Added optional middleware param to emulator start for metrics

cmd/emulator/main.go

@@ -43,7 +43,12 @@ func defaultServiceKey(
 }
 
 func main() {
-	if err := start.Cmd(defaultServiceKey).Execute(); err != nil {
+	config := start.StartConfig{
+		GetServiceKey:   defaultServiceKey,
+		RestMiddlewares: []start.HttpMiddleware{},
+	}
+
+	if err := start.Cmd(config).Execute(); err != nil {
 		start.Exit(1, err.Error())
 	}
 }

cmd/emulator/start/start.go

@@ -22,6 +22,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"log"
+	"net/http"
 	"os"
 	"strings"
 	"time"
@@ -91,7 +92,14 @@ type serviceKeyFunc func(
 	hashAlgo crypto.HashAlgorithm,
 ) (crypto.PrivateKey, crypto.SignatureAlgorithm, crypto.HashAlgorithm)
 
-func Cmd(getServiceKey serviceKeyFunc) *cobra.Command {
+type HttpMiddleware func(http.Handler) http.Handler
+
+type StartConfig struct {
+	GetServiceKey   serviceKeyFunc
+	RestMiddlewares []HttpMiddleware
+}
+
+func Cmd(config StartConfig) *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "start",
 		Short: "Starts the Flow emulator server",
@@ -123,7 +131,7 @@ func Cmd(getServiceKey serviceKeyFunc) *cobra.Command {
 
 				servicePublicKey = servicePrivateKey.PublicKey()
 			} else { // if we don't provide any config values use the serviceKeyFunc to obtain the key
-				servicePrivateKey, serviceKeySigAlgo, serviceKeyHashAlgo = getServiceKey(
+				servicePrivateKey, serviceKeySigAlgo, serviceKeyHashAlgo = config.GetServiceKey(
 					conf.Init,
 					serviceKeySigAlgo,
 					serviceKeyHashAlgo,
@@ -216,6 +224,9 @@ func Cmd(getServiceKey serviceKeyFunc) *cobra.Command {
 
 			emu := server.NewEmulatorServer(logger, serverConf)
 			if emu != nil {
+				for _, middleware := range config.RestMiddlewares {
+					emu.UseRestMiddleware(middleware)
+				}
 				emu.Start()
 			} else {
 				Exit(-1, "")

server/access/rest.go

@@ -82,6 +82,12 @@ func (r *RestServer) Stop() {
 	_ = r.server.Shutdown(context.Background())
 }
 
+func (r *RestServer) UseMiddleware(middleware func(http.Handler) http.Handler) {
+	if r.server != nil {
+		r.server.Handler = middleware(r.server.Handler)
+	}
+}
+
 func NewRestServer(logger *zerolog.Logger, blockchain *emulator.Blockchain, adapter *adapters.AccessAdapter, chain flow.Chain, host string, port int, debug bool) (*RestServer, error) {
 
 	debugLogger := zerolog.Logger{}

server/server.go

@@ -20,6 +20,7 @@ package server
 
 import (
 	"fmt"
+	"net/http"
 	"os"
 	"sort"
 	"time"
@@ -511,3 +512,9 @@ func sanitizeConfig(conf *Config) *Config {
 
 	return conf
 }
+
+func (s *EmulatorServer) UseRestMiddleware(middleware func(http.Handler) http.Handler) {
+	if s.rest != nil {
+		s.rest.UseMiddleware(middleware)
+	}
+}