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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 Windows, this currently uses the "physical DNS hostname" computer name.
/// This may change in the future.
///
/// On Unix, this returns the result of the `gethostname` function from the
/// `libc` linked into the program.
pub fn hostname() -> io::Result<OsString> {
#[cfg(windows)]
{
use winapi_util::sysinfo::{get_computer_name, ComputerNameKind};
get_computer_name(ComputerNameKind::PhysicalDnsHostname)
}
#[cfg(unix)]
{
gethostname()
}
#[cfg(not(any(windows, unix)))]
{
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().unwrap());
}
}
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