uefi-test-runner: SNP: use smoltcp to UDP packet

Properly deconstruct the response. This improves the maintainability of
this test and to better understand what is going on.

Author: phip1611

Cargo.lock

@@ -8,6 +8,7 @@ edition = "2024"
 [dependencies]
 uefi-raw = { path = "../uefi-raw" }
 uefi = { path = "../uefi", features = ["alloc", "global_allocator", "panic_handler", "logger", "qemu", "log-debugcon"] }
+smoltcp = { version = "0.12.0", default-features = false, features = ["medium-ethernet", "proto-ipv4", "socket-udp"] }
 
 log.workspace = true
 

uefi-test-runner/Cargo.toml

@@ -179,8 +179,19 @@ pub fn test() {
     let n = receive(simple_network.deref_mut(), &mut buffer).unwrap();
     debug!("Reply has {n} bytes");
 
+    let recv_frame = smoltcp::wire::EthernetFrame::new_checked(&buffer).unwrap();
+    // Check the packet was sent to the MAC that we expected.
+    assert_eq!(
+        recv_frame.dst_addr(),
+        smoltcp::wire::EthernetAddress::from_bytes(&EXPECTED_MAC)
+    );
+
     // Check payload in UDP packet that was reversed by our EchoService.
-    assert_eq!(buffer[42..47], [4, 4, 3, 2, 1]);
+    {
+        let recv_ipv4 = smoltcp::wire::Ipv4Packet::new_checked(recv_frame.payload()).unwrap();
+        let udp_packet = smoltcp::wire::UdpPacket::new_checked(recv_ipv4.payload()).unwrap();
+        assert_eq!(udp_packet.payload(), &[4, 4, 3, 2, 1]);
+    }
 
     // Get stats
     let res = simple_network.collect_statistics();