src/java.base/share/classes/java/nio/channels/SocketChannel.java - master - githubmirror/jdk22

src/java.base/share/classes/java/nio/channels/SocketChannel.java
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Pavel Rappo
8294377: Prepare to stop auto-inheriting documentation for subclasses of exceptions whose documentation is inherited
10 окт 2022, 19:54
10 окт 2022, 19:54eb90c4f
/*
 * Copyright (c) 2000, 2022, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.nio.channels;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.NetPermission;
import java.net.ProtocolFamily;
import java.net.StandardProtocolFamily;
import java.net.Socket;
import java.net.SocketOption;
import java.net.SocketAddress;
import java.net.UnixDomainSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.spi.AbstractSelectableChannel;
import java.nio.channels.spi.SelectorProvider;
import static java.util.Objects.requireNonNull;

/**
 * A selectable channel for stream-oriented connecting sockets.
 *
 * <p> A socket channel is created by invoking one of the {@code open} methods of
 * this class. The no-arg {@link #open() open} method opens a socket channel
 * for an <i>Internet protocol</i> socket. The {@link #open(ProtocolFamily)}
 * method is used to open a socket channel for a socket of a specified protocol
 * family. 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> Socket options are configured using the {@link #setOption(SocketOption,Object)
 * setOption} method. Socket channels for  <i>Internet protocol</i> sockets support
 * 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>
 *
 * <p> Socket channels for <i>Unix domain</i> sockets support:
 * <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_LINGER SO_LINGER} </th>
 *     <td> Linger on close if data is present (when configured in blocking mode
 *          only) </td>
 *   </tr>
 * </tbody>
 * </table>
 * </blockquote>
 *
 * <p> 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>
 *
 * @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 instance of this class.
     *
     * @param  provider
     *         The provider that created this channel
     */
    protected SocketChannel(SelectorProvider provider) {
        super(provider);
    }

    /**
     * Opens a socket channel for an <i>Internet protocol</i> socket.
     *
     * <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
     *
     * @see     <a href="../../net/doc-files/net-properties.html#Ipv4IPv6">
     *          java.net.preferIPv4Stack</a> system property
     */
    public static SocketChannel open() throws IOException {
        return SelectorProvider.provider().openSocketChannel();
    }

    /**
     * Opens a socket channel. The {@code family} parameter specifies the
     * {@link ProtocolFamily protocol family} of the channel's socket.
     *
     * <p> The new channel is created by invoking the {@link
     * java.nio.channels.spi.SelectorProvider#openSocketChannel(ProtocolFamily)
     * openSocketChannel(ProtocolFamily)} method of the system-wide default.
     * {@link java.nio.channels.spi.SelectorProvider} object.</p>
     *
     * @param   family
     *          The protocol family
     *
     * @return  A new socket channel
     *
     * @throws  UnsupportedOperationException
     *          If the specified protocol family is not supported. For example,
     *          suppose the parameter is specified as {@link
     *          java.net.StandardProtocolFamily#INET6 StandardProtocolFamily.INET6}
     *          but IPv6 is not enabled on the platform.
     * @throws  IOException
     *          If an I/O error occurs
     *
     * @see     <a href="../../net/doc-files/net-properties.html#Ipv4IPv6">
     *          java.net.preferIPv4Stack</a> system property
     *
     * @since 15
     */
    public static SocketChannel open(ProtocolFamily family) throws IOException {
        return SelectorProvider.provider().openSocketChannel(requireNonNull(family));
    }

    /**
     * Opens a socket channel and connects it to a remote address.
     *
     * <p> If the remote address is an {@link InetSocketAddress} then this
     * 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}, and then returning that channel.
     *
     * <p> If the remote address is a {@link UnixDomainSocketAddress} then this
     * works 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}, 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 address 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
     *
     * @see     <a href="../../net/doc-files/net-properties.html#Ipv4IPv6">
     *          java.net.preferIPv4Stack</a> system property
     */
    public static SocketChannel open(SocketAddress remote)
        throws IOException
    {
        SocketChannel sc;
        requireNonNull(remote);
        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 |}&nbsp;{@link SelectionKey#OP_READ} {@code |}&nbsp;{@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 --

