headBucket method

Future<HeadBucketOutput> headBucket({ required String bucket, String? expectedBucketOwner, })

You can use this operation to determine if a bucket exists and if you have permission to access it. The action returns a 200 OK HTTP status code if the bucket exists and you have permission to access it. You can make a HeadBucket call on any bucket name to any Region in the partition, and regardless of the permissions on the bucket, you will receive a response header with the correct bucket location so that you can then make a proper, signed request to the appropriate Regional endpoint.

Authentication and authorization

General purpose buckets - Request to public buckets that grant the s3:ListBucket permission publicly do not need to be signed. All other HeadBucket requests must be authenticated and signed by using IAM credentials (access key ID and secret access key for the IAM identities). All headers with the x-amz- prefix, including x-amz-copy-source, must be signed. For more information, see REST Authentication.

Directory buckets - You must use IAM credentials to authenticate and authorize your access to the HeadBucket API operation, instead of using the temporary security credentials through the CreateSession API operation.

Amazon Web Services CLI or SDKs handles authentication and authorization on your behalf.

Permissions

• General purpose bucket permissions - To use this operation, you must have permissions to perform the s3:ListBucket action. The bucket owner has this permission by default and can grant this permission to others. For more information about permissions, see Managing access permissions to your Amazon S3 resources in the Amazon S3 User Guide.
• Directory bucket permissions - You must have the s3express:CreateSession permission in the Action element of a policy. If no session mode is specified, the session will be created with the maximum allowable privilege, attempting ReadWrite first, then ReadOnly if ReadWrite is not permitted. If you want to explicitly restrict the access to be read-only, you can set the s3express:SessionMode condition key to ReadOnly on the bucket.

  For more information about example bucket policies, see Example bucket policies for S3 Express One Zone and Amazon Web Services Identity and Access Management (IAM) identity-based policies for S3 Express One Zone in the Amazon S3 User Guide.

HTTP Host header syntax

Directory buckets - The HTTP Host header syntax is Bucket-name.s3express-zone-id.region-code.amazonaws.com.

May throw NotFound.

Parameter bucket : The bucket name.

Directory buckets - When you use this operation with a directory bucket, you must use virtual-hosted-style requests in the format Bucket-name.s3express-zone-id.region-code.amazonaws.com. Path-style requests are not supported. Directory bucket names must be unique in the chosen Zone (Availability Zone or Local Zone). Bucket names must follow the format bucket-base-name--zone-id--x-s3 (for example, amzn-s3-demo-bucket--usw2-az1--x-s3). For information about bucket naming restrictions, see Directory bucket naming rules in the Amazon S3 User Guide.

Access points - When you use this action with an access point for general purpose buckets, you must provide the alias of the access point in place of the bucket name or specify the access point ARN. When you use this action with an access point for directory buckets, you must provide the access point name in place of the bucket name. When using the access point ARN, you must direct requests to the access point hostname. The access point hostname takes the form AccessPointName-AccountId.s3-accesspoint.Region.amazonaws.com. When using this action with an access point through the Amazon Web Services SDKs, you provide the access point ARN in place of the bucket name. For more information about access point ARNs, see Using access points in the Amazon S3 User Guide.

Object Lambda access points - When you use this API operation with an Object Lambda access point, provide the alias of the Object Lambda access point in place of the bucket name. If the Object Lambda access point alias in a request is not valid, the error code InvalidAccessPointAliasError is returned. For more information about InvalidAccessPointAliasError, see List of Error Codes. S3 on Outposts - When you use this action with S3 on Outposts, you must direct requests to the S3 on Outposts hostname. The S3 on Outposts hostname takes the form AccessPointName-AccountId.outpostID.s3-outposts.Region.amazonaws.com. When you use this action with S3 on Outposts, the destination bucket must be the Outposts access point ARN or the access point alias. For more information about S3 on Outposts, see What is S3 on Outposts? in the Amazon S3 User Guide.

Parameter expectedBucketOwner : The account ID of the expected bucket owner. If the account ID that you provide does not match the actual owner of the bucket, the request fails with the HTTP status code 403 Forbidden (access denied).

Implementation

Future<HeadBucketOutput> headBucket({
  required String bucket,
  String? expectedBucketOwner,
}) async {
  final headers = <String, String>{
    if (expectedBucketOwner != null)
      'x-amz-expected-bucket-owner': expectedBucketOwner.toString(),
  };
  final $result = await _protocol.sendRaw(
    method: 'HEAD',
    requestUri: '/${Uri.encodeComponent(bucket)}',
    headers: headers,
    exceptionFnMap: _exceptionFns,
  );
  final $elem = await _s.xmlFromResponse($result);
  return HeadBucketOutput(
    accessPointAlias: _s.extractHeaderBoolValue(
        $result.headers, 'x-amz-access-point-alias'),
    bucketArn:
        _s.extractHeaderStringValue($result.headers, 'x-amz-bucket-arn'),
    bucketLocationName: _s.extractHeaderStringValue(
        $result.headers, 'x-amz-bucket-location-name'),
    bucketLocationType: _s
        .extractHeaderStringValue(
            $result.headers, 'x-amz-bucket-location-type')
        ?.let(LocationType.fromString),
    bucketRegion:
        _s.extractHeaderStringValue($result.headers, 'x-amz-bucket-region'),
  );
}