Dynamic Event Handler Registration (#135)

- Discord_RegisterHandlers() exported
- C# wrapper updated
- Dynamically sub/unsub to events
- Better mutex locking, for safety!

examples/button-clicker/Assets/DiscordRpc.cs

@@ -87,6 +87,9 @@ public class DiscordRpc
     [DllImport("discord-rpc", EntryPoint = "Discord_Respond", CallingConvention = CallingConvention.Cdecl)]
     public static extern void Respond(string userId, Reply reply);
 
+    [DllImport("discord-rpc", EntryPoint = "Discord_UpdateHandlers", CallingConvention = CallingConvention.Cdecl)]
+    public static extern void UpdateHandlers(ref EventHandlers handlers);
+
     public static void UpdatePresence(RichPresence presence)
     {
         var presencestruct = presence.GetStruct();

include/discord_rpc.h

@@ -80,6 +80,8 @@ DISCORD_EXPORT void Discord_ClearPresence(void);
 
 DISCORD_EXPORT void Discord_Respond(const char* userid, /* DISCORD_REPLY_ */ int reply);
 
+DISCORD_EXPORT void Discord_UpdateHandlers(DiscordEventHandlers* handlers);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif

src/discord_rpc.cpp

@@ -60,6 +60,7 @@ static char LastErrorMessage[256];
 static int LastDisconnectErrorCode{0};
 static char LastDisconnectErrorMessage[256];
 static std::mutex PresenceMutex;
+static std::mutex HandlerMutex;
 static QueuedMessage QueuedPresence{};
 static MsgQueue<QueuedMessage, MessageQueueSize> SendQueue;
 static MsgQueue<JoinRequest, JoinQueueSize> JoinAskQueue;
@@ -212,15 +213,15 @@ static void Discord_UpdateConnection(void)
         // writes
         if (QueuedPresence.length) {
             QueuedMessage local;
-            PresenceMutex.lock();
+            {
+                std::lock_guard<std::mutex> guard(PresenceMutex);
                 local.Copy(QueuedPresence);
                 QueuedPresence.length = 0;
-            PresenceMutex.unlock();
+            }
             if (!Connection->Write(local.buffer, local.length)) {
                 // if we fail to send, requeue
-                PresenceMutex.lock();
+                std::lock_guard<std::mutex> guard(PresenceMutex);
                 QueuedPresence.Copy(local);
-                PresenceMutex.unlock();
             }
         }
 
@@ -250,6 +251,19 @@ static bool RegisterForEvent(const char* evtName)
     return false;
 }
 
+static bool DeregisterForEvent(const char* evtName)
+{
+    auto qmessage = SendQueue.GetNextAddMessage();
+    if (qmessage) {
+        qmessage->length =
+          JsonWriteUnsubscribeCommand(qmessage->buffer, sizeof(qmessage->buffer), Nonce++, evtName);
+        SendQueue.CommitAdd();
+        SignalIOActivity();
+        return true;
+    }
+    return false;
+}
+
 extern "C" DISCORD_EXPORT void Discord_Initialize(const char* applicationId,
                                                   DiscordEventHandlers* handlers,
                                                   int autoRegister,
@@ -266,12 +280,15 @@ extern "C" DISCORD_EXPORT void Discord_Initialize(const char* applicationId,
 
     Pid = GetProcessId();
 
+    {
+        std::lock_guard<std::mutex> guard(HandlerMutex);
         if (handlers) {
             Handlers = *handlers;
         }
         else {
             Handlers = {};
         }
+    }
 
     if (Connection) {
         return;
@@ -279,20 +296,9 @@ extern "C" DISCORD_EXPORT void Discord_Initialize(const char* applicationId,
 
     Connection = RpcConnection::Create(applicationId);
     Connection->onConnect = []() {
+        Discord_UpdateHandlers(&Handlers);
         WasJustConnected.exchange(true);
         ReconnectTimeMs.reset();
-
-        if (Handlers.joinGame) {
-            RegisterForEvent("ACTIVITY_JOIN");
-        }
-
-        if (Handlers.spectateGame) {
-            RegisterForEvent("ACTIVITY_SPECTATE");
-        }
-
-        if (Handlers.joinRequest) {
-            RegisterForEvent("ACTIVITY_JOIN_REQUEST");
-        }
     };
     Connection->onDisconnect = [](int err, const char* message) {
         LastDisconnectErrorCode = err;
@@ -318,10 +324,11 @@ extern "C" DISCORD_EXPORT void Discord_Shutdown(void)
 
 extern "C" DISCORD_EXPORT void Discord_UpdatePresence(const DiscordRichPresence* presence)
 {
-    PresenceMutex.lock();
+    {
+        std::lock_guard<std::mutex> guard(PresenceMutex);
         QueuedPresence.length = JsonWriteRichPresenceObj(
             QueuedPresence.buffer, sizeof(QueuedPresence.buffer), Nonce++, Pid, presence);
-    PresenceMutex.unlock();
+    }
     SignalIOActivity();
 }
 
@@ -360,26 +367,39 @@ extern "C" DISCORD_EXPORT void Discord_RunCallbacks(void)
 
     if (isConnected) {
         // if we are connected, disconnect cb first
+        std::lock_guard<std::mutex> guard(HandlerMutex);
         if (wasDisconnected && Handlers.disconnected) {
             Handlers.disconnected(LastDisconnectErrorCode, LastDisconnectErrorMessage);
         }
     }
 
