add message metadata support

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

drpc.go

@@ -2,7 +2,6 @@
 package drpc // import "go.unistack.org/micro-client-drpc/v3"
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"net"
@@ -615,6 +614,8 @@ func (c *drpcClient) Publish(ctx context.Context, msg client.Message, opts ...cl
 }
 
 func (c *drpcClient) publish(ctx context.Context, ps []client.Message, opts ...client.PublishOption) error {
+	var body []byte
+
 	options := client.NewPublishOptions(opts...)
 
 	// get proxy
@@ -633,24 +634,22 @@ func (c *drpcClient) publish(ctx context.Context, ps []client.Message, opts ...c
 	for _, p := range ps {
 		md := metadata.Copy(omd)
 		md[metadata.HeaderContentType] = p.ContentType()
-		md[metadata.HeaderTopic] = p.Topic()
-
-		cf, err := c.newCodec(p.ContentType())
-		if err != nil {
-			return errors.InternalServerError("go.micro.client", err.Error())
-		}
-
-		var body []byte
 
 		// passed in raw data
 		if d, ok := p.Payload().(*codec.Frame); ok {
 			body = d.Data
 		} else {
-			b := bytes.NewBuffer(nil)
-			if err := cf.Write(b, &codec.Message{Type: codec.Event}, p.Payload()); err != nil {
+			// use codec for payload
+			cf, err := c.newCodec(p.ContentType())
+			if err != nil {
 				return errors.InternalServerError("go.micro.client", err.Error())
 			}
-			body = b.Bytes()
+			// set the body
+			b, err := cf.Marshal(p.Payload())
+			if err != nil {
+				return errors.InternalServerError("go.micro.client", err.Error())
+			}
+			body = b
 		}
 
 		topic := p.Topic()
@@ -658,6 +657,9 @@ func (c *drpcClient) publish(ctx context.Context, ps []client.Message, opts ...c
 			topic = exchange
 		}
 
+		for k, v := range p.Metadata() {
+			md.Set(k, v)
+		}
 		md.Set(metadata.HeaderTopic, topic)
 		msgs = append(msgs, &broker.Message{Header: md, Body: body})
 	}