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gh-159999: Fix needs_input for bz2 and zlib decompressors - #160696
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BZ2Decompressor and zlib._ZlibDecompressor had a bug where, if the input ran out right as the output buffer filled up, needs_input was set to true even though there was still decompressed data waiting. Callers would go looking for more input when they should have been draining the buffer. While in there, I found a related problem in bz2’s decompress_buf(). It checked for exhausted input before checking for a full output buffer, so even with max_length=-1 it could hand back just the first 32 KiB of a block’s output. I reordered the checks. Both fixes follow what was done for lzma in bpo-21872 (pythonGH-14048). One knock-on effect: gzip._GzipReader was relying on the old behavior. It raised EOFError whenever decompress(b"") returned nothing, but that can now legitimately happen on a valid stream. It now only raises when reading the file gives back no data, which is what DecompressReader already does. Compatibility note: if anyone copied gzip’s old loop for use with BZ2Decompressor, they could see the same spurious EOFError. lzma has worked this way since 3.9, so this just makes bz2 and zlib consistent with it.
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BZ2Decompressor and zlib._ZlibDecompressor had a bug where, if the input ran out right as the output buffer filled up, needs_input was set to true even though there was still decompressed data waiting. Callers would go looking for more input when they should have been draining the buffer.
While in there, I found a related problem in bz2’s decompress_buf(). It checked for exhausted input before checking for a full output buffer, so even with max_length=-1 it could hand back just the first 32 KiB of a block’s output. I reordered the checks.
Both fixes follow what was done for lzma in bpo-21872 (GH-14048).
One knock-on effect: gzip._GzipReader was relying on the old behavior. It raised EOFError whenever decompress(b"") returned nothing, but that can now legitimately happen on a valid stream. It now only raises when reading the file gives back no data, which is what DecompressReader already does.
Compatibility note: if anyone copied gzip’s old loop for use with BZ2Decompressor, they could see the same spurious EOFError. lzma has worked this way since 3.9, so this just makes bz2 and zlib consistent with it.
BZ2Decompressorandzlib._ZlibDecompressorsetneeds_input=Truewhile output is still buffered #159999