Add metrics for internal API requests (#2310)

* Add response size and requests total to internal handler

* Move MustRegister calls to New* funcs

* Move MustRegister back to init

* Init at some place, minimize changes

roomserver/internal/input/input.go

@@ -167,6 +167,7 @@ func (r *Inputer) startWorkerForRoom(roomID string) {
 // will look to see if we have a worker for that room which has its
 // own consumer. If we don't, we'll start one.
 func (r *Inputer) Start() error {
+	prometheus.MustRegister(roomserverInputBackpressure, processRoomEventDuration)
 	_, err := r.JetStream.Subscribe(
 		"", // This is blank because we specified it in BindStream.
 		func(m *nats.Msg) {
@@ -421,10 +422,6 @@ func (r *Inputer) WriteOutputEvents(roomID string, updates []api.OutputEvent) er
 	return nil
 }
 
-func init() {
-	prometheus.MustRegister(roomserverInputBackpressure)
-}
-
 var roomserverInputBackpressure = prometheus.NewGaugeVec(
 	prometheus.GaugeOpts{
 		Namespace: "dendrite",

roomserver/internal/input/input_events.go

@@ -37,10 +37,6 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
-func init() {
-	prometheus.MustRegister(processRoomEventDuration)
-}
-
 // TODO: Does this value make sense?
 const MaximumMissingProcessingTime = time.Minute * 2