opam-mirror/mirage/unikernel.ml

open Lwt.Infix

let argument_error = 64

external reraise : exn -> 'a = "%reraise"

module Make
  (BLOCK : Mirage_block.S)
  (Time : Mirage_time.S)
  (Pclock : Mirage_clock.PCLOCK)
  (Stack : Tcpip.Stack.V4V6)
  (HTTP : Http_mirage_client.S) = struct

  module Part = Mirage_block_partition.Make(BLOCK)
  module KV = Tar_mirage.Make_KV_RW(Part)
  module Cache = OneFFS.Make(Part)

  module SM = Map.Make(String)
  module SSet = Set.Make(String)

  module HM = Map.Make(struct
      type t = Mirage_crypto.Hash.hash
      let compare = compare (* TODO remove polymorphic compare *)
    end)

  let hash_to_string = function
    | `MD5 -> "md5"
    | `SHA1 -> "sha1"
    | `SHA224 -> "sha224"
    | `SHA256 -> "sha256"
    | `SHA384 -> "sha384"
    | `SHA512 -> "sha512"

  let hash_of_string = function
    | "md5" -> Ok `MD5
    | "sha256" -> Ok `SHA256
    | "sha512" -> Ok `SHA512
    | h -> Error (`Msg ("unknown hash algorithm: " ^ h))

  let hex_to_string h =
    let `Hex h = Hex.of_string h in
    h

  let hex_of_string s =
    match Hex.to_string (`Hex s) with
    | d -> Ok d
    | exception Invalid_argument err -> Error (`Msg err)

  let hm_to_s hm =
    HM.fold (fun h v acc ->
        hash_to_string h ^ "=" ^ hex_to_string v ^ "\n" ^ acc)
      hm ""

  module Git = struct
    let decode_digest filename str =
      let hex h s =
        match hex_of_string s with
        | Ok d -> Some (h, d)
        | Error `Msg msg ->
          Logs.warn (fun m -> m "%s invalid hex (%s) %s" filename msg s); None
      in
      match String.split_on_char '=' str with
      | [ data ] -> hex `MD5 data
      | [ "md5" ; data ] -> hex `MD5 data
      | [ "sha256" ; data ] -> hex `SHA256 data
      | [ "sha512" ; data ] -> hex `SHA512 data
      | [ hash ; _ ] -> Logs.warn (fun m -> m "%s unknown hash %s" filename hash); None
      | _ -> Logs.warn (fun m -> m "%s unexpected hash format %S" filename str); None

    let extract_urls filename str =
      (* in an opam file, there may be:
         url { src: <string> checksum: [ STRING ] } <- list of hash
         url { src: <string> checksum: STRING } <- single hash
         url { archive: <string> checksum: STRING } <- MD5
      *)
      let open OpamParserTypes.FullPos in
      let opamfile = OpamParser.FullPos.string str filename in
      let url_section =
        List.find_opt (function
            | { pelem = Section ({ section_kind = { pelem = "url" ; _ } ; _ }) ; _} -> true | _ -> false)
          opamfile.file_contents
      in
      match url_section with
      | Some { pelem = Section ({ section_items = { pelem = items ; _ }; _}) ; _ } ->
        begin
          let url =
            List.find_opt
              (function { pelem = Variable ({ pelem = "src" ; _ }, _); _ } -> true | _ -> false)
              items
          and archive =
            List.find_opt
              (function { pelem = Variable ({ pelem = "archive" ; _ }, _); _ } -> true | _ -> false)
              items
          and checksum =
            List.find_opt
              (function { pelem = Variable ({ pelem = "checksum" ; _ }, _); _ } -> true | _ -> false)
              items
          in
          let url =
            match url, archive with
            | Some { pelem = Variable (_, { pelem = String url ; _ }) ; _ }, None -> Some url
            | None, Some { pelem = Variable (_, { pelem = String url ; _ }); _ } -> Some url
            | _ ->
              Logs.warn (fun m -> m "%s neither src nor archive present" filename); None
          in
          let csum =
            match checksum with
            | Some { pelem = Variable (_, { pelem = List { pelem = csums ; _ } ; _ }); _ } ->
              let csums =
                List.fold_left (fun acc ->
                    function
                    | { pelem = String csum ; _ } ->
                      begin match decode_digest filename csum with
                        | None -> acc
                        | Some (h, v) ->
                          HM.update h (function
                              | None -> Some v
                              | Some v' when String.equal v v' -> None
                              | Some v' ->
                                Logs.warn (fun m -> m "for %s, hash %s, multiple keys are present: %s %s"
                                              (Option.value ~default:"NONE" url) (hash_to_string h) (hex_to_string v) (hex_to_string v'));
                                None)
                            acc
                      end
                    | _ -> acc) HM.empty csums
              in
              Some csums
            | Some { pelem = Variable (_, { pelem = String csum ; _ }) ; _ } ->
              begin match decode_digest filename csum with
                | None -> None
                | Some (h, v) -> Some (HM.singleton h v)
              end
            | _ ->
              Logs.warn (fun m -> m "couldn't decode checksum in %s" filename);
              None
          in
          match url, csum with
          | Some url, Some cs -> Some (url, cs)
          | _ -> None
        end
      | _ -> Logs.debug (fun m -> m "no url section for %s" filename); None

