peek() reads a byte from the stream without advancing to the next one. That is, successive calls to peek() will return the same value, as will the next call to read().
This function is part of the Stream class, and can be called by any class that inherits from it (Wire, Serial, etc). See the Stream class main page for more information.
stream.peek()
None.
The next byte (or character), or -1 if none is available. Data type: int.