/*
 * Copyright (c) 2009, 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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 * questions.
 */
package com.sun.nio.sctp;

import java.net.SocketAddress;
import java.net.InetAddress;
import java.io.IOException;
import java.util.Set;
import java.nio.ByteBuffer;
import java.nio.channels.spi.AbstractSelectableChannel;
import java.nio.channels.spi.SelectorProvider;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.SelectionKey;

/**
 * A selectable channel for message-oriented connected SCTP sockets.
 *
 * <P> An SCTP channel can only control one SCTP association.
 * An {@code SCTPChannel} is created by invoking one of the
 * {@link #open open} methods of this class. A newly-created channel is open but
 * not yet connected, that is, there is no association setup with a remote peer.
 * An attempt to invoke an I/O operation upon an unconnected
 * channel will cause a {@link java.nio.channels.NotYetConnectedException} to be
 * thrown. An association can be setup by connecting the channel using one of
 * its {@link #connect connect} methods. Once connected, the channel remains
 * connected until it is closed. Whether or not a channel is connected may be
 * determined by invoking {@link #getRemoteAddresses getRemoteAddresses}.
 *
 * <p> SCTP channels support <i>non-blocking connection:</i>&nbsp;A
 * 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 options are configured using the
 * {@link #setOption(SctpSocketOption,Object) setOption} method. An SCTP
 * channel support the following options:
 * <blockquote>
 * <table border>
 *   <tr>
 *     <th>Option Name</th>
 *     <th>Description</th>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SCTP_DISABLE_FRAGMENTS
 *                                          SCTP_DISABLE_FRAGMENTS} </td>
 *     <td> Enables or disables message fragmentation </td>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SCTP_EXPLICIT_COMPLETE
 *                                          SCTP_EXPLICIT_COMPLETE} </td>
 *     <td> Enables or disables explicit message completion </td>
 *   </tr>
 *    <tr>
 *     <td> {@link SctpStandardSocketOption#SCTP_FRAGMENT_INTERLEAVE
 *                                          SCTP_FRAGMENT_INTERLEAVE} </td>
 *     <td> Controls how the presentation of messages occur for the message
 *          receiver </td>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SCTP_INIT_MAXSTREAMS
 *                                          SCTP_INIT_MAXSTREAMS} </td>
 *     <td> The maximum number of streams requested by the local endpoint during
 *          association initialization </td>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SCTP_NODELAY SCTP_NODELAY} </td>
 *     <td> Enables or disable a Nagle-like algorithm </td>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SCTP_PRIMARY_ADDR
 *                                          SCTP_PRIMARY_ADDR} </td>
 *     <td> Requests that the local SCTP stack use the given peer address as the
 *          association primary </td>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SCTP_SET_PEER_PRIMARY_ADDR
 *                                          SCTP_SET_PEER_PRIMARY_ADDR} </td>
 *     <td> Requests that the peer mark the enclosed address as the association
 *          primary </td>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SO_SNDBUF
 *                                          SO_SNDBUF} </td>
 *     <td> The size of the socket send buffer </td>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SO_RCVBUF
 *                                          SO_RCVBUF} </td>
 *     <td> The size of the socket receive buffer </td>
 *   </tr>
 *   <tr>
 *     <td> {@link SctpStandardSocketOption#SO_LINGER
 *                                          SO_LINGER} </td>
 *     <td> Linger on close if data is present (when configured in blocking mode
 *          only) </td>
 *   </tr>
 * </table>
 * </blockquote>
 * Additional (implementation specific) options may also be supported. The list
 * of options supported is obtained by invoking the {@link #supportedOptions()
 * supportedOptions}  method.
 *
 * <p> SCTP 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 send or receive operation while an invocation of one
 * of these methods is in progress will block until that invocation is complete.
 *
 * @since 1.7
 */
public abstract class SctpChannel
    extends AbstractSelectableChannel
{
    /**
     * Initializes a new instance of this class.
     *
     * @param  provider
     *         The selector provider for this channel
     */
    protected SctpChannel(SelectorProvider provider) {
        super(provider);
    }

    /**
     * Opens an SCTP channel.
     *
     * <P> The new channel is unbound and unconnected.
     *
     * @return  A new SCTP channel
     *
     * @throws  UnsupportedOperationException
     *          If the SCTP protocol is not supported
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public static SctpChannel open() throws
        IOException {
        return new sun.nio.ch.SctpChannelImpl((SelectorProvider)null);
    }

