Implement Flow.write and write_from

lib_eio/flow.ml

@@ -70,11 +70,14 @@ let string_source s : source =
       len
   end
 
-class virtual sink = object (_ : <Generic.t; ..>)
+class virtual sink = object (self : <Generic.t; ..>)
   method probe _ = None
   method virtual copy : 'a. (#source as 'a) -> unit
+  method write bufs = self#copy (cstruct_source bufs)
 end
 
+let write (t : #sink) (bufs : Cstruct.t list) = t#write bufs
+
 let copy (src : #source) (dst : #sink) = dst#copy src
 
 let copy_string s = copy (string_source s)
@@ -91,10 +94,13 @@ let buffer_sink b =
           Buffer.add_string b (Cstruct.to_string ~len:got buf)
         done
       with End_of_file -> ()
+
+    method! write bufs =
+      List.iter (fun buf -> Buffer.add_bytes b (Cstruct.to_bytes buf)) bufs
   end
 
 class virtual two_way = object (_ : <source; sink; ..>)
-  method probe _ = None
+  inherit sink
   method read_methods = []
 
   method virtual shutdown : shutdown_command -> unit

lib_eio/flow.mli

@@ -62,8 +62,17 @@ type read_method += Read_source_buffer of ((Cstruct.t list -> int) -> unit)
 class virtual sink : object
   inherit Generic.t
   method virtual copy : 'a. (#source as 'a) -> unit
+
+  method write : Cstruct.t list -> unit
+  (** The default implementation is [copy (cstruct_source ...)], but it can be overridden for speed. *)
 end
 
+val write : #sink -> Cstruct.t list -> unit
+(** [write dst bufs] writes all bytes from [bufs].
+
+    This is a low level API, consider using {!copy} if possible as it
+    may allow optimizations. *)
+
 val copy : #source -> #sink -> unit
 (** [copy src dst] copies data from [src] to [dst] until end-of-file. *)
 

lib_eio_linux/eio_linux.ml

@@ -1044,6 +1044,8 @@ let flow fd =
 
     method read_methods = []
 
+    method write bufs = Low_level.writev fd bufs
+
     method copy src =
       match get_fd_opt src with
       | Some src -> fast_copy_try_splice src fd

lib_eio_luv/eio_luv.ml

@@ -597,6 +597,10 @@ let flow fd = object (_ : <source; sink; ..>)
 
   method read_methods = []
 
+  method write bufs =
+    let bufs = List.map Cstruct.to_bigarray bufs in
+    File.write fd bufs |> or_raise
+
   method copy src =
     let buf = Luv.Buffer.create 4096 in
     try
@@ -624,6 +628,10 @@ let socket sock = object
     let buf = Cstruct.to_bigarray buf in
     Stream.read_into sock buf
 
+  method! write bufs =
+    let bufs = List.map Cstruct.to_bigarray bufs in
+    Stream.write sock bufs
+
   method copy src =
     let buf = Luv.Buffer.create 4096 in
     try

tests/flow.md

@@ -107,3 +107,14 @@ Copying from src using `Read_source_buffer`:
 +dst: wrote (rsb) ["bar"]
 - : unit = ()
 ```
+
+## write
+
+```ocaml
+# run @@ fun () ->
+  let dst = Eio_mock.Flow.make "dst" in
+  Eio_mock.Flow.on_copy_bytes dst [`Return 6];
+  Eio.Flow.write dst [Cstruct.of_string "foobar"];;
++dst: wrote "foobar"
+- : unit = ()
+```

tests/network.md

@@ -695,3 +695,33 @@ Both attempts time out:
 +mock time is now 20
 Exception: Eio__Net.Connection_failure Eio__Time.Timeout.
 ```
+
+## read/write on SOCK_DGRAM
+
+```ocaml
+# Eio_main.run @@ fun _ ->
+  Switch.run @@ fun sw ->
+  let a, b = Eio_unix.socketpair ~sw ~domain:Unix.PF_UNIX ~ty:Unix.SOCK_DGRAM () in
+  ignore (Eio_unix.FD.peek a : Unix.file_descr);
+  ignore (Eio_unix.FD.peek b : Unix.file_descr);
+  let l = [ "foo"; "bar"; "foobar"; "cellar door" ] in
+  let buf = Cstruct.create 32 in
+  let write bufs = Eio.Flow.write a (List.map Cstruct.of_string bufs) in
+  let read () =
+    let n = Eio.Flow.read b buf in
+    traceln "Got: %d bytes: %S" n Cstruct.(to_string (sub buf 0 n))
+  in
+  List.iter (fun sbuf -> write [sbuf]) l;
+  List.iter (fun _ -> read ()) l;
+  write ["abaca"; "bb"];
+  read ();
+  Eio.Flow.close a;
+  Eio.Flow.close b;;
++Got: 3 bytes: "foo"
++Got: 3 bytes: "bar"
++Got: 6 bytes: "foobar"
++Got: 11 bytes: "cellar door"
++Got: 7 bytes: "abacabb"
+- : unit = ()
+```
+