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exception Read_error of string
exception Write_error of string
module type T =
sig
type t
val to_yojson : t -> Yojson.Safe.t
val of_yojson : Yojson.Safe.t -> t Ppx_deriving_yojson_runtime.error_or
val default : t
end
module type FI = functor (M: T) ->
sig
val write_internal : M.t -> string -> unit
val read_internal : string -> M.t
val replace_internal : string -> string -> unit
end
module Make : FI = functor (M: T) -> struct
let write_internal x file_name =
let yt = M.to_yojson x in
let ys = Yojson.Safe.to_string yt in
let fd = Unix.openfile file_name [Unix.O_CREAT;Unix.O_WRONLY] 0o664 in
let () =
try
Unix.lockf fd Unix.F_TLOCK 0
with _ ->
Unix.close fd; raise (Write_error "write lock unavailable")
in
let oc = Unix.out_channel_of_descr fd in
let () = Unix.ftruncate fd 0 in
let () = Printf.fprintf oc "%s" ys in
let () = Unix.fsync fd in
let () = Unix.lockf fd Unix.F_ULOCK 0 in
close_out_noerr oc
let read_internal file_name =
let fd =
try
Unix.openfile file_name [Unix.O_RDONLY] 0o664
with Unix.Unix_error (e,f,p) ->
let out =
Printf.sprintf "%s %s: %s" (Unix.error_message e) f p
in raise (Read_error out)
in
let () =
try
Unix.lockf fd Unix.F_TEST 0
with _ ->
Unix.close fd; raise (Read_error "read lock unavailable")
in
let ic = Unix.in_channel_of_descr fd in
let ys = really_input_string ic (in_channel_length ic) in
let yt = Yojson.Safe.from_string ys in
let ct_res = M.of_yojson yt in
let ct = Result.value ct_res ~default:M.default in
close_in_noerr ic; ct
let replace_internal dst src =
let tmp = src ^ ".tmp" in
try
let () = FileUtil.cp ~force:Force [src] tmp in
let () = FileUtil.rm ~force:Force [dst] in
FileUtil.mv ~force:Force tmp dst
with _ -> raise (Write_error "replace error")
end
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