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package java.security;

import java.util.Enumeration;

import java.util.WeakHashMap;

import java.util.Objects;

import sun.security.jca.GetInstance;

import sun.security.util.Debug;

import sun.security.util.SecurityConstants;

/**

 * A Policy object is responsible for determining whether code executing

 * in the Java runtime environment has permission to perform a

 * security-sensitive operation.

 *

 * <p> There is only one Policy object installed in the runtime at any

 * given time.  A Policy object can be installed by calling the

 * {@code setPolicy} method.  The installed Policy object can be

 * obtained by calling the {@code getPolicy} method.

 *

 * <p> If no Policy object has been installed in the runtime, a call to

 * {@code getPolicy} installs an instance of the default Policy

 * implementation (a default subclass implementation of this abstract class).

 * The default Policy implementation can be changed by setting the value

 * of the {@code policy.provider} security property to the fully qualified

 * name of the desired Policy subclass implementation. The system class loader

 * is used to load this class.

 *

 * <p> Application code can directly subclass Policy to provide a custom

 * implementation.  In addition, an instance of a Policy object can be

 * constructed by invoking one of the {@code getInstance} factory methods

 * with a standard type.  The default policy type is "JavaPolicy".

 *

 * <p> Once a Policy instance has been installed (either by default, or by

 * calling {@code setPolicy}), the Java runtime invokes its

 * {@code implies} method when it needs to

 * determine whether executing code (encapsulated in a ProtectionDomain)

 * can perform SecurityManager-protected operations.  How a Policy object

 * retrieves its policy data is up to the Policy implementation itself.

 * The policy data may be stored, for example, in a flat ASCII file,

 * in a serialized binary file of the Policy class, or in a database.

 *

 * <p> The {@code refresh} method causes the policy object to

 * refresh/reload its data.  This operation is implementation-dependent.

 * For example, if the policy object stores its data in configuration files,

 * calling {@code refresh} will cause it to re-read the configuration

 * policy files.  If a refresh operation is not supported, this method does

 * nothing.  Note that refreshed policy may not have an effect on classes

 * in a particular ProtectionDomain. This is dependent on the Policy

 * provider's implementation of the {@code implies}

 * method and its PermissionCollection caching strategy.

 *

 * @author Roland Schemers

 * @author Gary Ellison

 * @since 1.2

 * @see java.security.Provider

 * @see java.security.ProtectionDomain

 * @see java.security.Permission

 * @see java.security.Security security properties

 */

public abstract class Policy {

    /**

     * A read-only empty PermissionCollection instance.

     * @since 1.6

     */

    public static final PermissionCollection UNSUPPORTED_EMPTY_COLLECTION =

                        new UnsupportedEmptyCollection();

    // Information about the system-wide policy.

    private static class PolicyInfo {

        // the system-wide policy

        final Policy policy;

        // a flag indicating if the system-wide policy has been initialized

        final boolean initialized;

        PolicyInfo(Policy policy, boolean initialized) {

            this.policy = policy;

            this.initialized = initialized;

        }

    }

    // PolicyInfo is volatile since we apply DCL during initialization.

    // For correctness, care must be taken to read the field only once and only

    // write to it after any other initialization action has taken place.

    private static volatile PolicyInfo policyInfo = new PolicyInfo(null, false);

    private static final Debug debug = Debug.getInstance("policy");

    // Default policy provider

    private static final String DEFAULT_POLICY =

        "sun.security.provider.PolicyFile";

    // Cache mapping ProtectionDomain.Key to PermissionCollection

    private WeakHashMap<ProtectionDomain.Key, PermissionCollection> pdMapping;

    /** package private for AccessControlContext and ProtectionDomain */

    static boolean isSet() {

        PolicyInfo pi = policyInfo;

        return pi.policy != null && pi.initialized == true;

    }

    private static void checkPermission(String type) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new SecurityPermission("createPolicy." + type));

        }

    }

    /**

     * Returns the installed Policy object. This value should not be cached,

     * as it may be changed by a call to {@code setPolicy}.

     * This method first calls

     * {@code SecurityManager.checkPermission} with a

     * {@code SecurityPermission("getPolicy")} permission

     * to ensure it's ok to get the Policy object.

     *

     * @return the installed Policy.

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow

     *        getting the Policy object.

     *

     * @see SecurityManager#checkPermission(Permission)

     * @see #setPolicy(java.security.Policy)

     */

    public static Policy getPolicy()

    {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null)

            sm.checkPermission(SecurityConstants.GET_POLICY_PERMISSION);

        return getPolicyNoCheck();

    }

    /**

     * Returns the installed Policy object, skipping the security check.

     * Used by ProtectionDomain and getPolicy.

     *

     * @return the installed Policy.

