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// Copyright (c) 2004 Brian Wellington (bwelling@xbill.org)
package org.xbill.DNS;
/**
* An class for parsing DNS messages.
*
* @author Brian Wellington
*/
public class DNSInput {
private byte [] array;
private int pos;
private int end;
private int saved_pos;
private int saved_end;
/**
* Creates a new DNSInput
* @param input The byte array to read from
*/
public
DNSInput(byte [] input) {
array = input;
pos = 0;
end = array.length;
saved_pos = -1;
saved_end = -1;
}
/**
* Returns the current position.
*/
public int
current() {
return pos;
}
/**
* Returns the number of bytes that can be read from this stream before
* reaching the end.
*/
public int
remaining() {
return end - pos;
}
private void
require(int n) throws WireParseException{
if (n > remaining()) {
throw new WireParseException("end of input");
}
}
/**
* Marks the following bytes in the stream as active.
* @param len The number of bytes in the active region.
* @throws IllegalArgumentException The number of bytes in the active region
* is longer than the remainder of the input.
*/
public void
setActive(int len) {
if (len > array.length - pos) {
throw new IllegalArgumentException("cannot set active " +
"region past end of input");
}
end = pos + len;
}
/**
* Clears the active region of the string. Further operations are not
* restricted to part of the input.
*/
public void
clearActive() {
end = array.length;
}
/**
* Returns the position of the end of the current active region.
*/
public int
saveActive() {
return end;
}
/**
* Restores the previously set active region. This differs from setActive() in
* that restoreActive() takes an absolute position, and setActive takes an
* offset from the current location.
* @param pos The end of the active region.
*/
public void
restoreActive(int pos) {
if (pos > array.length) {
throw new IllegalArgumentException("cannot set active " +
"region past end of input");
}
end = pos;
}
/**
* Resets the current position of the input stream to the specified index,
* and clears the active region.
* @param index The position to continue parsing at.
* @throws IllegalArgumentException The index is not within the input.
*/
public void
jump(int index) {
if (index >= array.length) {
throw new IllegalArgumentException("cannot jump past " +
"end of input");
}
pos = index;
end = array.length;
}
/**
* Saves the current state of the input stream. Both the current position and
* the end of the active region are saved.
* @throws IllegalArgumentException The index is not within the input.
*/
public void
save() {
saved_pos = pos;
saved_end = end;
}
/**
* Restores the input stream to its state before the call to {@link #save}.
*/
public void
restore() {
if (saved_pos < 0) {
throw new IllegalStateException("no previous state");
}
pos = saved_pos;
end = saved_end;
saved_pos = -1;
saved_end = -1;
}
/**
* Reads an unsigned 8 bit value from the stream, as an int.
* @return An unsigned 8 bit value.
* @throws WireParseException The end of the stream was reached.
*/
public int
readU8() throws WireParseException {
require(1);
return (array[pos++] & 0xFF);
}
/**
* Reads an unsigned 16 bit value from the stream, as an int.
* @return An unsigned 16 bit value.
* @throws WireParseException The end of the stream was reached.
*/
public int
readU16() throws WireParseException {
require(2);
int b1 = array[pos++] & 0xFF;
int b2 = array[pos++] & 0xFF;
return ((b1 << 8) + b2);
}
/**
* Reads an unsigned 32 bit value from the stream, as a long.
* @return An unsigned 32 bit value.
* @throws WireParseException The end of the stream was reached.
*/
public long
readU32() throws WireParseException {
require(4);
int b1 = array[pos++] & 0xFF;
int b2 = array[pos++] & 0xFF;
int b3 = array[pos++] & 0xFF;
int b4 = array[pos++] & 0xFF;
return (((long)b1 << 24) + (b2 << 16) + (b3 << 8) + b4);
}
/**
* Reads a byte array of a specified length from the stream into an existing
* array.
* @param b The array to read into.
* @param off The offset of the array to start copying data into.
* @param len The number of bytes to copy.
* @throws WireParseException The end of the stream was reached.
*/
public void
readByteArray(byte [] b, int off, int len) throws WireParseException {
require(len);
System.arraycopy(array, pos, b, off, len);
pos += len;
}
/**
* Reads a byte array of a specified length from the stream.
* @return The byte array.
* @throws WireParseException The end of the stream was reached.
*/
public byte []
readByteArray(int len) throws WireParseException {
require(len);
byte [] out = new byte[len];
System.arraycopy(array, pos, out, 0, len);
pos += len;
return out;
}
/**
* Reads a byte array consisting of the remainder of the stream (or the
* active region, if one is set.
* @return The byte array.
*/
public byte []
readByteArray() {
int len = remaining();
byte [] out = new byte[len];
System.arraycopy(array, pos, out, 0, len);
pos += len;
return out;
}
/**
* Reads a counted string from the stream. A counted string is a one byte
* value indicating string length, followed by bytes of data.
* @return A byte array containing the string.
* @throws WireParseException The end of the stream was reached.
*/
public byte []
readCountedString() throws WireParseException {
require(1);
int len = array[pos++] & 0xFF;
return readByteArray(len);
}
}
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