[Samba] Check user's access rights / permissions in CIFS folders (from Linux)

[Nitin Garg]

I'm connecting to a Windows CIFS share from a Linux machine using libsmbclient. Is there a way for me to know if the user has write permissions to a particular file/folder?
I know that smbcacls can be used to get the ACLs, something like the following:
REVISION:1,
OWNER:S-1-5-21-1021440835-268907629-4167533493-1165,
GROUP:S-1-5-21-1021440835-268907629-4167533493-513,
ACL:S-1-1-0:0/16/0x001200a9,
ACL:S-1-5-18:0/16/0x001f01ff,
ACL:S-1-5-32-544:0/16/0x001f01ff,
ACL:S-1-5-21-1021440835-268907629-4167533493-500:0/16/0x001f01ff,
smbc_getxattr() in libsmbclient.h also returns these attributes.
But how do I use this information to calculate the effective rights of the current user?
I think I could do it if I get the SID of the current user and the groups that this user is a member of. But I'm not sure how to do that from a Linux box.
Samba version: 3.2.15

Regards,Nitin