mod_carbons: Improve performance by delaying creation of carbon payload

If there are no other sessions which also enabled carbons then the
carbons wrapper is not used and the potentially expensive clone
operation was a waste of cycles.

1 files changed, 15 insertions, 11 deletions

diff --git a/plugins/mod_carbons.lua b/plugins/mod_carbons.lua
index 1dcd4a07..0f8c7c60 100644
--- a/plugins/mod_carbons.lua
+++ b/plugins/mod_carbons.lua
@@ -74,17 +74,7 @@ local function message_handler(event, c2s)
 		return
 	end
 
-	-- Create the carbon copy and wrap it as per the Stanza Forwarding XEP
-	local copy = st.clone(stanza);
-	if c2s and not orig_to then
-		stanza.attr.to = bare_from;
-	end
-	copy.attr.xmlns = "jabber:client";
-	local carbon = st.message{ from = bare_jid, type = orig_type, }
-		:tag(c2s and "sent" or "received", { xmlns = xmlns_carbons })
-			:tag("forwarded", { xmlns = xmlns_forward })
-				:add_child(copy):reset();
-
+	local carbon;
 	user_sessions = user_sessions and user_sessions.sessions;
 	for _, session in pairs(user_sessions) do
 		-- Carbons are sent to resources that have enabled it
@@ -93,6 +83,20 @@ local function message_handler(event, c2s)
 		and session ~= target_session
 		-- and isn't among the top resources that would receive the message per standard routing rules
 		and (c2s or session.priority ~= top_priority) then
+			if not carbon then
+				-- Create the carbon copy and wrap it as per the Stanza Forwarding XEP
+				local copy = st.clone(stanza);
+				if c2s and not orig_to then
+					stanza.attr.to = bare_from;
+				end
+				copy.attr.xmlns = "jabber:client";
+				carbon = st.message{ from = bare_jid, type = orig_type, }
+					:tag(c2s and "sent" or "received", { xmlns = xmlns_carbons })
+						:tag("forwarded", { xmlns = xmlns_forward })
+							:add_child(copy):reset();
+
+			end
+
 			carbon.attr.to = session.full_jid;
 			module:log("debug", "Sending carbon to %s", session.full_jid);
 			session.send(carbon);