Fix for byte string incompatibility in ResponseModelFactory.body() on py3

[aljp]

I would like to fix this warning I see a lot using silk with python3.5 and django 1.9: Response to request with pk 97a4673c-ba72-485b-88cf-f3a35e583b7b has content type application/json but was unable to parse it

In the ResponseModelFactory.body(...) method it seems to hit this exception on python3 because the content variable is a byte string, not because it is an invalid json string. I have added a check to test if it is not a str type object, then if so decode the bytes.

I do not have much experience in python2/3 compatibility so a extra pair of eyes to double check would be appreciated.

[avelis]

@aljp Is there a unit test you can add to assert that this will work as expected on Python2 & Python3?

[aljp]

I wrote a unit test for this but it seems that trying to test invalid json will throw an exception within the tests due to Logger.warn('Response to request with pk %s has content type %s but was unable to parse it' % (self.request.pk, content_type)) , i.e.

Traceback (most recent call last):
  File "/Users/adam/Projects/silk/project/silk/model_factory.py", line 231, in body
    body = json.dumps(json.loads(content), sort_keys=True, indent=4)
  File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/json/__init__.py", line 319, in loads
    return _default_decoder.decode(s)
  File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/adam/Projects/silk/project/tests/test_compat.py", line 42, in test_python3_invalid_content_compat
    body, content = factory.body()
  File "/Users/adam/Projects/silk/project/silk/model_factory.py", line 233, in body
    Logger.warn('Response to request with pk %s has content type %s but was unable to parse it' % (self.request.pk, content_type))
AttributeError: 'NoneType' object has no attribute 'pk'

[aljp]

In the meantime I have commented out two tests which ensure that invalid json content returns the appropriate empty string from ResponseModelFactory in python 2 and 3

After a quick read it seems I may have to instantiate a DataCollector() and mock the request on that object to get these invalid json tests to pass? I will gladly have another look tomorrow to test if that is the case.

[avelis]

@aljp Thanks for writing the unit tests and the contribution!