diff --git a/mirage/bad.ml b/mirage/bad.ml
index 2a5a491..8b40ea2 100644
--- a/mirage/bad.ml
+++ b/mirage/bad.ml
@@ -39,7 +39,9 @@ let archives =
     "https://github.com/chetmurthy/pa_ppx/archive/0.01.tar.gz" ;
     "https://github.com/chambart/ocaml-1/archive/lto.tar.gz" ;
     "https://github.com/Kappa-Dev/KaSim/archive/v3.5-250915.tar.gz" ;
-    "https://github.com/bsansouci/bsb-native/archive/1.9.4.tar.gz"
+    "https://github.com/bsansouci/bsb-native/archive/1.9.4.tar.gz";
+    "https://github.com/sanette/oplot/archive/0.7.tar.gz";
+    "https://github.com/ulrikstrid/ocaml-cookie/releases/download/0.1.8/session-cookie-lwt-0.1.8.tbz";
   ]
 
   and bad_request = [
diff --git a/mirage/config.ml b/mirage/config.ml
index df11684..b83ed76 100644
--- a/mirage/config.ml
+++ b/mirage/config.ml
@@ -94,9 +94,9 @@ let tcp = tcpv4v6_of_stackv4v6 stack
 
 let git_client, alpn_client =
   let happy_eyeballs = generic_happy_eyeballs stack dns in
-  let git_happy_eyeballs = git_happy_eyeballs stack dns happy_eyeballs in
-  merge_git_clients (git_tcp tcp git_happy_eyeballs)
-    (git_http ~authenticator:tls_authenticator tcp git_happy_eyeballs),
+  let git = mimic_happy_eyeballs stack dns happy_eyeballs in
+  merge_git_clients (git_tcp tcp git)
+    (git_http ~authenticator:tls_authenticator tcp git),
   paf_client ~pclock:default_posix_clock tcp (mimic_happy_eyeballs stack dns happy_eyeballs)
 
 let program_block_size =
diff --git a/mirage/unikernel.ml b/mirage/unikernel.ml
index febb628..5bbb9ba 100644
--- a/mirage/unikernel.ml
+++ b/mirage/unikernel.ml
@@ -18,9 +18,28 @@ module Make
   module SM = Map.Make(String)
   module SSet = Set.Make(String)
 
+  let compare_hash h h' =
+    match h, h' with
+    | `SHA512, `SHA512 -> 0
+    | `SHA512, _ -> 1
+    | _, `SHA512 -> -1
+    | `SHA384, `SHA384 -> 0
+    | `SHA384, _ -> 1
+    | _, `SHA384 -> -1
+    | `SHA256, `SHA256 -> 0
+    | `SHA256, _ -> 1
+    | _, `SHA256 -> -1
+    | `SHA224, `SHA224 -> 0
+    | `SHA224, _ -> 1
+    | _, `SHA224 -> -1
+    | `SHA1, `SHA1 -> 0
+    | `SHA1, `MD5 -> 1
+    | `MD5, `MD5 -> 0
+    | `MD5, _ -> -1
+
   module HM = Map.Make(struct
       type t = Mirage_crypto.Hash.hash
-      let compare = compare (* TODO remove polymorphic compare *)
+      let compare = compare_hash
     end)
 
   let hash_to_string = function
@@ -41,6 +60,8 @@ module Make
     let `Hex h = Hex.of_string h in
     h
 
+  let hex_to_key h = Mirage_kv.Key.v (hex_to_string h)
+
   let hex_of_string s =
     match Hex.to_string (`Hex s) with
     | d -> Ok d
@@ -61,17 +82,16 @@ module Make
           Lwt.return acc
         | Ok steps ->
           Lwt_list.fold_left_s (fun acc (step, _) ->
-              let full_path = Mirage_kv.Key.add path step in
-              Store.exists store full_path >>= function
+              Store.exists store step >>= function
               | Error e ->
                 Logs.err (fun m -> m "error %a for exists %a" Store.pp_error e
-                             Mirage_kv.Key.pp full_path);
+                             Mirage_kv.Key.pp step);
                 Lwt.return acc
               | Ok None ->
-                Logs.warn (fun m -> m "no typ for %a" Mirage_kv.Key.pp full_path);
+                Logs.warn (fun m -> m "no typ for %a" Mirage_kv.Key.pp step);
                 Lwt.return acc
-              | Ok Some `Value -> Lwt.return (full_path :: acc)
-              | Ok Some `Dictionary -> go store full_path acc) acc steps
+              | Ok Some `Value -> Lwt.return (step :: acc)
+              | Ok Some `Dictionary -> go store step acc) acc steps
       in
       go store Mirage_kv.Key.empty []
 
