fix: error handling on reporting kafka broker stats (#18)

Author: siddhanta-rath

publisher/kafka.go

@@ -113,9 +113,16 @@ func (pr *Kafka) ReportStats() {
 		switch e := v.(type) {
 		case *kafka.Stats:
 			var stats map[string]interface{}
-			json.Unmarshal([]byte(e.String()), &stats)
-
-			brokers := stats["brokers"].(map[string]interface{})
+			if err := json.Unmarshal([]byte(e.String()), &stats); err != nil {
+				logger.Errorf("failed to unmarshal kafka stats: %v", err)
+				continue
+			}
+			brokersRawJson, ok := stats["brokers"]
+			if !ok || brokersRawJson == nil {
+				logger.Errorf("kafka broker stats missing or null brokers field")
+				continue
+			}
+			brokers := brokersRawJson.(map[string]interface{})
 			metrics.Gauge("kafka_tx_messages_total", stats["txmsgs"], "")
 			metrics.Gauge("kafka_tx_messages_bytes_total", stats["txmsg_bytes"], "")
 			for _, broker := range brokers {