[PATCH v3 1/1] dts: rework packet addressing

[jspewock@iol.unh.edu]

From: Jeremy Spewock <jspewock@iol.unh.edu>

This patch updates the _adjust_addresses method of test suites so
that addresses of packets are only modified if the developer did not
configure them beforehand. This allows for developers to have more
control over the content of their packets when sending them through the
framework.

Signed-off-by: Jeremy Spewock <jspewock@iol.unh.edu>
---
 dts/framework/test_suite.py | 75 ++++++++++++++++++++++++++-----------
 1 file changed, 54 insertions(+), 21 deletions(-)

diff --git a/dts/framework/test_suite.py b/dts/framework/test_suite.py
index 051509fb86..69388ff5ab 100644
--- a/dts/framework/test_suite.py
+++ b/dts/framework/test_suite.py
@@ -225,7 +225,7 @@ def send_packets_and_capture(
         Returns:
             A list of received packets.
         """
-        packets = [self._adjust_addresses(packet) for packet in packets]
+        packets = self._adjust_addresses(packets)
         return self.tg_node.send_packets_and_capture(
             packets,
             self._tg_port_egress,
@@ -243,41 +243,74 @@ def get_expected_packet(self, packet: Packet) -> Packet:
         Returns:
             `packet` with injected L2/L3 addresses.
         """
-        return self._adjust_addresses(packet, expected=True)
+        return self._adjust_addresses([packet], expected=True)[0]
 
-    def _adjust_addresses(self, packet: Packet, expected: bool = False) -> Packet:
+    def _adjust_addresses(self, packets: list[Packet], expected: bool = False) -> list[Packet]:
         """L2 and L3 address additions in both directions.
 
+        Packets in `packets` will be directly modified in this method. The returned list of packets
+        however will be copies of the modified packets in order to keep the two lists distinct.
+
+        Only missing addresses are added to packets, existing addresses will not be overridden. If
+        any packet in `packets` has multiple IP layers (using GRE, for example) only the inner-most
+        IP layer will have its addresses adjusted.
+
         Assumptions:
             Two links between SUT and TG, one link is TG -> SUT, the other SUT -> TG.
 
         Args:
-            packet: The packet to modify.
+            packets: The packets to modify.
             expected: If :data:`True`, the direction is SUT -> TG,
                 otherwise the direction is TG -> SUT.
+
+        Returns:
+            A list containing copies of all packets in `packets` after modification.
         """
-        if expected:
-            # The packet enters the TG from SUT
-            # update l2 addresses
-            packet.src = self._sut_port_egress.mac_address
-            packet.dst = self._tg_port_ingress.mac_address
+        ret_packets = []
+        for packet in packets:
+            # The fields parameter of a packet does not include fields of the payload, so this can
+            # only be the Ether src/dst.
+            pkt_src_is_unset = "src" not in packet.fields
+            pkt_dst_is_unset = "dst" not in packet.fields
+            num_ip_layers = packet.layers().count(IP)
+
+            if num_ip_layers > 0:
+                # Update the last IP layer if there are multiple (the framework should be modifying
+                # the packet address instead of the tunnel address if there is one).
+                l3_to_use = packet.getlayer(IP, num_ip_layers)
+                ip_src_is_unset = "src" not in l3_to_use.fields
+                ip_dst_is_unset = "dst" not in l3_to_use.fields
+            else:
+                ip_src_is_unset = None
+                ip_dst_is_unset = None
 
-            # The packet is routed from TG egress to TG ingress
-            # update l3 addresses
-            packet.payload.src = self._tg_ip_address_egress.ip.exploded
-            packet.payload.dst = self._tg_ip_address_ingress.ip.exploded
-        else:
-            # The packet leaves TG towards SUT
             # update l2 addresses
-            packet.src = self._tg_port_egress.mac_address
-            packet.dst = self._sut_port_ingress.mac_address
+            # If `expected` is :data:`True`, the packet enters the TG from SUT, otherwise the
+            # packet leaves the TG towards the SUT
+            if pkt_src_is_unset:
+                packet.src = (
+                    self._sut_port_egress.mac_address
+                    if expected
+                    else self._tg_port_egress.mac_address
+                )
+            if pkt_dst_is_unset:
+                packet.dst = (
+                    self._tg_port_ingress.mac_address
+                    if expected
+                    else self._sut_port_ingress.mac_address
+                )
 
-            # The packet is routed from TG egress to TG ingress
             # update l3 addresses
-            packet.payload.src = self._tg_ip_address_egress.ip.exploded
-            packet.payload.dst = self._tg_ip_address_ingress.ip.exploded
+            # The packet is routed from TG egress to TG ingress regardless of whether it is
+            # expected or not.
+            if ip_src_is_unset:
+                l3_to_use.src = self._tg_ip_address_egress.ip.exploded
+
+            if ip_dst_is_unset:
+                l3_to_use.dst = self._tg_ip_address_ingress.ip.exploded
+            ret_packets.append(Ether(packet.build()))
 
-        return Ether(packet.build())
+        return ret_packets
 
     def verify(self, condition: bool, failure_description: str) -> None:
         """Verify `condition` and handle failures.
-- 
2.46.0