docs: add deadletter topic example (#48)

examples/docker-compose.yml

@@ -41,6 +41,7 @@ services:
                          cub kafka-ready -b kafka:9092 1 20 && \
                          kafka-topics --create --topic standart-topic --if-not-exists --zookeeper zookeeper:2181 --partitions 1 --replication-factor 1 && \
                          kafka-topics --create --topic retry-topic --if-not-exists --zookeeper zookeeper:2181 --partitions 1 --replication-factor 1 && \
+                         kafka-topics --create --topic error-topic --if-not-exists --zookeeper zookeeper:2181 --partitions 1 --replication-factor 1 && \
                          sleep infinity'"
     environment:
       KAFKA_BROKER_ID: ignored

examples/with-deadletter/main.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"github.com/Trendyol/kafka-konsumer"
+	"os"
+	"os/signal"
+	"time"
+)
+
+const (
+	topicName           = "standart-topic"
+	retryTopicName      = "retry-topic"
+	deadLetterTopicName = "error-topic"
+)
+
+func main() {
+	producer, _ := kafka.NewProducer(kafka.ProducerConfig{
+		Writer: kafka.WriterConfig{
+			Brokers: []string{"localhost:29092"},
+		},
+	})
+
+	_ = producer.Produce(context.Background(), kafka.Message{
+		Topic: topicName,
+		Key:   []byte("1"),
+		Value: []byte(`{ "foo": "bar" }`),
+	})
+
+	consumerCfg := &kafka.ConsumerConfig{
+		Concurrency: 1,
+		Reader: kafka.ReaderConfig{
+			Brokers: []string{"localhost:29092"},
+			Topic:   topicName,
+			GroupID: "konsumer.group.test",
+		},
+		RetryEnabled: true,
+		RetryConfiguration: kafka.RetryConfiguration{
+			DeadLetterTopic: deadLetterTopicName,
+			Brokers:         []string{"localhost:29092"},
+			Topic:           retryTopicName,
+			StartTimeCron:   "*/1 * * * *",
+			WorkDuration:    50 * time.Second,
+			MaxRetry:        1,
+		},
+		ConsumeFn: consumeFn,
+	}
+
+	consumer, _ := kafka.NewConsumer(consumerCfg)
+	defer consumer.Stop()
+
+	consumer.Consume()
+
+	fmt.Println("Consumer started...!")
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt)
+	<-c
+}
+
+func consumeFn(message kafka.Message) error {
+	fmt.Printf("Message From %s with value %s", message.Topic, string(message.Value))
+	// returns error to be sent to dead-letter topic
+	return errors.New("consumer error")
+}