Tighten DHCP port matching (#174)

lib/proxy/udp_packet_helper.rs

@@ -17,10 +17,50 @@ impl UdpPacketHelper for UdpPacket<&[u8]> {
     }
 
     fn is_dhcp_request(&self) -> bool {
-        self.src_port() == Self::BOOTPC_PORT || self.dst_port() == Self::BOOTPS_PORT
+        self.src_port() == Self::BOOTPC_PORT && self.dst_port() == Self::BOOTPS_PORT
     }
 
     fn is_dhcp_response(&self) -> bool {
-        self.src_port() == Self::BOOTPS_PORT || self.dst_port() == Self::BOOTPC_PORT
+        self.src_port() == Self::BOOTPS_PORT && self.dst_port() == Self::BOOTPC_PORT
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::UdpPacketHelper;
+    use smoltcp::wire::UdpPacket;
+
+    #[test]
+    fn test_is_dhcp_request_requires_both_standard_ports() {
+        assert!(is_dhcp_request(68, 67));
+        assert!(!is_dhcp_request(68, 9999));
+        assert!(!is_dhcp_request(9999, 67));
+    }
+
+    #[test]
+    fn test_is_dhcp_response_requires_both_standard_ports() {
+        assert!(is_dhcp_response(67, 68));
+        assert!(!is_dhcp_response(67, 9999));
+        assert!(!is_dhcp_response(9999, 68));
+    }
+
+    fn is_dhcp_request(src_port: u16, dst_port: u16) -> bool {
+        let buffer = udp_packet_buffer(src_port, dst_port);
+        let udp_pkt = UdpPacket::new_unchecked(&buffer[..]);
+        udp_pkt.is_dhcp_request()
+    }
+
+    fn is_dhcp_response(src_port: u16, dst_port: u16) -> bool {
+        let buffer = udp_packet_buffer(src_port, dst_port);
+        let udp_pkt = UdpPacket::new_unchecked(&buffer[..]);
+        udp_pkt.is_dhcp_response()
+    }
+
+    fn udp_packet_buffer(src_port: u16, dst_port: u16) -> [u8; 8] {
+        let mut buffer = [0; 8];
+        let mut udp_pkt = UdpPacket::new_unchecked(&mut buffer[..]);
+        udp_pkt.set_src_port(src_port);
+        udp_pkt.set_dst_port(dst_port);
+        buffer
     }
 }