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Head Object

s3_head_object R Documentation

The HEAD operation retrieves metadata from an object without returning the object itself

Description

The HEAD operation retrieves metadata from an object without returning the object itself. This operation is useful if you're interested only in an object's metadata.

A HEAD request has the same options as a GET operation on an object. The response is identical to the GET response except that there is no response body. Because of this, if the HEAD request generates an error, it returns a generic code, such as ⁠400 Bad Request⁠, ⁠403 Forbidden⁠, ⁠404 Not Found⁠, ⁠405 Method Not Allowed⁠, ⁠412 Precondition Failed⁠, or ⁠304 Not Modified⁠. It's not possible to retrieve the exact exception of these error codes.

Request headers are limited to 8 KB in size. For more information, see Common Request Headers.

Directory buckets - For directory buckets, you must make requests for this API operation to the Zonal endpoint. These endpoints support virtual-hosted-style requests in the format ⁠https://bucket_name.s3express-az_id.region.amazonaws.com/key-name ⁠. Path-style requests are not supported. For more information, see Regional and Zonal endpoints in the Amazon S3 User Guide.

Permissions

  • General purpose bucket permissions - To use HEAD, you must have the s3:GetObject permission. You need the relevant read object (or version) permission for this operation. For more information, see Actions, resources, and condition keys for Amazon S3 in the Amazon S3 User Guide.

    If the object you request doesn't exist, the error that Amazon S3 returns depends on whether you also have the s3:ListBucket permission.

    • If you have the s3:ListBucket permission on the bucket, Amazon S3 returns an HTTP status code ⁠404 Not Found⁠ error.

    • If you don’t have the s3:ListBucket permission, Amazon S3 returns an HTTP status code ⁠403 Forbidden⁠ error.

  • Directory bucket permissions - To grant access to this API operation on a directory bucket, we recommend that you use the create_session API operation for session-based authorization. Specifically, you grant the s3express:CreateSession permission to the directory bucket in a bucket policy or an IAM identity-based policy. Then, you make the create_session API call on the bucket to obtain a session token. With the session token in your request header, you can make API requests to this operation. After the session token expires, you make another create_session API call to generate a new session token for use. Amazon Web Services CLI or SDKs create session and refresh the session token automatically to avoid service interruptions when a session expires. For more information about authorization, see create_session .

Encryption

Encryption request headers, like x-amz-server-side-encryption, should not be sent for HEAD requests if your object uses server-side encryption with Key Management Service (KMS) keys (SSE-KMS), dual-layer server-side encryption with Amazon Web Services KMS keys (DSSE-KMS), or server-side encryption with Amazon S3 managed encryption keys (SSE-S3). The x-amz-server-side-encryption header is used when you PUT an object to S3 and want to specify the encryption method. If you include this header in a HEAD request for an object that uses these types of keys, you’ll get an HTTP ⁠400 Bad Request⁠ error. It's because the encryption method can't be changed when you retrieve the object.

If you encrypt an object by using server-side encryption with customer-provided encryption keys (SSE-C) when you store the object in Amazon S3, then when you retrieve the metadata from the object, you must use the following headers to provide the encryption key for the server to be able to retrieve the object's metadata. The headers are:

  • x-amz-server-side-encryption-customer-algorithm

  • x-amz-server-side-encryption-customer-key

  • x-amz-server-side-encryption-customer-key-MD5

For more information about SSE-C, see Server-Side Encryption (Using Customer-Provided Encryption Keys) in the Amazon S3 User Guide.

Directory bucket permissions - For directory buckets, only server-side encryption with Amazon S3 managed keys (SSE-S3) (AES256) is supported.

Versioning

  • If the current version of the object is a delete marker, Amazon S3 behaves as if the object was deleted and includes x-amz-delete-marker: true in the response.

  • If the specified version is a delete marker, the response returns a ⁠405 Method Not Allowed⁠ error and the Last-Modified: timestamp response header.

  • Directory buckets - Delete marker is not supported by directory buckets.

  • Directory buckets - S3 Versioning isn't enabled and supported for directory buckets. For this API operation, only the null value of the version ID is supported by directory buckets. You can only specify null to the versionId query parameter in the request.

HTTP Host header syntax

Directory buckets - The HTTP Host header syntax is Bucket_name.s3express-az_id.region.amazonaws.com.

The following actions are related to head_object:

  • get_object

  • get_object_attributes

Usage

s3_head_object(Bucket, IfMatch, IfModifiedSince, IfNoneMatch,
  IfUnmodifiedSince, Key, Range, VersionId, SSECustomerAlgorithm,
  SSECustomerKey, SSECustomerKeyMD5, RequestPayer, PartNumber,
  ExpectedBucketOwner, ChecksumMode)

Arguments

Bucket

[required] The name of the bucket that contains the object.

Directory buckets - When you use this operation with a directory bucket, you must use virtual-hosted-style requests in the format Bucket_name.s3express-az_id.region.amazonaws.com. Path-style requests are not supported. Directory bucket names must be unique in the chosen Availability Zone. Bucket names must follow the format bucket_base_name--az-id--x-s3 (for example, DOC-EXAMPLE-BUCKET--usw2-az2--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, you must provide the alias of the access point in place of the bucket name or specify the access point ARN. 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.

Access points and Object Lambda access points are not supported by directory buckets.

S3 on Outposts - When you use this action with Amazon 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 through the Amazon Web Services SDKs, you provide the Outposts access point ARN in place of the bucket name. For more information about S3 on Outposts ARNs, see What is S3 on Outposts? in the Amazon S3 User Guide.

IfMatch

Return the object only if its entity tag (ETag) is the same as the one specified; otherwise, return a 412 (precondition failed) error.

If both of the If-Match and If-Unmodified-Since headers are present in the request as follows:

  • If-Match condition evaluates to true, and;

  • If-Unmodified-Since condition evaluates to false;

Then Amazon S3 returns ⁠200 OK⁠ and the data requested.

For more information about conditional requests, see RFC 7232.

IfModifiedSince

Return the object only if it has been modified since the specified time; otherwise, return a 304 (not modified) error.

If both of the If-None-Match and If-Modified-Since headers are present in the request as follows:

  • If-None-Match condition evaluates to false, and;

  • If-Modified-Since condition evaluates to true;

Then Amazon S3 returns the ⁠304 Not Modified⁠ response code.

For more information about conditional requests, see RFC 7232.

IfNoneMatch

Return the object only if its entity tag (ETag) is different from the one specified; otherwise, return a 304 (not modified) error.

If both of the If-None-Match and If-Modified-Since headers are present in the request as follows:

  • If-None-Match condition evaluates to false, and;

  • If-Modified-Since condition evaluates to true;

Then Amazon S3 returns the ⁠304 Not Modified⁠ response code.

For more information about conditional requests, see RFC 7232.

IfUnmodifiedSince

Return the object only if it has not been modified since the specified time; otherwise, return a 412 (precondition failed) error.

If both of the If-Match and If-Unmodified-Since headers are present in the request as follows:

  • If-Match condition evaluates to true, and;

  • If-Unmodified-Since condition evaluates to false;

Then Amazon S3 returns ⁠200 OK⁠ and the data requested.

For more information about conditional requests, see RFC 7232.

Key

[required] The object key.

Range

HeadObject returns only the metadata for an object. If the Range is satisfiable, only the ContentLength is affected in the response. If the Range is not satisfiable, S3 returns a ⁠416 - Requested Range Not Satisfiable⁠ error.

VersionId

Version ID used to reference a specific version of the object.

For directory buckets in this API operation, only the null value of the version ID is supported.

SSECustomerAlgorithm

Specifies the algorithm to use when encrypting the object (for example, AES256).

This functionality is not supported for directory buckets.

SSECustomerKey

Specifies the customer-provided encryption key for Amazon S3 to use in encrypting data. This value is used to store the object and then it is discarded; Amazon S3 does not store the encryption key. The key must be appropriate for use with the algorithm specified in the x-amz-server-side-encryption-customer-algorithm header.

This functionality is not supported for directory buckets.

SSECustomerKeyMD5

Specifies the 128-bit MD5 digest of the encryption key according to RFC 1321. Amazon S3 uses this header for a message integrity check to ensure that the encryption key was transmitted without error.

This functionality is not supported for directory buckets.

RequestPayer
PartNumber

Part number of the object being read. This is a positive integer between 1 and 10,000. Effectively performs a 'ranged' HEAD request for the part specified. Useful querying about the size of the part and the number of parts in this object.

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).

ChecksumMode

To retrieve the checksum, this parameter must be enabled.

In addition, if you enable ChecksumMode and the object is encrypted with Amazon Web Services Key Management Service (Amazon Web Services KMS), you must have permission to use the kms:Decrypt action for the request to succeed.

Value

A list with the following syntax: 

list(
  DeleteMarker = TRUE|FALSE,
  AcceptRanges = "string",
  Expiration = "string",
  Restore = "string",
  ArchiveStatus = "ARCHIVE_ACCESS"|"DEEP_ARCHIVE_ACCESS",
  LastModified = as.POSIXct(
    "2015-01-01"
  ),
  ContentLength = 123,
  ChecksumCRC32 = "string",
  ChecksumCRC32C = "string",
  ChecksumSHA1 = "string",
  ChecksumSHA256 = "string",
  ETag = "string",
  MissingMeta = 123,
  VersionId = "string",
  CacheControl = "string",
  ContentDisposition = "string",
  ContentEncoding = "string",
  ContentLanguage = "string",
  ContentType = "string",
  Expires = as.POSIXct(
    "2015-01-01"
  ),
  WebsiteRedirectLocation = "string",
  ServerSideEncryption = "AES256"|"aws:kms"|"aws:kms:dsse",
  Metadata = list(
    "string"
  ),
  SSECustomerAlgorithm = "string",
  SSECustomerKeyMD5 = "string",
  SSEKMSKeyId = "string",
  BucketKeyEnabled = TRUE|FALSE,
  StorageClass = "STANDARD"|"REDUCED_REDUNDANCY"|"STANDARD_IA"|"ONEZONE_IA"|"INTELLIGENT_TIERING"|"GLACIER"|"DEEP_ARCHIVE"|"OUTPOSTS"|"GLACIER_IR"|"SNOW"|"EXPRESS_ONEZONE",
  RequestCharged = "requester",
  ReplicationStatus = "COMPLETE"|"PENDING"|"FAILED"|"REPLICA"|"COMPLETED",
  PartsCount = 123,
  ObjectLockMode = "GOVERNANCE"|"COMPLIANCE",
  ObjectLockRetainUntilDate = as.POSIXct(
    "2015-01-01"
  ),
  ObjectLockLegalHoldStatus = "ON"|"OFF"
)

Request syntax

svc$head_object(
  Bucket = "string",
  IfMatch = "string",
  IfModifiedSince = as.POSIXct(
    "2015-01-01"
  ),
  IfNoneMatch = "string",
  IfUnmodifiedSince = as.POSIXct(
    "2015-01-01"
  ),
  Key = "string",
  Range = "string",
  VersionId = "string",
  SSECustomerAlgorithm = "string",
  SSECustomerKey = raw,
  SSECustomerKeyMD5 = "string",
  RequestPayer = "requester",
  PartNumber = 123,
  ExpectedBucketOwner = "string",
  ChecksumMode = "ENABLED"
)

Examples

## Not run: 
# The following example retrieves an object metadata.
svc$head_object(
  Bucket = "examplebucket",
  Key = "HappyFace.jpg"
)

## End(Not run)