S3 / Client / head_object

head_object#

S3.Client.head_object(**kwargs)#

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.

Note

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 CreateSession 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 CreateSession 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 CreateSession 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 CreateSession.

Encryption

Note

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.

Note

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.

Note

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 HeadObject:

Request Syntax

response = client.head_object(
    Bucket='string',
    IfMatch='string',
    IfModifiedSince=datetime(2015, 1, 1),
    IfNoneMatch='string',
    IfUnmodifiedSince=datetime(2015, 1, 1),
    Key='string',
    MirrorDestination='string',
    Range='string',
    VersionId='string',
    SSECustomerAlgorithm='string',
    SSECustomerKey='string',
    RequestPayer='requester',
    PartNumber=123,
    ExpectedBucketOwner='string'
)

Parameters:

Bucket (string) –
[REQUIRED]

The name of the bucket containing the object.

When using this action with an access point, 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.

When using 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 using this action with S3 on Outposts through the Amazon Web Services SDKs, you provide the Outposts bucket ARN in place of the bucket name. For more information about S3 on Outposts ARNs, see Using Amazon S3 on Outposts in the Amazon S3 User Guide.
IfMatch (string) – Return the object only if its entity tag (ETag) is the same as the one specified; otherwise, return a 412 (precondition failed) error.
IfModifiedSince (datetime) – Return the object only if it has been modified since the specified time; otherwise, return a 304 (not modified) error.
IfNoneMatch (string) – Return the object only if its entity tag (ETag) is different from the one specified; otherwise, return a 304 (not modified) error.
IfUnmodifiedSince (datetime) – Return the object only if it has not been modified since the specified time; otherwise, return a 412 (precondition failed) error.
Key (string) –
[REQUIRED]

The object key.
MirrorDestination (string) – Mirror source for object reads.
Range (string) – 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 (string) – VersionId used to reference a specific version of the object.
SSECustomerAlgorithm (string) – Specifies the algorithm to use to when encrypting the object (for example, AES256).
SSECustomerKey (string) – 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.
SSECustomerKeyMD5 (string) –
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.

Please note that this parameter is automatically populated if it is not provided. Including this parameter is not required
RequestPayer (string) – Ignored by COS if present.
PartNumber (integer) – 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 (string) – Ignored by COS if present.

Return type:

dict

Returns:

Response Syntax

{
    'DeleteMarker': True|False,
    'AcceptRanges': 'string',
    'Expiration': 'string',
    'Restore': 'string',
    'LastModified': datetime(2015, 1, 1),
    'ContentLength': 123,
    'ETag': 'string',
    'MissingMeta': 123,
    'VersionId': 'string',
    'CacheControl': 'string',
    'ContentDisposition': 'string',
    'ContentEncoding': 'string',
    'ContentLanguage': 'string',
    'ContentType': 'string',
    'Expires': datetime(2015, 1, 1),
    'WebsiteRedirectLocation': 'string',
    'ServerSideEncryption': 'AES256',
    'Metadata': {
        'string': 'string'
    },
    'RetentionExpirationDate': datetime(2015, 1, 1),
    'RetentionLegalHoldCount': 123,
    'RetentionPeriod': 123,
    'SSECustomerAlgorithm': 'string',
    'SSECustomerKeyMD5': 'string',
    'SSEKMSKeyId': 'string',
    'StorageClass': 'ACCELERATED'|'STANDARD'|'REDUCED_REDUNDANCY'|'STANDARD_IA'|'ONEZONE_IA'|'INTELLIGENT_TIERING'|'GLACIER'|'DEEP_ARCHIVE'|'OUTPOSTS'|'GLACIER_IR',
    'RequestCharged': 'requester',
    'ReplicationStatus': 'COMPLETE'|'PENDING'|'FAILED'|'REPLICA',
    'PartsCount': 123,
    'ObjectLockMode': 'GOVERNANCE'|'COMPLIANCE',
    'ObjectLockRetainUntilDate': datetime(2015, 1, 1),
    'ObjectLockLegalHoldStatus': 'ON'|'OFF',
    'IbmRestoredCopyStorageClass': 'ACCELERATED'|'STANDARD'|'REDUCED_REDUNDANCY'|'STANDARD_IA'|'ONEZONE_IA'|'INTELLIGENT_TIERING'|'GLACIER'|'DEEP_ARCHIVE'|'OUTPOSTS'|'GLACIER_IR',
    'IbmTransition': 'string'
}

