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# 使用存储桶策略管理对 Amazon S3 存储桶的访问
<a name="examples-s3-bucket-policies"></a>

您可以设置、获取或删除*存储桶策略*来管理对 Amazon S3 存储桶的访问。

## 先决条件
<a name="codeExamplePrereq"></a>

在开始之前，建议您先阅读[开始使用 适用于 C\$1\$1 的 AWS SDK](getting-started.md)。

下载示例代码并按[代码示例入门](getting-started-code-examples.md)中所述构建解决方案。

要运行这些示例，您的代码用于发出请求的用户配置文件必须具有适当的权限 AWS （适用于服务和操作）。有关更多信息，请参阅[提供 AWS 凭证](credentials.md)。

## 设置存储桶策略
<a name="set-s3-bucket-policy"></a>

您可以为特定 S3 存储桶设置存储桶策略，方法`S3Client`是调用`PutBucketPolicy`函数并在中为其提供存储桶名称和策略的 JSON 表示形式[PutBucketPolicyRequest](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-s3/html/class_aws_1_1_s3_1_1_model_1_1_put_bucket_policy_request.html)。

 **代码** 

```
//! Build a policy JSON string.
/*!
  \param userArn: Aws user Amazon Resource Name (ARN).
      For more information, see https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_identifiers.html#identifiers-arns.
  \param bucketName: Name of a bucket.
  \return String: Policy as JSON string.
*/

Aws::String getPolicyString(const Aws::String &userArn,
                            const Aws::String &bucketName) {
    return
            "{\n"
            "   \"Version\":\"2012-10-17\",\n"
            "   \"Statement\":[\n"
            "       {\n"
            "           \"Sid\": \"1\",\n"
            "           \"Effect\": \"Allow\",\n"
            "           \"Principal\": {\n"
            "               \"AWS\": \""
            + userArn +
            "\"\n""           },\n"
            "           \"Action\": [ \"s3:getObject\" ],\n"
            "           \"Resource\": [ \"arn:aws:s3:::"
            + bucketName +
            "/*\" ]\n"
            "       }\n"
            "   ]\n"
            "}";
}
```

```
bool AwsDoc::S3::putBucketPolicy(const Aws::String &bucketName,
                                 const Aws::String &policyBody,
                                 const Aws::S3::S3ClientConfiguration &clientConfig) {
    Aws::S3::S3Client s3Client(clientConfig);

    std::shared_ptr<Aws::StringStream> request_body =
            Aws::MakeShared<Aws::StringStream>("");
    *request_body << policyBody;

    Aws::S3::Model::PutBucketPolicyRequest request;
    request.SetBucket(bucketName);
    request.SetBody(request_body);

    Aws::S3::Model::PutBucketPolicyOutcome outcome =
            s3Client.PutBucketPolicy(request);

    if (!outcome.IsSuccess()) {
        std::cerr << "Error: putBucketPolicy: "
                  << outcome.GetError().GetMessage() << std::endl;
    } else {
        std::cout << "Set the following policy body for the bucket '" <<
                  bucketName << "':" << std::endl << std::endl;
        std::cout << policyBody << std::endl;
    }

    return outcome.IsSuccess();
}
```

**注意**  
[Aws:: Utils:: Json:: JsonValue](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-core/html/class_aws_1_1_utils_1_1_json_1_1_json_value.html) 实用程序类可以用来帮助你构造要传递给的有效 JSON 对象。`PutBucketPolicy`

请参阅 [Github](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/s3/put_bucket_policy.cpp) 上的完整示例。

## 获取存储桶策略
<a name="get-s3-bucket-policy"></a>

要检索 Amazon S3 存储桶的策略，请调用 `S3Client`'s `GetBucketPolicy` 函数，将存储桶的名称传递给它[GetBucketPolicyRequest](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-s3/html/class_aws_1_1_s3_1_1_model_1_1_get_bucket_policy_request.html)。

 **代码** 

```
bool AwsDoc::S3::getBucketPolicy(const Aws::String &bucketName,
                                 const Aws::S3::S3ClientConfiguration &clientConfig) {
    Aws::S3::S3Client s3Client(clientConfig);

    Aws::S3::Model::GetBucketPolicyRequest request;
    request.SetBucket(bucketName);

    Aws::S3::Model::GetBucketPolicyOutcome outcome =
            s3Client.GetBucketPolicy(request);

    if (!outcome.IsSuccess()) {
        const Aws::S3::S3Error &err = outcome.GetError();
        std::cerr << "Error: getBucketPolicy: "
                  << err.GetExceptionName() << ": " << err.GetMessage() << std::endl;
    } else {
        Aws::StringStream policy_stream;
        Aws::String line;

        outcome.GetResult().GetPolicy() >> line;
        policy_stream << line;

        std::cout << "Retrieve the policy for bucket '" << bucketName << "':\n\n" <<
                  policy_stream.str() << std::endl;
    }

    return outcome.IsSuccess();
}
```

请参阅 [Github](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/s3/get_bucket_policy.cpp) 上的完整示例。

## 删除存储桶策略
<a name="delete-s3-bucket-policy"></a>

要删除存储桶策略，请调用 `S3Client`'s `DeleteBucketPolicy` 函数，并在中为其提供存储桶名称[DeleteBucketPolicyRequest](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-s3/html/class_aws_1_1_s3_1_1_model_1_1_delete_bucket_policy_request.html)。

 **代码** 

```
bool AwsDoc::S3::deleteBucketPolicy(const Aws::String &bucketName,
                                    const Aws::S3::S3ClientConfiguration &clientConfig) {
    Aws::S3::S3Client client(clientConfig);

    Aws::S3::Model::DeleteBucketPolicyRequest request;
    request.SetBucket(bucketName);

    Aws::S3::Model::DeleteBucketPolicyOutcome outcome = client.DeleteBucketPolicy(request);

    if (!outcome.IsSuccess()) {
        const Aws::S3::S3Error &err = outcome.GetError();
        std::cerr << "Error: deleteBucketPolicy: " <<
                  err.GetExceptionName() << ": " << err.GetMessage() << std::endl;
    } else {
        std::cout << "Policy was deleted from the bucket." << std::endl;
    }

    return outcome.IsSuccess();
}
```

即使存储桶中还没有策略，该函数也会成功。如果您指定的存储桶名称不存在，或者您没有访问该存储桶的权限，会引发 `AmazonServiceException`。

请参阅 [Github](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/s3/delete_bucket_policy.cpp) 上的完整示例。

## 更多信息
<a name="more-info"></a>
+  [PutBucketPolicy](https://docs.aws.amazon.com/AmazonS3/latest/API/PutBucketPolicy.html)在 Amazon 简单存储服务 API 参考中
+  [GetBucketPolicy](https://docs.aws.amazon.com/AmazonS3/latest/API/GetBucketPolicy.html)在 Amazon 简单存储服务 API 参考中
+  [DeleteBucketPolicy](https://docs.aws.amazon.com/AmazonS3/latest/API/DeleteBucketPolicy.html)在 Amazon 简单存储服务 API 参考中
+  《Amazon Simple Storage Service 用户指南》中的[访问策略语言概述](https://docs.aws.amazon.com/AmazonS3/latest/dev/access-policy-language-overview.html)
+  《Amazon Simple Storage Service 用户指南》中的[存储桶策略示例](https://docs.aws.amazon.com/AmazonS3/latest/dev/example-bucket-policies.html)