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 * Copyright (c) 1995, 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 java.net;

import java.io.FileDescriptor;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Objects;

import java.util.Set;

import sun.net.NetProperties;

import sun.net.PlatformSocketImpl;

import sun.nio.ch.NioSocketImpl;

/**

 * The abstract class {@code SocketImpl} is a common superclass

 * of all classes that actually implement sockets. It is used to

 * create both client and server sockets.

 *

 * @implNote Client and server sockets created with the {@code Socket} and

 * {@code SocketServer} public constructors create a system-default

 * {@code SocketImpl}. The JDK historically used a {@code SocketImpl}

 * implementation type named "PlainSocketImpl" that has since been replaced by a

 * newer implementation. The JDK continues to ship with the older implementation

 * to allow code to run that depends on unspecified behavior that differs between

 * the old and new implementations. The old implementation will be used if the

 * Java virtual machine is started with the system property {@systemProperty

 * jdk.net.usePlainSocketImpl} set to use the old implementation. It may also be

 * set in the JDK's network configuration file, located in {@code

 * ${java.home}/conf/net.properties}. The value of the property is the string

 * representation of a boolean. If set without a value then it defaults to {@code

 * true}, hence running with {@code -Djdk.net.usePlainSocketImpl} or {@code

 * -Djdk.net.usePlainSocketImpl=true} will configure the Java virtual machine

 * to use the old implementation. The property and old implementation will be

 * removed in a future version.

 *

 * @author  unascribed

 * @since   1.0

 */

public abstract class SocketImpl implements SocketOptions {

    private static final boolean USE_PLAINSOCKETIMPL = usePlainSocketImpl();

    private static boolean usePlainSocketImpl() {

        PrivilegedAction<String> pa = () -> NetProperties.get("jdk.net.usePlainSocketImpl");

        String s = AccessController.doPrivileged(pa);

        return (s != null) && !s.equalsIgnoreCase("false");

    }

    /**

     * Creates an instance of platform's SocketImpl

     */

    @SuppressWarnings("unchecked")

    static <S extends SocketImpl & PlatformSocketImpl> S createPlatformSocketImpl(boolean server) {

        if (USE_PLAINSOCKETIMPL) {

            return (S) new PlainSocketImpl(server);

        } else {

            return (S) new NioSocketImpl(server);

        }

    }

    /**

     * The file descriptor object for this socket.

     */

    protected FileDescriptor fd;

    /**

     * The IP address of the remote end of this socket.

     */

    protected InetAddress address;

    /**

     * The port number on the remote host to which this socket is connected.

     */

    protected int port;

    /**

     * The local port number to which this socket is connected.

     */

    protected int localport;

    /**

     * Initialize a new instance of this class

     */

    public SocketImpl() { }

    /**

     * Creates either a stream or a datagram socket.

     *

     * @param      stream   if {@code true}, create a stream socket;

     *                      otherwise, create a datagram socket.

     *               socket.

     */

    protected abstract void create(boolean stream) throws IOException;

    /**

     * Connects this socket to the specified port on the named host.

     *

     * @param      host   the name of the remote host.

     * @param      port   the port number.

     *               remote host.

     */

    protected abstract void connect(String host, int port) throws IOException;

    /**

     * Connects this socket to the specified port number on the specified host.

     *

     * @param      address   the IP address of the remote host.

     * @param      port      the port number.

     *               connection.

     */

    protected abstract void connect(InetAddress address, int port) throws IOException;

    /**

     * Connects this socket to the specified port number on the specified host.

     * A timeout of zero is interpreted as an infinite timeout. The connection

     * will then block until established or an error occurs.

     *

     * @param      address   the Socket address of the remote host.

     * @param     timeout  the timeout value, in milliseconds, or zero for no timeout.

     *               connection.

     * @since 1.4

     */

    protected abstract void connect(SocketAddress address, int timeout) throws IOException;

    /**

     * Binds this socket to the specified local IP address and port number.

     *

     * @param      host   an IP address that belongs to a local interface.

     * @param      port   the port number.

     */

    protected abstract void bind(InetAddress host, int port) throws IOException;

    /**

     * Sets the maximum queue length for incoming connection indications

     * (a request to connect) to the {@code count} argument. If a

     * connection indication arrives when the queue is full, the

     * connection is refused.

