Shuyi Chen | d7955ce | 2013-05-22 14:51:55 -0700 | [diff] [blame] | 1 | // Copyright (c) 2004 Brian Wellington (bwelling@xbill.org) |
| 2 | |
| 3 | package org.xbill.DNS; |
| 4 | |
| 5 | /** |
| 6 | * An class for parsing DNS messages. |
| 7 | * |
| 8 | * @author Brian Wellington |
| 9 | */ |
| 10 | |
| 11 | public class DNSInput { |
| 12 | |
| 13 | private byte [] array; |
| 14 | private int pos; |
| 15 | private int end; |
| 16 | private int saved_pos; |
| 17 | private int saved_end; |
| 18 | |
| 19 | /** |
| 20 | * Creates a new DNSInput |
| 21 | * @param input The byte array to read from |
| 22 | */ |
| 23 | public |
| 24 | DNSInput(byte [] input) { |
| 25 | array = input; |
| 26 | pos = 0; |
| 27 | end = array.length; |
| 28 | saved_pos = -1; |
| 29 | saved_end = -1; |
| 30 | } |
| 31 | |
| 32 | /** |
| 33 | * Returns the current position. |
| 34 | */ |
| 35 | public int |
| 36 | current() { |
| 37 | return pos; |
| 38 | } |
| 39 | |
| 40 | /** |
| 41 | * Returns the number of bytes that can be read from this stream before |
| 42 | * reaching the end. |
| 43 | */ |
| 44 | public int |
| 45 | remaining() { |
| 46 | return end - pos; |
| 47 | } |
| 48 | |
| 49 | private void |
| 50 | require(int n) throws WireParseException{ |
| 51 | if (n > remaining()) { |
| 52 | throw new WireParseException("end of input"); |
| 53 | } |
| 54 | } |
| 55 | |
| 56 | /** |
| 57 | * Marks the following bytes in the stream as active. |
| 58 | * @param len The number of bytes in the active region. |
| 59 | * @throws IllegalArgumentException The number of bytes in the active region |
| 60 | * is longer than the remainder of the input. |
| 61 | */ |
| 62 | public void |
| 63 | setActive(int len) { |
| 64 | if (len > array.length - pos) { |
| 65 | throw new IllegalArgumentException("cannot set active " + |
| 66 | "region past end of input"); |
| 67 | } |
| 68 | end = pos + len; |
| 69 | } |
| 70 | |
| 71 | /** |
| 72 | * Clears the active region of the string. Further operations are not |
| 73 | * restricted to part of the input. |
| 74 | */ |
| 75 | public void |
| 76 | clearActive() { |
| 77 | end = array.length; |
| 78 | } |
| 79 | |
| 80 | /** |
| 81 | * Returns the position of the end of the current active region. |
| 82 | */ |
| 83 | public int |
| 84 | saveActive() { |
| 85 | return end; |
| 86 | } |
| 87 | |
| 88 | /** |
| 89 | * Restores the previously set active region. This differs from setActive() in |
| 90 | * that restoreActive() takes an absolute position, and setActive takes an |
| 91 | * offset from the current location. |
| 92 | * @param pos The end of the active region. |
| 93 | */ |
| 94 | public void |
| 95 | restoreActive(int pos) { |
| 96 | if (pos > array.length) { |
| 97 | throw new IllegalArgumentException("cannot set active " + |
| 98 | "region past end of input"); |
| 99 | } |
| 100 | end = pos; |
| 101 | } |
| 102 | |
| 103 | /** |
| 104 | * Resets the current position of the input stream to the specified index, |
| 105 | * and clears the active region. |
| 106 | * @param index The position to continue parsing at. |
| 107 | * @throws IllegalArgumentException The index is not within the input. |
| 108 | */ |
| 109 | public void |
| 110 | jump(int index) { |
| 111 | if (index >= array.length) { |
| 112 | throw new IllegalArgumentException("cannot jump past " + |
| 113 | "end of input"); |
| 114 | } |
| 115 | pos = index; |
| 116 | end = array.length; |
| 117 | } |
| 118 | |
| 119 | /** |
| 120 | * Saves the current state of the input stream. Both the current position and |
| 121 | * the end of the active region are saved. |
| 122 | * @throws IllegalArgumentException The index is not within the input. |
| 123 | */ |
| 124 | public void |
| 125 | save() { |
| 126 | saved_pos = pos; |
| 127 | saved_end = end; |
| 128 | } |
| 129 | |
