feat: fixes bug when writing to many files concurrently

Basically there's a bug in the vectorized i/o which I think may be
behind the problems I've seen with Blink sending POST bodies.

This goes back to regular write-ops for non-vectorized inputs (which
should be plenty!)

packages/riot-stdlib/file.ml

@@ -50,6 +50,15 @@ end
 
 let to_reader t = Rio.Reader.of_read_src (module Read) t
 
+let read_to_string path =
+  if not (exists path) then Error (`File_not_found path)
+  else
+    let file = open_read path in
+    let reader = to_reader file in
+    let buf = Buffer.create 512 in
+    let* _ = Rio.read_to_end reader ~buf in
+    Ok (Buffer.contents buf)
+
 module Write = struct
   type t = write_file
 
@@ -64,10 +73,14 @@ module Write = struct
     | Error err -> Error err
 
   let write t ~buf =
-    let bufs = Rio.Iovec.from_string buf in
-    write_owned_vectored t ~bufs
+    File.write t.fd ~pos:0 ~len:(String.length buf) (Bytes.unsafe_of_string buf)
 
   let flush _t = Ok ()
 end
 
 let to_writer t = Rio.Writer.of_write_src (module Write) t
+
+let write ?permissions path ~content:buf =
+  let file = open_write ?permissions path in
+  let dst = to_writer file in
+  Rio.write_all dst ~buf

packages/riot-stdlib/telemetry_app.ml

@@ -25,5 +25,6 @@ module Dispatcher = struct
 end
 
 let start () = Dispatcher.start_link ()
+
 let emit = Dispatcher.emit
 let attach = Telemetry.attach

packages/riot/riot.mli

@@ -667,6 +667,14 @@ module File : sig
   val to_reader : read_file -> read_file IO.Reader.t
   val to_writer : write_file -> write_file IO.Writer.t
   val exists : string -> bool
+
+  val write : ?permissions:int -> string -> content:string -> (unit, [> `Noop ]) IO.io_result
+  val read_to_string : 
+string ->
+( string,
+  [> `File_not_found of string
+  ] )
+IO.io_result
 end
 
 module Net : sig

test/concurrent_file_reads.ml

@@ -0,0 +1,50 @@
+open Riot
+
+type Message.t += ContentMatch of string | Error of string
+
+let () =
+  Riot.run_with_status ~on_error:(fun _ -> 1) @@ fun () ->
+  let _ = Logger.start () in
+  Logger.set_log_level (Some Debug);
+  let main = self () in
+  let proc_count = 10_000 in
+  let _ =
+    spawn (fun () ->
+        for id = 0 to proc_count do
+          spawn (fun () ->
+              let dir = Filename.temp_dir "_riot_test" (Int.to_string id) in
+              Sys.chdir dir;
+              let filename = dir ^ "/" ^ "test_" ^ Int.to_string id in
+              let content = filename in
+              let () = File.write filename ~content |> Result.get_ok in
+              let msg =
+                match File.read_to_string filename with
+                | Ok actual ->
+                    if String.equal actual content then ContentMatch filename
+                    else
+                      Error
+                        (Format.sprintf
+                           "%d: the content did not match! %S != %S\n\
+                            filename: %s" id actual content filename)
+                | Error (`File_not_found file) ->
+                    let cwd = Sys.getcwd () in
+                    Error
+                      (Format.sprintf
+                         "%d: file not found: %S in %S because cwd is %S" id
+                         file dir cwd)
+                | Error (#IO.io_error as e) ->
+                    let err = Format.asprintf "%d: error: %a" id IO.pp_err e in
+                    Error err
+              in
+              send main msg)
+          |> ignore
+        done)
+  in
+
+  for _i = 0 to proc_count do
+    match receive_any () with
+    | ContentMatch _filename -> ()
+    | Error str -> failwith str
+    | _ -> ()
+  done;
+  Ok 0

test/dune

@@ -205,3 +205,9 @@
  (name terminate_when_main_terminates_test)
  (modules terminate_when_main_terminates_test)
  (libraries riot))
+
+(test
+ (package riot)
+ (name concurrent_file_reads)
+ (modules concurrent_file_reads)
+ (libraries riot))