    module Null_write = struct
      (* we have to provide a WRITER, but we don't actually want to write. *)
      type out_channel = |
      type 'a t = 'a Lwt.t
      let really_write o _ = match o with (_ : out_channel) -> .
    end
    module String_read = struct
      type in_channel = {
        data : string;
        mutable offset : int;
      }
      type 'a t = 'a Lwt.t
      let really_read t buf =
        let buf_len = Cstruct.length buf in
        if String.length t.data - t.offset < buf_len then
          raise Stdlib.End_of_file;
        Cstruct.blit_from_string t.data t.offset buf 0 buf_len;
        t.offset <- t.offset + buf_len;
        Lwt.pause ()
      let read t buf =
        let len = min (String.length t.data - t.offset) (Cstruct.length buf) in
        Cstruct.blit_from_string t.data t.offset buf 0 len;
        Lwt.pause () >>= fun () ->
        t.offset <- t.offset + len;
        Lwt.return len
      let skip t n =
        t.offset <- t.offset + n; Lwt.pause ()
    end
    module Index = Tar_gz.Make(Lwt)(Null_write)(String_read)

    let find_urls index =
      let ic =
        Index.of_in_channel ~internal:(Cstruct.create 0x1000)
          { String_read.data = index ; offset = 0 ; }
      in
      let rec do_it acc =
        Lwt.try_bind
          (fun () -> Index.get_next_header ic)
          (fun hdr ->
             (* XXX: Int64.to_int *)
             let file_size = Int64.to_int hdr.file_size in
             Logs.debug (fun m -> m "%s: %Ld" hdr.file_name hdr.file_size);
             if String.starts_with hdr.Tar.Header.file_name ~prefix:"/packages/" &&
                String.ends_with hdr.Tar.Header.file_name ~suffix:"/opam" then begin
               let buf = Cstruct.create file_size in
               Index.really_read ic buf >>= fun () ->
               Index.skip ic (Tar.Header.compute_zero_padding_length hdr) >>= fun () ->
               let data = Cstruct.to_string buf in
               (* TODO report parser errors *)
               let acc =
                 try
                   let url_csums = extract_urls hdr.file_name data in
                   Option.fold ~none:acc ~some:(fun (url, csums) ->
                       if HM.cardinal csums = 0 then
                         (Logs.warn (fun m -> m "no checksums for %s, ignoring" url); acc)
                       else
                         SM.update url (function
                             | None -> Some csums
                             | Some csums' ->
                               if HM.for_all (fun h v ->
                                   match HM.find_opt h csums with
                                   | None -> true | Some v' -> String.equal v v')
                                   csums'
                               then
                                 Some (HM.union (fun _h v _v' -> Some v) csums csums')
                               else begin
                                 Logs.warn (fun m -> m "mismatching hashes for %s: %s vs %s"
                                               url (hm_to_s csums') (hm_to_s csums));
                                 None
                               end) acc) url_csums
                 with _ ->
                   Logs.warn (fun m -> m "some error in %s, ignoring" hdr.file_name);
                   acc
               in
               (do_it [@tailcall]) acc
             end else begin
               Logs.debug (fun m -> m "skipping %d bytes" file_size);
               Index.skip ic file_size >>= fun () ->
               Index.skip ic (Tar.Header.compute_zero_padding_length hdr) >>= fun () ->
               (do_it [@tailcall]) acc
             end
          )
          (function
            | Tar.Header.End_of_stream ->
              Lwt.return acc
            | e -> reraise e)
      in
      do_it SM.empty
  end

  module Disk = struct
    type t = {
      mutable md5s : string SM.t ;
      mutable sha512s : string SM.t ;
      dev : KV.t ;
      dev_md5s : Cache.t ;
      dev_sha512s : Cache.t ;
    }

