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kafka.go
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kafka.go
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package pubsub
import (
"errors"
"log"
"github.com/NYTimes/gizmo/config"
"github.com/Shopify/sarama"
"github.com/golang/protobuf/proto"
)
var (
// KafkaRequiredAcks will be used in Kafka configs
// to set the 'RequiredAcks' value.
KafkaRequiredAcks = sarama.WaitForAll
)
// KafkaPublisher is an experimental publisher that provides an implementation for
// Kafka using the Shopify/sarama library.
type KafkaPublisher struct {
producer sarama.SyncProducer
topic string
}
// NewKafkaPublisher will initiate a new experimental Kafka publisher.
func NewKafkaPublisher(cfg *config.Kafka) (*KafkaPublisher, error) {
var err error
p := &KafkaPublisher{}
if len(cfg.Topic) == 0 {
return p, errors.New("topic name is required")
}
p.topic = cfg.Topic
sconfig := sarama.NewConfig()
sconfig.Producer.Retry.Max = cfg.MaxRetry
sconfig.Producer.RequiredAcks = KafkaRequiredAcks
p.producer, err = sarama.NewSyncProducer(cfg.BrokerHosts, sconfig)
return p, err
}
// Publish will marshal the proto message and emit it to the Kafka topic.
func (p *KafkaPublisher) Publish(key string, m proto.Message) error {
mb, err := proto.Marshal(m)
if err != nil {
return err
}
return p.PublishRaw(key, mb)
}
// PublishRaw will emit the byte array to the Kafka topic.
func (p *KafkaPublisher) PublishRaw(key string, m []byte) error {
msg := &sarama.ProducerMessage{
Topic: p.topic,
Key: sarama.StringEncoder(key),
Value: sarama.ByteEncoder(m),
}
// TODO: do something with this partition/offset values
_, _, err := p.producer.SendMessage(msg)
return err
}
// Stop will close the pub connection.
func (p *KafkaPublisher) Stop() error {
return p.producer.Close()
}
type (
// KafkaSubscriber is an experimental subscriber implementation for Kafka. It is only capable of consuming a
// single partition so multiple may be required depending on your setup.
KafkaSubscriber struct {
cnsmr sarama.Consumer
topic string
partition int32
offset func() int64
broadcastOffset func(int64)
kerr error
stop chan chan error
}
// KafkaSubMessage is an SubscriberMessage implementation
// that will broadcast the message's offset when Done().
KafkaSubMessage struct {
message *sarama.ConsumerMessage
broadcastOffset func(int64)
}
)
// Message will return the message payload.
func (m *KafkaSubMessage) Message() []byte {
return m.message.Value
}
// Done will emit the message's offset.
func (m *KafkaSubMessage) Done() error {
m.broadcastOffset(m.message.Offset)
return nil
}
// NewKafkaSubscriber will initiate a the experimental Kafka consumer.
func NewKafkaSubscriber(cfg *config.Kafka, offsetProvider func() int64, offsetBroadcast func(int64)) (*KafkaSubscriber, error) {
var (
err error
)
s := &KafkaSubscriber{
offset: offsetProvider,
broadcastOffset: offsetBroadcast,
partition: cfg.Partition,
stop: make(chan chan error, 1),
}
if len(cfg.BrokerHosts) == 0 {
return s, errors.New("at least 1 broker host is required")
}
if len(cfg.Topic) == 0 {
return s, errors.New("topic name is required")
}
s.topic = cfg.Topic
sconfig := sarama.NewConfig()
sconfig.Consumer.Return.Errors = true
s.cnsmr, err = sarama.NewConsumer(cfg.BrokerHosts, sconfig)
return s, err
}
// Start will start consuming message on the Kafka topic
// partition and emit any messages to the returned channel.
// On start up, it will call the offset func provider to the subscriber
// to lookup the offset to start at.
// If it encounters any issues, it will populate the Err() error
// and close the returned channel.
func (s *KafkaSubscriber) Start() <-chan SubscriberMessage {
output := make(chan SubscriberMessage)
pCnsmr, err := s.cnsmr.ConsumePartition(s.topic, s.partition, s.offset())
if err != nil {
// TODO: what should we do here?
log.Print("unable to create partition consumer: ", err)
close(output)
return output
}
go func(s *KafkaSubscriber, c sarama.PartitionConsumer, output chan SubscriberMessage) {
defer close(output)
var msg *sarama.ConsumerMessage
errs := c.Errors()
msgs := c.Messages()
for {
select {
case exit := <-s.stop:
exit <- c.Close()
return
case kerr := <-errs:
s.kerr = kerr
return
case msg = <-msgs:
output <- &KafkaSubMessage{
message: msg,
broadcastOffset: s.broadcastOffset,
}
}
}
}(s, pCnsmr, output)
return output
}
// Stop willablock until the consumer has stopped consuming messages
// and return any errors seen on consumer close.
func (s *KafkaSubscriber) Stop() error {
exit := make(chan error)
s.stop <- exit
// close result from the partition consumer
err := <-exit
if err != nil {
return err
}
return s.cnsmr.Close()
}
// Err will contain any errors that occurred during
// consumption. This method should be checked after
// a user encounters a closed channel.
func (s *KafkaSubscriber) Err() error {
return s.kerr
}
// GetKafkaPartitions is a helper function to look up which partitions are available
// via the given brokers for the given topic. This should be called only on startup.
func GetKafkaPartitions(brokerHosts []string, topic string) (partitions []int32, err error) {
if len(brokerHosts) == 0 {
return partitions, errors.New("at least 1 broker host is required")
}
if len(topic) == 0 {
return partitions, errors.New("topic name is required")
}
var cnsmr sarama.Consumer
cnsmr, err = sarama.NewConsumer(brokerHosts, sarama.NewConfig())
if err != nil {
return partitions, err
}
defer func() {
if cerr := cnsmr.Close(); cerr != nil && err == nil {
err = cerr
}
}()
return cnsmr.Partitions(topic)
}