@@ -98,6 +118,19 @@ module Make
       *)
       let open OpamParserTypes.FullPos in
       let opamfile = OpamParser.FullPos.string str filename in
+      let unavailable =
+        List.exists
+          (function
+            | { pelem = Variable ({ pelem = "available" ; _ },
+                                  { pelem = (Bool false | List { pelem = [{ pelem = Bool false; _ }] ; _ }); _ })
+              ; _ } -> true
+            | _ -> false)
+          opamfile.file_contents
+      in
+      if unavailable then
+        (Logs.info (fun m -> m "%s is marked unavailable, skipping" filename);
+         None)
+      else
       let url_section =
         List.find_opt (function
             | { pelem = Section ({ section_kind = { pelem = "url" ; _ } ; _ }) ; _} -> true | _ -> false)
@@ -208,6 +241,10 @@ module Make
       dev_sha512s : Cache.t ;
     }
 
+    let pending = Mirage_kv.Key.v "pending"
+
+    let to_delete = Mirage_kv.Key.v "to-delete"
+
     let empty dev dev_md5s dev_sha512s = { md5s = SM.empty ; sha512s = SM.empty ; dev; dev_md5s; dev_sha512s }
 
     let to_hex d =
@@ -237,10 +274,13 @@ module Make
         Lwt.return_unit
 
     let find_key t h key =
+      assert (List.length (Mirage_kv.Key.segments key) = 1);
       match
         match h with
-        | `MD5 -> SM.find_opt key t.md5s
-        | `SHA512 -> SM.find_opt key t.sha512s
+        | `MD5 ->
+          Option.map Mirage_kv.Key.v (SM.find_opt (Mirage_kv.Key.basename key) t.md5s)
+        | `SHA512 ->
+          Option.map Mirage_kv.Key.v (SM.find_opt (Mirage_kv.Key.basename key) t.sha512s)
         | `SHA256 -> Some key
         | _ -> None
       with
@@ -250,13 +290,12 @@ module Make
     let read_chunked t h v f a =
       match find_key t h v with
       | Error `Not_found ->
-        Lwt.return (Error (`Not_found (Mirage_kv.Key.v v)))
-      | Ok x ->
-        let key = Mirage_kv.Key.v x in
+        Lwt.return (Error (`Not_found v))
+      | Ok key ->
         KV.size t.dev key >>= function
         | Error e ->
-          Logs.err (fun m -> m "error %a while reading %s %s"
-                       KV.pp_error e (hash_to_string h) v);
+          Logs.err (fun m -> m "error %a while reading %s %a"
+                       KV.pp_error e (hash_to_string h) Mirage_kv.Key.pp v);
           Lwt.return (Error (`Not_found key))
         | Ok len ->
           let chunk_size = 4096 in
@@ -265,15 +304,262 @@ module Make
               KV.get_partial t.dev key ~offset ~length:chunk_size >>= function
               | Ok data ->
                 f a data >>= fun a ->
-                read_more a (offset + chunk_size)
+                read_more a Optint.Int63.(add offset (of_int chunk_size))
               | Error e ->
-                Logs.err (fun m -> m "error %a while reading %s %s"
-                             KV.pp_error e (hash_to_string h) v);
+                Logs.err (fun m -> m "error %a while reading %s %a"
+                             KV.pp_error e (hash_to_string h) Mirage_kv.Key.pp v);
                 Lwt.return (Error e)
             else
               Lwt.return (Ok a)
           in
-          read_more a 0
+          read_more a Optint.Int63.zero
+
+    (*
+    module HM_running = struct
+      
+      let empty h =
+        let module H = (val Mirage_crypto.Hash.module_of h) in
+        (* We need MD5, SHA256 and SHA512. [h] is likely one of the
+           aforementioned and in that case we don't compute the same hash twice
+        *)
+        HM.empty
+        |> HM.add `MD5 Mirage_crypto.Hash.MD5.empty
+        |> HM.add `SHA256 Mirage_crypto.Hash.SHA256.empty
+        |> HM.add `SHA512 Mirage_crypto.Hash.SHA512.empty
+        |> HM.add h H.empty
+
+      let feed t data =
+        HM.map (fun h v ->
+            let module H = (val Mirage_crypto.Hash.module_of h) in
+            H.feed v data)
+          t
+
+      let get =
+        HM.map (fun h v ->
+            let module H = (val Mirage_crypto.Hash.module_of h) in
+            H.get v)
+
+
+    end
+       *)
+
+    module Running_hash = struct
+      type _ t =
+        | MD5 : Mirage_crypto.Hash.MD5.t -> [> `MD5 ] t
+        | SHA1 : Mirage_crypto.Hash.SHA1.t -> [> `SHA1 ] t
+        | SHA224 : Mirage_crypto.Hash.SHA224.t -> [> `SHA224 ] t
+        | SHA256 : Mirage_crypto.Hash.SHA256.t -> [> `SHA256 ] t
+        | SHA384 : Mirage_crypto.Hash.SHA384.t -> [> `SHA384 ] t
