Serial.readBytesUntil() reads characters from the serial buffer into an array. The function terminates (checks being done in this order) if the determined length has been read, if it times out (see Serial.setTimeout()), or if the terminator character is detected (in which case the function returns the characters up to the last character before the supplied terminator). The terminator itself is not returned in the buffer.
Serial.readBytesUntil() returns the number of characters read into the buffer. A 0 means that the
length parameter <= 0, a time out occurred before any other input, or a termination character was found before any other input.
Serial.readBytesUntil() inherits from the Stream utility class.
Serial.readBytesUntil(character, buffer, length)
Serial: serial port object. See the list of available serial ports for each board on the Serial main page.
character: the character to search for. Allowed data types:
buffer: the buffer to store the bytes in. Allowed data types: array of
length: the number of bytes to read. Allowed data types: