--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/mod_carbons.lua	Fri Jan 16 14:02:14 2015 +0100
@@ -0,0 +1,111 @@
+-- XEP-0280: Message Carbons implementation for Prosody
+-- Copyright (C) 2011 Kim Alvefur
+--
+-- This file is MIT/X11 licensed.
+
+local st = require "util.stanza";
+local jid_bare = require "util.jid".bare;
+local xmlns_carbons = "urn:xmpp:carbons:2";
+local xmlns_forward = "urn:xmpp:forward:0";
+local full_sessions, bare_sessions = full_sessions, bare_sessions;
+
+local function toggle_carbons(event)
+	local origin, stanza = event.origin, event.stanza;
+	local state = stanza.tags[1].name;
+	module:log("debug", "%s %sd carbons", origin.full_jid, state);
+	origin.want_carbons = state == "enable" and stanza.tags[1].attr.xmlns;
+	return origin.send(st.reply(stanza));
+end
+module:hook("iq-set/self/"..xmlns_carbons..":disable", toggle_carbons);
+module:hook("iq-set/self/"..xmlns_carbons..":enable", toggle_carbons);
+
+local function message_handler(event, c2s)
+	local origin, stanza = event.origin, event.stanza;
+	local orig_type = stanza.attr.type;
+	local orig_from = stanza.attr.from;
+	local orig_to = stanza.attr.to;
+	
+	if not (orig_type == nil
+			or orig_type == "normal"
+			or orig_type == "chat") then
+		return -- No carbons for messages of type error or headline
+	end
+
+	-- Stanza sent by a local client
+	local bare_jid = jid_bare(orig_from);
+	local target_session = origin;
+	local top_priority = false;
+	local user_sessions = bare_sessions[bare_jid];
+
+	-- Stanza about to be delivered to a local client
+	if not c2s then
+		bare_jid = jid_bare(orig_to);
+		target_session = full_sessions[orig_to];
+		user_sessions = bare_sessions[bare_jid];
+		if not target_session and user_sessions then
+			-- The top resources will already receive this message per normal routing rules,
+			-- so we are going to skip them in order to avoid sending duplicated messages.
+			local top_resources = user_sessions.top_resources;
+			top_priority = top_resources and top_resources[1].priority
+		end
+	end
+
+	if not user_sessions then
+		module:log("debug", "Skip carbons for offline user");
+		return -- No use in sending carbons to an offline user
+	end
+
+	if stanza:get_child("private", xmlns_carbons) then
+		if not c2s then
+			stanza:maptags(function(tag)
+				if not ( tag.attr.xmlns == xmlns_carbons and tag.name == "private" ) then
+					return tag;
+				end
+			end);
+		end
+		module:log("debug", "Message tagged private, ignoring");
+		return
+	elseif stanza:get_child("no-copy", "urn:xmpp:hints") then
+		module:log("debug", "Message has no-copy hint, ignoring");
+		return
+	elseif stanza:get_child("x", "http://jabber.org/protocol/muc#user") then
+		module:log("debug", "MUC PM, ignoring");
+		return
+	end
+
+	-- Create the carbon copy and wrap it as per the Stanza Forwarding XEP
+	local copy = st.clone(stanza);
+	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();
+
+	user_sessions = user_sessions and user_sessions.sessions;
+	for _, session in pairs(user_sessions) do
+		-- Carbons are sent to resources that have enabled it
+		if session.want_carbons
+		-- but not the resource that sent the message, or the one that it's directed to
+		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
+			carbon.attr.to = session.full_jid;
+			module:log("debug", "Sending carbon to %s", session.full_jid);
+			session.send(carbon);
+		end
+	end
+end
+
+local function c2s_message_handler(event)
+	return message_handler(event, true)
+end
+
+-- Stanzas sent by local clients
+module:hook("pre-message/host", c2s_message_handler, 1);
+module:hook("pre-message/bare", c2s_message_handler, 1);
+module:hook("pre-message/full", c2s_message_handler, 1);
+-- Stanzas to local clients
+module:hook("message/bare", message_handler, 1);
+module:hook("message/full", message_handler, 1);
+
+module:add_feature(xmlns_carbons);