/*

 * Copyright 1997-2008 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.security;

import java.util.ArrayList;

import java.util.List;

import sun.security.util.Debug;

import sun.security.util.SecurityConstants;

/**

 * An AccessControlContext is used to make system resource access decisions

 * based on the context it encapsulates.

 *

 * <p>More specifically, it encapsulates a context and

 * has a single method, <code>checkPermission</code>,

 * that is equivalent to the <code>checkPermission</code> method

 * in the AccessController class, with one difference: The AccessControlContext

 * <code>checkPermission</code> method makes access decisions based on the

 * context it encapsulates,

 * rather than that of the current execution thread.

 *

 * <p>Thus, the purpose of AccessControlContext is for those situations where

 * a security check that should be made within a given context

 * actually needs to be done from within a

 * <i>different</i> context (for example, from within a worker thread).

 *

 * <p> An AccessControlContext is created by calling the

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

 * The <code>getContext</code> method takes a "snapshot"

 * of the current calling context, and places

 * it in an AccessControlContext object, which it returns. A sample call is

 * the following:

 *

 * <pre>

 *   AccessControlContext acc = AccessController.getContext()

 * </pre>

 *

 * <p>

 * Code within a different context can subsequently call the

 * <code>checkPermission</code> method on the

 * previously-saved AccessControlContext object. A sample call is the

 * following:

 *

 * <pre>

 *   acc.checkPermission(permission)

 * </pre>

 *

 * @see AccessController

 *

 * @author Roland Schemers

 */

public final class AccessControlContext {

    private ProtectionDomain context[];

    private boolean isPrivileged;

    // Note: This field is directly used by the virtual machine

    // native codes. Don't touch it.

    private AccessControlContext privilegedContext;

    private DomainCombiner combiner = null;

    private static boolean debugInit = false;

    private static Debug debug = null;

    static Debug getDebug()

    {

        if (debugInit)

            return debug;

        else {

            if (Policy.isSet()) {

                debug = Debug.getInstance("access");

                debugInit = true;

            }

            return debug;

        }

    }

    /**

     * Create an AccessControlContext with the given array of ProtectionDomains.

     * Context must not be null. Duplicate domains will be removed from the

     * context.

     *

     * @param context the ProtectionDomains associated with this context.

     * The non-duplicate domains are copied from the array. Subsequent

     * changes to the array will not affect this AccessControlContext.

     * @throws NullPointerException if <code>context</code> is <code>null</code>

     */

    public AccessControlContext(ProtectionDomain context[])

    {

        if (context.length == 0) {

            this.context = null;

        } else if (context.length == 1) {

            if (context[0] != null) {

                this.context = context.clone();

            } else {

                this.context = null;

            }

        } else {

            List<ProtectionDomain> v = new ArrayList<ProtectionDomain>(context.length);

            for (int i =0; i< context.length; i++) {

                if ((context[i] != null) &&  (!v.contains(context[i])))

                    v.add(context[i]);

            }

            if (!v.isEmpty()) {

                this.context = new ProtectionDomain[v.size()];

                this.context = v.toArray(this.context);

            }

        }

    }

    /**

     * Create a new <code>AccessControlContext</code> with the given

     * <code>AccessControlContext</code> and <code>DomainCombiner</code>.

     * This constructor associates the provided

     * <code>DomainCombiner</code> with the provided

     * <code>AccessControlContext</code>.

     *

     * <p>

     *

     * @param acc the <code>AccessControlContext</code> associated

     *          with the provided <code>DomainCombiner</code>.

     *

     * @param combiner the <code>DomainCombiner</code> to be associated

     *          with the provided <code>AccessControlContext</code>.

     *

     * @exception NullPointerException if the provided

     *          <code>context</code> is <code>null</code>.

     *

     * @exception SecurityException if a security manager is installed and the

     *          caller does not have the "createAccessControlContext"

     *          {@link SecurityPermission}

     * @since 1.3

     */

    public AccessControlContext(AccessControlContext acc,

                                DomainCombiner combiner) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(SecurityConstants.CREATE_ACC_PERMISSION);

        }

        this.context = acc.context;

        // we do not need to run the combine method on the

        // provided ACC.  it was already "combined" when the

        // context was originally retrieved.

