Method leftPadHex

java/lib/src/main/java/io/github/ccxt/base/Crypto.java:536–542

(String s, int len)

    }

    private static String leftPadHex(String s, int len) {
        if (s.length() >= len) return s;
        StringBuilder sb = new StringBuilder(len);
        for (int i = s.length(); i < len; i++) sb.append('0');
        sb.append(s);
        return sb.toString();
    }

    private static byte[] hexToBytes(String hex) {
        // return Hex.decode(hex.replaceFirst("^0x", ""));