Use compressed content instead of changing original object

[melbic]

This fixes a bug that the upload of a file is not possible when gzip is activated (django-cms/django-filer#885)

When gzip activated, the current version changes the actual object and overwrites its current file
with the gzipped datastream. When the object instance is simultaneously used by other "algorithms" (e.g. django-filer) this ends in wrong behavior/exceptions.

[jschneier]

Hi, I think is another report of the same issue. My worry is that I don't think your fix will work, as the reporter says they are seeing an exception with the .size parameter not existing, the zbuf object doesn't have a .size property either.

[jschneier]

As such this PR was submitted. I'm trying to deal with this issue now but I don't understand it yet, any help would be greatly appreciated.

[melbic]

Yes, the size method/ivar is the problem there, but it only occurs because we exchange the existing file in content with the new ByteIO stream. My approach is to leave the object the way it was and only save the new stream to S3.

You may test the behavior by installing django-filer==1.1.0 enable GZIP for the images and upload an image. It will silent fail.
The exception happening here:

django.db.models.fields.FieldFile._get_size:
    def _get_size(self):
        self._require_file()
        if not self._committed:
            return self.file.size <----
        return self.storage.size(self.name)

[melbic]

@jschneier I'd really like to switch back to the pypi version instead of using our fork. Any progression in the matter of this PR?

[jschneier]

Can you please add a test. Or the outlines of one and I can take a go at adding it if you don't have the time.

[melbic]

Ok, I try to find the time this or the next week.

[melbic]

I just tried to adjust test_s3boto.py::test_storage_save_gzip, but unfortunately I wasn't able to figure out what exactly the arguments in key.set_contents_from_file.assert_called_with should be for gzipped data. Any hints?

[gposton]

@jschneier, we've ran into this bug as well... I commented on #74, but this PR seems to be more recent. Can we get this merged? Our issue is the same. Cannot upload small files. We've verified the PR fixes our issue on python 2.7.9, boto 2.48, django 1.6.8. Would like to remain on main-stream if possible :)

[gposton]

Not sure if this helps, but the issue is not present in this combo: python 2.7.9, boto 2.36, django-storages 1.1.8

[gposton]

I suspect this broke in 1.6.6 w/ the change from StringIO to ByteIO: 1c64e83