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pubsub.go
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pubsub.go
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// Copyright 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package pubsub
import (
"context"
"log"
"os"
"os/signal"
"syscall"
"time"
"cloud.google.com/go/pubsub"
"github.com/datacommonsorg/mixer/internal/util"
)
// Subscribe does the following:
// 1) Create a subscriber within the instance.
// 2) Start a receiver in a goroutine.
// 3) Have a goroutine to delete the subscriber on server shutdown.
//
// TODO(shifucun): Add unittest.
func Subscribe(
ctx context.Context,
project string,
prefix string,
topic string,
worker func(ctx context.Context, msg *pubsub.Message) error,
) error {
// Create pubsub client.
client, err := pubsub.NewClient(ctx, project)
if err != nil {
return err
}
// Always create a new subscriber with default expiration date of 2 days.
subID := prefix + util.RandomString()
expiration, _ := time.ParseDuration("36h")
retention, _ := time.ParseDuration("24h")
subscriber, err := client.CreateSubscription(ctx, subID,
pubsub.SubscriptionConfig{
Topic: client.Topic(topic),
ExpirationPolicy: expiration,
RetentionDuration: retention,
})
if err != nil {
return err
}
log.Printf("Created subscriber with id: %s\n", subID)
// Start the receiver in a goroutine.
go func() {
err = subscriber.Receive(
ctx,
func(ctx context.Context, msg *pubsub.Message) {
msg.Ack()
err = worker(ctx, msg)
if err != nil {
log.Printf("Subscriber can not complete task: %v", err)
}
})
if err != nil {
log.Printf("Cloud pubsub receive: %v", err)
}
}()
// Create a go routine to check server shutdown and delete the subscriber.
c := make(chan os.Signal, 1)
signal.Notify(c, syscall.SIGINT, syscall.SIGTERM)
go func() {
<-c
err := subscriber.Delete(ctx)
if err != nil {
log.Fatalf("Failed to delete subscriber: %v", err)
}
log.Printf("Deleted subscriber: %v", subscriber)
os.Exit(1)
}()
return nil
}