Object Storage - How to retrieve object metadata with GetObjectAttributes

Objective

This guide explains how to use the GetObjectAttributes S3¹ API operation to retrieve metadata attributes from objects in your OVHcloud Object Storage buckets without downloading the object body.

Requirements

• A Public Cloud project in your OVHcloud account
• An Object Storage user already created
• AWS CLI installed and configured

Instructions

Why use GetObjectAttributes?

Inspecting an object's metadata traditionally requires at least 2 separate API calls: HeadObject to retrieve the ETag, size, and storage class, and ListParts to enumerate the parts of multipart objects. Each additional call adds latency, which becomes significant at scale in data pipelines, integrity verification workflows, or storage auditing systems.

GetObjectAttributes consolidates all attribute retrieval into a single selective API call. You request exactly the attributes you need; the service returns only those fields — no object body is transferred.

Key benefits:

• No body transfer: retrieve metadata only, regardless of object size.
• Selective response: receive only the attributes you request.
• Any S3-compatible client: works with AWS CLI, any S3 SDK, and direct HTTP calls.

Supported attributes

You select which attributes to retrieve by listing them in the x-amz-object-attributes request header (space-separated for AWS CLI, comma-separated for raw HTTP). Attributes not listed are absent from the response.

The Last-Modified response header is always returned regardless of which attributes are requested.

Retrieve object attributes

# Retrieve ETag and size
aws s3api get-object-attributes \
  --bucket <bucket_name> \
  --key <object_key> \
  --object-attributes ETag ObjectSize

{
    "LastModified": "2026-04-15T10:23:45+00:00",
    "ETag": "d41d8cd98f00b204e9800998ecf8427e",
    "ObjectSize": 1048576
}

aws s3api get-object-attributes \
  --bucket <bucket_name> \
  --key <object_key> \
  --object-attributes ETag Checksum ObjectParts StorageClass ObjectSize

curl -X GET \
  -H "x-amz-object-attributes: ETag,ObjectSize" \
  --aws-sigv4 "aws:amz:<region>:s3" \
  --user "<access_key>:<secret_key>" \
  "https://s3.<region>.io.cloud.ovh.net/<bucket_name>/<object_key>?attributes"

Checksum attribute

When Checksum is requested, the response includes the algorithm and value stored with the object at upload time. If the object was uploaded without a checksum, the Checksum element is absent from the response — this is not an error.

Supported checksum algorithms on OVHcloud Object Storage:

aws s3api get-object-attributes \
  --bucket <bucket_name> \
  --key <object_key> \
  --object-attributes Checksum

{
    "LastModified": "2026-04-15T10:23:45+00:00",
    "Checksum": {
        "ChecksumCRC32": "aGVsbG8="
    }
}

{
    "LastModified": "2026-04-15T10:23:45+00:00"
}

curl -X GET \
  -H "x-amz-object-attributes: Checksum" \
  --aws-sigv4 "aws:amz:<region>:s3" \
  --user "<access_key>:<secret_key>" \
  "https://s3.<region>.io.cloud.ovh.net/<bucket_name>/<object_key>?attributes"

ObjectParts attribute (multipart objects)

When ObjectParts is requested on a multipart object, the response lists all parts with their number, size, and optional checksum. For single-part (non-multipart) objects, ObjectParts is returned as an empty element.

Pagination: results are paginated at up to 1000 parts per response.

# List all parts (default: up to 1000)
aws s3api get-object-attributes \
  --bucket <bucket_name> \
  --key <object_key> \
  --object-attributes ObjectParts

{
    "LastModified": "2026-04-20T08:10:00+00:00",
    "ObjectParts": {
        "TotalPartsCount": 3,
        "MaxParts": 1000,
        "IsTruncated": false,
        "Parts": [
            { "PartNumber": 1, "Size": 5242880 },
            { "PartNumber": 2, "Size": 5242880 },
            { "PartNumber": 3, "Size": 1048576 }
        ]
    }
}

curl -X GET \
  -H "x-amz-object-attributes: ObjectParts" \
  --aws-sigv4 "aws:amz:<region>:s3" \
  --user "<access_key>:<secret_key>" \
  "https://s3.<region>.io.cloud.ovh.net/<bucket_name>/<object_key>?attributes"

# First page
aws s3api get-object-attributes \
  --bucket <bucket_name> \
  --key <object_key> \
  --object-attributes ObjectParts \
  --max-parts 1000

# Next page - use NextPartNumberMarker from the previous response
aws s3api get-object-attributes \
  --bucket <bucket_name> \
  --key <object_key> \
  --object-attributes ObjectParts \
  --max-parts 1000 \
  --part-number-marker <next_part_number_marker>

# First page
curl -X GET \
  -H "x-amz-object-attributes: ObjectParts" \
  -H "x-amz-max-parts: 1000" \
  --aws-sigv4 "aws:amz:<region>:s3" \
  --user "<access_key>:<secret_key>" \
  "https://s3.<region>.io.cloud.ovh.net/<bucket_name>/<object_key>?attributes"

# Next page
curl -X GET \
  -H "x-amz-object-attributes: ObjectParts" \
  -H "x-amz-max-parts: 1000" \
  -H "x-amz-part-number-marker: <next_part_number_marker>" \
  --aws-sigv4 "aws:amz:<region>:s3" \
  --user "<access_key>:<secret_key>" \
  "https://s3.<region>.io.cloud.ovh.net/<bucket_name>/<object_key>?attributes"

Versioned objects

By default, GetObjectAttributes operates on the current version of the object. To retrieve attributes for a specific version, add --version-id to the request.

aws s3api get-object-attributes \
  --bucket <bucket_name> \
  --key <object_key> \
  --version-id <version_id> \
  --object-attributes ETag ObjectSize StorageClass

curl -X GET \
  -H "x-amz-object-attributes: ETag,ObjectSize" \
  --aws-sigv4 "aws:amz:<region>:s3" \
  --user "<access_key>:<secret_key>" \
  "https://s3.<region>.io.cloud.ovh.net/<bucket_name>/<object_key>?attributes&versionId=<version_id>"

Encrypted objects (SSE-C)

For objects encrypted with SSE-C (customer-provided keys), you must supply the three encryption headers with every GetObjectAttributes request. The service does not store the key.

aws s3api get-object-attributes \
  --bucket <bucket_name> \
  --key <object_key> \
  --object-attributes ETag ObjectSize \
  --sse-customer-algorithm AES256 \
  --sse-customer-key <base64_encoded_256_bit_key> \
  --sse-customer-key-md5 <base64_encoded_md5_of_key>

curl -X GET \
  -H "x-amz-object-attributes: ETag,ObjectSize" \
  -H "x-amz-server-side-encryption-customer-algorithm: AES256" \
  -H "x-amz-server-side-encryption-customer-key: <base64_encoded_key>" \
  -H "x-amz-server-side-encryption-customer-key-MD5: <base64_md5_of_key>" \
  --aws-sigv4 "aws:amz:<region>:s3" \
  --user "<access_key>:<secret_key>" \
  "https://s3.<region>.io.cloud.ovh.net/<bucket_name>/<object_key>?attributes"

IAM permissions

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¹: S3 is a trademark of Amazon Technologies, Inc. OVHcloud's service is not sponsored by, endorsed by, or otherwise affiliated with Amazon Technologies, Inc.