HDDS-16072. Implement GetObjectAttributes: ETag, ObjectSize, StorageClass, and ObjectParts count

[Gargi-jais11]

What changes were proposed in this pull request?

Implement the initial GetObjectAttributes support in the S3 Gateway.

PR Changes:

• API : GET /{bucket}/{key}?attributes
• Required header: x-amz-object-attributes
• Supported attributes:
  - ETag — object ETag (MD5 or composite hash for multipart objects)
  - ObjectSize — object size in bytes
  - StorageClass — storage/replication class
  - ObjectParts — for multipart objects,
• Response format: XML GetObjectAttributesResponse with Last-Modified response header
• Error handling: 404 NoSuchKey when the object does not exist, 403 AccessDenied on authorization failure, 400 InvalidArgument when the attributes header is missing or invalid
• Audit and metrics: GET_OBJECT_ATTRIBUTES audit action and success/failure metrics

Out of scope:

• Populating Checksum - non-MD5 checksums are not stored in ozone.
• ObjectParts.Part[] with per-part PartNumber / Size -> this will be implemented in follow-up PR
• Pagination (MaxParts, markers, real IsTruncated behavior) -> this will be implemented in followip PR
• versionId and SSE-C -> Not implemented in ozone

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-16072

How was this patch tested?

Added unit test and integration test.
Manually tested:

bash-5.1$ BUCKET=get-attr-test-bucket
KEY=get-attr-test-key
bash-5.1$ aws s3api create-bucket --bucket "$BUCKET" --endpoint-url http://s3g:9878/
{
    "Location": "http://s3g:9878/get-attr-test-bucket"
}
bash-5.1$ echo "hello-get-object-attributes" | aws s3 cp - "s3://$BUCKET/$KEY" --endpoint-url http://s3g:9878/
bash-5.1$ aws s3api get-object-attributes \
  --bucket "$BUCKET" \
  --key "$KEY" \
  --object-attributes ETag ObjectSize StorageClass \
  --endpoint-url http://s3g:9878/
{
    "LastModified": "Mon, 03 Aug 2026 06:39:03 GMT",
    "ETag": "\"88fa5b0b7b11af7d6bdd31a64e1cad0a\"",
    "StorageClass": "STANDARD",
    "ObjectSize": 28
}
--------------------------------
// Test multipart ObjectParts
--------------------------------
bash-5.1$ dd if=/dev/zero of=/tmp/mpu-test.bin bs=1M count=15
15+0 records in
15+0 records out
15728640 bytes (16 MB, 15 MiB) copied, 0.00987967 s, 1.6 GB/s
bash-5.1$ aws s3 cp /tmp/mpu-test.bin "s3://$BUCKET/mpu-key" --endpoint-url http://s3g:9878/
upload: ../../tmp/mpu-test.bin to s3://get-attr-test-bucket/mpu-key
bash-5.1$ aws s3api get-object-attributes   --bucket "$BUCKET"   --key "mpu-key"   --object-attributes ETag ObjectSize ObjectParts   --endpoint-url http://s3g:9878/
{
    "LastModified": "Mon, 03 Aug 2026 06:40:01 GMT",
    "ETag": "\"cb075a2e9cd2c450e3822ba742921b31-2\"",
    "ObjectParts": {
        "TotalPartsCount": 2,
        "PartNumberMarker": 0,
        "NextPartNumberMarker": 0,
        "MaxParts": 0,
        "IsTruncated": false
    },
    "ObjectSize": 15728640
}

[yandrey321]

can key.isFile() return true for the key ends with '/'?

[Gargi-jais11]

No — for FSO directory keys, isFile() is false. A file key has isFile()==true. the trailing-slash check only gates directory access without /.

[Gargi-jais11]

@yandrey321 Please take a look again, I have updated the PR.

[priyeshkaratha]

Thanks @Gargi-jais11 for working on this. Please check the provided inline comment.

[priyeshkaratha]

Thanks @Gargi-jais11 for updating the patch. Changes LGTM

[chungen0126]

Overall, LGTM. Just some nits.