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 * Copyright (c) 1995, 2017, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.net;

import java.io.UnsupportedEncodingException;
import java.io.CharArrayWriter;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException ;
import java.util.BitSet;
import java.util.Objects;
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:
 *
 * <ul>
 * <li>The alphanumeric characters &quot;{@code a}&quot; through
 * &quot;{@code z}&quot;, &quot;{@code A}&quot; through
 * &quot;{@code Z}&quot; and &quot;{@code 0}&quot;
 * through &quot;{@code 9}&quot; remain the same.
 * <li>The special characters &quot;{@code .}&quot;,
 * &quot;{@code -}&quot;, &quot;{@code *}&quot;, and
 * &quot;{@code _}&quot; remain the same.
 * <li>The space character &quot; &nbsp; &quot; is
 * converted into a plus sign &quot;{@code +}&quot;.
 * <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
 * &quot;<i>{@code %xy}</i>&quot;, 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 &quot;The
 * string &#252;@foo-bar&quot; would get converted to
 * &quot;The+string+%C3%BC%40foo-bar&quot; because in UTF-8 the character
 * &#252; is encoded as two bytes C3 (hex) and BC (hex), and the
 * character @ is encoded as one byte 40 (hex).
 *
 * @author Herb Jellinek
 * @since 1.0
 */
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 = GetPropertyAction.privilegedGetProperty("file.encoding");
 }

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

 /**
 * Translates a string into {@code x-www-form-urlencoded}
 * format. This method uses the platform's default encoding
 * as the encoding scheme to obtain the bytes for unsafe characters.
 *
 * @param s {@code String} 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}.
 */
 @Deprecated
 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}
 * format using a specific encoding scheme.
 * <p>
 * This method behaves the same as {@linkplain encode(String s, Charset charset)}
 * except that it will {@linkplain java.nio.charset.Charset#forName look up the charset}
 * using the given encoding name.
 *
 * @param s {@code String} 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}.
 * @throws 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 {
 if (enc == null) {
 throw new NullPointerException("charsetName");
 }

 try {
 Charset charset = Charset.forName(enc);
 return encode(s, charset);
 } catch (IllegalCharsetNameException | UnsupportedCharsetException e) {
 throw new UnsupportedEncodingException(enc);
 }
 }

 /**
 * Translates a string into {@code application/x-www-form-urlencoded}
 * format using a specific {@linkplain java.nio.charset.Charset Charset}.
 * This method uses the supplied charset 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 incompatibilities.</em>
 *
 * @param s {@code String} to be translated.
 * @param charset the given charset
 * @return the translated {@code String}.
 * @throws NullPointerException if {@code s} or {@code charset} is {@code null}.
 * @see URLDecoder#decode(java.lang.String, java.nio.charset.Charset)
 * @since 10
 */
 public static String encode(String s, Charset charset) {
 Objects.requireNonNull(charset, "charset");

 boolean needToChange = false;
 StringBuilder out = new StringBuilder(s.length());
 CharArrayWriter charArrayWriter = new CharArrayWriter();

 for (int i = 0; i < s.length();) {
 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);
 i++;
 } else {
 // convert to external encoding before hex conversion
 do {
 charArrayWriter.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 byte 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");
 */
 charArrayWriter.write(d);
 i++;
 }
 }
 }
 i++;
 } while (i < s.length() && !dontNeedEncoding.get((c = (int) s.charAt(i))));

 charArrayWriter.flush();
 String str = new String(charArrayWriter.toCharArray());
 byte[] ba = str.getBytes(charset);
 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);
 }
 charArrayWriter.reset();
 needToChange = true;
 }
 }

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