/
example_test.go
335 lines (308 loc) · 10.8 KB
/
example_test.go
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// Copyright 2020 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
package pscompat_test
import (
"context"
"fmt"
"sync"
"time"
"cloud.google.com/go/pubsub"
"cloud.google.com/go/pubsublite/pscompat"
"golang.org/x/sync/errgroup"
"golang.org/x/xerrors"
)
func ExamplePublisherClient_Publish() {
ctx := context.Background()
const topic = "projects/my-project/locations/zone/topics/my-topic"
publisher, err := pscompat.NewPublisherClient(ctx, topic)
if err != nil {
// TODO: Handle error.
}
defer publisher.Stop()
var results []*pubsub.PublishResult
r := publisher.Publish(ctx, &pubsub.Message{
Data: []byte("hello world"),
})
results = append(results, r)
// Publish more messages ...
var publishFailed bool
for _, r := range results {
id, err := r.Get(ctx)
if err != nil {
// TODO: Handle error.
publishFailed = true
continue
}
fmt.Printf("Published a message with a message ID: %s\n", id)
}
// NOTE: A failed PublishResult indicates that the publisher client
// encountered a fatal error and has permanently terminated. After the fatal
// error has been resolved, a new publisher client instance must be created to
// republish failed messages.
if publishFailed {
fmt.Printf("Publisher client terminated due to error: %v\n", publisher.Error())
}
}
// This example illustrates how to set batching settings for publishing. Note
// that batching settings apply per partition. If BufferedByteLimit is being
// used to bound memory usage, keep in mind the number of partitions in the
// topic.
func ExamplePublisherClient_Publish_batchingSettings() {
ctx := context.Background()
const topic = "projects/my-project/locations/zone/topics/my-topic"
settings := pscompat.PublishSettings{
DelayThreshold: 50 * time.Millisecond,
CountThreshold: 200,
BufferedByteLimit: 5e8,
}
publisher, err := pscompat.NewPublisherClientWithSettings(ctx, topic, settings)
if err != nil {
// TODO: Handle error.
}
defer publisher.Stop()
var results []*pubsub.PublishResult
r := publisher.Publish(ctx, &pubsub.Message{
Data: []byte("hello world"),
})
results = append(results, r)
// Publish more messages ...
var publishFailed bool
for _, r := range results {
id, err := r.Get(ctx)
if err != nil {
// TODO: Handle error.
publishFailed = true
continue
}
fmt.Printf("Published a message with a message ID: %s\n", id)
}
// NOTE: A failed PublishResult indicates that the publisher client
// encountered a fatal error and has permanently terminated. After the fatal
// error has been resolved, a new publisher client instance must be created to
// republish failed messages.
if publishFailed {
fmt.Printf("Publisher client terminated due to error: %v\n", publisher.Error())
}
}
// This example illustrates how to handle various publishing errors. Some errors
// can be automatically handled (e.g. backend unavailable and buffer overflow),
// while others are fatal errors that should be inspected.
// If the application has a low tolerance to backend unavailability, set a lower
// PublishSettings.Timeout value to detect and alert.
func ExamplePublisherClient_Publish_errorHandling() {
ctx := context.Background()
const topic = "projects/my-project/locations/zone/topics/my-topic"
settings := pscompat.PublishSettings{
// The PublisherClient will terminate when it cannot connect to backends for
// more than 10 minutes.
Timeout: 10 * time.Minute,
// Sets a conservative publish buffer byte limit, per partition.
BufferedByteLimit: 1e8,
}
publisher, err := pscompat.NewPublisherClientWithSettings(ctx, topic, settings)
if err != nil {
// TODO: Handle error.
}
defer publisher.Stop()
var toRepublish []*pubsub.Message
var mu sync.Mutex
g := new(errgroup.Group)
for i := 0; i < 10; i++ {
msg := &pubsub.Message{
Data: []byte(fmt.Sprintf("message-%d", i)),
}
result := publisher.Publish(ctx, msg)
g.Go(func() error {
id, err := result.Get(ctx)
if err != nil {
// NOTE: A failed PublishResult indicates that the publisher client has
// permanently terminated. A new publisher client instance must be
// created to republish failed messages.
fmt.Printf("Publish error: %v\n", err)
// Oversized messages cannot be published.
if !xerrors.Is(err, pscompat.ErrOversizedMessage) {
mu.Lock()
toRepublish = append(toRepublish, msg)
mu.Unlock()
}
return err
}
fmt.Printf("Published a message with a message ID: %s\n", id)
return nil
})
}
if err := g.Wait(); err != nil {
fmt.Printf("Publisher client terminated due to error: %v\n", publisher.Error())
switch {
case xerrors.Is(publisher.Error(), pscompat.ErrBackendUnavailable):
// TODO: Create a new publisher client to republish failed messages.
case xerrors.Is(publisher.Error(), pscompat.ErrOverflow):
// TODO: Create a new publisher client to republish failed messages.
// Throttle publishing. Note that backend unavailability can also cause
// buffer overflow before the ErrBackendUnavailable error.
default:
// TODO: Inspect and handle fatal error.
}
}
}
func ExampleSubscriberClient_Receive() {
ctx := context.Background()
const subscription = "projects/my-project/locations/zone/subscriptions/my-subscription"
subscriber, err := pscompat.NewSubscriberClient(ctx, subscription)
if err != nil {
// TODO: Handle error.
