Question

我对 GCP Pub/Sub REST API 感到困惑。

背景：我正在尝试使用 GCP Pub/Sub 编写应用程序，其中该语言不会作为客户端库退出（我正在尝试使用 R）。

因此，我需要依赖提供的 REST API：https://cloud.google.com/pubsub/docs/reference/rest

根据我对 REST API 的理解，我们必须使用请求订阅：https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.subscriptions/pull

问题：我的困惑是这是一个 POST 请求

POST https://pubsub.googleapis.com/v1/{subscription}:pull

这个 POST 请求有一个响应：

{
  "receivedMessages": [
    {
      object (ReceivedMessage)
    }
  ]
}

我怎样才能收到来自 POST 请求的响应？这对我来说没有意义。

我的目标是订阅消息的 Pub/Sub 订阅，类似于 Python 库 here：

<块引用>

要订阅 Cloud Pub/Sub 中的数据，您需要创建一个基于并订阅该主题，传递回调函数。

import os
from google.cloud import pubsub_v1

topic_name = 'projects/{project_id}/topics/{topic}'.format(
    project_id=os.getenv('GOOGLE_CLOUD_PROJECT'),
    topic='MY_TOPIC_NAME',  # Set this to something appropriate.
)

subscription_name = 'projects/{project_id}/subscriptions/{sub}'.format(
    project_id=os.getenv('GOOGLE_CLOUD_PROJECT'),
    sub='MY_SUBSCRIPTION_NAME',  # Set this to something appropriate.
)

def callback(message):
    print(message.data)
    message.ack()

with pubsub_v1.SubscriberClient() as subscriber:
    subscriber.create_subscription(
        name=subscription_name, topic=topic_name)
    future = subscriber.subscribe(subscription_name, callback)
    try:
        future.result()
    except KeyboardInterrupt:
        future.cancel()

Answer 1

Cloud Pub/Sub 客户端库使用 streaming pull 来接收消息而不是拉取消息。它还将用户从这些实际请求中抽象出来。客户端库本身接收消息列表，然后调用用户提供的回调。

如果您直接使用拉取请求，那么您需要遍历响应中的每条消息，并在每条消息上调用您的用户回调。在所有支持的语言（例如 Python）的 Cloud Pub/Sub documentation 中有一个示例：

from google.api_core import retry
from google.cloud import pubsub_v1

# TODO(developer)
# project_id = "your-project-id"
# subscription_id = "your-subscription-id"

subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path(project_id, subscription_id)

NUM_MESSAGES = 3

# Wrap the subscriber in a 'with' block to automatically call close() to
# close the underlying gRPC channel when done.
with subscriber:
    # The subscriber pulls a specific number of messages. The actual
    # number of messages pulled may be smaller than max_messages.
    response = subscriber.pull(
        request={"subscription": subscription_path, "max_messages": NUM_MESSAGES},
        retry=retry.Retry(deadline=300),
    )

    ack_ids = []
    for received_message in response.received_messages:
        print(f"Received: {received_message.message.data}.")
        ack_ids.append(received_message.ack_id)

    # Acknowledges the received messages so they will not be sent again.
    subscriber.acknowledge(
        request={"subscription": subscription_path, "ack_ids": ack_ids}
    )

    print(
        f"Received and acknowledged {len(response.received_messages)} messages from {subscription_path}."
    )

如何使用 GCP Pub/Sub 从订阅中提取消息？

1 个答案: