/*

 * Copyright (c) 1999, 2013, Oracle and/or its affiliates. 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.  Oracle designates this

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

 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.lang.reflect;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Arrays;

import java.util.Collections;

import java.util.HashMap;

import java.util.HashSet;

import java.util.IdentityHashMap;

import java.util.List;

import java.util.Map;

import java.util.Objects;

import java.util.Set;

import java.util.concurrent.atomic.AtomicInteger;

import java.util.concurrent.atomic.AtomicLong;

import java.util.stream.Collectors;

import java.util.stream.Stream;

import jdk.internal.loader.BootLoader;

import jdk.internal.module.Modules;

import jdk.internal.misc.Unsafe;

import jdk.internal.misc.VM;

import jdk.internal.reflect.CallerSensitive;

import jdk.internal.reflect.Reflection;

import jdk.internal.loader.ClassLoaderValue;

import sun.reflect.misc.ReflectUtil;

import sun.security.action.GetPropertyAction;

import sun.security.util.SecurityConstants;

/**

 *

 * {@code Proxy} provides static methods for creating objects that act like instances

 * of interfaces but allow for customized method invocation.

 * To create a proxy instance for some interface {@code Foo}:

 * <pre>{@code

 *     InvocationHandler handler = new MyInvocationHandler(...);

 *     Foo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),

 *                                          new Class<?>[] { Foo.class },

 *                                          handler);

 * }</pre>

 *

 * <p>

 * A <em>proxy class</em> is a class created at runtime that implements a specified

 * list of interfaces, known as <em>proxy interfaces</em>. A <em>proxy instance</em>

 * is an instance of a proxy class.

 *

 * Each proxy instance has an associated <i>invocation handler</i>

 * object, which implements the interface {@link InvocationHandler}.

 * A method invocation on a proxy instance through one of its proxy

 * interfaces will be dispatched to the {@link InvocationHandler#invoke

 * invoke} method of the instance's invocation handler, passing the proxy

 * instance, a {@code java.lang.reflect.Method} object identifying

 * the method that was invoked, and an array of type {@code Object}

 * containing the arguments.  The invocation handler processes the

 * encoded method invocation as appropriate and the result that it

 * returns will be returned as the result of the method invocation on

 * the proxy instance.

 *

 * <p>A proxy class has the following properties:

 *

 * <ul>

 * <li>The unqualified name of a proxy class is unspecified.  The space

 * of class names that begin with the string {@code "$Proxy"}

 * should be, however, reserved for proxy classes.

 *

 * <li>The package and module in which a proxy class is defined is specified

 * <a href="#membership">below</a>.

 *

 * <li>A proxy class is <em>final and non-abstract</em>.

 *

 * <li>A proxy class extends {@code java.lang.reflect.Proxy}.

 *

 * <li>A proxy class implements exactly the interfaces specified at its

 * creation, in the same order. Invoking {@link Class#getInterfaces getInterfaces}

 * on its {@code Class} object will return an array containing the same

 * list of interfaces (in the order specified at its creation), invoking

 * {@link Class#getMethods getMethods} on its {@code Class} object will return

 * an array of {@code Method} objects that include all of the

 * methods in those interfaces, and invoking {@code getMethod} will

 * find methods in the proxy interfaces as would be expected.

 *

 * <li>The {@link java.security.ProtectionDomain} of a proxy class

 * is the same as that of system classes loaded by the bootstrap class

 * loader, such as {@code java.lang.Object}, because the code for a

 * proxy class is generated by trusted system code.  This protection

 * domain will typically be granted {@code java.security.AllPermission}.

 *

 * <li>The {@link Proxy#isProxyClass Proxy.isProxyClass} method can be used

 * to determine if a given class is a proxy class.

