cloudevents golang sdk - Pub/Sub with and without ordering key

pubsub-no-order-main.go

package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"time"

	"cloud.google.com/go/pubsub"
	cepubsub "github.com/cloudevents/sdk-go/protocol/pubsub/v2"
	ce "github.com/cloudevents/sdk-go/v2"
	"github.com/google/uuid"
	"github.com/kelseyhightower/envconfig"
)

// export PROJECTID=skymeyer-playground
// export TOPICID=test-ordering
// export SUBSCRIPTIONID=test-ordering-sub
type envConfig struct {
	ProjectID      string
	TopicID        string
	SubscriptionID string
}

type Example struct {
	Foo string
}

func receive(ctx context.Context, event ce.Event) error {

	fmt.Printf("Event Context: %+v\n", event.Context)

	data := &Example{}
	if err := event.DataAs(data); err != nil {
		fmt.Printf("Got Data Error: %s\n", err.Error())
	}

	fmt.Printf("Data processed: %+v\n", data)
	fmt.Printf("----------------------------\n")
	return nil
}

func main() {
	ctx := context.Background()

	var env envConfig
	if err := envconfig.Process("", &env); err != nil {
		log.Printf("[ERROR] Failed to process env var: %s", err)
		os.Exit(1)
	}

	t, err := cepubsub.New(context.Background(),
		cepubsub.WithProjectID(env.ProjectID),
		cepubsub.WithTopicID(env.TopicID),
		cepubsub.WithSubscriptionID(env.SubscriptionID),
		cepubsub.WithReceiveSettings(&pubsub.ReceiveSettings{
			MaxOutstandingMessages: 1, // This is key to not get parallel messages
		}),

		// Both topic and subscription are created in advance. Note:
		// Ensure your subscription has message ordering enabled when it was created in GCP.
		cepubsub.AllowCreateTopic(false),
		cepubsub.AllowCreateSubscription(false),
	)
	if err != nil {
		log.Fatalf("failed to create pubsub protocol, %s", err.Error())
	}

	c, err := ce.NewClient(t)

	if err != nil {
		log.Fatalf("failed to create client, %s", err.Error())
	}

	log.Printf("Producing messages without ordering key ...\n")

	for i := 1; i <= 5; i++ {

		// Create a new event with incremental counter
		event := ce.NewEvent()
		event.SetID(uuid.New().String())
		event.SetType("example.stuff")
		event.SetSource("example/stuff")
		event.SetData(ce.ApplicationJSON, &Example{Foo: fmt.Sprintf("bar_%d", i)})

		log.Printf("Producing message %d [%s]...\n", i, event.ID())
		if res := c.Send(ctx, event); !ce.IsACK(res) {
			log.Fatalf("failed sending %d: %+v", i, res)
		}
	}

	log.Println("Wait a bit before starting receiver ...")
	time.Sleep(5 * time.Second)

	log.Println("Created client, listening...")

	if err := c.StartReceiver(ctx, receive); err != nil {
		log.Fatalf("failed to start pubsub receiver, %s", err.Error())
	}
}

pubsub-no-order-output.txt

$ go run ./pubsub-no-order
2022/02/08 01:31:35 Producing messages without ordering key ...
2022/02/08 01:31:35 Producing message 1 [a3a23fe9-9f93-4363-8506-53a329a27026]...
2022/02/08 01:31:36 Producing message 2 [eb6d771c-5435-4d1c-875d-0d19bc764463]...
2022/02/08 01:31:36 Producing message 3 [2da1a55c-2bc6-48a2-a27d-22fc370a9d4e]...
2022/02/08 01:31:36 Producing message 4 [49301d40-c1f6-4165-ab1d-506deda160c5]...
2022/02/08 01:31:36 Producing message 5 [b71fe450-afe0-4106-93a4-765f75cf8682]...
2022/02/08 01:31:36 Wait a bit before starting receiver ...
2022/02/08 01:31:41 Created client, listening...
{"level":"info","ts":1644312701.750985,"logger":"fallback","caller":"[email protected]/protocol.go:195","msg":"starting subscriber for Topic \"\", Subscription \"test-ordering-sub\""}
{"level":"info","ts":1644312701.751117,"logger":"fallback","caller":"[email protected]/protocol.go:198","msg":"conn is&{false false skymeyer-playground 0xc000476200  <nil> test-ordering-sub <nil> {0 0} 0xc00012b0c0 <nil> <nil> false }"}
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: 2da1a55c-2bc6-48a2-a27d-22fc370a9d4e
  datacontenttype: application/json

Data processed: &{Foo:bar_3}
----------------------------
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: b71fe450-afe0-4106-93a4-765f75cf8682
  datacontenttype: application/json

Data processed: &{Foo:bar_5}
----------------------------
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: 49301d40-c1f6-4165-ab1d-506deda160c5
  datacontenttype: application/json

Data processed: &{Foo:bar_4}
----------------------------
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: a3a23fe9-9f93-4363-8506-53a329a27026
  datacontenttype: application/json

Data processed: &{Foo:bar_1}
----------------------------
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: eb6d771c-5435-4d1c-875d-0d19bc764463
  datacontenttype: application/json

Data processed: &{Foo:bar_2}
----------------------------

pubsub-with-order-main.go

package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"time"

	"cloud.google.com/go/pubsub"
	cepubsub "github.com/cloudevents/sdk-go/protocol/pubsub/v2"
	ce "github.com/cloudevents/sdk-go/v2"
	"github.com/google/uuid"
	"github.com/kelseyhightower/envconfig"
	"google.golang.org/api/option"
)

// export PROJECTID=skymeyer-playground
// export TOPICID=test-ordering
// export SUBSCRIPTIONID=test-ordering-sub
type envConfig struct {
	ProjectID      string
	TopicID        string
	SubscriptionID string
}

type Example struct {
	Foo string
}

func receive(ctx context.Context, event ce.Event) error {

	fmt.Printf("Event Context: %+v\n", event.Context)

	data := &Example{}
	if err := event.DataAs(data); err != nil {
		fmt.Printf("Got Data Error: %s\n", err.Error())
	}

	fmt.Printf("Data processed: %+v\n", data)
	fmt.Printf("----------------------------\n")
	return nil
}

func main() {
	ctx := context.Background()

	var env envConfig
	if err := envconfig.Process("", &env); err != nil {
		log.Printf("[ERROR] Failed to process env var: %s", err)
		os.Exit(1)
	}

	// When producing messages with ordering, you probably want to send them to a specific region.
	// This is only really required in case there are multiple producers spread across different
	// regions to ensure all message with the same ordering key end up in the same region, see:
	// https://cloud.google.com/pubsub/docs/ordering#receiving_messages_in_order
	// https://cloud.google.com/pubsub/docs/reference/service_apis_overview#service_endpoints
	psc, err := pubsub.NewClient(ctx, env.ProjectID,
		option.WithEndpoint("us-central1-pubsub.googleapis.com:443"),
	)
	if err != nil {
		log.Fatalf("failed setting up pubsub client: %+v", err)
	}

	t, err := cepubsub.New(context.Background(),
		cepubsub.WithProjectID(env.ProjectID),
		cepubsub.WithTopicID(env.TopicID),
		cepubsub.WithSubscriptionID(env.SubscriptionID),
		cepubsub.WithReceiveSettings(&pubsub.ReceiveSettings{
			MaxOutstandingMessages: 1, // This is key to not get parallel messages
		}),

		// Both topic and subscription are created in advance. Note:
		// Ensure your subscription has message ordering enabled when it was created in GCP.
		cepubsub.AllowCreateTopic(false),
		cepubsub.AllowCreateSubscription(false),

