code: def _read_join_ack(self, bits, size, kind):
          
          temp = self._read_fileng(20)
  
          data = dict(
              kind=kind,
              length=size + 1,
              subtype='MP_JOIN-ACK',
              join=dict(
                  ack=dict(
                      hmac=temp,
                  ),
              ),
          )
  
          return data
docs: Read Join Connection option for Third ACK.
  
          Positional arguments:
              * bits - str, 4-bit data
              * size - int, length of option
              * kind - int, 30 (Multipath TCP)
  
          Returns:
              * dict -- extracted Join Connection (MP_JOIN-ACK) option for Third ACK
  
          Structure of MP_JOIN-ACK [RFC 6824]:
                                   1                   2                   3
               0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
              +---------------+---------------+-------+-----------------------+
              |     Kind      |  Length = 24  |Subtype|      (reserved)       |
              +---------------+---------------+-------+-----------------------+
              |                                                               |
              |                                                               |
              |                   Sender's HMAC (160 bits)                    |
              |                                                               |
              |                                                               |
              +---------------------------------------------------------------+
  
              Octets      Bits        Name                        Description
                0           0     tcp.mp.kind                 Kind (30)
                1           8     tcp.mp.length               Length (24)
                2          16     tcp.mp.subtype              Subtype (1|ACK)
                2          20     -                           Reserved (must be zero)
                4          32     tcp.mp.join.ack.hmac        Sender's HMAC