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Re: error classes

From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Date: Thu, 18 Apr 2013 11:43:45 +0200
Message-ID: <516FC051.4050705@ericsson.com>
To: public-media-capture@w3.org
Jim,

Harald recently sent a proposal [1] on error handling. Does it (propose) 
answers to your questions, or some of them?

Stefan


[1] 
http://lists.w3.org/Archives/Public/public-media-capture/2013Apr/0158.html

On 2013-04-12 16:40, Jim Barnett wrote:
> In our previous discussions of error handling, I think that we agreed
> that we would use exceptions for errors that were immediately detectable
> (argument type mismatches and the like).  Someone (Adam?) said that the
> IDL will create some of these for us automatically.  If that’s the case,
> it would be great if he could send an explanation/link around so that we
> can understand exactly what we get for free.
>
> There is an ongoing discussion of how to handle the gUM success and
> failure callbacks. This is a case where the code requests an operation
> and knows that at some point it will get notification of either success
> or failure.    There is also another kind of error, namely those that
> occur later in processing, for example network problems when using
> PeerConnection or running out of memory while recording.  There is no
> corresponding success event to go with these.  Instead they represent
> problems that can come up at any point during processing.
>
> Both the success and failure callbacks and the runtime errors define
> error classes containing information about the error.  Currently each
> spec defines its own classes, and there’s a lot of rather unsystematic
> overlap in these definitions, and I think it’s time to start cleaning it
> up.
>
> 1.The gUM spec has NavigatorUserMediaError with attributes name,
> message, and constraintName
>
> 2.The recording spec has RecordingError with attributes name and message
>
> 3.The webRTC  spec has RTCError with attributes name and message, along
> with RTCSDPError which adds sdpLineNumber.
>
> 4.The image capture spec has PhotoErrorEvent with attribute photoError
> (which may be equivalent to ‘name’ in the other specs.)
>
> 5.The image capture spec also has SettingsErrorEvent with attribute
> PhotoSettings (which looks a bit like constraintName in the guM spec.)
>
> The errors in the image capture spec inherit from event, but none of the
> other errors inherit from any class.
>
> It seems like we all want an error class with name and message
> attributes. There is a DOMError class defined at
> http://dom.spec.whatwg.org/#errors which has a name attribute, but we
> would need to extend it to hold ‘message’ as well.  DOMError comes with
> a table listing the legal values for name, but it can be extended.  Some
> of the  names that are already defined could be used as is, such as
> ‘NetworkError’ or ‘TimeoutError’.
>
> So the first question is:  should each spec extend DOMError separately
> or should we define the base error class in the gUM spec and let the
> other specs inherit it?  If we do put something in the gUM spec,  it
> would have to have a generic name like ‘MediaError’, since a lot of the
> errors it would be used for are not tied to gUM.   On the whole, I think
> inheriting would be cleaner.  Each spec would have to define the new
> values for ‘name’ that it required, but wouldn’t need the extra class
> definition.   (Each spec should probably also explain which of the
> existing DOMError names it would use, so that programmers know the full
> range of error names that the API might use.)
>
> If we do choose to inherit/extend, it would make sense to define some
> sort of ConstraintError (which would have a ‘constraintName’ attribute)
> in conjunction with the Constrainable interface so that other specs
> would reuse both.   If Constrainable gets extended to handle settings as
> well (or if a separate Settings interface is defined), SettingsError
> would follow the same pattern.
>
> Another question involves the details of how the error handler works.
> In our current specs, the error object is passed directly to  the
> onerror event handler.  A while back Travis sent around a proposal for a
> slightly different model.
> http://lists.w3.org/Archives/Public/public-media-capture/2012Dec/0167.html
> In this model, the error object is an _/attribute/_ of the class (e.g.
> MediaRecorder).   The UA sets this attribute to an appropriate value
> when an error occurs and then calls the onerror handler, which then
> looks at the attribute to get the error information.    I’m not sure how
> important this distinction is, but we have to decide which model to use
> (and all four specs should use the same model.)
>
> -Jim
>
Received on Thursday, 18 April 2013 09:44:09 UTC

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