    let empty dev dev_md5s dev_sha512s = { md5s = SM.empty ; sha512s = SM.empty ; dev; dev_md5s; dev_sha512s }

    let to_hex d =
      let d = Cstruct.to_string d in
      hex_to_string d

    let marshal_sm (sm : string SM.t) =
      let version = char_of_int 1 in
      String.make 1 version ^ Marshal.to_string sm []

    let unmarshal_sm s =
      let version = int_of_char s.[0] in
      match version with
      | 1 -> Ok (Marshal.from_string s 1 : string SM.t)
      | _ -> Error ("Unsupported version " ^ string_of_int version)

    let update_caches t =
      Cache.write t.dev_md5s (marshal_sm t.md5s) >>= fun r ->
      (match r with
       | Ok () -> Logs.info (fun m -> m "Set 'md5s'")
       | Error e -> Logs.warn (fun m -> m "Failed to write 'md5s': %a" Cache.pp_write_error e));
      Cache.write t.dev_sha512s (marshal_sm t.sha512s) >>= fun r ->
      match r with
      | Ok () -> Logs.info (fun m -> m "Set 'sha512s'"); Lwt.return_unit
      | Error e ->
        Logs.warn (fun m -> m "Failed to write 'sha512s': %a" Cache.pp_write_error e);
        Lwt.return_unit

    let find_key t h key =
      match
        match h with
        | `MD5 -> SM.find_opt key t.md5s
        | `SHA512 -> SM.find_opt key t.sha512s
        | `SHA256 -> Some key
        | _ -> None
      with
      | None -> Error `Not_found
      | Some x -> Ok x

    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
        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 key))
        | Ok len ->
          let chunk_size = 4096 in
          let rec read_more a offset =
            if offset < len then
              KV.get_partial t.dev key ~offset ~length:chunk_size >>= function
              | Ok data ->
                f a data >>= fun a ->
                read_more a (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 (Error e)
            else
              Lwt.return (Ok a)
          in
          read_more a 0

    (* on disk, we use a flat file system where the filename is the sha256 of the data *)
    let init ~verify dev dev_md5s dev_sha512s =
      KV.list dev Mirage_kv.Key.empty >>= function
      | Error e -> Logs.err (fun m -> m "error %a listing kv" KV.pp_error e); assert false
      | Ok entries ->
        let t = empty dev dev_md5s dev_sha512s in
        Cache.read t.dev_md5s >>= fun r ->
        (match r with
         | Ok Some s -> Result.iter (fun md5s -> t.md5s <- md5s) (unmarshal_sm s)
         | Ok None -> Logs.debug (fun m -> m "No md5s cached")
         | Error e -> Logs.warn (fun m -> m "Error reading md5s cache: %a" Cache.pp_error e));
        Cache.read t.dev_sha512s >>= fun r ->
        (match r with
         | Ok Some s -> Result.iter (fun sha512s -> t.sha512s <- sha512s) (unmarshal_sm s)
         | Ok None -> Logs.debug (fun m -> m "No sha512s cached")
         | Error e -> Logs.warn (fun m -> m "Error reading sha512s cache: %a" Cache.pp_error e));
        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) ->
            if !idx mod 10 = 0 then Gc.full_major () ;
            match typ with
            | `Dictionary ->
              Logs.warn (fun m -> m "unexpected dictionary at %s" name);
              Lwt.return_unit
            | `Value ->
              let open Mirage_crypto.Hash in
              let sha256_final =
                if verify 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, \
                                            computed %s (should remove)"
                                   name (to_hex digest))
                  in
                  Some f
                else
                  None
              and md5_final =
                if not (SSet.mem name md5s) then
                  let f s =
                    let digest = MD5.get s in
                    t.md5s <- SM.add (to_hex digest) name t.md5s
                  in
                  Some f
                else if verify then
                  let f s =
                    let digest = MD5.get s |> to_hex in
                    match SM.find_opt digest t.md5s with
                    | Some x when String.equal name x -> ()
                    | y ->
                      Logs.err (fun m -> m "corrupt MD5 data for %s, \
                                            expected %a, computed %s"
                                   name Fmt.(option ~none:(any "NONE") string) y
                                   digest)
                  in
                  Some f
                else
                  None
              and sha512_final =
                if not (SSet.mem name sha512s) then
                  let f s =
                    let digest = SHA512.get s in
                    t.sha512s <- SM.add (to_hex digest) name t.sha512s
                  in
                  Some f
                else if verify then
                  let f s =
                    let digest = SHA512.get s |> to_hex in
                    match SM.find_opt digest t.sha512s with
                    | Some x when String.equal name x -> ()
                    | y ->
                      Logs.err (fun m -> m "corrupt SHA512 data for %s, \
                                            expected %a, computed %s"
                                   name Fmt.(option ~none:(any "NONE") string) y
                                   digest)
                  in
                  Some f
                else
                  None
              in
              match sha256_final, md5_final, sha512_final with
              | None, None, None -> Lwt.return_unit
              | _ ->
                read_chunked t `SHA256 name
                  (fun (sha256, md5, sha512) data ->
                     let cs = Cstruct.of_string data in
                     Lwt.return
                       (Option.map (fun t -> SHA256.feed t cs) sha256,
                        Option.map (fun t -> MD5.feed t cs) md5,
                        Option.map (fun t -> SHA512.feed t cs) sha512))
                  (Option.map (fun _ -> SHA256.empty) sha256_final,
                   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)
                | 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))
          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
        | Ok Some `Value -> true
        | Ok Some `Dictionary ->
          Logs.err (fun m -> m "unexpected dictionary for %s %s"
                       (hash_to_string h) 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);
          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
        | 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);
          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

