/*

 * 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,

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 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package java.lang.reflect;

import java.lang.ref.WeakReference;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Arrays;

import java.util.IdentityHashMap;

import java.util.Map;

import java.util.Objects;

import java.util.concurrent.atomic.AtomicLong;

import java.util.function.BiFunction;

import sun.misc.ProxyGenerator;

import sun.misc.VM;

import sun.reflect.CallerSensitive;

import sun.reflect.Reflection;

import sun.reflect.misc.ReflectUtil;

import sun.security.util.SecurityConstants;

/**

 * {@code Proxy} provides static methods for creating dynamic proxy

 * classes and instances, and it is also the superclass of all

 * dynamic proxy classes created by those methods.

 *

 * <p>To create a proxy for some interface {@code Foo}:

 * <pre>

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

 *     Class<?> proxyClass = Proxy.getProxyClass(Foo.class.getClassLoader(), Foo.class);

 *     Foo f = (Foo) proxyClass.getConstructor(InvocationHandler.class).

 *                     newInstance(handler);

 * </pre>

 * or more simply:

 * <pre>

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

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

 *                                          handler);

 * </pre>

 *

 * <p>A <i>dynamic proxy class</i> (simply referred to as a <i>proxy

 * class</i> below) is a class that implements a list of interfaces

 * specified at runtime when the class is created, with behavior as

 * described below.

 *

 * A <i>proxy interface</i> is such an interface that is implemented

 * by a proxy class.

 *

 * A <i>proxy instance</i> 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>Proxy classes are <em>public, final, and not abstract</em> if

 * all proxy interfaces are public.</li>

 *

 * <li>Proxy classes are <em>non-public, final, and not abstract</em> if

 * any of the proxy interfaces is non-public.</li>

 *

 * <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>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.

 *

 * <li>If a proxy class implements a non-public interface, then it will

 * be defined in the same package as that interface.  Otherwise, the

 * package of a proxy class is also unspecified.  Note that package

 * sealing will not prevent a proxy class from being successfully defined

 * in a particular package at runtime, and neither will classes already

 * defined by the same class loader and the same package with particular

 * signers.

 *

 * <li>Since a proxy class implements all of the interfaces specified at

 * its creation, invoking {@code getInterfaces} on its

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

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

 * {@code 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 Proxy#isProxyClass Proxy.isProxyClass} method will

 * return true if it is passed a proxy class-- a class returned by

 * {@code Proxy.getProxyClass} or the class of an object returned by

 * {@code Proxy.newProxyInstance}-- and false otherwise.

 *

 * <li>The {@code 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>Each proxy class has one public constructor that takes one argument,

 * an implementation of the interface {@link InvocationHandler}, to set

 * the invocation handler for a proxy instance.  Rather than having to use

 * the reflection API to access the public constructor, a proxy instance

 * can be also be created by calling the {@link Proxy#newProxyInstance

 * Proxy.newProxyInstance} method, which combines the actions of calling

 * {@link Proxy#getProxyClass Proxy.getProxyClass} with invoking the

 * constructor with an invocation handler.

 * </ul>

 *

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

 *

 * <ul>

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

 * interfaces implemented by its proxy class {@code Foo}, 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>Methods Duplicated in Multiple Proxy Interfaces</h3>

 *

 * <p>When two or more interfaces of a proxy class 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 classes

     */

    private static final WeakCache<ClassLoader, Class<?>[], Class<?>>

        proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());

    /**

     * 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.

     *

     * <p>There are several restrictions on the parameters that may be

     * passed to {@code Proxy.getProxyClass}:

     *

     * <ul>

     * <li>All of the {@code Class} objects in the

     * {@code interfaces} array must represent interfaces, not

     * classes or primitive types.

     *

     * <li>No two elements in the {@code interfaces} array may

     * refer to identical {@code Class} objects.

     *

     * <li>All of the interface types must be visible by name through the

     * specified class loader.  In other words, for class loader

     * {@code cl} and every interface {@code i}, the following

     * expression must be true:

     * <pre>

     *     Class.forName(i.getName(), false, cl) == i

     * </pre>

     *

     * <li>All non-public interfaces must be in the same package;

     * otherwise, it would not be possible for the proxy class to

     * implement all of the interfaces, regardless of what package it is

     * defined in.

