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.
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
25
26package com.sun.jdi.connect.spi;
27
28import 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.
55 *
56 * @since 1.5
57 */
58
59public abstract class Connection {
60
61    /**
62     * Reads a packet from the target VM.
63     *
64     * <p> Attempts to read a JDWP packet from the target VM.
65     * A read operation may block indefinitely and only returns
66     * when it reads all bytes of a packet, or in the case of a
67     * transport service that is based on a stream-oriented
68     * communication protocol, the end of stream is encountered.
69     *
70     * <p> Reading a packet does not do any integrity checking on
71     * the packet aside from a check that the length of the packet
72     * (as indicated by the value of the {@code length} field, the
73     * first four bytes of the packet) is 11 or more bytes.
74     * If the value of the {@code length} value is less then 11
75     * then an {@code IOException} is thrown.
76     *
77     * <p> Returns a byte array of a length equal to the length
78     * of the received packet, or a byte array of length 0 when an
79     * end of stream is encountered. If end of stream is encountered
80     * after some, but not all bytes of a packet, are read then it
81     * is considered an I/O error and an {@code IOException} is
82     * thrown. The first byte of the packet is stored in element
83     * {@code 0} of the byte array, the second in element {@code 1},
84     * and so on. The bytes in the byte array are laid out as per the
85     * <a href="{@docRoot}/../specs/jdwp/jdwp-spec.html">
86     * JDWP specification</a>. That is, all fields in the packet
87     * are in big endian order as per the JDWP specification.
88     *
89     * <p> This method may be invoked at any time.  If another thread has
90     * already initiated a {@link #readPacket readPacket} on this
91     * connection then the invocation of this method will block until the
92     * first operation is complete.
93     *
94     * @return  the packet read from the target VM
95     *
96     * @throws  ClosedConnectionException
97     *          If the connection is closed, or another thread closes
98     *          the connection while the readPacket is in progress.
99     *
100     * @throws  java.io.IOException
101     *          If the length of the packet (as indictaed by the first
102     *          4 bytes) is less than 11 bytes, or an I/O error occurs.
103     *
104     *
105     */
106    public abstract byte[] readPacket() throws IOException;
107
108    /**
109     * Writes a packet to the target VM.
110     *
111     * <p> Attempts to write, or send, a JDWP packet to the target VM.
112     * A write operation only returns after writing the entire packet
113     * to the target VM. Writing the entire packet does not mean
114     * the entire packet has been transmitted to the target VM
115     * but rather that all bytes have been written to the
116     * transport service. A transport service based on a TCP/IP connection
117     * may, for example, buffer some or all of the packet before
118     * transmission on the network.
119     *
120     * <p> The byte array provided to this method should be laid out
121     * as per the <a
122     * href="{@docRoot}/../specs/jdwp/jdwp-spec.html">
123     * JDWP specification</a>. That is, all fields in the packet
124     * are in big endian order. The first byte, that is element
125     * {@code pkt[0]}, is the first byte of the {@code length} field.
126     * {@code pkt[1]} is the second byte of the {@code length} field,
127     * and so on.
128     *
129     * <p> Writing a packet does not do any integrity checking on
130     * the packet aside from checking the packet length. Checking
131     * the packet length requires checking that the value of the
132     * {@code length} field (as indicated by the first four bytes
133     * of the packet) is 11 or greater. Consequently the length of
134     * the byte array provided to this method, that is
135     * {@code pkt.length}, must be 11 or more, and must be equal
136     * or greater than the value of the {@code length} field. If the
137     * length of the byte array is greater than the value of
138     * the {@code length} field then all bytes from element
139     * {@code pkt[length]} onwards are ignored. In other words,
140     * any additional bytes that follow the packet in the byte
141     * array are ignored and will not be transmitted to the target
142     * VM.
143     *
144     * <p> A write operation may block or may complete immediately.
145     * The exact circumstances when an operation blocks depends on
146     * the transport service. In the case of a TCP/IP connection to
147     * the target VM, the writePacket method may block if there is
148     * network congestion or there is insufficient space to buffer
149     * the packet in the underlying network system.
150     *
151     * <p> This method may be invoked at any time.  If another thread has
152     * already initiated a write operation upon this Connection then
153     * a subsequent invocation of this method will block until the first
154     * operation is complete.
155     *
156     * @param   pkt
157     *          The packet to write to the target VM.
158     *
159     * @throws  ClosedConnectionException
160     *          If the connection is closed, or another thread closes
161     *          the connection while the write operation is in progress.
162     *
163     * @throws  java.io.IOException
164     *          If an I/O error occurs.
165     *
166     * @throws  IllegalArgumentException
167     *          If the value of the {@code length} field is invalid,
168     *          or the byte array is of insufficient length.
169     */
170    public abstract void writePacket(byte pkt[]) throws IOException;
171
172    /**
173     * Closes this connection.
174     *
175     * <p> If the connection is already closed then invoking this method
176     * has no effect. After a connection is closed, any further attempt
177     * calls to {@link #readPacket readPacket} or {@link #writePacket
178     * writePacket} will throw a {@link ClosedConnectionException}.
179     *
180     * <p> Any thread currently blocked in an I/O operation ({@link
181     * #readPacket readPacket} or {@link #writePacket writePacket})
182     * will throw a {@link ClosedConnectionException}).
183     *
184     * <p> This method may be invoked at any time.  If some other thread has
185     * already invoked it, however, then another invocation will block until
186     * the first invocation is complete, after which it will return without
187     * effect.
188     *
189     * @throws  java.io.IOException
190     *          If an I/O error occurs
191     */
192    public abstract void close() throws IOException;
193
194    /**
195     * Tells whether or not this connection is open.
196     *
197     * @return {@code true} if and only if this connection is open
198     */
199    public abstract boolean isOpen();
200}
201