+        | SHA512 : Mirage_crypto.Hash.SHA512.t -> [> `SHA512 ] t
+
+      let empty : _ -> _ t = function
+        | `MD5 -> MD5 Mirage_crypto.Hash.MD5.empty
+        | `SHA1 -> SHA1 Mirage_crypto.Hash.SHA1.empty
+        | `SHA224 -> SHA224 Mirage_crypto.Hash.SHA224.empty
+        | `SHA256 -> SHA256 Mirage_crypto.Hash.SHA256.empty
+        | `SHA384 -> SHA384 Mirage_crypto.Hash.SHA384.empty
+        | `SHA512 -> SHA512 Mirage_crypto.Hash.SHA512.empty
+
+      let feed t data =
+        let open Mirage_crypto.Hash in
+        match t with
+        | MD5 t -> MD5 (MD5.feed t data)
+        | SHA1 t -> SHA1 (SHA1.feed t data)
+        | SHA224 t -> SHA224 (SHA224.feed t data)
+        | SHA256 t -> SHA256 (SHA256.feed t data)
+        | SHA384 t -> SHA384 (SHA384.feed t data)
+        | SHA512 t -> SHA512 (SHA512.feed t data)
+
+      let get t =
+        let open Mirage_crypto.Hash in
+        match t with
+        | MD5 t -> MD5.get t
+        | SHA1 t -> SHA1.get t
+        | SHA224 t -> SHA224.get t
+        | SHA256 t -> SHA256.get t
+        | SHA384 t -> SHA384.get t
+        | SHA512 t -> SHA512.get t
+    end
+
+    type 'a digests = {
+      md5 : Mirage_crypto.Hash.MD5.t;
+      sha256 : Mirage_crypto.Hash.SHA256.t;
+      sha512 : Mirage_crypto.Hash.SHA512.t;
+      csum : 'a Running_hash.t;
+    }
+
+    let empty_digests h =
+      let open Mirage_crypto.Hash in
+      {
+        md5 = MD5.empty;
+        sha256 = SHA256.empty;
+        sha512 = SHA512.empty;
+        csum = Running_hash.empty h;
+      }
+
+    let update_digests { md5; sha256; sha512; csum } data =
+      let open Mirage_crypto.Hash in
+      let data = Cstruct.of_string data in
+      {
+        md5 = MD5.feed md5 data;
+        sha256 = SHA256.feed sha256 data;
+        sha512 = SHA512.feed sha512 data;
+        csum = Running_hash.feed csum data;
+      }
+
+    let init_write csums =
+      let hash, csum = HM.max_binding csums in
+      (hash, csum), Ok (empty_digests hash, `Init)
+
+    let content_length_of_string s =
+      match Int64.of_string s with
+      | len when len >= 0L -> `Fixed len
+      | _ | exception _ -> `Bad_response
+
+    let body_length headers =
+      match H2.Headers.get_multi headers "content-length" with
+      | [] -> `Unknown
+      | [ x ] ->  content_length_of_string x
+      | hd :: tl ->
+        (* if there are multiple content-length headers we require them all to be
+         * exactly equal. *)
+        if List.for_all (String.equal hd) tl then
+          content_length_of_string hd
+        else
+          `Bad_response
+
+    let body_length (response : Http_mirage_client.response) =
+      if response.status <> `OK then
+        `Bad_response
+      else
+        body_length response.headers
+
+    let pending_key (hash, csum) =
+      match hash with
+      | `SHA512 ->
+        (* We can't use hex because the filename would become too long for tar *)
+        Mirage_kv.Key.(pending / hash_to_string hash / Base64.encode_string ~alphabet:Base64.uri_safe_alphabet ~pad:false csum)
+      | _ ->
+        Mirage_kv.Key.(pending / hash_to_string hash / hex_to_string csum)
+
+    let to_delete_key (hash, csum) =
+      let rand = "random" in (* FIXME: generate random string *)
+      let encoded_csum =
+        match hash with
+        | `SHA512 ->
+          (* We can't use hex because the filename would become too long for tar *)
+          Base64.encode_string ~alphabet:Base64.uri_safe_alphabet ~pad:false csum
+        | _ ->
+          hex_to_string csum
+      in
+      Mirage_kv.Key.(to_delete / hash_to_string hash / (encoded_csum ^ "." ^ rand))
+
+    let write_partial t (hash, csum) =
+      (* XXX: we may be in trouble if different hash functions are used for the same archive *)
+      let key = pending_key (hash, csum) in
+      let ( >>>= ) = Lwt_result.bind in
+      fun response r data ->
+        Lwt.return r >>>= fun (digests, acc) ->
+        let digests = update_digests digests data in
+        match acc with
+        | `Init ->
+          begin match body_length response with
+          | `Bad_response -> Lwt.return (Error `Bad_response)
+          | `Fixed size ->
+            KV.allocate t.dev key (Optint.Int63.of_int64 size)
+            |> Lwt_result.map_error (fun e -> `Write_error e)
+            >>>= fun () ->
