/*
 * @(#)ProxySelector.java	1.3 03/08/09
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.net;

import java.io.IOException;
import java.util.List;
import sun.security.util.SecurityConstants;

/**
 * Selects the proxy server to use, if any, when connecting to the
 * network resource referenced by a URL. A proxy selector is a
 * concrete sub-class of this class and is registered by invoking the
 * {@link java.net.ProxySelector#setDefault setDefault} method. The
 * currently registered proxy selector can be retrieved by calling
 * {@link java.net.ProxySelector#getDefault getDefault} method.
 * 
 * <p> When a proxy selector is registered, for instance, a subclass
 * of URLConnection class should call the {@link #select select}
 * method for each URL request so that the proxy selector can decide
 * if a direct, or proxied connection should be used. The {@link
 * #select select} method returns an iterator over a collection with
 * the preferred connection approach.
 *
 * <p> If a connection cannot be established to a proxy (PROXY or
 * SOCKS) servers then the caller should call the proxy selector's
 * {@link #connectFailed connectFailed} method to notify the proxy
 * selector that the proxy server is unavailable. </p>
 *
 * @version 1.3, 03/08/09
 * @author Yingxian Wang
 * @author Jean-Christophe Collet
 * @since 1.5
 */
public abstract class ProxySelector {
    /**
     * The system wide proxy selector that selects the proxy server to
     * use, if any, when connecting to a remote object referenced by
     * an URL.
     *
     * @see #setDefault(ProxySelector)
     */
    private static ProxySelector theProxySelector;

    static { 
	try {
	    Class c = Class.forName("sun.net.spi.DefaultProxySelector");
	    if (c != null && ProxySelector.class.isAssignableFrom(c)) {
		theProxySelector = (ProxySelector) c.newInstance();
	    }
	} catch (Exception e) {
	    theProxySelector = null;
	}
    }

    /**
     * Gets the system-wide proxy selector.
     *
     * @throws  SecurityException
     *          If a security manager has been installed and it denies
     * {@link NetPermission}<tt>("getProxySelector")</tt>
     * @see #setDefault(ProxySelector)
     * @return the system-wide <code>ProxySelector</code> 
     * @since 1.5
     */
    public static ProxySelector getDefault() {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    sm.checkPermission(SecurityConstants.GET_PROXYSELECTOR_PERMISSION);
	}
	return theProxySelector;
    }
  
    /**
     * Sets (or unsets) the system-wide proxy selector.
     *
     * Note: non-standard protocol handlers may ignore this setting.
     *
     * @param ps The HTTP proxy selector, or
     *		<code>null</code> to unset the proxy selector.
     *
     * @throws  SecurityException
     *          If a security manager has been installed and it denies
     * {@link NetPermission}<tt>("setProxySelector")</tt>
     *
     * @see #getDefault()
     * @since 1.5
     */
    public static void setDefault(ProxySelector ps) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    sm.checkPermission(SecurityConstants.SET_PROXYSELECTOR_PERMISSION);
	}
	theProxySelector = ps;
    }
    
    /**
     * Selects all the applicable proxies based on the protocol to
     * access the resource with and a destination address to access
     * the resource at.
     * The format of the URI is defined as follow:
     * <UL>
     * <LI>http URI for http connections</LI>
     * <LI>https URI for https connections
     * <LI>ftp URI for ftp connections</LI>
     * <LI><code>socket://host:port</code><br>
     *     for tcp client sockets connections</LI>
     * </UL>
     *
     * @param	uri
     *		The URI that a connection is required to
     *
     * @return	a List of Proxies. Each element in the
     *		the List is of type 
     *          {@link java.net.Proxy Proxy};
     *          when no proxy is available, the list will
     *          contain one element of type
     *          {@link java.net.Proxy Proxy}
     *          that represents a direct connection.
     * @throws IllegalArgumentException if either argument is null
     */
    public abstract List<Proxy> select(URI uri);

    /**
     * Called to indicate that a connection could not be established
     * to a proxy/socks server. An implementation of this method can
     * temporarily remove the proxies or reorder the sequence of
     * proxies returned by select(String, String), using the address
     * and they kind of IOException given.
     *
     * @param   uri
     *          The URI that the proxy at sa failed to serve.
     * @param	sa
     *		The socket address of the proxy/SOCKS server
     *
     * @param	ioe
     *		The I/O exception thrown when the connect failed.
     * @throws IllegalArgumentException if either argument is null
     */
    public abstract void connectFailed(URI uri, SocketAddress sa, IOException ioe);
}