/
consumer.go
84 lines (67 loc) · 2.31 KB
/
consumer.go
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package event
import (
"context"
"github.com/ONSdigital/dp-image-importer/schema"
kafka "github.com/ONSdigital/dp-kafka/v2"
"github.com/ONSdigital/log.go/v2/log"
)
//go:generate moq -out mock/handler.go -pkg mock . Handler
// Handler represents a handler for processing a single event.
type Handler interface {
Handle(ctx context.Context, ImageUploaded *ImageUploaded) error
}
// Consume converts messages to event instances, and pass the event to the provided handler.
func Consume(ctx context.Context, cg kafka.IConsumerGroup, handler Handler, numWorkers int) {
// func to be executed by each worker in a goroutine
workerConsume := func(workerNum int) {
for {
select {
case message, ok := <-cg.Channels().Upstream:
logData := log.Data{"message_offset": message.Offset(), "worker_num": workerNum}
if !ok {
log.Info(ctx, "upstream channel closed - closing event consumer loop", logData)
return
}
err := processMessage(ctx, message, handler)
if err != nil {
log.Error(ctx, "failed to process message", err, logData)
}
log.Info(ctx, "message committed", logData)
message.Release()
log.Info(ctx, "message released", logData)
case <-cg.Channels().Closer:
log.Info(ctx, "closing event consumer loop because closer channel is closed", log.Data{"worker_num": workerNum})
return
}
}
}
// workers to consume messages in parallel
for w := 1; w <= numWorkers; w++ {
go workerConsume(w)
}
}
// processMessage unmarshals the provided kafka message into an event and calls the handler.
// After the message is successfully handled, it is committed.
func processMessage(ctx context.Context, message kafka.Message, handler Handler) error {
defer message.Commit()
logData := log.Data{"message_offset": message.Offset()}
event, err := unmarshal(message)
if err != nil {
log.Error(ctx, "failed to unmarshal event", err, logData)
return err
}
logData["event"] = event
log.Info(ctx, "event received", logData)
err = handler.Handle(ctx, event)
if err != nil {
log.Error(ctx, "failed to handle event", err)
return err
}
return nil
}
// unmarshal converts a event instance to []byte.
func unmarshal(message kafka.Message) (*ImageUploaded, error) {
var event ImageUploaded
err := schema.ImageUploadedEvent.Unmarshal(message.GetData(), &event)
return &event, err
}