mirage-crypto-rng-mirage: provide a module type S

The goal is to remove the mirage-random opam package from the chain. It is a
fine moment to do so, since we need to touch all the users thereof anyways
due to the fact that generate now produces string.

mirage/unikernel.ml

@@ -1,4 +1,4 @@
-module Main (R : Mirage_random.S) = struct
+module Main (R : Mirage_crypto_rng_mirage.S) = struct
   let start _r =
     Logs.info (fun m -> m "using Fortuna, entropy sources: %a"
                   Fmt.(list ~sep:(any ", ") Mirage_crypto_rng.Entropy.pp_source)

rng/mirage/mirage_crypto_rng_mirage.ml

@@ -27,6 +27,22 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *)
 
+module type S = sig
+  type g = Mirage_crypto_rng.g
+  module Entropy :
+    sig
+      type source = Mirage_crypto_rng.Entropy.source
+      val sources : unit -> source list
+      val pp_source : Format.formatter -> source -> unit
+      val register_source : string -> source
+    end
+
+  val generate_into : ?g:g -> bytes -> ?off:int -> int -> unit
+  val generate : ?g:g -> int -> string
+
+  val accumulate : g option -> Entropy.source -> [`Acc of string -> unit]
+end
+
 let src = Logs.Src.create "mirage-crypto-rng-mirage" ~doc:"Mirage crypto RNG mirage"
 module Log = (val Logs.src_log src : Logs.LOG)
 

rng/mirage/mirage_crypto_rng_mirage.mli

@@ -26,14 +26,49 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *)
 
+module type S = sig
+  type g = Mirage_crypto_rng.g
+  (** A generator (PRNG) with its state. *)
+
+  (** Entropy sources and collection *)
+  module Entropy :
+    sig
+      (** Entropy sources. *)
+      type source = Mirage_crypto_rng.Entropy.source
+
+      val sources : unit -> source list
+      (** [sources ()] returns the list of available sources. *)
+
+      val pp_source : Format.formatter -> source -> unit
+      (** [pp_source ppf source] pretty-prints the entropy [source] on [ppf]. *)
+
+      val register_source : string -> source
+      (** [register_source name] registers [name] as entropy source. *)
+    end
+
+  val generate_into : ?g:g -> bytes -> ?off:int -> int -> unit
+  (** [generate_into ~g buf ~off len] invokes
+      {{!Generator.generate_into}generate_into} on [g] or
+      {{!generator}default generator}. The random data is put into [buf] starting
+      at [off] (defaults to 0) with [len] bytes. *)
+
+  val generate : ?g:g -> int -> string
+  (** Invoke {!generate_into} on [g] or {{!generator}default generator} and a
+      freshly allocated string. *)
+
+  val accumulate : g option -> Entropy.source -> [`Acc of string -> unit]
+  (** [accumulate g source] is a function [data -> unit] to feed entropy to the
+      RNG. This is useful if your system has a special entropy source. *)
+end
+
 module Make (T : Mirage_time.S) (M : Mirage_clock.MCLOCK) : sig
+  include S
+
   val initialize :
     ?g:'a -> ?sleep:int64 -> 'a Mirage_crypto_rng.generator -> unit Lwt.t
   (** [initialize ~g ~sleep generator] sets the default generator to the
       [generator] and sets up periodic entropy feeding for that rng. This
       function fails ([Lwt.fail]) if it is called a second time. The argument
       [~sleep] is measured in ns, and used as sleep between cpu assisted random
       number collection. It defaults to one second. *)
-
-  include module type of Mirage_crypto_rng
 end