Moderation delay WIP (#132):

* handle message retractation (proof of concept)

prosody-modules/mod_muc_moderation_delay/delay.lib.lua

@@ -1,11 +1,45 @@
 -- SPDX-FileCopyrightText: 2024 John Livingston <https://www.john-livingston.fr/>
 -- SPDX-License-Identifier: AGPL-3.0-only
-local async = require "util.async";
+local st = require "util.stanza";
+local timer = require "util.timer";
 local get_moderation_delay = module:require("config").get_moderation_delay;
 
 local muc_util = module:require "muc/util";
 local valid_roles = muc_util.valid_roles;
 
+local xmlns_fasten = "urn:xmpp:fasten:0";
+local xmlns_moderated_0 = "urn:xmpp:message-moderate:0";
+local xmlns_retract_0 = "urn:xmpp:message-retract:0";
+local xmlns_moderated_1 = "urn:xmpp:message-moderate:1";
+local xmlns_retract_1 = "urn:xmpp:message-retract:1";
+local xmlns_st_id = "urn:xmpp:sid:0";
+
+local queued_messages_retracted = {};
+
+local function is_retractation_for_stanza_id(stanza)
+  -- XEP 0425 was revised in 2023. For now, mod_muc_moderation uses the previous version.
+  -- But we will make the code compatible with both.
+  local apply_to = stanza:get_child("apply-to", xmlns_fasten);
+  if apply_to and apply_to.attr.id then
+    local moderated = apply_to:get_child("moderated", xmlns_moderated_0);
+    if moderated then
+      local retract = moderated:get_child("retract", xmlns_retract_0);
+      if retract then
+        return apply_to.attr.id;
+      end
+    end
+  end
+
+  local moderated = stanza:get_child("moderated", xmlns_moderated_1);
+  if moderated then
+    if moderated:get_child("retract", xmlns_retract_1) then
+      return moderated.attr.id;
+    end
+  end
+
+  return nil;
+end
+
 local function handle_broadcast_message(event)
   local room, stanza = event.room, event.stanza;
   local delay = get_moderation_delay(room);
@@ -17,10 +51,35 @@ local function handle_broadcast_message(event)
   if stanza.attr.type ~= "groupchat" then
     return;
   end
+
+  -- detect retractations:
+  local retracted_stanza_id = is_retractation_for_stanza_id(stanza);
+  if retracted_stanza_id then
+    module:log("debug", "Got a retractation message for %s", retracted_stanza_id);
+    if queued_messages_retracted[retracted_stanza_id] == false then
+      module:log("info", "Got a retractation message, for message %s that is currently waiting for broadcast. Cancelling.", retracted_stanza_id);
+      queued_messages_retracted[retracted_stanza_id] = true;
+      -- and we continue...
+    end
+  end
+
   if not stanza:get_child("body") then
+    -- Dont want to delay message without body.
+    -- This is usually messages like "xxx is typing", or any other service message.
+    -- This also should concern retractation messages.
+    -- Clients that will receive retractation messages for message they never got, should just drop them. And that's ok.
     return;
   end
 
+  local stanza_id = nil; -- message stanza id... can be nil!
+  local stanza_id_child = stanza:get_child("stanza-id", xmlns_st_id);
+  if not stanza_id_child then
+    -- this can happen when muc is not archived!
+    -- in such case, message retractation is not possible.
+    -- so, this is a normal use case, and we should handle it properly.
+  else
+    stanza_id = stanza_id_child.attr.id;
+  end
   local id = stanza.attr.id;
   if not id then
     -- message should alway have an id, but just in case...
@@ -28,15 +87,15 @@ local function handle_broadcast_message(event)
     return;
   end
 
-  -- TODO: detect message retractation, and stop broadcast for any waiting message.
-
   -- Message must be delayed, except for:
   -- * room moderators
   -- * the user that sent the message (if they don't get the echo quickly, their clients could have weird behaviours)
-
-  module:log("debug", "Message must be delayed by %i seconds, sending first broadcast wave.", delay);
+  module:log("debug", "Message %s / %s must be delayed by %i seconds, sending first broadcast wave.", id, stanza_id, delay);
+  if stanza_id then
+    queued_messages_retracted[stanza_id] = false;
+  end
   local moderator_role_value = valid_roles["moderator"];
-  local func = function (nick, occupant)
+  local cond_func = function (nick, occupant)
     if valid_roles[occupant.role or "none"] >= moderator_role_value then
       return true;
     end
@@ -45,13 +104,28 @@ local function handle_broadcast_message(event)
     end
     return false;
   end;
-  room:broadcast(stanza, func);
-  async.sleep(delay);
-  module:log("debug", "Message has been delayed, sending to remaining participants.");
-  room:broadcast(stanza, function (nick, occupant)
-    return not func(nick, occupant);
+
+  local cloned_stanza = st.clone(stanza); -- we must clone, to send a copy for the second wave.
+  room:broadcast(stanza, cond_func);
+
+  timer.add_task(delay, function ()
+    if stanza_id then
+      if queued_messages_retracted[stanza_id] == true then
+        module:log("info", "Message %s was retracted during the delay, cancelling the broadcast.", stanza_id);
+        queued_messages_retracted[stanza_id] = nil;
+        return;
+      end
+
+      queued_messages_retracted[stanza_id] = nil;
+    end
+  
+    module:log("debug", "Message %s has been delayed, sending to remaining participants.", id);
+    room:broadcast(cloned_stanza, function (nick, occupant)
+      return not cond_func(nick, occupant);
+    end);
   end);
-  return true; -- stop the default process
+
+  return true; -- stop the default broadcast_message processing.
 end
 
 return {