import tarfile


def patch_tarfile():
    """Fix low-level functions in the standard tarfile module to support
       tarfiles with numeric fields that only contain spaces, such as
       those written by Apache Maven/plexus-archiver.

       See http://bugs.python.org/issue15858 for more information.
    """
    def nti(s):
        """Convert a number field to a python number.
        """
        # There are two possible encodings for a number field, see
        # tarfile.itn().
        if s[0] in (0o200, 0o377):
            n = 0
            for i in range(len(s) - 1):
                n <<= 8
                n += s[i + 1]
            if s[0] == 0o377:
                n = -(256 ** (len(s) - 1) - n)
        else:
            try:
                # *** PATCH ***
                # Inlined nts() (since its arguments differ across
                # Python versions) and then added .lstrip(' ') and
                # treating space as a terminator after that.
                p = s.find(b"\0")
                if p != -1:
                    s = s[:p]
                u = s.decode('ascii', 'strict')
                u = u.lstrip(' ')
                if ' ' in u:
                    u = u.split(' ', 1)[0]
                n = int(u or "0", 8)
            except ValueError:
                if hasattr(tarfile, 'InvalidHeaderError'):
                    raise tarfile.InvalidHeaderError("invalid header")
                else:
                    raise tarfile.HeaderError("invalid header")
        return n

    tarfile.nti = nti