create symlink on exFAT filesystem (macOS way)

ln.py

#!/usr/bin/env python3
import argparse
import hashlib
import os

SMB_SYMHDRLEN = (4+1)+(4+1)+(32+1)
MAXPATHLEN = 0x400

# see smbfs_create_windows_symlink_data
def symlink(target: str, link: str) -> None:
	if os.path.exists(link):
		raise FileExistsError
	body = target.encode()
	if len(body) > MAXPATHLEN:
		raise ValueError
	hdr = f'Xsym\n{len(body):04d}\n{hashlib.md5(body).hexdigest()}\n'.encode()
	assert len(hdr) == SMB_SYMHDRLEN
	if len(body) < MAXPATHLEN:
		body += b'\n'
	body = body.ljust(MAXPATHLEN, b' ')
	with open(link, 'wb') as f:
		f.write(hdr + body)

def main() -> None:
	import argparse
	parser = argparse.ArgumentParser()
	parser.add_argument('target')
	parser.add_argument('link')
	args = parser.parse_args()
	symlink(args.target, args.link)

if __name__ == '__main__':
	main()