 * </ul>

 *

 * <p>A proxy instance has the following properties:

 *

 * <ul>

 * <li>Given a proxy instance {@code proxy} and one of the

 * interfaces, {@code Foo}, implemented by its proxy class, the

 * following expression will return true:

 * <pre>

 *     {@code proxy instanceof Foo}

 * </pre>

 * and the following cast operation will succeed (rather than throwing

 * a {@code ClassCastException}):

 * <pre>

 *     {@code (Foo) proxy}

 * </pre>

 *

 * <li>Each proxy instance has an associated invocation handler, the one

 * that was passed to its constructor.  The static

 * {@link Proxy#getInvocationHandler Proxy.getInvocationHandler} method

 * will return the invocation handler associated with the proxy instance

 * passed as its argument.

 *

 * <li>An interface method invocation on a proxy instance will be

 * encoded and dispatched to the invocation handler's {@link

 * InvocationHandler#invoke invoke} method as described in the

 * documentation for that method.

 *

 * <li>An invocation of the {@code hashCode},

 * {@code equals}, or {@code toString} methods declared in

 * {@code java.lang.Object} on a proxy instance will be encoded and

 * dispatched to the invocation handler's {@code invoke} method in

 * the same manner as interface method invocations are encoded and

 * dispatched, as described above.  The declaring class of the

 * {@code Method} object passed to {@code invoke} will be

 * {@code java.lang.Object}.  Other public methods of a proxy

 * instance inherited from {@code java.lang.Object} are not

 * overridden by a proxy class, so invocations of those methods behave

 * like they do for instances of {@code java.lang.Object}.

 * </ul>

 *

 * <h3><a name="membership">Package and Module Membership of Proxy Class</a></h3>

 *

 * The package and module to which a proxy class belongs are chosen such that

 * the accessibility of the proxy class is in line with the accessibility of

 * the proxy interfaces. Specifically, the package and the module membership

 * of a proxy class defined via the

 * {@link Proxy#getProxyClass(ClassLoader, Class[])} or

 * {@link Proxy#newProxyInstance(ClassLoader, Class[], InvocationHandler)}

 * methods is specified as follows:

 *

 * <ol>

 * <li>If all the proxy interfaces are in <em>exported</em> packages:

 * <ol type="a">

 * <li>if all the proxy interfaces are <em>public</em>, then the proxy class is

 *     <em>public</em> in a package exported by the

 *     {@linkplain ClassLoader#getUnnamedModule() unnamed module} of the specified

 *     loader. The name of the package is unspecified.</li>

 *

 * <li>if at least one of all the proxy interfaces is <em>non-public</em>, then

 *     the proxy class is <em>non-public</em> in the package and module of the

 *     non-public interfaces. All the non-public interfaces must be in the same

 *     package and module; otherwise, proxying them is

 *     <a href="#restrictions">not possible</a>.</li>

 * </ol>

 * </li>

 * <li>If at least one proxy interface is a <em>non-exported</em> package:

 * <ol type="a">

 * <li>if all the proxy interfaces are <em>public</em>, then the proxy class is

 *     <em>public</em> in a <em>non-exported</em> package of

 *     <a href="#dynamicmodule"><em>dynamic module</em>.</a>

 *     The names of the package and the module are unspecified.</li>

 *

 * <li>if at least one of all the proxy interfaces is <em>non-public</em>, then

 *     the proxy class is <em>non-public</em> in the package and module of the

 *     non-public interfaces. All the non-public interfaces must be in the same

 *     package and module; otherwise, proxying them is

 *     <a href="#restrictions">not possible</a>.</li>

 * </ol>

 * </li>

 * </ol>

 *

 * <p>

 * Note that if proxy interfaces with a mix of accessibilities --

 * exported public, exported non-public, non-exported public, non-exported non-public --

 * are proxied by the same instance, then the proxy class's accessibility is

 * governed by the least accessible proxy interface.

 * <p>

 * Note that it is possible for arbitrary code to obtain access to a proxy class

 * in an exported package with {@link AccessibleObject#setAccessible setAccessible},

 * whereas a proxy class in a non-exported package is never accessible to

 * code outside the module of the proxy class.