Response Structure

(dict) –
- DeleteMarker (boolean) –
  
  Specifies whether the object retrieved was (true) or was not (false) a Delete Marker. If false, this response header does not appear in the response.
- AcceptRanges (string) –
  
  Indicates that a range of bytes was specified.
- Expiration (string) –
  
  If the object expiration is configured (see PUT Bucket lifecycle), the response includes this header. It includes the expiry-date and rule-id key-value pairs providing object expiration information. The value of the rule-id is URL-encoded.
- Restore (string) –
  
  If the object is an archived object (an object whose storage class is GLACIER), the response includes this header if either the archive restoration is in progress (see RestoreObject or an archive copy is already restored.
  
  If an archive copy is already restored, the header value indicates when Amazon S3 is scheduled to delete the object copy. For example:
  
  x-amz-restore: ongoing-request="false", expiry-date="Fri, 21 Dec 2012 00:00:00 GMT"
  
  If the object restoration is in progress, the header returns the value ongoing-request="true".
  
  For more information about archiving objects, see Transitioning Objects: General Considerations.
- LastModified (datetime) –
  
  Date and time when the object was last modified.
- ContentLength (integer) –
  
  Size of the body in bytes.
- ETag (string) –
  
  An entity tag (ETag) is an opaque identifier assigned by a web server to a specific version of a resource found at a URL.
- MissingMeta (integer) –
  
  This is set to the number of metadata entries not returned in x-amz-meta headers. This can happen if you create metadata using an API like SOAP that supports more flexible metadata than the REST API. For example, using SOAP, you can create metadata whose values are not legal HTTP headers.
- VersionId (string) –
  
  Version of the object.
- CacheControl (string) –
  
  Specifies caching behavior along the request/reply chain.
- ContentDisposition (string) –
  
  Specifies presentational information for the object.
- ContentEncoding (string) –
  
  Indicates what content encodings have been applied to the object and thus what decoding mechanisms must be applied to obtain the media-type referenced by the Content-Type header field.
- ContentLanguage (string) –
  
  The language the content is in.
- ContentType (string) –
  
  A standard MIME type describing the format of the object data.
- Expires (datetime) –
  
  The date and time at which the object is no longer cacheable.
- WebsiteRedirectLocation (string) –
  
  If the bucket is configured as a website, redirects requests for this object to another object in the same bucket or to an external URL. Amazon S3 stores the value of this header in the object metadata.
- ServerSideEncryption (string) –
  
  The server-side encryption algorithm used when you store this object in Amazon S3 (for example, AES256, aws:kms, aws:kms:dsse).
  
  Note
  For directory buckets, only server-side encryption with Amazon S3 managed keys (SSE-S3) ( AES256) is supported.
- Metadata (dict) –
  
  A map of metadata to store with the object in S3.
  - (string) –
    - (string) –
- RetentionExpirationDate (datetime) – Date on which it will be legal to delete or modify the object. You can only specify this or the Retention-Period header. If both are specified a 400 error will be returned. If neither is specified the bucket’s DefaultRetention period will be used.
- RetentionLegalHoldCount (integer) – Returns the count of legal holds on the object. If there are no legal holds, the header is not returned
- RetentionPeriod (integer) – Retention period to store on the object in seconds. If this field and Retention-Expiration-Date are specified a 400 error is returned. If neither is specified the bucket’s DefaultRetention period will be used. 0 is a legal value assuming the bucket’s minimum retention period is also 0.
- SSECustomerAlgorithm (string) –
  
  If server-side encryption with a customer-provided encryption key was requested, the response will include this header confirming the encryption algorithm used.
- SSECustomerKeyMD5 (string) –
  
  If server-side encryption with a customer-provided encryption key was requested, the response will include this header to provide round-trip message integrity verification of the customer-provided encryption key.
- SSEKMSKeyId (string) –
  
  If present, specifies the ID of the Amazon Web Services Key Management Service (Amazon Web Services KMS) symmetric customer managed key that was used for the object.
- StorageClass (string) –
  
  Provides storage class information of the object. Amazon S3 returns this header for all objects except for S3 Standard storage class objects.
  
