docs: def post_build(self, pkt, pay):
          """
          Apply the previous methods according to the writing cipher type.
          """
          # Compute the length of TLSPlaintext fragment
          hdr, frag = pkt[:5], pkt[5:]
          if not isinstance(self.tls_session.rcs.cipher, Cipher_NULL):
              frag = self._tls_auth_encrypt(frag)
  
          if self.len is not None:
              # The user gave us a 'len', let's respect this ultimately
              hdr = hdr[:3] + struct.pack("!H", self.len)
          else:
              # Update header with the length of TLSCiphertext.inner
              hdr = hdr[:3] + struct.pack("!H", len(frag))
  
          # Now we commit the pending write state if it has been triggered. We
          # update nothing if the pwcs was not set. This probably means that
          # we're working out-of-context (and we need to keep the default wcs).
          if self.tls_session.triggered_pwcs_commit:
              if self.tls_session.pwcs is not None:
                  self.tls_session.wcs = self.tls_session.pwcs
                  self.tls_session.pwcs = None
              self.tls_session.triggered_pwcs_commit = False
  
          return hdr + frag + pay