ccsds_spp/src/header/apid.rs

use crate::check_buffer_len;
use crate::bits::*;
use crate::error::PacketError;


/// # Application Process Identifier
///
/// The APID shall provide the naming mechanism for the managed data path.
///
/// The APID may uniquely identify the individual sending or receiving application
/// process within a particular space vehicle.
///
/// For Idle Packets the APID shall be ‘11111111111’.
///
/// ## NOTES
/// - The APID is unique only within its naming domain.
/// - There are no restrictions on the selection of APIDs except for the APID
///   for Idle Packets stated above. In particular, APIDs are not required to
///   be numbered consecutively.
/// - The Recommended Standard used a reserved APID to carry specific PDUs by,
///   for example, CFDP and LTP. This capability of acting as ‘shim’ protocol
///   is preserved; that is, SPP can still carry PDUs of other protocols, but
///   the coupling of APIDs to protocols is now mission specific. Missions may
///   use the optional Packet Secondary Header to create an extended naming
///   domain, but such uses are not specifically defined in this protocol.
///   This is reflected by the fact that the only reserved value is now the
///   one for Idle Packets.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct ApId
{
   value: u16
}

impl ApId
{
   /// The 16 bit version of the mask for the ApId bits in the header.
   pub const MASK_U16: u16 = 0b0000011111111111;

   /// The 8 bit array version of the mask for the ApId bits in the header.
   /// The 
   pub const MASK_ARR: [u8; 2] = [0b00000111, 0b11111111];
}

impl From<u16> for ApId
{
   fn from(value: u16) -> Self
   {
      ApId
      {
         value
      }
   }
}

impl From<ApId> for u16
{
   fn from(apid: ApId) -> u16
   {
      apid.value
   }
}

impl FromBytes for ApId
{
   type Error = PacketError;

   fn from_bytes(bytes: &[u8]) -> Result<Parsed<Self>, Self::Error>
   {
      check_buffer_len!(2usize, bytes);

      let id: u16 = (((bytes[0] & ApId::MASK_ARR[0]) as u16) << 8) |
                    (((bytes[1] & ApId::MASK_ARR[1]) as u16));

      Ok(Parsed::new(2usize, id.into()))
   }
}

impl IntoBytes for ApId
{
   type Error = PacketError;

   fn into_bytes(self, buffer: &mut [u8]) -> Result<usize, Self::Error>
   {
      check_buffer_len!(2usize, buffer);

      let id: u16 = self.value;

      buffer[0] = ((id >> 8) as u8) & ApId::MASK_ARR[0];
      buffer[1] = (id as u8) & ApId::MASK_ARR[1];

      Ok(2usize)
   }
}

impl FromBits for ApId
{
   type Error = PacketError;

   fn from_bits(bytes: &[u8], mask: &[u8]) -> Result<Self, Self::Error>
   {
      check_buffer_len!(2usize, bytes, mask);

      let id: u16 = (((bytes[0] & mask[0]) as u16) << 8) |
                    ((bytes[1] & mask[1]) as u16);

      Ok(id.into())
   }
}

impl IntoBits for ApId
{
   type Error = PacketError;

   fn into_bits(self, bytes: &mut [u8], mask: &[u8]) -> Result<(), Self::Error>
   {
      check_buffer_len!(2usize, bytes, mask);

      update_masked_bits_arr(&mut [bytes[0], bytes[1]], &[mask[0], mask[1]],
                             &self.value.to_be_bytes());

      Ok(())
   }
}