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

clientapi/routing/register.go

@@ -64,11 +64,6 @@ const (
 	sessionIDLength   = 24
 )
 
-func init() {
-	// Register prometheus metrics. They must be registered to be exposed.
-	prometheus.MustRegister(amtRegUsers)
-}
-
 // sessionsDict keeps track of completed auth stages for each session.
 // It shouldn't be passed by value because it contains a mutex.
 type sessionsDict struct {

clientapi/routing/routing.go

@@ -37,6 +37,7 @@ import (
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	"github.com/nats-io/nats.go"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/sirupsen/logrus"
 )
 
@@ -60,6 +61,8 @@ func Setup(
 	extRoomsProvider api.ExtraPublicRoomsProvider,
 	mscCfg *config.MSCs, natsClient *nats.Conn,
 ) {
+	prometheus.MustRegister(amtRegUsers, sendEventDuration)
+
 	rateLimits := httputil.NewRateLimits(&cfg.RateLimiting)
 	userInteractiveAuth := auth.NewUserInteractive(userAPI, cfg)
 

clientapi/routing/sendevent.go

@@ -46,10 +46,6 @@ var (
 	userRoomSendMutexes sync.Map // (roomID+userID) -> mutex. mutexes to ensure correct ordering of sendEvents
 )
 
-func init() {
-	prometheus.MustRegister(sendEventDuration)
-}
-
 var sendEventDuration = prometheus.NewHistogramVec(
 	prometheus.HistogramOpts{
 		Namespace: "dendrite",