Function test_read

net_util/src/tap.rs:781–837

()

    #[test]
    fn test_read() {
        let tap_ip_guard = TAP_IP_LOCK.lock().unwrap();

        let mut tap = Tap::new(1).unwrap();
        let ip_addr = IpAddr::V4((*tap_ip_guard).parse().unwrap());
        let netmask = IpAddr::V4(SUBNET_MASK.parse().unwrap());
        tap.set_ip_addr(ip_addr, Some(netmask)).unwrap();
        tap.enable().unwrap();

        // Send a packet to the interface. We expect to be able to receive it on the associated fd.
        pnet_send_packet(tap.if_name_as_str());

        let mut buf = [0u8; 4096];

        let mut found_packet_sz = None;

        // In theory, this could actually loop forever if something keeps sending data through the
        // tap interface, but it's highly unlikely.
        while found_packet_sz.is_none() {
            let size = tap.read(&mut buf).unwrap();

            // We skip the first 10 bytes because the IFF_VNET_HDR flag is set when the interface
            // is created, and the legacy header is 10 bytes long without a certain flag which
            // is not set in Tap::new().
            let eth_bytes = &buf[10..size];

            let packet = EthernetPacket::new(eth_bytes).unwrap();
            if packet.get_ethertype() != EtherTypes::Ipv4 {
                // not an IPv4 packet
                continue;
            }

            let ipv4_bytes = &eth_bytes[14..];
            let packet = Ipv4Packet::new(ipv4_bytes).unwrap();

            // Our packet should carry an UDP payload, and not contain IP options.
            if packet.get_next_level_protocol() != IpNextHeaderProtocols::Udp
                && packet.get_header_length() != 5
            {
                continue;
            }

            let udp_bytes = &ipv4_bytes[20..];

            let udp_len = UdpPacket::new(udp_bytes).unwrap().get_length() as usize;

            // Skip the header bytes.
            let inner_string = str::from_utf8(&udp_bytes[8..udp_len]).unwrap();

            if inner_string.eq(DATA_STRING) {
                found_packet_sz = Some(size);
                break;
            }
        }

        assert!(found_packet_sz.is_some());
    }