ClientError (404) in S3Boto3Storage when calling write()

[va-andrew]

When S3Boto3Storage has gzip enabled, the following code generates an error when writing to an S3 key that does not already exist:

with my_storage.open('new_key.txt', 'wb') as f:
    f.write(b'hello')

The stack trace indicates an error is happening for S3Boto3StorageFile._get_file():

            ...
            if self._storage.gzip and self.obj.content_encoding == 'gzip':
                self._file = GzipFile(mode=self._mode, fileobj=self._file, mtime=0.0)

Basically, by checking self.obj.content_encoding, Boto3 is performing a HeadObject() operation on the key, even though it doesn't exist yet, which is generating the 404.

Should the relevant code instead use the content-encoding guessed from the newly created file? That's what the S3Boto3Storage.save() method does and it doesn't have this issue.