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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * 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
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   *
   * 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.nio.channels;
  
  import java.io.IOException;
  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 {@link #open 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 <tt>-1</tt>.  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 support the following options:
   * <blockquote>
   * <table border summary="Socket options">
   *   <tr>
   *     <th>Option Name</th>
   *     <th>Description</th>
   *   </tr>
   *   <tr>
   *     <td> {@link java.net.StandardSocketOptions#SO_SNDBUF SO_SNDBUF} </td>
   *     <td> The size of the socket send buffer </td>
   *   </tr>
   *   <tr>
   *     <td> {@link java.net.StandardSocketOptions#SO_RCVBUF SO_RCVBUF} </td>
   *     <td> The size of the socket receive buffer </td>
   *   </tr>
   *   <tr>
   *     <td> {@link java.net.StandardSocketOptions#SO_KEEPALIVE SO_KEEPALIVE} </td>
   *     <td> Keep connection alive </td>
   *   </tr>
   *   <tr>
   *     <td> {@link java.net.StandardSocketOptions#SO_REUSEADDR SO_REUSEADDR} </td>
   *     <td> Re-use address </td>
   *   </tr>
   *   <tr>
   *     <td> {@link java.net.StandardSocketOptions#SO_LINGER SO_LINGER} </td>
   *     <td> Linger on close if data is present (when configured in blocking mode
   *          only) </td>
   *   </tr>
   *   <tr>
   *     <td> {@link java.net.StandardSocketOptions#TCP_NODELAY TCP_NODELAY} </td>
   *     <td> Disable the Nagle algorithm </td>
   *   </tr>
   * </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>
   *
   * @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.
       *
       * <p> The new channel is created by invoking the {@link
       * SelectorProvider#openSocketChannel
       * openSocketChannel} method of the system-wide default {@link
       * 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();
      }
  
      /**
       * Opens a socket channel and connects it to a remote address.
       *
       * <p> 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 <tt>remote</tt>, 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 address 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 = open();
          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 <tt>(</tt>{@link SelectionKey#OP_CONNECT}
       * <tt>|</tt>&nbsp;{@link SelectionKey#OP_READ} <tt>|</tt>&nbsp;{@link
       * SelectionKey#OP_WRITE}<tt>)</tt>.  </p>
       *
       * @return  The valid-operation set
       */
      public final int validOps() {
          return (SelectionKey.OP_READ
                  | SelectionKey.OP_WRITE
                  | SelectionKey.OP_CONNECT);
      }
  
  
      // -- Socket-specific operations --
  
      /**
       * @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
       *
       * @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.
       *
       * <p> The returned object will not declare any public methods that are not
       * declared in the {@link Socket} class.  </p>
       *
       * @return  A socket associated with this channel
       */
      public abstract Socket socket();
  
      /**
       * Tells whether or not this channel's network socket is connected.
       *
       * @return  <tt>true</tt> 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  <tt>true</tt> 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 <tt>true</tt>.  Otherwise this method returns
       * <tt>false</tt> 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> This method performs exactly the same security checks as the {@link
       * Socket} class.  That is, if a security manager has been
       * installed then this method verifies that its {@link
       * SecurityManager#checkConnect checkConnect} method permits
       * connecting to the address and port number of the given remote endpoint.
       *
       * <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  <tt>true</tt> if a connection was established,
       *          <tt>false</tt> 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 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 IOException} to be thrown.
       *
       * <p> If this channel is already connected then this method will not block
       * and will immediately return <tt>true</tt>.  If this channel is in
       * non-blocking mode then this method will return <tt>false</tt> 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 <tt>true</tt> 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  <tt>true</tt> 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 is bound and connected to an Internet Protocol
       * socket address then the return value from this method is of type {@link
       * java.net.InetSocketAddress}.
       *
       * @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
       */
      public abstract int read(ByteBuffer dst) throws IOException;
  
      /**
       * @throws  NotYetConnectedException
       *          If this channel is not yet connected
       */
      public abstract long read(ByteBuffer[] dsts, int offset, int length)
          throws IOException;
  
      /**
       * @throws  NotYetConnectedException
       *          If this channel is not yet connected
       */
      public final long read(ByteBuffer[] dsts) throws IOException {
          return read(dsts, 0, dsts.length);
      }
  
      /**
       * @throws  NotYetConnectedException
       *          If this channel is not yet connected
       */
      public abstract int write(ByteBuffer src) throws IOException;
  
      /**
       * @throws  NotYetConnectedException
       *          If this channel is not yet connected
       */
      public abstract long write(ByteBuffer[] srcs, int offset, int length)
          throws IOException;
  
      /**
       * @throws  NotYetConnectedException
       *          If this channel is not yet connected
       */
      public final long write(ByteBuffer[] srcs) throws IOException {
          return write(srcs, 0, srcs.length);
      }
  
      /**
       * {@inheritDoc}
       * <p>
       * 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.
       *
       * @return  The {@code SocketAddress} that the socket is bound to, or the
       *          {@code SocketAddress} representing the loopback address 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;
  
  }
  