New submission from Walt Askew <[email protected]>:
The seekable method on gzip.GzipFile always returns True, even if the
underlying buffer is not seekable. However, if seek is called on the GzipFile,
the seek will fail unless the underlying buffer is seekable. This can cause
consumers of the GzipFile object to mistakenly believe calling seek on the
object is safe, when in fact it will lead to an exception.
For example, this led to a bug when I was trying to use requests & boto3 to
stream & decompress an S3 upload like so:
resp = requests.get(uri, stream=True)
decompressed = gzip.GzipFile(fileobj=resp.raw)
boto3.client('s3').upload_fileobj(decompressed, Bucket=bucket, Key=key)
boto3 checks the seekable method on the the GzipFile, chooses a code path based
on the file being seekable but later raises an exception when the seek call
fails because the underlying HTTP stream is not seekable.
----------
components: Library (Lib)
messages: 314613
nosy: Walt Askew
priority: normal
severity: normal
status: open
title: GzipFile's .seekable() returns True even if underlying buffer is not
seekable
versions: Python 3.6
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Python tracker <[email protected]>
<https://bugs.python.org/issue33173>
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