mimic

A simple protocol dispatcher
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Library mimic
Module Mimic
module Mirage_protocol : sig ... end
type flow = private ..

The type for flows. A flow represents the state of a single reliable stream stream that is connected to an endpoint.

include Mirage_flow.S with type flow := flow and type error = [ `Msg of string | `Not_found | `Cycle ]
type error = [
| `Msg of string
| `Not_found
| `Cycle
]

The type for flow errors.

val pp_error : error Fmt.t

pp_error is the pretty-printer for errors.

type nonrec write_error#row

The type for write errors.

and write_error = private [>
| Mirage_flow.write_error
]

The type for write errors.

val pp_write_error : write_error Fmt.t

pp_write_error is the pretty-printer for write errors.

read flow blocks until some data is available and returns a fresh buffer containing it.

The returned buffer will be of a size convenient to the flow implementation, but will always have at least 1 byte.

If the remote endpoint calls close then calls to read will keep returning data until all the in-flight data has been read. read flow will return `Eof when the remote endpoint has called close and when there is no more in-flight data.

val write : flow -> Cstruct.t -> ( unit, write_error ) result Lwt.t

write flow buffer writes a buffer to the flow. There is no indication when the buffer has actually been read and, therefore, it must not be reused. The contents may be transmitted in separate packets, depending on the underlying transport. The result Ok () indicates success, Error `Closed indicates that the connection is now closed and therefore the data could not be written. Other errors are possible.

val writev : flow -> Cstruct.t list -> ( unit, write_error ) result Lwt.t

writev flow buffers writes a sequence of buffers to the flow. There is no indication when the buffers have actually been read and, therefore, they must not be reused. The result Ok () indicates success, Error `Closed indicates that the connection is now closed and therefore the data could not be written. Other errors are possible.

val close : flow -> unit Lwt.t

close flow flushes all pending writes and signals the remote endpoint that there will be no future writes. Once the remote endpoint has read all pending data, it is expected that calls to read on the remote return `Eof.

Note it is still possible for the remote endpoint to write to the flow and for the local endpoint to call read. This state where the local endpoint has called close but the remote endpoint has not called close is similar to that of a half-closed TCP connection or a Unix socket after shutdown(SHUTDOWN_WRITE).

close flow waits until the remote endpoint has also called close before returning. At this point no data can flow in either direction and resources associated with the flow can be freed.

type ctx

The type for contexts. It's a heterogeneous map of values to help mimic to instantiate a new flow via resolve.

type 'edn value

The type for witnesses whose lookup value is of type 'edn.

module Fun : sig ... end
val make : name:string -> 'edn value

make ~name is a new witness.

val add : 'edn value -> 'edn -> ctx -> ctx

add w v ctx is ctx with w bound to v.

val get : 'edn value -> ctx -> 'edn option

get w ctx is the value of w's binding in ctx, if any.

val fold : 'edn value -> ( 'k, 'edn option Lwt.t ) Fun.args -> k:'k -> ctx -> ctx
val merge : ctx -> ctx -> ctx
val empty : ctx

empty is the empty context.

type ('edn, 'flow) protocol
val register : ?priority:int -> name:string -> (module Mirage_protocol.S with type endpoint = 'edn and type flow = 'flow) -> 'edn value * ( 'edn, 'flow ) protocol

register ?priority ~name (module Protocol) registers the given Protocol into the internal global Mimic's state as a possible transmission protocol available via resolve.

?priority is used to help mimic to choose between multiple solutions according to the given context. Mimic will choose the lower-priority solution.

name helps the end-user to know which solution mimic will dynamically via log outputs.

register returns 2 values:

  • a witness as the required value to initiate a transmission via the given Protocol implementation
  • a protocol which can help the end-user to destruct a flow to its structural type via repr.
module type REPR = sig ... end
val repr : ( 'edn, 'flow ) protocol -> (module REPR with type t = 'flow)

repr protocol gives a module definition with an OCaml constructor to help the end-user to destruct the structural type of a given flow:

module Protocol
  : Mirage_protocol.S with type flow = Lwt_unix.file_descr

let edn, protocol = Mimic.register ~name:"protocol" (module Protocol)
module R = (val (Mimic.repr protocol))

let () = Mimic.resolve ~ctx >>= function
  | Ok (R.T lwt_unix_file_descr) -> ...
  | ...
val resolve : ctx -> ( flow, [> error ] ) result Lwt.t

resolve ctx tries to instantiate a flow from the given ctx.

type edn =
| Edn : 'edn value * 'edn -> edn(*

The type of a value and its witness.

*)
type (_, _) refl =
| Refl : ( 'a, 'a ) refl
val equal : 'a value -> 'b value -> ( 'a, 'b ) refl option

equal a b returns a proof that a and b are structurally equal.

val unfold : ctx -> ( edn list, [> `Cycle ] ) result Lwt.t

unfold ctx applies any functions available into the given ctx and and possible to compute according to available values and return a list of what these functions return.

It's useful to do an introspection of what mimic does when it resolves the given ctx. From that and equal, the user is able to introspect what mimic generated and which protocol it is able to instantiate then.

al:resolve} is:
    {[
      let resolve ctx =
        unfold ctx >>= function
        | Ok lst -> connect lst
        | Error _ as err -> Lwt.return err
    ]}
val connect : edn list -> ( flow, [> error ] ) result Lwt.t

connect values tries to instantiate a flow from given values and registered protocols (see register).

module Merge (A : sig ... end) (B : sig ... end) : sig ... end