https://chromedevtools.github.io/devtools-protocol/tot/Network#event-loadingFailed

Example:

{"method":"Network.loadingFailed","params":{"requestId":"1000019154.7022","timestamp":519853.465592,"type":"Fetch","errorText":"net::ERR_INTERNET_DISCONNECTED","canceled":false}

It looks like Gutenberg is observing the contents of the errorText field )-:

https://github.com/WordPress/gutenberg/blob/3e43bccd1b51f11f6acf7f8eea5f70e3753444d5/packages/e2e-tests/config/setup-test-framework.js#L122

Given the frequency of usage via https://wiki.mozilla.org/Remote/GutenbergCDPUsage#Events this comes at the very ending of the list. So I don't think it is important right now to get implemented.

This is among the events we see in a gutenberg run: https://wiki.mozilla.org/Remote/PuppeteerCDPUsage#In_Wordpress_gutenberg_test_suite

So what's the difference between those different sites, and especially what does the "In Wordpress gutenberg test suite" section mean compared to the events as listed on GutenbergCDPUsage?

(In reply to Henrik Skupin (:whimboo) [⌚️UTC+2] from comment #4)

So what's the difference between those different sites, and especially what does the "In Wordpress gutenberg test suite" section mean compared to the events as listed on GutenbergCDPUsage?

It's the subset of events encountered during a gutenberg run that are also used somehow in Puppeteer. So to support gutenberg's use of Puppeteer, it makes sense to prioritize those events over others. As we investigate how the events are actually used, we might change the priority.

In the case of loadingFailed, it's relatively infrequent because we usually expect resources to load successfully in a test, but it might be used as part of error handling in test suite setup, for example.

This event gets emitted because Puppeteer by default enables the Network domain. But it doesn't look like that the RequestFailed event from Puppeteer is used by Gutenberg. I would suggest we keep it of the track for Gutenberg for now.

We might be able to use the http-on-failed-opening-request observer notification similar to devtools to detect security check failures:

https://searchfox.org/mozilla-central/rev/46e3b1ce2cc120a188f6940b5c6eab6b24530e4f/devtools/server/actors/network-monitor/network-observer.js#310-324

See also bug 1638259 comment 21 for issues with CSP and loading resouces like style sheets.