I'm going to copy this to the mediawiki-api list, too.

On Fri, Jan 25, 2013 at 8:01 AM, Daniel Kinzler <daniel@brightbyte.de> wrote:
> Hi all!
>
> Wikidata (technically, Wikibase) uses a lot of JS/API based editing, and we have
> several times hit upon the question of how to best report errors from the API.
> I'll try to break the issue down into several concrete questions. But first off,
> the status quo as I understand it:
>
> * errors are reported using an error code (a string) and a free form error
> message. The message is usually not internationalized, though sometimes it is.
> * warnings are reported as free form text.
> * Additional information can be added to both errors and warnings, but there is
> no standard way to do this.
> * Errors exposed by the API are often not generated but just passed through by
> the API; Typically, a generic error code is used with the original error message
> (e.g. from an exception).

Sounds generally correct. Anything coming out of the API
internationalized is probably either being passed through from
something else or being generated in an extension.

> So, here are my questions:
>
> * Should error messages returned by the API be translated? Or should the
> translation be left to JavaScript in the client?
> ** In both cases, it would be nice to have a consistent relationship between
> error codes and the corresponding system message.
> ** If translation is done on the client, we need to pass any message parameters
> separately.
> ** The message key would have to somehow be derived or mapped from the error code.

It would be nice to have internationalized and parameterized error
messages from the API. The problem is that if we want to do anything
without waiting for "API version 2", we want to avoid as much as
possible breaking backwards compatibility with existing clients. Which
probably means that we'll want to add a parameter for the client to
specify the new style errors and warnings; this can double as
selecting the language the errors should be returned in.

I'd have to look at what existing code does as far as errors/warnings
before making a more concrete proposal.

> * When using system messages to translate the error codes from the API, these
> messages will often contain wikitext. How can we best avoid this? Wikitext is
> likely to be quite useless to the client - it would be better to return HTML; or
> pass all the message keys and parameters, and let the client generate the message.

I'd suggest that messages actually returned by the API should be in
plain text, and should ''not'' use the MediaWiki namespace. In terms
of the Message class, $msg->useDatabase( false )->text(). This makes
things sensible for bots and such; they will often be writing errors
to a log file or showing them in some user interface where HTML
parsing is probably not available.

The message key and parameters should (optionally?) be returned for
the client to format as HTML or whatever. And the client is welcome to
use the MediaWiki namespace. This is sensible for Javascript user
interface and such.

Unfortunately, it seems that the message key prefix "api-error-" is
already in use.

> * Status objects are often used to collect errors and warnings the occur while
> trying to perform some task. It would be nice if the API would provide a
> standard way to put the contents of a Status object into the result (well, at
> least the errors and warnings).

It seems it does, at least sort of: ApiResult has a
convertStatusToArray() method.

> Any thoughts on that?
>
> -- daniel

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