remove extunix dep just for tcp keepalive

capnp-rpc-unix.opam

@@ -17,7 +17,6 @@ depends: [
   "astring"
   "fmt" {>= "0.8.7"}
   "logs"
-  "extunix"
   "base64" {>= "3.0.0"}
   "dune" {>= "3.16"}
   "ipaddr" {>= "5.3.0" }

unix/dune

@@ -1,4 +1,7 @@
 (library
  (name capnp_rpc_unix)
  (public_name capnp-rpc-unix)
- (libraries eio.unix astring capnp-rpc capnp-rpc-net fmt logs mirage-crypto-rng.unix cmdliner cstruct extunix))
+ (libraries eio.unix astring capnp-rpc capnp-rpc-net fmt logs mirage-crypto-rng.unix cmdliner cstruct)
+ (foreign_stubs
+  (language c)
+  (names sockopt_stubs)))

unix/keepalive.ml

@@ -1,8 +1 @@
-let have_tcp_keepidle =
-  try ExtUnix.All.have_sockopt_int ExtUnix.All.TCP_KEEPIDLE
-  with ExtUnix.All.Not_available _ -> false
-
-let try_set_idle socket i =
-  if have_tcp_keepidle then (
-    ExtUnix.All.setsockopt_int socket ExtUnix.All.TCP_KEEPIDLE i
-  )
+external try_set_idle : Unix.file_descr -> int -> unit = "capnp_rpc_set_keepidle"

unix/keepalive.mli

@@ -0,0 +1 @@
+external try_set_idle : Unix.file_descr -> int -> unit = "capnp_rpc_set_keepidle"

unix/sockopt_stubs.c

@@ -0,0 +1,40 @@
+#include <caml/mlvalues.h>
+#include <caml/memory.h>
+
+#ifdef _WIN32
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#define KEEPIDLE_OPT (-1)
+#else
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+
+/* macOS uses TCP_KEEPALIVE instead of TCP_KEEPIDLE */
+#if defined(TCP_KEEPIDLE)
+#define KEEPIDLE_OPT TCP_KEEPIDLE
+#elif defined(TCP_KEEPALIVE)
+#define KEEPIDLE_OPT TCP_KEEPALIVE
+#else
+#define KEEPIDLE_OPT (-1)
+#endif
+#endif
+
+CAMLprim value capnp_rpc_set_keepidle(value v_fd, value v_time)
+{
+  CAMLparam2(v_fd, v_time);
+#if KEEPIDLE_OPT == (-1)
+  (void)v_fd;
+  (void)v_time;
+#else
+#ifdef _WIN32
+  SOCKET fd = Handle_val(v_fd);
+#else
+  int fd = Int_val(v_fd);
+#endif
+  int time = Int_val(v_time);
+  setsockopt(fd, IPPROTO_TCP, KEEPIDLE_OPT, &time, sizeof(time));
+#endif
+  CAMLreturn(Val_unit);
+}