Add WillSendMessage to loopback delegate and make source addresses more plausible

Author: ksperling-apple

src/messaging/tests/MessagingContext.h

@@ -94,7 +94,7 @@ class MessagingContext : public PlatformMemoryUser
 
     MessagingContext() :
         mInitialized(false), mAliceAddress(Transport::PeerAddress::UDP(GetAddress(), CHIP_PORT + 1)),
-        mBobAddress(Transport::PeerAddress::UDP(GetAddress(), CHIP_PORT))
+        mBobAddress(LoopbackTransport::LoopbackPeer(mAliceAddress))
     {}
     // TODO Replace VerifyOrDie with Pigweed assert after transition app/tests to Pigweed.
     // TODO Currently src/app/icd/server/tests is using MessagingConetext as dependency.

src/transport/raw/tests/NetworkTestHelpers.h

@@ -64,6 +64,10 @@ class LoopbackTransportDelegate
 public:
     virtual ~LoopbackTransportDelegate() {}
 
+    // Called by the loopback transport when a message is requested to be sent.
+    // This is called even if the message is subsequently rejected or dropped.
+    virtual void WillSendMessage(const Transport::PeerAddress & peer, const System::PacketBufferHandle & message) {}
+
     // Called by the loopback transport when it drops one of a configurable number of messages (mDroppedMessageCount) after a
     // configurable allowed number of messages (mNumMessagesToAllowBeforeDropping)
     virtual void OnMessageDropped() {}
@@ -72,6 +76,18 @@ class LoopbackTransportDelegate
 class LoopbackTransport : public Transport::Base
 {
 public:
+    // In test scenarios using the loopback transport, we're only ever given
+    // the address we're sending to, but we don't have any information about
+    // what our local address is. Assume our fake addresses come in pairs of
+    // even and odd port numbers, so we can calculate one from the other by
+    // flipping the LSB of the port number.
+    static Transport::PeerAddress LoopbackPeer(const Transport::PeerAddress & address)
+    {
+        Transport::PeerAddress other(address);
+        other.SetPort(address.GetPort() ^ 1);
+        return other;
+    }
+
     void InitLoopbackTransport(System::Layer * systemLayer)
     {
         Reset();
@@ -100,14 +116,19 @@ class LoopbackTransport : public Transport::Base
         {
             auto item = std::move(_this->mPendingMessageQueue.front());
             _this->mPendingMessageQueue.pop();
-            _this->HandleMessageReceived(item.mDestinationAddress, std::move(item.mPendingMessage));
+            _this->HandleMessageReceived(LoopbackPeer(item.mDestinationAddress), std::move(item.mPendingMessage));
         }
     }
 
     static constexpr uint32_t kUnlimitedMessageCount = std::numeric_limits<uint32_t>::max();
 
     CHIP_ERROR SendMessage(const Transport::PeerAddress & address, System::PacketBufferHandle && msgBuf) override
     {
+        if (mDelegate != nullptr)
+        {
+            mDelegate->WillSendMessage(address, msgBuf);
+        }
+
         if (mNumMessagesToAllowBeforeError == 0)
         {
             ReturnErrorOnFailure(mMessageSendError);