return add["Transmission WebUI"](torrent);
                        console.log('unknown err', err);
            }, {'X-Transmission-Session-Id': add["Transmission WebUI"].token});

                case 'addTorrent':
                    return console.log("unhandled global message: " + msg.name, msg);
        }, false);


Basically, I add some utilities (cross-site AJAX, console.log()) settings handler (both onload, and onchange) and callbacks keyed by the client-name in preferences. Safari annoyingly requires you to pass messages around for different security contexts. This means that global.html can’t reach into DOM or console.log(), and injected scripts (more on that in a sec) can’t do cross-site AJAX, or directly access preferences. I made my global context able to console.log(), and respond to the message addTorrent. This means that injected start & end scripts can fire this, and it will be run in global context, and global can trigger log message, and I can handle that in an injected script.

Transmission requires X-Transmission-Session-Id header token to prevent XSS, so I do some K-leet trickery with recursive calling, if it’s not set.

Injected Scripts

I made a file called end.js and set it in Extension Builder, under “End Scripts”. This file will replace all links with torrent functions, handle global console.log()s


// text for notification
var icon = "";
var title = "Torrent";

// click handler
var torrentClick = function(evt){
    var href = this.href;

    var message = "Torrent added:" + href.split('/').pop();

    if (window.webkitNotifications.checkPermission() == 0) {
        window.webkitNotifications.createNotification(icon, title, message).show();
            window.webkitNotifications.createNotification(icon, title, message).show();
    safari.self.tab.dispatchMessage("addTorrent", href);

// add handler to all torrent links
var links = document.querySelectorAll("a");
for (i in links){
    if (links[i] && links[i].getAttribute){
        var href = (links[i].getAttribute('href')+"").split('?').shift();
        if (href && (href.substring(0,7) === "magnet:" || href.substr(-8) === ".torrent")){
            links[i].removeEventListener("click", torrentClick, false);
            links[i].addEventListener("click", torrentClick, false);

// handle events from global
safari.self.addEventListener("message", function(msg){
        case "log": // handle global console logs
            return console.log("global:", msg.message);
        default: // unhandled
            return console.log("tab: " + msg.name, msg);
}, false);

You can see my handler for global page console.log()'s, at the end. Basically, the rest of this script replaces all links with torrentClick() function, which fires addTorrent & sends an HTML5 notification. I do a links[i].removeEventListener because I was seeing doubled-up click handlers for whatever reason. Sweet!


I wanted some preferences for the user to configure the torrent back-end. Mine (in Extension Builder) looked like this:


As you can see, I am securely storing user/password. I currently only have 1 client available (Transmission WebUI), but if you look at global.html, you can see how to add more, using add callbacks, and you can also see how I messed with my settings. Sweet!


Automating TV torrent downloads

I want Stooge, my NAS to be able to keep track of my favorite shows, and download new episodes when they come out.

David KonsumerWritten by David Konsumer who lives and works in Portland and makes rad stuff. You should follow him on Twitter & Github