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.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
.
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 theLast-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 specifynull
to theversionId
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
.
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.
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
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 formatbucket_base_name--az-id--x-s3
(for example,DOC-EXAMPLE-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, 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
andIf-Unmodified-Since
headers are present in the request as follows:If-Match
condition evaluates totrue
, and;If-Unmodified-Since
condition evaluates tofalse
;
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
andIf-Modified-Since
headers are present in the request as follows:If-None-Match
condition evaluates tofalse
, and;If-Modified-Since
condition evaluates totrue
;
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
andIf-Modified-Since
headers are present in the request as follows:If-None-Match
condition evaluates tofalse
, and;If-Modified-Since
condition evaluates totrue
;
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
andIf-Unmodified-Since
headers are present in the request as follows:If-Match
condition evaluates totrue
, and;If-Unmodified-Since
condition evaluates tofalse
;
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 a416 - Requested Range Not Satisfiable
error.ResponseCacheControl
Sets the
Cache-Control
header of the response.ResponseContentDisposition
Sets the
Content-Disposition
header of the response.ResponseContentEncoding
Sets the
Content-Encoding
header of the response.ResponseContentLanguage
Sets the
Content-Language
header of the response.ResponseContentType
Sets the
Content-Type
header of the response.ResponseExpires
Sets the
Expires
header of the response.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 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
kms:Decrypt
action to retrieve the checksum.
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"
),
ExpiresString = "string",
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$head_object(
Bucket = "string",
IfMatch = "string",
IfModifiedSince = as.POSIXct(
"2015-01-01"
),
IfNoneMatch = "string",
IfUnmodifiedSince = as.POSIXct(
"2015-01-01"
),
Key = "string",
Range = "string",
ResponseCacheControl = "string",
ResponseContentDisposition = "string",
ResponseContentEncoding = "string",
ResponseContentLanguage = "string",
ResponseContentType = "string",
ResponseExpires = as.POSIXct(
"2015-01-01"
),
VersionId = "string",
SSECustomerAlgorithm = "string",
SSECustomerKey = raw,
SSECustomerKeyMD5 = "string",
RequestPayer = "requester",
PartNumber = 123,
ExpectedBucketOwner = "string",
ChecksumMode = "ENABLED"
)
Examples¶
## Not run:
# The following example retrieves an object metadata.
svc$head_object(
Bucket = "examplebucket",
Key = "HappyFace.jpg"
)
## End(Not run)