     *

     * <li>For any set of member methods of the specified interfaces

     * that have the same signature:

     * <ul>

     * <li>If the return type of any of the methods is a primitive

     * type or void, then all of the methods must have that same

     * return type.

     * <li>Otherwise, one of the methods must have a return type that

     * is assignable to all of the return types of the rest of the

     * methods.

     * </ul>

     *

     * <li>The resulting proxy class must not exceed any limits imposed

     * on classes by the virtual machine.  For example, the VM may limit

     * the number of interfaces that a class may implement to 65535; in

     * that case, the size of the {@code interfaces} array must not

     * exceed 65535.

     * </ul>

     *

     * <p>If any of these restrictions are violated,

     * {@code Proxy.getProxyClass} will throw an

     * {@code IllegalArgumentException}.  If the {@code interfaces}

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

     * {@code NullPointerException} will be thrown.

     *

     * <p>Note that the order of the specified proxy interfaces is

     * significant: two requests for a proxy class with the same combination

     * of interfaces but in a different order will result in two distinct

     * proxy classes.

     *

     * @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 restrictions on the

     *          parameters that may be passed to {@code getProxyClass}

     *          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}

     */

    @CallerSensitive

    public static Class<?> getProxyClass(ClassLoader loader,

                                         Class<?>... interfaces)

        throws IllegalArgumentException

    {

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

        final SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);

        }

        return getProxyClass0(loader, intfs);

    }

    /*

     * 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 via the defineClass0 method.

     */

    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);

        }

    }

    /**

     * Generate a proxy class.  Must call the checkProxyAccess method

     * to perform permission checks before calling this.

     */

    private static Class<?> getProxyClass0(ClassLoader loader,

                                           Class<?>... interfaces) {

        if (interfaces.length > 65535) {

            throw new IllegalArgumentException("interface limit exceeded");

        }

        // If the proxy class defined by the given loader implementing

        // the given interfaces exists, this will simply return the cached copy;

        // otherwise, it will create the proxy class via the ProxyClassFactory

        return proxyClassCache.get(loader, interfaces);

    }

    /*

     * a key used for proxy class with 0 implemented interfaces

     */

    private static final Object key0 = new Object();

    /*

     * Key1 and Key2 are optimized for the common use of dynamic proxies

     * that implement 1 or 2 interfaces.

     */

    /*

     * a key used for proxy class with 1 implemented interface

     */

    private static final class Key1 extends WeakReference<Class<?>> {

        private final int hash;

        Key1(Class<?> intf) {

            super(intf);

            this.hash = intf.hashCode();

        }

        @Override

        public int hashCode() {

            return hash;

        }

        @Override

        public boolean equals(Object obj) {

            Class<?> intf;

            return this == obj ||

                   obj != null &&

                   obj.getClass() == Key1.class &&

                   (intf = get()) != null &&

                   intf == ((Key1) obj).get();

        }

    }

    /*

     * a key used for proxy class with 2 implemented interfaces

     */

    private static final class Key2 extends WeakReference<Class<?>> {

        private final int hash;

        private final WeakReference<Class<?>> ref2;

        Key2(Class<?> intf1, Class<?> intf2) {

            super(intf1);

            hash = 31 * intf1.hashCode() + intf2.hashCode();

            ref2 = new WeakReference<>(intf2);

        }

        @Override

        public int hashCode() {

            return hash;

        }

        @Override

        public boolean equals(Object obj) {

            Class<?> intf1, intf2;

            return this == obj ||

                   obj != null &&

                   obj.getClass() == Key2.class &&

                   (intf1 = get()) != null &&

                   intf1 == ((Key2) obj).get() &&

                   (intf2 = ref2.get()) != null &&

                   intf2 == ((Key2) obj).ref2.get();

        }

    }

    /*

     * a key used for proxy class with any number of implemented interfaces

     * (used here for 3 or more only)

     */

    private static final class KeyX {

        private final int hash;

        private final WeakReference<Class<?>>[] refs;

        @SuppressWarnings("unchecked")

        KeyX(Class<?>[] interfaces) {

            hash = Arrays.hashCode(interfaces);

            refs = (WeakReference<Class<?>>[])new WeakReference<?>[interfaces.length];

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

                refs[i] = new WeakReference<>(interfaces[i]);

            }

        }

        @Override

        public int hashCode() {

            return hash;

        }