ircd::server: Add opts::prio value; special case prio value in link selection.

include/ircd/server/request.h

@@ -136,6 +136,15 @@ struct ircd::server::request::opts
 	/// set this option to false.
 	bool contiguous_content {true};
 
+	/// Priority indication is factored into the link selection algorithm for
+	/// making this request to the peer. It is not the only factor, and the
+	/// default is usually sufficient. Lower priority values are favored when
+	/// two requests are compared. When the priority is set to the lowest
+	/// possible value, a dedicated link may be opened to the peer even if the
+	/// maximum number of links are already open; other limits may be exceeded;
+	/// use that value with caution.
+	int16_t priority {0};
+
 	/// Only applies when using dynamic content allocation with a chunked
 	/// encoded response. This will hint the chunk vector. Ideally it can be
 	/// set to the number of chunks expected in a response to avoid growth of

ircd/server.cc

@@ -494,6 +494,9 @@ catch(const std::exception &e)
 ircd::server::link *
 ircd::server::peer::link_get(const request &request)
 {
+	assert(request.opt);
+	const auto &prio(request.opt->priority);
+
 	if(links.empty())
 		return &link_add(1);
 
@@ -559,6 +562,20 @@ ircd::server::peer::link_get(const request &request)
 		best = &cand;
 	}
 
+	// Even though the prio is set to the super special value we allow the
+	// normal loop to first come up with a best link which already is open
+	// rather than unconditionally opening a new connection.
+	if(prio == std::numeric_limits<std::remove_reference<decltype(prio)>::type>::min())
+	{
+		if(!best)
+			return &link_add(1);
+
+		if(best->tag_committed())
+			return &link_add(1);
+
+		return best;
+	}
+
 	if(links_maxed)
 		return best;
 

modules/media/media.cc

@@ -114,7 +114,7 @@ try
 		downloading_dock.notify_all();
 	}};
 
-	if(exists(m::room{room_id}))
+	if(exists(room_id))
 		return room_id;
 
 	const unique_buffer<mutable_buffer> buf