Gopherizing some puppeteer code

Why?

As developers we sometimes get a bad case of the shiny new object syndrome. I hate to say it but every time I start hacking on something new, the urge to add something new is quite overwhelming. It is really tough to keep an interest in projects for a long time and it starts to become tedious the deeper you go into the weeds. I suppose this is why people list growth as one of their top motivations.

I consider that anything new is an opportunity for growth, and doing something over and over in a similar manner quickly becomes a tedious. I’ve been building various types of scrapers since 2011, and it all started because I wanted to automate a workflow and save myself some time. The time spent on automating this was probably more than if I had done this by hand but it was interesting interacting via http from code and crunching the data automatically.

The amount of data on the web is pretty crazy, you have various sources and multiple types of data that can be combined in very interesting ways. Back in those days dropshipping was becoming huge and people were performing arbitrage across Amazon/Ebay/local flea-markets etc.. Tools that were able to perform analytics across these shops were quite trendy, and the market was slightly less crowded, so for me building crawlers seemed like a nice idea to build out a good customer base.

Nowadays due to RAG systems, gathering data automatically, breaking it down and feeding it into embedding models and storing it in vector databases for LLM information enhancement has come back into the spotlight. In between then and now there have been a few changes in the way data is served up for consumption. Off the top of my head:

  • single page apps have gained huge traction, most everyone turning to building their content in a js bundle, loading everything on the fly as the page loads
  • websites have become fussy about having their data used by unknown parties, so they have been closing down access and have become very litigious(#TODO: maybe add some cases of court cases Linkedin vs those guys, Financial Times vs OpenAI)
  • bot detection and prevention – this one is funny since it is like a flywheel, it built 2 lucrative markets overnight – bot services and anti bot protection
  • TBH, it’s difficult to predict where this might be heading, it kind of feels like people have been aiming to move all their datas into data centers but since data is becoming so guarded…will they move back to paper?

All your data are belong to us

Because of SPAs and the wide adoption of js in websites it is much more convenient to use some sort of browser automation to crawl pages and extract the information. This makes it less prone to badgering the servers, and having to reverse engineer the page content loading, so you will probably want to use either a chrome developer tools protocol or webdriver flavored communications protocol with the browser. Back in the day IIRC I have also used the PyQt bindings for acessing the Qt browser component but nowadays its mostly straight-up browsers.

These days my goto is puppeteer. It’s a weird tool that can be easily be used to scrape data from pages. The reason I say it is weird is mainly due to the deceiving nature of the internals, essentially using two js engines that communicate via the cdp protocol that is a a very dense beast and does not play nice with complex objects.

Recently it has become more appealing to me to use strongly typed languages. This is probably because I have started to narrow down my experiments to very small code samples that illustrate one thing at time. I would go as far as to call it experiment driven development. Duck typing is fun as you can print pretty much anything you want. I was thinking to use rust but it has a very tough learning curve. Node is pretty nice with mjs but it’s confusing sometimes when it crosses over between the two event loops, also while it is good for communicating on cdp it is not really designed for sync code and python is a bit boring for me so I decided to look at go. Since it is a google language I expected it to have decent support for cdp, and the learning curve is slightly gentler than rust.

How?

Looking at the alternatives there are two that stand out chromedp and rod. Rod looks like it is the prodigal son of behave and cucumber some well established BDD frameworks. Personally I am not finding the MustYaddaYadda... very readable and combining it with other custom APIs would probably make it become inconsistent. It has a few nice things in the way it abstracts iframes but I am just unable to go past the higher level API.

In the end I wound up choosing chromedp. It works pretty well for most use cases, there are some places where it doesn’t quite cut it and I wish it did, but by now I have come to terms there is no one technology to rule them all, wouldn’t it be nice if that existed?

