fix(rpc): ignore sigpipe on macos clients (#7299)

RPC clients that suddenly disconnect will no longer raise sigpipe and
make dune terminate.

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

CHANGES.md

@@ -1,6 +1,9 @@
 Unreleased
 ----------
 
+- RPC: Ignore SIGPIPE when clients suddenly disconnect on OSX (#7299, partially
+  fixes #6879, @rgrinberg)
+
 - Always clean up the UI on exit. (#7271, fixes #7142 @rgrinberg)
 
 - Bootstrap: remove reliance on shell. Previously, we'd use the shell to get

src/csexp_rpc/csexp_rpc.ml

@@ -61,9 +61,11 @@ module Socket = struct
     let bind fd sock = Unix.bind fd sock
   end
 
-  module Mac : Unix_socket = struct
+  module Mac = struct
     external pthread_chdir : string -> unit = "dune_pthread_chdir" [@@noalloc]
 
+    external set_nosigpipe : Unix.file_descr -> unit = "dune_set_nosigpipe"
+
     let with_chdir fd ~socket ~f =
       let old = Sys.getcwd () in
       let dir = Filename.dirname socket in
@@ -114,6 +116,8 @@ module Socket = struct
   let bind = make ~original:U.bind ~backup:Sel.bind
 
   let connect = make ~original:U.connect ~backup:Sel.connect
+
+  let maybe_set_nosigpipe fd = if is_osx () then Mac.set_nosigpipe fd
 end
 
 let debug = Option.is_some (Env.get Env.initial "DUNE_RPC_DEBUG")
@@ -328,6 +332,7 @@ module Server = struct
         Worker.task async ~f:(fun () ->
             Transport.accept transport
             |> Option.map ~f:(fun client ->
+                   Socket.maybe_set_nosigpipe fd;
                    let in_ = Unix.in_channel_of_descr client in
                    let out = Unix.out_channel_of_descr client in
                    (in_, out)))

src/csexp_rpc/pthread_chdir_stubs.c

@@ -10,6 +10,8 @@
 #if defined(__APPLE__)
 
 #include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/socket.h>
 #include <unistd.h>
 #include <fcntl.h>
 
@@ -19,7 +21,6 @@ CAMLprim value dune_pthread_chdir_is_osx(value unit)
   CAMLreturn(Val_true);
 }
 
-
 #ifndef SYS___pthread_chdir
 # define SYS___pthread_chdir 348
 #endif
@@ -40,8 +41,23 @@ CAMLprim value dune_pthread_chdir(value dir) {
   CAMLreturn (Val_unit); 
 }
 
+CAMLprim value dune_set_nosigpipe(value v_socket) {
+  CAMLparam1(v_socket);
+  int socket = Int_val(v_socket);
+  int opt = 1;
+  int ret = setsockopt(socket, SOL_SOCKET, SO_NOSIGPIPE, &opt, sizeof(int));
+  if (ret < 0) {
+    uerror("setsockopt", Nothing);
+  }
+  CAMLreturn(Val_unit);
+}
+
 #else
 
+CAMLprim value dune_set_nosigpipe(value v_socket) {
+  caml_invalid_argument("only implemented on macos");
+}
+
 CAMLprim value dune_pthread_chdir_is_osx(value unit)
 {
   CAMLparam1(unit);