Split parent message resolution into two steps.

bridge/config/config.go

@@ -42,6 +42,17 @@ type Message struct {
 	Extra     map[string][]interface{}
 }
 
+func (msg *Message) CanonicalParentMsgID() string {
+	if msg.Extra != nil && len(msg.Extra["canonical_parent_mid"]) == 1 {
+		return msg.Extra["canonical_parent_mid"][0].(string)
+	}
+	return ""
+}
+
+func (msg *Message) IsThreadable() bool {
+	return msg.CanonicalParentMsgID() != ""
+}
+
 type FileInfo struct {
 	Name    string
 	Data    *[]byte

gateway/gateway.go

@@ -56,6 +56,10 @@ func New(cfg config.Gateway, r *Router) *Gateway {
 
 // Find the canonical ID that the message is keyed under in cache
 func (gw *Gateway) FindCanonicalMsgID(protocol string, mID string) string {
+	if mID == "" {
+		return ""
+	}
+
 	ID := protocol + " " + mID
 	if gw.Messages.Contains(ID) {
 		return mID
@@ -250,13 +254,16 @@ func (gw *Gateway) handleMessage(msg config.Message, dest *bridge.Bridge) []*BrM
 		return brMsgIDs
 	}
 
+	// Perform single intensive operation to resolve parent msg ID through
+	// cache, which allows us to rethread messages.
+	gw.resolveCanonicalParentMsgID(&msg)
+
 	originchannel := msg.Channel
 	origmsg := msg
 	channels := gw.getDestChannel(&msg, *dest)
 	for _, channel := range channels {
-		if parentID, isThreaded := gw.handleThreading(&msg, dest, channel); isThreaded {
-			msg.ParentID = parentID
-		}
+		// Performs rethreading.
+		msg.ParentID =  gw.getParentID(&msg, dest, channel)
 
 		// Only send the avatar download event to ourselves.
 		if msg.Event == config.EventAvatarDownload {
@@ -431,22 +438,31 @@ func (gw *Gateway) modifyMessage(msg *config.Message) {
 	}
 }
 
-func (gw *Gateway) handleThreading(msg *config.Message, dest *bridge.Bridge, channel config.ChannelInfo) (string, bool) {
+func (gw *Gateway) resolveCanonicalParentMsgID(msg *config.Message) {
+	if msg.ParentID != "" {
+		extras := make([]interface{}, 1)
+		extras[0] = gw.FindCanonicalMsgID(msg.Protocol, msg.ParentID)
+		msg.Extra["canonical_parent_mid"] = extras
+	}
+}
+
+func (gw *Gateway) getParentID(msg *config.Message, dest *bridge.Bridge, channel config.ChannelInfo) string {
 	if msg.ParentID == "" {
 		// Message is not threaded.
-		return "", false
+		return ""
 	}
 
-	canonicalParentMsgID := gw.FindCanonicalMsgID(msg.Protocol, msg.ParentID)
-	if !dest.GetBool("PreserveThreading") || canonicalParentMsgID == "" {
+	if !dest.GetBool("PreserveThreading") || !msg.IsThreadable() {
 		// Mark message as unthreaded, either because disabled or uncached.
-		return "unthreaded", true
+		return "unthreaded"
 	}
 
-	if parentID := gw.getDestMsgID(msg.Protocol+" "+canonicalParentMsgID, dest, channel); parentID != "" {
-		return parentID, true
+	if downstreamID := gw.getDestMsgID(msg.Protocol+" "+msg.CanonicalParentMsgID(), dest, channel); downstreamID != "" {
+		return downstreamID
 	}
-	return canonicalParentMsgID, true
+
+	// If all else fails, this must be the original parent message.
+	return msg.CanonicalParentMsgID()
 }
 
 // handleFiles uploads or places all files on the given msg to the MediaServer and