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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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,

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 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package java.nio.channels;

import java.io.IOException;

import java.net.InetSocketAddress;

import java.net.ProtocolFamily;

import java.net.StandardProtocolFamily;

import java.net.Socket;

import java.net.SocketOption;

import java.net.SocketAddress;

import java.nio.ByteBuffer;

import java.nio.channels.spi.AbstractSelectableChannel;

import java.nio.channels.spi.SelectorProvider;

/**

 * A selectable channel for stream-oriented connecting sockets.

 *

 * <p> A socket channel is created by invoking one of the open methods of this class.

 * It is not possible to create a channel for an arbitrary,

 * pre-existing socket. A newly-created socket channel is open but not yet

 * connected.  An attempt to invoke an I/O operation upon an unconnected

 * channel will cause a {@link NotYetConnectedException} to be thrown.  A

 * socket channel can be connected by invoking its {@link #connect connect}

 * method; once connected, a socket channel remains connected until it is

 * closed.  Whether or not a socket channel is connected may be determined by

 * invoking its {@link #isConnected isConnected} method.

 *

 * <p> Socket channels support <i>non-blocking connection:</i>&nbsp;A socket

 * channel may be created and the process of establishing the link to the

 * remote socket may be initiated via the {@link #connect connect} method for

 * later completion by the {@link #finishConnect finishConnect} method.

 * Whether or not a connection operation is in progress may be determined by

 * invoking the {@link #isConnectionPending isConnectionPending} method.

 *

 * <p> Socket channels support <i>asynchronous shutdown,</i> which is similar

 * to the asynchronous close operation specified in the {@link Channel} class.

 * If the input side of a socket is shut down by one thread while another

 * thread is blocked in a read operation on the socket's channel, then the read

 * operation in the blocked thread will complete without reading any bytes and

 * will return {@code -1}.  If the output side of a socket is shut down by one

 * thread while another thread is blocked in a write operation on the socket's

 * channel, then the blocked thread will receive an {@link

 * AsynchronousCloseException}.

 *

 * <p>Two kinds of socket channel are supported: <i>IP</i> (Internet Protocol) and

 * <i>Unix Domain</i> depending on which open method is used to create them and which

 * subtype of {@link SocketAddress} that they support for local and remote addresses.

 * <i>IP</i> channels are created using {@link #open()}. They use {@link

 * InetSocketAddress} addresses and support both IPv4 and IPv6 TCP/IP.

 * <i>Unix Domain</i> channels are created using {@link #open(ProtocolFamily)}

 * with the family parameter set to {@link StandardProtocolFamily#UNIX}.

 * They use {@link UnixDomainSocketAddress}es and also

 * do not support the {@link #socket()} method. Note, it is also possible to

 * create channels that support either IPv4 or IPv6 only through the

 * {@link #open(ProtocolFamily)} method.

 *

 * <p> Socket options are configured using the {@link #setOption(SocketOption,Object)

 * setOption} method. <i>IP</i> socket channels support the following options:

 * <blockquote>

 * <table class="striped">

 * <caption style="display:none">Socket options</caption>

 * <thead>

 *   <tr>

 *     <th scope="col">Option Name</th>

 *     <th scope="col">Description</th>

 *   </tr>

 * </thead>

 * <tbody>

 *   <tr>

 *     <th scope="row"> {@link java.net.StandardSocketOptions#SO_SNDBUF SO_SNDBUF} </th>

 *     <td> The size of the socket send buffer </td>

 *   </tr>

 *   <tr>

 *     <th scope="row"> {@link java.net.StandardSocketOptions#SO_RCVBUF SO_RCVBUF} </th>

 *     <td> The size of the socket receive buffer </td>

 *   </tr>

 *   <tr>

 *     <th scope="row"> {@link java.net.StandardSocketOptions#SO_KEEPALIVE SO_KEEPALIVE} </th>

 *     <td> Keep connection alive </td>

 *   </tr>

 *   <tr>

 *     <th scope="row"> {@link java.net.StandardSocketOptions#SO_REUSEADDR SO_REUSEADDR} </th>

 *     <td> Re-use address </td>

 *   </tr>

 *   <tr>

 *     <th scope="row"> {@link java.net.StandardSocketOptions#SO_LINGER SO_LINGER} </th>

 *     <td> Linger on close if data is present (when configured in blocking mode

 *          only) </td>

 *   </tr>

 *   <tr>

 *     <th scope="row"> {@link java.net.StandardSocketOptions#TCP_NODELAY TCP_NODELAY} </th>

 *     <td> Disable the Nagle algorithm </td>

 *   </tr>

 * </tbody>

 * </table>

 * </blockquote>

 * Additional (implementation specific) options may also be supported.