}
cctx, cancel := context.WithCancel(ctx)
err = subscriber.Receive(cctx, func(ctx context.Context, m *pubsub.Message) {
// TODO: Handle message.
// NOTE: May be called concurrently; synchronize access to shared memory.
m.Ack()
})
if err != nil {
// TODO: Handle error.
}
// Call cancel from the receiver callback or another goroutine to stop
// receiving.
cancel()
}
// If the application has a low tolerance to backend unavailability, set a lower
// ReceiveSettings.Timeout value to detect and alert.
func ExampleSubscriberClient_Receive_errorHandling() {
ctx := context.Background()
const subscription = "projects/my-project/locations/zone/subscriptions/my-subscription"
settings := pscompat.ReceiveSettings{
// The SubscriberClient will terminate when it cannot connect to backends
// for more than 5 minutes.
Timeout: 5 * time.Minute,
}
subscriber, err := pscompat.NewSubscriberClientWithSettings(ctx, subscription, settings)
if err != nil {
// TODO: Handle error.
}
for {
cctx, cancel := context.WithCancel(ctx)
err = subscriber.Receive(cctx, func(ctx context.Context, m *pubsub.Message) {
// TODO: Handle message.
// NOTE: May be called concurrently; synchronize access to shared memory.
m.Ack()
})
if err != nil {
fmt.Printf("Subscriber client stopped receiving due to error: %v\n", err)
if xerrors.Is(err, pscompat.ErrBackendUnavailable) {
// TODO: Alert if necessary. Receive can be retried.
} else {
// TODO: Handle fatal error.
break
}
}
// Call cancel from the receiver callback or another goroutine to stop
// receiving.
cancel()
}
}
// This example shows how to throttle SubscriberClient.Receive, which aims for
// high throughput by default. By limiting the number of messages and/or bytes
// being processed at once, you can bound your program's resource consumption.
// Note that ReceiveSettings apply per partition, so keep in mind the number of
// partitions in the associated topic.
func ExampleSubscriberClient_Receive_maxOutstanding() {
ctx := context.Background()
const subscription = "projects/my-project/locations/zone/subscriptions/my-subscription"
settings := pscompat.ReceiveSettings{
MaxOutstandingMessages: 5,
MaxOutstandingBytes: 10e6,
}
subscriber, err := pscompat.NewSubscriberClientWithSettings(ctx, subscription, settings)
if err != nil {
// TODO: Handle error.
}
cctx, cancel := context.WithCancel(ctx)
err = subscriber.Receive(cctx, func(ctx context.Context, m *pubsub.Message) {
// TODO: Handle message.
// NOTE: May be called concurrently; synchronize access to shared memory.
m.Ack()
})
if err != nil {
// TODO: Handle error.
}
// Call cancel from the receiver callback or another goroutine to stop
// receiving.
cancel()
}
// This example shows how to manually assign which topic partitions a
// SubscriberClient should connect to. If not specified, the SubscriberClient
// will use Pub/Sub Lite's partition assignment service to automatically
// determine which partitions it should connect to.
func ExampleSubscriberClient_Receive_manualPartitionAssignment() {
ctx := context.Background()
const subscription = "projects/my-project/locations/zone/subscriptions/my-subscription"
settings := pscompat.ReceiveSettings{
// NOTE: The corresponding topic must have 2 or more partitions.
Partitions: []int{0, 1},
}
subscriber, err := pscompat.NewSubscriberClientWithSettings(ctx, subscription, settings)
if err != nil {
// TODO: Handle error.
}
cctx, cancel := context.WithCancel(ctx)
err = subscriber.Receive(cctx, func(ctx context.Context, m *pubsub.Message) {
// TODO: Handle message.
// NOTE: May be called concurrently; synchronize access to shared memory.
m.Ack()
})
if err != nil {
// TODO: Handle error.
}
// Call cancel from the receiver callback or another goroutine to stop
// receiving.
cancel()
}
func ExampleParseMessageMetadata_publisher() {
ctx := context.Background()
const topic = "projects/my-project/locations/zone/topics/my-topic"
publisher, err := pscompat.NewPublisherClient(ctx, topic)
if err != nil {
// TODO: Handle error.
}
defer publisher.Stop()
result := publisher.Publish(ctx, &pubsub.Message{Data: []byte("payload")})
id, err := result.Get(ctx)
if err != nil {
// TODO: Handle error.
}
metadata, err := pscompat.ParseMessageMetadata(id)
if err != nil {
// TODO: Handle error.
}
fmt.Printf("Published message to partition %d with offset %d\n", metadata.Partition, metadata.Offset)
}
func ExampleParseMessageMetadata_subscriber() {
ctx := context.Background()
const subscription = "projects/my-project/locations/zone/subscriptions/my-subscription"
subscriber, err := pscompat.NewSubscriberClient(ctx, subscription)
if err != nil {
// TODO: Handle error.
}
err = subscriber.Receive(ctx, func(ctx context.Context, m *pubsub.Message) {
// TODO: Handle message.
m.Ack()
metadata, err := pscompat.ParseMessageMetadata(m.ID)
if err != nil {
// TODO: Handle error.
}
fmt.Printf("Received message from partition %d with offset %d\n", metadata.Partition, metadata.Offset)
})
if err != nil {
// TODO: Handle error.
}
}