/* * Copyright (c) 2003, 2006, 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 */ 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();}