writeBytesOffset(b, off, len) {
			if ((off < 0) || (off > b.length) || (len < 0) ||
				((off + len) - b.length > 0)) {
				throw new IndexOutOfBoundsException();
			}
			this.ensureCapacity(this.count + len);
			System.arraycopy(b, off, this.buf, this.count, len);
			this.count += len;
		}
Writes <code>len</code> bytes from the specified byte array
starting at offset <code>off</code> to this byte array output stream.

@param   b     the data.
@param   off   the start offset in the data.
@param   len   the number of bytes to write.