| /* |
| * Copyright (c) 2000, 2002, 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.jndi.dns; |
| |
| |
| import javax.naming.*; |
| |
| |
| /** |
| * The Header class represents the header of a DNS message. |
| * |
| * @author Scott Seligman |
| */ |
| |
| |
| class Header { |
| |
| static final int HEADER_SIZE = 12; // octets in a DNS header |
| |
| // Masks and shift amounts for DNS header flag fields. |
| static final short QR_BIT = (short) 0x8000; |
| static final short OPCODE_MASK = (short) 0x7800; |
| static final int OPCODE_SHIFT = 11; |
| static final short AA_BIT = (short) 0x0400; |
| static final short TC_BIT = (short) 0x0200; |
| static final short RD_BIT = (short) 0x0100; |
| static final short RA_BIT = (short) 0x0080; |
| static final short RCODE_MASK = (short) 0x000F; |
| |
| int xid; // ID: 16-bit query identifier |
| boolean query; // QR: true if query, false if response |
| int opcode; // OPCODE: 4-bit opcode |
| boolean authoritative; // AA |
| boolean truncated; // TC |
| boolean recursionDesired; // RD |
| boolean recursionAvail; // RA |
| int rcode; // RCODE: 4-bit response code |
| int numQuestions; |
| int numAnswers; |
| int numAuthorities; |
| int numAdditionals; |
| |
| /* |
| * Returns a representation of a decoded DNS message header. |
| * Does not modify or store a reference to the msg array. |
| */ |
| Header(byte[] msg, int msgLen) throws NamingException { |
| decode(msg, msgLen); |
| } |
| |
| /* |
| * Decodes a DNS message header. Does not modify or store a |
| * reference to the msg array. |
| */ |
| private void decode(byte[] msg, int msgLen) throws NamingException { |
| |
| try { |
| int pos = 0; // current offset into msg |
| |
| if (msgLen < HEADER_SIZE) { |
| throw new CommunicationException( |
| "DNS error: corrupted message header"); |
| } |
| |
| xid = getShort(msg, pos); |
| pos += 2; |
| |
| // Flags |
| short flags = (short) getShort(msg, pos); |
| pos += 2; |
| query = (flags & QR_BIT) == 0; |
| opcode = (flags & OPCODE_MASK) >>> OPCODE_SHIFT; |
| authoritative = (flags & AA_BIT) != 0; |
| truncated = (flags & TC_BIT) != 0; |
| recursionDesired = (flags & RD_BIT) != 0; |
| recursionAvail = (flags & RA_BIT) != 0; |
| rcode = (flags & RCODE_MASK); |
| |
| // RR counts |
| numQuestions = getShort(msg, pos); |
| pos += 2; |
| numAnswers = getShort(msg, pos); |
| pos += 2; |
| numAuthorities = getShort(msg, pos); |
| pos += 2; |
| numAdditionals = getShort(msg, pos); |
| pos += 2; |
| |
| } catch (IndexOutOfBoundsException e) { |
| throw new CommunicationException( |
| "DNS error: corrupted message header"); |
| } |
| } |
| |
| /* |
| * Returns the 2-byte unsigned value at msg[pos]. The high |
| * order byte comes first. |
| */ |
| private static int getShort(byte[] msg, int pos) { |
| return (((msg[pos] & 0xFF) << 8) | |
| (msg[pos + 1] & 0xFF)); |
| } |
| } |