Twitch Extensions Part 5 – Dev Environment

This week we are actually going to write some code! Amazing I know! We’ll be using nodeJS and some basic shell scripting, here just for some simplicity. 

First off apologies for being 3 days late on this entry in the series!

In Part 4 we wrote about the Twitch Developer Rig and what it can/can’t do. One of the useful thing’s it can do for you is “host your files” for you when your extension is in Local test.

The Hosting options in the Developer rig.
The Hosting options in the Developer rig.

The Developer Rig, will either just “dumb serve” a folder of static files, or you can give it a full command to run, handy for WebPack/React/JS things that people need to pre-compile first.

But this big thing it won’t do is SSL Termination so whilst you can easily test your extension in the Rig, you won’t be able to easily test it on Twitch, which is the purpose of this little Dev Environment.

Personally at the moment I tend to write my Extensions in pure/vanilla JavaScript without libraries, since in most cases I’m just running a few fetch requests and drawing DOM elements, but the more interesting parts come with my compilation/bundling for hosting. The “rig” that I use is Developer Rig compatible since it is just a node command. But I’ve normally started it in a terminal as I’m testing on the actual Twitch website.

So what is the aim here?

To create a nodeJS Server that will

  • “static” host the HTML, JS and CSS for an extension,
  • do some clean up on JS/CSS, both for development and production,
  • work behind (a real) SSL for testing on the Twitch website (or rig)
  • be representative of Hosted test and above

What does that look like?

Well first we need to setup a bunch of folders, and we’ll set it up in a “nice” way for using Version control, some people may prefer to keep a separate repo for their EBS from their frontend for easier deploy. The choice is yours there! I use a mix, because being inconsistent is fun!

Proposed folder structure for your extension repository
Proposed folder structure for your extension repository

assets – for storing your screenshots, discovery images, icons and other bits and pieces that live on “Version Details”

ebs – the folder for building you EBS in

website – the folder for building a website in if your Extension has/needs one, usually would include your Privacy Policy.

extension – this is where our extension actually lives and is the folder we’ll be poking about in today.

The Extension Folder

The Folders in the Extension Folder
The Folders in the Extension Folder

assets – another assets folders? For storing any front end specific bits and pieces. You probably don’t need this.

build/release – build is where our “compiled” extension will sit

releases – I like to store my old/previous versions of the extension here for future reference

develop – the place we actually write our code

For Version Control, you would generally, touch build and release with a blank file (or .gitkeep if using Git) and then ignore those folders from version control.

We are going to be using the “static” part of NodeJS Express to serve the build folder, and use a super exciting bash script to populate the build folder from the develop folder.

Usually I’ll keep a dev folder in the develop folder, as I’ll keep the “pre-release” version of the extension in develop and the compiled/zip’ed version in releases.

The Bash Script though?

yeah, I use a bash script, it’s my preferred method, but anything it can do you can achieve in similar stuff such as WebPack, but you may want to run all sorts of things when you “deploy” you Extension Frontend during testing. And whilst I am considering other methods, I prefer the simple Bash script.

The Server

The server itself is relatively straight forward, you can refer to the Code on Github, but here is the key part we are interested in

const listen = 8050;
 
const express = require('express');
const app = express();
 
/*
Setup Express to Listen on a Port
*/
app.listen(listen, function () {
console.log('booted express on', listen);
})
 
/*
Setup a "Log" Event for file loading.
So you can see what is trying to be loaded
*/
app.use(function(req, res, next) {
console.log('received from', req.get('X-Forwarded-For'), ':', req.method, req.originalUrl);
next();
});
/*
Setup express Static to server those files
*/
app.use('/extension/', express.static(__dirname + '/build/'));

This will raise an express static server on port 8050, and then prepare to host the contents of build on the route extension.

So this will give us a URL of http://127.0.0.1/extension/ and if you remember in Part 3, we wrote about the structure of a URL of a Hosted test/Live extension being https://ClientID.ext-twitch.tv/ClientID/md5/yourHTML instantly our Development Environment is closer to the Production Environment.

To further this, I like to put my views into different folders. So the viewer will be in panel or video and if I offer both I’ll have both. The Config will be in config or something random for extra security on private Extensions. And Mobile in mobile if I need to serve different JS to the user.