    /**
     * Opens an SCTP channel and connects it to a remote address.
     *
     * <P> This is a convenience method and is equivalent to evaluating the
     * following expression:
     * <blockquote><pre>
     * open().connect(remote, maxOutStreams, maxInStreams);
     * </pre></blockquote>
     *
     * @param  remote
     *         The remote address to which the new channel is to be connected
     *
     * @param  maxOutStreams
     *         The number of streams that the application wishes to be able
     *         to send to. Must be non negative and no larger than {@code 65536}.
     *         {@code 0} to use the endpoints default value.
     *
     * @param  maxInStreams
     *         The maximum number of inbound streams the application is prepared
     *         to support. Must be non negative and no larger than {@code 65536}.
     *         {@code 0} to use the endpoints default value.
     *
     * @return  A new SCTP channel connected to the given address
     *
     * @throws  java.nio.channels.AsynchronousCloseException
     *          If another thread closes this channel
     *          while the connect operation is in progress
     *
     * @throws  java.nio.channels.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  java.nio.channels.UnresolvedAddressException
     *          If the given remote address is not fully resolved
     *
     * @throws  java.nio.channels.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 peer
     *
     * @throws  UnsupportedOperationException
     *          If the SCTP protocol is not supported
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public static SctpChannel open(SocketAddress remote, int maxOutStreams,
                   int maxInStreams) throws IOException {
        SctpChannel ssc = SctpChannel.open();
        ssc.connect(remote, maxOutStreams, maxInStreams);
        return ssc;
    }

    /**
     * Returns the association on this channel's socket.
     *
     * @return  the association, or {@code null} if the channel's socket is not
     *          connected.
     *
     * @throws  ClosedChannelException
     *          If the channel is closed
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract Association association() throws IOException;

    /**
     * Binds the channel's socket to a local address.
     *
     * <P> This method is used to establish a relationship between the socket
     * and the local addresses. Once a relationship is established then
     * the socket remains bound until the channel is closed. This relationship
     * may not necesssarily be with the address {@code local} as it may be removed
     * by {@link #unbindAddress unbindAddress}, but there will always be at least
     * one local address bound to the channel's socket once an invocation of
     * this method successfully completes.
     *
     * <P> Once the channel's socket has been successfully bound to a specific
     * address, that is not automatically assigned, more addresses
     * may be bound to it using {@link #bindAddress bindAddress}, or removed
     * using {@link #unbindAddress unbindAddress}.
     *
     * @param  local
     *         The local address to bind the socket, or {@code null} to
     *         bind the socket to an automatically assigned socket address
     *
     * @return  This channel
     *
     * @throws  java.nio.channels.AlreadyConnectedException
     *          If this channel is already connected
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  java.nio.channels.ConnectionPendingException
     *          If a non-blocking connection operation is already in progress on this channel
     *
     * @throws  java.nio.channels.AlreadyBoundException
     *          If this channel is already bound
     *
     * @throws  java.nio.channels.UnsupportedAddressTypeException
     *          If the type of the given address is not supported
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract SctpChannel bind(SocketAddress local)
        throws IOException;

    /**
     * Adds the given address to the bound addresses for the channel's
     * socket.
     *
     * <P> The given address must not be the {@link
     * java.net.InetAddress#isAnyLocalAddress wildcard} address.
     * The channel must be first bound using {@link #bind bind} before
     * invoking this method, otherwise {@link
     * java.nio.channels.NotYetBoundException} is thrown. The {@link #bind bind}
     * method takes a {@code SocketAddress} as its argument which typically
     * contains a port number as well as an address. Addresses subquently bound
     * using this method are simply addresses as the SCTP port number remains
     * the same for the lifetime of the channel.
     *
     * <P> Adding addresses to a connected association is optional functionality.
     * If the endpoint supports dynamic address reconfiguration then it may
     * send the appropriate message to the peer to change the peers address
     * lists.
     *
     * @param  address
     *         The address to add to the bound addresses for the socket
     *
     * @return  This channel
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  java.nio.channels.ConnectionPendingException
     *          If a non-blocking connection operation is already in progress on
     *          this channel
     *
     * @throws  java.nio.channels.NotYetBoundException
     *          If this channel is not yet bound
     *
     * @throws  java.nio.channels.AlreadyBoundException
     *          If this channel is already bound to the given address
     *
     * @throws  IllegalArgumentException
     *          If address is {@code null} or the {@link
     *          java.net.InetAddress#isAnyLocalAddress wildcard} address
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract SctpChannel bindAddress(InetAddress address)
         throws IOException;

