/*
 * Created: 17 April 1997
 * Author: Bert Bos <bert@w3.org>
 *
 * unescape: http://www.w3.org/International/unescape.java
 *
 * Copyright © 1997 World Wide Web Consortium, (Massachusetts
 * Institute of Technology, European Research Consortium for
 * Informatics and Mathematics, Keio University). All Rights Reserved. 
 * This work is distributed under the W3C® Software License [1] 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.
 *
 * [1] http://www.w3.org/Consortium/Legal/2002/copyright-software-20021231
 */

  private static String unescape(String s) {
    StringBuffer sbuf = new StringBuffer () ;
    int l  = s.length() ;
    int ch = -1 ;
    int b, sumb = 0;
    for (int i = 0, more = -1 ; i < l ; i++) {
      /* Get next byte b from URL segment s */
      switch (ch = s.charAt(i)) {
	case '%':
	  ch = s.charAt (++i) ;
	  int hb = (Character.isDigit ((char) ch) 
		    ? ch - '0'
		    : 10+Character.toLowerCase((char) ch) - 'a') & 0xF ;
	  ch = s.charAt (++i) ;
	  int lb = (Character.isDigit ((char) ch)
		    ? ch - '0'
		    : 10+Character.toLowerCase ((char) ch)-'a') & 0xF ;
	  b = (hb << 4) | lb ;
	  break ;
	case '+':
	  b = ' ' ;
	  break ;
	default:
	  b = ch ;
      }
      /* Decode byte b as UTF-8, sumb collects incomplete chars */
      if ((b & 0xc0) == 0x80) {			// 10xxxxxx (continuation byte)
	sumb = (sumb << 6) | (b & 0x3f) ;	// Add 6 bits to sumb
	if (--more == 0) sbuf.append((char) sumb) ; // Add char to sbuf
      } else if ((b & 0x80) == 0x00) {		// 0xxxxxxx (yields 7 bits)
	sbuf.append((char) b) ;			// Store in sbuf
      } else if ((b & 0xe0) == 0xc0) {		// 110xxxxx (yields 5 bits)
	sumb = b & 0x1f;
	more = 1;				// Expect 1 more byte
      } else if ((b & 0xf0) == 0xe0) {		// 1110xxxx (yields 4 bits)
	sumb = b & 0x0f;
	more = 2;				// Expect 2 more bytes
      } else if ((b & 0xf8) == 0xf0) {		// 11110xxx (yields 3 bits)
	sumb = b & 0x07;
	more = 3;				// Expect 3 more bytes
      } else if ((b & 0xfc) == 0xf8) {		// 111110xx (yields 2 bits)
	sumb = b & 0x03;
	more = 4;				// Expect 4 more bytes
      } else /*if ((b & 0xfe) == 0xfc)*/ {	// 1111110x (yields 1 bit)
	sumb = b & 0x01;
	more = 5;				// Expect 5 more bytes
      }
      /* We don't test if the UTF-8 encoding is well-formed */
    }
    return sbuf.toString() ;
  }