Use GetBucketPolicy with an AWS SDK or CLI

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();
}

The following command retrieves the bucket policy for a bucket named my-bucket:

aws s3api get-bucket-policy --bucket my-bucket

Output:

{
    "Policy": "{\"Version\":\"2008-10-17\",\"Statement\":[{\"Sid\":\"\",\"Effect\":\"Allow\",\"Principal\":\"*\",\"Action\":\"s3:GetObject\",\"Resource\":\"arn:aws:s3:::my-bucket/*\"},{\"Sid\":\"\",\"Effect\":\"Deny\",\"Principal\":\"*\",\"Action\":\"s3:GetObject\",\"Resource\":\"arn:aws:s3:::my-bucket/secret/*\"}]}"
}

Get and put a bucket policyThe following example shows how you can download an Amazon S3 bucket policy, make modifications to the file, and then use put-bucket-policy to apply the modified bucket policy. To download the bucket policy to a file, you can run:

aws s3api get-bucket-policy --bucket mybucket --query Policy --output text > policy.json

You can then modify the policy.json file as needed. Finally you can apply this modified policy back to the S3 bucket by running:

policy.json file as needed. Finally you can apply this modified policy back to the S3 bucket by running:

file as needed. Finally you can apply this modified policy back to the S3 bucket by running:

aws s3api put-bucket-policy --bucket mybucket --policy file://policy.json

import software.amazon.awssdk.services.s3.model.S3Exception;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.GetBucketPolicyRequest;
import software.amazon.awssdk.services.s3.model.GetBucketPolicyResponse;

/**
 * Before running this Java V2 code example, set up your development
 * environment, including your credentials.
 * <p>
 * For more information, see the following documentation topic:
 * <p>
 * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 */

public class GetBucketPolicy {
    public static void main(String[] args) {
        final String usage = """

            Usage:
                <bucketName>

            Where:
                bucketName - The Amazon S3 bucket to get the policy from.
            """;

        if (args.length != 1) {
            System.out.println(usage);
            System.exit(1);
        }

        String bucketName = args[0];
        System.out.format("Getting policy for bucket: \"%s\"\n\n", bucketName);
        Region region = Region.US_EAST_1;
        S3Client s3 = S3Client.builder()
            .region(region)
            .build();

        String polText = getPolicy(s3, bucketName);
        System.out.println("Policy Text: " + polText);
        s3.close();
    }

    /**
     * Retrieves the policy for the specified Amazon S3 bucket.
     *
     * @param s3 the {@link S3Client} instance to use for making the request
     * @param bucketName the name of the S3 bucket for which to retrieve the policy
     * @return the policy text for the specified bucket, or an empty string if an error occurs
     */
    public static String getPolicy(S3Client s3, String bucketName) {
        String policyText;
        System.out.format("Getting policy for bucket: \"%s\"\n\n", bucketName);
        GetBucketPolicyRequest policyReq = GetBucketPolicyRequest.builder()
            .bucket(bucketName)
            .build();

        try {
            GetBucketPolicyResponse policyRes = s3.getBucketPolicy(policyReq);
            policyText = policyRes.policy();
            return policyText;

        } catch (S3Exception e) {
            System.err.println(e.awsErrorDetails().errorMessage());
            System.exit(1);
        }

        return "";
    }
}

Get the bucket policy.

import {
  GetBucketPolicyCommand,
  S3Client,
  S3ServiceException,
} from "@aws-sdk/client-s3";

/**
 * Logs the policy for a specified bucket.
 * @param {{ bucketName: string }}
 */
export const main = async ({ bucketName }) => {
  const client = new S3Client({});

  try {
    const { Policy } = await client.send(
      new GetBucketPolicyCommand({
        Bucket: bucketName,
      }),
    );
    console.log(`Policy for "${bucketName}":\n${Policy}`);
  } catch (caught) {
    if (
      caught instanceof S3ServiceException &&
      caught.name === "NoSuchBucket"
    ) {
      console.error(
        `Error from S3 while getting policy from ${bucketName}. The bucket doesn't exist.`,
      );
    } else if (caught instanceof S3ServiceException) {
      console.error(
        `Error from S3 while getting policy from ${bucketName}.  ${caught.name}: ${caught.message}`,
      );
    } else {
      throw caught;
    }
  }
};

suspend fun getPolicy(bucketName: String): String? {
    println("Getting policy for bucket $bucketName")

    val request =
        GetBucketPolicyRequest {
            bucket = bucketName
        }

    S3Client { region = "us-east-1" }.use { s3 ->
        val policyRes = s3.getBucketPolicy(request)
        return policyRes.policy
    }
}

Example 1: This command outputs the bucket policy associated with the given S3 bucket.

Get-S3BucketPolicy -BucketName 'amzn-s3-demo-bucket'

class BucketWrapper:
    """Encapsulates S3 bucket actions."""

    def __init__(self, bucket):
        """
        :param bucket: A Boto3 Bucket resource. This is a high-level resource in Boto3
                       that wraps bucket actions in a class-like structure.
        """
        self.bucket = bucket
        self.name = bucket.name


    def get_policy(self):
        """
        Get the security policy of the bucket.

        :return: The security policy of the specified bucket, in JSON format.
        """
        try:
            policy = self.bucket.Policy()
            logger.info(
                "Got policy %s for bucket '%s'.", policy.policy, self.bucket.name
            )
        except ClientError:
            logger.exception("Couldn't get policy for bucket '%s'.", self.bucket.name)
            raise
        else:
            return json.loads(policy.policy)

# Wraps an Amazon S3 bucket policy.
class BucketPolicyWrapper
  attr_reader :bucket_policy

  # @param bucket_policy [Aws::S3::BucketPolicy] A bucket policy object configured with an existing bucket.
  def initialize(bucket_policy)
    @bucket_policy = bucket_policy
  end

  # Gets the policy of a bucket.
  #
  # @return [Aws::S3::GetBucketPolicyOutput, nil] The current bucket policy.
  def policy
    policy = @bucket_policy.data.policy
    policy.respond_to?(:read) ? policy.read : policy
  rescue Aws::Errors::ServiceError => e
    puts "Couldn't get the policy for #{@bucket_policy.bucket.name}. Here's why: #{e.message}"
    nil
  end

end