You should be using the ZipArchive class if you have the complete file. This ought to efficiently give you Entries via the Zip directory at the end of the file.
The Reader interface is intended for use on Streams that aren't seekable (e.g. NetworkStreams) so you don't know the end of the file and can't seek to parts.
The Reader interface is intended for use on Streams that aren't seekable (e.g. NetworkStreams) so you don't know the end of the file and can't seek to parts.