/*

 * Copyright (c) 2005, 2019, 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 com.sun.net.httpserver.spi;

import java.io.IOException;

import java.net.*;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Iterator;

import java.util.ServiceLoader;

import java.util.ServiceConfigurationError;

import com.sun.net.httpserver.*;

/**

 * Service provider class for HttpServer.

 * Sub-classes of HttpServerProvider provide an implementation of

 * {@link HttpServer} and associated classes. Applications do not normally use

 * this class. See {@link #provider()} for how providers are found and loaded.

 */

public abstract class HttpServerProvider {

    /**

     * creates a HttpServer from this provider

     *

     * @param  addr

     *         the address to bind to. May be {@code null}

     *

     * @param  backlog

     *         the socket backlog. A value of {@code zero} means the systems default

     */

    public abstract HttpServer createHttpServer(InetSocketAddress addr,

                                                int backlog)

        throws IOException;

    /**

     * creates a HttpsServer from this provider

     *

     * @param  addr

     *         the address to bind to. May be {@code null}

     *

     * @param  backlog

     *         the socket backlog. A value of {@code zero} means the systems default

     */

    public abstract HttpsServer createHttpsServer(InetSocketAddress addr,

                                                  int backlog)

        throws IOException;

    private static final Object lock = new Object();

    private static HttpServerProvider provider = null;

    /**

     * Initializes a new instance of this class.

     *

     * @throws  SecurityException

     *          If a security manager has been installed and it denies

     *          {@link RuntimePermission}{@code ("httpServerProvider")}

     */

    protected HttpServerProvider() {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null)

            sm.checkPermission(new RuntimePermission("httpServerProvider"));

    }

    private static boolean loadProviderFromProperty() {

        String cn = System.getProperty("com.sun.net.httpserver.HttpServerProvider");

        if (cn == null)

            return false;

        try {

            @SuppressWarnings("deprecation")

            Object o = Class.forName(cn, true,

                                     ClassLoader.getSystemClassLoader()).newInstance();

            provider = (HttpServerProvider)o;

            return true;

        } catch (ClassNotFoundException |

                 IllegalAccessException |

                 InstantiationException |

                 SecurityException x) {

            throw new ServiceConfigurationError(null, x);

        }

    }

    private static boolean loadProviderAsService() {

        Iterator<HttpServerProvider> i =

            ServiceLoader.load(HttpServerProvider.class,

                               ClassLoader.getSystemClassLoader())

                .iterator();

        for (;;) {

            try {

                if (!i.hasNext())

                    return false;

                provider = i.next();

                return true;

            } catch (ServiceConfigurationError sce) {

                if (sce.getCause() instanceof SecurityException) {

                    // Ignore the security exception, try the next provider

                    continue;

                }

                throw sce;

            }

        }

    }

    /**

     * Returns the system wide default HttpServerProvider for this invocation of

     * the Java virtual machine.

     *

     * <p> The first invocation of this method locates the default provider

     * object as follows: </p>

     *

     * <ol>

     *

     *   <li><p> If the system property

     *   {@systemProperty com.sun.net.httpserver.HttpServerProvider}

     *   is defined then it is taken to be the fully-qualified name

     *   of a concrete provider class.

     *   The class is loaded and instantiated; if this process fails then an

     *   unspecified unchecked error or exception is thrown.  </p></li>

     *

     *   <li><p> If a provider class has been installed in a jar file that is

     *   visible to the system class loader, and that jar file contains a

     *   provider-configuration file named

     *   {@code com.sun.net.httpserver.HttpServerProvider} in the resource

     *   directory {@code META-INF/services}, then the first class name

     *   specified in that file is taken.  The class is loaded and

     *   instantiated; if this process fails then an unspecified unchecked error

     *   or exception is thrown.  </p></li>

     *

     *   <li><p> Finally, if no provider has been specified by any of the above

     *   means then the system-default provider class is instantiated and the

     *   result is returned.  </p></li>

     *

     * </ol>

     *

     * <p> Subsequent invocations of this method return the provider that was

     * returned by the first invocation.  </p>

     *

     * @return  The system-wide default HttpServerProvider

     */

    public static HttpServerProvider provider () {

        synchronized (lock) {

            if (provider != null)

                return provider;

            return (HttpServerProvider)AccessController

                .doPrivileged(new PrivilegedAction<Object>() {

                        public Object run() {

                            if (loadProviderFromProperty())

                                return provider;

                            if (loadProviderAsService())

                                return provider;

                            provider = new sun.net.httpserver.DefaultHttpServerProvider();

                            return provider;

                        }

                    });

        }

    }

}