    def __init__(self, fobj):
        """
        fobj is a file-like object as an icns resource
        """
        # signature : (start, length)
        self.dct = dct = {}
        self.fobj = fobj
        sig, filesize = nextheader(fobj)
        if sig != b'icns':
            raise SyntaxError('not an icns file')
        i = HEADERSIZE
        while i < filesize:
            sig, blocksize = nextheader(fobj)
            if blocksize <= 0:
                raise SyntaxError('invalid block header')
            i += HEADERSIZE
            blocksize -= HEADERSIZE
            dct[sig] = (i, blocksize)
            fobj.seek(blocksize, 1)
            i += blocksize
The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.