You can install it via go get -u github.com/chromedp/chromedp and then you can start using it in your code. It has quite a few submodules and related projects that you may want to use depending on your concrete use case.
Generally if your use case is only data extraction and you have no tricky actions to deal with(page is bot resistant, some elements are loaded at later times, iframe hell etc…).

import ( "context" "log" "time" "github.com/chromedp/chromedp" "github.com/chromedp/cdproto/cdp" // for slightly more advanced use cases "github.com/chromedp/cdproto/browser" "github.com/chromedp/cdproto/dom" "github.com/chromedp/cdproto/storage" "github.com/chromedp/cdproto/network"
)
Enter fullscreen mode
Exit fullscreen mode

The pleasant surprises

Well, calling them surprises is a bit of a stretch, I have been golang over the years and I have to admit it is a pretty nice ecosystem and language.
chromedp automates chrome or any binary that you are able to communicate with via cdp. The API is somewhat intuitive, haven’t found myself diving into the guts of it very often to figure out how stuff works. The good part is that once you extract the data from the nodes you are interested in you can map it to go structs and make use of the go typing system.

For example you can grab a list of elements via selector:

 var productNodes []*cdp.Node if err := chromedp.Run(ctx, // visit the target page chromedp.Navigate("https://scrapingclub.com/exercise/list_infinite_scroll/"), chromedp.Evaluate(script, nil), chromedp.WaitVisible(".post:nth-child(60)"), chromedp.Nodes(`.post`, &productNodes, chromedp.ByQueryAll), ); err != nil { log.Fatal("Error while trying to grab product items.", err) }
Enter fullscreen mode
Exit fullscreen mode

then map each element to a struct

 for _, node := range productNodes { if err := chromedp.Run(ctx, chromedp.Text(`h4`, &name, chromedp.ByQuery, chromedp.FromNode(node)), chromedp.Text(`h5`, &price, chromedp.ByQuery, chromedp.FromNode(node)), ); err != nil { log.Fatal("Error while trying to grab product items.", err) } products = append(products, Product{name: name, price: price}) }
Enter fullscreen mode
Exit fullscreen mode

Another nice perk is that go is built with concurrency in mind so crunching the extracted data can be a lot more performant than in puppeteer.

Yet another pretty nifty thing I found is that you can deliver a binary that can be compiled for multiple platforms and can be distributed easily. This is a huge plus given that you may not really know who the user of the tool might be in the end.

The ugly parts

The way to communicate with the browser is still through the cdp protocol and sometimes you need to pass objects only objects that can be serialized.

If you need to work with objects that can’t be serialized you will need to inject js into the page context and interact with it.

When you have a page that contains iframes it is problematic to trigger events on the elements inside them. You can extract data from it but triggering events gets messy as you need js for that.
An example of how you might extract data from an iframe might look something like this:

 var iframes []*cdp.Node if err := chromedp.Run(ctx, chromedp.Nodes(`iframe`, &iframes, chromedp.ByQuery)); err != nil { fmt.Println(err) } if err := chromedp.Run(ctx, chromedp.Nodes(`iframe`, &iframes, chromedp.ByQuery, chromedp.FromNode(iframes[0]))); err != nil { fmt.Println(err) } var text string if err := chromedp.Run(ctx, chromedp.Text("#second-nested-iframe", &text, chromedp.ByQuery, chromedp.FromNode(iframes[0])), ); err != nil { fmt.Println(err) }
Enter fullscreen mode
Exit fullscreen mode

But in order to trigger events on elements inside the iframe you can’t just use the chromedp API, and since chromedp.Evaluate does not take a Node as context you will need to perform all the actions in javascript and that will make the resulting code a bit of a mishmash of go and js.

puppeteer also has some extra packages that can be used like puppeteer-stealth but chromedp does not seem to have an equivalent for that at this time. The rod package has rod stealth but I haven’t tried it since the API is not to my liking.

The other slightly dissappointing missing feature is that when running in headless mode all the GPU features are disabled because it is running in a headless-chrome container which does not have a display server. Puppeteer is able to run with GPU features enabled allowing it to pass the webgl fingerprinting tests.

Conclusion

  • in some ways puppeteer is still better than chromedp, working with iframes falls short
  • rod is a nice alternative but its API looks like it was designed for testing, reminds me of cucumber
  • chromedp is a nice alternative to puppeteer if you are looking to build a binary that can be distributed easily
  • it is a bit more performant than puppeteer due to the concurrency model in go

Discover more from Coursity

Subscribe to get the latest posts to your email.

Comments

No comments yet. Why don’t you start the discussion?

Leave a Reply

Your email address will not be published. Required fields are marked *