 *

 * <p> Socket channels are safe for use by multiple concurrent threads.  They

 * support concurrent reading and writing, though at most one thread may be

 * reading and at most one thread may be writing at any given time.  The {@link

 * #connect connect} and {@link #finishConnect finishConnect} methods are

 * mutually synchronized against each other, and an attempt to initiate a read

 * or write operation while an invocation of one of these methods is in

 * progress will block until that invocation is complete.  </p>

 *

 * <p><i>Unix Domain</i> channels support a subset of the options listed above.

 *

 * @author Mark Reinhold

 * @author JSR-51 Expert Group

 * @since 1.4

 */

public abstract class SocketChannel

    extends AbstractSelectableChannel

    implements ByteChannel, ScatteringByteChannel, GatheringByteChannel, NetworkChannel

{

    /**

     * Initializes a new <i>IP</i> instance of this class.

     *

     * @param  provider

     *         The provider that created this channel

     */

    protected SocketChannel(SelectorProvider provider) {

        super(provider);

    }

    /**

     * Opens an <i>IP</i> socket channel.

     *

     * <p> The new channel is created by invoking the {@link

     * java.nio.channels.spi.SelectorProvider#openSocketChannel

     * openSocketChannel} method of the system-wide default {@link

     * java.nio.channels.spi.SelectorProvider} object.  </p>

     *

     * @return  A new socket channel

     *

     * @throws  IOException

     *          If an I/O error occurs

     */

    public static SocketChannel open() throws IOException {

        return SelectorProvider.provider().openSocketChannel();

    }

    /**

     * Returns a {@link SocketChannel} of the given {@link ProtocolFamily}.

     *

     * @param family the protocol family

     *

     * @return a SocketChannel

     *

     * @throws IOException if an I/O error occurs

     * @throws UnsupportedAddressTypeException if the protocol family is not supported

     * @since 14

     */

    public static SocketChannel open(ProtocolFamily family) throws IOException {

        return SelectorProvider.provider().openSocketChannel(family);

    }

    /**

     * Opens a socket channel and connects it to a remote address.

     * Depending on the type of {@link SocketAddress} supplied, the returned object

     * is an <i>IP</i> or <i>Unix Domain</i> channel.

     *

     * <p> For {@link InetSocketAddress}es this convenience method works as if by invoking the {@link #open()}

     * method, invoking the {@link #connect(SocketAddress) connect} method upon

     * the resulting socket channel, passing it {@code remote}, which must be an

     * {@link InetSocketAddress} and then returning that channel.  </p>

     *

     * <p> For {@link UnixDomainSocketAddress}es it works as if by invoking the {@link

     * #open(ProtocolFamily)} method with {@link StandardProtocolFamily#UNIX} as parameter,

     * invoking the {@link #connect(SocketAddress) connect} method upon

     * the resulting socket channel, passing it {@code remote}, which must be a

     * {@link UnixDomainSocketAddress} and then returning that channel.  </p>

     *

     * @param  remote

     *         The remote address to which the new channel is to be connected

     *

     * @return  A new, and connected, socket channel

     *

     * @throws  AsynchronousCloseException

     *          If another thread closes this channel

     *          while the connect operation is in progress

     *

     * @throws  ClosedByInterruptException

     *          If another thread interrupts the current thread

     *          while the connect operation is in progress, thereby

     *          closing the channel and setting the current thread's

     *          interrupt status

     *

     * @throws  UnresolvedAddressException

     *          If the given remote is an InetSocketAddress that is not fully resolved

     *

     * @throws  UnsupportedAddressTypeException

     *          If the type of the given remote address is not supported

     *

     * @throws  SecurityException

     *          If a security manager has been installed

     *          and it does not permit access to the given remote endpoint

     *

     * @throws  IOException

     *          If some other I/O error occurs

     */

    public static SocketChannel open(SocketAddress remote)

        throws IOException

    {

        SocketChannel sc;

        if (remote instanceof InetSocketAddress)

            sc = open();

        else if (remote instanceof UnixDomainSocketAddress)

            sc = open(StandardProtocolFamily.UNIX);

        else

            throw new UnsupportedAddressTypeException();

        try {

            sc.connect(remote);

        } catch (Throwable x) {

            try {

                sc.close();

            } catch (Throwable suppressed) {

                x.addSuppressed(suppressed);

            }

            throw x;

        }

        assert sc.isConnected();

        return sc;

    }

    /**

     * Returns an operation set identifying this channel's supported

     * operations.

     *

     * <p> Socket channels support connecting, reading, and writing, so this

     * method returns {@code (}{@link SelectionKey#OP_CONNECT}

     * {@code |} {@link SelectionKey#OP_READ} {@code |} {@link

     * SelectionKey#OP_WRITE}{@code )}.

     *

     * @return  The valid-operation set

     */

    public final int validOps() {

        return (SelectionKey.OP_READ

                | SelectionKey.OP_WRITE

                | SelectionKey.OP_CONNECT);

    }

    // -- Socket-specific operations --

    /**

     * {@inheritDoc}

     *

     * <p> Note, for <i>Unix Domain</i> channels, a file is created in the file-system

     * with the same name as this channel's bound address. This file persists after

     * the channel is closed, and must be removed before another channel can bind

     *

     * @throws  ConnectionPendingException

     *          If a non-blocking connect operation is already in progress on

     *          this channel

     * @throws  AlreadyBoundException               {@inheritDoc}

     * @throws  UnsupportedAddressTypeException     {@inheritDoc}

     * @throws  ClosedChannelException              {@inheritDoc}

     * @throws  IOException                         {@inheritDoc}

     * @throws  SecurityException

     *          If a security manager has been installed and its

     *          {@link SecurityManager#checkListen checkListen} method denies

     *          the operation for <i>IP</i> channels; or for <i>Unix Domain</i>

     *          channels, if the security manager denies "read" or "write"

     *          {@link java.io.FilePermission} for the local path.

     *

     * @since 1.7

     */

    @Override

    public abstract SocketChannel bind(SocketAddress local)

        throws IOException;

    /**

     * @throws  UnsupportedOperationException           {@inheritDoc}

     * @throws  IllegalArgumentException                {@inheritDoc}

     * @throws  ClosedChannelException                  {@inheritDoc}

     * @throws  IOException                             {@inheritDoc}

     *

     * @since 1.7

     */

    @Override

    public abstract <T> SocketChannel setOption(SocketOption<T> name, T value)

        throws IOException;

    /**

     * Shutdown the connection for reading without closing the channel.

     *

     * <p> Once shutdown for reading then further reads on the channel will

     * return {@code -1}, the end-of-stream indication. If the input side of the

     * connection is already shutdown then invoking this method has no effect.

     *

     * @return  The channel

     *

     * @throws  NotYetConnectedException

     *          If this channel is not yet connected

     * @throws  ClosedChannelException

     *          If this channel is closed

     * @throws  IOException

     *          If some other I/O error occurs

     *

     * @since 1.7

     */

    public abstract SocketChannel shutdownInput() throws IOException;

    /**

     * Shutdown the connection for writing without closing the channel.

     *

     * <p> Once shutdown for writing then further attempts to write to the

     * channel will throw {@link ClosedChannelException}. If the output side of

     * the connection is already shutdown then invoking this method has no

     * effect.

     *

     * @return  The channel

     *

     * @throws  NotYetConnectedException

     *          If this channel is not yet connected

     * @throws  ClosedChannelException

     *          If this channel is closed

     * @throws  IOException

     *          If some other I/O error occurs

     *

     * @since 1.7

     */

    public abstract SocketChannel shutdownOutput() throws IOException;

    /**

     * Retrieves a socket associated with this channel if it is an <i>IP</i>

     * channel. The operation is not supported for <i>Unix Domain</i> channels.

     *

     * <p> The returned object will not declare any public methods that are not

     * declared in the {@link java.net.Socket} class.  </p>

     *

     * @return  A socket associated with this channel

     *

     * @throws UnsupportedOperationException is this is a <i>Unix Domain</i> channel

     */

    public abstract Socket socket();

    /**

     * Tells whether or not this channel's network socket is connected.

     *

     * @return  {@code true} if, and only if, this channel's network socket

     *          is {@link #isOpen open} and connected

     */

    public abstract boolean isConnected();

    /**

     * Tells whether or not a connection operation is in progress on this

     * channel.

     *

     * @return  {@code true} if, and only if, a connection operation has been

     *          initiated on this channel but not yet completed by invoking the

     *          {@link #finishConnect finishConnect} method

     */

    public abstract boolean isConnectionPending();

    /**

     * Connects this channel's socket.

     *

     * <p> If this channel is in non-blocking mode then an invocation of this

     * method initiates a non-blocking connection operation.  If the connection

     * is established immediately, as can happen with a local connection, then

     * this method returns {@code true}.  Otherwise this method returns

     * {@code false} and the connection operation must later be completed by

     * invoking the {@link #finishConnect finishConnect} method.

     *

     * <p> If this channel is in blocking mode then an invocation of this

     * method will block until the connection is established or an I/O error

     * occurs.

     *

     * <p> For <i>IP</i> channels, this method performs exactly the same security checks

     * as the {@link java.net.Socket} class.  That is, if a security manager has been

     * installed then this method verifies that its {@link

     * java.lang.SecurityManager#checkConnect checkConnect} method permits

     * connecting to the address and port number of the given remote endpoint.

     *

     * <p> For <i>Unix Domain</i> channels, this method performs a security

     * manager {@link SecurityManager#checkPermission(Permission)} using

     * a {@link java.io.FilePermission} constructed with the path from the

     * destination address and "read,write" as the actions.

     *

     * <p> This method may be invoked at any time.  If a read or write

     * operation upon this channel is invoked while an invocation of this

     * method is in progress then that operation will first block until this

     * invocation is complete.  If a connection attempt is initiated but fails,

     * that is, if an invocation of this method throws a checked exception,

     * then the channel will be closed.  </p>

     *

     * @param  remote

     *         The remote address to which this channel is to be connected

     *

     * @return  {@code true} if a connection was established,

     *          {@code false} if this channel is in non-blocking mode

     *          and the connection operation is in progress

     *

     * @throws  AlreadyConnectedException

     *          If this channel is already connected

     *

     * @throws  ConnectionPendingException

     *          If a non-blocking connection operation is already in progress

     *          on this channel

     *

     * @throws  ClosedChannelException

     *          If this channel is closed

     *

     * @throws  AsynchronousCloseException

     *          If another thread closes this channel

     *          while the connect operation is in progress

     *

     * @throws  ClosedByInterruptException

     *          If another thread interrupts the current thread

     *          while the connect operation is in progress, thereby

     *          closing the channel and setting the current thread's

     *          interrupt status

     *

     * @throws  UnresolvedAddressException

     *          If the given remote address is an InetSocketAddress which is not fully resolved

     *

     * @throws  UnsupportedAddressTypeException

     *          If the type of the given remote address is not supported

     *

     * @throws  SecurityException

     *          If a security manager has been installed

     *          and it does not permit access to the given remote endpoint

     *

     * @throws  IOException

     *          If some other I/O error occurs

     */

    public abstract boolean connect(SocketAddress remote) throws IOException;

    /**

     * Finishes the process of connecting a socket channel.

     *

     * <p> A non-blocking connection operation is initiated by placing a socket

     * channel in non-blocking mode and then invoking its {@link #connect

     * connect} method.  Once the connection is established, or the attempt has

     * failed, the socket channel will become connectable and this method may

     * be invoked to complete the connection sequence.  If the connection

     * operation failed then invoking this method will cause an appropriate

     * {@link java.io.IOException} to be thrown.

     *

     * <p> If this channel is already connected then this method will not block

     * and will immediately return {@code true}.  If this channel is in

     * non-blocking mode then this method will return {@code false} if the

     * connection process is not yet complete.  If this channel is in blocking

     * mode then this method will block until the connection either completes

     * or fails, and will always either return {@code true} or throw a checked

     * exception describing the failure.

     *

     * <p> This method may be invoked at any time.  If a read or write

     * operation upon this channel is invoked while an invocation of this

     * method is in progress then that operation will first block until this

     * invocation is complete.  If a connection attempt fails, that is, if an

     * invocation of this method throws a checked exception, then the channel

     * will be closed.  </p>

     *

     * @return  {@code true} if, and only if, this channel's socket is now

     *          connected

     *

     * @throws  NoConnectionPendingException

     *          If this channel is not connected and a connection operation

     *          has not been initiated

     *

     * @throws  ClosedChannelException

     *          If this channel is closed

     *

     * @throws  AsynchronousCloseException

     *          If another thread closes this channel

     *          while the connect operation is in progress

     *

     * @throws  ClosedByInterruptException

     *          If another thread interrupts the current thread

     *          while the connect operation is in progress, thereby

     *          closing the channel and setting the current thread's