ircd:Ⓜ️:room::message: Add interface for edit contents.

include/ircd/m/room/message.h

@@ -53,6 +53,12 @@ struct ircd::m::room::message
 	/// must clean that up if required. Empty if not a reply or malformed.
 	string_view reply_to_body() const noexcept;
 
+	/// The event ID of the replaced event; empty if not a replace
+	id::event replace_event() const noexcept;
+
+	/// The new content body; empty if not a replace or replace was empty!
+	string_view replace_body() const noexcept;
+
 	/// C2S v1.3 11.3.1 message body stripped of any reply fallback. This is
 	/// the proper way to read the message rather than reading "body" direct;
 	/// returns "body" if not reply.

matrix/room_message.cc

@@ -35,6 +35,77 @@ const noexcept
 	return body;
 }
 
+ircd::string_view
+ircd::m::room::message::replace_body()
+const noexcept
+{
+	const auto replace_event
+	{
+		this->replace_event()
+	};
+
+	if(!replace_event)
+		return {};
+
+	const json::object m_new_content
+	{
+		this->source["m.new_content"]
+	};
+
+	if(!json::type(m_new_content, json::OBJECT))
+		return {};
+
+	const json::string body
+	{
+		m_new_content["body"]
+	};
+
+	return body;
+}
+
+ircd::m::event::id
+ircd::m::room::message::replace_event()
+const noexcept try
+{
+	const m::relates_to &m_relates_to
+	{
+		json::get<"m.relates_to"_>(*this)
+	};
+
+	if(json::get<"rel_type"_>(m_relates_to) != "m.replace")
+		return {};
+
+	const auto &event_id
+	{
+		json::get<"event_id"_>(m_relates_to)
+	};
+
+	if(!event_id || !valid(m::id::EVENT, event_id))
+		return {};
+
+	return event_id;
+}
+catch(const json::error &e)
+{
+	log::derror
+	{
+		log, "Failed to extract m.relates_to m.replace event_id :%s",
+		e.what(),
+	};
+
+	return {};
+}
+catch(const std::exception &e)
+{
+	log::error
+	{
+		log, "Failed to extract m.relates_to m.replace event_id :%s",
+		e.what(),
+	};
+
+	return {};
+}
+
 ircd::string_view
 ircd::m::room::message::reply_to_body()
 const noexcept