When unpacking a large gzipped file on Windows, total_out "overflows" after decompressing past 4 GiB.

For example, if I create a file with compressed zeros (on Linux) like this:

head -c $((5 * 1024 * 1024 * 1024)) /dev/zero | gzip -1 > zeros.gz

and then try to decompress that on Windows with the code below, then flate2 panics due to subtraction overflow on:

https://github.com/rust-lang/flate2-rs/blob/9d3582860d3666a2771ea8933b396fda57560ec8/src/ffi/zlib_rs.rs#L109

Although the panic is in flate2, I think the issue is in zlib-rs. I tried adding a short log line there and it shows total_out is wrapping over a 32-bit boundary, going from 4294959496 to 392.

It seems that total_out has type z_size:

and z_size is an alias for c_ulong:

but c_ulong is a 32-bit integer on Windows systems, even if the host is 64-bit. Would it make sense for total_out (and maybe total_in?) to be a type that's always 64 bits?

Thanks!

Reproducer:

use std::{env, fs::File, io::Read, path::PathBuf};

use flate2::read::GzDecoder;

fn main() {
    let input_path = PathBuf::from(env::args_os().skip(1).next().unwrap());

    let file = File::open(&input_path).unwrap();
    let mut decoder = GzDecoder::new(file);
    let mut buf = [0u8; 8192];

    loop {
        let n = decoder.read(&mut buf).unwrap();
        if n == 0 {
            break;
        }
    }
}