HDDS-15600. Fix ListObjects response for encoding-type and empty delimiter

[Gargi-jais11]

What changes were proposed in this pull request?

Ozone S3 Gateway fails s3-tests ListObjects cases that AWS S3 passes:

• test_bucket_list_encoding_basic — With EncodingType=url, keys and CommonPrefixes containing spaces are encoded with + (Java URLEncoder form encoding) instead of AWS-style %20.
  Example: prefix quux ab/ is returned as quux+ab/ but should be quux%20ab/.
• test_bucket_list_delimiter_empty — When Delimiter='' is sent, listing behavior is correct (all keys returned, no CommonPrefixes), but the response incorrectly includes a Delimiter field. AWS omits Delimiter from the XML when the client passes an empty delimiter.

• test_bucket_list_prefix_unreadable — ListObjects with Prefix='\x0a' (newline) should echo the prefix in the response and return empty Contents/CommonPrefixes. Ozone may not preserve or echo the control-character prefix correctly.
  No conclusion is made on the root cause of this test failure. Skipping it to be fixed in this PR.

https://ozone.s3.peterxcli.dev/#latest-run-section

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-15600

How was this patch tested?

Before fix:

1. encoding type:

bash-5.1$ aws s3api list-objects --bucket buck1 --encoding-type url --delimiter / --endpoint-url http://s3g:9878/
{
"Contents": [
{
"Key": "asdf%2Bb",
"LastModified": "2026-06-19T09:51:39.569Z",
"ETag": "\"f75b8179e4bbe7e2b4a074dcef62de95\"",
"Size": 8,
"StorageClass": "STANDARD",
"Owner": {
"DisplayName": "testuser",
"ID": "bb2bd7ca4a327f84e6cd3979f8fa3828a50a08893c1b68f9d6715352c8d07b93"
}
}
],
"CommonPrefixes": [
{
"Prefix": "foo/"
},
{
"Prefix": "foo%2B1/"
},
{
"Prefix": "quux+ab/". <----------------- wrong output
}
],
"RequestCharged": null,
"Prefix": ""
}

2. empty delimiter:

bash-5.1$ aws --debug s3api list-objects \
--bucket buck1 \
--delimiter "" \
--endpoint-url http://s3g:9878 2>&1 \
| grep -oE '<Prefix>[^<]*</Prefix>|<Delimiter>[^<]*</Delimiter>|<KeyCount>[^<]*</KeyCount>'
<Prefix></Prefix>
<KeyCount>0</KeyCount>
<Delimiter></Delimiter>. <---------- should not be present

After fix:

1. encoding-type:

bash-5.1$ aws s3api list-objects --bucket buck1 --encoding-type url --delimiter / --endpoint-url http://s3g:9878/
{
"Contents": [
{
"Key": "asdf%2Bb",
"LastModified": "2026-06-19T09:08:58.933Z",
"ETag": "\"f75b8179e4bbe7e2b4a074dcef62de95\"",
"Size": 8,
"StorageClass": "STANDARD",
"Owner": {
"DisplayName": "testuser",
"ID": "bb2bd7ca4a327f84e6cd3979f8fa3828a50a08893c1b68f9d6715352c8d07b93"
}
}
],
"CommonPrefixes": [
{
"Prefix": "foo/"
},
{
"Prefix": "foo%2B1/"
},
{
"Prefix": "quux%20ab/" <------------------------correct output
}
],
"RequestCharged": null,
"Prefix": null
}

2. empty delimeter :

bash-5.1$ aws --debug s3api list-objects \
--bucket buck1 \
--delimiter "" \
--endpoint-url http://s3g:9878 2>&1 \
| grep -oE '<Prefix>[^<]*</Prefix>|<Delimiter>[^<]*</Delimiter>|<KeyCount>[^<]*</KeyCount>'
<KeyCount>0</KeyCount>. <-------------------- no empty delimiter present

[adoroszlai]

Thanks @Gargi-jais11 for the patch.

[chungen0126]

Thanks @Gargi-jais11 for working on this. Overall, looks good to me. Just a nit.

[Gargi-jais11]

@ivandika3 please review this patch.

[Russole]

Thanks @Gargi-jais11 for the patch. I’ve left a few review comments.

[Gargi-jais11]

@Russole Please take a look, I have updated the Pr.

[Russole]

Thanks @Gargi-jais11 for the patch. LGTM!

[Gargi-jais11]

Thanks @adoroszlai , @Russole and @chungen0126 for reviewing the patch.