feat(otelgrpc): allow setting dynamic per-request metric attributes

CHANGELOG.md

@@ -15,6 +15,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Add the `WithSource` option to the `go.opentelemetry.io/contrib/bridges/otelslog` log bridge to set the `code.*` attributes in the log record that includes the source location where the record was emitted. (#6253)
 - Add `ContextWithStartTime` and `StartTimeFromContext` to `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp`, which allows setting the start time using go context. (#6137)
 - Set the `code.*` attributes in `go.opentelemetry.io/contrib/bridges/otelzap` if the `zap.Logger` was created with the `AddCaller` or `AddStacktrace` option. (#6268)
+- Add new `WithMetricsAttributesFn` option to allow setting dynamic, per-request metric attributes in `go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc`. (#6281)
 
 ### Changed 
 

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

@@ -4,6 +4,8 @@
 package otelgrpc // import "go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc"
 
 import (
+	"context"
+
 	"google.golang.org/grpc/stats"
 
 	"go.opentelemetry.io/otel"
@@ -29,21 +31,26 @@ const (
 // Deprecated: Use stats handlers instead.
 type InterceptorFilter func(*InterceptorInfo) bool
 
+// MetricAttributesFn is a optional function which will be called per request returning a slice
+// of attribute.KeyValue to be appended to metric attributes recorded by the stats.Handler.
+type MetricAttributesFn func(ctx context.Context, payload any) []attribute.KeyValue
+
 // Filter is a predicate used to determine whether a given request in
 // should be instrumented by the attached RPC tag info.
 // A Filter must return true if the request should be instrumented.
 type Filter func(*stats.RPCTagInfo) bool
 
 // config is a group of options for this instrumentation.
 type config struct {
-	Filter            Filter
-	InterceptorFilter InterceptorFilter
-	Propagators       propagation.TextMapPropagator
-	TracerProvider    trace.TracerProvider
-	MeterProvider     metric.MeterProvider
-	SpanStartOptions  []trace.SpanStartOption
-	SpanAttributes    []attribute.KeyValue
-	MetricAttributes  []attribute.KeyValue
+	Filter             Filter
+	InterceptorFilter  InterceptorFilter
+	Propagators        propagation.TextMapPropagator
+	TracerProvider     trace.TracerProvider
+	MeterProvider      metric.MeterProvider
+	SpanStartOptions   []trace.SpanStartOption
+	SpanAttributes     []attribute.KeyValue
+	MetricAttributes   []attribute.KeyValue
+	MetricAttributesFn MetricAttributesFn
 
 	ReceivedEvent bool
 	SentEvent     bool
@@ -303,3 +310,18 @@ func (o metricAttributesOption) apply(c *config) {
 func WithMetricAttributes(a ...attribute.KeyValue) Option {
 	return metricAttributesOption{a: a}
 }
+
+type metricAttributesFnOption struct{ f MetricAttributesFn }
+
+func (o metricAttributesFnOption) apply(c *config) {
+	if o.f != nil {
+		c.MetricAttributesFn = o.f
+	}
+}
+
+// WithMetricAttributesFn returns an Option to set the MetricAttributesFn function which
+// will be called on each gRPC request to append metric attributes to recorded instruments
+// by the stats.Handler.
+func WithMetricAttributesFn(f MetricAttributesFn) Option {
+	return metricAttributesFnOption{f: f}
+}

instrumentation/google.golang.org/grpc/otelgrpc/internal/test/test_utils.go

@@ -36,11 +36,10 @@ import (
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/grpclog"
+	testpb "google.golang.org/grpc/interop/grpc_testing"
 	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/status"
 	"google.golang.org/protobuf/proto"
-
-	testpb "google.golang.org/grpc/interop/grpc_testing"
 )
 
 var (

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

@@ -152,6 +152,16 @@ func (c *config) handleRPC(ctx context.Context, rs stats.RPCStats, isServer bool
 	case *stats.InPayload:
 		if gctx != nil {
 			messageId = atomic.AddInt64(&gctx.inMessages, 1)
+
+			// If a MetricAttributesFn is defined call this function and update the gRPCContext with the metric attributes
+			// returned by ths function.
+			if f := c.MetricAttributesFn; f != nil {
+				attrs := f(ctx, rs.Payload)
+
+				gctx.metricAttrs = append(gctx.metricAttrs, attrs...)
+				metricAttrs = append(metricAttrs, attrs...)
+			}
+
 			c.rpcInBytes.Record(ctx, int64(rs.Length), metric.WithAttributeSet(attribute.NewSet(metricAttrs...)))
 		}