[OWASP-ESAPI] Encoder feedback

[Gregory Rubin]

I knew that I had this rattling around somewhere.  It needs to be
checked and all that stuff (I had to extract it from some more domain
specific code).

public static String escapeForJavaScript(String input) {
    if(null == input) {
        return null;
    }

    StringBuffer buf = new StringBuffer(input.length() + 2);
    int len = input.length();

    for(int x = 0; x < len; x++) {
        int value = input.codePointAt(x);
        if(isJavaScriptStringSafe(value)) {
            buf.append(Character.toChars(value));
        } else {
            switch (value) {
                case 0x0A: // newline
                    buf.append("\\n");
                    break;

                case 0x09: // tab
                    buf.append("\\t");
                    break;

                case 0x22: // Double-quote
                    buf.append("\\\"");
                    break;

                case 0x27: // single-quote
                    buf.append("\\'");
                    break;

                case 0x5C: // backslash
                    buf.append("\\\\");
                    break;

                default:
                    buf.append(String.format("\\u%1$04X", value));
            }
        }
    }

    return buf.toString();
}

private static final String javaScriptStringSafeOther = ".,;: ()?!_-+*&{}[]@#";

private static boolean isJavaScriptStringSafe(int codepoint) {
    if(Character.isLetterOrDigit(codepoint))
        return true;

    int len = javaScriptStringSafeOther.length();
    // Check the whitelisted special characters
    for(int x = 0; x < len; x++)
        if(codepoint == javaScriptStringSafeOther.codePointAt(x))
            return true;

    return false;
}