/*
 * Copyright (c) 2005, 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 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
     *   {@code 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;
                        }
                    });
        }
    }

}