improve tracing

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

carrier.go

@@ -2,6 +2,7 @@ package kgo
 
 import (
 	"github.com/twmb/franz-go/pkg/kgo"
+	"go.unistack.org/micro/v3/metadata"
 )
 
 // RecordCarrier injects and extracts traces from a kgo.Record.
@@ -51,3 +52,25 @@ func (c RecordCarrier) Keys() []string {
 	}
 	return out
 }
+
+func setHeaders(r *kgo.Record, md metadata.Metadata) {
+	seen := make(map[string]struct{})
+loop:
+	for k, v := range md {
+		for i := 0; i < len(r.Headers); i++ {
+			if r.Headers[i].Key == k {
+				// Key exist, update the value.
+				r.Headers[i].Value = []byte(v)
+				continue loop
+			} else if _, ok := seen[k]; ok {
+				continue loop
+			}
+			// Key does not exist, append new header.
+			r.Headers = append(r.Headers, kgo.RecordHeader{
+				Key:   k,
+				Value: []byte(v),
+			})
+			seen[k] = struct{}{}
+		}
+	}
+}

kgo.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"math/rand"
+	"net/http"
 	"strings"
 	"sync"
 	"time"
@@ -275,7 +276,7 @@ func (k *Broker) publish(ctx context.Context, msgs []*broker.Message, opts ...br
 		if options.BodyOnly || k.opts.Codec.String() == "noop" {
 			rec.Value = msg.Body
 			for k, v := range msg.Header {
-				rec.Headers = append(rec.Headers, kgo.RecordHeader{Key: k, Value: []byte(v)})
+				rec.Headers = append(rec.Headers, kgo.RecordHeader{Key: http.CanonicalHeaderKey(k), Value: []byte(v)})
 			}
 		} else {
 			rec.Value, err = k.opts.Codec.Marshal(msg)

tracer.go

@@ -58,15 +58,15 @@ func (m *hookTracer) OnProduceRecordBuffered(r *kgo.Record) {
 		md.Set(h.Key, string(h.Value))
 	}
 
-	// Inject the span context into the record.
-	// t.propagators.Inject(ctx, NewRecordCarrier(r))
-	// Update the record context.
-
 	if !ok {
 		r.Context, _ = m.tracer.Start(metadata.NewOutgoingContext(r.Context, md), r.Topic+" publish", opts...)
 	} else {
 		r.Context, _ = m.tracer.Start(r.Context, r.Topic+" publish", opts...)
 	}
+
+	md, _ = metadata.FromOutgoingContext(r.Context)
+
+	setHeaders(r, md)
 }
 
 // OnProduceRecordUnbuffered continues and ends the "publish" span for an
@@ -75,7 +75,7 @@ func (m *hookTracer) OnProduceRecordBuffered(r *kgo.Record) {
 // It sets attributes with values unset when producing and records any error
 // that occurred during the publish operation.
 func (m *hookTracer) OnProduceRecordUnbuffered(r *kgo.Record, err error) {
-	span, _ := tracer.SpanFromContext(r.Context)
+	if span, ok := tracer.SpanFromContext(r.Context); ok {
 		span.AddLabels(
 			semconv.MessagingKafkaDestinationPartition(int(r.Partition)),
 		)
@@ -84,6 +84,7 @@ func (m *hookTracer) OnProduceRecordUnbuffered(r *kgo.Record, err error) {
 		}
 		span.Finish()
 	}
+}
 
 // OnFetchRecordBuffered starts a new span for the "receive" operation on a
 // buffered record.
@@ -124,16 +125,15 @@ func (m *hookTracer) OnFetchRecordBuffered(r *kgo.Record) {
 		md.Set(h.Key, string(h.Value))
 	}
 
-	// Extract the span context from the record.
-	// ctx := t.propagators.Extract(r.Context, NewRecordCarrier(r))
-	// Start the "receive" span.
 	if !ok {
 		r.Context, _ = m.tracer.Start(metadata.NewIncomingContext(r.Context, md), r.Topic+" receive", opts...)
 	} else {
 		r.Context, _ = m.tracer.Start(r.Context, r.Topic+" receive", opts...)
 	}
 
-	// Update the record context.
+	md, _ = metadata.FromIncomingContext(r.Context)
+
+	setHeaders(r, md)
 }
 
 // OnFetchRecordUnbuffered continues and ends the "receive" span for an