metadata: add default headers

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

broker/broker.go

@@ -112,6 +112,13 @@ type Message struct {
 	Body RawMessage
 }
 
+// NewMessage create broker message with topic filled
+func NewMessage(topic string) *Message {
+	m := &Message{Header: metadata.New(2)}
+	m.Header.Set(metadata.HeaderTopic, topic)
+	return m
+}
+
 // Subscriber is a convenience return type for the Subscribe method
 type Subscriber interface {
 	// Options returns subscriber options

broker/memory.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/google/uuid"
 	"github.com/unistack-org/micro/v3/logger"
+	"github.com/unistack-org/micro/v3/metadata"
 	maddr "github.com/unistack-org/micro/v3/util/addr"
 	mnet "github.com/unistack-org/micro/v3/util/net"
 	"github.com/unistack-org/micro/v3/util/rand"
@@ -113,14 +114,14 @@ func (m *memoryBroker) BatchPublish(ctx context.Context, msgs []*Message, opts .
 	if m.opts.Codec == nil {
 		m.RLock()
 		for _, msg := range msgs {
-			topic, _ := msg.Header.Get("Micro-Topic")
+			topic, _ := msg.Header.Get(metadata.HeaderTopic)
 			vs = append(vs, msgWrapper{topic: topic, body: m})
 		}
 		m.RUnlock()
 	} else {
 		m.RLock()
 		for _, msg := range msgs {
-			topic, _ := msg.Header.Get("Micro-Topic")
+			topic, _ := msg.Header.Get(metadata.HeaderTopic)
 			buf, err := m.opts.Codec.Marshal(msg)
 			if err != nil {
 				m.RUnlock()

broker/memory_test.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 	"testing"
+
+	"github.com/unistack-org/micro/v3/metadata"
 )
 
 func TestMemoryBatchBroker(t *testing.T) {
@@ -30,9 +32,9 @@ func TestMemoryBatchBroker(t *testing.T) {
 	for i := 0; i < count; i++ {
 		message := &Message{
 			Header: map[string]string{
-				"Micro-Topic": topic,
-				"foo":         "bar",
-				"id":          fmt.Sprintf("%d", i),
+				metadata.HeaderTopic: topic,
+				"foo":                "bar",
+				"id":                 fmt.Sprintf("%d", i),
 			},
 			Body: []byte(`"hello world"`),
 		}
@@ -75,9 +77,9 @@ func TestMemoryBroker(t *testing.T) {
 	for i := 0; i < count; i++ {
 		message := &Message{
 			Header: map[string]string{
-				"Micro-Topic": topic,
-				"foo":         "bar",
-				"id":          fmt.Sprintf("%d", i),
+				metadata.HeaderTopic: topic,
+				"foo":                "bar",
+				"id":                 fmt.Sprintf("%d", i),
 			},
 			Body: []byte(`"hello world"`),
 		}