		// Following settings are for the event producer specifically to allow producing messages
		// with an ordering key passed along in the producer context (see below).
		cepubsub.WithMessageOrdering(),
		cepubsub.WithClient(psc), // see note above regarding regional endpoint client
	)
	if err != nil {
		log.Fatalf("failed to create pubsub protocol, %s", err.Error())
	}

	c, err := ce.NewClient(t)

	if err != nil {
		log.Fatalf("failed to create client, %s", err.Error())
	}

	// Create an ordering key and pass it along to our producer context
	orderKey := uuid.New().String()
	pctx := cepubsub.WithOrderingKey(ctx, orderKey)
	log.Printf("Producing messages with ordering key %q ...\n", orderKey)

	for i := 1; i <= 5; i++ {

		// Create a new event with incremental counter
		event := ce.NewEvent()
		event.SetID(uuid.New().String())
		event.SetType("example.stuff")
		event.SetSource("example/stuff")
		event.SetData(ce.ApplicationJSON, &Example{Foo: fmt.Sprintf("bar_%d", i)})

		log.Printf("Producing message %d [%s]...\n", i, event.ID())
		if res := c.Send(pctx, event); !ce.IsACK(res) {
			log.Fatalf("failed sending %d: %+v", i, res)
		}
	}

	log.Println("Wait a bit before starting receiver ...")
	time.Sleep(5 * time.Second)

	log.Println("Created client, listening...")

	if err := c.StartReceiver(ctx, receive); err != nil {
		log.Fatalf("failed to start pubsub receiver, %s", err.Error())
	}
}

pubsub-with-order-output.txt

$ go run ./pubsub-with-order
2022/02/08 01:32:00 Producing messages with ordering key "e55e405b-4f3b-40e6-9b6e-d6bee672b100" ...
2022/02/08 01:32:00 Producing message 1 [a59f3356-f0f6-4eeb-9ddc-54acc44e47a4]...
2022/02/08 01:32:02 Producing message 2 [06cd231c-6ccf-4a76-94c2-743784d7848a]...
2022/02/08 01:32:02 Producing message 3 [38361a02-f508-40e6-b7af-cc3004c787f9]...
2022/02/08 01:32:03 Producing message 4 [ca585f32-d382-4789-bcff-836d66a191ac]...
2022/02/08 01:32:03 Producing message 5 [cfa566f5-9bdb-4e38-9c58-c4f1ed7029bf]...
2022/02/08 01:32:03 Wait a bit before starting receiver ...
2022/02/08 01:32:08 Created client, listening...
{"level":"info","ts":1644312728.664626,"logger":"fallback","caller":"[email protected]/protocol.go:195","msg":"starting subscriber for Topic \"\", Subscription \"test-ordering-sub\""}
{"level":"info","ts":1644312728.664775,"logger":"fallback","caller":"[email protected]/protocol.go:198","msg":"conn is&{false false skymeyer-playground 0xc000616200  <nil> test-ordering-sub <nil> {0 0} 0xc000618240 <nil> <nil> true }"}
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: a59f3356-f0f6-4eeb-9ddc-54acc44e47a4
  datacontenttype: application/json

Data processed: &{Foo:bar_1}
----------------------------
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: 06cd231c-6ccf-4a76-94c2-743784d7848a
  datacontenttype: application/json

Data processed: &{Foo:bar_2}
----------------------------
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: 38361a02-f508-40e6-b7af-cc3004c787f9
  datacontenttype: application/json

Data processed: &{Foo:bar_3}
----------------------------
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: ca585f32-d382-4789-bcff-836d66a191ac
  datacontenttype: application/json

Data processed: &{Foo:bar_4}
----------------------------
Event Context: Context Attributes,
  specversion: 1.0
  type: example.stuff
  source: example/stuff
  id: cfa566f5-9bdb-4e38-9c58-c4f1ed7029bf
  datacontenttype: application/json

Data processed: &{Foo:bar_5}
----------------------------