  module Serve = struct
    let ptime_to_http_date ptime =
      let (y, m, d), ((hh, mm, ss), _) = Ptime.to_date_time ptime
      and weekday = match Ptime.weekday ptime with
        | `Mon -> "Mon" | `Tue -> "Tue" | `Wed -> "Wed" | `Thu -> "Thu"
        | `Fri -> "Fri" | `Sat -> "Sat" | `Sun -> "Sun"
      and month =
        [| "Jan" ; "Feb" ; "Mar" ; "Apr" ; "May" ; "Jun" ;
           "Jul" ; "Aug" ; "Sep" ; "Oct" ; "Nov" ; "Dec" |]
    in
    let m' = Array.get month (pred m) in
    Printf.sprintf "%s, %02d %s %04d %02d:%02d:%02d GMT" weekday d m' y hh mm ss

    let update_lock = Lwt_mutex.create ()

    let not_modified request (modified, etag) =
      match Httpaf.Headers.get request.Httpaf.Request.headers "if-modified-since" with
      | Some ts -> String.equal ts modified
      | None -> match Httpaf.Headers.get request.Httpaf.Request.headers "if-none-match" with
        | Some etags -> List.mem etag (String.split_on_char ',' etags)
        | None -> false

    let not_found reqd path =
      let data = "Resource not found " ^ path in
      let headers = Httpaf.Headers.of_list
          [ "content-length", string_of_int (String.length data) ] in
      let resp = Httpaf.Response.create ~headers `Not_found in
      Httpaf.Reqd.respond_with_string reqd resp data

    let respond_with_empty reqd resp =
      let hdr =
        Httpaf.Headers.add_unless_exists resp.Httpaf.Response.headers
          "connection" "close"
      in
      let resp = { resp with Httpaf.Response.headers = hdr } in
      Httpaf.Reqd.respond_with_string reqd resp ""

    (* From the OPAM manual, all we need:
       /repo -- repository configuration file
       /cache -- cached archives
       /index.tar.gz -- archive containing the whole repository contents
    *)
    (* may include "announce: [ string { filter } ... ]" *)
    (* use Key_gen.remote for browse & upstream *)

    (* for repo and index.tar.gz:
        if Last_modified.not_modified request then
          let resp = Httpaf.Response.create `Not_modified in
          respond_with_empty reqd resp
        else *)
    let dispatch store hook_url update _flow _conn reqd =
      let request = Httpaf.Reqd.request reqd in
      Logs.info (fun f -> f "requested %s" request.Httpaf.Request.target);
      match String.split_on_char '/' request.Httpaf.Request.target with
      | [ ""; x ] when String.equal x hook_url ->
        Lwt.async update;
        let data = "Update in progress" in
        let mime_type = "text/plain" in
        let headers = [
          "content-type", mime_type ;
          "content-length", string_of_int (String.length data) ;
        ] 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
      | "" :: "cache" :: hash_algo :: _ :: hash :: [] ->
        (* `<hash-algo>/<first-2-hash-characters>/<hash>` *)
        begin
          match hash_of_string hash_algo with
          | Error `Msg msg ->
            Logs.warn (fun m -> m "error decoding hash algo: %s" msg);
            not_found reqd request.Httpaf.Request.target
          | Ok h ->
            Lwt.async (fun () ->
                (Disk.last_modified store h hash >|= function
                  | Error _ ->
                    Logs.warn (fun m -> m "error retrieving last modified");
                    (* XXX *)
                    ptime_to_http_date (Ptime.v (Pclock.now_d_ps ()))
                  | Ok v -> ptime_to_http_date (Ptime.v v)) >>= fun last_modified ->
                if not_modified request (last_modified, hash) then
                  let resp = Httpaf.Response.create `Not_modified in
                  respond_with_empty reqd resp;
                  Lwt.return_unit
                else
                  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 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", size ;
                    ]
                    in
                    let headers = Httpaf.Headers.of_list headers in
                    let resp = Httpaf.Response.create ~headers `OK in
                    let body = Httpaf.Reqd.respond_with_streaming reqd resp in
                    Disk.read_chunked store h hash (fun () chunk ->
                        let wait, wakeup = Lwt.task () in
                        Httpaf.Body.write_string body chunk;
                        Httpaf.Body.flush body (Lwt.wakeup wakeup);
                        wait) () >|= fun _ ->
                    Httpaf.Body.close_writer body)
        end
      | _ ->
        Logs.warn (fun m -> m "unknown request %s" request.Httpaf.Request.target);
        not_found reqd request.Httpaf.Request.target

