How do i tell in Perl what the size of a file inside a gzip archive is without unpacking the whole file?

I have a bunch of ridiculously big files (multiple gigabytes in size) that do have a really high compression ratio (1:200 or better). I have to process those and would like to at least show some kind of progress estimate. For that reason i'd like to know the size of the file inside the .gz, so i can compare it with what i pulled out already.

However, since unpacking the whole file in advance each time is rather prohibitive and a waste of time, i'd like to figure the size out without doing that.

I know it is possible. I can just open gzip files with Total Commander and the viewer plugin will show me the right size. (I know it's not unpacking because it shows me the size immediately, which wouldn't really be possible with a 10GB file inside the gzip.)

There probably are some header fields that contain that information.

However looking through the docs of various CPAN modules i couldn't find anything that fits the bill. IO::Uncompress::Gunzip lets me get at a header, but it doesn't contain any file size information.

Any suggestions?