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group.go
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group.go
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// Package group provides a consumer group implementation.
package group
import (
"context"
"errors"
"fmt"
"github.com/Shopify/sarama"
"github.com/beatlabs/patron/component/async"
"github.com/beatlabs/patron/component/async/kafka"
"github.com/beatlabs/patron/internal/validation"
"github.com/beatlabs/patron/log"
opentracing "github.com/opentracing/opentracing-go"
)
// Factory definition of a consumer factory.
type Factory struct {
name string
group string
topics []string
brokers []string
oo []kafka.OptionFunc
}
// New constructor.
func New(name, group string, topics, brokers []string, oo ...kafka.OptionFunc) (*Factory, error) {
if name == "" {
return nil, errors.New("name is required")
}
if group == "" {
return nil, errors.New("group is required")
}
if validation.IsStringSliceEmpty(brokers) {
return nil, errors.New("brokers are empty or have an empty value")
}
if validation.IsStringSliceEmpty(topics) {
return nil, errors.New("topics are empty or have an empty value")
}
return &Factory{name: name, group: group, topics: topics, brokers: brokers, oo: oo}, nil
}
func (c *consumer) OutOfOrder() bool {
return false
}
// Create a new consumer.
func (f *Factory) Create() (async.Consumer, error) {
config, err := kafka.DefaultSaramaConfig(f.name)
if err != nil {
return nil, err
}
cc := kafka.ConsumerConfig{
Brokers: f.brokers,
Buffer: config.ChannelBufferSize,
SaramaConfig: config,
}
c := &consumer{
topics: f.topics,
group: f.group,
traceTag: opentracing.Tag{Key: "group", Value: f.group},
config: cc,
}
for _, o := range f.oo {
err = o(&c.config)
if err != nil {
return nil, fmt.Errorf("could not apply OptionFunc to consumer : %w", err)
}
}
return c, nil
}
// consumer members can be injected or overwritten with the usage of OptionFunc arguments.
type consumer struct {
topics []string
group string
traceTag opentracing.Tag
cnl context.CancelFunc
cg sarama.ConsumerGroup
config kafka.ConsumerConfig
}
// Close handles closing consumer.
func (c *consumer) Close() error {
if c.cnl != nil {
c.cnl()
}
if c.cg != nil {
err := c.cg.Close()
if err != nil {
return fmt.Errorf("failed to close consumer: %w", err)
}
}
return nil
}
// Consume starts consuming messages from a Kafka topic.
func (c *consumer) Consume(ctx context.Context) (<-chan async.Message, <-chan error, error) {
ctx, cnl := context.WithCancel(ctx)
c.cnl = cnl
cg, err := sarama.NewConsumerGroup(c.config.Brokers, c.group, c.config.SaramaConfig)
if err != nil {
return nil, nil, fmt.Errorf("failed to create consumer: %w", err)
}
c.cg = cg
log.Infof("consuming messages from topics '%#v' using group '%s'", c.topics, c.group)
chMsg := make(chan async.Message, c.config.Buffer)
chErr := make(chan error, c.config.Buffer)
go func() {
for {
select {
case <-ctx.Done():
log.Info("canceling consuming messages requested")
closeConsumer(c.cg)
return
case consumerError := <-c.cg.Errors():
chErr <- consumerError
closeConsumer(c.cg)
return
}
}
}()
// Iterate over consumer sessions.
go func() {
hnd := handler{consumer: c, messages: chMsg}
for {
err := c.cg.Consume(ctx, c.topics, hnd)
if err != nil {
chErr <- err
}
}
}()
return chMsg, chErr, nil
}
func closeConsumer(cns sarama.ConsumerGroup) {
if cns == nil {
return
}
err := cns.Close()
if err != nil {
log.Errorf("failed to close consumer group: %v", err)
}
}
type handler struct {
consumer *consumer
messages chan async.Message
}
func (h handler) Setup(_ sarama.ConsumerGroupSession) error { return nil }
func (h handler) Cleanup(_ sarama.ConsumerGroupSession) error { return nil }
func (h handler) ConsumeClaim(sess sarama.ConsumerGroupSession, claim sarama.ConsumerGroupClaim) error {
ctx := sess.Context()
for msg := range claim.Messages() {
kafka.TopicPartitionOffsetDiffGaugeSet(h.consumer.group, msg.Topic, msg.Partition, claim.HighWaterMarkOffset(), msg.Offset)
kafka.MessageStatusCountInc(kafka.MessageReceived, h.consumer.group, msg.Topic)
m, err := kafka.ClaimMessage(ctx, msg, h.consumer.config.DecoderFunc, sess)
if err != nil {
kafka.MessageStatusCountInc(kafka.MessageClaimErrors, h.consumer.group, msg.Topic)
return err
}
kafka.MessageStatusCountInc(kafka.MessageDecoded, h.consumer.group, msg.Topic)
h.messages <- m
}
return nil
}