FEAT: path hash in packet (#473)

closes #474

---------

Co-authored-by: Alexey Zharkov <62723911+Az3git@users.noreply.github.com>

Author: PaulRalnikov

source/device/switch.cpp

@@ -32,10 +32,6 @@ TimeNs Switch::process() {
         return total_processing_time;
     }
     Packet packet = optional_packet.value();
-    if (packet.flow == nullptr) {
-        LOG_WARN("No flow in packet");
-        return total_processing_time;
-    }
 
     std::shared_ptr<ILink> next_link = get_link_to_destination(packet);
 
@@ -65,6 +61,7 @@ TimeNs Switch::process() {
         return total_processing_time;
     }
     packet.ttl--;
+    packet.path_hash ^= std::hash<Id>{}(get_id());
 
     // TODO: increase total_processing_time correctly
     next_link->schedule_arrival(packet);

source/packet.hpp

@@ -7,6 +7,8 @@
 
 namespace sim {
 
+using PathHash = std::uint32_t;
+
 struct Packet {
     Packet(SizeByte a_size = SizeByte(0), IFlow* a_flow = nullptr,
            Id a_source_id = "", Id a_dest_id = "",
@@ -30,6 +32,7 @@ struct Packet {
     SizeByte delivered_data_size_at_origin;  // For ACK this is inherited from
                                              // data packet
     TTL ttl = std::numeric_limits<TTL>::max();
+    PathHash path_hash = 0;
     bool ecn_capable_transport;
     bool congestion_experienced;
 };

test/switch/test_switch.cpp

@@ -6,6 +6,7 @@
 
 #include "../_mocks/flow_mock.hpp"
 #include "../utils/fake_packet.hpp"
+#include "device/host.hpp"
 #include "device/switch.hpp"
 #include "host_mock.hpp"
 #include "link_mock.hpp"
@@ -164,4 +165,59 @@ TEST_F(TestSwitch, test_one_sender) { test_senders(1); }
 
 TEST_F(TestSwitch, test_multiple_senders) { test_senders(5); }
 
+// this test checks that packets passed throw same path have equal path hash
+// and packets passed throw different pathes have different path hashes
+TEST_F(TestSwitch, test_path_hash) {
+    // topology:
+    // sender  --- switch_1
+    //   |            |
+    //   |            |
+    // switch_2 -- receiver
+    auto sender = std::make_shared<sim::Host>("sender");
+    auto switch_1 = std::make_shared<sim::Switch>("switch_1");
+    auto switch_2 = std::make_shared<sim::Switch>("switch_2");
+    auto receiver = std::make_shared<sim::Host>("receiver");
+
+    auto link_sender_to_switch_1 = std::make_shared<LinkMock>(sender, switch_1);
+    switch_1->add_inlink(link_sender_to_switch_1);
+
+    auto link_sender_to_switch_2 = std::make_shared<LinkMock>(sender, switch_2);
+    switch_2->add_inlink(link_sender_to_switch_2);
+
+    auto link_switch_1_to_receiver =
+        std::make_shared<LinkMock>(switch_1, receiver);
+    switch_1->update_routing_table(receiver->get_id(),
+                                   link_switch_1_to_receiver);
+
+    auto link_switch_2_to_receiver =
+        std::make_shared<LinkMock>(switch_2, receiver);
+    switch_2->update_routing_table(receiver->get_id(),
+                                   link_switch_2_to_receiver);
+
+    sim::Packet packet_template(SizeByte(1), nullptr, sender->get_id(),
+                                receiver->get_id());
+    sim::Packet first_packet_route_1(packet_template);
+    sim::Packet second_packet_route_1(packet_template);
+    sim::Packet packet_route_2(packet_template);
+
+    link_sender_to_switch_1->set_ingress_packet(first_packet_route_1);
+    switch_1->process();
+    link_sender_to_switch_1->set_ingress_packet(second_packet_route_1);
+    switch_1->process();
+    auto arrived_packets_route_1 =
+        link_switch_1_to_receiver->get_arrived_packets();
+    ASSERT_EQ(arrived_packets_route_1.size(), 2);
+
+    ASSERT_EQ(arrived_packets_route_1[0].path_hash,
+              arrived_packets_route_1[1].path_hash);
+
+    link_sender_to_switch_2->set_ingress_packet(packet_route_2);
+    switch_2->process();
+    auto arrived_packets_route_2 =
+        link_switch_2_to_receiver->get_arrived_packets();
+    ASSERT_EQ(arrived_packets_route_2.size(), 1);
+    ASSERT_NE(arrived_packets_route_2[0].path_hash,
+              arrived_packets_route_1[0].path_hash);
+}
+
 }  // namespace test