    /**
     * Removes the given address from the bound addresses for the channel's
     * socket.
     *
     * <P> The given address must not be the {@link
     * java.net.InetAddress#isAnyLocalAddress wildcard} address.
     * The channel must be first bound using {@link #bind bind} before
     * invoking this method, otherwise {@link java.nio.channels.NotYetBoundException}
     * is thrown. If this method is invoked on a channel that does not have
     * {@code address} as one of its bound addresses or that has only one
     * local address bound to it, then this method throws
     * {@link IllegalUnbindException}.
     * The initial address that the channel's socket is bound to using {@link
     * #bind bind} may be removed from the bound addresses for the channel's socket.
     *
     * <P> Removing addresses from a connected association is optional
     * functionality. If the endpoint supports dynamic address reconfiguration
     * then it may send the appropriate message to the peer to change the peers
     * address lists.
     *
     * @param  address
     *         The address to remove from the bound addresses for the socket
     *
     * @return  This channel
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  java.nio.channels.ConnectionPendingException
     *          If a non-blocking connection operation is already in progress on
     *          this channel
     *
     * @throws  java.nio.channels.NotYetBoundException
     *          If this channel is not yet bound
     *
     * @throws  IllegalArgumentException
     *          If address is {@code null} or the {@link
     *          java.net.InetAddress#isAnyLocalAddress wildcard} address
     *
     * @throws  IllegalUnbindException
     *          If {@code address} is not bound to the channel's socket. or
     *          the channel has only one address bound to it
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract SctpChannel unbindAddress(InetAddress address)
         throws IOException;

    /**
     * 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> 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 peer.
     *
     * <p> This method may be invoked at any time. If a {@link #send send} or
     * {@link #receive receive} 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.
     *
     * @param  remote
     *         The remote peer 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  java.nio.channels.AlreadyConnectedException
     *          If this channel is already connected
     *
     * @throws  java.nio.channels.ConnectionPendingException
     *          If a non-blocking connection operation is already in progress on
     *          this channel
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  java.nio.channels.AsynchronousCloseException
     *          If another thread closes this channel
     *          while the connect operation is in progress
     *
     * @throws  java.nio.channels.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  java.nio.channels.UnresolvedAddressException
     *          If the given remote address is not fully resolved
     *
     * @throws  java.nio.channels.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 peer
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract boolean connect(SocketAddress remote) throws IOException;

    /**
     * Connects this channel's socket.
     *
     * <P> This is a convience method and is equivalent to evaluating the
     * following expression:
     * <blockquote><pre>
     * setOption(SctpStandardSocketOption.SCTP_INIT_MAXSTREAMS, SctpStandardSocketOption.InitMaxStreams.create(maxInStreams, maxOutStreams))
     *  .connect(remote);
     * </pre></blockquote>
     *
     * <P> The {@code maxOutStreams} and {@code maxInStreams} parameters
     * represent the maximum number of streams that the application wishes to be
     * able to send to and receive from. They are negotiated with the remote
     * peer and may be limited by the operating system.
     *
     * @param  remote
     *         The remote peer to which this channel is to be connected
     *
     * @param  maxOutStreams
     *         Must be non negative and no larger than {@code 65536}.
     *         {@code 0} to use the endpoints default value.
     *
     * @param  maxInStreams
     *         Must be non negative and no larger than {@code 65536}.
     *         {@code 0} to use the endpoints default value.
     *
     * @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  java.nio.channels.AlreadyConnectedException
     *          If this channel is already connected
     *
     * @throws  java.nio.channels.ConnectionPendingException
     *          If a non-blocking connection operation is already in progress on
     *          this channel
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  java.nio.channels.AsynchronousCloseException
     *          If another thread closes this channel
     *          while the connect operation is in progress
     *
     * @throws  java.nio.channels.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  java.nio.channels.UnresolvedAddressException
     *          If the given remote address is not fully resolved
     *
     * @throws  java.nio.channels.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 peer
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract boolean connect(SocketAddress remote,
                                    int maxOutStreams,
                                    int maxInStreams)
        throws IOException;

    /**
     * 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} method
     */
    public abstract boolean isConnectionPending();

