Added a new method to proto presence message to check for newer message

ably/proto_presence_message.go

@@ -2,6 +2,7 @@ package ably
 
 import (
 	"fmt"
+	"strings"
 )
 
 // PresenceAction describes the possible actions members in the presence set can emit (TP2).
@@ -58,3 +59,16 @@ func (m PresenceMessage) String() string {
 		"update",
 	}[m.Action], m.ClientID, m.Data)
 }
+
+// RTP2b1
+func (msg *PresenceMessage) isServerSynthesizedPresenceMessage() bool {
+	return strings.HasPrefix(msg.ID, msg.ConnectionID)
+}
+
+func (oldMessage *PresenceMessage) IsNewerThan(incomingMessage *PresenceMessage) bool {
+	if oldMessage.isServerSynthesizedPresenceMessage() ||
+		incomingMessage.isServerSynthesizedPresenceMessage() {
+		return oldMessage.Timestamp > incomingMessage.Timestamp
+	}
+	return false
+}

ably/realtime_presence.go

@@ -173,10 +173,6 @@ func (pres *RealtimePresence) processIncomingMessage(msg *protocolMessage, syncS
 		pres.syncStart(syncSerial)
 	}
 
-	isSynthesizedLeave := func(oldMsg *PresenceMessage, newMsg *PresenceMessage) bool {
-		return false
-	}
-
 	// RTP17
 	for _, presenceMember := range msg.Presence {
 		memberKey := presenceMember.ClientID
@@ -206,8 +202,7 @@ func (pres *RealtimePresence) processIncomingMessage(msg *protocolMessage, syncS
 		memberKey := presenceMember.ConnectionID + presenceMember.ClientID
 
 		if oldPresenceMember, ok := pres.members[memberKey]; ok { // RTP2a
-			if isSynthesizedLeave(oldPresenceMember, presenceMember) && // // RTP2b1
-				oldPresenceMember.Timestamp >= presenceMember.Timestamp {
+			if oldPresenceMember.IsNewerThan(presenceMember) { // RTP2b1
 				continue // do not process message with older timestamp // RTP2b1a
 			}
 		}