Which then makes it even easier or a developer to remember to use relative links to their CSS/JS from the HTML, since my views are in sub folders, and the whole Dev Server is serving from a sub folder.

But what about the rest of the file? That is a basic Folder watcher, using Chokiar, that will watch for any change in the develop/dev directly and then run script.sh

This script will

  • dump the current contents of build,
  • copy the folder structure
  • copy over any “common” assets in the assets folder (background images/icons for example)
  • copy over each HTML file, in some cases run a minify process
  • compile each JS file and CSS file together into one file and run it thru minifies (but not mangles*)

*Twitch disallows magnification, except in some cases

The script will call the NPM globally installed instances of:

  • html-minifier (not in this example but I use it on occasion)
  • uglify-es which provides uglifyjs
  • uglicfycss

I like to build different parts of my extensions into different script/css files and then use my develop/build process to combine them into one file. Here is FlightSimTrack’s current layout for example. Left being the built/compiled and right being the Development version.

FlightSimTracks structure
FlightSimTracks structure

You can see how my many JS/CSS on the right are folded down into singular files. And make it easy to include CSS Resets/grid systems into each view when loading/merging those files from a common folder, which only exists on the right/develop side.

FlightSimTrack, for example, has a few parts, such as

  • the maps,
  • the player information
  • Twitch Auth and PubSub handler

Which I’ve split into three files for ease of reading and modification, you can use one mega JS file or whatever compilation method you want, or not at all an include many script files! You just need to avoid magnification.

The only difference between my script.sh and my build.sh is build will generally HTML Minify where script doesn’t and build will compile the JS and drop and console.log commands, they don’t work on a released extension (and are disallowed by policy), so you may as well drop them from the files to keep the file size down! Great for Mobile users.

Summary

This will then give us a Development server, running on a Sub Folder, with files similar to what you would use in production. So this should be analogous to the Production result for your Extension.

Just one more thing

We forgot one thing, what about SSL? Oh that old chestnut! The final piece of the puzzle!

There are two easy ways to provide SSL Termination, both have their nuances but I prefer the second.

Method 1

NGROK, is a Free (or paid for product), that will create a temporary public URL to a running service on your machine.

So in this example you’d just do ./ngrok http 8050 and then the UI will display a URL to copy/paste into the Twitch Developer Console for your “Testing Base URI” just remember to add /extension/ to the end, since that is the mount point for your build. And now you have SSL Termination!

The Dev Console configured with a NGROK URL
The Dev Console configured with a NGROK URL

NGROK may have some other funnies such as rate limits, but for current limits please refer to their website and pricing structures.

Method 2

This is my preferred method, instead of using NGROK (or paying for a constant URL with NGROK).

I use a reverse SSH Tunnel, and get NGINX on a server to handle SSL Termination with a “real” free from LetsEncrypt Certificate.

Setup is the same on the user side, instead of running ngrok I ssh -R 8050:127.0.0.1:8050 username@example.com

This means I never have to update the Developer Console with a new URL, and for testing purposes all my Extensions use the Same URL. I just change the server running at the end of the tunnel. And if I start work on a new extension, I can use the exact same hosting settings.

NGINX is configured to do the normal SSL Termination stuff, then I just proxypass. Here is a config example from my live server that handles my Extension hosting.

server {
    listen someip:443;
    listen [::]:443;

    server_name example.com;

    ssl on;
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    include /etc/letsencrypt/options-ssl-nginx.conf;

    resolver_timeout 10s;

    ssl_dhparam /etc/nginx/dhparam.pem;

    location / {
        proxy_pass http://overssh8050;

           proxy_set_header Upgrade $http_upgrade;
           proxy_set_header Connection 'upgrade';
           proxy_set_header Host $host;
           proxy_cache_bypass $http_upgrade;
           proxy_redirect off;
           proxy_http_version 1.1;
           proxy_set_header Host $host;
           proxy_set_header X-Real-IP $remote_addr;
           proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
           proxy_set_header X-Forwarded-Proto $scheme;
    }
}

upstream overssh8050 {
    server 127.0.0.1:8050;
    keepalive 8;
}

I’ll usually use a second port/SSH tunnel/SSL’ed domain to talk to my EBS running locally. And my script.sh/build.sh can be configured to use different EBS URL’s in the fetch commands you may do. One less thing to forget to swap when building for release/review queuing.

Summary, for real

That is it for this weeks post, you can have a poke about in the GitHub Repository at BarryCarlyon/twitch_extension_blog_series both for the Server.js and script files and the folder structure.

Now you should be able to setup a local test server, that is similar in URL structure to a released Twitch Extension, and provide SSL to that test server, so you can test the Extension on Twitch, OR in the Rig, two of the most common pitfalls Developers face when starting to build extensions.

BUT MOTHER I CRAVE VIOLENCE

Well, until I write the next part if you want to read more about the Developer Side of Extensions, you can pop a visit over the to the Documentation or take a look at Twitch’s Introductory Page and you can always join us on the “TwitchDev Discord Server”, visit the Developer Support Page for the current invite link!

Why you think you are good enough to even write blog posts on Extensions? I made a one or two of them Extensions of various types.

Twitch Extensions: Part 3 – The Architecture of an Extension

In Part 2 we spoke a fair bit about “the path and file name of the HTML file you wish to load, it is a relative path to the Testing Base URI/final upload URL”, and this week we will cover why I mentioned that every time!

So, this week The Architecture of a Twitch Extension!

An example of Architecture from Wikipedia, The Pyramids at Gizah - © CC BY-SA 2.0
An example of Architecture from Wikipedia, The Pyramids at Gizah – © CC BY-SA 2.0

Basic Architecture

We have covered before that essentially a Twitch Extension is a “Website” that is iFrame’ed onto the Twitch Page, into an integration slot, but what does that actually look like?

The Twitch Architecture Overview
The Twitch Architecture Overview – According to Twitch

This is the “stack” that represents how an Extension is loaded, to illustrate this, we’ll use FlightSimTrack installed to the FlightSimTrack Twitch channel

  • First we have the Twitch Channel page – the “Browser” above
  • Then the Twitch Extension “supervisor”, this basically handles any handshaking between the outer Twitch and the inner Extension, we can’t cover more about it as it’s not documented anywhere, and that is my theory on what it does! It is mentioned in passing in the documentation
  • Then the Extension itself – the “iFrame” above

Relative path? WHY?

So why “relative path”? Well here is what the URL to the Panel looks like for FlightSimTrack

https://q6gmlap07mpxekhpspevz2sq5xjth7.ext-twitch.tv/q6gmlap07mpxekhpspevz2sq5xjth7/ 0.0.2/78753d6eeea69840398d8e46ff018e3b/panel/index.html?anchor=panel&language=en&locale=en-US&mode=viewer&state=released&platform=web

The first thing we’ll notice is that the index.html is in a sub folder of the domain. And NOW you know why we said “the path and file name of the HTML file you wish to load, it is a relative path to the Testing Base URI/final upload URL” every, single, time. And it’s a common hiccup that Extension Developers run into, a number of people come into the Developer Discord needing extension help, and they either made a mistake packaging the Zip for upload (we’ll cover Upload procedure in a future post), or the developer has used an “absolute” link to a JS/CSS file (starting /style.css or https://example.com/style.css for example, instead of just style.css).

But lets break down this URL, into it’s parts

URL breakdown

https://extClientID.ext-twitch.tv/extClientID/Version/md5OfZip/path_to_file_for_integration_point.html?querystring

We’ll cover the Query string parameters more in a future post, but you can read about them in the Extension Documentation Reference

The most important one to be aware of right now is anchor which tells you which integration slot this is. In this example it’s a panel, and FlightSimTrack’s panel is configured to load panel/index.html for this integration slot.

