Allow setting per-request custom metrics in gRPC stats handler.

Similar to #5876 but for gRPC.

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"
@@ -36,14 +38,15 @@ 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 func(ctx context.Context, payload any) []attribute.KeyValue
 
 	ReceivedEvent bool
 	SentEvent     bool
@@ -285,3 +288,19 @@ func (o metricAttributesOption) apply(c *config) {
 func WithMetricAttributes(a ...attribute.KeyValue) Option {
 	return metricAttributesOption{a: a}
 }
+
+type metricAttributesFnOption struct {
+	f func(ctx context.Context, payload any) []attribute.KeyValue
+}
+
+func (o metricAttributesFnOption) apply(c *config) {
+	if o.f != nil {
+		c.MetricAttributesFn = o.f
+	}
+}
+
+// WithMetricAttributesFn returns an Option to add custom attributes to the metrics
+// based on the incoming request.
+func WithMetricAttributesFn(f func(ctx context.Context, payload any) []attribute.KeyValue) Option {
+	return metricAttributesFnOption{f: f}
+}

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

@@ -147,10 +147,19 @@ func (c *config) handleRPC(ctx context.Context, rs stats.RPCStats, isServer bool
 	}
 
 	switch rs := rs.(type) {
-	case *stats.Begin:
 	case *stats.InPayload:
 		if gctx != nil {
-			messageId = atomic.AddInt64(&gctx.messagesReceived, 1)
+			// Run this once on InPayload and record the attributes for the entire RPC.
+			if c.MetricAttributesFn != nil {
+				fnMetricAttrs := c.MetricAttributesFn(ctx, rs.Payload)
+
+				// Record them for the entire RPC.
+				gctx.metricAttrs = append(gctx.metricAttrs, fnMetricAttrs...)
+
+				// For this run we need to manually add them to the metricAttrs slice.
+				metricAttrs = append(metricAttrs, fnMetricAttrs...)
+			}
+
 			c.rpcRequestSize.Record(ctx, int64(rs.Length), metric.WithAttributeSet(attribute.NewSet(metricAttrs...)))
 		}
 
@@ -164,6 +173,7 @@ func (c *config) handleRPC(ctx context.Context, rs stats.RPCStats, isServer bool
 				),
 			)
 		}
+
 	case *stats.OutPayload:
 		if gctx != nil {
 			messageId = atomic.AddInt64(&gctx.messagesSent, 1)
@@ -180,11 +190,12 @@ func (c *config) handleRPC(ctx context.Context, rs stats.RPCStats, isServer bool
 				),
 			)
 		}
-	case *stats.OutTrailer:
+
 	case *stats.OutHeader:
 		if p, ok := peer.FromContext(ctx); ok {
 			span.SetAttributes(peerAttr(p.Addr.String())...)
 		}
+
 	case *stats.End:
 		var rpcStatusAttr attribute.KeyValue
 
@@ -216,6 +227,7 @@ func (c *config) handleRPC(ctx context.Context, rs stats.RPCStats, isServer bool
 			c.rpcRequestsPerRPC.Record(ctx, atomic.LoadInt64(&gctx.messagesReceived), recordOpts...)
 			c.rpcResponsesPerRPC.Record(ctx, atomic.LoadInt64(&gctx.messagesSent), recordOpts...)
 		}
+
 	default:
 		return
 	}