 *

 * <p>

 * Throughout this specification, a "non-exported package" refers to a package that

 * is not exported to all modules. Specifically, it refers to a package that

 * either is not exported at all by its containing module or is exported in a

 * qualified fashion by its containing module.

 *

 * <h3><a name="dynamicmodule">Dynamic Modules</a></h3>

 * <p>

 * A dynamic module is a named module generated at runtime. A proxy class

 * defined in a dynamic module is encapsulated and not accessible to any module.

 * Calling {@link Constructor#newInstance(Object...)} on a proxy class in

 * a dynamic module will throw {@code IllegalAccessException};

 * {@code Proxy.newProxyInstance} method should be used instead.

 *

 * <p>

 * A dynamic module can read the modules of all of the superinterfaces of a proxy class

 * and the modules of the types referenced by all public method signatures

 * of a proxy class.  If a superinterface or a referenced type, say {@code T},

 * is in a non-exported package, the {@linkplain java.lang.reflect.Module module}

 * of {@code T} is updated to export the package of {@code T} to the dynamic module.

 *

 * <h3>Methods Duplicated in Multiple Proxy Interfaces</h3>

 *

 * <p>When two or more proxy interfaces contain a method with

 * the same name and parameter signature, the order of the proxy class's

 * interfaces becomes significant.  When such a <i>duplicate method</i>

 * is invoked on a proxy instance, the {@code Method} object passed

 * to the invocation handler will not necessarily be the one whose

 * declaring class is assignable from the reference type of the interface

 * that the proxy's method was invoked through.  This limitation exists

 * because the corresponding method implementation in the generated proxy

 * class cannot determine which interface it was invoked through.

 * Therefore, when a duplicate method is invoked on a proxy instance,

 * the {@code Method} object for the method in the foremost interface

 * that contains the method (either directly or inherited through a

 * superinterface) in the proxy class's list of interfaces is passed to

 * the invocation handler's {@code invoke} method, regardless of the

 * reference type through which the method invocation occurred.

 *

 * <p>If a proxy interface contains a method with the same name and

 * parameter signature as the {@code hashCode}, {@code equals},

 * or {@code toString} methods of {@code java.lang.Object},

 * when such a method is invoked on a proxy instance, the

 * {@code Method} object passed to the invocation handler will have

 * {@code java.lang.Object} as its declaring class.  In other words,

 * the public, non-final methods of {@code java.lang.Object}

 * logically precede all of the proxy interfaces for the determination of

 * which {@code Method} object to pass to the invocation handler.

 *

 * <p>Note also that when a duplicate method is dispatched to an

 * invocation handler, the {@code invoke} method may only throw

 * checked exception types that are assignable to one of the exception

 * types in the {@code throws} clause of the method in <i>all</i> of

 * the proxy interfaces that it can be invoked through.  If the

 * {@code invoke} method throws a checked exception that is not

 * assignable to any of the exception types declared by the method in one

 * of the proxy interfaces that it can be invoked through, then an

 * unchecked {@code UndeclaredThrowableException} will be thrown by

 * the invocation on the proxy instance.  This restriction means that not

 * all of the exception types returned by invoking

 * {@code getExceptionTypes} on the {@code Method} object

 * passed to the {@code invoke} method can necessarily be thrown

 * successfully by the {@code invoke} method.

 *

 * @author      Peter Jones

 * @see         InvocationHandler

 * @since       1.3

 */

public class Proxy implements java.io.Serializable {

    private static final long serialVersionUID = -2222568056686623797L;

    /** parameter types of a proxy class constructor */

    private static final Class<?>[] constructorParams =

        { InvocationHandler.class };

    /**

     * a cache of proxy constructors with

     * {@link Constructor#setAccessible(boolean) accessible} flag already set

     */

    private static final ClassLoaderValue<Constructor<?>> proxyCache =

        new ClassLoaderValue<>();

    /**

     * the invocation handler for this proxy instance.

