1/*
2 * Copyright (c) 2000, 2002, 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
26package com.sun.jndi.dns;
27
28
29import javax.naming.*;
30
31
32/**
33 * The Header class represents the header of a DNS message.
34 *
35 * @author Scott Seligman
36 */
37
38
39class Header {
40
41    static final int HEADER_SIZE = 12;  // octets in a DNS header
42
43    // Masks and shift amounts for DNS header flag fields.
44    static final short QR_BIT =         (short) 0x8000;
45    static final short OPCODE_MASK =    (short) 0x7800;
46    static final int   OPCODE_SHIFT =   11;
47    static final short AA_BIT =         (short) 0x0400;
48    static final short TC_BIT =         (short) 0x0200;
49    static final short RD_BIT =         (short) 0x0100;
50    static final short RA_BIT =         (short) 0x0080;
51    static final short RCODE_MASK =     (short) 0x000F;
52
53    int xid;                    // ID:  16-bit query identifier
54    boolean query;              // QR:  true if query, false if response
55    int opcode;                 // OPCODE:  4-bit opcode
56    boolean authoritative;      // AA
57    boolean truncated;          // TC
58    boolean recursionDesired;   // RD
59    boolean recursionAvail;     // RA
60    int rcode;                  // RCODE:  4-bit response code
61    int numQuestions;
62    int numAnswers;
63    int numAuthorities;
64    int numAdditionals;
65
66    /*
67     * Returns a representation of a decoded DNS message header.
68     * Does not modify or store a reference to the msg array.
69     */
70    Header(byte[] msg, int msgLen) throws NamingException {
71        decode(msg, msgLen);
72    }
73
74    /*
75     * Decodes a DNS message header.  Does not modify or store a
76     * reference to the msg array.
77     */
78    private void decode(byte[] msg, int msgLen) throws NamingException {
79
80        try {
81            int pos = 0;        // current offset into msg
82
83            if (msgLen < HEADER_SIZE) {
84                throw new CommunicationException(
85                        "DNS error: corrupted message header");
86            }
87
88            xid = getShort(msg, pos);
89            pos += 2;
90
91            // Flags
92            short flags = (short) getShort(msg, pos);
93            pos += 2;
94            query = (flags & QR_BIT) == 0;
95            opcode = (flags & OPCODE_MASK) >>> OPCODE_SHIFT;
96            authoritative = (flags & AA_BIT) != 0;
97            truncated = (flags & TC_BIT) != 0;
98            recursionDesired = (flags & RD_BIT) != 0;
99            recursionAvail = (flags & RA_BIT) != 0;
100            rcode = (flags & RCODE_MASK);
101
102            // RR counts
103            numQuestions = getShort(msg, pos);
104            pos += 2;
105            numAnswers = getShort(msg, pos);
106            pos += 2;
107            numAuthorities = getShort(msg, pos);
108            pos += 2;
109            numAdditionals = getShort(msg, pos);
110            pos += 2;
111
112        } catch (IndexOutOfBoundsException e) {
113            throw new CommunicationException(
114                    "DNS error: corrupted message header");
115        }
116    }
117
118    /*
119     * Returns the 2-byte unsigned value at msg[pos].  The high
120     * order byte comes first.
121     */
122    private static int getShort(byte[] msg, int pos) {
123        return (((msg[pos] & 0xFF) << 8) |
124                (msg[pos + 1] & 0xFF));
125    }
126}
127