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	/*
	* Copyright (c) 2000, 2020, 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> 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 \|} {@link SelectionKey#OP_READ} {@code \|} {@link
	* SelectionKey#OP_WRITE}{@code )}.
	*
	* @return The valid-operation set
	*/
	public final int validOps() {
	return (SelectionKey.OP_READ
	\| SelectionKey.OP_WRITE
	\| SelectionKey.OP_CONNECT);
	}


	// -- Socket-specific operations --

	/**
	* 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
	*/
	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}
	*
	* 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;
	}

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