    /**
     * Finishes the process of connecting an SCTP channel.
     *
     * <P> A non-blocking connection operation is initiated by placing a socket
     * channel in non-blocking mode and then invoking one of its {@link #connect
     * connect} methods.  Once the connection is established, or the attempt has
     * failed, the 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 {@link #send send} or {@link #receive receive}
     * 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.
     *
     * @return  {@code true} if, and only if, this channel's socket is now
     *          connected
     *
     * @throws  java.nio.channels.NoConnectionPendingException
     *          If this channel is not connected and a connection operation
     *          has not been initiated
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  java.nio.channels.AsynchronousCloseException
     *          If another thread closes this channel
     *          while the connect operation is in progress
     *
     * @throws  java.nio.channels.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 all of the socket addresses to which this channel's socket is
     * bound.
     *
     * @return  All the socket addresses that this channel's socket is
     *          bound to, or an empty {@code Set} if the channel's socket is not
     *          bound
     *
     * @throws  ClosedChannelException
     *          If the channel is closed
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public abstract Set<SocketAddress> getAllLocalAddresses()
        throws IOException;

    /**
     * Returns all of the remote addresses to which this channel's socket
     * is connected.
     *
     * <P> If the channel is connected to a remote peer that is bound to
     * multiple addresses then it is these addresses that the channel's socket
     * is connected.
     *
     * @return  All of the remote addresses to which this channel's socket
     *          is connected, or an empty {@code Set} if the channel's socket is
     *          not connected
     *
     * @throws  ClosedChannelException
     *          If the channel is closed
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public abstract Set<SocketAddress> getRemoteAddresses()
        throws IOException;

    /**
     * Shutdown a connection without closing the channel.
     *
     * <P> Sends a shutdown command to the remote peer, effectively preventing
     * any new data from being written to the socket by either peer. Further
     * sends will throw {@link java.nio.channels.ClosedChannelException}. The
     * channel remains open to allow the for any data (and notifications) to be
     * received that may have been sent by the peer before it received the
     * shutdown command. If the channel is already shutdown then invoking this
     * method has no effect.
     *
     * @return  This channel
     *
     * @throws  java.nio.channels.NotYetConnectedException
     *          If this channel is not yet connected
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract SctpChannel shutdown() throws IOException;

    /**
     * Returns the value of a socket option.
     *
     * @param   name
     *          The socket option
     *
     * @return  The value of the socket option. A value of {@code null} may be
     *          a valid value for some socket options.
     *
     * @throws  UnsupportedOperationException
     *          If the socket option is not supported by this channel
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  IOException
     *          If an I/O error occurs
     *
     * @see SctpStandardSocketOption
     */
    public abstract <T> T getOption(SctpSocketOption<T> name)
        throws IOException;

    /**
     * Sets the value of a socket option.
     *
     * @param   name
     *          The socket option
     *
     * @param   value
     *          The value of the socket option. A value of {@code null} may be
     *          a valid value for some socket options.
     *
     * @return  This channel
     *
     * @throws  UnsupportedOperationException
     *          If the socket option is not supported by this channel
     *
     * @throws  IllegalArgumentException
     *          If the value is not a valid value for this socket option
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  IOException
     *          If an I/O error occurs
     *
     * @see SctpStandardSocketOption
     */
    public abstract <T> SctpChannel setOption(SctpSocketOption<T> name, T value)
        throws IOException;

    /**
     * Returns a set of the socket options supported by this channel.
     *
     * <P> This method will continue to return the set of options even after the
     * channel has been closed.
     *
     * @return  A set of the socket options supported by this channel
     */
    public abstract Set<SctpSocketOption<?>> supportedOptions();

    /**
     * Returns an operation set identifying this channel's supported operations.
     *
     * <P> SCTP 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
     */
    @Override
    public final int validOps() {
        return (SelectionKey.OP_READ |
                SelectionKey.OP_WRITE |
                SelectionKey.OP_CONNECT);
    }

