add opentracing spans for metrics

vendor/github.com/Shopify/sarama/metadata_request.go

@@ -0,0 +1,52 @@
+package sarama
+
+type MetadataRequest struct {
+	Topics []string
+}
+
+func (r *MetadataRequest) encode(pe packetEncoder) error {
+	err := pe.putArrayLength(len(r.Topics))
+	if err != nil {
+		return err
+	}
+
+	for i := range r.Topics {
+		err = pe.putString(r.Topics[i])
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (r *MetadataRequest) decode(pd packetDecoder, version int16) error {
+	topicCount, err := pd.getArrayLength()
+	if err != nil {
+		return err
+	}
+	if topicCount == 0 {
+		return nil
+	}
+
+	r.Topics = make([]string, topicCount)
+	for i := range r.Topics {
+		topic, err := pd.getString()
+		if err != nil {
+			return err
+		}
+		r.Topics[i] = topic
+	}
+	return nil
+}
+
+func (r *MetadataRequest) key() int16 {
+	return 3
+}
+
+func (r *MetadataRequest) version() int16 {
+	return 0
+}
+
+func (r *MetadataRequest) requiredVersion() KafkaVersion {
+	return minVersion
+}