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1   /*
2    * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
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24   */
25  
26  package com.sun.jdi.connect.spi;
27  
28  import java.io.IOException;
29  
30  /**
31   * A connection between a debugger and a target VM which it debugs.
32   *
33   * <p> A Connection represents a bi-directional communication channel
34   * between a debugger and a target VM. A Connection is created when
35   * {@link com.sun.jdi.connect.spi.TransportService TransportService}
36   * establishes a connection and successfully handshakes with a target
37   * VM. A TransportService implementation provides a reliable
38   * JDWP packet transportation service and consequently a Connection
39   * provides a reliable flow of JDWP packets between the debugger
40   * and the target VM. A Connection is stream oriented, that is, the
41   * JDWP packets written to a connection are read by the target VM
42   * in the order in which they were written. Similiarly packets written
43   * to a Connection by the target VM are read by the debugger in the
44   * order in which they were written.
45   *
46   * <p> A connection is either open or closed. It is open upon creation,
47   * and remains open until it is closed. Once closed, it remains closed,
48   * and any attempt to invoke an I/O operation upon it will cause a
49   * {@link ClosedConnectionException} to be thrown. A connection can
50   * be tested by invoking the {@link #isOpen isOpen} method.
51   *
52   * <p> A Connection is safe for access by multiple concurrent threads,
53   * although at most one thread may be reading and at most one thread may
54   * be writing at any given time. </p>
55   *
56   * @since 1.5
57   */
58  
59  @jdk.Exported
60  public abstract class Connection {
61  
62      /**
63       * Reads a packet from the target VM.
64       *
65       * <p> Attempts to read a JDWP packet from the target VM.
66       * A read operation may block indefinitely and only returns
67       * when it reads all bytes of a packet, or in the case of a
68       * transport service that is based on a stream-oriented
69       * communication protocol, the end of stream is encountered.
70       *
71       * <p> Reading a packet does not do any integrity checking on
72       * the packet aside from a check that the length of the packet
73       * (as indicated by the value of the <tt>length</tt> field, the
74       * first four bytes of the packet) is 11 or more bytes.
75       * If the value of the <tt>length</tt> value is less then 11
76       * then an <tt>IOException</tt> is thrown.
77       *
78       * <p> Returns a byte array of a length equal to the length
79       * of the received packet, or a byte array of length 0 when an
80       * end of stream is encountered. If end of stream is encountered
81       * after some, but not all bytes of a packet, are read then it
82       * is considered an I/O error and an <tt>IOException</tt> is
83       * thrown. The first byte of the packet is stored in element
84       * <tt>0</tt> of the byte array, the second in element <tt>1</tt>,
85       * and so on. The bytes in the byte array are laid out as per the
86       * <a href="../../../../../../../../../technotes/guides/jpda/jdwp-spec.html">
87       * JDWP specification</a>. That is, all fields in the packet
88       * are in big endian order as per the JDWP specification.
89       *
90       * <p> This method may be invoked at any time.  If another thread has
91       * already initiated a {@link #readPacket readPacket} on this
92       * connection then the invocation of this method will block until the
93       * first operation is complete. </p>
94       *
95       * @return  the packet read from the target VM
96       *
97       * @throws  ClosedConnectionException
98       *          If the connection is closed, or another thread closes
99       *          the connection while the readPacket is in progress.
100      *
101      * @throws  java.io.IOException
102      *          If the length of the packet (as indictaed by the first
103      *          4 bytes) is less than 11 bytes, or an I/O error occurs.
104      *
105      *
106      */
107     public abstract byte[] readPacket() throws IOException;
108 
109     /**
110      * Writes a packet to the target VM.
111      *
112      * <p> Attempts to write, or send, a JDWP packet to the target VM.
113      * A write operation only returns after writing the entire packet
114      * to the target VM. Writing the entire packet does not mean
115      * the entire packet has been transmitted to the target VM
116      * but rather that all bytes have been written to the
117      * transport service. A transport service based on a TCP/IP connection
118      * may, for example, buffer some or all of the packet before
119      * transmission on the network.
120      *
121      * <p> The byte array provided to this method should be laid out
122      * as per the <a
123      * href="../../../../../../../../../technotes/guides/jpda/jdwp-spec.html">
124      * JDWP specification</a>. That is, all fields in the packet
125      * are in big endian order. The first byte, that is element
126      * <tt>pkt[0]</tt>, is the first byte of the <tt>length</tt> field.
127      * <tt>pkt[1]</tt> is the second byte of the <tt>length</tt> field,
128      * and so on.
129      *
130      * <p> Writing a packet does not do any integrity checking on
131      * the packet aside from checking the packet length. Checking
132      * the packet length requires checking that the value of the
133      * <tt>length</tt> field (as indicated by the first four bytes
134      * of the packet) is 11 or greater. Consequently the length of
135      * the byte array provided to this method, that is
136      * <tt>pkt.length</tt>, must be 11 or more, and must be equal
137      * or greater than the value of the <tt>length</tt> field. If the
138      * length of the byte array is greater than the value of
139      * the <tt>length</tt> field then all bytes from element
140      * <tt>pkt[length]</tt> onwards are ignored. In other words,
141      * any additional bytes that follow the packet in the byte
142      * array are ignored and will not be transmitted to the target
143      * VM.
144      *
145      * <p> A write operation may block or may complete immediately.
146      * The exact circumstances when an operation blocks depends on
147      * the transport service. In the case of a TCP/IP connection to
148      * the target VM, the writePacket method may block if there is
149      * network congestion or there is insufficient space to buffer
150      * the packet in the underlying network system.
151      *
152      * <p> This method may be invoked at any time.  If another thread has
153      * already initiated a write operation upon this Connection then
154      * a subsequent invocation of this method will block until the first
155      * operation is complete. </p>
156      *
157      * @param   pkt
158      *          The packet to write to the target VM.
159      *
160      * @throws  ClosedConnectionException
161      *          If the connection is closed, or another thread closes
162      *          the connection while the write operation is in progress.
163      *
164      * @throws  java.io.IOException
165      *          If an I/O error occurs.
166      *
167      * @throws  IllegalArgumentException
168      *          If the value of the <tt>length</tt> field is invalid,
169      *          or the byte array is of insufficient length.
170      */
171     public abstract void writePacket(byte pkt[]) throws IOException;
172 
173     /**
174      * Closes this connection.
175      *
176      * <p> If the connection is already closed then invoking this method
177      * has no effect. After a connection is closed, any further attempt
178      * calls to {@link #readPacket readPacket} or {@link #writePacket
179      * writePacket} will throw a {@link ClosedConnectionException}.
180      *
181      * <p> Any thread currently blocked in an I/O operation ({@link
182      * #readPacket readPacket} or {@link #writePacket writePacket})
183      * will throw a {@link ClosedConnectionException}).
184      *
185      * <p> This method may be invoked at any time.  If some other thread has
186      * already invoked it, however, then another invocation will block until
187      * the first invocation is complete, after which it will return without
188      * effect. </p>
189      *
190      * @throws  java.io.IOException
191      *          If an I/O error occurs
192      */
193     public abstract void close() throws IOException;
194 
195     /**
196      * Tells whether or not this connection is open.  </p>
197      *
198      * @return <tt>true</tt> if, and only if, this connection is open
199      */
200     public abstract boolean isOpen();
201 }