read the data in chunks and send them chunk-wise

mirage/config.ml

@@ -66,7 +66,7 @@ let mirror =
       package ~min:"3.7.0" "git-paf" ;
       package "opam-file-format" ;
       package ~min:"2.1.0" ~sublibs:[ "gz" ] "tar" ;
-      package ~pin:"git+https://github.com/hannesm/ocaml-tar.git#kv-rw" "tar-mirage" ;
+      package ~pin:"git+https://github.com/hannesm/ocaml-tar.git#kv-rw-kv-5" "tar-mirage" ;
       package ~pin:"git+https://github.com/reynir/mirage-block-partition.git" "mirage-block-partition" ;
       package ~pin:"git+https://git.robur.io/reynir/oneffs.git" "oneffs" ;
     ]

mirage/unikernel.ml

@@ -382,6 +382,32 @@ module Make
                        KV.pp_error e (hash_to_string h) v);
           Error `Not_found
 
+    let read_chunked t h v f =
+      match find_key t h v with
+      | Error _ as e -> Lwt.return e
+      | Ok x ->
+        let key = Mirage_kv.Key.v x in
+        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);
+          Lwt.return (Error `Not_found)
+        | Ok len ->
+          let chunk_size = 4096 in
+          let rec read_more offset =
+            if offset < len then
+              KV.get_partial t.dev key ~offset ~length:chunk_size >>= function
+              | Ok data -> f data ; read_more (offset + chunk_size)
+              | Error e ->
+                Logs.err (fun m -> m "error %a while reading %s %s"
+                             KV.pp_error e (hash_to_string h) v);
+                Lwt.return_unit
+            else
+              Lwt.return_unit
+          in
+          read_more 0 >|= fun () ->
+          Ok ()
+
     let last_modified t h v =
       match find_key t h v with
       | Error _ as e -> Lwt.return e
@@ -389,7 +415,18 @@ module Make
         KV.last_modified t.dev (Mirage_kv.Key.v x) >|= function
         | Ok data -> Ok data
         | Error e ->
-          Logs.err (fun m -> m "error %a while reading %s %s"
+          Logs.err (fun m -> m "error %a while last_modified %s %s"
+                       KV.pp_error e (hash_to_string h) 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
+        | 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);
           Error `Not_found
     end
@@ -626,22 +663,27 @@ stamp: %S
                   respond_with_empty reqd resp;
                   Lwt.return_unit
                 else
-                  Disk.read store h hash >>= function
+                  Disk.size store h hash >>= function
                   | Error _ ->
+                    Logs.warn (fun m -> m "error retrieving size");
                     not_found reqd request.Httpaf.Request.target;
                     Lwt.return_unit
-                  | Ok data ->
+                  | Ok size ->
+                    let size = string_of_int size in
                     let mime_type = "application/octet-stream" in
                     let headers = [
                       "content-type", mime_type ;
                       "etag", hash ;
                       "last-modified", last_modified ;
-                      "content-length", string_of_int (String.length data) ;
+                      "content-length", size ;
-                    ] in
+                    ]
+                    in
                     let headers = Httpaf.Headers.of_list headers in
                     let resp = Httpaf.Response.create ~headers `OK in
-                    Httpaf.Reqd.respond_with_string reqd resp data ;
+                    let body = Httpaf.Reqd.respond_with_streaming reqd resp in
-                    Lwt.return_unit)
+                    Disk.read_chunked store h hash (fun chunk ->
+                        Httpaf.Body.write_string body chunk) >|= fun _ ->
+                    Httpaf.Body.close_writer body)
         end
       | _ ->
         Logs.warn (fun m -> m "unknown request %s" request.Httpaf.Request.target);