pubsub.ml

(* service definition 
message SeekRequest {
  string subscription = 1;
  oneof target {
    google.protobuf.Timestamp time = 2;
    string snapshot = 3;
  }
}
message SeekResponse {
}
service Subscriber {
  rpc Seek(SeekRequest) returns (SeekResponse);
}
*)

(* option 1: explicit Request/Response messages *)
module SeekRequest : sig
  (** The time to seek to. *)
  type target = Time of Ptime.t | Snapshot of string

  (** Request for the `Seek` method. *)
  type t = {
    subscription : string;
    target : target;
  }
end

module SeekResponse : sig
  type t = unit
end

module Subscriber : sig
  val seek : SeekRequest.t -> SeekResponse.t
end

(* option 2: partial import as labelled arguments *)
module SeekRequest : sig
  type target = Time of Ptime.t | Snapshot of string
end

module Subscriber : sig
  val seek : subscription:string -> target:SeekRequest.target -> unit
end

(* option 3: full import w/ polymorphic variants *)
module Subscriber : sig
  val seek : subscription:string -> target:[< `Time of Ptime.t | `Snapshot of string] -> unit
end

(* option 4: full import w/ optional arguments *)
module Subscriber : sig
  val seek : ?time:Ptime.t -> ?snapshot:string -> subscription:string -> unit
end

(* option 5: full import w/ function duplication for every oneof permutation *)
module Subscriber : sig
  val seek_time : subscription:string -> time:Ptime.t -> unit
  val seek_snapshot : subscription:string -> snapshot:string -> unit
end