     */

    static Policy getPolicyNoCheck()

    {

        PolicyInfo pi = policyInfo;

        // Use double-check idiom to avoid locking if system-wide policy is

        // already initialized

        if (pi.initialized == false || pi.policy == null) {

            synchronized (Policy.class) {

                pi = policyInfo;

                if (pi.policy == null) {

                    return loadPolicyProvider();

                }

            }

        }

        return pi.policy;

    }

    /**

     * Loads and instantiates a Policy implementation specified by the

     * policy.provider security property. Note that this method should only

     * be called by getPolicyNoCheck and from within a synchronized block with

     * an intrinsic lock on the Policy.class.

     */

    private static Policy loadPolicyProvider() {

        String policyProvider =

            AccessController.doPrivileged(new PrivilegedAction<>() {

                @Override

                public String run() {

                    return Security.getProperty("policy.provider");

                }

            });

        /*

         * If policy.provider is not set or is set to the default provider,

         * simply instantiate it and return.

         */

        if (policyProvider == null || policyProvider.isEmpty() ||

            policyProvider.equals(DEFAULT_POLICY))

        {

            Policy polFile = new sun.security.provider.PolicyFile();

            policyInfo = new PolicyInfo(polFile, true);

            return polFile;

        }

        /*

         * Locate, load, and instantiate the policy.provider impl using

         * the system class loader. While doing so, install the bootstrap

         * provider to avoid potential recursion.

         */

        Policy polFile = new sun.security.provider.PolicyFile();

        policyInfo = new PolicyInfo(polFile, false);

        Policy pol = AccessController.doPrivileged(new PrivilegedAction<>() {

            @Override

            public Policy run() {

                try {

                    ClassLoader scl = ClassLoader.getSystemClassLoader();

                    @SuppressWarnings("deprecation")

                    Object o = Class.forName(policyProvider, true, scl).newInstance();

                    return (Policy)o;

                } catch (Exception e) {

                    if (debug != null) {

                        debug.println("policy provider " + policyProvider +

                                      " not available");

                        e.printStackTrace();

                    }

                    return null;

                }

            }

        });

        if (pol == null) {

            // Fallback and use the system default implementation

            if (debug != null) {

                debug.println("using " + DEFAULT_POLICY);

            }

            pol = polFile;

        }

        policyInfo = new PolicyInfo(pol, true);

        return pol;

    }

    /**

     * Sets the system-wide Policy object. This method first calls

     * {@code SecurityManager.checkPermission} with a

     * {@code SecurityPermission("setPolicy")}

     * permission to ensure it's ok to set the Policy.

     *

     * @param p the new system Policy object.

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow

     *        setting the Policy.

     *

     * @see SecurityManager#checkPermission(Permission)

     * @see #getPolicy()

     *

     */

    public static void setPolicy(Policy p)

    {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) sm.checkPermission(

                                 new SecurityPermission("setPolicy"));

        if (p != null) {

            initPolicy(p);

        }

        synchronized (Policy.class) {

            policyInfo = new PolicyInfo(p, p != null);

        }

    }

    /**

     * Initialize superclass state such that a legacy provider can

     * handle queries for itself.

     *

     * @since 1.4

     */

    private static void initPolicy (final Policy p) {

        /*

         * A policy provider not on the bootclasspath could trigger

         * security checks fulfilling a call to either Policy.implies

         * or Policy.getPermissions. If this does occur the provider

         * must be able to answer for it's own ProtectionDomain

         * without triggering additional security checks, otherwise

         * the policy implementation will end up in an infinite

         * recursion.

         *

         * To mitigate this, the provider can collect it's own

         * ProtectionDomain and associate a PermissionCollection while

         * it is being installed. The currently installed policy

         * provider (if there is one) will handle calls to

         * Policy.implies or Policy.getPermissions during this

         * process.

         *

         * This Policy superclass caches away the ProtectionDomain and

         * statically binds permissions so that legacy Policy

         * implementations will continue to function.

         */

        ProtectionDomain policyDomain =

        AccessController.doPrivileged(new PrivilegedAction<>() {

            public ProtectionDomain run() {

                return p.getClass().getProtectionDomain();

            }

        });

        /*

         * Collect the permissions granted to this protection domain

         * so that the provider can be security checked while processing

         * calls to Policy.implies or Policy.getPermissions.

         */

        PermissionCollection policyPerms = null;

        synchronized (p) {

            if (p.pdMapping == null) {

                p.pdMapping = new WeakHashMap<>();

           }

        }

        if (policyDomain.getCodeSource() != null) {

            Policy pol = policyInfo.policy;

            if (pol != null) {

                policyPerms = pol.getPermissions(policyDomain);

            }

            if (policyPerms == null) { // assume it has all

                policyPerms = new Permissions();

                policyPerms.add(SecurityConstants.ALL_PERMISSION);

            }

            synchronized (p.pdMapping) {

                // cache of pd to permissions

                p.pdMapping.put(policyDomain.key, policyPerms);

            }

        }

        return;

    }

    /**

     * Returns a Policy object of the specified type.

     *

     * <p> This method traverses the list of registered security providers,

     * starting with the most preferred Provider.

     * A new Policy object encapsulating the

     * PolicySpi implementation from the first

     * Provider that supports the specified type is returned.

     *

     * <p> Note that the list of registered providers may be retrieved via

     * the {@link Security#getProviders() Security.getProviders()} method.

