Decode an escaped string from VBScript in Java

Question

I tried to decode the following string,

String str  = "AT%26amp%3BT%20Network%20Client%20%u2013%20IBM";

System.out.println(StringEscapeUtils.unescapeHtml(str));
try {
    System.out.println("res:"+java.net.URLDecoder.decode(str, "UTF-8"));
} catch (UnsupportedEncodingException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

Both methods fail as below,

AT%26amp%3BT%20Network%20Client%20%u2013%20IBM
Exception in thread "main" java.lang.IllegalArgumentException: URLDecoder: Illegal hex characters in escape (%) pattern - For input string: "u2"
    at java.net.URLDecoder.decode(URLDecoder.java:173)
    at decrypt.DecryptHtml.main(DecryptHtml.java:19)

The source of the string is a VBS script that uses the Escape function . How can I decode this string?

Answer 1

Unfortunately, from reading the documentation, it appears that Microsoft Has Done It Again (tm): "non standard xxx", where here "xxx" is "escaping format".

Specifically, in the documentation of the VBScript function , it is said that:

[...]Unicode characters that have a value greater than 255 are stored using the %uxxxx format.

(Hey, MS: there is no such thing as "Unicode characters"; those are called code points )

Great. So you need your own decoding function.

Fortunately, we use Java. And since this proprietary escape sequence only covers Unicode code points in the Basic Multilingual Plane (U+0000 to U+FFFF), and since char is a UTF-16 code unit, and since there is a 1 to 1 mapping between BMP and UTF-16, this makes our job a little easier.

Here is the code:

public final class MSUnescaper
{
    private static final char PERCENT = '%';
    private static final char NONSTANDARD_PCT_ESCAPE = 'u';

    private MSUnescaper()
    {
    }

    public static String unescape(final String input)
    {
        final StringBuilder sb = new StringBuilder(input.length());
        final CharBuffer buf = CharBuffer.wrap(input);

        char c;

        while (buf.hasRemaining()) {
            c = buf.get();
            if (c != PERCENT) {
                sb.append(c);
                continue;
            }
            if (!buf.hasRemaining())
                throw new IllegalArgumentException();
            c = buf.get();
            sb.append(c == NONSTANDARD_PCT_ESCAPE
                ? msEscape(buf) : standardEscape(buf, c));
        }

        return sb.toString();
    }

    private static char standardEscape(final CharBuffer buf, final char c)
    {
        if (!buf.hasRemaining())
            throw new IllegalArgumentException();
        final char[] array = { c, buf.get() };
        return (char) Integer.parseInt(new String(array), 16);
    }

    private static char msEscape(final CharBuffer buf)
    {
        if (buf.remaining() < 4)
            throw new IllegalArgumentException();
        final char[] array = new char[4];
        buf.get(array);
        return (char) Integer.parseInt(new String(array), 16);
    }

    public static void main(final String... args)
    {
        final String input = "AT%26amp%3BT%20Network%20Client%20%u2013%20IBM";
        System.out.println(unescape(input));
    }
}

Output:

AT&T Network Client – IBM

Answer 2

String str = "AT%26amp%3BT%20Network%20Client%20%[here]u[here]2013%20IBM" I think this string is invalid. %u20 is not valid charecter. If you remove u from your string you can encode it. For reference: w3schools html url encodeing