     * @serial

     */

    protected InvocationHandler h;

    /**

     * Prohibits instantiation.

     */

    private Proxy() {

    }

    /**

     * Constructs a new {@code Proxy} instance from a subclass

     * (typically, a dynamic proxy class) with the specified value

     * for its invocation handler.

     *

     * @param  h the invocation handler for this proxy instance

     *

     * @throws NullPointerException if the given invocation handler, {@code h},

     *         is {@code null}.

     */

    protected Proxy(InvocationHandler h) {

        Objects.requireNonNull(h);

        this.h = h;

    }

    /**

     * Returns the {@code java.lang.Class} object for a proxy class

     * given a class loader and an array of interfaces.  The proxy class

     * will be defined by the specified class loader and will implement

     * all of the supplied interfaces.  If any of the given interfaces

     * is non-public, the proxy class will be non-public. If a proxy class

     * for the same permutation of interfaces has already been defined by the

     * class loader, then the existing proxy class will be returned; otherwise,

     * a proxy class for those interfaces will be generated dynamically

     * and defined by the class loader.

     *

     * @param   loader the class loader to define the proxy class

     * @param   interfaces the list of interfaces for the proxy class

     *          to implement

     * @return  a proxy class that is defined in the specified class loader

     *          and that implements the specified interfaces

     * @throws  IllegalArgumentException if any of the <a href="#restrictions">

     *          restrictions</a> on the parameters are violated

     * @throws  SecurityException if a security manager, <em>s</em>, is present

     *          and any of the following conditions is met:

     *          <ul>

     *             <li> the given {@code loader} is {@code null} and

     *             the caller's class loader is not {@code null} and the

     *             invocation of {@link SecurityManager#checkPermission

     *             s.checkPermission} with

     *             {@code RuntimePermission("getClassLoader")} permission

     *             denies access.</li>

     *             <li> for each proxy interface, {@code intf},

     *             the caller's class loader is not the same as or an

     *             ancestor of the class loader for {@code intf} and

     *             invocation of {@link SecurityManager#checkPackageAccess

     *             s.checkPackageAccess()} denies access to {@code intf}.</li>

     *          </ul>

     * @throws  NullPointerException if the {@code interfaces} array

     *          argument or any of its elements are {@code null}

     *

     * @deprecated Proxy classes generated in a named module are encapsulated and not

     *      accessible to code outside its module.

     *      {@link Constructor#newInstance(Object...) Constructor.newInstance} will throw

     *      {@code IllegalAccessException} when it is called on an inaccessible proxy class.

     *      Use {@link #newProxyInstance(ClassLoader, Class[], InvocationHandler)}

     *      to create a proxy instance instead.

     *

     * @see <a href="#membership">Package and Module Membership of Proxy Class</a>

     */

    @Deprecated

    @CallerSensitive

    public static Class<?> getProxyClass(ClassLoader loader,

                                         Class<?>... interfaces)

        throws IllegalArgumentException

    {

        Class<?> caller = System.getSecurityManager() == null

                              ? null

                              : Reflection.getCallerClass();

        return getProxyConstructor(caller, loader, interfaces)

            .getDeclaringClass();

    }

    /**

     * Returns the {@code Constructor} object of a proxy class that takes a

     * single argument of type {@link InvocationHandler}, given a class loader

     * and an array of interfaces. The returned constructor will have the

     * {@link Constructor#setAccessible(boolean) accessible} flag already set.

