Function readSerialStringUntil

src/fl/remote/transport/serial.h:197–242

template<typename SerialIn>
fl::optional<fl::string> readSerialStringUntil(SerialIn& serial, char delimiter, char skipChar, fl::optional<u32> timeoutMs) {
    // Follows Arduino Serial.readStringUntil() API - blocks until delimiter found
    fl::sstream buffer;

    u32 startTime = fl::millis();

    // Read characters until we find delimiter or timeout
    while (true) {
        // Check timeout (only if timeout is set)
        if (timeoutMs.has_value()) {
            if (fl::millis() - startTime >= timeoutMs.value()) {
                // Timeout occurred - return nullopt
                return fl::nullopt;
            }
        }

        // Try to read next character
        int c = serial.read();

        // Handle -1 (no data available) like Arduino's timedRead():
        // Keep trying until timeout (or forever if no timeout set)
        if (c == -1) {
            // Brief 1us yield instead of 1ms delay for fast USB CDC polling.
            fl::delayMicroseconds(1);
            continue;
        }

        // Found delimiter - complete
        if (c == delimiter) {
            break;
        }

        // Skip specified character (e.g., '\r' for cross-platform line endings)
        if (c == skipChar) {
            continue;
        }

        // Valid character - add to buffer
        buffer << static_cast<char>(c);
    }

    // Convert to string and trim whitespace
    fl::string result = buffer.str();
    result.trim();
    return result;
}

template<typename SerialOut>
void writeSerialLine(SerialOut& serial, const fl::string& str) {