Notes on web browser automation

2019-01-08 - Progress - Tony Finch

I spent a few hours on Friday looking in to web browser automation. Here are some notes on what I learned.


I have some old code called superglue-janet which drives the JISC / JANET / UKERNA domain registry web site. The web site has some dynamic JavaScript behaviour, and it looks to me like the browser front-end is relatively tightly coupled to the server back-end in a way that I expected would make reverse engineering unwise. So I decided to drive the web site using browser automation tools. My code is written in JavaScript, using PhantomJS (a headless browser based on QtWebKit) and CasperJS (convenience utilities for PhantomJS).

Rewrite needed

PhantomJS is now deprecated, so the code needs a re-work. I also want to use TypeScript instead, where I would previously have used JavaScript.

Current landscape

The modern way to do things is to use a full-fat browser in headless mode and control it using the standard WebDriver protocol.

For Firefox this means using the geckodriver proxy which is a Rust program that converts the WebDriver JSON-over-HTTP protocol to Firefox's native Marionette protocol.

[Aside: Marionette is a full-duplex protocol that exchanges JSON messages prefixed by a message length. It fits into a similar design space to Microsoft's Language Server Protocol, but LSP uses somewhat more elaborate HTTP-style framing and JSON-RPC message format. It's kind of a pity that Marionette doesn't use JSON-RPC.]

The WebDriver protocol came out of the Selenium browser automation project where earlier (incompatible) versions were known as the JSON Wire Protocol.

What I tried out

I thought it would make sense to write the WebDriver client in TypeScript. The options seemed to be:

  • selenium-webdriver, which has Selenium's bindings for node.js. This involves a second proxy written in Java which goes between node and geckodriver. I did not like the idea of a huge wobbly pile of proxies.

  • aka wdio, a native node.js WebDriver client. I chose to try this, and got it going fairly rapidly.

What didn't work

I had enormous difficulty getting anything to work with wdio and TypeScript. It turns out that the wdio typing was only committed a couple of days before my attempt, so I had accidentally found myself on the bleeding edge. I can't tell whether my failure was due to lack of documentation or brokenness in the type declarations...

What next

I need to find a better WebDriver client library. The wdio framework is very geared towards testing rather than general automation (see the wdio "getting started" guide for example) so if I use it I'll be talking to its guts rather than the usual public interface. And it won't be very stable.

I could write it in Perl but that wouldn't really help to reduce the amount of untyped code I'm writing :-)