public interface AclFileAttributeView
extends FileOwnerAttributeView

A file attribute view that supports reading or updating a file's Access Control Lists (ACL) or file owner attributes.

ACLs are used to specify access rights to file system objects. An ACL is an ordered list of access-control-entries, each specifying a UserPrincipal and the level of access for that user principal. This file attribute view defines the getAcl, and setAcl methods to read and write ACLs based on the ACL model specified in RFC 3530: Network File System (NFS) version 4 Protocol. This file attribute view is intended for file system implementations that support the NFSv4 ACL model or have a well-defined mapping between the NFSv4 ACL model and the ACL model used by the file system. The details of such mapping are implementation dependent and are therefore unspecified.

This class also extends FileOwnerAttributeView so as to define methods to get and set the file owner.

When a file system provides access to a set of file-systems that are not homogeneous then only some of the file systems may support ACLs. The supportsFileAttributeView method can be used to test if a file system supports ACLs.

Interoperability

RFC 3530 allows for special user identities to be used on platforms that support the POSIX defined access permissions. The special user identities are "OWNER@", "GROUP@", and "EVERYONE@". When both the AclFileAttributeView and the PosixFileAttributeView are supported then these special user identities may be included in ACL entries that are read or written. The file system's UserPrincipalLookupService may be used to obtain a UserPrincipal to represent these special identities by invoking the lookupPrincipalByName method.

Usage Example: Suppose we wish to add an entry to an existing ACL to grant "joe" access:

// lookup "joe"
     UserPrincipal joe = file.getFileSystem().getUserPrincipalLookupService()
         .lookupPrincipalByName("joe");

     // get view
     AclFileAttributeView view = Files.getFileAttributeView(file, AclFileAttributeView.class);

     // create ACE to give "joe" read access
     AclEntry entry = AclEntry.newBuilder()
         .setType(AclEntryType.ALLOW)
         .setPrincipal(joe)
         .setPermissions(AclEntryPermission.READ_DATA, AclEntryPermission.READ_ATTRIBUTES)
         .build();

     // read ACL, insert ACE, re-write ACL
     List<AclEntry> acl = view.getAcl();
     acl.add(0, entry);   // insert before any DENY entries
     view.setAcl(acl);

Dynamic Access

Where dynamic access to file attributes is required, the attributes supported by this attribute view are as follows:

Name	Type
"acl"	List<AclEntry>
"owner"	UserPrincipal

The getAttribute method may be used to read the ACL or owner attributes as if by invoking the getAcl or getOwner methods.

The setAttribute method may be used to update the ACL or owner attributes as if by invoking the setAcl or setOwner methods.

Setting the ACL when creating a file

Implementations supporting this attribute view may also support setting the initial ACL when creating a file or directory. The initial ACL may be provided to methods such as createFile or createDirectory as an FileAttribute with name "acl:acl" and a value that is the list of AclEntry objects.

Where an implementation supports an ACL model that differs from the NFSv4 defined ACL model then setting the initial ACL when creating the file must translate the ACL to the model supported by the file system. Methods that create a file should reject (by throwing IOException) any attempt to create a file that would be less secure as a result of the translation.

String name()

List<AclEntry> getAcl()
               throws IOException

Reads the access control list.

When the file system uses an ACL model that differs from the NFSv4 defined ACL model, then this method returns an ACL that is the translation of the ACL to the NFSv4 ACL model.

The returned list is modifiable so as to facilitate changes to the existing ACL. The setAcl method is used to update the file's ACL attribute.

void setAcl(List<AclEntry> acl)
     throws IOException

Updates (replace) the access control list.

Where the file system supports Access Control Lists, and it uses an ACL model that differs from the NFSv4 defined ACL model, then this method must translate the ACL to the model supported by the file system. This method should reject (by throwing IOException) any attempt to write an ACL that would appear to make the file more secure than would be the case if the ACL were updated. Where an implementation does not support a mapping of AclEntryType.AUDIT or AclEntryType.ALARM entries, then this method ignores these entries when writing the ACL.

If an ACL entry contains a user-principal that is not associated with the same provider as this attribute view then ProviderMismatchException is thrown. Additional validation, if any, is implementation dependent.

If the file system supports other security related file attributes (such as a file access-permissions for example), the updating the access control list may also cause these security related attributes to be updated.