Stream.find() functions don't find bytes as of 0x80 from HardwareSerial/SoftwareSerial

[baer61]

HardwareSerial/SoftwareSerial::read() return a byte where the functions are defined to return an int. The implicit conversion from "unsigned char/uint8_t" to int returns 0xFFAA (= -86) for the received byte 0xAA.
The function Stream::findMulti() then tests the integer returned by Stream::timedRead() with "c < 0" instead of "c == -1" to distinguish between a received byte and -1 for still nothing available on the stream.
Therefore the function Stream.find() comes back with -1 after timeout, although read() received the byte 0xAA.
It took a lot of time to find out the reason why I didn't found the start byte 0xAA on the stream from my MP3 module response.

[matthijskooijman]

Nice find, thanks! Your explanation seems sound to me (though I haven't looked at the code yet).

However, further development on the Stream class will happen at https://github.com/arduino/ArduinoCore-API, so maybe you can re-open your issue there (or maybe an admin could move this issue)?