[Files.save_as]: just write directly to special files

Arvid Jakobsson · Arvid Jakobsson · commit 1d7a95665edb · 2026-04-29T08:49:22.000+02:00
Also, if [name] is a symbolic link, resolve it first.
diff --git a/files.ml b/files.ml
@@ -67,7 +67,7 @@ let mkdir_p ?(perm=0o755) path =
   in
   aux path
 
-let save_as name ?(mode=0o644) f =
+let save_as_regular name ?(mode=0o644) f =
   (* not using make_temp_file cause same dir is needed for atomic rename *)
   let temp = Printf.sprintf "%s.save.%d.tmp" name (U.gettid ()) in
   bracket (Unix.openfile temp [Unix.O_WRONLY;Unix.O_CREAT] mode) Unix.close begin fun fd ->
@@ -81,3 +81,13 @@ let save_as name ?(mode=0o644) f =
     with
       exn -> Exn.suppress Unix.unlink temp; raise exn
   end
+
+let save_as name ?mode f =
+  let name =
+    match (Unix.lstat name).st_kind with
+    | Unix.S_LNK -> Unix.realpath name
+    | (exception Unix.Unix_error (Unix.ENOENT, _, _)) | _ -> name
+  in
+  match (Unix.stat name).st_kind with
+  | Unix.S_REG | (exception Unix.Unix_error (Unix.ENOENT, _, _)) -> save_as_regular name ?mode  f
+  | _ -> Out_channel.with_open_gen [ Open_wronly ] 0 name f
diff --git a/files.mli b/files.mli
@@ -22,11 +22,14 @@ val open_out_append_text : string -> out_channel
 val mkdir_p : ?perm:Unix.file_perm -> string -> unit
 
 (** [save_as filename ?mode f] is similar to
-    [Control.with_open_file_bin] except that writing is done to a
+    [Control.with_open_file_bin] for regular files, except that writing is done to a
     temporary file that will be renamed to [filename] after [f] has
     succesfully terminated. Therefore this guarantee that either
     [filename] will not be modified or will contain whatever [f] was
     writing to it as a side-effect.
 
+    There is no such special treatment for special files, instead they
+    are written to directly.
+
     FIXME windows *)
 val save_as : string -> ?mode:Unix.file_perm -> (out_channel -> unit) -> unit
