Terms&Conditions (#18) WIP:

* Converse module to display terms.
* Prosody module to send terms.

prosody-modules/mod_muc_peertubelivechat_terms/README.md

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+<!--
+SPDX-FileCopyrightText: 2024 John Livingston <https://www.john-livingston.fr/>
+
+SPDX-License-Identifier: AGPL-3.0-only
+-->
+
+# mod_muc_peertubelivechat_terms
+
+This module is a custom module to handle Terms&Conditions in the livechat Peertube plugin.
+
+This module is part of peertube-plugin-livechat, and is under the same LICENSE.
+
+## Features
+
+When a new occupant session is created for a MUC, this module will send to the user the global terms,
+and the MUC-specific terms (if defined).
+
+This is done by sending groupchat messages.
+These messages will contain a "x-livechat-terms" tag, so that livechat front-end can detect these messages, and display them differently.
+For standard XMPP clients, these messages will show as standard MUC message coming from a specific nickname.
+
+## Configuration
+
+This modules take following options.
+
+### muc_terms_service_nickname
+
+The nickname that will be used by service messages.
+This module reserves the nickname, so than nobody can use it in MUC rooms
+(we don't want any user to spoof this nickname).
+
+### muc_terms
+
+The global terms.

prosody-modules/mod_muc_peertubelivechat_terms/mod_muc_peertubelivechat_terms.lua

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+-- mod_muc_peertubelivechat_terms
+--
+-- SPDX-FileCopyrightText: 2024 John Livingston <https://www.john-livingston.fr/>
+-- SPDX-License-Identifier: AGPL-3.0-only
+--
+-- This file is AGPL-v3 licensed.
+-- Please see the Peertube livechat plugin copyright information.
+-- https://livingston.frama.io/peertube-plugin-livechat/credits/
+--
+local jid_escape = require "util.jid".escape;
+local jid_resource = require "util.jid".resource;
+local st = require "util.stanza";
+local id = require "util.id";
+
+local service_nickname = module:get_option_string("muc_terms_service_nickname", "Service");
+local global_terms = module:get_option_string("muc_terms", "");
+
+-- send the terms when joining:
+function send_terms(event)
+  local origin = event.origin;
+	local room = event.room;
+	local occupant = event.occupant;
+  if global_terms then
+    local from = room.jid .. '/' .. jid_escape(service_nickname);
+    module:log("debug", "Sending global terms to %s from %s (room %s)", occupant.jid, from, room);
+    local message = st.message({
+			type = "groupchat",
+			to = occupant.jid,
+			from = from,
+			id = id.medium()
+		}, global_terms)
+      :tag('x-livechat-terms', { type = "global" }):up(); -- adding a custom tag to specify that it is a "terms" message, so that frontend can display it with a special template.
+		origin.send(message);
+  end
+end
+-- Note: we could do that on muc-occupant-joined or muc-occupant-session-new.
+-- The first will not send it to multiple clients, the second will.
+-- After some reflexion, i will try muc-occupant-session-new, and see if it works as expected.
+module:hook("muc-occupant-session-new", send_terms);
+
+-- reserve the service_nickname:
+function enforce_nick_policy(event)
+  local origin, stanza = event.origin, event.stanza;
+  local requested_nick = jid_resource(stanza.attr.to);
+  local room = event.room;
+	if not room then return; end
+
+  if requested_nick == service_nickname then
+    module:log("debug", "Occupant tried to use the %s reserved nickname, blocking it.", service_nickname);
+    local reply = st.error_reply(stanza, "cancel", "conflict", nil, room.jid):up();
+		origin.send(reply);
+    return true;
+  end
+end
+module:hook("muc-occupant-pre-join", enforce_nick_policy);
+module:hook("muc-occupant-pre-change", enforce_nick_policy);
+
+-- security check: we must remove all "x-livechat-terms" tag, to be sure nobody tries to spoof terms!
+module:hook("muc-occupant-groupchat", function(event)
+  event.stanza:maptags(function (child)
+    if child.name == 'x-livechat-terms' then
+      return nil;
+    end
+    return child;
+  end);
+end, 100);