refactor(Learnocaml_store): Move Json_codec to Learnocaml_api

Motivation:
- Learnocaml_store contained Json_codec
- learnocaml_client.ml relies on Json_codec
- Learnocaml_store depends on Learnocaml_api
- Learnocaml_store pulls irmin-git.unix and cryptokit
  - unlike Learnocaml_api
  - and these two dependencies are unneeded for compiling learnocaml_client.ml

Author: erikmd

src/main/dune

@@ -43,7 +43,6 @@
             cohttp-lwt-unix
             grading_cli
             learnocaml_data
-	    learnocaml_store
             learnocaml_api)
 )
 (install

src/main/learnocaml_client.ml

@@ -452,7 +452,7 @@ let console_report ?(verbose=false) ex report =
   List.iter (fun i -> print_endline (format_item i)) report;
   print_newline ()
 
-module Api_client = Learnocaml_api.Client (Learnocaml_store.Json_codec)
+module Api_client = Learnocaml_api.Client (Learnocaml_api.Json_codec)
 
 let fetch server_url req =
   let url path args =

src/server/learnocaml_server.ml

@@ -754,7 +754,7 @@ module Request_handler = struct
 
 end
 
-module Api_server = Api.Server (Json_codec) (Request_handler)
+module Api_server = Api.Server (Api.Json_codec) (Request_handler)
 
 let init_teacher_token () =
   Token.Index.get () >>= function tokens ->

src/state/learnocaml_api.ml

@@ -253,6 +253,23 @@ module type JSON_CODEC = sig
   val encode: ?minify:bool -> 'a J.encoding -> 'a -> string
 end
 
+(* Erik: Json_codec was initially in learnocaml_store.ml,
+   which induced unneeded dependencies:
+   learn-ocaml-client -> irmin-git.unix, cryptokit *)
+module Json_codec = struct
+  let decode enc s =
+    (match s with
+     | "" -> `O []
+     | s -> Ezjsonm.from_string s)
+    |> J.destruct enc
+
+  let encode ?minify enc x =
+    match J.construct enc x with
+    | `A _ | `O _ as json -> Ezjsonm.to_string ?minify json
+    | `Null -> ""
+    | _ -> assert false
+end
+
 module Conversions (Json: JSON_CODEC) = struct
 
   let response_codec

src/state/learnocaml_api.mli

@@ -196,6 +196,9 @@ module type JSON_CODEC = sig
   val encode: ?minify:bool -> 'a Json_encoding.encoding -> 'a -> string
 end
 
+(** Used both for file i/o and request handling *)
+module Json_codec: JSON_CODEC
+
 module type REQUEST_HANDLER = sig
   type 'resp ret
 

src/state/learnocaml_store.ml

@@ -17,26 +17,13 @@ let sync_dir = ref (Filename.concat (Sys.getcwd ()) "sync")
 
 let data_dir = ref (Filename.concat !sync_dir "data")
 
-module Json_codec = struct
-  let decode enc s =
-    (match s with
-     | "" -> `O []
-     | s -> Ezjsonm.from_string s)
-    |> J.destruct enc
-
-  let encode ?minify enc x =
-    match J.construct enc x with
-    | `A _ | `O _ as json -> Ezjsonm.to_string ?minify json
-    | `Null -> ""
-    | _ -> assert false
-end
 let get_from_file enc p =
   Lwt_io.(with_file ~mode: Input p read) >|=
-    Json_codec.decode enc
+    Learnocaml_api.Json_codec.decode enc
 
 let write_to_file enc s p =
   let open Lwt_io in
-  let s = Json_codec.encode enc s in
+  let s = Learnocaml_api.Json_codec.encode enc s in
   with_file ~mode:output p @@ fun oc -> write oc s
 
 let sanitise_path prefix subpath =
@@ -217,7 +204,7 @@ module Exercise = struct
     let save () =
       Lazy.force tbl >>= fun tbl ->
       let l = Hashtbl.fold (fun _ s acc -> s::acc) tbl [] in
-      let s = Json_codec.encode (J.list enc) l in
+      let s = Learnocaml_api.Json_codec.encode (J.list enc) l in
       write (store_file ()) s
 
     let get id =
@@ -503,7 +490,7 @@ module Save = struct
     in
     Lwt.catch (fun () ->
         write ~no_create:(Token.is_teacher token) ~extra file
-          (Json_codec.encode ~minify:false enc save))
+          (Learnocaml_api.Json_codec.encode ~minify:false enc save))
       (function
         | Not_found -> Lwt.fail_with "Unregistered teacher token"
         | e -> Lwt.fail e)
@@ -566,7 +553,7 @@ module Student = struct
 
     let save () =
       Lazy.force map >>= fun map ->
-      let s = Json_codec.encode store_enc !map in
+      let s = Learnocaml_api.Json_codec.encode store_enc !map in
       write (store_file ()) s
 
     let get_student map token =

src/state/learnocaml_store.mli

@@ -20,7 +20,7 @@ val data_dir: string ref
 (** {2 Utility server-side conversion functions} *)
 
 (** Used both for file i/o and request handling *)
-module Json_codec: Learnocaml_api.JSON_CODEC
+
 val get_from_file : 'a Json_encoding.encoding -> string -> 'a Lwt.t
 val write_to_file : 'a Json_encoding.encoding -> 'a -> string -> unit Lwt.t