        //

        // at this point in time, we simply throw away the old

        // combiner and use the newly provided one.

        this.combiner = combiner;

    }

    /**

     * package private for AccessController

     */

    AccessControlContext(ProtectionDomain context[], DomainCombiner combiner) {

        if (context != null) {

            this.context = context.clone();

        }

        this.combiner = combiner;

    }

    /**

     * package private constructor for AccessController.getContext()

     */

    AccessControlContext(ProtectionDomain context[],

                                 boolean isPrivileged)

    {

        this.context = context;

        this.isPrivileged = isPrivileged;

    }

    /**

     * Returns true if this context is privileged.

     */

    boolean isPrivileged()

    {

        return isPrivileged;

    }

    /**

     * get the assigned combiner from the privileged or inherited context

     */

    DomainCombiner getAssignedCombiner() {

        AccessControlContext acc;

        if (isPrivileged) {

            acc = privilegedContext;

        } else {

            acc = AccessController.getInheritedAccessControlContext();

        }

        if (acc != null) {

            return acc.combiner;

        }

        return null;

    }

    /**

     * Get the <code>DomainCombiner</code> associated with this

     * <code>AccessControlContext</code>.

     *

     * <p>

     *

     * @return the <code>DomainCombiner</code> associated with this

     *          <code>AccessControlContext</code>, or <code>null</code>

     *          if there is none.

     *

     * @exception SecurityException if a security manager is installed and

     *          the caller does not have the "getDomainCombiner"

     *          {@link SecurityPermission}

     * @since 1.3

     */

    public DomainCombiner getDomainCombiner() {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(SecurityConstants.GET_COMBINER_PERMISSION);

        }

        return combiner;

    }

    /**

     * Determines whether the access request indicated by the

     * specified permission should be allowed or denied, based on

     * the security policy currently in effect, and the context in

     * this object. The request is allowed only if every ProtectionDomain

     * in the context implies the permission. Otherwise the request is

     * denied.

     *

     * <p>

     * This method quietly returns if the access request

     * is permitted, or throws a suitable AccessControlException otherwise.

     *

     * @param perm the requested permission.

     *

     * @exception AccessControlException if the specified permission

     * is not permitted, based on the current security policy and the

     * context encapsulated by this object.

     * @exception NullPointerException if the permission to check for is null.

     */

    public void checkPermission(Permission perm)

        throws AccessControlException

    {

        boolean dumpDebug = false;

        if (perm == null) {

            throw new NullPointerException("permission can't be null");

        }

        if (getDebug() != null) {

            // If "codebase" is not specified, we dump the info by default.

            dumpDebug = !Debug.isOn("codebase=");

            if (!dumpDebug) {

                // If "codebase" is specified, only dump if the specified code

                // value is in the stack.

                for (int i = 0; context != null && i < context.length; i++) {

                    if (context[i].getCodeSource() != null &&

                        context[i].getCodeSource().getLocation() != null &&

                        Debug.isOn("codebase=" + context[i].getCodeSource().getLocation().toString())) {

                        dumpDebug = true;

                        break;

                    }

                }

            }

            dumpDebug &= !Debug.isOn("permission=") ||

                Debug.isOn("permission=" + perm.getClass().getCanonicalName());

            if (dumpDebug && Debug.isOn("stack")) {

                Thread.currentThread().dumpStack();

            }

            if (dumpDebug && Debug.isOn("domain")) {

                if (context == null) {

                    debug.println("domain (context is null)");

                } else {

                    for (int i=0; i< context.length; i++) {

                        debug.println("domain "+i+" "+context[i]);

                    }

                }

            }

        }

        /*

         * iterate through the ProtectionDomains in the context.

         * Stop at the first one that doesn't allow the

         * requested permission (throwing an exception).

         *

         */

        /* if ctxt is null, all we had on the stack were system domains,

           or the first domain was a Privileged system domain. This

           is to make the common case for system code very fast */

        if (context == null)

            return;

        for (int i=0; i< context.length; i++) {

            if (context[i] != null &&  !context[i].implies(perm)) {

                if (dumpDebug) {

                    debug.println("access denied " + perm);

                }

                if (Debug.isOn("failure") && debug != null) {

                    // Want to make sure this is always displayed for failure,

                    // but do not want to display again if already displayed

                    // above.

                    if (!dumpDebug) {

                        debug.println("access denied " + perm);

                    }

                    Thread.currentThread().dumpStack();

                    final ProtectionDomain pd = context[i];

                    final Debug db = debug;

                    AccessController.doPrivileged (new PrivilegedAction<Void>() {

                        public Void run() {

                            db.println("domain that failed "+pd);

                            return null;

                        }

                    });

                }

                throw new AccessControlException("access denied "+perm, perm);

            }

        }

        // allow if all of them allowed access

        if (dumpDebug) {

            debug.println("access allowed "+perm);

        }

        return;

    }

    /**

     * Take the stack-based context (this) and combine it with the

     * privileged or inherited context, if need be.