  • extClientID is obvious, it’s the ClientID of your Extension
  • Extensions live on the domain extClientID.ext-twitch.tv, why a different domain for each extension and separate to Twitch? This prevents any issues with Cookies from the “main” Twitch Website, so there won’t be any session hijacking or other crazy things, you can read a little more on that in the documentation
  • Version – the version of the extension that these files are for
  • md5 of the zip file that was uploaded, during testing you might go to Hosted test/local test (two Stages of the Extension Lifecycle that we’ll cover next week) a few times, so the md5 will change, this is a easy “cache defeat” when you are Hosted testing
  • Final part is the path and html file you specified in the console to load for this integration slot

Asset Hosting for FlightSimTrack
Asset Hosting for FlightSimTrack

The URL structure is the same for every integration point, and all files are considered “public”, which is something to consider when building in things for Channel Moderators to use.

That about covers everything for the frontend

Well, what about the Backend?

Oh you want the backend to do you?

The Twitch Architecture Overview
The Twitch Architecture Overview – According to Twitch again!

First of all it’s important to note than a Backend, also referred to as EBS or Extension Backend Service, is entirely optional, depending on your Extension, what/how it functions or what it does, it might not even need an EBS, either from calling Public API’s or from it being completely self contained.

The SSL Requirement

But for those Extensions that need an EBS, there is essentially one rule, it must serves it’s contents over SSL, this isn’t just good for Security, but is required as the Twitch Website is over SSL and browsers will reject Mixed Content (loading non SSL content from SSL).

So

  • Loading from the EBS? Needs to be https://urltoyourebs/
  • Loading from a Public API? Needs to be https://someapi/
  • Loading from a Websocket? Needs to be wss://somesocket/
  • Loading an image from a CDN? Needs to be https://somecdn/image.png

To illustrate some examples:

  • FlightSimTrack viewer, nothing at all (images are on the Twitch Extensions CDN and map tiles come from map tile vendors over SSL)
  • FlightSimTrack config, EBS lives at https://twitch.extensions.barrycarlyon.co.uk/
  • CohhCarnage Panel Extension, uses an API at https://extensions.cohhilition.com/ and a socket at wss://extensions.cohhilition.com/
  • Dropped Frames video Extension, no API or socket at all, but images from a CDN, usually Twitter/Twitch avatars directly from Twitter/Twitch over HTTPs, it receives from Twitch PubSub only.

You can see that they all all work over endpoints/routes protected by SSL.

We’ll cover how to build a “custom” EBS, and verifying identity in a future post, this week it’s just “Architecture”, the long and short of it, is you are basically just building a Custom API to interact between your front end and backend. A common way I describe Extensions, is as follows

Extensions are a website, where the front end is on a different server to the backend, and you can’t do server side rendering

– Barry Carlyon on “Well what is an Extension anyway!”

Languages

Whilst a Twitch extension is “limited” to HTML and JavaScript, your EBS/Backend API can be in any language you want. But when it comes to examples, samples and boilerplates you’ll generally find them in JavaScript (via NodeJS) or Go, (since Twitch is a “Go House”). We’ll be using NodeJS in this series, merely because it’s potentially the easiest for people to understand and convert knowledge between different languages.

If you want to jump ahead, you can check out the Developer Rig, which will provide you access to a number of Extension Examples, which are also available on the TwitchDev GitHub, or my own Twitch Profile Extension (which demonstrates how to call the Twitch API via an “EBS” proxy), these examples are designed to highlight a specific function of Twitch Extensions, rather than a “practical” example.

Real Certificates only

Naturally this needs to use “real” SSL Certificates, as apposed to self signed, which is “bearable” for testing with. Generally you’ll find Extension Developers will whip out LetsEncrypt as it’s free and easy to setup, and straightforward to setup a testing system.

Summary

So that covers the Architecture of an Extension

Not really sure what else to add, here is a photo of my cat, Sprite.

Sprite has invaded this Blog Post
Sprite has invaded this Blog Post

What about next week?

Next week we will be looking at the Developer Rig and how/when to use it and setting up a Dev environment suitable for developing a Twitch Extension!

BUT MOTHER I CRAVE VIOLENCE

Well, until I write the next part if you want to read more about the Developer Side of Extensions, you can pop a visit over the to the Documentation or take a look at Twitch’s Introductory Page and you can always join us on the “TwitchDev Discord Server”, visit the Developer Support Page for the current invite link!

Why you think you are good enough to even write blog posts on Extensions? I made a one or two of them Extensions of various types.