fix(rpc): ignore sigpipe on linux

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

<!-- ps-id: bca90be1-43e5-4e3f-a56c-08901d4d4863 -->

CHANGES.md

@@ -1,8 +1,8 @@
 Unreleased
 ----------
 
-- RPC: Ignore SIGPIPE when clients suddenly disconnect on OSX (#7299, partially
-  fixes #6879, @rgrinberg)
+- RPC: Ignore SIGPIPE when clients suddenly disconnect (#7299, #7319, fixes
+  #6879, @rgrinberg)
 
 - Always clean up the UI on exit. (#7271, fixes #7142 @rgrinberg)
 

src/csexp_rpc/csexp_rpc.ml

@@ -128,7 +128,13 @@ module Session = struct
   type state =
     | Closed
     | Open of
-        { out_channel : out_channel
+        { out_buf : Io_buffer.t
+        ; fd : Unix.file_descr
+        ; (* A mutex for modifying [out_buf].
+
+             Needed as long as we use threads for async IO. Once we switch to
+             event based IO, we won't need this mutex anymore *)
+          write_mutex : Mutex.t
         ; in_channel : in_channel
         ; writer : Worker.t
         ; reader : Worker.t
@@ -139,13 +145,22 @@ module Session = struct
     ; mutable state : state
     }
 
-  let create in_channel out_channel =
+  let create fd in_channel =
     let id = Id.gen () in
     if debug then
       Log.info [ Pp.textf "RPC created new session %d" (Id.to_int id) ];
     let* reader = Worker.create () in
     let+ writer = Worker.create () in
-    let state = Open { in_channel; out_channel; reader; writer } in
+    let state =
+      Open
+        { fd
+        ; in_channel
+        ; out_buf = Io_buffer.create ()
+        ; write_mutex = Mutex.create ()
+        ; writer
+        ; reader
+        }
+    in
     { id; state }
 
   let string_of_packet = function
@@ -159,10 +174,11 @@ module Session = struct
   let close t =
     match t.state with
     | Closed -> ()
-    | Open { in_channel = _; out_channel; reader; writer } ->
+    | Open { write_mutex = _; fd = _; in_channel; out_buf = _; reader; writer }
+      ->
       Worker.stop reader;
       Worker.stop writer;
-      close_out_noerr out_channel;
+      close_in_noerr in_channel;
       t.state <- Closed
 
   let read t =
@@ -203,6 +219,30 @@ module Session = struct
       debug res;
       res
 
+  external send : Unix.file_descr -> Bytes.t -> int -> int -> int = "dune_send"
+
+  let write = if Sys.linux then send else Unix.single_write
+
+  let rec csexp_write_loop fd out_buf token write_mutex =
+    Mutex.lock write_mutex;
+    if Io_buffer.flushed out_buf token then Mutex.unlock write_mutex
+    else
+      (* We always make sure to try and write the entire buffer.
+          This should minimize the amount of [write] calls we need
+          to do *)
+      let written =
+        let bytes = Io_buffer.bytes out_buf in
+        let pos = Io_buffer.pos out_buf in
+        let len = Io_buffer.length out_buf in
+        try write fd bytes pos len
+        with exn ->
+          Mutex.unlock write_mutex;
+          reraise exn
+      in
+      Io_buffer.read out_buf written;
+      Mutex.unlock write_mutex;
+      csexp_write_loop fd out_buf token write_mutex
+
   let write t sexps =
     if debug then
       Log.info
@@ -218,21 +258,23 @@ module Session = struct
       | Some sexps ->
         Code_error.raise "attempting to write to a closed channel"
           [ ("sexp", Dyn.(list Sexp.to_dyn) sexps) ])
-    | Open { writer; out_channel; _ } -> (
+    | Open { writer; fd; out_buf; write_mutex; _ } -> (
       match sexps with
       | None ->
         (try
-           Unix.shutdown
-             (Unix.descr_of_out_channel out_channel)
-             Unix.SHUTDOWN_ALL
+           (* TODO this hack is temporary until we get rid of dune rpc init *)
+           Unix.shutdown fd Unix.SHUTDOWN_ALL
          with Unix.Unix_error (_, _, _) -> ());
         close t;
         Fiber.return ()
       | Some sexps -> (
         let+ res =
+          Mutex.lock write_mutex;
+          Io_buffer.write_csexps out_buf sexps;
+          let flush_token = Io_buffer.flush_token out_buf in
+          Mutex.unlock write_mutex;
           Worker.task writer ~f:(fun () ->
-              List.iter sexps ~f:(Csexp.to_channel out_channel);
-              flush out_channel)
+              csexp_write_loop fd out_buf flush_token write_mutex)
         in
         match res with
         | Ok () -> ()
@@ -327,8 +369,7 @@ module Server = struct
             Transport.accept transport
             |> Option.map ~f:(fun client ->
                    let in_ = Unix.in_channel_of_descr client in
-                   let out = Unix.out_channel_of_descr client in
-                   (in_, out)))
+                   (client, in_)))
       in
       let loop () =
         let* accept = accept () in
@@ -349,8 +390,8 @@ module Server = struct
                  accepted."
             ];
           Fiber.return None
-        | Ok (Some (in_, out)) ->
-          let+ session = Session.create in_ out in
+        | Ok (Some (fd, in_)) ->
+          let+ session = Session.create fd in_ in
           Some session
       in
       Fiber.Stream.In.create loop
@@ -413,9 +454,8 @@ module Client = struct
             let transport = Transport.create t.sockaddr in
             t.transport <- Some transport;
             let client = Transport.connect transport in
-            let out = Unix.out_channel_of_descr client in
             let in_ = Unix.in_channel_of_descr client in
-            (in_, out))
+            (client, in_))
       in
       Worker.stop async;
       match task with

