20103640fa
As described in issue #14, the registry API does not allow image names with uppercase-characters in them. However, the Nix package set has several top-level keys with uppercase characters in them which could previously not be retrieved using Nixery. This change implements a method for retrieving those keys, but it is explicitly only working for the top-level package set as nested sets (such as `haskellPackages`) often contain packages that differ in case only.
293 lines
11 KiB
Nix
293 lines
11 KiB
Nix
# Copyright 2019 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# https://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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# This file contains a modified version of dockerTools.buildImage that, instead
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# of outputting a single tarball which can be imported into a running Docker
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# daemon, builds a manifest file that can be used for serving the image over a
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# registry API.
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{
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# Image Name
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name,
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# Image tag, the Nix's output hash will be used if null
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tag ? null,
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# Files to put on the image (a nix store path or list of paths).
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contents ? [],
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# Packages to install by name (which must refer to top-level attributes of
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# nixpkgs). This is passed in as a JSON-array in string form.
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packages ? "[]",
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# Optional bash script to run on the files prior to fixturizing the layer.
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extraCommands ? "", uid ? 0, gid ? 0,
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# Docker's lowest maximum layer limit is 42-layers for an old
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# version of the AUFS graph driver. We pick 24 to ensure there is
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# plenty of room for extension. I believe the actual maximum is
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# 128.
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maxLayers ? 24,
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# Configuration for which package set to use when building.
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#
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# Both channels of the public nixpkgs repository as well as imports
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# from private repositories are supported.
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#
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# This setting can be invoked with three different formats:
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#
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# 1. nixpkgs!$channel (e.g. nixpkgs!nixos-19.03)
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# 2. git!$repo!$rev (e.g. git!git@github.com:NixOS/nixpkgs.git!master)
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# 3. path!$path (e.g. path!/var/local/nixpkgs)
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#
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# '!' was chosen as the separator because `builtins.split` does not
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# support regex escapes and there are few other candidates. It
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# doesn't matter much because this is invoked by the server.
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pkgSource ? "nixpkgs!nixos-19.03"
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}:
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let
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# If a nixpkgs channel is requested, it is retrieved from Github (as
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# a tarball) and imported.
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fetchImportChannel = channel:
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let url = "https://github.com/NixOS/nixpkgs-channels/archive/${channel}.tar.gz";
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in import (builtins.fetchTarball url) {};
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# If a git repository is requested, it is retrieved via
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# builtins.fetchGit which defaults to the git configuration of the
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# outside environment. This means that user-configured SSH
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# credentials etc. are going to work as expected.
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fetchImportGit = url: rev:
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let
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# builtins.fetchGit needs to know whether 'rev' is a reference
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# (e.g. a branch/tag) or a revision (i.e. a commit hash)
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#
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# Since this data is being extrapolated from the supplied image
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# tag, we have to guess if we want to avoid specifying a format.
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#
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# There are some additional caveats around whether the default
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# branch contains the specified revision, which need to be
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# explained to users.
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spec = if (builtins.stringLength rev) == 40 then {
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inherit url rev;
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} else {
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inherit url;
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ref = rev;
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};
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in import (builtins.fetchGit spec) {};
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importPath = path: import (builtins.toPath path) {};
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source = builtins.split "!" pkgSource;
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sourceType = builtins.elemAt source 0;
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pkgs = with builtins;
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if sourceType == "nixpkgs"
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then fetchImportChannel (elemAt source 2)
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else if sourceType == "git"
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then fetchImportGit (elemAt source 2) (elemAt source 4)
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else if sourceType == "path"
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then importPath (elemAt source 2)
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else builtins.throw("Invalid package set source specification: ${pkgSource}");
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in
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# Since this is essentially a re-wrapping of some of the functionality that is
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# implemented in the dockerTools, we need all of its components in our top-level
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# namespace.
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with builtins;
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with pkgs;
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with dockerTools;
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let
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tarLayer = "application/vnd.docker.image.rootfs.diff.tar";
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baseName = baseNameOf name;
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# deepFetch traverses the top-level Nix package set to retrieve an item via a
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# path specified in string form.
