Add Application errors for Mediawiki API to x-analytics
Sounds like application errors are reported to MediaWiki-API-Error header when an API request is in error. Adding this field to x-Analytics allows us to be able to quantify API errors using webrequest table.
Now, this doesn't include errors like 404s or 503 so only part of the errors from the API will be reported.
Now, this doesn't include errors like 404s or 503 so only part of the errors from the API will be reported.
The API never generates 404s, and never intentionally generates 5xx (they only get generated in case of PHP fatals or things being so badly screwed up that exceptions aren't being caught). A 400 might be generated by certain special actions that can't report errors in a normal way (e.g. the proposed TimedMediaHandler action=timedtext that doesn't return a normal API-formatted response, or possibly the various feed modules in the future), and a CORS failure may return a 403 in line with the CORS specification (which isn't strictly "API" since it's at the level of the HTTP transport rather than the API itself).