fixup md

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

grpc.go

@@ -718,6 +718,10 @@ func (g *grpcClient) publish(ctx context.Context, ps []client.Message, opts ...c
 	if v, ok := os.LookupEnv("MICRO_PROXY"); ok {
 		exchange = v
 	}
+	// get the exchange
+	if len(options.Exchange) > 0 {
+		exchange = options.Exchange
+	}
 
 	msgs := make([]*broker.Message, 0, len(ps))
 
@@ -729,7 +733,11 @@ func (g *grpcClient) publish(ctx context.Context, ps []client.Message, opts ...c
 	for _, p := range ps {
 		md := metadata.Copy(omd)
 		md[metadata.HeaderContentType] = p.ContentType()
-
+		topic := p.Topic()
+		if len(exchange) > 0 {
+			topic = exchange
+		}
+		md.Set(metadata.HeaderTopic, topic)
 		iter := p.Metadata().Iterator()
 		var k, v string
 		for iter.Next(&k, &v) {
@@ -753,15 +761,6 @@ func (g *grpcClient) publish(ctx context.Context, ps []client.Message, opts ...c
 			body = b
 		}
 
-		topic := p.Topic()
-		if len(exchange) > 0 {
-			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})
 	}