fn create_client_request()

in mini-sntp/src/lib.rs [113:153]

• 29 lines of code
• 3 McCabe index (conditional complexity)

fn create_client_request() -> ([u8; 48], chrono::DateTime<chrono::Utc>) {
    let sntp_epoch = sntp_epoch();

    let mut buf = [0_u8; 48];
    buf[0] = 0b00_011_011; // version_number: 3, mode: 3 (client)

    let transmit_timestamp = chrono::Utc::now();

    #[cfg(test)]
    let transmit_timestamp = transmit_timestamp - chrono::Duration::seconds(30); // simulate unsynced local clock

    let mut duration_since_sntp_epoch = transmit_timestamp - sntp_epoch;

    let integral_part = duration_since_sntp_epoch.num_seconds();
    duration_since_sntp_epoch =
        duration_since_sntp_epoch - chrono::Duration::seconds(integral_part);

    assert!(integral_part >= 0 && integral_part < i64::from(u32::max_value()));
    #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
    let integral_part = (integral_part as u32).to_be_bytes();
    buf[40..44].copy_from_slice(&integral_part[..]);

    let fractional_part = duration_since_sntp_epoch
        .num_nanoseconds()
        .expect("can't overflow nanoseconds");
    let fractional_part = (fractional_part << 32) / 1_000_000_000;
    assert!(fractional_part >= 0 && fractional_part < i64::from(u32::max_value()));
    #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
    let fractional_part = (fractional_part as u32).to_be_bytes();
    buf[44..48].copy_from_slice(&fractional_part[..]);

    let packet = Packet::parse(buf, sntp_epoch);
    #[cfg(test)]
    let packet = dbg!(packet);

    // Re-extract transmit timestamp from the packet. This may not be the same as the original `transmit_timestamp`
    // that was serialized into the packet due to rounding. Specifically, it's usually off by 1ns.
    let transmit_timestamp = packet.transmit_timestamp;

    (buf, transmit_timestamp)
}