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
}
