#
cargo/util/
hostname.rs

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    // Copied from https://github.com/BurntSushi/ripgrep/blob/7099e174acbcbd940f57e4ab4913fee4040c826e/crates/cli/src/hostname.rs

    use std::{ffi::OsString, io};

    /// Returns the hostname of the current system.
    ///
    /// It is unusual, although technically possible, for this routine to return
    /// an error. It is difficult to list out the error conditions, but one such
    /// possibility is platform support.
    ///
    /// # Platform specific behavior
    ///
    /// On Unix, this returns the result of the `gethostname` function from the
    /// `libc` linked into the program.
    pub fn hostname() -> io::Result<OsString> {
        #[cfg(unix)]
        {
            gethostname()
        }
        #[cfg(not(unix))]
        {
            Err(io::Error::new(
                io::ErrorKind::Other,
                "hostname could not be found on unsupported platform",
            ))
        }
    }

    #[cfg(unix)]
    fn gethostname() -> io::Result<OsString> {
        use std::os::unix::ffi::OsStringExt;

        // SAFETY: There don't appear to be any safety requirements for calling
        // sysconf.
        let limit = unsafe { libc::sysconf(libc::_SC_HOST_NAME_MAX) };
        if limit == -1 {
            // It is in theory possible for sysconf to return -1 for a limit but
            // *not* set errno, in which case, io::Error::last_os_error is
            // indeterminate. But untangling that is super annoying because std
            // doesn't expose any unix-specific APIs for inspecting the errno. (We
            // could do it ourselves, but it just doesn't seem worth doing?)
            return Err(io::Error::last_os_error());
        }
        let Ok(maxlen) = usize::try_from(limit) else {
            let msg = format!("host name max limit ({}) overflowed usize", limit);
            return Err(io::Error::new(io::ErrorKind::Other, msg));
        };
        // maxlen here includes the NUL terminator.
        let mut buf = vec![0; maxlen];
        // SAFETY: The pointer we give is valid as it is derived directly from a
        // Vec. Similarly, `maxlen` is the length of our Vec, and is thus valid
        // to write to.
        let rc = unsafe { libc::gethostname(buf.as_mut_ptr().cast::<libc::c_char>(), maxlen) };
        if rc == -1 {
            return Err(io::Error::last_os_error());
        }
        // POSIX says that if the hostname is bigger than `maxlen`, then it may
        // write a truncate name back that is not necessarily NUL terminated (wtf,
        // lol). So if we can't find a NUL terminator, then just give up.
        let Some(zeropos) = buf.iter().position(|&b| b == 0) else {
            let msg = "could not find NUL terminator in hostname";
            return Err(io::Error::new(io::ErrorKind::Other, msg));
        };
        buf.truncate(zeropos);
        buf.shrink_to_fit();
        Ok(OsString::from_vec(buf))
    }

    #[cfg(test)]
    mod tests {
        use super::*;

        #[test]
        fn print_hostname() {
            println!("{:?}", hostname());
        }
    }