Converting c string to integer to unsigned char
Not sure if or why you want to convert char* to int, but if you need to, there are atoi(), atol(), strtol(), strtoul() to consider, or rolling your own function.
Pros and cons are discussed here. Main thing to note is that atoi() and atol() have no error handling, but if the char* you feed them is completely under control and predictable, that need not be a problem.
BTW I would try to get the websocket to send the correct single bytes instead of string representations of numbers, if at all possible.