S3 / Client / head_object

head_object#

S3.Client.head_object(**kwargs)#

The HEAD action retrieves metadata from an object without returning the object itself. This action is useful if you’re only interested in an object’s metadata. To use HEAD, you must have READ access to the object.

A HEAD request has the same options as a GET action 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 400 Bad Request, 403 Forbidden or 404 Not Found code. It is not possible to retrieve the exact exception beyond these error codes.

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:

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).

Note

Encryption request headers, like x-amz-server-side-encryption, should not be sent for GET requests if your object uses server-side encryption with KMS keys (SSE-KMS) or server-side encryption with Amazon S3–managed encryption keys (SSE-S3). If your object does use these types of keys, you’ll get an HTTP 400 BadRequest error.
The last modified property in this case is the creation date of the object.

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

Consider the following when using request headers:

Consideration 1 – 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.

Consideration 2 – 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.

Permissions

You need the relevant read object (or version) permission for this operation. For more information, see Specifying Permissions in a Policy. If the object you request does not exist, the error 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 (“no such key”) error.
If you don’t have the s3:ListBucket permission, Amazon S3 returns an HTTP status code 403 (“access denied”) error.

The following actions are related to HeadObject:

See also: AWS API Documentation

Request Syntax

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

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 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 (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.
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) – Confirms that the requester knows that they will be charged for the request. Bucket owners need not specify this parameter in their requests. For information about downloading objects from Requester Pays buckets, see Downloading Objects in Requester Pays Buckets in the Amazon S3 User Guide.
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) – The account ID of the expected bucket owner. If the bucket is owned by a different account, the request fails with the HTTP status code 403 Forbidden (access denied).
ChecksumMode (string) –
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.

Return type:

dict

Returns:

Response Syntax

{
    'DeleteMarker': True|False,
    'AcceptRanges': 'string',
    'Expiration': 'string',
    'Restore': 'string',
    'ArchiveStatus': 'ARCHIVE_ACCESS'|'DEEP_ARCHIVE_ACCESS',
    'LastModified': datetime(2015, 1, 1),
    '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': datetime(2015, 1, 1),
    'WebsiteRedirectLocation': 'string',
    'ServerSideEncryption': 'AES256'|'aws:kms',
    'Metadata': {
        'string': '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',
    'RequestCharged': 'requester',
    'ReplicationStatus': 'COMPLETE'|'PENDING'|'FAILED'|'REPLICA',
    'PartsCount': 123,
    'ObjectLockMode': 'GOVERNANCE'|'COMPLIANCE',
    'ObjectLockRetainUntilDate': datetime(2015, 1, 1),
    'ObjectLockLegalHoldStatus': 'ON'|'OFF'
}

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.
- ArchiveStatus (string) –
  
  The archive state of the head object.
- LastModified (datetime) –
  
  Creation date of the object.
- ContentLength (integer) –
  
  Size of the body in bytes.
- ChecksumCRC32 (string) –
  
  The base64-encoded, 32-bit CRC32 checksum of the object. This will only be present if it was uploaded with the object. With multipart uploads, this may not be a checksum value of the object. For more information about how checksums are calculated with multipart uploads, see Checking object integrity in the Amazon S3 User Guide.
- ChecksumCRC32C (string) –
  
  The base64-encoded, 32-bit CRC32C checksum of the object. This will only be present if it was uploaded with the object. With multipart uploads, this may not be a checksum value of the object. For more information about how checksums are calculated with multipart uploads, see Checking object integrity in the Amazon S3 User Guide.
- ChecksumSHA1 (string) –
  
  The base64-encoded, 160-bit SHA-1 digest of the object. This will only be present if it was uploaded with the object. With multipart uploads, this may not be a checksum value of the object. For more information about how checksums are calculated with multipart uploads, see Checking object integrity in the Amazon S3 User Guide.
- ChecksumSHA256 (string) –
  
  The base64-encoded, 256-bit SHA-256 digest of the object. This will only be present if it was uploaded with the object. With multipart uploads, this may not be a checksum value of the object. For more information about how checksums are calculated with multipart uploads, see Checking object integrity in the Amazon S3 User Guide.
- 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) –
  
  Specifies 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 storing this object in Amazon S3 (for example, AES256, aws:kms).
- Metadata (dict) –
  
  A map of metadata to store with the object in S3.
  - (string) –
    - (string) –
- 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 encryption customer managed key that was used for the object.
- BucketKeyEnabled (boolean) –
  
  Indicates whether the object uses an S3 Bucket Key for server-side encryption with Amazon Web Services KMS (SSE-KMS).
- 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.

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': {
        '...': '...',
    },
}