is_rarfile does not set the pos to the file header

[0xMattina]

rarfile/rarfile.py

Lines 348 to 367 in db1df33

	def get_rar_version(xfile):
	"""Check quickly whether file is rar archive.
	"""
	with XFile(xfile) as fd:
	buf = fd.read(len(RAR5_ID))
	if buf.startswith(RAR_ID):
	return RAR_V3
	elif buf.startswith(RAR5_ID):
	return RAR_V5
	return 0
	def is_rarfile(xfile):
	"""Check quickly whether file is rar archive.
	"""
	try:
	return get_rar_version(xfile) > 0
	except OSError:
	# File not found or not accessible, ignore
	return False

CPython versions tested on:

3.12

Operating systems tested on:

Windows

Test code:

import tarfile
from io import BytesIO

import rarfile

if __name__ == '__main__':
    with open(r"d:\test.zip", "rb") as fp_file:
        fp_io = BytesIO(fp_file.read())

    print("before <is_tarfile> pos:", fp_io.tell())
    print("<is_tarfile> result:", tarfile.is_tarfile(fp_io))
    print("after <is_tarfile> pos:", fp_io.tell())
    print()
    print("before <is_rarfile> pos:", fp_io.tell())
    print("<is_rarfile> result:", rarfile.is_rarfile(fp_io))
    print("after <is_rarfile> pos:", fp_io.tell())

Output:

before <is_tarfile> pos: 0
<is_tarfile> result: False
after <is_tarfile> pos: 0

before <is_rarfile> pos: 0
<is_rarfile> result: False
after <is_rarfile> pos: 8

When the args xfile is BytesIO, is_rarfile don't set pos to the value before call.
I tried some other libraries, and tarfile is a std library, it will set pos to the value before call.
I think if is_rarfile does the same, it will improve the logic and consistency of the code.