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	/*
	* Copyright (c) 2003, 2013, 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 com.sun.jdi.connect.spi;

	import java.io.IOException;

	/**
	* A connection between a debugger and a target VM which it debugs.
	*
	* <p> A Connection represents a bi-directional communication channel
	* between a debugger and a target VM. A Connection is created when
	* {@link com.sun.jdi.connect.spi.TransportService TransportService}
	* establishes a connection and successfully handshakes with a target
	* VM. A TransportService implementation provides a reliable
	* JDWP packet transportation service and consequently a Connection
	* provides a reliable flow of JDWP packets between the debugger
	* and the target VM. A Connection is stream oriented, that is, the
	* JDWP packets written to a connection are read by the target VM
	* in the order in which they were written. Similiarly packets written
	* to a Connection by the target VM are read by the debugger in the
	* order in which they were written.
	*
	* <p> A connection is either open or closed. It is open upon creation,
	* and remains open until it is closed. Once closed, it remains closed,
	* and any attempt to invoke an I/O operation upon it will cause a
	* {@link ClosedConnectionException} to be thrown. A connection can
	* be tested by invoking the {@link #isOpen isOpen} method.
	*
	* <p> A Connection is safe for access by multiple concurrent threads,
	* although at most one thread may be reading and at most one thread may
	* be writing at any given time. </p>
	*
	* @since 1.5
	*/

	@jdk.Exported
	public abstract class Connection {

	/**
	* Reads a packet from the target VM.
	*
	* <p> Attempts to read a JDWP packet from the target VM.
	* A read operation may block indefinitely and only returns
	* when it reads all bytes of a packet, or in the case of a
	* transport service that is based on a stream-oriented
	* communication protocol, the end of stream is encountered.
	*
	* <p> Reading a packet does not do any integrity checking on
	* the packet aside from a check that the length of the packet
	* (as indicated by the value of the <tt>length</tt> field, the
	* first four bytes of the packet) is 11 or more bytes.
	* If the value of the <tt>length</tt> value is less then 11
	* then an <tt>IOException</tt> is thrown.
	*
	* <p> Returns a byte array of a length equal to the length
	* of the received packet, or a byte array of length 0 when an
	* end of stream is encountered. If end of stream is encountered
	* after some, but not all bytes of a packet, are read then it
	* is considered an I/O error and an <tt>IOException</tt> is
	* thrown. The first byte of the packet is stored in element
	* <tt>0</tt> of the byte array, the second in element <tt>1</tt>,
	* and so on. The bytes in the byte array are laid out as per the
	* <a href="../../../../../../../../../technotes/guides/jpda/jdwp-spec.html">
	* JDWP specification</a>. That is, all fields in the packet
	* are in big endian order as per the JDWP specification.
	*
	* <p> This method may be invoked at any time. If another thread has
	* already initiated a {@link #readPacket readPacket} on this
	* connection then the invocation of this method will block until the
	* first operation is complete. </p>
	*
	* @return the packet read from the target VM
	*
	* @throws ClosedConnectionException
	* If the connection is closed, or another thread closes
	* the connection while the readPacket is in progress.
	*
	* @throws java.io.IOException
	* If the length of the packet (as indictaed by the first
	* 4 bytes) is less than 11 bytes, or an I/O error occurs.
	*
	*
	*/
	public abstract byte[] readPacket() throws IOException;

	/**
	* Writes a packet to the target VM.
	*
	* <p> Attempts to write, or send, a JDWP packet to the target VM.
	* A write operation only returns after writing the entire packet
	* to the target VM. Writing the entire packet does not mean
	* the entire packet has been transmitted to the target VM
	* but rather that all bytes have been written to the
	* transport service. A transport service based on a TCP/IP connection
	* may, for example, buffer some or all of the packet before
	* transmission on the network.
	*
	* <p> The byte array provided to this method should be laid out
	* as per the <a
	* href="../../../../../../../../../technotes/guides/jpda/jdwp-spec.html">
	* JDWP specification</a>. That is, all fields in the packet
	* are in big endian order. The first byte, that is element
	* <tt>pkt[0]</tt>, is the first byte of the <tt>length</tt> field.
	* <tt>pkt[1]</tt> is the second byte of the <tt>length</tt> field,
	* and so on.
	*
	* <p> Writing a packet does not do any integrity checking on
	* the packet aside from checking the packet length. Checking
	* the packet length requires checking that the value of the
	* <tt>length</tt> field (as indicated by the first four bytes
	* of the packet) is 11 or greater. Consequently the length of
	* the byte array provided to this method, that is
	* <tt>pkt.length</tt>, must be 11 or more, and must be equal
	* or greater than the value of the <tt>length</tt> field. If the
	* length of the byte array is greater than the value of
	* the <tt>length</tt> field then all bytes from element
	* <tt>pkt[length]</tt> onwards are ignored. In other words,
	* any additional bytes that follow the packet in the byte
	* array are ignored and will not be transmitted to the target
	* VM.
	*
	* <p> A write operation may block or may complete immediately.
	* The exact circumstances when an operation blocks depends on
	* the transport service. In the case of a TCP/IP connection to
	* the target VM, the writePacket method may block if there is
	* network congestion or there is insufficient space to buffer
	* the packet in the underlying network system.
	*
	* <p> This method may be invoked at any time. If another thread has
	* already initiated a write operation upon this Connection then
	* a subsequent invocation of this method will block until the first
	* operation is complete. </p>
	*
	* @param pkt
	* The packet to write to the target VM.
	*
	* @throws ClosedConnectionException
	* If the connection is closed, or another thread closes
	* the connection while the write operation is in progress.
	*
	* @throws java.io.IOException
	* If an I/O error occurs.
	*
	* @throws IllegalArgumentException
	* If the value of the <tt>length</tt> field is invalid,
	* or the byte array is of insufficient length.
	*/
	public abstract void writePacket(byte pkt[]) throws IOException;

	/**
	* Closes this connection.
	*
	* <p> If the connection is already closed then invoking this method
	* has no effect. After a connection is closed, any further attempt
	* calls to {@link #readPacket readPacket} or {@link #writePacket
	* writePacket} will throw a {@link ClosedConnectionException}.
	*
	* <p> Any thread currently blocked in an I/O operation ({@link
	* #readPacket readPacket} or {@link #writePacket writePacket})
	* will throw a {@link ClosedConnectionException}).
	*
	* <p> This method may be invoked at any time. If some other thread has
	* already invoked it, however, then another invocation will block until
	* the first invocation is complete, after which it will return without
	* effect. </p>
	*
	* @throws java.io.IOException
	* If an I/O error occurs
	*/
	public abstract void close() throws IOException;

	/**
	* Tells whether or not this connection is open. </p>
	*
	* @return <tt>true</tt> if, and only if, this connection is open
	*/
	public abstract boolean isOpen();
	}

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