Unreal SDK failing to handle fragmented messages (clockworklabs#4002)

# Description of Changes

Updated the handler from OnRawMessage to OnBinaryMessage as OnRawMessage
seems to have a bug that won't report the BytesRemaining for incomplete
messages. OnBinaryMessage properly returns a bool flag like how the C#
implementation works.

# API and ABI breaking changes

N/A

# Expected complexity level and risk

2 - Underlying framework change on how messages are handled

# Testing

Blackholio was no longer working and is back in working order; however
Unreal test framework has been broken due to the work on Result<> as the
companion PR has not been merged.

- [x] Rebuilt and ran Unreal Blackholio

Author: JasonAtClockwork

sdks/unreal/src/SpacetimeDbSdk/Source/SpacetimeDbSdk/Private/Connection/Websocket.cpp

@@ -81,7 +81,7 @@ void UWebsocketManager::Connect(const FString& ServerUrl)
 	WebSocket->OnConnected().AddUObject(this, &UWebsocketManager::HandleConnected);
 	WebSocket->OnConnectionError().AddUObject(this, &UWebsocketManager::HandleConnectionError);
 	WebSocket->OnMessage().AddUObject(this, &UWebsocketManager::HandleMessageReceived);
-	WebSocket->OnRawMessage().AddUObject(this, &UWebsocketManager::HandleBinaryMessageReceived);
+	WebSocket->OnBinaryMessage().AddUObject(this, &UWebsocketManager::HandleBinaryMessageReceived);
 	WebSocket->OnClosed().AddUObject(this, &UWebsocketManager::HandleClosed);
 
 	UE_LOG(LogTemp, Log, TEXT("UWebsocketManager::Connect: Connecting to %s..."), *ServerUrl);
@@ -173,7 +173,7 @@ void UWebsocketManager::HandleMessageReceived(const FString& Message)
 	OnMessageReceived.Broadcast(Message);
 }
 
-void UWebsocketManager::HandleBinaryMessageReceived(const void* Data, SIZE_T Size, SIZE_T BytesRemaining)
+void UWebsocketManager::HandleBinaryMessageReceived(const void* Data, SIZE_T Size, bool bIsLastFragment)
 {
 	if (Size == 0)
 	{
@@ -183,30 +183,25 @@ void UWebsocketManager::HandleBinaryMessageReceived(const void* Data, SIZE_T Siz
 	// Handle binary messages, which may be fragmented
 	const uint8* Bytes = static_cast<const uint8*>(Data);
 
-	if (IncompleteMessage.Num() > 0 && !bAwaitingBinaryFragments)
-	{
-		UE_LOG(LogTemp, Error, TEXT("Received binary fragment while previous data pending"));
-	}
-
-	// Append new incoming bytes to any incomplete message
+	// Append this fragment to our buffer
 	IncompleteMessage.Append(Bytes, Size);
 
-	if (BytesRemaining > 0)
+	// If this is the last fragment, we have the complete message
+	if (bIsLastFragment)
+	{
+		// We have the complete message
+		TArray<uint8> MessageBytes = IncompleteMessage;
+		IncompleteMessage.Reset();
+		bAwaitingBinaryFragments = false;
+
+		// Forward the complete binary payload to listeners.
+		OnBinaryMessageReceived.Broadcast(MessageBytes);
+	}
+	else
 	{
-		// Still expecting more fragments
+		// More fragments are coming
 		bAwaitingBinaryFragments = true;
-		return;
 	}
-
-	// Final fragment received, reset and process
-	bAwaitingBinaryFragments = false;
-
-	TArray<uint8> MessageBytes = IncompleteMessage;
-	IncompleteMessage.Reset();
-
-	// Forward the complete binary payload to listeners.
-	OnBinaryMessageReceived.Broadcast(MessageBytes);
-
 }
 
 void UWebsocketManager::HandleClosed(int32 StatusCode, const FString& Reason, bool bWasClean)

sdks/unreal/src/SpacetimeDbSdk/Source/SpacetimeDbSdk/Public/Connection/Websocket.h

@@ -106,7 +106,7 @@ class SPACETIMEDBSDK_API UWebsocketManager : public UObject
 	/** Handler for incoming text messages */
 	void HandleMessageReceived(const FString& Message);
 	/** Handler for incoming binary messages */
-	void HandleBinaryMessageReceived(const void* Data, SIZE_T Size, SIZE_T BytesRemaining);
+	void HandleBinaryMessageReceived(const void* Data, SIZE_T Size, bool bIsLastFragment);
 	/** Handler for socket close */
 	void HandleClosed(int32 StatusCode, const FString& Reason, bool bWasClean);