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The spec allows for multi-member files. Some libraries and utilities seem to solve this problem (incorrectly?) by simply ignoring everything past the first member -- even when valid (e.g., DotNetZip, 7-Zip)
For 2.7 and 3.4, the data that has been decompressed but not yet read before the exception was raised is still available:
Modifying Martin's example slightly:
>>> f = BytesIO()
>>> with GzipFile(fileobj=f, mode="wb") as z:
... z.write(b"data")
...
4
>>> f.write(b"garbage")
7
>>> f.seek(0)
0
>>> with GzipFile(fileobj=f, mode="rb") as z:
... try:
... z.read(1)
... z.read()
... except OSError as e:
... z.extrabuf[z.offset - z.extrastart:]
... e
...
b'd'
b'ata'
OSError('Not a gzipped file',)
My issue is that catching and handling this specific exception is a little more involved because there are 3(?) different OSErrors (IOError on 2.7) that could potentially be raised during the read. But mostly:
OSError('CRC check failed 0x447ba3f9 != 0x225cb2a3',) -- would be bad one to mistake for it.
Maybe a specific Exception type to catch for an invalid header, and a better method to read the remaining buffer when handling it?