Fix /metrics, /debug/requests, /debug/events + additional flag for en…

…abling those (#957)

* Debug endpoints restored (/debug/requests, /debug/events, /metrics); Command line parameter added to control the feature

* Update go/grpcwebproxy/main.go

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

* fix heading go/grpcwebproxy/main.go

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

Co-authored-by: Evgeny Mikerin <evgeny.mikerin@jpmchase.com>
Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

go/grpcwebproxy/main.go

@@ -21,7 +21,7 @@ import (
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/pflag"
 	"golang.org/x/net/context"
-	_ "golang.org/x/net/trace" // register in DefaultServerMux
+	"golang.org/x/net/trace" // register in DefaultServerMux
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/grpclog"
 	"google.golang.org/grpc/metadata"
@@ -44,6 +44,8 @@ var (
 
 	flagHttpMaxWriteTimeout = pflag.Duration("server_http_max_write_timeout", 10*time.Second, "HTTP server config, max write duration.")
 	flagHttpMaxReadTimeout  = pflag.Duration("server_http_max_read_timeout", 10*time.Second, "HTTP server config, max read duration.")
+
+	enableRequestDebug = pflag.Bool("enable_request_debug", false, "whether to enable (/debug/requests) and connection(/debug/events) monitoring; also controls prometheus monitoring (/metrics)")
 )
 
 func main() {
@@ -103,8 +105,12 @@ func main() {
 
 	if *runHttpServer {
 		// Debug server.
-		debugServer := buildServer(wrappedGrpc)
-		http.Handle("/metrics", promhttp.Handler())
+		var debugServer *http.Server
+		if *enableRequestDebug {
+			debugServer = buildDebugServer(wrappedGrpc, promhttp.Handler())
+		} else {
+			debugServer = buildServer(wrappedGrpc)
+		}
 		debugListener := buildListenerOrFail("http", *flagHttpPort)
 		serveServer(debugServer, debugListener, "http", errChan)
 	}
@@ -121,6 +127,25 @@ func main() {
 	// TODO(mwitkow): Add graceful shutdown.
 }
 
+func buildDebugServer(wrappedGrpc *grpcweb.WrappedGrpcServer, metricsHandler http.Handler) *http.Server {
+	return &http.Server{
+		WriteTimeout: *flagHttpMaxWriteTimeout,
+		ReadTimeout:  *flagHttpMaxReadTimeout,
+		Handler: http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
+			switch req.URL.Path {
+			case "/metrics":
+				metricsHandler.ServeHTTP(resp, req)
+			case "/debug/requests":
+				trace.Traces(resp, req)
+			case "/debug/events":
+				trace.Events(resp, req)
+			default:
+				wrappedGrpc.ServeHTTP(resp, req)
+			}
+		}),
+	}
+}
+
 func buildServer(wrappedGrpc *grpcweb.WrappedGrpcServer) *http.Server {
 	return &http.Server{
 		WriteTimeout: *flagHttpMaxWriteTimeout,