/*
 * @(#)URLEncoder.java	1.28 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.net;

import java.io.ByteArrayOutputStream;
import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.BitSet;
import java.security.AccessController;
import java.security.PrivilegedAction;
import sun.security.action.GetBooleanAction;
import sun.security.action.GetPropertyAction;

/**
 * Utility class for HTML form encoding. This class contains static methods
 * for converting a String to the <CODE>application/x-www-form-urlencoded</CODE> MIME
 * format. For more information about HTML form encoding, consult the HTML 
 * <A HREF="http://www.w3.org/TR/html4/">specification</A>. 
 *
 * <p>
 * When encoding a String, the following rules apply:
 *
 * <p>
 * <ul>
 * <li>The alphanumeric characters "<code>a</code>" through
 *     "<code>z</code>", "<code>A</code>" through
 *     "<code>Z</code>" and "<code>0</code>" 
 *     through "<code>9</code>" remain the same.
 * <li>The special characters "<code>.</code>",
 *     "<code>-</code>", "<code>*</code>", and
 *     "<code>_</code>" remain the same. 
 * <li>The space character "<code> </code>" is
 *     converted into a plus sign "<code>+</code>".
 * <li>All other characters are unsafe and are first converted into
 *     one or more bytes using some encoding scheme. Then each byte is
 *     represented by the 3-character string
 *     "<code>%<i>xy</i></code>", where <i>xy</i> is the
 *     two-digit hexadecimal representation of the byte. 
 *     The recommended encoding scheme to use is UTF-8. However, 
 *     for compatibility reasons, if an encoding is not specified, 
 *     then the default encoding of the platform is used.
 * </ul>
 *
 * <p>
 * For example using UTF-8 as the encoding scheme the string "The
 * string ü@foo-bar" would get converted to
 * "The+string+%C3%BC%40foo-bar" because in UTF-8 the character
 * ü is encoded as two bytes C3 (hex) and BC (hex), and the
 * character @ is encoded as one byte 40 (hex).
 *
 * @author  Herb Jellinek
 * @version 1.28, 01/23/03
 * @since   JDK1.0
 */
public class URLEncoder {
    static BitSet dontNeedEncoding;
    static final int caseDiff = ('a' - 'A');
    static String dfltEncName = null;

    static {

	/* The list of characters that are not encoded has been
	 * determined as follows:
	 *
	 * RFC 2396 states:
	 * -----
	 * Data characters that are allowed in a URI but do not have a
	 * reserved purpose are called unreserved.  These include upper
	 * and lower case letters, decimal digits, and a limited set of
	 * punctuation marks and symbols. 
	 *
	 * unreserved  = alphanum | mark
	 *
	 * mark        = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
	 *
	 * Unreserved characters can be escaped without changing the
	 * semantics of the URI, but this should not be done unless the
	 * URI is being used in a context that does not allow the
	 * unescaped character to appear.
	 * -----
	 *
	 * It appears that both Netscape and Internet Explorer escape
	 * all special characters from this list with the exception
	 * of "-", "_", ".", "*". While it is not clear why they are
	 * escaping the other characters, perhaps it is safest to
	 * assume that there might be contexts in which the others
	 * are unsafe if not escaped. Therefore, we will use the same
	 * list. It is also noteworthy that this is consistent with
	 * O'Reilly's "HTML: The Definitive Guide" (page 164).
	 *
	 * As a last note, Intenet Explorer does not encode the "@"
	 * character which is clearly not unreserved according to the
	 * RFC. We are being consistent with the RFC in this matter,
	 * as is Netscape.
	 *
	 */

	dontNeedEncoding = new BitSet(256);
	int i;
	for (i = 'a'; i <= 'z'; i++) {
	    dontNeedEncoding.set(i);
	}
	for (i = 'A'; i <= 'Z'; i++) {
	    dontNeedEncoding.set(i);
	}
	for (i = '0'; i <= '9'; i++) {
	    dontNeedEncoding.set(i);
	}
	dontNeedEncoding.set(' '); /* encoding a space to a + is done
				    * in the encode() method */
	dontNeedEncoding.set('-');
	dontNeedEncoding.set('_');
	dontNeedEncoding.set('.');
	dontNeedEncoding.set('*');

    	dfltEncName = (String)AccessController.doPrivileged (
	    new GetPropertyAction("file.encoding")
    	);
    }

