Add header suppor for Kafka broker plugin; (#2470)

plugins/broker/kafka/options.go

@@ -80,6 +80,21 @@ func (h *consumerGroupHandler) ConsumeClaim(sess sarama.ConsumerGroupSession, cl
 			continue
 		}
 
+		if p.m.Body == nil {
+			p.m.Body = msg.Value
+		}
+		// if we don't have headers, create empty map
+		if m.Header == nil {
+			m.Header = make(map[string]string)
+		}
+		for _, header := range msg.Headers {
+			m.Header[string(header.Key)] = string(header.Value)
+		}
+		m.Header["Micro-Topic"] = msg.Topic // only for RPC server, it somehow inspect Header for topic
+		if _, ok := m.Header["Content-Type"]; !ok {
+			m.Header["Content-Type"] = "application/json" // default to json codec
+		}
+
 		err := h.handler(p)
 		if err == nil && h.subopts.AutoAck {
 			sess.MarkMessage(msg, "")