如何使用Go指定Google Pub/Sub拉取的消息数量？

在调用Pub/Sub的拉取消息API时，通过指定最大拉取消息数参数为2即可实现需求，不同语言的客户端SDK都提供了对应的配置项：

• Python客户端示例：

from google.cloud import pubsub_v1

subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path("你的项目ID", "你的订阅ID")

# 拉取最多2条消息
pull_response = subscriber.pull(
    request={"subscription": subscription_path, "max_messages": 2}
)

# 处理拉取到的消息
for msg in pull_response.received_messages:
    print(f"收到消息内容：{msg.message.data.decode('utf-8')}")
    # 确认消息，避免重复拉取
    subscriber.acknowledge(
        request={"subscription": subscription_path, "ack_ids": [msg.ack_id]}
    )

• Java客户端示例：

import com.google.cloud.pubsub.v1.SubscriberClient;
import com.google.pubsub.v1.ProjectSubscriptionName;
import com.google.pubsub.v1.PullRequest;
import com.google.pubsub.v1.ReceivedMessage;

import java.io.IOException;
import java.util.List;

public class PubSubPullExample {
    public static void main(String[] args) throws IOException {
        String projectId = "你的项目ID";
        String subscriptionId = "你的订阅ID";
        ProjectSubscriptionName subscriptionName = ProjectSubscriptionName.of(projectId, subscriptionId);

        try (SubscriberClient subscriberClient = SubscriberClient.create()) {
            // 构建拉取请求，设置最大消息数为2
            PullRequest request = PullRequest.newBuilder()
                    .setSubscription(subscriptionName.toString())
                    .setMaxMessages(2)
                    .build();

            // 执行拉取
            var response = subscriberClient.pull(request);
            List<ReceivedMessage> messages = response.getReceivedMessagesList();

            // 处理消息并确认
            for (ReceivedMessage msg : messages) {
                System.out.println("收到消息：" + msg.getMessage().getData().toStringUtf8());
                subscriberClient.acknowledge(subscriptionName.toString(), List.of(msg.getAckId()));
            }
        }
    }
}

需要注意：如果订阅中可用的消息数量不足2条，API会返回当前所有可用的消息，不会等待凑够2条再返回。

内容的提问来源于stack exchange，提问作者Gabriel Belloni