    /**
     * Binds the channel's socket to a local address.
     *
     * <p> This method is used to establish an association between the socket
     * and a local address. For <i>Internet Protocol</i> sockets, once an
     * association is established then the socket remains bound until the
     * channel is closed. If the {@code local} parameter has the value {@code
     * null} then the socket will be bound to an address that is assigned
     * automatically.
     *
     * @apiNote
     * Binding a socket channel to a <i>Unix Domain</i> socket creates a file
     * corresponding to the file path in the {@link UnixDomainSocketAddress}. This
     * file persists after the channel is closed, and must be removed before
     * another socket can bind to the same name. If a socket channel to a Unix
     * Domain socket is <i>implicitly</i> bound by connecting it without calling
     * bind first, then its socket is
     * <a href="../../../java/net/UnixDomainSocketAddress.html#unnamed">unnamed</a>
     * with no corresponding socket file in the file-system. If a socket channel
     * to a Unix Domain socket is <i>automatically</i> bound by calling {@code
     * bind(null)} this results in an unnamed socket also.
     *
     * @implNote
     * Each platform enforces an implementation specific maximum length for the
     * name of a <i>Unix Domain</i> socket. This limitation is enforced when a
     * channel is bound. The maximum length is typically close to and generally
     * not less than 100 bytes.
     *
     * @param   local The address to bind the socket, or {@code null} to bind
     *          the socket to an automatically assigned socket address
     *
     * @return  This channel
     *
     * @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 an <i>Internet protocol</i> socket address,
     *          or for a <i>Unix domain</i> socket address if it denies
     *          {@link NetPermission}{@code("accessUnixDomainSocket")}.
     *
     * @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.
     *
     * @return  A socket associated with this channel
     *
     * @throws  UnsupportedOperationException
     *          If the channel's socket is not an <i>Internet protocol</i> socket
     */
    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 channels to <i>Internet protocol</i> sockets, 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 channels to <i>Unix Domain</i> sockets, this method checks
     * {@link java.net.NetPermission NetPermission}{@code
     * ("accessUnixDomainSocket")} with the security manager's {@link
     * SecurityManager#checkPermission(java.security.Permission)
     * checkPermission} method.
     *
     * <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 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 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
     *          interrupt status
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract boolean finishConnect() throws IOException;

    /**
     * Returns the remote address to which this channel's socket is connected.
     *
     * <p> Where the channel's socket is bound and connected to an <i>Internet
     * Protocol</i> socket address then the return value is of type
     * {@link java.net.InetSocketAddress}.
     *
     * <p> Where the channel's socket is bound and connected to a <i>Unix Domain</i>
     * socket address, the returned address is a {@link UnixDomainSocketAddress}.
     *
     * @return  The remote address; {@code null} if the channel's socket is not
     *          connected
     *
     * @throws  ClosedChannelException
     *          If the channel is closed
     * @throws  IOException
     *          If an I/O error occurs
     *
     * @since 1.7
     */
    public abstract SocketAddress getRemoteAddress() throws IOException;

    // -- ByteChannel operations --

    /**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     * @throws  ClosedChannelException      {@inheritDoc}
     * @throws  AsynchronousCloseException  {@inheritDoc}
     * @throws  ClosedByInterruptException  {@inheritDoc}
     */
    public abstract int read(ByteBuffer dst) throws IOException;

    /**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     * @throws  ClosedChannelException      {@inheritDoc}
     * @throws  AsynchronousCloseException  {@inheritDoc}
     * @throws  ClosedByInterruptException  {@inheritDoc}
     */
    public abstract long read(ByteBuffer[] dsts, int offset, int length)
        throws IOException;

    /**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     * @throws  ClosedChannelException      {@inheritDoc}
     * @throws  AsynchronousCloseException  {@inheritDoc}
     * @throws  ClosedByInterruptException  {@inheritDoc}
     */
    public final long read(ByteBuffer[] dsts) throws IOException {
        return read(dsts, 0, dsts.length);
    }

    /**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     * @throws  ClosedChannelException      {@inheritDoc}
     * @throws  AsynchronousCloseException  {@inheritDoc}
     * @throws  ClosedByInterruptException  {@inheritDoc}
     */
    public abstract int write(ByteBuffer src) throws IOException;

    /**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     * @throws  ClosedChannelException      {@inheritDoc}
     * @throws  AsynchronousCloseException  {@inheritDoc}
     * @throws  ClosedByInterruptException  {@inheritDoc}
     */
    public abstract long write(ByteBuffer[] srcs, int offset, int length)
        throws IOException;

    /**
     * @throws  NotYetConnectedException
     *          If this channel is not yet connected
     * @throws  ClosedChannelException      {@inheritDoc}
     * @throws  AsynchronousCloseException  {@inheritDoc}
     * @throws  ClosedByInterruptException  {@inheritDoc}
     */
    public final long write(ByteBuffer[] srcs) throws IOException {
        return write(srcs, 0, srcs.length);
    }

    /**
     * {@inheritDoc}
     *
     * If there is a security manager set, its {@code checkConnect} method is
     * called with the local address and {@code -1} as its arguments to see
     * if the operation is allowed. If the operation is not allowed,
     * a {@code SocketAddress} representing the
     * {@link java.net.InetAddress#getLoopbackAddress loopback} address and the
     * local port of the channel's socket is returned.
     *
     * <p> Where the channel is bound to a Unix Domain socket address, the socket
     * address is a {@link UnixDomainSocketAddress}. If there is a security manager
     * set, its {@link SecurityManager#checkPermission(java.security.Permission)
     * checkPermission} method is called with {@link NetPermission}{@code
     * ("accessUnixDomainSocket")}. If the operation is not allowed an unnamed
     * {@link UnixDomainSocketAddress} is returned.
     *
     * @return  The {@code SocketAddress} that the socket is bound to, or the
     *          {@code SocketAddress} representing the loopback address or empty
     *          path if denied by the security manager, or {@code null} if the
     *          channel's socket is not bound
     *
     * @throws  ClosedChannelException     {@inheritDoc}
     * @throws  IOException                {@inheritDoc}
     */
    @Override
    public abstract SocketAddress getLocalAddress() throws IOException;
}