+            KV.set_partial t.dev key ~offset:Optint.Int63.zero data
+            |> Lwt_result.map_error (fun e -> `Write_error e) >>>= fun () ->
+            let len = String.length data in
+            let offset = Optint.Int63.of_int len in
+            Lwt.return_ok (digests, `Fixed_body (size, offset))
+          | `Unknown ->
+            Lwt.return_ok (digests, `Unknown data)
+          end
+        | `Fixed_body (size, offset) ->
+          KV.set_partial t.dev key ~offset data
+          |> Lwt_result.map_error (fun e -> `Write_error e) >>>= fun () ->
+          let len = String.length data in
+          let offset = Optint.Int63.(add offset (of_int len)) in
+          Lwt.return_ok (digests, `Fixed_body (size, offset))
+        | `Unknown body ->
+          Lwt.return_ok (digests, `Unknown (body ^ data))
+
+    let digests_to_hm digests =
+      HM.empty
+      |> HM.add `MD5
+        (Cstruct.to_string (Mirage_crypto.Hash.MD5.get digests.md5))
+      |> HM.add `SHA256
+        (Cstruct.to_string (Mirage_crypto.Hash.SHA256.get digests.sha256))
+      |> HM.add `SHA512
+        (Cstruct.to_string (Mirage_crypto.Hash.SHA512.get digests.sha512))
+
+    let check_csums_digests csums digests =
+      let csums' = digests_to_hm digests in
+      let common_bindings = List.filter (fun (h, _) -> HM.mem h csums) (HM.bindings csums') in
+      List.length common_bindings > 0 &&
+      List.for_all
+        (fun (h, csum) -> String.equal csum (HM.find h csums))
+        common_bindings
+
+    let finalize_write t (hash, csum) ~url (body : [ `Unknown of string | `Fixed_body of int64 * Optint.Int63.t | `Init ]) csums digests =
+      let sizes_match, body_size_in_header =
+        match body with
+        | `Fixed_body (reported, actual) -> Optint.Int63.(equal (of_int64 reported) actual), true
+        | `Unknown _ -> true, false
+        | `Init -> assert false
+      in
+      let source = pending_key (hash, csum) in
+      if check_csums_digests csums digests && sizes_match then
+        let sha256 = to_hex (Mirage_crypto.Hash.SHA256.get digests.sha256)
+        and md5 = to_hex (Mirage_crypto.Hash.MD5.get digests.md5)
+        and sha512 = to_hex (Mirage_crypto.Hash.SHA512.get digests.sha512) in
+        let dest = Mirage_kv.Key.v sha256 in
+        begin match body with
+        | `Unknown body ->
+          Logs.info (fun m -> m "downloaded %s, now writing" url);
+          KV.set t.dev dest body
+        | `Fixed_body (_reported_size, _actual_size) ->
+          Logs.info (fun m -> m "downloaded %s" url);
+          KV.rename t.dev ~source ~dest
+        | `Init -> assert false
+        end >|= function
+        | Ok () ->
+          t.md5s <- SM.add md5 sha256 t.md5s;
+          t.sha512s <- SM.add sha512 sha256 t.sha512s
+        | Error e ->
+          Logs.err (fun m -> m "Write failure for %s: %a" url KV.pp_write_error e)
+      else begin
+        (if sizes_match then
+           Logs.err (fun m -> m "Bad checksum %s: computed %s expected %s" url
+                        (hash_to_string hash) (hex_to_string csum))
+         else match body with
+           | `Fixed_body (reported, actual) ->
+             Logs.err (fun m -> m "Size mismatch %s: received %a bytes expected %Lu bytes"
+                          url Optint.Int63.pp actual reported)
+           | `Unknown _ -> assert false
+           | `Init -> assert false);
+        if body_size_in_header then
+          (* if the checksums mismatch we want to delete the file. We are only
+             able to do so if it was the latest created file, so we expect and
+             error. Ideally, we want to match for `Append_only or other errors *)
+          KV.remove t.dev source >>= function
+          | Ok () -> Lwt.return_unit
+          | Error e ->
+            (* we failed to delete the file so we mark it for deletion *)
+            let dest = to_delete_key (hash, csum) in
+            Logs.warn (fun m -> m "Failed to remove %a: %a. Moving it to %a"
+                          Mirage_kv.Key.pp source KV.pp_write_error e Mirage_kv.Key.pp dest);
+            KV.rename t.dev ~source ~dest >|= function
+            | Ok () -> ()
+            | Error e ->
+              Logs.warn (fun m -> m "Error renaming file %a -> %a: %a"
+                            Mirage_kv.Key.pp source Mirage_kv.Key.pp dest KV.pp_write_error e)
+        else
+          Lwt.return_unit
+      end
+
 
