consumer/consumer.go

package consumer

import (
	"context"
	"fmt"
	"sync"
	"sync/atomic"
	"time"

	"git.loafle.net/commons/logging-go"
	oek "git.loafle.net/overflow/external-go/kafka"
	"github.com/segmentio/kafka-go"
)

type Consumer struct {
	ConsumerHandler ConsumerHandler

	ctx      ConsumerCtx
	stopChan chan struct{}
	stopWg   sync.WaitGroup
}

func (c *Consumer) Start() error {
	if c.stopChan != nil {
		return fmt.Errorf("%s already running. Stop it before starting it again", c.logHeader())
	}

	if nil == c.ConsumerHandler {
		return fmt.Errorf("%s ConsumerHandler must be specified", c.logHeader())
	}
	if err := c.ConsumerHandler.Validate(); nil != err {
		return fmt.Errorf("%s validate error %v", c.logHeader(), err)
	}

	c.ctx = c.ConsumerHandler.ConsumerCtx()
	if nil == c.ctx {
		return fmt.Errorf("%s ConsumerCtx is nil", c.logHeader())
	}

	if err := c.ConsumerHandler.Init(c.ctx); nil != err {
		return fmt.Errorf("%s Init error %v", c.logHeader(), err)
	}

	c.stopChan = make(chan struct{})

	c.stopWg.Add(1)
	go c.handleConsumer()

	return nil
}

func (c *Consumer) Stop(ctx context.Context) error {
	if c.stopChan == nil {
		return fmt.Errorf("%s must be started before stopping it", c.logHeader())
	}
	close(c.stopChan)
	c.stopWg.Wait()

	c.ConsumerHandler.Destroy(c.ctx)

	c.stopChan = nil

	return nil
}

func (c *Consumer) logHeader() string {
	return fmt.Sprintf("Consumer[%s]:", c.ConsumerHandler.GetName())
}

func (c *Consumer) handleConsumer() {
	defer func() {
		c.ConsumerHandler.OnStop(c.ctx)
		logging.Logger().Infof("%s Stopped", c.logHeader())
		c.stopWg.Done()
	}()

	if err := c.ConsumerHandler.OnStart(c.ctx); nil != err {
		logging.Logger().Error(err)
		return
	}

	stopChan := make(chan struct{})
	receiveDoneChan := make(chan error)

	go c.handleReceive(stopChan, receiveDoneChan)

	logging.Logger().Infof("%s Started", c.logHeader())

	select {
	case <-receiveDoneChan:
		close(stopChan)
	case <-c.stopChan:
		close(stopChan)
		<-receiveDoneChan
	}
}

func (c *Consumer) handleReceive(stopChan <-chan struct{}, doneChan chan<- error) {
	var (
		m        kafka.Message
		stopping atomic.Value
		err      error
	)

	defer func() {
		doneChan <- err
	}()

	reader := oek.Reader(c.ConsumerHandler.GetConsumerName())
	if nil == reader {
		err = fmt.Errorf("%s Reader[%s] is not valid", c.logHeader(), c.ConsumerHandler.GetConsumerName())
		return
	}

	for {
		readChan := make(chan struct{})
		go func() {
			m, err = reader.ReadMessage(context.Background())
			if err != nil {
				if nil == stopping.Load() {
					logging.Logger().Errorf("%s %v", c.logHeader(), err)
				}
			}

			close(readChan)
		}()

		select {
		case <-c.stopChan:
			stopping.Store(true)
			return
		case <-readChan:
		}

		if nil != err {
			select {
			case <-c.stopChan:
				return
			case <-time.After(time.Second):
			}
			continue
		}

		fmt.Printf("message at topic/partition/offset %v/%v/%v: %s = %s\n", m.Topic, m.Partition, m.Offset, string(m.Key), string(m.Value))
	}

}