    /**
     * You can't call the constructor.
     */
    private URLEncoder() { }

    /**
     * Translates a string into <code>x-www-form-urlencoded</code>
     * format. This method uses the platform's default encoding
     * as the encoding scheme to obtain the bytes for unsafe characters.
     *
     * @param   s   <code>String</code> to be translated.
     * @deprecated The resulting string may vary depending on the platform's
     *             default encoding. Instead, use the encode(String,String)
     *             method to specify the encoding.
     * @return  the translated <code>String</code>.
     */
    public static String encode(String s) {

	String str = null;

	try {
	    str = encode(s, dfltEncName);
	} catch (UnsupportedEncodingException e) {
	    // The system should always have the platform default
	}

	return str;
    }

    /**
     * Translates a string into <code>application/x-www-form-urlencoded</code>
     * format using a specific encoding scheme. This method uses the
     * supplied encoding scheme to obtain the bytes for unsafe
     * characters.
     * <p>
     * <em><strong>Note:</strong> The <a href=
     * "http://www.w3.org/TR/html40/appendix/notes.html#non-ascii-chars">
     * World Wide Web Consortium Recommendation</a> states that
     * UTF-8 should be used. Not doing so may introduce
     * incompatibilites.</em>
     *
     * @param   s   <code>String</code> to be translated.
     * @param   enc   The name of a supported 
     *    <a href="../lang/package-summary.html#charenc">character
     *    encoding</a>.
     * @return  the translated <code>String</code>.
     * @exception  UnsupportedEncodingException
     *             If the named encoding is not supported
     * @see URLDecoder#decode(java.lang.String, java.lang.String)
     * @since 1.4
     */
    public static String encode(String s, String enc) 
	throws UnsupportedEncodingException {

	boolean needToChange = false;
	boolean wroteUnencodedChar = false; 
	int maxBytesPerChar = 10; // rather arbitrary limit, but safe for now
        StringBuffer out = new StringBuffer(s.length());
	ByteArrayOutputStream buf = new ByteArrayOutputStream(maxBytesPerChar);

	OutputStreamWriter writer = new OutputStreamWriter(buf, enc);

	for (int i = 0; i < s.length(); i++) {
	    int c = (int) s.charAt(i);
	    //System.out.println("Examining character: " + c);
	    if (dontNeedEncoding.get(c)) {
		if (c == ' ') {
		    c = '+';
		    needToChange = true;
		}
		//System.out.println("Storing: " + c);
		out.append((char)c);
		wroteUnencodedChar = true;
	    } else {
		// convert to external encoding before hex conversion
		try {
		    if (wroteUnencodedChar) { // Fix for 4407610
		    	writer = new OutputStreamWriter(buf, enc);
			wroteUnencodedChar = false;
		    }
		    writer.write(c);
		    /*
		     * If this character represents the start of a Unicode
		     * surrogate pair, then pass in two characters. It's not
		     * clear what should be done if a bytes reserved in the 
		     * surrogate pairs range occurs outside of a legal
		     * surrogate pair. For now, just treat it as if it were 
		     * any other character.
		     */
		    if (c >= 0xD800 && c <= 0xDBFF) {
			/*
			  System.out.println(Integer.toHexString(c) 
			  + " is high surrogate");
			*/
			if ( (i+1) < s.length()) {
			    int d = (int) s.charAt(i+1);
			    /*
			      System.out.println("\tExamining " 
			      + Integer.toHexString(d));
			    */
			    if (d >= 0xDC00 && d <= 0xDFFF) {
				/*
				  System.out.println("\t" 
				  + Integer.toHexString(d) 
				  + " is low surrogate");
				*/
				writer.write(d);
				i++;
			    }
			}
		    }
		    writer.flush();
		} catch(IOException e) {
		    buf.reset();
		    continue;
		}
		byte[] ba = buf.toByteArray();
		for (int j = 0; j < ba.length; j++) {
		    out.append('%');
		    char ch = Character.forDigit((ba[j] >> 4) & 0xF, 16);
		    // converting to use uppercase letter as part of
		    // the hex value if ch is a letter.
		    if (Character.isLetter(ch)) {
			ch -= caseDiff;
		    }
		    out.append(ch);
		    ch = Character.forDigit(ba[j] & 0xF, 16);
		    if (Character.isLetter(ch)) {
			ch -= caseDiff;
		    }
		    out.append(ch);
		}
		buf.reset();
		needToChange = true;
	    }
	}

	return (needToChange? out.toString() : s);
    }
}