nc 0.9.7

Access system calls directly
Documentation 
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// Copyright (c) 2020 Xu Shaohua <shaohua@biofan.org>. All rights reserved.
// Use of this source is governed by Apache-2.0 License that can be found
// in the LICENSE file.

fn main() {
    {
        let mut groups = vec![];
        let ret = unsafe { nc::getgroups(&mut groups) };
        assert!(ret.is_ok());
        let total_num = ret.unwrap();
        groups.resize(total_num as usize, 0);

        let ret = unsafe { nc::getgroups(&mut groups) };
        assert!(ret.is_ok());
        assert_eq!(ret, Ok(total_num));
    }

    {
        let mut groups = vec![0; 8];
        let mut ret = unsafe { nc::getgroups(&mut groups) };
        while ret.is_err() && ret == Err(nc::EINVAL) {
            groups.resize(groups.len() * 2, 0);
            ret = unsafe { nc::getgroups(&mut groups) };
        }
    }
}