Comment 3 for bug 1652716

The storlet not setting metadata isn't a problem with the request, but rather with the server so I think 5XX is more appropriate. Unrelated to the status we should definitely add a message as you have suggested.

Regarding the design specification remark. If we let the user control this, we can mask out buggy storlets that should change the metadata but don't (I admit that thinly example I have in mind is Content-Type which we currently do not allow to change anyway). Lets keep this in mind when we actually get to it.