pnet::transport_channel_iterator!

macro_rules! transport_channel_iterator {
    ($ty:ident, $iter:ident, $func:ident) => (
        /// An iterator over packets of type $ty
        pub struct $iter<'a> {
            tr: &'a mut TransportReceiver
        }
        /// Return a packet iterator with packets of type $ty for some transport receiver
        pub fn $func(tr: &mut TransportReceiver) -> $iter {
            $iter {
                tr: tr
            }
        }
        impl<'a> $iter<'a> {
            /// Get the next ($ty, IpAddr) pair for the given channel
            pub fn next(&mut self) -> io::Result<($ty, net::IpAddr)> {
                let mut caddr: libc::sockaddr_storage = unsafe { mem::zeroed() };
                let res = internal::recv_from(self.tr.socket.fd, &mut self.tr.buffer[..], &mut caddr);

                let offset = match self.tr.channel_type {
                    Layer4(Ipv4(_)) => {
                        let ip_header = Ipv4Packet::new(&self.tr.buffer[..]).unwrap();

                        ip_header.get_header_length() as usize * 4usize
                    },
                    Layer3(_) => {
                        fixup_packet(&mut self.tr.buffer[..]);

                        0
                    },
                    _ => 0
                };
                return match res {
                    Ok(len) => {
                        let packet = $ty::new(&self.tr.buffer[offset..len]).unwrap();
                        let addr = internal::sockaddr_to_addr(
                                        &caddr,
                                        mem::size_of::<libc::sockaddr_storage>()
                                   );
                        Ok((packet, addr.unwrap().ip()))
                    },
                    Err(e) => Err(e),
                };

                #[cfg(any(target_os = "freebsd", target_os = "macos"))]
                fn fixup_packet(buffer: &mut [u8]) {
                    use packet::ipv4::MutableIpv4Packet;

                    let buflen = buffer.len();
                    let mut new_packet = MutableIpv4Packet::new(buffer).unwrap();

                    let length = u16::from_be(new_packet.get_total_length());
                    new_packet.set_total_length(length);

                    // OS X does this awesome thing where it removes the header length
                    // from the total length sometimes.
                    let length = new_packet.get_total_length() as usize +
                                 (new_packet.get_header_length() as usize * 4usize);
                    if length == buflen {
                        new_packet.set_total_length(length as u16)
                    }

                    let offset = u16::from_be(new_packet.get_fragment_offset());
                    new_packet.set_fragment_offset(offset);
                }

                #[cfg(all(not(target_os = "freebsd"), not(target_os = "macos")))]
                fn fixup_packet(_buffer: &mut [u8]) {}
            }
        }
    )
}

Create an iterator for some packet type.

Usage: transport_channel_iterator!(Ipv4Packet, // Type to iterate over Ipv4TransportChannelIterator, // Name for iterator struct ipv4_packet_iter) // Name of function to create iterator