Use ring buffer for message handling

This can sometimes avoid dropping the wrong messages if syncing chats
takes too long.

user.go

@@ -67,7 +67,8 @@ type User struct {
 	chatListReceived chan struct{}
 	syncPortalsDone  chan struct{}
 
-	messages chan PortalMessage
+	messageInput  chan PortalMessage
+	messageOutput chan PortalMessage
 
 	syncStart chan struct{}
 	syncWait  sync.WaitGroup
@@ -177,12 +178,14 @@ func (bridge *Bridge) NewUser(dbUser *database.User) *User {
 		chatListReceived: make(chan struct{}, 1),
 		syncPortalsDone:  make(chan struct{}, 1),
 		syncStart:        make(chan struct{}, 1),
-		messages:         make(chan PortalMessage, bridge.Config.Bridge.UserMessageBuffer),
+		messageInput:     make(chan PortalMessage),
+		messageOutput:    make(chan PortalMessage, bridge.Config.Bridge.UserMessageBuffer),
 	}
 	user.RelaybotWhitelisted = user.bridge.Config.Bridge.Permissions.IsRelaybotWhitelisted(user.MXID)
 	user.Whitelisted = user.bridge.Config.Bridge.Permissions.IsWhitelisted(user.MXID)
 	user.Admin = user.bridge.Config.Bridge.Permissions.IsAdmin(user.MXID)
 	go user.handleMessageLoop()
+	go user.runMessageRingBuffer()
 	return user
 }
 
@@ -791,10 +794,22 @@ func (user *User) GetPortalByJID(jid types.WhatsAppID) *Portal {
 	return user.bridge.GetPortalByJID(user.PortalKey(jid))
 }
 
+func (user *User) runMessageRingBuffer() {
+	for msg := range user.messageInput {
+		select {
+		case user.messageOutput <- msg:
+		default:
+			user.log.Warnln("Buffer is full, dropping message in", msg.chat)
+			<-user.messageOutput
+			user.messageOutput<-msg
+		}
+	}
+}
+
 func (user *User) handleMessageLoop() {
 	for {
 		select {
-		case msg := <-user.messages:
+		case msg := <-user.messageOutput:
 			user.GetPortalByJID(msg.chat).messages <- msg
 		case <-user.syncStart:
 			user.log.Debugln("Processing of incoming messages is locked")
@@ -806,14 +821,6 @@ func (user *User) handleMessageLoop() {
 	}
 }
 
-func (user *User) putMessage(message PortalMessage) {
-	select {
-	case user.messages <- message:
-	default:
-		user.log.Warnln("Buffer is full, dropping message in", message.chat)
-	}
-}
-
 func (user *User) HandleNewContact(contact whatsapp.Contact) {
 	user.log.Debugfln("Contact message: %+v", contact)
 	go func() {
@@ -843,39 +850,39 @@ func (user *User) HandleBatteryMessage(battery whatsapp.BatteryMessage) {
 }
 
 func (user *User) HandleTextMessage(message whatsapp.TextMessage) {
-	user.putMessage(PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp})
+	user.messageInput <- PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp}
 }
 
 func (user *User) HandleImageMessage(message whatsapp.ImageMessage) {
-	user.putMessage(PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp})
+	user.messageInput <- PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp}
 }
 
 func (user *User) HandleStickerMessage(message whatsapp.StickerMessage) {
-	user.putMessage(PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp})
+	user.messageInput <- PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp}
 }
 
 func (user *User) HandleVideoMessage(message whatsapp.VideoMessage) {
-	user.putMessage(PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp})
+	user.messageInput <- PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp}
 }
 
 func (user *User) HandleAudioMessage(message whatsapp.AudioMessage) {
-	user.putMessage(PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp})
+	user.messageInput <- PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp}
 }
 
 func (user *User) HandleDocumentMessage(message whatsapp.DocumentMessage) {
-	user.putMessage(PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp})
+	user.messageInput <- PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp}
 }
 
 func (user *User) HandleContactMessage(message whatsapp.ContactMessage) {
-	user.putMessage(PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp})
+	user.messageInput <- PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp}
 }
 
 func (user *User) HandleLocationMessage(message whatsapp.LocationMessage) {
-	user.putMessage(PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp})
+	user.messageInput <- PortalMessage{message.Info.RemoteJid, user, message, message.Info.Timestamp}
 }
 
 func (user *User) HandleMessageRevoke(message whatsappExt.MessageRevocation) {
-	user.putMessage(PortalMessage{message.RemoteJid, user, message, 0})
+	user.messageInput <- PortalMessage{message.RemoteJid, user, message, 0}
 }
 
 type FakeMessage struct {