fn if_name_mtu()

in src/linux.rs [308:348]

• 35 lines of code
• 3 McCabe index (conditional complexity)

fn if_name_mtu(if_index: i32, fd: &mut RouteSocket) -> Result<(String, usize)> {
    // Send RTM_GETLINK message to get interface information for the given interface index.
    let msg_seq = RouteSocket::new_seq();
    let msg = IfInfoMsg::new(if_index, msg_seq);
    fd.write_all((&msg).into())?;

    // Receive RTM_GETLINK response.
    let (_hdr, mut buf) = read_msg_with_seq(fd, msg_seq, RTM_NEWLINK)?;
    debug_assert!(size_of::<ifinfomsg>() <= buf.len());
    let buf = buf.split_off(size_of::<ifinfomsg>());

    // Parse through the attributes to find the interface name and MTU.
    let mut ifname = None;
    let mut mtu = None;
    for attr in RtAttrs(buf.as_slice()).by_ref() {
        match attr.hdr.rta_type {
            IFLA_IFNAME => {
                let name = CStr::from_bytes_until_nul(attr.msg)
                    .map_err(|err| Error::new(ErrorKind::Other, err))?;
                ifname = Some(
                    name.to_str()
                        .map_err(|err| Error::new(ErrorKind::Other, err))?
                        .to_string(),
                );
            }
            IFLA_MTU => {
                mtu = Some(
                    parse_c_int(attr.msg)?
                        .try_into()
                        .map_err(|e: TryFromIntError| unlikely_err(e.to_string()))?,
                );
            }
            _ => (),
        }
        if let (Some(ifname), Some(mtu)) = (ifname.as_ref(), mtu.as_ref()) {
            return Ok((ifname.clone(), *mtu));
        }
    }

    Err(default_err())
}