| 130 | /** |
| 131 | * Restores the input stream to its state before the call to {@link #save}. |
| 132 | */ |
| 133 | public void |
| 134 | restore() { |
| 135 | if (saved_pos < 0) { |
| 136 | throw new IllegalStateException("no previous state"); |
| 137 | } |
| 138 | pos = saved_pos; |
| 139 | end = saved_end; |
| 140 | saved_pos = -1; |
| 141 | saved_end = -1; |
| 142 | } |
| 143 | |
| 144 | /** |
| 145 | * Reads an unsigned 8 bit value from the stream, as an int. |
| 146 | * @return An unsigned 8 bit value. |
| 147 | * @throws WireParseException The end of the stream was reached. |
| 148 | */ |
| 149 | public int |
| 150 | readU8() throws WireParseException { |
| 151 | require(1); |
| 152 | return (array[pos++] & 0xFF); |
| 153 | } |
| 154 | |
| 155 | /** |
| 156 | * Reads an unsigned 16 bit value from the stream, as an int. |
| 157 | * @return An unsigned 16 bit value. |
| 158 | * @throws WireParseException The end of the stream was reached. |
| 159 | */ |
| 160 | public int |
| 161 | readU16() throws WireParseException { |
| 162 | require(2); |
| 163 | int b1 = array[pos++] & 0xFF; |
| 164 | int b2 = array[pos++] & 0xFF; |
| 165 | return ((b1 << 8) + b2); |
| 166 | } |
| 167 | |
| 168 | /** |
| 169 | * Reads an unsigned 32 bit value from the stream, as a long. |
| 170 | * @return An unsigned 32 bit value. |
| 171 | * @throws WireParseException The end of the stream was reached. |
| 172 | */ |
| 173 | public long |
| 174 | readU32() throws WireParseException { |
| 175 | require(4); |
| 176 | int b1 = array[pos++] & 0xFF; |
| 177 | int b2 = array[pos++] & 0xFF; |
| 178 | int b3 = array[pos++] & 0xFF; |
| 179 | int b4 = array[pos++] & 0xFF; |
| 180 | return (((long)b1 << 24) + (b2 << 16) + (b3 << 8) + b4); |
| 181 | } |
| 182 | |
| 183 | /** |
| 184 | * Reads a byte array of a specified length from the stream into an existing |
| 185 | * array. |
| 186 | * @param b The array to read into. |
| 187 | * @param off The offset of the array to start copying data into. |
| 188 | * @param len The number of bytes to copy. |
| 189 | * @throws WireParseException The end of the stream was reached. |
| 190 | */ |
| 191 | public void |
| 192 | readByteArray(byte [] b, int off, int len) throws WireParseException { |
| 193 | require(len); |
| 194 | System.arraycopy(array, pos, b, off, len); |
| 195 | pos += len; |
| 196 | } |
| 197 | |
| 198 | /** |
| 199 | * Reads a byte array of a specified length from the stream. |
| 200 | * @return The byte array. |
| 201 | * @throws WireParseException The end of the stream was reached. |
| 202 | */ |
| 203 | public byte [] |
| 204 | readByteArray(int len) throws WireParseException { |
| 205 | require(len); |
| 206 | byte [] out = new byte[len]; |
| 207 | System.arraycopy(array, pos, out, 0, len); |
| 208 | pos += len; |
| 209 | return out; |
| 210 | } |
| 211 | |
| 212 | /** |
| 213 | * Reads a byte array consisting of the remainder of the stream (or the |
| 214 | * active region, if one is set. |
| 215 | * @return The byte array. |
| 216 | */ |
| 217 | public byte [] |
| 218 | readByteArray() { |
| 219 | int len = remaining(); |
| 220 | byte [] out = new byte[len]; |
| 221 | System.arraycopy(array, pos, out, 0, len); |
| 222 | pos += len; |
| 223 | return out; |
| 224 | } |
| 225 | |
| 226 | /** |
| 227 | * Reads a counted string from the stream. A counted string is a one byte |
| 228 | * value indicating string length, followed by bytes of data. |
| 229 | * @return A byte array containing the string. |
| 230 | * @throws WireParseException The end of the stream was reached. |
| 231 | */ |
| 232 | public byte [] |
| 233 | readCountedString() throws WireParseException { |
| 234 | require(1); |
| 235 | int len = array[pos++] & 0xFF; |
| 236 | return readByteArray(len); |
| 237 | } |
| 238 | |
| 239 | } |