pub const HEADER_SIZE: usize = std::mem::size_of::<Header>();
#[repr(C, packed)]
pub struct Header {
pub hmac: [u8; 32],
pub sequence_number: u64,
pub ack_sequence_number: u64,
pub ack_bits: [u8; 4],
pub packet_type: u8,
pub padding: u8,
pub body_length: u16,
}