/* URLEncoder.java -- Class to convert strings to a properly encoded URL
   Copyright (C) 1998, 1999, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
 
GNU Classpath is distributed 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.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

As a special exception, if you link this library with other files to
produce an executable, this library does not by itself cause the
resulting executable to be covered by the GNU General Public License.
This exception does not however invalidate any other reasons why the
executable file might be covered by the GNU General Public License. */

package java.net;

import java.io.UnsupportedEncodingException;

/**
 * Written using on-line Java Platform 1.2/1.4 API Specification, as well
 * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
 * Status:  Believed complete and correct.
 */

/**
  * This utility class contains static methods that converts a 
  * string into a fully encoded URL string in x-www-form-urlencoded
  * format.  This format replaces certain disallowed characters with
  * encoded equivalents.  All upper case and lower case letters in the
  * US alphabet remain as is, the space character (' ') is replaced with
  * '+' sign, and all other characters are converted to a "%XX" format
  * where XX is the hexadecimal representation of that character in a
  * certain encoding (by default "UTF-8".
  * <p>
  * This method is very useful for encoding strings to be sent to CGI scripts
  *
  * @author Aaron M. Renn (address@hidden)
  * @author Warren Levy <address@hidden>
  * @author Mark Wielaard (address@hidden)
  */
public class URLEncoder
{
  /**
   * This method translates the passed in string into x-www-form-urlencoded
   * format using the standard "UTF-8" character encoding to hex-encode the
   * unsafe characters.
   *
   * @param s The String to convert
   *
   * @return The converted String
   */
  public static String encode(String s)
  {
    try
      {
        return encode(s, "UTF-8");
      }
    catch (UnsupportedEncodingException uee)
      {
        // Should never happen since UTF-8 should always be supported
	return s;
      }
  }

  /**
   * This method translates the passed in string into x-www-form-urlencoded
   * format using the character encoding to hex-encode the unsafe characters.
   *
   * @param s The String to convert
   * @param encoding The encoding to use for unsafe characters
   *
   * @return The converted String
   *
   * @since 1.4
   */
  public static String encode(String s, String encoding)
    throws UnsupportedEncodingException
  {
    StringBuffer result = new StringBuffer();
    int length = s.length();
    int start = 0;
    int i = 0;

    while (true)
    {
      while ( i < length && isSafe(s.charAt(i)) )
	i++;

      // Safe character can just be added
      result.append(s.substring(start, i));

      // Are we done?
      if (i >= length)
	return result.toString();
      else if (s.charAt(i) == ' ')
        {
	  result.append('+');  // Replace space char with plus symbol.
	  i++;
	}
      else
	{
	  // Get all unsafe characters
	  start = i;
	  char c;
	  while ( i < length && (c = s.charAt(i)) != ' ' && !isSafe(c) )
	    i++;

	  // Convert them to %XY encoded strings
	  String unsafe = s.substring(start,i);
	  byte bytes[] = unsafe.getBytes(encoding);
	  for (int j = 0; j < bytes.length; j++)
	    {
	      result.append('%');
	      result.append(Integer.toHexString(((int) bytes[j]) & 0xFF));
	    }
	}
      start = i;
    }
  }

  /**
   * Private static method that returns true if the given char is either
   * a uppercase or lowercase letter from 'a' till 'z', or a digit froim
   * '0' till '9', or one of the characters '-', '_', '.' or '*'. Such
   * 'safe' character don't have to be url encoded.
   */
  private static boolean isSafe(char c)
  {
    return  ((c >= 'a' && c <= 'z') ||
	     (c >= 'A' && c <= 'Z') ||
	     (c >= '0' && c <= '9') ||
	     c == '-' || c == '_' || c == '.' || c == '*');
  }

  /**
   * Private constructor that does nothing. Included to avoid a default
   * public constructor being created by the compiler.
   */
  private URLEncoder() { }

} // class URLEncoder