Module Irmin_traces.Trace_commonSource

Trace_common contains utility to simplify the management of files using the following layout:

- Magic (Magic.t, 8 bytes)
- Version (int32, 4 bytes)
- Length of header (varint, >=1 byte)
- Header (header_t, _ bytes)
- Arbitrary long series of rows, of unspecified length, each prefixed by their length:
  - Length of row (varint, >=1 byte)
  - Row (row_t, _ bytes)

This file is meant to be used from Tezos. OCaml version 4.09 and the 32bit architecture should be supported.

Example

  module Example = struct
    module V2 = struct
      let version = 2

      type header = unit [@@deriving repr]
      type row = [ `A | `B | `C ] [@@deriving repr]
    end

    module V1 = struct
      let version = 1

      type header = unit [@@deriving repr]
      type row = [ `A | `B ] [@@deriving repr]

      let to_v2 x = (x :> V2.row)
    end

    module V0 = struct
      let version = 0

      type header = unit [@@deriving repr]
      type row = [ `A of int | `B of int ] [@@deriving repr]

      let to_v1 = function `A _ -> `A | `B _ -> `B
    end

    module Latest = V2
    include Latest

    include Trace_common.Io (struct
      module Latest = Latest

      let magic = Trace_common.Magic.of_string "Magique_"

      let get_version_converter = function
        | 2 ->
            Trace_common.Version_converter
              {
                header_t = V2.header_t;
                row_t = V2.row_t;
                upgrade_header = Fun.id;
                upgrade_row = Fun.id;
              }
        | 1 ->
            Version_converter
              {
                header_t = V1.header_t;
                row_t = V1.row_t;
                upgrade_header = Fun.id;
                upgrade_row = V1.to_v2;
              }
        | 0 ->
            Version_converter
              {
                header_t = V0.header_t;
                row_t = V0.row_t;
                upgrade_header = Fun.id;
                upgrade_row = (fun x -> V0.to_v1 x |> V1.to_v2);
              }
        | i -> Fmt.invalid_arg "Unknown Example version %d" i
    end)
  end