-    if (WasJustConnected.exchange(false) && Handlers.ready) {
+    if (WasJustConnected.exchange(false)) {
+        std::lock_guard<std::mutex> guard(HandlerMutex);
+        if (Handlers.ready) {
             Handlers.ready();
         }
+    }
 
-    if (GotErrorMessage.exchange(false) && Handlers.errored) {
+    if (GotErrorMessage.exchange(false)) {
+        std::lock_guard<std::mutex> guard(HandlerMutex);
+        if (Handlers.errored) {
             Handlers.errored(LastErrorCode, LastErrorMessage);
         }
-
-    if (WasJoinGame.exchange(false) && Handlers.joinGame) {
-        Handlers.joinGame(JoinGameSecret);
     }
 
-    if (WasSpectateGame.exchange(false) && Handlers.spectateGame) {
+    if (WasJoinGame.exchange(false)) {
+        std::lock_guard<std::mutex> guard(HandlerMutex);
+        if (Handlers.joinGame) {
+            Handlers.joinGame(JoinGameSecret);
+        }
+    }
+
+    if (WasSpectateGame.exchange(false)) {
+        std::lock_guard<std::mutex> guard(HandlerMutex);
+        if (Handlers.spectateGame) {
             Handlers.spectateGame(SpectateGameSecret);
         }
+    }
 
     // Right now this batches up any requests and sends them all in a burst; I could imagine a world
     // where the implementer would rather sequentially accept/reject each one before the next invite
@@ -388,17 +408,50 @@ extern "C" DISCORD_EXPORT void Discord_RunCallbacks(void)
     // not it should be trivial for the implementer to make a queue themselves.
     while (JoinAskQueue.HavePendingSends()) {
         auto req = JoinAskQueue.GetNextSendMessage();
+        {
+            std::lock_guard<std::mutex> guard(HandlerMutex);
             if (Handlers.joinRequest) {
                 DiscordJoinRequest djr{req->userId, req->username, req->discriminator, req->avatar};
                 Handlers.joinRequest(&djr);
             }
+        }
         JoinAskQueue.CommitSend();
     }
 
     if (!isConnected) {
         // if we are not connected, disconnect message last
+        std::lock_guard<std::mutex> guard(HandlerMutex);
         if (wasDisconnected && Handlers.disconnected) {
             Handlers.disconnected(LastDisconnectErrorCode, LastDisconnectErrorMessage);
         }
     }
 }
+
+extern "C" DISCORD_EXPORT void Discord_UpdateHandlers(DiscordEventHandlers* newHandlers)
+{
+    if (newHandlers) {
+
+#define HANDLE_EVENT_REGISTRATION(handler_name, event) \
+        if (!Handlers.handler_name && newHandlers->handler_name) { \
+            RegisterForEvent(event); \
+        } \
+        else if (Handlers.handler_name && !newHandlers->handler_name) { \
+            DeregisterForEvent(event); \
+        }
+
+        std::lock_guard<std::mutex> guard(HandlerMutex);
+        HANDLE_EVENT_REGISTRATION(joinGame, "ACTIVITY_JOIN")
+        HANDLE_EVENT_REGISTRATION(spectateGame, "ACTIVITY_SPECTATE")
+        HANDLE_EVENT_REGISTRATION(joinRequest, "ACTIVITY_JOIN_REQUEST")
+
+#undef HANDLE_EVENT_REGISTRATION
+
+        Handlers = *newHandlers;
+    }
+    else
+    {
+        std::lock_guard<std::mutex> guard(HandlerMutex);
+        Handlers = {};
+    }
+    return;
+}

src/serialization.cpp

@@ -197,6 +197,25 @@ size_t JsonWriteSubscribeCommand(char* dest, size_t maxLen, int nonce, const cha
     return writer.Size();
 }
 
+size_t JsonWriteUnsubscribeCommand(char* dest, size_t maxLen, int nonce, const char* evtName)
+{
+    JsonWriter writer(dest, maxLen);
+
+    {
+        WriteObject obj(writer);
+
+        JsonWriteNonce(writer, nonce);
+
+        WriteKey(writer, "cmd");
+        writer.String("UNSUBSCRIBE");
+
+        WriteKey(writer, "evt");
+        writer.String(evtName);
+    }
+
+    return writer.Size();
+}
+
 size_t JsonWriteJoinReply(char* dest, size_t maxLen, const char* userId, int reply, int nonce)
 {
     JsonWriter writer(dest, maxLen);

src/serialization.h

@@ -47,6 +47,8 @@ size_t JsonWriteRichPresenceObj(char* dest,
                                 const DiscordRichPresence* presence);
 size_t JsonWriteSubscribeCommand(char* dest, size_t maxLen, int nonce, const char* evtName);
 
+size_t JsonWriteUnsubscribeCommand(char* dest, size_t maxLen, int nonce, const char* evtName);
+
 size_t JsonWriteJoinReply(char* dest, size_t maxLen, const char* userId, int reply, int nonce);
 
 // I want to use as few allocations as I can get away with, and to do that with RapidJson, you need