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// Copyright 2018 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_test
import (
"fmt"
"log"
"time"
"cloud.google.com/go/pubsub/apiv1"
"golang.org/x/net/context"
pubsubpb "google.golang.org/genproto/googleapis/pubsub/v1"
)
func ExampleSubscriberClient_Pull_lengthyClientProcessing() {
projectID := "some-project"
subscriptionID := "some-subscription"
ctx := context.Background()
client, err := pubsub.NewSubscriberClient(ctx)
if err != nil {
log.Fatal(err)
}
defer client.Close()
sub := fmt.Sprintf("projects/%s/subscriptions/%s", projectID, subscriptionID)
// Be sure to tune the MaxMessages parameter per your project's needs, and accordingly
// adjust the ack behavior below to batch acknowledgements.
req := pubsubpb.PullRequest{
Subscription: sub,
MaxMessages: 1,
}
fmt.Println("Listening..")
for {
res, err := client.Pull(ctx, &req)
if err != nil {
log.Fatal(err)
}
// client.Pull returns an empty list if there are no messages available in the
// backlog. We should skip processing steps when that happens.
if len(res.ReceivedMessages) == 0 {
continue
}
var recvdAckIDs []string
for _, m := range res.ReceivedMessages {
recvdAckIDs = append(recvdAckIDs, m.AckId)
}
var done = make(chan struct{})
var delay = 0 * time.Second // Tick immediately upon reception
var ackDeadline = 10 * time.Second
// Continuously notify the server that processing is still happening on this batch.
go func() {
for {
select {
case <-ctx.Done():
return
case <-done:
return
case <-time.After(delay):
err := client.ModifyAckDeadline(ctx, &pubsubpb.ModifyAckDeadlineRequest{
Subscription: sub,
AckIds: recvdAckIDs,
AckDeadlineSeconds: int32(ackDeadline.Seconds()),
})
if err != nil {
log.Fatal(err)
}
delay = ackDeadline - 5*time.Second // 5 seconds grace period.
}
}
}()
for _, m := range res.ReceivedMessages {
// Process the message here, possibly in a goroutine.
log.Printf("Got message: %s", string(m.Message.Data))
err := client.Acknowledge(ctx, &pubsubpb.AcknowledgeRequest{
Subscription: sub,
AckIds: []string{m.AckId},
})
if err != nil {
log.Fatal(err)
}
}
close(done)
}
}
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