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package java.security;

/**

 * A <code>DomainCombiner</code> provides a means to dynamically

 * update the ProtectionDomains associated with the current

 * <code>AccessControlContext</code>.

 *

 * <p> A <code>DomainCombiner</code> is passed as a parameter to the

 * appropriate constructor for <code>AccessControlContext</code>.

 * The newly constructed context is then passed to the

 * <code>AccessController.doPrivileged(..., context)</code> method

 * to bind the provided context (and associated <code>DomainCombiner</code>)

 * with the current execution Thread.  Subsequent calls to

 * <code>AccessController.getContext</code> or

 * <code>AccessController.checkPermission</code>

 * cause the <code>DomainCombiner.combine</code> to get invoked.

 *

 * <p> The combine method takes two arguments.  The first argument represents

 * an array of ProtectionDomains from the current execution Thread,

 * since the most recent call to <code>AccessController.doPrivileged</code>.

 * If no call to doPrivileged was made, then the first argument will contain

 * all the ProtectionDomains from the current execution Thread.

 * The second argument represents an array of inherited ProtectionDomains,

 * which may be <code>null</code>.  ProtectionDomains may be inherited

 * from a parent Thread, or from a privileged context.  If no call to

 * doPrivileged was made, then the second argument will contain the

 * ProtectionDomains inherited from the parent Thread.  If one or more calls

 * to doPrivileged were made, and the most recent call was to

 * doPrivileged(action, context), then the second argument will contain the

 * ProtectionDomains from the privileged context.  If the most recent call

 * was to doPrivileged(action), then there is no privileged context,

 * and the second argument will be <code>null</code>.

 *

 * <p> The <code>combine</code> method investigates the two input arrays

 * of ProtectionDomains and returns a single array containing the updated

 * ProtectionDomains.  In the simplest case, the <code>combine</code>

 * method merges the two stacks into one.  In more complex cases,

 * the <code>combine</code> method returns a modified

 * stack of ProtectionDomains.  The modification may have added new

 * ProtectionDomains, removed certain ProtectionDomains, or simply

 * updated existing ProtectionDomains.  Re-ordering and other optimizations

 * to the ProtectionDomains are also permitted.  Typically the

 * <code>combine</code> method bases its updates on the information

 * encapsulated in the <code>DomainCombiner</code>.

 *

 * <p> After the <code>AccessController.getContext</code> method

 * receives the combined stack of ProtectionDomains back from

 * the <code>DomainCombiner</code>, it returns a new

 * AccessControlContext that has both the combined ProtectionDomains

 * as well as the <code>DomainCombiner</code>.

 *

 * @see AccessController

 * @see AccessControlContext

 * @since 1.3

 */

public interface DomainCombiner {

    /**

     * Modify or update the provided ProtectionDomains.

     * ProtectionDomains may be added to or removed from the given

     * ProtectionDomains.  The ProtectionDomains may be re-ordered.

     * Individual ProtectionDomains may be modified (with a new

     * set of Permissions, for example).

     *

     * <p>

     *

     * @param currentDomains the ProtectionDomains associated with the

     *          current execution Thread, up to the most recent

     *          privileged <code>ProtectionDomain</code>.

     *          The ProtectionDomains are are listed in order of execution,

     *          with the most recently executing <code>ProtectionDomain</code>

     *          residing at the beginning of the array. This parameter may

     *          be <code>null</code> if the current execution Thread

     *          has no associated ProtectionDomains.<p>

     *

     * @param assignedDomains an array of inherited ProtectionDomains.

     *          ProtectionDomains may be inherited from a parent Thread,

     *          or from a privileged <code>AccessControlContext</code>.

     *          This parameter may be <code>null</code>

     *          if there are no inherited ProtectionDomains.

     *

     * @return a new array consisting of the updated ProtectionDomains,

     *          or <code>null</code>.

     */

    ProtectionDomain[] combine(ProtectionDomain[] currentDomains,

                                ProtectionDomain[] assignedDomains);

}