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(** This module defines the messages of the P2p layers.

    P2p messages are parameterized by a generic upper-layer message type
    ['msg]. The P2p layer serializes these ['msg] using a ['msg encoding']
    provided by the client of this lib.

    The P2p protocol is simple and can be deduced mostly from the message type.
    To make the network topology more dynamic, it implements a simple peer
    swapping mechanism which works as follows.

    Peer A sends a message : [Swap_request (point, peer)] to B.
    If B is already connected to the peer, the message is ignored.
    Otherwise B picks a peer [peer'] at point [point'] and connect to [peer]. If
    successful, it sends a response [Swap_ack (point', peer')] to A. Upon
    reception of [Swap_ack]. B tries to connected to [peer']. If successful,
    it disconnect from [peer]. *)

(* TODO: https://gitlab.com/tezos/tezos/-/issues/4610
     It would be interesting to measure the effect of the swap request
     mechanism on an actual network. Is it the added complexity worth it,
     wouldn't it  be enough to rely on [Advertise]? *)

type 'msg t =
  | Bootstrap  (** Welcome message sent by a peer upon connection *)
  | Advertise of P2p_point.Id.t list
      (** Response to a [Bootstrap] message, contains list of known points *)
  | Swap_request of P2p_point.Id.t * P2p_peer.Id.t
      (** Propose new peer/point and ask a peer/point to swap with *)
  | Swap_ack of P2p_point.Id.t * P2p_peer.Id.t
      (** Response to a swap request and propose peer/point to swap with. *)
  | Message of 'msg  (** Generic upper-layer message *)
  | Disconnect  (** Ending of connection, unused for now *)

val encoding : 'a P2p_params.app_message_encoding list -> 'a t Data_encoding.t