1 // Copyright (c) 1999-2004 Brian Wellington (bwelling (at) xbill.org) 2 3 package org.xbill.DNS; 4 5 /** 6 * DNS Name Compression object. 7 * @see Message 8 * @see Name 9 * 10 * @author Brian Wellington 11 */ 12 13 public class Compression { 14 15 private static class Entry { 16 Name name; 17 int pos; 18 Entry next; 19 } 20 21 private static final int TABLE_SIZE = 17; 22 private static final int MAX_POINTER = 0x3FFF; 23 private Entry [] table; 24 private boolean verbose = Options.check("verbosecompression"); 25 26 /** 27 * Creates a new Compression object. 28 */ 29 public 30 Compression() { 31 table = new Entry[TABLE_SIZE]; 32 } 33 34 /** 35 * Adds a compression entry mapping a name to a position in a message. 36 * @param pos The position at which the name is added. 37 * @param name The name being added to the message. 38 */ 39 public void 40 add(int pos, Name name) { 41 if (pos > MAX_POINTER) 42 return; 43 int row = (name.hashCode() & 0x7FFFFFFF) % TABLE_SIZE; 44 Entry entry = new Entry(); 45 entry.name = name; 46 entry.pos = pos; 47 entry.next = table[row]; 48 table[row] = entry; 49 if (verbose) 50 System.err.println("Adding " + name + " at " + pos); 51 } 52 53 /** 54 * Retrieves the position of the given name, if it has been previously 55 * included in the message. 56 * @param name The name to find in the compression table. 57 * @return The position of the name, or -1 if not found. 58 */ 59 public int 60 get(Name name) { 61 int row = (name.hashCode() & 0x7FFFFFFF) % TABLE_SIZE; 62 int pos = -1; 63 for (Entry entry = table[row]; entry != null; entry = entry.next) { 64 if (entry.name.equals(name)) 65 pos = entry.pos; 66 } 67 if (verbose) 68 System.err.println("Looking for " + name + ", found " + pos); 69 return pos; 70 } 71 72 } 73
