Raise an exception when the header cannot be parsed

[wojcikstefan]

Also refactors unit tests so that they produce an expected output upon success and failure.

The main rationale behind MimeTypeParseException is that if somebody sends a request as follows:

requests.get(url, headers={ 'Accept': 'text' })

... the server should respond with a 400 saying that the header is not formatted properly. Right now, we'd have to do the validation outside of the library (introducing somewhat duplicate code) or we'd have to catch a ValueError (because (type, subtype) = full_type.split('/') would raise ValueError: need more than 1 value to unpack), which is too generic. Merging this PR will help me submit a similar PR to https://github.com/martinblech/mimerender utilizing the new exception type and returning a valid response.

[dbtsai]

Thanks. Merged.

[wojcikstefan]

Great, thank you @dbtsai! Could you release an updated pypi package?

[dbtsai]

Let me do it durning the weekend. Thanks.

[dbtsai]

@wojcikstefan The build is broken with your patch, https://travis-ci.org/dbtsai/python-mimeparse/builds/105085056
Can you fix it? Thanks.

[wojcikstefan]

Yup, will do. Thanks for pointing that out!

[mattbriancon]

This was a backwards-incompatible change and should have been released under a new major version. I'm guessing there are currently a lot of broken builds out there right now.

[dbtsai]

@wojcikstefan Can you address the concerns raised by @mattbriancon? Thanks.

[wojcikstefan]

@mattbriancon could you elaborate? Providing an invalid mime type format already resulted in an exception here (though it indeed was a different exception type - ValueError vs MimeTypeParseException, which doesn't inherit from ValueError). Is that the incompatibility you refer to? Or is it the fact that the exception's message uses a .format function that's incompatible with py2.6 (which wasn't in tested as one of the supported versions)?

[mattbriancon]

It's the change in the exception type.

https://github.com/django-tastypie/django-tastypie/blob/master/tastypie/utils/mime.py#L37-L40

[mattbriancon]

Tracking the issue here: django-tastypie/django-tastypie#1429

[wojcikstefan]

@mattbriancon let me clone django-tastypie and propose a fix to python-mimeparse that'll fix your tests.

[wojcikstefan]

@mattbriancon @dbtsai I just opened #13 - it should fix the issue.