| // Copyright (c) 1999-2004 Brian Wellington (bwelling@xbill.org) |
| |
| package org.xbill.DNS; |
| |
| /** |
| * DNS Name Compression object. |
| * @see Message |
| * @see Name |
| * |
| * @author Brian Wellington |
| */ |
| |
| public class Compression { |
| |
| private static class Entry { |
| Name name; |
| int pos; |
| Entry next; |
| } |
| |
| private static final int TABLE_SIZE = 17; |
| private static final int MAX_POINTER = 0x3FFF; |
| private Entry [] table; |
| private boolean verbose = Options.check("verbosecompression"); |
| |
| /** |
| * Creates a new Compression object. |
| */ |
| public |
| Compression() { |
| table = new Entry[TABLE_SIZE]; |
| } |
| |
| /** |
| * Adds a compression entry mapping a name to a position in a message. |
| * @param pos The position at which the name is added. |
| * @param name The name being added to the message. |
| */ |
| public void |
| add(int pos, Name name) { |
| if (pos > MAX_POINTER) |
| return; |
| int row = (name.hashCode() & 0x7FFFFFFF) % TABLE_SIZE; |
| Entry entry = new Entry(); |
| entry.name = name; |
| entry.pos = pos; |
| entry.next = table[row]; |
| table[row] = entry; |
| if (verbose) |
| System.err.println("Adding " + name + " at " + pos); |
| } |
| |
| /** |
| * Retrieves the position of the given name, if it has been previously |
| * included in the message. |
| * @param name The name to find in the compression table. |
| * @return The position of the name, or -1 if not found. |
| */ |
| public int |
| get(Name name) { |
| int row = (name.hashCode() & 0x7FFFFFFF) % TABLE_SIZE; |
| int pos = -1; |
| for (Entry entry = table[row]; entry != null; entry = entry.next) { |
| if (entry.name.equals(name)) |
| pos = entry.pos; |
| } |
| if (verbose) |
| System.err.println("Looking for " + name + ", found " + pos); |
| return pos; |
| } |
| |
| } |