otelgrpc: add custom attributes to the stats handler

Fixes #3894

CHANGELOG.md

@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Support for stdoutlog exporter in `go.opentelemetry.io/contrib/config`. (#5850)
 - Add macOS ARM64 platform to the compatibility testing suite. (#5868)
+- Add custom attributes to the stats handler in `go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc`. (#5133)
 
 ### Removed
 

instrumentation/google.golang.org/grpc/otelgrpc/config.go

@@ -42,6 +42,7 @@ type config struct {
 	TracerProvider    trace.TracerProvider
 	MeterProvider     metric.MeterProvider
 	SpanStartOptions  []trace.SpanStartOption
+	Attributes        []attribute.KeyValue
 
 	ReceivedEvent bool
 	SentEvent     bool
@@ -257,3 +258,16 @@ func (o spanStartOption) apply(c *config) {
 func WithSpanOptions(opts ...trace.SpanStartOption) Option {
 	return spanStartOption{opts}
 }
+
+type attributesOption struct{ a []attribute.KeyValue }
+
+func (o attributesOption) apply(c *config) {
+	if o.a != nil {
+		c.Attributes = o.a
+	}
+}
+
+// WithAttributes returns an Option to add custom attributes to the spans and metrics.
+func WithAttributes(a ...attribute.KeyValue) Option {
+	return attributesOption{a: a}
+}

instrumentation/google.golang.org/grpc/otelgrpc/stats_handler.go

@@ -58,6 +58,9 @@ func (h *serverHandler) TagRPC(ctx context.Context, info *stats.RPCTagInfo) cont
 
 	name, attrs := internal.ParseFullMethod(info.FullMethodName)
 	attrs = append(attrs, RPCSystemGRPC)
+
+	attrs = append(attrs, h.config.Attributes...)
+
 	ctx, _ = h.tracer.Start(
 		trace.ContextWithRemoteSpanContext(ctx, trace.SpanContextFromContext(ctx)),
 		name,
@@ -98,6 +101,9 @@ func NewClientHandler(opts ...Option) stats.Handler {
 func (h *clientHandler) TagRPC(ctx context.Context, info *stats.RPCTagInfo) context.Context {
 	name, attrs := internal.ParseFullMethod(info.FullMethodName)
 	attrs = append(attrs, RPCSystemGRPC)
+
+	attrs = append(attrs, h.config.Attributes...)
+
 	ctx, _ = h.tracer.Start(
 		ctx,
 		name,