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/**
* A file attribute view that supports reading or updating a file's Access
* Control Lists (ACL) or file owner attributes.
*
* <p> ACLs are used to specify access rights to file system objects. An ACL is
* an ordered list of {@link AclEntry access-control-entries}, each specifying a
* {@link UserPrincipal} and the level of access for that user principal. This
* file attribute view defines the {@link #getAcl() getAcl}, and {@link
* #setAcl(List) setAcl} methods to read and write ACLs based on the ACL
* model specified in <a href="http://www.ietf.org/rfc/rfc3530.txt"><i>RFC 3530:
* Network File System (NFS) version 4 Protocol</i></a>. This file attribute view
* is intended for file system implementations that support the NFSv4 ACL model
* or have a <em>well-defined</em> 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.
*
* <p> This class also extends {@code FileOwnerAttributeView} so as to define
* methods to get and set the file owner.
*
* <p> When a file system provides access to a set of {@link FileStore
* file-systems} that are not homogeneous then only some of the file systems may
* support ACLs. The {@link FileStore#supportsFileAttributeView
* supportsFileAttributeView} method can be used to test if a file system
* supports ACLs.
*
* <a name="interop"><h4>Interoperability</h4></a>
*
* RFC 3530 allows for special user identities to be used on platforms that
* support the POSIX defined access permissions. The special user identities
* are "{@code OWNER@}", "{@code GROUP@}", and "{@code EVERYONE@}". When both
* the {@code AclFileAttributeView} and the {@link PosixFileAttributeView}
* are supported then these special user identities may be included in ACL {@link
* AclEntry entries} that are read or written. The file system's {@link
* UserPrincipalLookupService} may be used to obtain a {@link UserPrincipal}
* to represent these special identities by invoking the {@link
* UserPrincipalLookupService#lookupPrincipalByName lookupPrincipalByName}
* method. </p>
*
* <p> <b>Usage Example:</b>
* Suppose we wish to add an entry to an existing ACL to grant "joe" access:
* <pre>
* // 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);
* </pre>
*
* <h4> Dynamic Access </h4>
* <p> Where dynamic access to file attributes is required, the attributes
* supported by this attribute view are as follows:
* <blockquote>
* <table border="1" cellpadding="8">
* <tr>
* <th> Name </th>
* <th> Type </th>
* </tr>
* <tr>
* <td> "acl" </td>
* <td> {@link List}<{@link AclEntry}> </td>
* </tr>
* <tr>
* <td> "owner" </td>
* <td> {@link UserPrincipal} </td>
* </tr>
* </table>
* </blockquote>
*
* <p> The {@link Files#getAttribute getAttribute} method may be used to read
* the ACL or owner attributes as if by invoking the {@link #getAcl getAcl} or
* {@link #getOwner getOwner} methods.
*
* <p> The {@link Files#setAttribute setAttribute} method may be used to
* update the ACL or owner attributes as if by invoking the {@link #setAcl setAcl}
* or {@link #setOwner setOwner} methods.
*
* <h4> Setting the ACL when creating a file </h4>
*
* <p> 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 {@link Files#createFile createFile} or {@link
* Files#createDirectory createDirectory} as an {@link FileAttribute} with {@link
* FileAttribute#name name} {@code "acl:acl"} and a {@link FileAttribute#value
* value} that is the list of {@code AclEntry} objects.
*
* <p> 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 {@link IOException IOException})
* any attempt to create a file that would be less secure as a result of the
* translation.
*
* @since 1.7
*/
public interface AclFileAttributeView
extends FileOwnerAttributeView
{
/**
* Returns the name of the attribute view. Attribute views of this type
* have the name {@code "acl"}.
*/
/**
* Reads the access control list.
*
* <p> 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.
*
* <p> The returned list is modifiable so as to facilitate changes to the
* existing ACL. The {@link #setAcl setAcl} method is used to update
* the file's ACL attribute.
*
* @return an ordered list of {@link AclEntry entries} representing the
* ACL
*
* @throws IOException
* if an I/O error occurs
* @throws SecurityException
* In the case of the default provider, a security manager is
* installed, and it denies {@link RuntimePermission}<tt>("accessUserInformation")</tt>
* or its {@link SecurityManager#checkRead(String) checkRead} method
* denies read access to the file.
*/
/**
* Updates (replace) the access control list.
*
* <p> 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 {@link IOException 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 {@link AclEntryType#AUDIT} or {@link
* AclEntryType#ALARM} entries, then this method ignores these entries when
* writing the ACL.
*
* <p> If an ACL entry contains a {@link AclEntry#principal user-principal}
* that is not associated with the same provider as this attribute view then
* {@link ProviderMismatchException} is thrown. Additional validation, if
* any, is implementation dependent.
*
* <p> If the file system supports other security related file attributes
* (such as a file {@link PosixFileAttributes#permissions
* access-permissions} for example), the updating the access control list
* may also cause these security related attributes to be updated.
*
* @param acl
* the new access control list
*
* @throws IOException
* if an I/O error occurs or the ACL is invalid
* @throws SecurityException
* In the case of the default provider, a security manager is
* installed, it denies {@link RuntimePermission}<tt>("accessUserInformation")</tt>
* or its {@link SecurityManager#checkWrite(String) checkWrite}
* method denies write access to the file.
*/
}