     (* on disk, we use a flat file system where the filename is the sha256 of the data *)
     let init ~verify_sha256 dev dev_md5s dev_sha512s =
@@ -298,11 +584,17 @@ module Make
         let md5s = SSet.of_list (List.map snd (SM.bindings t.md5s))
         and sha512s = SSet.of_list (List.map snd (SM.bindings t.sha512s)) in
         let idx = ref 1 in
-        Lwt_list.iter_s (fun (name, typ) ->
+        (* XXX: should we do something about pending downloads?? *)
+        let entries =
+          List.filter (fun (p, _) ->
+              not (Mirage_kv.Key.equal p pending || Mirage_kv.Key.equal p to_delete))
+            entries
+        in
+        Lwt_list.iter_s (fun (path, typ) ->
             if !idx mod 10 = 0 then Gc.full_major () ;
             match typ with
             | `Dictionary ->
-              Logs.warn (fun m -> m "unexpected dictionary at %s" name);
+              Logs.warn (fun m -> m "unexpected dictionary at %a" Mirage_kv.Key.pp path);
               Lwt.return_unit
             | `Value ->
               let open Mirage_crypto.Hash in
@@ -310,28 +602,28 @@ module Make
                 if verify_sha256 then
                   let f s =
                     let digest = SHA256.get s in
-                    if not (String.equal name (to_hex digest)) then
-                      Logs.err (fun m -> m "corrupt SHA256 data for %s, \
+                    if not (String.equal (Mirage_kv.Key.basename path) (to_hex digest)) then
+                      Logs.err (fun m -> m "corrupt SHA256 data for %a, \
                                             computed %s (should remove)"
-                                   name (to_hex digest))
+                                   Mirage_kv.Key.pp path (to_hex digest))
                   in
                   Some f
                 else
                   None
               and md5_final =
-                if not (SSet.mem name md5s) then
+                if not (SSet.mem (Mirage_kv.Key.basename path) md5s) then
                   let f s =
                     let digest = MD5.get s in
-                    t.md5s <- SM.add (to_hex digest) name t.md5s
+                    t.md5s <- SM.add (to_hex digest) (Mirage_kv.Key.basename path) t.md5s
                   in
                   Some f
                 else
                   None
               and sha512_final =
-                if not (SSet.mem name sha512s) then
+                if not (SSet.mem (Mirage_kv.Key.basename path) sha512s) then
                   let f s =
                     let digest = SHA512.get s in
-                    t.sha512s <- SM.add (to_hex digest) name t.sha512s
+                    t.sha512s <- SM.add (to_hex digest) (Mirage_kv.Key.basename path) t.sha512s
                   in
                   Some f
                 else
@@ -340,7 +632,7 @@ module Make
               match sha256_final, md5_final, sha512_final with
               | None, None, None -> Lwt.return_unit
               | _ ->
-                read_chunked t `SHA256 name
+                read_chunked t `SHA256 path
                   (fun (sha256, md5, sha512) data ->
                      let cs = Cstruct.of_string data in
                      Lwt.return
@@ -351,85 +643,53 @@ module Make
                    Option.map (fun _ -> MD5.empty) md5_final,
                    Option.map (fun _ -> SHA512.empty) sha512_final) >|= function
                 | Error e ->
-                  Logs.err (fun m -> m "error %a of %s while computing digests"
-                               KV.pp_error e name)
+                  Logs.err (fun m -> m "error %a of %a while computing digests"
+                               KV.pp_error e Mirage_kv.Key.pp path)
                 | Ok (sha256, md5, sha512) ->
                   Option.iter (fun f -> f (Option.get sha256)) sha256_final;
                   Option.iter (fun f -> f (Option.get md5)) md5_final;
                   Option.iter (fun f -> f (Option.get sha512)) sha512_final;
-                  Logs.info (fun m -> m "added %s" name))
+                  Logs.info (fun m -> m "added %a" Mirage_kv.Key.pp path))
           entries >>= fun () ->
         update_caches t >|= fun () ->
         t
 
