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package java.nio.file.attribute;

import java.nio.file.*;

import java.util.Set;

import java.io.IOException;

/**

 * A file attribute view that provides a view of the file attributes commonly

 * associated with files on file systems used by operating systems that implement

 * the Portable Operating System Interface (POSIX) family of standards.

 *

 * <p> Operating systems that implement the <a href="http://www.opengroup.org">

 * POSIX</a> family of standards commonly use file systems that have a

 * file <em>owner</em>, <em>group-owner</em>, and related <em>access

 * permissions</em>. This file attribute view provides read and write access

 * to these attributes.

 *

 * <p> The {@link #readAttributes() readAttributes} method is used to read the

 * file's attributes. The file {@link PosixFileAttributes#owner() owner} is

 * represented by a {@link UserPrincipal} that is the identity of the file owner

 * for the purposes of access control. The {@link PosixFileAttributes#group()

 * group-owner}, represented by a {@link GroupPrincipal}, is the identity of the

 * group owner, where a group is an identity created for administrative purposes

 * so as to determine the access rights for the members of the group.

 *

 * <p> The {@link PosixFileAttributes#permissions() permissions} attribute is a

 * set of access permissions. This file attribute view provides access to the nine

 * permission defined by the {@link PosixFilePermission} class.

 * These nine permission bits determine the <em>read</em>, <em>write</em>, and

 * <em>execute</em> access for the file owner, group, and others (others

 * meaning identities other than the owner and members of the group). Some

 * operating systems and file systems may provide additional permission bits

 * but access to these other bits is not defined by this class in this release.

 *

 * <p> <b>Usage Example:</b>

 * Suppose we need to print out the owner and access permissions of a file:

 * <pre>

 *     Path file = ...

 *     PosixFileAttributes attrs = Files.getFileAttributeView(file, PosixFileAttributeView.class)

 *         .readAttributes();

 *     System.out.format("%s %s%n",

 *         attrs.owner().getName(),

 *         PosixFilePermissions.toString(attrs.permissions()));

 * </pre>

 *

 * <h4> Dynamic Access </h4>

 * <p> Where dynamic access to file attributes is required, the attributes

 * supported by this attribute view are as defined by {@link

 * BasicFileAttributeView} and {@link FileOwnerAttributeView}, and in addition,

 * the following attributes are supported:

 * <blockquote>

 * <table border="1" cellpadding="8">

 *   <tr>

 *     <th> Name </th>

 *     <th> Type </th>

 *   </tr>

 *  <tr>

 *     <td> "permissions" </td>

 *     <td> {@link Set}&lt;{@link PosixFilePermission}&gt; </td>

 *   </tr>

 *   <tr>

 *     <td> "group" </td>

 *     <td> {@link GroupPrincipal} </td>

 *   </tr>

 * </table>

 * </blockquote>

 *

 * <p> The {@link Files#getAttribute getAttribute} method may be used to read

 * any of these attributes, or any of the attributes defined by {@link

 * BasicFileAttributeView} as if by invoking the {@link #readAttributes

 * readAttributes()} method.

 *

 * <p> The {@link Files#setAttribute setAttribute} method may be used to update

 * the file's last modified time, last access time or create time attributes as

 * defined by {@link BasicFileAttributeView}. It may also be used to update

 * the permissions, owner, or group-owner as if by invoking the {@link

 * #setPermissions setPermissions}, {@link #setOwner setOwner}, and {@link

 * #setGroup setGroup} methods respectively.

 *

 * <h4> Setting Initial Permissions </h4>

 * <p> Implementations supporting this attribute view may also support setting

 * the initial permissions when creating a file or directory. The

 * initial permissions are provided to the {@link Files#createFile createFile}

 * or {@link Files#createDirectory createDirectory} methods as a {@link

 * FileAttribute} with {@link FileAttribute#name name} {@code "posix:permissions"}

 * and a {@link FileAttribute#value value} that is the set of permissions. The

 * following example uses the {@link PosixFilePermissions#asFileAttribute

 * asFileAttribute} method to construct a {@code FileAttribute} when creating a

 * file:

 *

 * <pre>

 *     Path path = ...

 *     Set<PosixFilePermission> perms =

 *         EnumSet.of(OWNER_READ, OWNER_WRITE, OWNER_EXECUTE, GROUP_READ);

 *     Files.createFile(path, PosixFilePermissions.asFileAttribute(perms));

 * </pre>

 *

 * <p> When the access permissions are set at file creation time then the actual

 * value of the permissions may differ that the value of the attribute object.

 * The reasons for this are implementation specific. On UNIX systems, for

 * example, a process has a <em>umask</em> that impacts the permission bits

 * of newly created files. Where an implementation supports the setting of

 * the access permissions, and the underlying file system supports access

 * permissions, then it is required that the value of the actual access

 * permissions will be equal or less than the value of the attribute

 * provided to the {@link Files#createFile createFile} or {@link

 * Files#createDirectory createDirectory} methods. In other words, the file may

 * be more secure than requested.

 *

 * @since 1.7

 */

public interface PosixFileAttributeView

    extends BasicFileAttributeView, FileOwnerAttributeView

{

    /**

     * Returns the name of the attribute view. Attribute views of this type

     * have the name {@code "posix"}.

     */

    @Override

    String name();

    /**

     * @throws  IOException                {@inheritDoc}

     * @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.

     */

    @Override

    PosixFileAttributes readAttributes() throws IOException;

    /**

     * Updates the file permissions.

     *

     * @param   perms

     *          the new set of permissions

     *

     * @throws  ClassCastException

     *          if the sets contains elements that are not of type {@code

     *          PosixFilePermission}

     * @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#checkWrite(String) checkWrite}

     *          method denies write access to the file.

     */

    void setPermissions(Set<PosixFilePermission> perms) throws IOException;

    /**

     * Updates the file group-owner.

     *

     * @param   group

     *          the new file group-owner

     *

     * @throws  IOException

     *          if an I/O error occurs

     * @throws  SecurityException

     *          In the case of the default provider, and 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.

     */

    void setGroup(GroupPrincipal group) throws IOException;

}