def _prepare_index(self):
# Add space for file size
self.index_offset += 8
# Space for num_signatures & num_additional_sections
self.index_offset += 4 + 4
# Write the magic and placeholder for the index
self.fileobj.write(b"MAR1" + packint(self.index_offset))
# Write placeholder for file size
self.fileobj.write(struct.pack(">Q", 0))
# Write num_signatures
self.fileobj.write(packint(len(self.signature_versions)))
# Write placeholder signatures
for algo_id, keyfile in self.signature_versions:
sig = MarSignature(algo_id, keyfile)
sig._offset = self.index_offset
self.index_offset += sig.size
self.signatures.append(sig)
# algoid
self.fileobj.write(packint(algo_id))
# numbytes
self.fileobj.write(packint(sig.sigsize))
# space for signature
self.fileobj.write("\0" * sig.sigsize)
# Write placeholder for number of additional sections
self.fileobj.write(packint(0))
