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#!/usr/bin/env python3
#
# Patch metadata in .ar files
#
import argparse
def ar_patch(ar, original, new_uid, new_gid, new_filemode):
"""
AR file headers
Offset Length Name Format
0 16 File identifier ASCII
16 12 File modification timestamp (in seconds) Decimal
28 6 Owner ID Decimal
34 6 Group ID Decimal
40 8 File mode (type and permission) Octal
48 10 File size in bytes Decimal
58 2 Ending characters 0x60 0x0A
"""
assert len(ar) > 0x24 , "Got empty archive?"
armap_time1 = None
armap_time2 = None
i = 8
while i < len(original):
file_name = original[i:][0:][:16].decode("ASCII")
file_size = int(original[i:][48:][:10].decode("ASCII").strip())
end = original[i:][58:][:2].decode("ASCII")
assert end == "`\n"
if file_name.strip() == "/":
armap_time1 = original[i+16:i+16+12]
elif file_name.strip() == "//":
armap_time2 = original[i+16:i+16+12]
if file_size % 2 != 0:
file_size += 1
i += file_size + 60
assert armap_time1 is not None
assert armap_time2 is not None
i = 8
while i < len(ar):
file_name = ar[i:][0:][:16].decode("ASCII")
file_size = int(ar[i:][48:][:10].decode("ASCII").strip())
end = ar[i:][58:][:2].decode("ASCII")
assert end == "`\n"
if file_name.strip() == "/":
ar[i+16:i+16+12] = armap_time1
elif file_name.strip() == "//":
ar[i+16:i+16+12] = armap_time2
else:
ar[i+28:i+28+6] = f"{new_uid:<6}".encode("ASCII")[:6]
ar[i+34:i+34+6] = f"{new_gid:<6}".encode("ASCII")[:6]
ar[i+40:i+40+8] = f"{new_filemode:<8}".encode("ASCII")[:8]
if file_size % 2 != 0:
file_size += 1
i += file_size + 60
def main():
parser = argparse.ArgumentParser(description="Patch metadata in .a files.")
parser.add_argument("target", help="path to the ar file to patch")
parser.add_argument("original", help="path to the original ar file")
parser.add_argument("uid", help="new uid")
parser.add_argument("gid", help="new gid")
parser.add_argument("filemode", help="new filemode")
args = parser.parse_args()
ar = None
with open(args.target, "rb") as ar_file:
ar = bytearray(ar_file.read())
original = None
with open(args.original, "rb") as original_ar_file:
original = bytearray(original_ar_file.read())
ar_patch(ar, original, args.uid, args.gid, args.filemode)
with open(args.target, "wb") as ar_file:
ar_file.write(ar)
if __name__ == '__main__':
main()
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