core/pkgs/build-support/fetchdocker/default.nix

{ stdenv, lib, coreutils, bash, gnutar, writeText }:
let
  stripScheme = builtins.replaceStrings [ "https://" "http://" ] [ "" "" ];
  stripNixStore = s: lib.removePrefix "${builtins.storeDir}/" s;
in { name, registry ? "https://registry-1.docker.io/v2/", repository ? "library"
, imageName, tag, imageLayers, imageConfig
, image ? "${stripScheme registry}/${repository}/${imageName}:${tag}" }:

# Make sure there are *no* slashes in the repository or container
# names since we use these to make the output derivation name for the
# nix-store path.
assert null
  == lib.findFirst (c: "/" == c) null (lib.stringToCharacters repository);
assert null
  == lib.findFirst (c: "/" == c) null (lib.stringToCharacters imageName);

let
  # Abuse paths to collapse possible double slashes
  repoTag0 = builtins.toString
    (/. + "/${stripScheme registry}/${repository}/${imageName}");
  repoTag1 = lib.removePrefix "/" repoTag0;

  layers = builtins.map stripNixStore imageLayers;

  manifest = writeText "manifest.json" (builtins.toJSON [{
    Config = stripNixStore imageConfig;
    Layers = layers;
    RepoTags = [ "${repoTag1}:${tag}" ];
  }]);

  repositories = writeText "repositories"
    (builtins.toJSON { ${repoTag1} = { ${tag} = lib.last layers; }; });

  imageFileStorePaths = writeText "imageFileStorePaths.txt"
    (lib.concatStringsSep "\n" ((lib.unique imageLayers) ++ [ imageConfig ]));
in stdenv.mkDerivation {
  builder = ./fetchdocker-builder.sh;
  buildInputs = [ coreutils ];
  preferLocalBuild = true;

  inherit name imageName repository tag;
  inherit bash gnutar manifest repositories;
  inherit imageFileStorePaths;

  passthru = { inherit image; };
}