add variadic counterOpts funcs to server and client metrics constructor

client_metrics.go

@@ -25,31 +25,32 @@ type ClientMetrics struct {
 // ClientMetrics when not using the default Prometheus metrics registry, for
 // example when wanting to control which metrics are added to a registry as
 // opposed to automatically adding metrics via init functions.
-func NewClientMetrics() *ClientMetrics {
+func NewClientMetrics(counterOpts ...CounterOption) *ClientMetrics {
+	opts := counterOptions(counterOpts)
 	return &ClientMetrics{
 		clientStartedCounter: prom.NewCounterVec(
-			prom.CounterOpts{
+			opts.apply(prom.CounterOpts{
 				Name: "grpc_client_started_total",
 				Help: "Total number of RPCs started on the client.",
-			}, []string{"grpc_type", "grpc_service", "grpc_method"}),
+			}), []string{"grpc_type", "grpc_service", "grpc_method"}),
 
 		clientHandledCounter: prom.NewCounterVec(
-			prom.CounterOpts{
+			opts.apply(prom.CounterOpts{
 				Name: "grpc_client_handled_total",
 				Help: "Total number of RPCs completed by the client, regardless of success or failure.",
-			}, []string{"grpc_type", "grpc_service", "grpc_method", "grpc_code"}),
+			}), []string{"grpc_type", "grpc_service", "grpc_method", "grpc_code"}),
 
 		clientStreamMsgReceived: prom.NewCounterVec(
-			prom.CounterOpts{
+			opts.apply(prom.CounterOpts{
 				Name: "grpc_client_msg_received_total",
 				Help: "Total number of RPC stream messages received by the client.",
-			}, []string{"grpc_type", "grpc_service", "grpc_method"}),
+			}), []string{"grpc_type", "grpc_service", "grpc_method"}),
 
 		clientStreamMsgSent: prom.NewCounterVec(
-			prom.CounterOpts{
+			opts.apply(prom.CounterOpts{
 				Name: "grpc_client_msg_sent_total",
 				Help: "Total number of gRPC stream messages sent by the client.",
-			}, []string{"grpc_type", "grpc_service", "grpc_method"}),
+			}), []string{"grpc_type", "grpc_service", "grpc_method"}),
 
 		clientHandledHistogramEnabled: false,
 		clientHandledHistogramOpts: prom.HistogramOpts{

metric_options.go

@@ -0,0 +1,35 @@
+package grpc_prometheus
+
+import (
+	prom "github.com/prometheus/client_golang/prometheus"
+)
+
+type CounterOption func(opts *prom.CounterOpts)
+
+type counterOptions []CounterOption
+
+func (co counterOptions) apply(o prom.CounterOpts) prom.CounterOpts {
+	for _, f := range co {
+		f(&o)
+	}
+	return o
+}
+
+func WithConstLabels(labels prom.Labels) CounterOption {
+	return func(o *prom.CounterOpts) {
+		o.ConstLabels = labels
+	}
+}
+
+type HistogramOption func(*prom.HistogramOpts)
+
+// WithHistogramBuckets allows you to specify custom bucket ranges for histograms if EnableHandlingTimeHistogram is on.
+func WithHistogramBuckets(buckets []float64) HistogramOption {
+	return func(o *prom.HistogramOpts) { o.Buckets = buckets }
+}
+
+func WithHistogramConstLabels(labels prom.Labels) HistogramOption {
+	return func(o *prom.HistogramOpts) {
+		o.ConstLabels = labels
+	}
+}

server_metrics.go

@@ -22,28 +22,29 @@ type ServerMetrics struct {
 // ServerMetrics when not using the default Prometheus metrics registry, for
 // example when wanting to control which metrics are added to a registry as
 // opposed to automatically adding metrics via init functions.
-func NewServerMetrics() *ServerMetrics {
+func NewServerMetrics(counterOpts ...CounterOption) *ServerMetrics {
+	opts := counterOptions(counterOpts)
 	return &ServerMetrics{
 		serverStartedCounter: prom.NewCounterVec(
-			prom.CounterOpts{
+			opts.apply(prom.CounterOpts{
 				Name: "grpc_server_started_total",
 				Help: "Total number of RPCs started on the server.",
-			}, []string{"grpc_type", "grpc_service", "grpc_method"}),
+			}), []string{"grpc_type", "grpc_service", "grpc_method"}),
 		serverHandledCounter: prom.NewCounterVec(
-			prom.CounterOpts{
+			opts.apply(prom.CounterOpts{
 				Name: "grpc_server_handled_total",
 				Help: "Total number of RPCs completed on the server, regardless of success or failure.",
-			}, []string{"grpc_type", "grpc_service", "grpc_method", "grpc_code"}),
+			}), []string{"grpc_type", "grpc_service", "grpc_method", "grpc_code"}),
 		serverStreamMsgReceived: prom.NewCounterVec(
-			prom.CounterOpts{
+			opts.apply(prom.CounterOpts{
 				Name: "grpc_server_msg_received_total",
 				Help: "Total number of RPC stream messages received on the server.",
-			}, []string{"grpc_type", "grpc_service", "grpc_method"}),
+			}), []string{"grpc_type", "grpc_service", "grpc_method"}),
 		serverStreamMsgSent: prom.NewCounterVec(
-			prom.CounterOpts{
+			opts.apply(prom.CounterOpts{
 				Name: "grpc_server_msg_sent_total",
 				Help: "Total number of gRPC stream messages sent by the server.",
-			}, []string{"grpc_type", "grpc_service", "grpc_method"}),
+			}), []string{"grpc_type", "grpc_service", "grpc_method"}),
 		serverHandledHistogramEnabled: false,
 		serverHandledHistogramOpts: prom.HistogramOpts{
 			Name:    "grpc_server_handling_seconds",
@@ -54,13 +55,6 @@ func NewServerMetrics() *ServerMetrics {
 	}
 }
 
-type HistogramOption func(*prom.HistogramOpts)
-
-// WithHistogramBuckets allows you to specify custom bucket ranges for histograms if EnableHandlingTimeHistogram is on.
-func WithHistogramBuckets(buckets []float64) HistogramOption {
-	return func(o *prom.HistogramOpts) { o.Buckets = buckets }
-}
-
 // EnableHandlingTimeHistogram enables histograms being registered when
 // registering the ServerMetrics on a Prometheus registry. Histograms can be
 // expensive on Prometheus servers. It takes options to configure histogram