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.
Permissions¶
-
General purpose bucket permissions - To use
HEAD
, you must have thes3: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. For more information about the permissions to S3 API operations by S3 resource types, see Required permissions for Amazon S3 API operations 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 code404 Not Found
error. -
If you don’t have the
s3:ListBucket
permission, Amazon S3 returns an HTTP status code403 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 thes3express:CreateSession
permission to the directory bucket in a bucket policy or an IAM identity-based policy. Then, you make thecreate_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 anothercreate_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, seecreate_session
.If you enable
x-amz-checksum-mode
in the request and the object is encrypted with Amazon Web Services Key Management Service (Amazon Web Services KMS), you must also have thekms:GenerateDataKey
andkms:Decrypt
permissions in IAM identity-based policies and KMS key policies for the KMS key to retrieve the checksum of the object.
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 - For directory buckets, there are only two supported options for server-side encryption: SSE-S3 and SSE-KMS. SSE-C isn't supported. For more information, see Protecting data with server-side encryption in the Amazon S3 User Guide.
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 theLast-Modified: timestamp
response header. -
Directory buckets - Delete marker is not supported for 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 specifynull
to theversionId
query parameter in the request.
HTTP Host header syntax¶
Directory buckets - The HTTP Host header syntax is
Bucket-name.s3express-zone-id.region-code.amazonaws.com
.
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://amzn-s3-demo-bucket.s3express-zone-id.region-code.amazonaws.com/key-name
.
Path-style requests are not supported. For more information about
endpoints in Availability Zones, see Regional and Zonal endpoints for
directory buckets in Availability
Zones
in the Amazon S3 User Guide. For more information about endpoints in
Local Zones, see Concepts for directory buckets in Local
Zones
in the Amazon S3 User Guide.
The following actions are related to head_object
:
-
get_object
-
get_object_attributes
Usage¶
s3_head_object(Bucket, IfMatch, IfModifiedSince, IfNoneMatch,
IfUnmodifiedSince, Key, Range, ResponseCacheControl,
ResponseContentDisposition, ResponseContentEncoding,
ResponseContentLanguage, ResponseContentType, ResponseExpires,
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
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 S3 on
Outposts, you must direct requests to the S3 on Outposts hostname. The
S3 on Outposts hostname takes the form
|
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
Then Amazon S3 returns 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
Then Amazon S3 returns the 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
Then Amazon S3 returns the 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
Then Amazon S3 returns 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 |
ResponseCacheControl |
Sets the |
ResponseContentDisposition |
Sets the |
ResponseContentEncoding |
Sets the |
ResponseContentLanguage |
Sets the |
ResponseContentType |
Sets the |
ResponseExpires |
Sets the |
VersionId |
Version ID used to reference a specific version of the object. For directory buckets in this API operation, only the
|
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
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 |
ChecksumMode |
To retrieve the checksum, this parameter must be enabled. General purpose buckets - If you enable checksum
mode and the object is uploaded with a checksum
and encrypted with an Key Management Service (KMS) key, you must have
permission to use the Directory buckets - If you enable
|
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",
ChecksumCRC64NVME = "string",
ChecksumSHA1 = "string",
ChecksumSHA256 = "string",
ChecksumType = "COMPOSITE"|"FULL_OBJECT",
ETag = "string",
MissingMeta = 123,
VersionId = "string",
CacheControl = "string",
ContentDisposition = "string",
ContentEncoding = "string",
ContentLanguage = "string",
ContentType = "string",
ContentRange = "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$head_object(
Bucket = "string",
IfMatch = "string",
IfModifiedSince = as.POSIXct(
"2015-01-01"
),
IfNoneMatch = "string",
IfUnmodifiedSince = as.POSIXct(
"2015-01-01"
),
Key = "string",
Range = "string",
ResponseCacheControl = "string",
ResponseContentDisposition = "string",
ResponseContentEncoding = "string",
ResponseContentLanguage = "string",
ResponseContentType = "string",
ResponseExpires = as.POSIXct(
"2015-01-01"
),
VersionId = "string",
SSECustomerAlgorithm = "string",
SSECustomerKey = "string",
SSECustomerKeyMD5 = "string",
RequestPayer = "requester",
PartNumber = 123,
ExpectedBucketOwner = "string",
ChecksumMode = "ENABLED"
)
Examples¶
## Not run:
# The following example retrieves an object metadata.
svc$head_object(
Bucket = "examplebucket",
Key = "HappyFace.jpg"
)
## End(Not run)