Pub/Sub without CloudEvents

Use Pub/Sub without CloudEvents.

介绍

Dapr uses CloudEvents to provide additional context to the event payload, enabling features like:

• 追踪
• Deduplication by message Id
• Content-type for proper deserialization of event’s data

For more information about CloudEvents, read the CloudEvents specification.

When adding Dapr to your application, some services may still need to communicate via raw pub/sub messages not encapsulated in CloudEvents. This may be for compatibility reasons, or because some apps are not using Dapr. Dapr enables apps to publish and subscribe to raw events that are not wrapped in a CloudEvent.

Warning

Not using CloudEvents disables support for tracing, event deduplication per messageId, content-type metadata, and any other features built using the CloudEvent schema.

Publishing raw messages

Dapr apps are able to publish raw events to pub/sub topics without CloudEvent encapsulation, for compatibility with non-Dapr apps.

To disable CloudEvent wrapping, set the rawPayload metadata to true as part of the publishing request. This allows subscribers to receive these messages without having to parse the CloudEvent schema.

• curl
• Python SDK
• PHP SDK

curl -X "POST" http://localhost:3500/v1.0/publish/pubsub/TOPIC_A?metadata.rawPayload=true -H "Content-Type: application/json" -d '{"order-number": "345"}'

from dapr.clients import DaprClient
with DaprClient() as d:
    req_data = {
        'order-number': '345'
    }
    # Create a typed message with content type and body
    resp = d.publish_event(
        pubsub_name='pubsub',
        topic='TOPIC_A',
        data=json.dumps(req_data),
        metadata=(
                     ('rawPayload', 'true')
                 )
    )
    # Print the request
    print(req_data, flush=True)

<?php
require_once __DIR__.'/vendor/autoload.php';
$app = \Dapr\App::create();
$app->run(function(\DI\FactoryInterface $factory) {
    $publisher = $factory->make(\Dapr\PubSub\Publish::class, ['pubsub' => 'pubsub']);
    $publisher->topic('TOPIC_A')->publish('data', ['rawPayload' => 'true']);
});

Subscribing to raw messages

Dapr apps are also able to subscribe to raw events coming from existing pub/sub topics that do not use CloudEvent encapsulation.

Programmatically subscribe to raw events

When subscribing programmatically, add the additional metadata entry for rawPayload so the Dapr sidecar automatically wraps the payloads into a CloudEvent that is compatible with current Dapr SDKs.

• Python
• PHP SDK

import flask
from flask import request, jsonify
from flask_cors import CORS
import json
import sys
app = flask.Flask(__name__)
CORS(app)
@app.route('/dapr/subscribe', methods=['GET'])
def subscribe():
    subscriptions = [{'pubsubname': 'pubsub',
                      'topic': 'deathStarStatus',
                      'route': 'dsstatus',
                      'metadata': {
                          'rawPayload': 'true',
                      } }]
    return jsonify(subscriptions)
@app.route('/dsstatus', methods=['POST'])
def ds_subscriber():
    print(request.json, flush=True)
    return json.dumps({'success':True}), 200, {'ContentType':'application/json'}
app.run()

<?php
require_once __DIR__.'/vendor/autoload.php';
$app = \Dapr\App::create(configure: fn(\DI\ContainerBuilder $builder) => $builder->addDefinitions(['dapr.subscriptions' => [
    new \Dapr\PubSub\Subscription(pubsubname: 'pubsub', topic: 'deathStarStatus', route: '/dsstatus', metadata: [ 'rawPayload' => 'true'] ),
]]));
$app->post('/dsstatus', function(
    #[\Dapr\Attributes\FromBody]
    \Dapr\PubSub\CloudEvent $cloudEvent,
    \Psr\Log\LoggerInterface $logger
    ) {
        $logger->alert('Received event: {event}', ['event' => $cloudEvent]);
        return ['status' => 'SUCCESS'];
    }
);
$app->start();

Declaratively subscribe to raw events

Subscription Custom Resources Definitions (CRDs) do not currently contain metadata attributes (issue #3225). At this time subscribing to raw events can only be done through programmatic subscriptions.

相关链接

• Learn more about how to publish and subscribe
• List of pub/sub components
• Read the API reference