-    let write t ~url data hm =
-      let cs = Cstruct.of_string data in
-      let sha256 = Mirage_crypto.Hash.digest `SHA256 cs |> to_hex
-      and md5 = Mirage_crypto.Hash.digest `MD5 cs |> to_hex
-      and sha512 = Mirage_crypto.Hash.digest `SHA512 cs |> to_hex
-      in
-      if
-        HM.for_all (fun h v ->
-            let v' =
-              match h with `MD5 -> md5 | `SHA256 -> sha256 | `SHA512 -> sha512 | _ -> assert false
-            in
-            let v = hex_to_string v in
-            if String.equal v v' then
-              true
-            else begin
-              Logs.err (fun m -> m "%s hash mismatch %s: expected %s, got %s" url
-                           (hash_to_string h) v v');
-              false
-            end) hm
-      then begin
-        KV.set t.dev (Mirage_kv.Key.v sha256) data >|= function
-        | Ok () ->
-          t.md5s <- SM.add md5 sha256 t.md5s;
-          t.sha512s <- SM.add sha512 sha256 t.sha512s;
-          Logs.debug (fun m -> m "wrote %s (%d bytes)" sha256
-                         (String.length data))
-        | Error e ->
-          Logs.err (fun m -> m "error %a while writing %s (key %s)"
-                       KV.pp_write_error e url sha256)
-      end else
-        Lwt.return_unit
-
     let exists t h v =
       match find_key t h v with
       | Error _ -> Lwt.return false
       | Ok x ->
-        KV.exists t.dev (Mirage_kv.Key.v x) >|= function
+        KV.exists t.dev x >|= function
         | Ok Some `Value -> true
         | Ok Some `Dictionary ->
-          Logs.err (fun m -> m "unexpected dictionary for %s %s"
-                       (hash_to_string h) v);
+          Logs.err (fun m -> m "unexpected dictionary for %s %a"
+                       (hash_to_string h) Mirage_kv.Key.pp v);
           false
         | Ok None -> false
         | Error e ->
-          Logs.err (fun m -> m "exists %s %s returned %a"
-                       (hash_to_string h) v KV.pp_error e);
+          Logs.err (fun m -> m "exists %s %a returned %a"
+                       (hash_to_string h) Mirage_kv.Key.pp v KV.pp_error e);
           false
 
