Source file commit_db.ml

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(*
   The writer writes commits to the storage and the commit tree.

   If some commits are written to the storage but not to the commit tree,
   the writer recover them and write them to the commit tree.

   A reader only reads commits from the commit tree.
*)

open Utils
open Result_lwt.Syntax

type entry = Commit.t =
  { parent : Commit_hash.t option
  ; index  : Index.t
  ; hash   : Commit_hash.t
  ; info   : Index.t
  }

type t =
  { storage_context : Storage.t
  ; mutable commit_tree : Commit_tree.t
  ; hashf : (module Hashfunc_intf.S)
  }

type Error.t += Conflict
let () = Error.register_printer @@ function
  | Conflict -> Some "Conflict found in Plebeia commit tree"
  | _ -> None

let commit_tree t = t.commit_tree

let compute_hash t = Commit.compute_hash t.hashf

let make_commit t = Commit.make t.hashf

let add_to_commit_tree t entry index =
  t.commit_tree <- Commit_tree.add t.commit_tree entry.hash {parent= entry.parent; index}

let mode t =
  let smode = Storage.mode t.storage_context in
  let ctmode = Commit_tree.mode t.commit_tree in
  if smode = ctmode then smode
  else assert false

(* Get new commits from the context storage and add them to the commit_tree.
   It does not commit the updated commit_tree.
*)
let read_additional_commits t =
  match mode t with
  | Reader -> Ok 0
  | Writer ->
      let rec aux cnt = function
        | None -> Ok cnt
        | Some i ->
            let entry, prev = Commit_storage.read t.storage_context i in
            (* We stop when we are sure that the entry is also in commit_tree *)
            match Commit_tree.find t.commit_tree entry.hash with
            | Some {parent=_; index= i'} ->
                if i <> i' then begin
                  (* Oops, conflict found *)
                  Log.error "Conflict commit: storage: %a roots: %a"
                    Index.pp i
                    Index.pp i';
                  Error Conflict end
                else
                  Ok cnt
            | None ->
                add_to_commit_tree t entry i;
                aux (cnt + 1) prev
      in
      match aux 0 (Storage.get_last_root_index t.storage_context) with
      | Ok 0 -> Ok 0
      | Ok n ->
          Log.debug "read %d new commits from %s" n
            (Storage.filename t.storage_context);
          from_Ok @@ Commit_tree.write t.commit_tree;
          Ok n
      | Error e -> Error e

(* hash collisions are overridden *)
let add t commit_entry =
  (* Write to storage *)
  let+=? i = Commit_storage.write t.storage_context commit_entry in
  (* the entry is written to the context just after the info part *)
  assert (Index.(commit_entry.info + Unsafe.of_int 3 = i));
  add_to_commit_tree t commit_entry i;
  from_Ok @@ Commit_tree.write t.commit_tree;
  Log.debug "Added commit %a" Commit.pp commit_entry

let mem t = Commit_tree.mem t.commit_tree

let find t h =
  match Commit_tree.find t.commit_tree h with
  | Some {parent=_; index= idx} ->
      let ctxt = t.storage_context in
      let entry = Commit_storage.read ctxt idx |> fst in
      Some entry
  | None -> None

let commit t =
  let*= () = Storage.commit t.storage_context in
  Commit_tree.commit t.commit_tree

let flush t =
  (* Flush the storage_context first, so that the commit_tree can be
     recovered from the storage_context by read_additional_commits. *)
  let*= () = Storage.flush t.storage_context in
  Commit_tree.flush t.commit_tree

let may_forget t =
  match Commit_tree.may_forget t.commit_tree with
  | Some ct -> t.commit_tree <- ct; true
  | None -> false

type Error.t += Conflicting_modes

let () = Error.register_printer (function
    | Conflicting_modes ->
        Some "Conflicting modes of the context and commit tree"
    | _ -> None)

(* Reader may call this *)
let create ~hash_func context commit_tree =
  let storage_context = context.Context.storage in
  let smode = Storage.mode storage_context in
  let ctmode = Commit_tree.mode commit_tree in
  if smode <> ctmode then
    Lwt.return_error Conflicting_modes
  else
    let hashf = Hashfunc.make hash_func 32 in
    let t = { storage_context; commit_tree; hashf } in
    match read_additional_commits t with
    | Error _ as e -> Lwt.return e
    | Ok 0 -> Lwt.return_ok t
    | Ok _ ->
        let+= _ = flush t in
        Ok t

let update_reader t =
  match mode t with
  | Reader ->
      let*= tmp = Commit_tree.update_reader t.commit_tree in
      t.commit_tree <- tmp;
      Storage.update_reader t.storage_context
  | _ -> Lwt.return_unit

let parent t entry =
  match entry.parent with
  | None -> Ok None (* entry is genesis *)
  | Some parent ->
      match Commit_tree.find t.commit_tree parent with
      | None -> Error `Not_found (* old entry may not exist *)
      | Some {parent=_grand_parent; index= i} ->
          let ctxt = t.storage_context in
          let (entry, _prev_index) = Commit_storage.read ctxt i in
          Ok (Some entry)

let fold f t acc =
  let*= () = update_reader t in
  Commit_tree.fold (fun h {index=i; parent=_} acc ->
      let ent, _ = Commit_storage.read t.storage_context i in
      assert (ent.hash = h);
      let parent = parent t ent in
      f ent ~parent acc) t.commit_tree acc

let to_list t = fold (fun ent ~parent:_ acc -> Lwt.return (ent::acc)) t []

let read_the_latest { storage_context; _} = Commit_storage.read_the_latest storage_context

let children t =
  let*= () = update_reader t in
  let+= f = Commit_tree.children t.commit_tree in
  fun h ->
    let hents = f h in
    List.map (fun (_, {Commit_tree.index; _}) ->
        fst @@ Commit_storage.read t.storage_context index)
      hents

let geneses t =
  let*= () = update_reader t in
  let+= hents = Commit_tree.geneses t.commit_tree in
  List.map (fun (_, {Commit_tree.index; _}) ->
      fst @@ Commit_storage.read t.storage_context index)
    hents

let ordered_fold f t acc =
  let*= () = update_reader t in
  let commit_tree = t.commit_tree in
  Commit_tree.ordered_fold (fun _ch ent ~children acc ->
      let ent = fst @@ Commit_storage.read t.storage_context ent.index in
      let children =
        List.map (fun (_,ent) ->
            fst @@ Commit_storage.read t.storage_context ent.Commit_tree.index) children
      in
      f ent ~children acc)
    commit_tree acc