  end

  let bad_archives = SSet.of_list Bad.archives

  let download_archives disk http_ctx store =
    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 () ->
        HM.fold (fun h v r ->
            r >>= function
            | true -> Disk.exists disk h (hex_to_string v)
            | false -> Lwt.return false)
          csums (Lwt.return true) >>= function
        | true ->
          Logs.debug (fun m -> m "ignoring %s (already present)" url);
          Lwt.return_unit
        | false ->
          incr idx;
          if !idx mod 10 = 0 then Gc.full_major () ;
          Logs.info (fun m -> m "downloading %s" url);
          Http_mirage_client.one_request
            ~alpn_protocol:HTTP.alpn_protocol
            ~authenticator:HTTP.authenticator
            ~ctx:http_ctx url >>= function
          | Ok (resp, Some str) ->
            if resp.status = `OK then begin
              Logs.info (fun m -> m "downloaded %s" url);
              Disk.write disk ~url str 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
            end
          | _ -> Lwt.return_unit)
      (SM.bindings urls) >>= fun () ->
    Disk.update_caches disk >|= fun () ->
    Logs.info (fun m -> m "downloading of %d urls done" (SM.cardinal urls))


  module Paf = Paf_mirage.Make(Stack.TCP)

  let start block _time _pclock stack http_ctx =
    BLOCK.get_info block >>= fun info ->
    let sectors_cache = Key_gen.sectors_cache () in
    let sectors =
      let cache_size = Int64.(mul 2L sectors_cache) in
      Int64.(sub info.size_sectors cache_size)
    in
    Part.connect sectors block >>= fun (kv, rest) ->
    let md5s, sha512s = Part.subpartition sectors_cache rest in
    KV.connect kv >>= fun kv ->
    Cache.connect md5s >>= fun md5s ->
    Cache.connect sha512s >>= fun sha512s ->
    Logs.info (fun m -> m "Available bytes in tar storage: %Ld" (KV.free kv));
    Disk.init ~verify:(Key_gen.verify ()) kv md5s sha512s >>= fun disk ->
    if Key_gen.check () then
      Lwt.return_unit
    else
      begin
        let url = Key_gen.remote () ^ "/index.tar.gz" in
        Paf.init ~port:(Key_gen.port ()) (Stack.tcp stack) >>= fun t ->
        let update () =
          Http_mirage_client.one_request
            ~alpn_protocol:HTTP.alpn_protocol
            ~authenticator:HTTP.authenticator
            ~ctx:http_ctx url >>= function
          | Ok (resp, Some str) ->
            if resp.status = `OK then
              download_archives disk http_ctx str
            else begin
              Logs.warn (fun m -> m "%s: %a (reason %s)"
                           url H2.Status.pp_hum resp.status resp.reason);
              Lwt.return_unit
            end
          | _ -> Lwt.return_unit
        in
        let service =
          Paf.http_service
            ~error_handler:(fun _ ?request:_ _ _ -> ())
            (Serve.dispatch disk (Key_gen.hook_url ()) update)
        in
        let `Initialized th = Paf.serve service t in
        Logs.info (fun f -> f "listening on %d/HTTP" (Key_gen.port ()));
        Lwt.async (fun () ->
            let rec go () =
              Time.sleep_ns (Duration.of_hour 1) >>= fun () ->
              update () >>= fun () ->
              go ()
            in
            go ());
        update () >>= fun () ->
        (th >|= fun _v -> ())
      end
end