     */

    AccessControlContext optimize() {

        // the assigned (privileged or inherited) context

        AccessControlContext acc;

        if (isPrivileged) {

            acc = privilegedContext;

        } else {

            acc = AccessController.getInheritedAccessControlContext();

        }

        // this.context could be null if only system code is on the stack;

        // in that case, ignore the stack context

        boolean skipStack = (context == null);

        // acc.context could be null if only system code was involved;

        // in that case, ignore the assigned context

        boolean skipAssigned = (acc == null || acc.context == null);

        if (acc != null && acc.combiner != null) {

            // let the assigned acc's combiner do its thing

            return goCombiner(context, acc);

        }

        // optimization: if neither have contexts; return acc if possible

        // rather than this, because acc might have a combiner

        if (skipAssigned && skipStack) {

            return this;

        }

        // optimization: if there is no stack context; there is no reason

        // to compress the assigned context, it already is compressed

        if (skipStack) {

            return acc;

        }

        int slen = context.length;

        // optimization: if there is no assigned context and the stack length

        // is less then or equal to two; there is no reason to compress the

        // stack context, it already is

        if (skipAssigned && slen <= 2) {

            return this;

        }

        // optimization: if there is a single stack domain and that domain

        // is already in the assigned context; no need to combine

        if ((slen == 1) && (context[0] == acc.context[0])) {

            return acc;

        }

        int n = (skipAssigned) ? 0 : acc.context.length;

        // now we combine both of them, and create a new context

        ProtectionDomain pd[] = new ProtectionDomain[slen + n];

        // first copy in the assigned context domains, no need to compress

        if (!skipAssigned) {

            System.arraycopy(acc.context, 0, pd, 0, n);

        }

        // now add the stack context domains, discarding nulls and duplicates

    outer:

        for (int i = 0; i < context.length; i++) {

            ProtectionDomain sd = context[i];

            if (sd != null) {

                for (int j = 0; j < n; j++) {

                    if (sd == pd[j]) {

                        continue outer;

                    }

                }

                pd[n++] = sd;

            }

        }

        // if length isn't equal, we need to shorten the array

        if (n != pd.length) {

            // optimization: if we didn't really combine anything

            if (!skipAssigned && n == acc.context.length) {

                return acc;

            } else if (skipAssigned && n == slen) {

                return this;

            }

            ProtectionDomain tmp[] = new ProtectionDomain[n];

            System.arraycopy(pd, 0, tmp, 0, n);

            pd = tmp;

        }

        //      return new AccessControlContext(pd, false);

        // Reuse existing ACC

        this.context = pd;

        this.combiner = null;

        this.isPrivileged = false;

        return this;

    }

    private AccessControlContext goCombiner(ProtectionDomain[] current,

                                        AccessControlContext assigned) {

        // the assigned ACC's combiner is not null --

        // let the combiner do its thing

        // XXX we could add optimizations to 'current' here ...

        if (getDebug() != null) {

            debug.println("AccessControlContext invoking the Combiner");

        }

        // No need to clone current and assigned.context

        // combine() will not update them

        ProtectionDomain[] combinedPds = assigned.combiner.combine(

            current, assigned.context);

        // return new AccessControlContext(combinedPds, assigned.combiner);

        // Reuse existing ACC

        this.context = combinedPds;

        this.combiner = assigned.combiner;

        this.isPrivileged = false;

        return this;

    }

    /**

     * Checks two AccessControlContext objects for equality.

     * Checks that <i>obj</i> is

     * an AccessControlContext and has the same set of ProtectionDomains

     * as this context.

     * <P>

     * @param obj the object we are testing for equality with this object.

     * @return true if <i>obj</i> is an AccessControlContext, and has the

     * same set of ProtectionDomains as this context, false otherwise.

     */

    public boolean equals(Object obj) {

        if (obj == this)

            return true;

        if (! (obj instanceof AccessControlContext))

            return false;

        AccessControlContext that = (AccessControlContext) obj;

        if (context == null) {

            return (that.context == null);

        }

        if (that.context == null)

            return false;

        if (!(this.containsAllPDs(that) && that.containsAllPDs(this)))

            return false;

        if (this.combiner == null)

            return (that.combiner == null);

        if (that.combiner == null)

            return false;

        if (!this.combiner.equals(that.combiner))

            return false;

        return true;

    }

    private boolean containsAllPDs(AccessControlContext that) {