     *

     * @param   caller passed from a public-facing @CallerSensitive method if

     *                 SecurityManager is set or {@code null} if there's no

     *                 SecurityManager

     * @param   loader the class loader to define the proxy class

     * @param   interfaces the list of interfaces for the proxy class

     *          to implement

     * @return  a Constructor of the proxy class taking single

     *          {@code InvocationHandler} parameter

     */

    private static Constructor<?> getProxyConstructor(Class<?> caller,

                                                      ClassLoader loader,

                                                      Class<?>... interfaces)

    {

        // optimization for single interface

        if (interfaces.length == 1) {

            Class<?> intf = interfaces[0];

            if (caller != null) {

                checkProxyAccess(caller, loader, intf);

            }

            return proxyCache.sub(intf).computeIfAbsent(

                loader,

                (ld, clv) -> new ProxyBuilder(ld, clv.key()).build()

            );

        } else {

            // interfaces cloned

            final Class<?>[] intfsArray = interfaces.clone();

            if (caller != null) {

                checkProxyAccess(caller, loader, intfsArray);

            }

            final List<Class<?>> intfs = Arrays.asList(intfsArray);

            return proxyCache.sub(intfs).computeIfAbsent(

                loader,

                (ld, clv) -> new ProxyBuilder(ld, clv.key()).build()

            );

        }

    }

    /*

     * Check permissions required to create a Proxy class.

     *

     * To define a proxy class, it performs the access checks as in

     * Class.forName (VM will invoke ClassLoader.checkPackageAccess):

     * 1. "getClassLoader" permission check if loader == null

     * 2. checkPackageAccess on the interfaces it implements

     *

     * To get a constructor and new instance of a proxy class, it performs

     * the package access check on the interfaces it implements

     * as in Class.getConstructor.

     *

     * If an interface is non-public, the proxy class must be defined by

     * the defining loader of the interface.  If the caller's class loader

     * is not the same as the defining loader of the interface, the VM

     * will throw IllegalAccessError when the generated proxy class is

     * being defined.

     */

    private static void checkProxyAccess(Class<?> caller,

                                         ClassLoader loader,

                                         Class<?> ... interfaces)

    {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            ClassLoader ccl = caller.getClassLoader();

            if (VM.isSystemDomainLoader(loader) && !VM.isSystemDomainLoader(ccl)) {

                sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);

            }

            ReflectUtil.checkProxyPackageAccess(ccl, interfaces);

        }

    }

    /**

     * Builder for a proxy class.

     *

     * If the module is not specified in this ProxyBuilder constructor,

     * it will map from the given loader and interfaces to the module

     * in which the proxy class will be defined.

     */

    private static final class ProxyBuilder {

        private static final Unsafe UNSAFE = Unsafe.getUnsafe();

        // prefix for all proxy class names

        private static final String proxyClassNamePrefix = "$Proxy";

        // next number to use for generation of unique proxy class names

        private static final AtomicLong nextUniqueNumber = new AtomicLong();

        // a reverse cache of defined proxy classes

        private static final ClassLoaderValue<Boolean> reverseProxyCache =

            new ClassLoaderValue<>();

        private static Class<?> defineProxyClass(Module m, List<Class<?>> interfaces) {

            String proxyPkg = null;     // package to define proxy class in

            int accessFlags = Modifier.PUBLIC | Modifier.FINAL;

            /*

             * Record the package of a non-public proxy interface so that the

             * proxy class will be defined in the same package.  Verify that

             * all non-public proxy interfaces are in the same package.

             */

            for (Class<?> intf : interfaces) {

                int flags = intf.getModifiers();

                if (!Modifier.isPublic(flags)) {

                    accessFlags = Modifier.FINAL;  // non-public, final

                    String pkg = intf.getPackageName();

                    if (proxyPkg == null) {

                        proxyPkg = pkg;

                    } else if (!pkg.equals(proxyPkg)) {

                        throw new IllegalArgumentException(

                                "non-public interfaces from different packages");

                    }

                }

            }

            if (proxyPkg == null) {

                // all proxy interfaces are public

                proxyPkg = m.isNamed() ? PROXY_PACKAGE_PREFIX + "." + m.getName()

                                       : PROXY_PACKAGE_PREFIX;

            } else if (proxyPkg.isEmpty() && m.isNamed()) {

                throw new IllegalArgumentException(

                        "Unnamed package cannot be added to " + m);

            }