     *

     * @param      backlog   the maximum length of the queue.

     */

    protected abstract void listen(int backlog) throws IOException;

    /**

     * Accepts a connection.

     *

     * @param      s   the accepted connection.

     *               connection.

     */

    protected abstract void accept(SocketImpl s) throws IOException;

    /**

     * Returns an input stream for this socket.

     *

     * @return     a stream for reading from this socket.

     *               input stream.

    */

    protected abstract InputStream getInputStream() throws IOException;

    /**

     * Returns an output stream for this socket.

     *

     * @return     an output stream for writing to this socket.

     *               output stream.

     */

    protected abstract OutputStream getOutputStream() throws IOException;

    /**

     * Returns the number of bytes that can be read from this socket

     * without blocking.

     *

     * @return     the number of bytes that can be read from this socket

     *             without blocking.

     *               number of bytes available.

     */

    protected abstract int available() throws IOException;

    /**

     * Closes this socket.

     *

     */

    protected abstract void close() throws IOException;

    /**

     * Closes this socket, ignoring any IOException that is thrown by close.

     */

    void closeQuietly() {

        try {

            close();

        } catch (IOException ignore) { }

    }

    /**

     * Places the input stream for this socket at "end of stream".

     * Any data sent to this socket is acknowledged and then

     * silently discarded.

     *

     * If you read from a socket input stream after invoking this method on the

     * socket, the stream's {@code available} method will return 0, and its

     * {@code read} methods will return {@code -1} (end of stream).

     *

     * socket.

     * @see java.net.Socket#shutdownOutput()

     * @see java.net.Socket#close()

     * @see java.net.Socket#setSoLinger(boolean, int)

     * @since 1.3

     */

    protected void shutdownInput() throws IOException {

      throw new IOException("Method not implemented!");

    }

    /**

     * Disables the output stream for this socket.

     * For a TCP socket, any previously written data will be sent

     * followed by TCP's normal connection termination sequence.

     *

     * If you write to a socket output stream after invoking

     * shutdownOutput() on the socket, the stream will throw

     * an IOException.

     *

     * socket.

     * @see java.net.Socket#shutdownInput()

     * @see java.net.Socket#close()

     * @see java.net.Socket#setSoLinger(boolean, int)

     * @since 1.3

     */

    protected void shutdownOutput() throws IOException {

      throw new IOException("Method not implemented!");

    }

    /**

     * Returns the value of this socket's {@code fd} field.

     *

     * @return  the value of this socket's {@code fd} field.

     * @see     java.net.SocketImpl#fd

     */

    protected FileDescriptor getFileDescriptor() {

        return fd;

    }

    /**

     * Returns the value of this socket's {@code address} field.

     *

     * @return  the value of this socket's {@code address} field.

     * @see     java.net.SocketImpl#address

     */

    protected InetAddress getInetAddress() {

        return address;

    }

    /**

     * Returns the value of this socket's {@code port} field.

     *

     * @return  the value of this socket's {@code port} field.

     * @see     java.net.SocketImpl#port

     */

    protected int getPort() {

        return port;

    }

    /**

     * Returns whether or not this SocketImpl supports sending

     * urgent data. By default, false is returned

     * unless the method is overridden in a sub-class

     *

     * @return  true if urgent data supported

     * @see     java.net.SocketImpl#address

     * @since 1.4

     */

    protected boolean supportsUrgentData () {

        return false; // must be overridden in sub-class

    }

    /**

     * Send one byte of urgent data on the socket.

     * The byte to be sent is the low eight bits of the parameter

     * @param data The byte of data to send

     *  sending the data.

     * @since 1.4

     */

    protected abstract void sendUrgentData (int data) throws IOException;

    /**

     * Returns the value of this socket's {@code localport} field.

     *

     * @return  the value of this socket's {@code localport} field.

     * @see     java.net.SocketImpl#localport

     */

    protected int getLocalPort() {

        return localport;

    }

    /**

     * Returns the address and port of this socket as a {@code String}.

     *

     * @return  a string representation of this socket.

     */

    public String toString() {

        return "Socket[addr=" + getInetAddress() +

            ",port=" + getPort() + ",localport=" + getLocalPort()  + "]";

    }

    void reset() {

        fd = null;

        address = null;

        port = 0;

        localport = 0;

    }

    /**

     * Sets performance preferences for this socket.

     *

     * <p> Sockets use the TCP/IP protocol by default.  Some implementations

     * may offer alternative protocols which have different performance

     * characteristics than TCP/IP.  This method allows the application to

     * express its own preferences as to how these tradeoffs should be made

     * when the implementation chooses from the available protocols.

     *

     * <p> Performance preferences are described by three integers

     * whose values indicate the relative importance of short connection time,

     * low latency, and high bandwidth.  The absolute values of the integers

     * are irrelevant; in order to choose a protocol the values are simply

     * compared, with larger values indicating stronger preferences. Negative

     * values represent a lower priority than positive values. If the

     * application prefers short connection time over both low latency and high

     * bandwidth, for example, then it could invoke this method with the values

     * {@code (1, 0, 0)}.  If the application prefers high bandwidth above low

     * latency, and low latency above short connection time, then it could

     * invoke this method with the values {@code (0, 1, 2)}.

     *

     * By default, this method does nothing, unless it is overridden in

     * a sub-class.

     *

     * @param  connectionTime

     *         An {@code int} expressing the relative importance of a short

     *         connection time

     *

     * @param  latency

     *         An {@code int} expressing the relative importance of low

     *         latency

     *

     * @param  bandwidth

     *         An {@code int} expressing the relative importance of high

     *         bandwidth

     *

     * @since 1.5

     */

    protected void setPerformancePreferences(int connectionTime,

                                          int latency,

                                          int bandwidth)

    {

        /* Not implemented yet */

    }

    /**

     * Called to set a socket option.

     *

     * @implSpec

     * The default implementation of this method first checks that the given

     * socket option {@code name} is not null, then throws {@code

     * UnsupportedOperationException}. Subclasses should override this method

     * with an appropriate implementation.

     *

     * @param <T> The type of the socket option value

     * @param name The socket option

     * @param value The value of the socket option. A value of {@code null}

     *              may be valid for some options.

     *

     * @throws UnsupportedOperationException if the SocketImpl does not

     *         support the option

     * @throws IllegalArgumentException if the value is not valid for

     *         the option

     * @throws IOException if an I/O error occurs, or if the socket is closed

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

     *

     * @since 9

     */

    protected <T> void setOption(SocketOption<T> name, T value) throws IOException {

        Objects.requireNonNull(name);

        throw new UnsupportedOperationException("'" + name + "' not supported");

    }

    /**

     * Called to get a socket option.

     *

     * @implSpec

     * The default implementation of this method first checks that the given

     * socket option {@code name} is not null, then throws {@code

     * UnsupportedOperationException}. Subclasses should override this method

     * with an appropriate implementation.

     *

     * @param <T> The type of the socket option value

     * @param name The socket option

     * @return the value of the named option

     *

     * @throws UnsupportedOperationException if the SocketImpl does not

     *         support the option

     * @throws IOException if an I/O error occurs, or if the socket is closed

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

     *

     * @since 9

     */

    protected <T> T getOption(SocketOption<T> name) throws IOException {

        Objects.requireNonNull(name);

        throw new UnsupportedOperationException("'" + name + "' not supported");

    }

    /**

     * Attempts to copy socket options from this SocketImpl to a target SocketImpl.

     * At this time, only the SO_TIMEOUT make sense to copy.

     */

    void copyOptionsTo(SocketImpl target) {

        try {

            Object timeout = getOption(SocketOptions.SO_TIMEOUT);

            if (timeout instanceof Integer) {

                target.setOption(SocketOptions.SO_TIMEOUT, timeout);

            }

        } catch (IOException ignore) { }

    }

    /**

     * Returns a set of SocketOptions supported by this impl

     * and by this impl's socket (Socket or ServerSocket)

     *

     * @implSpec

     * The default implementation of this method returns an empty set.

     * Subclasses should override this method with an appropriate implementation.

     *

     * @return a Set of SocketOptions

     *

     * @since 9

     */

    protected Set<SocketOption<?>> supportedOptions() {

        return Set.of();

    }

}