  For more information, see Storage Classes.
- RequestCharged (string) –
  
  If present, indicates that the requester was successfully charged for the request.
- ReplicationStatus (string) –
  
  Amazon S3 can return this header if your request involves a bucket that is either a source or a destination in a replication rule.
  
  In replication, you have a source bucket on which you configure replication and destination bucket or buckets where Amazon S3 stores object replicas. When you request an object ( GetObject) or object metadata ( HeadObject) from these buckets, Amazon S3 will return the x-amz-replication-status header in the response as follows:
  - If requesting an object from the source bucket, Amazon S3 will return the x-amz-replication-status header if the object in your request is eligible for replication. For example, suppose that in your replication configuration, you specify object prefix TaxDocs requesting Amazon S3 to replicate objects with key prefix TaxDocs. Any objects you upload with this key name prefix, for example TaxDocs/document1.pdf, are eligible for replication. For any object request with this key name prefix, Amazon S3 will return the x-amz-replication-status header with value PENDING, COMPLETED or FAILED indicating object replication status.
  - If requesting an object from a destination bucket, Amazon S3 will return the x-amz-replication-status header with value REPLICA if the object in your request is a replica that Amazon S3 created and there is no replica modification replication in progress.
  - When replicating objects to multiple destination buckets, the x-amz-replication-status header acts differently. The header of the source object will only return a value of COMPLETED when replication is successful to all destinations. The header will remain at value PENDING until replication has completed for all destinations. If one or more destinations fails replication the header will return FAILED.
  For more information, see Replication.
- PartsCount (integer) –
  
  The count of parts this object has. This value is only returned if you specify partNumber in your request and the object was uploaded as a multipart upload.
- ObjectLockMode (string) –
  
  The Object Lock mode, if any, that’s in effect for this object. This header is only returned if the requester has the s3:GetObjectRetention permission. For more information about S3 Object Lock, see Object Lock.
- ObjectLockRetainUntilDate (datetime) –
  
  The date and time when the Object Lock retention period expires. This header is only returned if the requester has the s3:GetObjectRetention permission.
- ObjectLockLegalHoldStatus (string) –
  
  Specifies whether a legal hold is in effect for this object. This header is only returned if the requester has the s3:GetObjectLegalHold permission. This header is not returned if the specified version of this object has never had a legal hold applied. For more information about S3 Object Lock, see Object Lock.
- IbmRestoredCopyStorageClass (string) – This header is only included if an object has transition metadata. This header will indicate the transition storage class and time of transition. If this header and the x-amz-restore header are both included, this header will indicate the time at which the object was originally archived.
- IbmTransition (string) – This header is only included if an object has transition metadata. This header will indicate the transition storage class and time of transition. If this header and the x-amz-restore header are both included, this header will indicate the time at which the object was originally archived.

Exceptions

S3.Client.exceptions.NoSuchKey

Examples

The following example retrieves an object metadata.

response = client.head_object(
    Bucket='examplebucket',
    Key='HappyFace.jpg',
)

print(response)

Expected Output:

{
    'AcceptRanges': 'bytes',
    'ContentLength': '3191',
    'ContentType': 'image/jpeg',
    'ETag': '"6805f2cfc46c0f04559748bb039d69ae"',
    'LastModified': datetime(2016, 12, 15, 1, 19, 41, 3, 350, 0),
    'Metadata': {
    },
    'VersionId': 'null',
    'ResponseMetadata': {
        '...': '...',
    },
}