The `http_api_debug` hook isn't called for all HTTP requests

[johnbillion]

In WP_Http::_dispatch_request(), the http_api_debug action isn't called if there are no available transports for the request. This means we miss a situation that is ripe for debugging.

Edit: There's more. See my comments below.

[johnbillion]

25747.diff​ (best viewed without whitespace changes) alters _dispatch_request() so it doesn't return the WP_Error immediately. It then gets passed to the http_api_debug hook as expected.

Anything that's hooking into this hook will need to ensure it handles boolean false as the $class parameter, as well as a string.

[johnbillion]

There are actually several places where an HTTP request's return value doesn't trigger the http_api_debug action. None of the following responses trigger it:

• Anything short-circuiting requests with the pre_http_request filter (​here).
• Invalid URLs (​here).
• Blocked requests (​here).
• Unwritable directories when streaming (​here).

We might need a little refactoring here, or a helper method to trigger this action.

[wonderboymusic]

Bump

[johnbillion]

25747.2.diff​ is a partial patch that I've had sitting around for ages. Probably needs some more work. And tests.

[johnbillion]

25747.3.diff​ introduces a much simpler patch than prior ones. It calls the http_api_debug hook on all erroneous responses. There's no need to call the hook for errors being returned by pre_http_request because it's already catchable via that filter.

In addition, I've changed the error code for the error returned when requests are blocked so that loggers, debuggers, etc can differentiate between an unexpected error and an expected one.

[johnbillion]

In 45504:

HTTP API: Ensure the http_api_debug hook is fired for all responses.

This means that logging and debugging functionality can access the error code and error message for erroneous responses under all conditions. The hook is not fired when a request is short-circuited with the pre_http_request filter, because this filter itself can be used in that situation.

Fixes #25747