uefi-test-runner: SNP: remove magic ethernet frame value

We still have the unfortunate situation that the SNP test
depends on DHCP of the PXE test, but now it is much clearer
how the UDP packet is sent via Ethernet and how the echo
service is used.

Author: phip1611

uefi-test-runner/src/proto/network/snp.rs

@@ -2,7 +2,9 @@
 
 use core::ops::DerefMut;
 use core::time::Duration;
-
+use smoltcp::wire::{
+    ETHERNET_HEADER_LEN, EthernetFrame, IPV4_HEADER_LEN, Ipv4Packet, UDP_HEADER_LEN, UdpPacket,
+};
 use uefi::boot::ScopedProtocol;
 use uefi::proto::network::MacAddress;
 use uefi::proto::network::snp::{InterruptStatus, ReceiveFlags, SimpleNetwork};
@@ -146,27 +148,52 @@ pub fn test() {
         )
         .expect("Failed to set receive filters");
 
-    // EthernetFrame(IPv4Packet(UDPPacket(Payload))).
-    // The ethernet frame header will be filled by `transmit()`.
-    // The UDP packet contains the byte sequence `4, 4, 3, 2, 1`.
-    //
-    // The packet is sent to the `EchoService` created by
-    // `cargo xtask run`. It runs on UDP port 21572.
-    let payload = b"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
-            \x45\x00\
-            \x00\x21\
-            \x00\x01\
-            \x00\x00\
-            \x10\
-            \x11\
-            \x07\x6a\
-            \xc0\xa8\x11\x0f\
-            \xc0\xa8\x11\x02\
-            \x54\x45\
-            \x54\x44\
-            \x00\x0d\
-            \xa9\xe4\
-            \x04\x01\x02\x03\x04";
+    // High-level payload to send to destination
+    let payload = [
+        4_u8, /* Number of elements for echo service */
+        1, 2, 3, 4,
+    ];
+    let frame = {
+        // IP that was obtained by PXE test running earlier
+        // TODO we should make these tests not depend on each other.
+        let src_ip = smoltcp::wire::Ipv4Address::new(192, 168, 17, 15);
+        let dst_ip = smoltcp::wire::Ipv4Address::new(192, 168, 17, 2);
+
+        let udp_packet_len = UDP_HEADER_LEN + payload.len();
+        let ipv4_packet_len = IPV4_HEADER_LEN + udp_packet_len;
+        let frame_len = ETHERNET_HEADER_LEN + ipv4_packet_len;
+
+        let mut buffer = vec![0u8; frame_len];
+
+        let mut frame = EthernetFrame::new_unchecked(buffer.as_mut_slice());
+        // Ethertype, SRC MAC, and DST MAC will be set by SNP's transmit().
+
+        let ipv4_packet_buffer = &mut frame.payload_mut()[0..ipv4_packet_len];
+        let mut ipv4_packet = Ipv4Packet::new_unchecked(ipv4_packet_buffer);
+        ipv4_packet.set_header_len(IPV4_HEADER_LEN as u8 /* no extensions */);
+        ipv4_packet.set_total_len(ipv4_packet_len as u16);
+        ipv4_packet.set_hop_limit(16);
+        ipv4_packet.set_next_header(smoltcp::wire::IpProtocol::Udp);
+        ipv4_packet.set_dont_frag(true);
+        ipv4_packet.set_ident(0x1337);
+        ipv4_packet.set_version(4);
+        ipv4_packet.set_src_addr(src_ip);
+        ipv4_packet.set_dst_addr(dst_ip);
+
+        let mut udp_packet = UdpPacket::new_unchecked(ipv4_packet.payload_mut());
+        udp_packet.set_len(udp_packet_len as u16);
+        udp_packet.set_src_port(21573);
+        udp_packet.set_dst_port(21572);
+        udp_packet.payload_mut().copy_from_slice(&payload);
+        assert!(udp_packet.check_len().is_ok());
+
+        udp_packet.fill_checksum(&src_ip.into(), &dst_ip.into());
+        // Do this last, as it depends on the other checksum.
+        ipv4_packet.fill_checksum();
+        assert!(ipv4_packet.check_len().is_ok());
+
+        buffer
+    };
 
     assert!(
         !simple_network
@@ -179,7 +206,7 @@ pub fn test() {
     simple_network
         .transmit(
             simple_network.mode().media_header_size as usize,
-            payload,
+            &frame,
             None,
             Some(simple_network.mode().broadcast_address),
             Some(ETHERNET_PROTOCOL_IPV4),
@@ -202,9 +229,9 @@ pub fn test() {
 
     // Check payload in UDP packet that was reversed by our EchoService.
     {
-        let recv_frame = smoltcp::wire::EthernetFrame::new_checked(&buffer).unwrap();
-        let recv_ipv4 = smoltcp::wire::Ipv4Packet::new_checked(recv_frame.payload()).unwrap();
-        let udp_packet = smoltcp::wire::UdpPacket::new_checked(recv_ipv4.payload()).unwrap();
+        let recv_frame = EthernetFrame::new_checked(&buffer).unwrap();
+        let recv_ipv4 = Ipv4Packet::new_checked(recv_frame.payload()).unwrap();
+        let udp_packet = UdpPacket::new_checked(recv_ipv4.payload()).unwrap();
         assert_eq!(udp_packet.payload(), &[4, 4, 3, 2, 1]);
     }