    /**
     * Receives a message into the given buffer and/or handles a notification.
     *
     * <P> If a message or notification is immediately available, or if this
     * channel is in blocking mode and one eventually becomes available, then
     * the message or notification is returned or handled, respectively. If this
     * channel is in non-blocking mode and a message or notification is not
     * immediately available then this method immediately returns {@code null}.
     *
     * <P> If this method receives a message it is copied into the given byte
     * buffer. The message is transferred into the given byte buffer starting at
     * its current position and the buffers position is incremented by the
     * number of bytes read. If there are fewer bytes remaining in the buffer
     * than are required to hold the message, or the underlying input buffer
     * does not contain the complete message, then an invocation of {@link
     * MessageInfo#isComplete isComplete} on the returned {@code
     * MessageInfo} will return {@code false}, and more invocations of this
     * method will be necessary to completely consume the messgae. Only
     * one message at a time will be partially delivered in any stream. The
     * socket option {@link SctpStandardSocketOption#SCTP_FRAGMENT_INTERLEAVE
     * SCTP_FRAGMENT_INTERLEAVE} controls various aspects of what interlacing of
     * messages occurs.
     *
     * <P> If this method receives a notification then the appropriate method of
     * the given handler, if there is one, is invoked. If the handler returns
     * {@link HandlerResult#CONTINUE CONTINUE} then this method will try to
     * receive another message/notification, otherwise, if {@link
     * HandlerResult#RETURN RETURN} is returned this method will return {@code
     * null}. If an uncaught exception is thrown by the handler it will be
     * propagated up the stack through this method.
     *
     * <P> This method may be invoked at any time. If another thread has
     * already initiated a receive operation upon this channel, then an
     * invocation of this method will block until the first operation is
     * complete. The given handler is invoked without holding any locks used
     * to enforce the above synchronization policy, that way handlers
     * will not stall other threads from receiving. A handler should not invoke
     * the {@code receive} method of this channel, if it does an
     * {@link IllegalReceiveException} will be thrown.
     *
     * @param  dst
     *         The buffer into which message bytes are to be transferred
     *
     * @param  attachment
     *         The object to attach to the receive operation; can be
     *         {@code null}
     *
     * @param  handler
     *         A handler to handle notifications from the SCTP stack, or {@code
     *         null} to ignore any notifications.
     *
     * @return  The {@code MessageInfo}, {@code null} if this channel is in
     *          non-blocking mode and no messages are immediately available or
     *          the notification handler returns {@link HandlerResult#RETURN
     *          RETURN} after handling a notification
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  java.nio.channels.AsynchronousCloseException
     *          If another thread closes this channel
     *          while the read operation is in progress
     *
     * @throws  java.nio.channels.ClosedByInterruptException
     *          If another thread interrupts the current thread
     *          while the read operation is in progress, thereby
     *          closing the channel and setting the current thread's
     *          interrupt status
     *
     * @throws  java.nio.channels.NotYetConnectedException
     *          If this channel is not yet connected
     *
     * @throws  IllegalReceiveException
     *          If the given handler invokes the {@code receive} method of this
     *          channel
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract <T> MessageInfo receive(ByteBuffer dst,
                                            T attachment,
                                            NotificationHandler<T> handler)
        throws IOException;

    /**
     * Sends a message via this channel.
     *
     * <P> If this channel is in non-blocking mode and there is sufficient room
     * in the underlying output buffer, or if this channel is in blocking mode
     * and sufficient room becomes available, then the remaining bytes in the
     * given byte buffer are transmitted as a single message. Sending a message
     * is atomic unless explicit message completion {@link
     * SctpStandardSocketOption#SCTP_EXPLICIT_COMPLETE SCTP_EXPLICIT_COMPLETE}
     * socket option is enabled on this channel's socket.
     *
     * <P> The message is transferred from the byte buffer as if by a regular
     * {@link java.nio.channels.WritableByteChannel#write(java.nio.ByteBuffer)
     * write} operation.
     *
     * <P> The bytes will be written to the stream number that is specified by
     * {@link MessageInfo#streamNumber streamNumber} in the given {@code
     * messageInfo}.
     *
     * <P> This method may be invoked at any time. If another thread has already
     * initiated a send operation upon this channel, then an invocation of
     * this method will block until the first operation is complete.
     *
     * @param  src
     *         The buffer containing the message to be sent
     *
     * @param  messageInfo
     *         Ancillary data about the message to be sent
     *
     * @return  The number of bytes sent, which will be either the number of
     *          bytes that were remaining in the messages buffer when this method
     *          was invoked or, if this channel is non-blocking, may be zero if
     *          there was insufficient room for the message in the underlying
     *          output buffer
     *
     * @throws  InvalidStreamExcepton
     *          If {@code streamNumner} is negative or greater than or equal to
     *          the maximum number of outgoing streams
     *
     * @throws  java.nio.channels.ClosedChannelException
     *          If this channel is closed
     *
     * @throws  java.nio.channels.AsynchronousCloseException
     *          If another thread closes this channel
     *          while the read operation is in progress
     *
     * @throws  java.nio.channels.ClosedByInterruptException
     *          If another thread interrupts the current thread
     *          while the read operation is in progress, thereby
     *          closing the channel and setting the current thread's
     *          interrupt status
     *
     * @throws  java.nio.channels.NotYetConnectedException
     *          If this channel is not yet connected
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public abstract int send(ByteBuffer src, MessageInfo messageInfo)
        throws IOException;
}