1 /*
2 * Copyright (c) 2003, 2017, 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
23 * questions.
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 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. Similarly 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.
55 *
56 * @since 1.5
57 */
58 public abstract class Connection {
59
60 /**
61 * Reads a packet from the target VM.
62 *
63 * <p> Attempts to read a JDWP packet from the target VM.
64 * A read operation may block indefinitely and only returns
65 * when it reads all bytes of a packet, or in the case of a
66 * transport service that is based on a stream-oriented
67 * communication protocol, the end of stream is encountered.
68 *
69 * <p> Reading a packet does not do any integrity checking on
70 * the packet aside from a check that the length of the packet
71 * (as indicated by the value of the {@code length} field, the
72 * first four bytes of the packet) is 11 or more bytes.
73 * If the value of the {@code length} value is less then 11
74 * then an {@code IOException} is thrown.
75 *
76 * <p> Returns a byte array of a length equal to the length
77 * of the received packet, or a byte array of length 0 when an
78 * end of stream is encountered. If end of stream is encountered
79 * after some, but not all bytes of a packet, are read then it
80 * is considered an I/O error and an {@code IOException} is
81 * thrown. The first byte of the packet is stored in element
82 * {@code 0} of the byte array, the second in element {@code 1},
83 * and so on. The bytes in the byte array are laid out as per the
84 * <a href="../../../../../../../../../technotes/guides/jpda/jdwp-spec.html">
85 * JDWP specification</a>. That is, all fields in the packet
86 * are in big endian order as per the JDWP specification.
87 *
88 * <p> This method may be invoked at any time. If another thread has
89 * already initiated a {@link #readPacket readPacket} on this
90 * connection then the invocation of this method will block until the
91 * first operation is complete.
92 *
93 * @return the packet read from the target VM
94 *
95 * @throws ClosedConnectionException
96 * If the connection is closed, or another thread closes
97 * the connection while the readPacket is in progress.
98 *
99 * @throws java.io.IOException
100 * If the length of the packet (as indictaed by the first
101 * 4 bytes) is less than 11 bytes, or an I/O error occurs.
102 *
103 *
104 */
105 public abstract byte[] readPacket() throws IOException;
106
107 /**
108 * Writes a packet to the target VM.
109 *
110 * <p> Attempts to write, or send, a JDWP packet to the target VM.
111 * A write operation only returns after writing the entire packet
112 * to the target VM. Writing the entire packet does not mean
113 * the entire packet has been transmitted to the target VM
114 * but rather that all bytes have been written to the
115 * transport service. A transport service based on a TCP/IP connection
116 * may, for example, buffer some or all of the packet before
117 * transmission on the network.
118 *
119 * <p> The byte array provided to this method should be laid out
120 * as per the <a
121 * href="../../../../../../../../../technotes/guides/jpda/jdwp-spec.html">
122 * JDWP specification</a>. That is, all fields in the packet
123 * are in big endian order. The first byte, that is element
124 * {@code pkt[0]}, is the first byte of the {@code length} field.
125 * {@code pkt[1]} is the second byte of the {@code length} field,
126 * and so on.
127 *
128 * <p> Writing a packet does not do any integrity checking on
129 * the packet aside from checking the packet length. Checking
130 * the packet length requires checking that the value of the
131 * {@code length} field (as indicated by the first four bytes
132 * of the packet) is 11 or greater. Consequently the length of
133 * the byte array provided to this method, that is
134 * {@code pkt.length}, must be 11 or more, and must be equal
135 * or greater than the value of the {@code length} field. If the
136 * length of the byte array is greater than the value of
137 * the {@code length} field then all bytes from element
138 * {@code pkt[length]} onwards are ignored. In other words,
139 * any additional bytes that follow the packet in the byte
140 * array are ignored and will not be transmitted to the target
141 * VM.
142 *
143 * <p> A write operation may block or may complete immediately.
144 * The exact circumstances when an operation blocks depends on
145 * the transport service. In the case of a TCP/IP connection to
146 * the target VM, the writePacket method may block if there is
147 * network congestion or there is insufficient space to buffer
148 * the packet in the underlying network system.
149 *
150 * <p> This method may be invoked at any time. If another thread has
151 * already initiated a write operation upon this Connection then
152 * a subsequent invocation of this method will block until the first
153 * operation is complete.
154 *
155 * @param pkt
156 * The packet to write to the target VM.
157 *
158 * @throws ClosedConnectionException
159 * If the connection is closed, or another thread closes
160 * the connection while the write operation is in progress.
161 *
162 * @throws java.io.IOException
163 * If an I/O error occurs.
164 *
165 * @throws IllegalArgumentException
166 * If the value of the {@code length} field is invalid,
167 * or the byte array is of insufficient length.
168 */
169 public abstract void writePacket(byte pkt[]) throws IOException;
170
171 /**
172 * Closes this connection.
173 *
174 * <p> If the connection is already closed then invoking this method
175 * has no effect. After a connection is closed, any further attempt
176 * calls to {@link #readPacket readPacket} or {@link #writePacket
177 * writePacket} will throw a {@link ClosedConnectionException}.
178 *
179 * <p> Any thread currently blocked in an I/O operation ({@link
180 * #readPacket readPacket} or {@link #writePacket writePacket})
181 * will throw a {@link ClosedConnectionException}).
182 *
183 * <p> This method may be invoked at any time. If some other thread has
184 * already invoked it, however, then another invocation will block until
185 * the first invocation is complete, after which it will return without
186 * effect.
187 *
188 * @throws java.io.IOException
189 * If an I/O error occurs
190 */
191 public abstract void close() throws IOException;
192
193 /**
194 * Tells whether or not this connection is open.
195 *
196 * @return {@code true} if and only if this connection is open
197 */
198 public abstract boolean isOpen();
199 }