The void processData is just something that isn't working yet.
Isn't working? Or, isn't called?
I'm not sure why you feel it necessary to print data each time you read a new character. data is not properly NULL terminated unless a carriage return arrives, so most of the time, data is not a valid array to pass to a function that expects a string (a NULL terminated array of chars).
You need to add
data[index] = '\0';
after
data[index] = dataStream;
index++;
dataStream is a lousy name for something that is not a stream, by the way.
Finally, strtok_r() is the thread-safe, and far more complex, version of strtok(). Since the Arduino is not multi-threaded, the advantages of using a thread-safe function escape me, while the disadvantages are obvious - larger code and far more variables to keep track of.