public static Bytes copyFrom(byte[] data, int start, int len) {
    if (data == null) {
      throw new NullPointerException("data must be non-null");
    }
    if (start + len > data.length) {
      len = data.length - start;
    }
    return new Bytes(data, start, len);
  }
Wrap an immutable byte array over a slice of a Bytes

@param data the byte array to be wrapped.
@param start the starting index of the slice
@param len the length of the slice. If start + len is larger than the size of {@code data}, the
    remaining data will be returned.
@return an immutable wrapper around the bytes in the slice from {@code start} to {@code start +
    len}
java_src/src/main/java/com/google/crypto/tink/util/Bytes.java