From 2312092e42db6ea595b72ac2bf4664ac2f390f0f Mon Sep 17 00:00:00 2001
From: Hannes Mehnert <hannes@mehnert.org>
Date: Mon, 4 Nov 2024 17:17:37 +0100
Subject: [PATCH] first write to a temporary filename, and rename later

---
 mirage/unikernel.ml | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mirage/unikernel.ml b/mirage/unikernel.ml
index 2102a15..1e1307b 100644
--- a/mirage/unikernel.ml
+++ b/mirage/unikernel.ml
@@ -312,8 +312,12 @@ module Make
         and sha512 = Ohex.encode Digestif.SHA512.(to_raw_string (get digests.sha512)) in
         let dest = Mirage_kv.Key.v sha256 in
         Logs.info (fun m -> m "downloaded %s, now writing" url);
-        (Lwt.finalize (fun () -> set_from_handle t.dev dest swap)
-           (fun () -> Swap.free swap))
+        let temp = Mirage_kv.Key.(v "pending" // dest) in
+        Lwt_result.bind
+          (Lwt.finalize (fun () -> set_from_handle t.dev temp swap)
+             (fun () -> Swap.free swap))
+          (fun () -> KV.rename t.dev ~source:temp ~dest
+                     |> Lwt_result.map_error (fun e -> `Write_error e))
         >|= function
         | Ok () ->
           remove_active url;