/*
 * @(#)SocketChannel.java	1.35 10/03/23
 *
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.nio.channels;

import java.io.IOException;
import java.net.Socket;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.spi.*;


/**
 * A selectable channel for stream-oriented connecting sockets.
 * 
 * <p> Socket channels are not a complete abstraction of connecting network
 * sockets.  Binding, shutdown, and the manipulation of socket options must be
 * done through an associated {@link java.net.Socket} object obtained by
 * invoking the {@link #socket() socket} method.  It is not possible to create
 * a channel for an arbitrary, pre-existing socket, nor is it possible to
 * specify the {@link java.net.SocketImpl} object to be used by a socket
 * associated with a socket channel.
 *
 * <p> A socket channel is created by invoking one of the {@link #open open}
 * methods of this class.  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> The input and output sides of a socket channel may independently be
 * <i>shut down</i> without actually closing the channel.  Shutting down the
 * input side of a channel by invoking the {@link java.net.Socket#shutdownInput
 * shutdownInput} method of an associated socket object will cause further
 * reads on the channel to return <tt>-1</tt>, the end-of-stream indication.
 * Shutting down the output side of the channel by invoking the {@link
 * java.net.Socket#shutdownOutput shutdownOutput} method of an associated
 * socket object will cause further writes on the channel to throw a {@link
 * ClosedChannelException}.
 *
 * <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 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
 * @version 1.35, 10/03/23
 * @since 1.4
 */

public abstract class SocketChannel
    extends AbstractSelectableChannel
    implements ByteChannel, ScatteringByteChannel, GatheringByteChannel
{

    /**
     * Initializes a new instance of this class.
     */
    protected SocketChannel(SelectorProvider provider) {
	super(provider);
    }

    /**
     * Opens a 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();
    }

    /**
     * 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
     *
     * @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();
	sc.connect(remote);
	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 --

    /**
     * Retrieves a socket associated with this channel.
     *
     * <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
     */
    public abstract Socket socket();

    /**
     * Tells whether or not this channel's network socket is connected.  </p>
     *
     * @return  <tt>true</tt> if, and only if, this channel's network socket
     *          is connected
     */
    public abstract boolean isConnected();

    /**
     * Tells whether or not a connection operation is in progress on this
     * channel.  </p>
     *
     * @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
     * 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> 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 java.io.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;


    // -- 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);
    }

}
