find/strip UTC timestamps from ZIP files' CD extra fields

apk-find-utc.py

#!/usr/bin/python3
# encoding: utf-8

import struct
import sys
import zipfile


def _has_timestamp(info):
    xtr = info.extra
    while len(xtr) >= 4:
        hdr_id, size = struct.unpack("<HH", xtr[:4])
        if size > len(xtr) - 4:
            break
        if hdr_id == 0x5455:
            return True
        xtr = xtr[size + 4:]
    return False


if __name__ == "__main__":
    with zipfile.ZipFile(sys.argv[1], "r") as zf:
        for info in zf.infolist():
            if _has_timestamp(info):
                print(info.filename)

# vim: set tw=80 sw=4 sts=4 et fdm=marker :

apk-strip-utc.py

#!/usr/bin/python3
# encoding: utf-8

import os
import struct
import sys
import zipfile

from collections import namedtuple

ZipData = namedtuple("ZipData", ("cd_offset", "eocd_offset", "cd_and_eocd"))


class ZipError(Exception):
    pass


def copy_apk(input_apk, output_apk):
    with zipfile.ZipFile(input_apk, "r") as zf:
        infos = zf.infolist()
    zdata = zip_data(input_apk)
    with open(input_apk, "rb") as fhi, open(output_apk, "w+b") as fho:
        _copy_bytes(fhi, fho, zdata.cd_offset)
        for info in infos:
            hdr = fhi.read(46)
            if hdr[:4] != b"\x50\x4b\x01\x02":
                raise ZipError("Expected central directory file header signature")
            n, m, k = struct.unpack("<HHH", hdr[28:34])
            hdr += fhi.read(n + m + k)
            xtr = _remove_timestamps(info)
            m_b = int.to_bytes(len(xtr), 2, "little")
            hdr = hdr[:30] + m_b + hdr[32:46 + n] + xtr + hdr[46 + n + m:]
            fho.write(hdr)
        eocd_offset = fho.tell()
        fho.write(zdata.cd_and_eocd[zdata.eocd_offset - zdata.cd_offset:])
        fho.seek(eocd_offset + 8)
        fho.write(struct.pack("<HHLL", len(infos), len(infos),
                              eocd_offset - zdata.cd_offset, zdata.cd_offset))


def _remove_timestamps(info):
    old_xtr = info.extra
    new_xtr = b""
    while len(old_xtr) >= 4:
        hdr_id, size = struct.unpack("<HH", old_xtr[:4])
        if size > len(old_xtr) - 4:
            break
        if hdr_id != 0x5455:
            new_xtr += old_xtr[:size + 4]
        old_xtr = old_xtr[size + 4:]
    return new_xtr + old_xtr


def _copy_bytes(fhi, fho, size, blocksize=4096):
    while size > 0:
        data = fhi.read(min(size, blocksize))
        if not data:
            break
        size -= len(data)
        fho.write(data)
    if size != 0:
        raise ZipError("Unexpected EOF")


def zip_data(apkfile, count=1024):
    with open(apkfile, "rb") as fh:
        fh.seek(-count, os.SEEK_END)
        data = fh.read()
        pos = data.rfind(b"\x50\x4b\x05\x06")
        if pos == -1:
            raise ZipError("Expected end of central directory record (EOCD)")
        fh.seek(pos - len(data), os.SEEK_CUR)
        eocd_offset = fh.tell()
        fh.seek(16, os.SEEK_CUR)
        cd_offset = int.from_bytes(fh.read(4), "little")
        fh.seek(cd_offset)
        cd_and_eocd = fh.read()
    return ZipData(cd_offset, eocd_offset, cd_and_eocd)


if __name__ == "__main__":
    copy_apk(sys.argv[1], sys.argv[2])

# vim: set tw=80 sw=4 sts=4 et fdm=marker :