Storage: google-resumable-media==0.4.0 Breaks Gzipped Downloads

[william-silversmith]

Environment details

1. Specify the API at the beginning of the title (for example, "BigQuery: ...")
   General, Core, and Other are also allowed as types

Google Storage blob.py

2. OS type and version

Ubuntu 14.04

3. Python version and virtual environment information: python --version

Python 3.6.8

4. google-cloud- version: pip show google-<service> or pip freeze

google-cloud-storage==1.19.0

Steps to reproduce

1. pip install google-resumable-media==0.4.0
2. blob.download_as_string()

Per the latest release of google-resumable-media, no decompression of content-encoding gzip is performed and raw bytes are returned.

See https://github.com/googleapis/google-resumable-media-python/releases

blob.download_as_string() formerly returned decompressed bytes, and now returns compressed bytes. We are using .blob instead of .get_blob for an HPC application and thus have no way of knowing what the content encoding is as the information is erased.

We actually LIKE the new functionality as we can now decide when to decompress, but we need to know the content encoding to avoid various kinds of problems that would be introduced by speculative decompression.

Code example

Here is our desired functionality.

    blob = bucket.blob( key )
    try:
      # blob handles the decompression so the encoding is None
      resp = blob.download_as_string(start=start, end=end)
      return resp, blob.content_encoding
    except google.cloud.exceptions.NotFound as err:
      return None, None

Adding this patch to google.cloud.storage.blob.py would solve this problem for us:

    def _do_download(
        self, transport, file_obj, download_url, headers, start=None, end=None
    ):
        """Perform a download without any error handling.

        This is intended to be called by :meth:`download_to_file` so it can
        be wrapped with error handling / remapping.

        :type transport:
            :class:`~google.auth.transport.requests.AuthorizedSession`
        :param transport: The transport (with credentials) that will
                          make authenticated requests.

        :type file_obj: file
        :param file_obj: A file handle to which to write the blob's data.

        :type download_url: str
        :param download_url: The URL where the media can be accessed.

        :type headers: dict
        :param headers: Optional headers to be sent with the request(s).

        :type start: int
        :param start: Optional, the first byte in a range to be downloaded.

        :type end: int
        :param end: Optional, The last byte in a range to be downloaded.
        """
        if self.chunk_size is None:
            download = Download(
                download_url, stream=file_obj, headers=headers, start=start, end=end
            )
>           response = download.consume(transport)
>           if 'Content-Encoding' in response.headers:
>               self.content_encoding = response.headers['Content-Encoding']
        else:
            download = ChunkedDownload(
                download_url,
                self.chunk_size,
                file_obj,
                headers=headers,
                start=start if start else 0,
                end=end,
            )

            while not download.finished:
                download.consume_next_chunk(transport)

[tseaver]

@william-silversmith Can you achieve what you need to reloading the blob's metadata? E.g.:

blob.reload()

At that point, the content_encoding property will be populated from the server.

[william-silversmith]

Unfortunately, this strategy would significantly reduce IO performance. Google support worked with us a few months ago to figure out how to reduce the number of requests (hundreds of millions of files). Originally we were using get_blob which generated an additional request. We're handling a petabyte of 3D image data with a random access requirement. We do this by chunking the image into a regular grid of files. In order to make this more affordable, some lossless compression is desirable. The reason it would be desirable to control when decompression occurs is that our method for transferring datasets currently requires decompressing and recompressing which seems a waste. I do think it's worth being a bit more explicit though: 1. The updated resumable media is breaking existing functionality for all users that use gzip (probably a lot!) as raw bytes are now returned. 2. It was broken in the spirit of letting users decide what to do with the data (a new feature), but blob is stripping that info away. I would be happy with the old functionality being restored, but if there's some option to decide when decompression occurs without additional network overhead, that would be even better.

…

On Mon, Sep 9, 2019, 12:30 PM Tres Seaver ***@***.***> wrote: @william-silversmith <https://github.com/william-silversmith> Can you achieve what you need to reloading the blob's metadata? E.g.: blob.reload() At that point, the content_encoding property will be populated from the server. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#9188?email_source=notifications&email_token=AATGQSMSJ2CBE6IZTKBPH7DQIZ2Z7A5CNFSM4IUN2UB2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD6IHH5A#issuecomment-529560564>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AATGQSNK2I25ENXO6BXYHEDQIZ2Z7ANCNFSM4IUN2UBQ> .

[tseaver]

@william-silversmith Thanks for clarifying. One issue here is that we would want to have the header-driven content_encoding value also available for chunked downloads, so we would need to rework your patch a bit.

@crwilcox, @frankyn Please chime in.

[frankyn]

@crwilcox reverted changes made in googleapis/google-resumable-media-python#103 and releasing a new version to unblock this issue: googleapis/google-resumable-media-python#104

Reassigning to him.