     let last_modified t h v =
       match find_key t h v with
       | Error _ as e -> Lwt.return e
       | Ok x ->
-        KV.last_modified t.dev (Mirage_kv.Key.v x) >|= function
+        KV.last_modified t.dev x >|= function
         | Ok data -> Ok data
         | Error e ->
-          Logs.err (fun m -> m "error %a while last_modified %s %s"
-                       KV.pp_error e (hash_to_string h) v);
+          Logs.err (fun m -> m "error %a while last_modified %s %a"
+                       KV.pp_error e (hash_to_string h) Mirage_kv.Key.pp v);
           Error `Not_found
 
     let size t h v =
       match find_key t h v with
       | Error _ as e -> Lwt.return e
       | Ok x ->
-        KV.size t.dev (Mirage_kv.Key.v x) >|= function
+        KV.size t.dev x >|= function
         | Ok s -> Ok s
         | Error e ->
-          Logs.err (fun m -> m "error %a while size %s %s"
-                       KV.pp_error e (hash_to_string h) v);
+          Logs.err (fun m -> m "error %a while size %s %a"
+                       KV.pp_error e (hash_to_string h) Mirage_kv.Key.pp v);
           Error `Not_found
     end
 
@@ -507,7 +767,10 @@ module Make
 
     let commit_id git_kv =
       Store.digest git_kv Mirage_kv.Key.empty >|= fun r ->
-      Result.get_ok r
+      Result.fold r ~ok:Fun.id
+        ~error:(fun e ->
+            Logs.err (fun m -> m "%a" Store.pp_error e);
+            exit 2)
 
     let repo commit =
       let upstream = List.hd (String.split_on_char '#' (Key_gen.remote ())) in
@@ -520,8 +783,12 @@ stamp: %S
 
     let modified git_kv =
       Store.last_modified git_kv Mirage_kv.Key.empty >|= fun r ->
-      let v = Result.fold ~ok:Fun.id ~error:(fun _ -> Pclock.now_d_ps ()) r in
-      ptime_to_http_date (Ptime.v v)
+      let v =
+        Result.fold r
+          ~ok:Fun.id
+          ~error:(fun _ -> Ptime.v (Pclock.now_d_ps ()))
+      in
+      ptime_to_http_date v
 
