random access uncompressed unencrypted ZipExtFile

[vvb2060]

Feature or enhancement

Proposal:

cpython/Lib/zipfile/__init__.py

Lines 1164 to 1177 in 78ffba4

	# Fast seek uncompressed unencrypted file
	elif self._compress_type == ZIP_STORED and self._decrypter is None and read_offset > 0:
	# disable CRC checking after first seeking - it would be invalid
	self._expected_crc = None
	# seek actual file taking already buffered data into account
	read_offset -= len(self._readbuffer) - self._offset
	self._fileobj.seek(read_offset, os.SEEK_CUR)
	self._left -= read_offset
	read_offset = 0
	# flush read buffer
	self._readbuffer = b''
	self._offset = 0
	elif read_offset < 0:
	# Position is before the current position. Reset the ZipExtFile

if read_offset < 0, ZipExtFile is reset and read from the beginning. I think read_offset > 0 is unnecessary.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• GH-128131: Random access uncompressed unencrypted ZipExtFile #128132
• GH-128131: Completely support random read access of uncompressed unencrypted files in ZipFile #128143

[danifus]

There is a bug in zipfile._SharedFile.seek() that affects concurrent reads of uncompressed, unencrypted files which should be merged along with this PR: #127856