This utility is for fixing zip files affected by this bug:

http://python.org/sf/679953

When creating a zip file over 2GB in size with the zipfile.py in
Python 2.3.4 or earlier, an error will occur when packing file sizes.

The method used for writing a zipfile using the 'w' mode is the following:

    Create the file::

        self.fp = open(fn, 'w')

    For each file added::

        # create template ZipInfo
        zinfo = ZipInfo(<<stuff>>)
        zinfo.header_offset = self.fp.tell()

        # Write it to the out file
        self.fp.write(zinfo.FileHeader())

        # Remember where the ZipInfo is
        zinfo.file_offset = self.fp.tell()

        # Write the compressed data

        # Fill in the real ZipInfo
        zinfo.CRC = <<CRC>>
        zinfo.compress_size = <<compressed size>>
        zinfo.file_size = <<file size>>
        here = self.fp.tell()

        # Seek back to the ZipInfo
        # Fill in the missing bits
        # Seek back to current position
        self.fp.seek(zinfo.header_offset + 14, 0)
        self.fp.write(<<pack CRC, compress_size, file_size>>)
        self.fp.seek(position, 0)

        # Add for later
        self.filelist.append(zinfo)
        self.NameToInfo[zinfo.filename] = zinfo
        
    On close::

        pos1 = self.fp.tell()
        for zinfo in self.filelist:
            # write a centdir entry for this zinfo
        pos2 = self.fp.tell()
        # write an end-of-zip-archive

It is the final step that fails, so in order to fix a broken zip file
we must be able to reconstruct self.filelist from a file with a corrupt
central directory.