(OBSOLETE) Recevoir des messages pouvant concerner différentes révisions de schéma

(OBSOLETE) Recevoir des messages pouvant concerner différentes révisions de schéma

Exemple de code

Go

Avant d'essayer cet exemple, suivez les instructions de configuration pour Go du guide de démarrage rapide de Pub/Sub : utiliser les bibliothèques clientes. Pour en savoir plus, consultez la documentation de référence sur l'API Pub/Sub Go.

Pour vous authentifier auprès de Pub/Sub, configurez les Identifiants par défaut de l'application. Pour en savoir plus, consultez Configurer l'authentification pour un environnement de développement local.

import (
	"context"
	"fmt"
	"io"
	"strings"
	"sync"
	"time"

	"cloud.google.com/go/pubsub"
	"github.com/linkedin/goavro/v2"
)

func subscribeWithAvroSchemaRevisions(w io.Writer, projectID, subID, avscFile string) error {
	// projectID := "my-project-id"
	// topicID := "my-topic"
	// avscFile = "path/to/an/avro/schema/file(.avsc)/formatted/in/json"
	ctx := context.Background()
	client, err := pubsub.NewClient(ctx, projectID)
	if err != nil {
		return fmt.Errorf("pubsub.NewClient: %w", err)
	}

	schemaClient, err := pubsub.NewSchemaClient(ctx, projectID)
	if err != nil {
		return fmt.Errorf("pubsub.NewSchemaClient: %w", err)
	}

	// Create the cache for the codecs for different revision IDs.
	revisionCodecs := make(map[string]*goavro.Codec)

	sub := client.Subscription(subID)
	ctx2, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	var mu sync.Mutex
	sub.Receive(ctx2, func(ctx context.Context, msg *pubsub.Message) {
		mu.Lock()
		defer mu.Unlock()
		name := msg.Attributes["googclient_schemaname"]
		revision := msg.Attributes["googclient_schemarevisionid"]

		codec, ok := revisionCodecs[revision]
		// If the codec doesn't exist in the map, this is the first time we
		// are seeing this revision. We need to fetch the schema and cache the
		// codec. It would be more typical to do this asynchronously, but is
		// shown here in a synchronous way to ease readability.
		if !ok {
			// Extract just the schema resource name
			path := strings.Split(name, "/")
			name = path[len(path)-1]
			schema, err := schemaClient.Schema(ctx, fmt.Sprintf("%s@%s", name, revision), pubsub.SchemaViewFull)
			if err != nil {
				fmt.Fprintf(w, "Nacking, cannot read message without schema: %v\n", err)
				msg.Nack()
				return
			}
			codec, err = goavro.NewCodec(schema.Definition)
			if err != nil {
				msg.Nack()
				fmt.Fprintf(w, "goavro.NewCodec err: %v\n", err)
			}
			revisionCodecs[revision] = codec
		}

		encoding := msg.Attributes["googclient_schemaencoding"]

		var state map[string]interface{}
		if encoding == "BINARY" {
			data, _, err := codec.NativeFromBinary(msg.Data)
			if err != nil {
				fmt.Fprintf(w, "codec.NativeFromBinary err: %v\n", err)
				msg.Nack()
				return
			}
			fmt.Fprintf(w, "Received a binary-encoded message:\n%#v\n", data)
			state = data.(map[string]interface{})
		} else if encoding == "JSON" {
			data, _, err := codec.NativeFromTextual(msg.Data)
			if err != nil {
				fmt.Fprintf(w, "codec.NativeFromTextual err: %v\n", err)
				msg.Nack()
				return
			}
			fmt.Fprintf(w, "Received a JSON-encoded message:\n%#v\n", data)
			state = data.(map[string]interface{})
		} else {
			fmt.Fprintf(w, "Unknown message type(%s), nacking\n", encoding)
			msg.Nack()
			return
		}
		fmt.Fprintf(w, "%s is abbreviated as %s\n", state["name"], state["post_abbr"])
		msg.Ack()
	})
	return nil
}

Étape suivante

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