Delete socket file before starting server

If Dream is started as a Unix socket server, then try to delete the
socket file before binding to it. If it doesn't exist, just carry on.

Fix #398

Author: yawaramin

src/http/http.ml

@@ -494,6 +494,11 @@ let serve_with_details
   let%lwt listen_address =
     match network with
     | `Unix path ->
+      (* Optimistically delete the socket file, if any. *)
+      let%lwt () =
+        try%lwt Lwt_unix.unlink path
+        with Unix.Unix_error (ENOENT, _, _) -> Lwt.return_unit
+      in
       Lwt.return (Lwt_unix.ADDR_UNIX path)
     | `Inet port ->
       let%lwt addresses =