expose the SSH_FXP_READDIR longname

[mickael-kerjean]

Each entry in a SSH_FXP_NAME reply carries three fields: filename, longname and attrs (source). The client currently ignore the longname field with:

_, data = unmarshalString(data) // discard longname

I have a use case which require to display things similarly to what the open ssh cli shows:

sftp> ls -l
drwxrwxr-x    ? mickael  mickael      4096 Jul  3 18:34 Android
drwxr-xr-x    ? mickael  mickael      4096 Jun  3 00:03 Desktop
drwxr-xr-x    ? mickael  mickael      4096 Jul  8 14:14 Documents

As of today, this is not possible and this PR fixes that

[puellanivis]

longname is not a part of this structure, it’s a part of the SSH_FXP_NAME name entry sub-structure: https://datatracker.ietf.org/doc/html/draft-ietf-secsh-filexfer-02#section-7

If you have need to access this and want to get it added in, it should be put in the fileInfo struct:

sftp/attrs.go

Lines 23 to 26 in fc82c35

	type fileInfo struct {
	name string
	stat *FileStat
	}

and then we can expose a LongName() string receiver method that you can then test with .(interface{ LongName() string }) to use it.