src/csexp_rpc/csexp_rpc_stubs.c

@@ -68,3 +68,34 @@ CAMLprim value dune_pthread_chdir(value unit) {
 }
 
 #endif
+
+#if __linux__
+
+#include <caml/threads.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+CAMLprim value dune_send(value v_fd, value v_bytes, value v_pos, value v_len) {
+  CAMLparam4(v_fd, v_bytes, v_pos, v_len);
+  int len = Long_val(v_len);
+  if (len > UNIX_BUFFER_SIZE) {
+    len = UNIX_BUFFER_SIZE;
+  }
+  int pos = Long_val(v_pos);
+  int fd = Int_val(v_fd);
+  char iobuf[UNIX_BUFFER_SIZE];
+  memmove(iobuf, &Byte(v_bytes, pos), len);
+  caml_release_runtime_system();
+  int ret = send(fd, iobuf, (int)len, MSG_NOSIGNAL);
+  caml_acquire_runtime_system();
+  if (ret == -1) {
+    uerror("send", Nothing);
+  };
+  CAMLreturn(Val_int(ret));
+}
+#else
+CAMLprim value dune_send(value v_fd, value v_bytes, value v_pos, value v_len) {
+  caml_invalid_argument("sendmsg without sigpipe only available on linux");
+}
+#endif

src/csexp_rpc/dune

@@ -7,6 +7,7 @@
   dune_util
   csexp
   fiber
+  threads.posix
   (re_export unix))
  (foreign_stubs
   (language c)

src/csexp_rpc/io_buffer.ml

@@ -0,0 +1,79 @@
+open Stdune
+
+type t =
+  { mutable bytes : Bytes.t (* underlying bytes *)
+  ; (* the position we can start reading from (until [pos_w]) *)
+    mutable pos_r : int
+  ; (* the position we can start writing to (until [Bytes.length bytes - 1]) *)
+    mutable pos_w : int
+  ; (* total number of bytes written to this buffer. 2^63 bytes should be
+       enough for anybody *)
+    mutable total_written : int
+  }
+
+type flush_token = int
+
+(* We can't use [Out_channel] for writes on Linux because we want to disable
+   sigpipes. Eventually we'll move to event based IO and ditch the threads,
+   so we'll need this anyway *)
+
+let create () =
+  { bytes = Bytes.create 8192; pos_r = 0; pos_w = 0; total_written = 0 }
+
+let maybe_resize_to_fit t write_size =
+  let buf_len = Bytes.length t.bytes in
+  let capacity = buf_len - t.pos_w in
+  if capacity < write_size then (
+    let needed = write_size - capacity - t.pos_r in
+    let new_size = min buf_len needed in
+    let bytes = Bytes.create new_size in
+    Bytes.blit ~src:t.bytes ~src_pos:t.pos_r ~dst:bytes ~dst_pos:0
+      ~len:(t.pos_w - t.pos_r);
+    t.bytes <- bytes;
+    t.pos_w <- t.pos_r;
+    t.pos_r <- 0)
+
+let write_char_exn t c =
+  Bytes.set t.bytes t.pos_w c;
+  t.pos_w <- t.pos_w + 1
+
+let write_string_exn t src =
+  let len = String.length src in
+  Bytes.blit_string ~src ~src_pos:0 ~dst:t.bytes ~dst_pos:t.pos_w ~len;
+  t.pos_w <- t.pos_w + len
+
+let read t len =
+  let pos_r = t.pos_r + len in
+  assert (pos_r <= t.pos_w);
+  t.pos_r <- pos_r;
+  t.total_written <- t.total_written + len
+
+let length t = t.pos_w - t.pos_r
+
+let flush_token t = t.total_written + length t
+
+let flushed t token = t.total_written >= token
+
+let write_csexps =
+  let rec loop t (csexp : Csexp.t) =
+    match csexp with
+    | Atom str ->
+      write_string_exn t (string_of_int (String.length str));
+      write_char_exn t ':';
+      write_string_exn t str
+    | List e ->
+      write_char_exn t '(';
+      List.iter ~f:(loop t) e;
+      write_char_exn t ')'
+  in
+  fun t csexps ->
+    let length =
+      List.fold_left csexps ~init:0 ~f:(fun acc csexp ->
+          acc + Csexp.serialised_length csexp)
+    in
+    maybe_resize_to_fit t length;
+    List.iter ~f:(loop t) csexps
+
+let pos t = t.pos_r
+
+let bytes t = t.bytes

src/csexp_rpc/io_buffer.mli

@@ -0,0 +1,31 @@
+(** A resizable IO buffer *)
+
+type t
+
+(** create a new io buffer *)
+val create : unit -> t
+
+(** [read t n] reads [n] bytes *)
+val read : t -> int -> unit
+
+(** [write t csexps] write [csexps] to [t] while resizing [t] as necessary *)
+val write_csexps : t -> Csexp.t list -> unit
+
+(** a flush token is used to determine when a write has been completely flushed *)
+type flush_token
+
+(** [flush_token t] will be flushed whenever everything in [t] will be written *)
+val flush_token : t -> flush_token
+
+(** [flushed t token] will return [true] once all the data that was present in
+    [t] when [token] was created will be written *)
+val flushed : t -> flush_token -> bool
+
+(** underlying raw buffer *)
+val bytes : t -> Bytes.t
+
+(** [pos t] in [bytes t] to read *)
+val pos : t -> int
+
+(** [length t] the number of bytes to read [bytes t] *)
+val length : t -> int