Why does the listing of an Aliyun OSS dir only contain last_modified meta when recursive is true?

[photino]

When recursive is false, the listing of an Aliyun OSS dir does not have a last_modified meta.

op.list_with(&dir)
    .recursive(false)
    .metakey(ContentLength | ContentType | LastModified)

[Xuanwo]

Hello, in most object storage services, directories are merely treated as a simple prefix ending with '/'. However, when users manually create 'abc/', the behavior may vary.

For list with recursive(false), we call object storage services using ListObjects with delimiter = "/". In this scenario, all paths that end with / are displayed in CommonPrefixes as plain strings without metadata.

For list with recursive(true), we call object storage services using ListObjects with delimiter = "". Here, all keys are listed in Contents along with their corresponding metadata. It's important to note that abc/ is treated as a normal object in this context, and is only converted into a directory because it ends with /.

It seems unfair to stat abc/ again when calling list with recursive(false), as this could potentially slow down the listing performance by up to 1000 times. Therefore, we choose to ignore them.

Technically, possessing the last_modified metadata for a directory is meaningless. Do you have specific requirements for this?

ref: https://help.aliyun.com/zh/oss/developer-reference/listobjectsv2?spm=a2c4g.11186623.0.0.63df4d4dvUvPLd

[photino]

The last_modified metadata for a directory is also optional in our case. I just did not unstandard what were the differences. Thanks a lot for your help.