     type t = {
       mutable commit_id : string ;
@@ -654,13 +921,14 @@ stamp: %S
             Logs.warn (fun m -> m "error decoding hash algo: %s" msg);
             not_found reqd request.Httpaf.Request.target
           | Ok h ->
+            let hash = Mirage_kv.Key.v hash in
             Lwt.async (fun () ->
                 (Disk.last_modified store h hash >|= function
                   | Error _ ->
                     Logs.warn (fun m -> m "error retrieving last modified");
                     t.modified
-                  | Ok v -> ptime_to_http_date (Ptime.v v)) >>= fun last_modified ->
-                if not_modified request (last_modified, hash) then
+                  | Ok v -> ptime_to_http_date v) >>= fun last_modified ->
+                if not_modified request (last_modified, Mirage_kv.Key.basename hash) then
                   let resp = Httpaf.Response.create `Not_modified in
                   respond_with_empty reqd resp;
                   Lwt.return_unit
@@ -671,11 +939,11 @@ stamp: %S
                     not_found reqd request.Httpaf.Request.target;
                     Lwt.return_unit
                   | Ok size ->
-                    let size = string_of_int size in
+                    let size = Optint.Int63.to_string size in
                     let mime_type = "application/octet-stream" in
                     let headers = [
                       "content-type", mime_type ;
-                      "etag", hash ;
+                      "etag", Mirage_kv.Key.basename hash ;
                       "last-modified", last_modified ;
                       "content-length", size ;
                     ]
@@ -685,6 +953,7 @@ stamp: %S
                     let body = Httpaf.Reqd.respond_with_streaming reqd resp in
                     Disk.read_chunked store h hash (fun () chunk ->
                         let wait, wakeup = Lwt.task () in
+                        (* FIXME: catch exception when body is closed *)
                         Httpaf.Body.write_string body chunk;
                         Httpaf.Body.flush body (Lwt.wakeup wakeup);
                         wait) () >|= fun _ ->
@@ -699,15 +968,17 @@ stamp: %S
   let bad_archives = SSet.of_list Bad.archives
 
   let download_archives disk http_client store =
+    (* FIXME: handle resuming partial downloads *)
     Git.find_urls store >>= fun urls ->
     let urls = SM.filter (fun k _ -> not (SSet.mem k bad_archives)) urls in
     let pool = Lwt_pool.create (Key_gen.parallel_downloads ()) (Fun.const Lwt.return_unit) in
     let idx = ref 0 in
     Lwt_list.iter_p (fun (url, csums) ->
         Lwt_pool.use pool @@ fun () ->
+        (* FIXME: check pending and to-delete *)
         HM.fold (fun h v r ->
             r >>= function
-            | true -> Disk.exists disk h (hex_to_string v)
+            | true -> Disk.exists disk h (hex_to_key v)
             | false -> Lwt.return false)
           csums (Lwt.return true) >>= function
         | true ->
@@ -717,16 +988,20 @@ stamp: %S
           incr idx;
           if !idx mod 10 = 0 then Gc.full_major () ;
           Logs.info (fun m -> m "downloading %s" url);
-          let body _response acc data = Lwt.return (acc ^ data) in
-          Http_mirage_client.request http_client url body "" >>= function
-          | Ok (resp, body) ->
-            if resp.status = `OK then begin
-              Logs.info (fun m -> m "downloaded %s" url);
-              Disk.write disk ~url body csums
-            end else begin
-              Logs.warn (fun m -> m "%s: %a (reason %s)"
-                            url H2.Status.pp_hum resp.status resp.reason);
-              Lwt.return_unit
+          let quux, body_init = Disk.init_write csums in
+          Http_mirage_client.request http_client url (Disk.write_partial disk quux) body_init >>= function
+          | Ok (resp, r) ->
+            begin match r with
+              | Error `Bad_response ->
+                Logs.warn (fun m -> m "%s: %a (reason %s)"
+                              url H2.Status.pp_hum resp.status resp.reason);
+                Lwt.return_unit
+              | Error `Write_error e ->
+                Logs.err (fun m -> m "%s: write error %a"
+                              url KV.pp_write_error e);
+                Lwt.return_unit
+              | Ok (digests, body) ->
+                Disk.finalize_write disk quux ~url body csums digests
             end
           | _ -> Lwt.return_unit)
       (SM.bindings urls) >>= fun () ->