[PATCH v2] dts: add time delay to async sniffer callback function

[Nicholas Pratte <npratte@iol.unh.edu>]

There exists a bug within i40e NICs in which the async sniffer does not
catch send packets as a result of the callback function sending packets
too quickly before the NICs are ready to start capturing.

There could be a multitude of reasons why this happens on these NICs, but
for the time being, inserting a one second delay in the callback function
will suffice.

Bugzilla ID: 1573
Signed-off-by: Nicholas Pratte <npratte@iol.unh.edu>
---
 .../testbed_model/traffic_generator/scapy.py          | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/dts/framework/testbed_model/traffic_generator/scapy.py b/dts/framework/testbed_model/traffic_generator/scapy.py
index be5ae3b895..434c0a231f 100644
--- a/dts/framework/testbed_model/traffic_generator/scapy.py
+++ b/dts/framework/testbed_model/traffic_generator/scapy.py
@@ -188,22 +188,24 @@ def _shell_create_sniffer(
                 when set to an empty string.
         """
         self._shell_set_packet_list(packets_to_send)
+        # We need to introduce a short delay in the sniffer sendp() for i40e NICs.
+        self.send_command("import time")
         sniffer_commands = [
             f"{self._sniffer_name} = AsyncSniffer(",
             f"iface='{recv_port.logical_name}',",
             "store=True,",
             # *args is used in the arguments of the lambda since Scapy sends parameters to the
             # callback function which we do not need for our purposes.
-            "started_callback=lambda *args: sendp(",
+            "started_callback=lambda *args: (time.sleep(1), sendp(",
             (
                 # Additional indentation is added to this line only for readability of the logs.
                 f"{self._python_indentation}{self._send_packet_list_name},"
-                f" iface='{send_port.logical_name}'),"
+                f" iface='{send_port.logical_name}')),"
             ),
             ")",
         ]
         if filter_config:
-            sniffer_commands.insert(-1, f"filter='{filter_config}'")
+            sniffer_commands.insert(-2, f"filter='{filter_config}'")
 
         self.send_command(f"\n{self._python_indentation}".join(sniffer_commands))
 
@@ -223,7 +225,8 @@ def _shell_start_and_stop_sniffing(self, duration: float) -> list[Packet]:
         """
         sniffed_packets_name = "gathered_packets"
         self.send_command(f"{self._sniffer_name}.start()")
-        time.sleep(duration)
+        # Insert a one second delay to prevent timeout errors from occurring
+        time.sleep(duration + 1)
         self.send_command(f"{sniffed_packets_name} = {self._sniffer_name}.stop(join=True)")
         # An extra newline is required here due to the nature of interactive Python shells
         packet_strs = self.send_command(
-- 
2.44.0