Add a way to capture message payloads in tests. (#21774)

One use in TestReadInteraction shows how this works.  More uses in
that file will need to be added to address the other TODOs.

src/app/tests/TestReadInteraction.cpp

@@ -2696,6 +2696,20 @@ void TestReadInteraction::TestPostSubscribeRoundtripChunkReportTimeout(nlTestSui
     ctx.CreateSessionBobToAlice();
 }
 
+namespace {
+
+void CheckForInvalidAction(nlTestSuite * apSuite, Test::MessageCapturer & messageLog)
+{
+    NL_TEST_ASSERT(apSuite, messageLog.MessageCount() == 1);
+    NL_TEST_ASSERT(apSuite, messageLog.IsMessageType(0, Protocols::InteractionModel::MsgType::StatusResponse));
+    CHIP_ERROR status;
+    NL_TEST_ASSERT(apSuite,
+                   StatusResponse::ProcessStatusResponse(std::move(messageLog.MessagePayload(0)), status) == CHIP_NO_ERROR);
+    NL_TEST_ASSERT(apSuite, status == CHIP_IM_GLOBAL_STATUS(InvalidAction));
+}
+
+} // anonymous namespace
+
 // Read Client sends the read request, Read Handler drops the response, then test injects unknown status reponse message for Read
 // Client.
 void TestReadInteraction::TestReadClientReceiveInvalidMessage(nlTestSuite * apSuite, void * apContext)
@@ -2750,6 +2764,9 @@ void TestReadInteraction::TestReadClientReceiveInvalidMessage(nlTestSuite * apSu
         payloadHeader.SetExchangeID(0);
         payloadHeader.SetMessageType(chip::Protocols::InteractionModel::MsgType::StatusResponse);
 
+        Test::MessageCapturer messageLog(ctx);
+        messageLog.mCaptureStandaloneAcks = false;
+
         rm->ClearRetransTable(readClient.mExchange.Get());
         NL_TEST_ASSERT(apSuite, ctx.GetLoopback().mSentMessageCount == 2);
         NL_TEST_ASSERT(apSuite, ctx.GetLoopback().mDroppedMessageCount == 1);
@@ -2760,12 +2777,12 @@ void TestReadInteraction::TestReadClientReceiveInvalidMessage(nlTestSuite * apSu
         readClient.OnMessageReceived(readClient.mExchange.Get(), payloadHeader, std::move(msgBuf));
         ctx.DrainAndServiceIO();
 
-        // TODO: Need to validate what status is being sent to the ReadHandler
         // The ReadHandler closed its exchange when it sent the Report Data (which we dropped).
         // Since we synthesized the StatusResponse to the ReadClient, instead of sending it from the ReadHandler,
         // the only messages here are the ReadClient's StatusResponse to the unexpected message and an MRP ack.
-        NL_TEST_ASSERT(apSuite, ctx.GetLoopback().mSentMessageCount == 2);
         NL_TEST_ASSERT(apSuite, delegate.mError == CHIP_IM_GLOBAL_STATUS(Busy));
+
+        CheckForInvalidAction(apSuite, messageLog);
     }
 
     engine->Shutdown();

src/messaging/tests/MessagingContext.cpp

@@ -20,6 +20,7 @@
 #include <credentials/tests/CHIPCert_unit_test_vectors.h>
 #include <lib/support/CodeUtils.h>
 #include <lib/support/ErrorStr.h>
+#include <protocols/secure_channel/Constants.h>
 
 namespace chip {
 namespace Test {
@@ -204,5 +205,16 @@ Messaging::ExchangeContext * MessagingContext::NewExchangeToBob(Messaging::Excha
     return mExchangeManager.NewContext(GetSessionAliceToBob(), delegate);
 }
 
+void MessageCapturer::OnMessageReceived(const PacketHeader & packetHeader, const PayloadHeader & payloadHeader,
+                                        const SessionHandle & session, DuplicateMessage isDuplicate,
+                                        System::PacketBufferHandle && msgBuf)
+{
+    if (mCaptureStandaloneAcks || !payloadHeader.HasMessageType(Protocols::SecureChannel::MsgType::StandaloneAck))
+    {
+        mCapturedMessages.emplace_back(Message{ packetHeader, payloadHeader, isDuplicate, msgBuf.CloneData() });
+    }
+    mOriginalDelegate.OnMessageReceived(packetHeader, payloadHeader, session, isDuplicate, std::move(msgBuf));
+}
+
 } // namespace Test
 } // namespace chip

src/messaging/tests/MessagingContext.h

@@ -30,6 +30,8 @@
 
 #include <nlunit-test.h>
 
+#include <vector>
+
 namespace chip {
 namespace Test {
 
@@ -65,7 +67,7 @@ class PlatformMemoryUser
 };
 
 /**
- * @brief The context of test cases for messaging layer. It wil initialize network layer and system layer, and create
+ * @brief The context of test cases for messaging layer. It will initialize network layer and system layer, and create
  *        two secure sessions, connected with each other. Exchanges can be created for each secure session.
  */
 class MessagingContext : public PlatformMemoryUser
@@ -213,5 +215,53 @@ class LoopbackMessagingContext : public LoopbackTransportManager, public Messagi
     using LoopbackTransportManager::GetSystemLayer;
 };
 
+// Class that can be used to capture decrypted message traffic in tests using
+// MessagingContext.
+class MessageCapturer : public SessionMessageDelegate
+{
+public:
+    MessageCapturer(MessagingContext & aContext) :
+        mSessionManager(aContext.GetSecureSessionManager()), mOriginalDelegate(aContext.GetExchangeManager())
+    {
+        // Interpose ourselves into the message flow.
+        mSessionManager.SetMessageDelegate(this);
+    }
+
+    ~MessageCapturer()
+    {
+        // Restore the normal message flow.
+        mSessionManager.SetMessageDelegate(&mOriginalDelegate);
+    }
+
+    struct Message
+    {
+        PacketHeader mPacketHeader;
+        PayloadHeader mPayloadHeader;
+        DuplicateMessage mIsDuplicate;
+        System::PacketBufferHandle mPayload;
+    };
+
+    size_t MessageCount() const { return mCapturedMessages.size(); }
+
+    template <typename MessageType, typename = std::enable_if_t<std::is_enum<MessageType>::value>>
+    bool IsMessageType(size_t index, MessageType type)
+    {
+        return mCapturedMessages[index].mPayloadHeader.HasMessageType(type);
+    }
+
+    System::PacketBufferHandle & MessagePayload(size_t index) { return mCapturedMessages[index].mPayload; }
+
+    bool mCaptureStandaloneAcks = true;
+
+private:
+    // SessionMessageDelegate implementation.
+    void OnMessageReceived(const PacketHeader & packetHeader, const PayloadHeader & payloadHeader, const SessionHandle & session,
+                           DuplicateMessage isDuplicate, System::PacketBufferHandle && msgBuf) override;
+
+    SessionManager & mSessionManager;
+    SessionMessageDelegate & mOriginalDelegate;
+    std::vector<Message> mCapturedMessages;
+};
+
 } // namespace Test
 } // namespace chip

src/transport/raw/MessageHeader.h

@@ -430,6 +430,7 @@ class PayloadHeader
 {
 public:
     constexpr PayloadHeader() { SetProtocol(Protocols::NotSpecified); }
+    constexpr PayloadHeader(const PayloadHeader &) = default;
     PayloadHeader & operator=(const PayloadHeader &) = default;
 
     /** Get the Session ID from this header. */