     *

     * @implNote

     * The JDK Reference Implementation additionally uses the

     * {@code jdk.security.provider.preferred}

     * {@link Security#getProperty(String) Security} property to determine

     * the preferred provider order for the specified algorithm. This

     * may be different than the order of providers returned by

     * {@link Security#getProviders() Security.getProviders()}.

     *

     * @param type the specified Policy type.  See the Policy section in the

     *    <a href=

     *    "{@docRoot}/../specs/security/standard-names.html#policy-types">

     *    Java Security Standard Algorithm Names Specification</a>

     *    for a list of standard Policy types.

     *

     * @param params parameters for the Policy, which may be null.

     *

     * @return the new {@code Policy} object

     *

     * @throws IllegalArgumentException if the specified parameters

     *         are not understood by the {@code PolicySpi} implementation

     *         from the selected {@code Provider}

     *

     * @throws NoSuchAlgorithmException if no {@code Provider} supports

     *         a {@code PolicySpi} implementation for the specified type

     *

     * @throws NullPointerException if {@code type} is {@code null}

     *

     * @throws SecurityException if the caller does not have permission

     *         to get a {@code Policy} instance for the specified type.

     *

     * @see Provider

     * @since 1.6

     */

    public static Policy getInstance(String type, Policy.Parameters params)

                throws NoSuchAlgorithmException {

        Objects.requireNonNull(type, "null type name");

        checkPermission(type);

        try {

            GetInstance.Instance instance = GetInstance.getInstance("Policy",

                                                        PolicySpi.class,

                                                        type,

                                                        params);

            return new PolicyDelegate((PolicySpi)instance.impl,

                                                        instance.provider,

                                                        type,

                                                        params);

        } catch (NoSuchAlgorithmException nsae) {

            return handleException(nsae);

        }

    }

    /**

     * Returns a Policy object of the specified type.

     *

     * <p> A new Policy object encapsulating the

     * PolicySpi implementation from the specified provider

     * is returned.   The specified provider must be registered

     * in the provider list.

     *

     * <p> Note that the list of registered providers may be retrieved via

     * the {@link Security#getProviders() Security.getProviders()} method.

     *

     * @param type the specified Policy type.  See the Policy section in the

     *    <a href=

     *    "{@docRoot}/../specs/security/standard-names.html#policy-types">

     *    Java Security Standard Algorithm Names Specification</a>

     *    for a list of standard Policy types.

     *

     * @param params parameters for the Policy, which may be null.

     *

     * @param provider the provider.

     *

     * @return the new {@code Policy} object

     *

     * @throws IllegalArgumentException if the specified provider

     *         is {@code null} or empty, or if the specified parameters are

     *         not understood by the {@code PolicySpi} implementation from

     *         the specified provider

     *

     * @throws NoSuchAlgorithmException if the specified provider does not

     *         support a {@code PolicySpi} implementation for the specified

     *         type

     *

     * @throws NoSuchProviderException if the specified provider is not

     *         registered in the security provider list

     *

     * @throws NullPointerException if {@code type} is {@code null}

     *

     * @throws SecurityException if the caller does not have permission

     *         to get a {@code Policy} instance for the specified type

     *

     * @see Provider

     * @since 1.6

     */

    public static Policy getInstance(String type,

                                Policy.Parameters params,

                                String provider)

                throws NoSuchProviderException, NoSuchAlgorithmException {

        Objects.requireNonNull(type, "null type name");

        if (provider == null || provider.isEmpty()) {

            throw new IllegalArgumentException("missing provider");

        }

        checkPermission(type);

        try {

            GetInstance.Instance instance = GetInstance.getInstance("Policy",

                                                        PolicySpi.class,

                                                        type,

                                                        params,

                                                        provider);

            return new PolicyDelegate((PolicySpi)instance.impl,

                                                        instance.provider,

                                                        type,

                                                        params);

        } catch (NoSuchAlgorithmException nsae) {

            return handleException(nsae);

        }

    }

    /**

     * Returns a Policy object of the specified type.

     *

     * <p> A new Policy object encapsulating the

     * PolicySpi implementation from the specified Provider

     * object is returned.  Note that the specified Provider object

     * does not have to be registered in the provider list.

     *

     * @param type the specified Policy type.  See the Policy section in the

     *    <a href=

     *    "{@docRoot}/../specs/security/standard-names.html#policy-types">

     *    Java Security Standard Algorithm Names Specification</a>

     *    for a list of standard Policy types.

     *

     * @param params parameters for the Policy, which may be null.

     *

     * @param provider the Provider.

     *

     * @return the new {@code Policy} object

     *

     * @throws IllegalArgumentException if the specified {@code Provider}

     *         is {@code null}, or if the specified parameters are not

     *         understood by the {@code PolicySpi} implementation from the

     *         specified {@code Provider}

     *

     * @throws NoSuchAlgorithmException if the specified {@code Provider}

     *         does not support a {@code PolicySpi} implementation for

     *         the specified type

     *