GH-105808: Fix a regression introduced in GH-101251 (#105910)

Fix a regression introduced in GH-101251, causing GzipFile.flush() to
not flush the compressor (nor pass along the zip_mode argument).

Lib/gzip.py

@@ -370,8 +370,9 @@ def close(self):
  def flush(self,zlib_mode=zlib.Z_SYNC_FLUSH):
  self._check_not_closed()
  if self.mode == WRITE:
- # Ensure the compressor's buffer is flushed
  self._buffer.flush()
+ # Ensure the compressor's buffer is flushed
+ self.fileobj.write(self.compress.flush(zlib_mode))
  self.fileobj.flush()
 
  def fileno(self):

Lib/test/test_gzip.py

@@ -9,6 +9,7 @@
 import struct
 import sys
 import unittest
+import zlib
 from subprocess import PIPE, Popen
 from test.support import import_helper
 from test.support import os_helper
@@ -616,6 +617,54 @@ def test_issue44439(self):
  self.assertEqual(f.write(q), LENGTH)
  self.assertEqual(f.tell(), LENGTH)
 
+ def test_flush_flushes_compressor(self):
+ # See issue GH-105808.
+ b = io.BytesIO()
+ message = b"important message here."
+ with gzip.GzipFile(fileobj=b, mode='w') as f:
+ f.write(message)
+ f.flush()
+ partial_data = b.getvalue()
+ full_data = b.getvalue()
+ self.assertEqual(gzip.decompress(full_data), message)
+ # The partial data should contain the gzip header and the complete
+ # message, but not the end-of-stream markers (so we can't just
+ # decompress it directly).
+ with self.assertRaises(EOFError):
+ gzip.decompress(partial_data)
+ d = zlib.decompressobj(wbits=-zlib.MAX_WBITS)
+ f = io.BytesIO(partial_data)
+ gzip._read_gzip_header(f)
+ read_message = d.decompress(f.read())
+ self.assertEqual(read_message, message)
+
+ def test_flush_modes(self):
+ # Make sure the argument to flush is properly passed to the
+ # zlib.compressobj; see issue GH-105808.
+ class FakeCompressor:
+ def __init__(self):
+ self.modes = []
+ def compress(self, data):
+ return b''
+ def flush(self, mode=-1):
+ self.modes.append(mode)
+ return b''
+ b = io.BytesIO()
+ fc = FakeCompressor()
+ with gzip.GzipFile(fileobj=b, mode='w') as f:
+ f.compress = fc
+ f.flush()
+ f.flush(50)
+ f.flush(zlib_mode=100)
+ # The implicit close will also flush the compressor.
+ expected_modes = [
+ zlib.Z_SYNC_FLUSH,
+ 50,
+ 100,
+ -1,
+ ]
+ self.assertEqual(fc.modes, expected_modes)
+
 
 class TestOpen(BaseTest):
  def test_binary_modes(self):

Misc/NEWS.d/next/Library/2023-06-19-11-31-55.gh-issue-105808.NL-quu.rst

@@ -0,0 +1 @@
+Fix a regression introduced in GH-101251 for 3.12, causing :meth:`gzip.GzipFile.flush` to not flush the compressor (nor pass along the ``zip_mode`` argument).