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(** Types of the abstract data types (ADT) which parameterize the P2p layer.

  Many types used in the P2p layer are parameterized by three type parameters:
    - ['msg]: type of messages exchanged between peers
    - ['peer_meta]: type of the metadata associated with peers (score, etc.)
    - ['conn_meta]: type of the metadata associated with connections

  These types are kept abstract from the P2p layer. It can only operate on
  them via a set of functions packed in a "configuration" record
  passed by the upper layer (see also [P2p] and [P2p.create]).

  This module defines the type of these configuration records. *)

(** Metadata for a peer *)
type 'peer_meta peer_meta_config = {
  peer_meta_encoding : 'peer_meta Data_encoding.t;
  peer_meta_initial : unit -> 'peer_meta;  (** Constructor *)
  score : 'peer_meta -> float;  (** Score of a peer, used for ordering *)
}

(** Metadata for a connection. *)
type 'conn_meta conn_meta_config = {
  conn_meta_encoding : 'conn_meta Data_encoding.t;
  conn_meta_value : unit -> 'conn_meta;  (** Constructor *)
  private_node : 'conn_meta -> bool;
      (** Returns true if peer at the other end of the connection is in private
      mode *)
}

type 'msg app_message_encoding =
  | Encoding : {
      tag : int;
      title : string;
      encoding : 'a Data_encoding.t;
      wrap : 'a -> 'msg;
      unwrap : 'msg -> 'a option;
      max_length : int option;
    }
      -> 'msg app_message_encoding

(** Application-level messages encoding, and version parameters *)
type 'msg message_config = {
  encoding : 'msg app_message_encoding list;  (** Encoding of the messages. *)
  chain_name : Distributed_db_version.Name.t;
      (** Identifier for this P2p protocol when establishing session. *)
  distributed_db_versions : Distributed_db_version.t list;
      (** List of versions supported by this P2p protocol. *)
      (* TODO: https://gitlab.com/tezos/tezos/-/issues/4593
         These last two fields aren't logically related to the `msg type,
         they should be moved somewhere else *)
}