From ece7355483a5d1e077781f5bdd39a6ba8bf59401 Mon Sep 17 00:00:00 2001
From: Patrick Ferris <patrick@sirref.org>
Date: Wed, 28 Feb 2024 13:19:12 +0000
Subject: [PATCH] Expose listen in linux

---
 lib_eio_linux/eio_linux.ml  |  1 -
 lib_eio_linux/eio_linux.mli | 22 ++++++++++++++++++++++
 lib_eio_linux/low_level.ml  | 29 +++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/lib_eio_linux/eio_linux.ml b/lib_eio_linux/eio_linux.ml
index 26390b450..8c97b54a3 100644
--- a/lib_eio_linux/eio_linux.ml
+++ b/lib_eio_linux/eio_linux.ml
@@ -262,7 +262,6 @@ let connect ~sw connect_addr =
   let sock = Fd.of_unix ~sw ~seekable:false ~close_unix:true sock_unix in
   Low_level.connect sock addr;
   (flow sock :> _ Eio_unix.Net.stream_socket)
-
 module Impl = struct
   type t = unit
   type tag = [`Unix | `Generic]
diff --git a/lib_eio_linux/eio_linux.mli b/lib_eio_linux/eio_linux.mli
index aa8cfa3d1..a17e2868e 100644
--- a/lib_eio_linux/eio_linux.mli
+++ b/lib_eio_linux/eio_linux.mli
@@ -147,6 +147,14 @@ module Low_level : sig
   val connect : fd -> Unix.sockaddr -> unit
   (** [connect fd addr] attempts to connect socket [fd] to [addr]. *)
 
+  val listen : 
+    reuse_addr:bool ->
+    reuse_port:bool ->
+    backlog:int ->
+    sw:Switch.t ->
+    Eio.Net.Sockaddr.stream ->
+    fd
+
   val await_readable : fd -> unit
   (** [await_readable fd] blocks until [fd] is readable (or has an error). *)
 
@@ -251,3 +259,17 @@ module Low_level : sig
   end
 
 end
+
+val flow : 
+    fd ->
+    [< `Close
+    | `File
+    | `Flow
+    | `Platform of [ `Generic | `Unix ]
+    | `R
+    | `Shutdown
+    | `Socket
+    | `Stream
+    | `Unix_fd
+    | `W ]
+    r
diff --git a/lib_eio_linux/low_level.ml b/lib_eio_linux/low_level.ml
index 9ba42b62f..8a9d6da39 100644
--- a/lib_eio_linux/low_level.ml
+++ b/lib_eio_linux/low_level.ml
@@ -233,6 +233,35 @@ let connect fd addr =
     raise ex
   )
 
+let listen ~reuse_addr ~reuse_port ~backlog ~sw listen_addr =
+  if reuse_addr then (
+    match listen_addr with
+    | `Tcp _ -> ()
+    | `Unix path ->
+      match Unix.lstat path with
+      | Unix.{ st_kind = S_SOCK; _ } -> Unix.unlink path
+      | _ -> ()
+      | exception Unix.Unix_error (Unix.ENOENT, _, _) -> ()
+      | exception Unix.Unix_error (code, name, arg) -> raise @@ Err.wrap code name arg
+  );
+  let addr = Eio_unix.Net.sockaddr_to_unix listen_addr in
+  let sock_unix = Unix.socket ~cloexec:true (Eio_unix.Net.socket_domain_of listen_addr) Unix.SOCK_STREAM 0 in
+  let sock = Fd.of_unix ~sw ~seekable:false ~close_unix:true sock_unix in
+  (* For Unix domain sockets, remove the path when done (except for abstract sockets). *)
+  begin match listen_addr with
+    | `Unix path ->
+      if String.length path > 0 && path.[0] <> Char.chr 0 then
+        Switch.on_release sw (fun () -> Unix.unlink path)
+    | `Tcp _ -> ()
+  end;
+  if reuse_addr then
+    Unix.setsockopt sock_unix Unix.SO_REUSEADDR true;
+  if reuse_port then
+    Unix.setsockopt sock_unix Unix.SO_REUSEPORT true;
+  Unix.bind sock_unix addr;
+  Unix.listen sock_unix backlog;
+  sock
+
 let send_msg fd ?(fds=[]) ?dst buf =
   Fd.use_exn "send_msg" fd @@ fun fd ->
   Fd.use_exn_list "send_msg" fds @@ fun fds ->