Saturday, October 31, 2020

Control Tracking JavaScript Using Sitecore Rule-based Configuration



Being able to control tracking JavaScript via Environment and Server role is a common problem that Sitecore developers are faced with. For example, your client doesn't want their Production Google Tag Manager or agency delivered tracking pixel scripts firing on any server / app instance other than their Production Content Delivery as it will spoil analytics.

Most of the time, developers will add some type of "if statement" code in Layouts or Renderings to help facilitate this, but this could be difficult to control and maintain based on the number of scripts you end up adding to you site(s). 

In addition, if you are using SXA and HTML snippets in your metadata partial design to house the scripts, this becomes even harder.

Post-Processing HTML

I wanted to focus on finding the sweet spot in Sitecore where I could inspect the entire HTML output after it had been glued together by the various pipelines, and then remove the target script from the HTML before it was transmitted to the browser.

Sitecore's httpRequestProcessed pipeline gives is the entry point, where we can leverage the MVC framework's result filter to manipulate the HTML.

I told my content authors to add a new attribute called "data-xp-off" to their scripts that I would use as the flag to determine if the script would be removed from the page.

For example:
<script data-xp-off>some tracking stuff</script>

Writing the Code

The first step was to create a new HttpRequest processer and associated configuration to inject into the httpRequestProcessed pipeline. Within this, I was able to access the HttpContext response filter object where I could perform the targeted script removal.

As you can see by the config, you can use whatever rule-based role config to apply the processor.

Next, I created a class based on the System.IO Stream class, where I overrode the Flush method. Within this new Flush method, I removed the script using a regular expression (based on the existence of the data-xp-off attribute within the html), and then wrote it to the response.

You will notice that I also included the "noscript" and "style" tags as an option for the filtering which was a bonus.

So you may ask me; "Martin, why did you not use the powers of the Html Agility Pack to perform your HTML manipulation?".  To be honest, that was my first approach. I wrote this code:

I discovered that the InnerHtml returned by the Agility Pack was making unintentional changes to my HTML markup, and that caused problems with client-side heavy components.  Digging into Sitecore's code, I discovered that they used the regular expression approach when injecting their Experience Editor "chrome" elements, and so I went down that path too.


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