disable prometheus if not configured (#663)

zrpc/internal/clientinterceptors/prometheusinterceptor.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/tal-tech/go-zero/core/metric"
+	"github.com/tal-tech/go-zero/core/prometheus"
 	"github.com/tal-tech/go-zero/core/timex"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/status"
@@ -35,6 +36,10 @@ var (
 // PrometheusInterceptor is an interceptor that reports to prometheus server.
 func PrometheusInterceptor(ctx context.Context, method string, req, reply interface{},
 	cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
+	if !prometheus.Enabled() {
+		return invoker(ctx, method, req, reply, cc, opts...)
+	}
+
 	startTime := timex.Now()
 	err := invoker(ctx, method, req, reply, cc, opts...)
 	metricClientReqDur.Observe(int64(timex.Since(startTime)/time.Millisecond), method)

zrpc/internal/clientinterceptors/prometheusinterceptor_test.go

@@ -6,25 +6,38 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/tal-tech/go-zero/core/prometheus"
 	"google.golang.org/grpc"
 )
 
 func TestPromMetricInterceptor(t *testing.T) {
 	tests := []struct {
-		name string
-		err  error
+		name   string
+		enable bool
+		err    error
 	}{
 		{
-			name: "nil",
-			err:  nil,
+			name:   "nil",
+			enable: true,
+			err:    nil,
 		},
 		{
-			name: "with error",
-			err:  errors.New("mock"),
+			name:   "with error",
+			enable: true,
+			err:    errors.New("mock"),
+		},
+		{
+			name: "disabled",
 		},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
+			if test.enable {
+				prometheus.StartAgent(prometheus.Config{
+					Host: "localhost",
+					Path: "/",
+				})
+			}
 			cc := new(grpc.ClientConn)
 			err := PrometheusInterceptor(context.Background(), "/foo", nil, nil, cc,
 				func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn,