Value Error when uploading resized images to Google Cloud Storage

My image model contains;

def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
    image_asset = img.open(self.image)
    image_name = uuid.uuid4()

    image_asset.thumbnail((1200, 1200), img.ANTIALIAS)
    fi_io = io.BytesIO()
    image_asset.save(fi_io, format='JPEG', quality=90)
    self.image = InMemoryUploadedFile(
        fi_io,
        'ImageField',
        '%s.jpg' % image_name,
        'image/jpeg',
        sys.getsizeof(fi_io), None
    )

    super(Image, self).save(force_update=force_update)

Whenever I attempt to save an image I get this error (the exact size depends on the file uploaded):

ValueError: Size 3984 was specified but the file-like object only had 3862 bytes remaining.

Without this code, the image saves fine. Also when switching to a Digital Ocean storage this exact code works without a problem.

[bgrace]

I think this is an error in the end user code which GCS rejects and the other services are more liberal about. The call sys.getsizeof(fi_io) yields the size of the BytesIO object, not the size of the buffer:

>>> iobuffer = io.BytesIO()  # empty buffer (0 bytes)
>>> sys.getsizeof(iobuffer)
88
>>> len(iobuffer.getbuffer())
0
>>> 

This following code works for me with django-storages and GCS when the returned thumbnail is saved to the model:

def generate_thumbnail(src):
    image = Image.open(src)  # in memory
    image.thumbnail(settings.THUMBNAIL_SIZE, Image.ANTIALIAS)
    buffer = BytesIO()
    image.save(buffer, 'JPEG')
    file_name = Path(src.name).name

    temp_file = InMemoryUploadedFile(buffer, None, file_name, 'image/jpeg', len(buffer.getbuffer()), None)
    return temp_file

[Daniil0891]

@bgrace Thanks a lot for a working solution!