--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_tos/mod_tos.lua	Wed Aug 25 16:05:09 2021 +0200
@@ -0,0 +1,83 @@
+local array = require"util.array";
+local st = require"util.stanza";
+
+local tos_version = assert(module:get_option("tos_version"), "tos_version must be set")
+
+local status_storage;
+if prosody.process_type == "prosody" or prosody.shutdown then
+	status_storage = module:open_store("tos_status", "keyval")
+end
+
+local documents = array{};
+
+local function validate_doc(doc)
+	if not doc.title or not doc.sources or #doc.sources < 1 then
+		return false, "document needs to have a title and at least one source"
+	end
+	for _, source in ipairs(doc.sources) do
+		if not source.url or not source.type then
+			return false, "document " .. doc.title .. " has a source without url or type"
+		end
+	end
+	return true, doc
+end
+
+for _, doc in ipairs(assert(module:get_option("tos_documents"), "tos_documents option is required")) do
+	local ok, doc_or_err = validate_doc(doc)
+	if not ok then
+		error("invalid TOS document: "..doc_or_err)
+	end
+	documents:push(doc);
+end
+
+local function send_tos_push(session)
+	local to = session.username .. "@" .. session.host .. "/" .. session.resource;
+	local push = st.message({
+		type = "headline",
+		to = to,
+	}, "In order to continue to use the service, you have to accept the current version of the Terms of Service.");
+	local tos = push:tag("tos-push", { xmlns = "urn:xmpp:tos:0" }):tag("tos", { version = tos_version });
+	for _, doc in ipairs(documents) do
+		local doc_tag = tos:tag("document"):text_tag("title", doc.title);
+		for _, source in ipairs(doc.sources) do
+			doc_tag:tag("source", { url = source.url,  type = source.type }):up();
+		end
+		doc_tag:up();
+	end
+	tos:up():up();
+	module:send(push);
+end
+
+local function check_tos(event)
+	local user = event.origin.username
+	assert(user)
+	local tos_status = status_storage:get(user)
+	if tos_status and tos_status.version and tos_status.version == tos_version then
+		module:log("debug", "user %s has signed the current tos", user);
+		return
+	end
+	module:log("debug", "user %s has not signed the current tos, sending tos push", user);
+	send_tos_push(event.origin)
+end
+
+local function handle_accept_tos_iq(event)
+	local user = event.origin.username;
+	assert(user);
+	local accept = event.stanza.tags[1];
+	local version = accept.attr["version"];
+	module:log("debug", "user %s has accepted ToS version %s", user, version);
+	if version ~= tos_version then
+		local reply = st.error_reply(event.stanza, "modify", "not-allowed", "Only the most recent version of the ToS can be accepted");
+		module:log("debug", "%s is not the most recent version (%s), rejecting", version, tos_version);
+		event.origin.send(reply);
+		return true;
+	end
+
+	status_storage:set(user, { version = tos_version });
+	local reply = st.reply(event.stanza);
+	event.origin.send(reply);
+	return true;
+end
+
+module:hook("presence/initial", check_tos, -100);
+module:hook("iq-set/bare/urn:xmpp:tos:0:accept", handle_accept_tos_iq);