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#
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# For top-level items, the name of the key yields the result directly. Nested
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# items are fetched by using dot-syntax, as in Nix itself.
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#
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# Due to a restriction of the registry API specification it is not possible to
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# pass uppercase characters in an image name, however the Nix package set
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# makes use of camelCasing repeatedly (for example for `haskellPackages`).
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#
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# To work around this, if no value is found on the top-level a second lookup
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# is done on the package set using lowercase-names. This is not done for
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# nested sets, as they often have keys that only differ in case.
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#
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# For example, `deepFetch pkgs "xorg.xev"` retrieves `pkgs.xorg.xev` and
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# `deepFetch haskellpackages.stylish-haskell` retrieves
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# `haskellPackages.stylish-haskell`.
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deepFetch = with lib; s: n:
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let path = splitString "." n;
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err = { error = "not_found"; pkg = n; };
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# The most efficient way I've found to do a lookup against
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# case-differing versions of an attribute is to first construct a
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# mapping of all lowercased attribute names to their differently cased
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# equivalents.
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#
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# This map is then used for a second lookup if the top-level
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# (case-sensitive) one does not yield a result.
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hasUpper = str: (match ".*[A-Z].*" str) != null;
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allUpperKeys = filter hasUpper (attrNames s);
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lowercased = listToAttrs (map (k: {
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name = toLower k;
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value = k;
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}) allUpperKeys);
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caseAmendedPath = map (v: if hasAttr v lowercased then lowercased."${v}" else v) path;
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fetchLower = attrByPath caseAmendedPath err s;
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in attrByPath path fetchLower s;
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# allContents is the combination of all derivations and store paths passed in
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# directly, as well as packages referred to by name.
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#
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# It accumulates potential errors about packages that could not be found to
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# return this information back to the server.
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allContents =
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# Folds over the results of 'deepFetch' on all requested packages to
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# separate them into errors and content. This allows the program to
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# terminate early and return only the errors if any are encountered.
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let splitter = attrs: res:
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if hasAttr "error" res
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then attrs // { errors = attrs.errors ++ [ res ]; }
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else attrs // { contents = attrs.contents ++ [ res ]; };
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init = { inherit contents; errors = []; };
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fetched = (map (deepFetch pkgs) (fromJSON packages));
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in foldl' splitter init fetched;
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contentsEnv = symlinkJoin {
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name = "bulk-layers";
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paths = allContents.contents;
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};
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# The image build infrastructure expects to be outputting a slightly different
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# format than the one we serve over the registry protocol. To work around its
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# expectations we need to provide an empty JSON file that it can write some
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# fun data into.
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emptyJson = writeText "empty.json" "{}";
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bulkLayers = mkManyPureLayers {
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name = baseName;
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configJson = emptyJson;
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closure = writeText "closure" "${contentsEnv} ${emptyJson}";
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# One layer will be taken up by the customisationLayer, so
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# take up one less.
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maxLayers = maxLayers - 1;
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};
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customisationLayer = mkCustomisationLayer {
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name = baseName;
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contents = contentsEnv;
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baseJson = emptyJson;
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inherit uid gid extraCommands;
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};
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# Inspect the returned bulk layers to determine which layers belong to the
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# image and how to serve them.
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#
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# This computes both an MD5 and a SHA256 hash of each layer, which are used
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# for different purposes. See the registry server implementation for details.
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#
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# Some of this logic is copied straight from `buildLayeredImage`.
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allLayersJson = runCommand "fs-layer-list.json" {
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buildInputs = [ coreutils findutils jq openssl ];
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} ''
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find ${bulkLayers} -mindepth 1 -maxdepth 1 | sort -t/ -k5 -n > layer-list
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echo ${customisationLayer} >> layer-list
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for layer in $(cat layer-list); do
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layerPath="$layer/layer.tar"
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layerSha256=$(sha256sum $layerPath | cut -d ' ' -f1)
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# The server application compares binary MD5 hashes and expects base64
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# encoding instead of hex.
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layerMd5=$(openssl dgst -md5 -binary $layerPath | openssl enc -base64)
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layerSize=$(wc -c $layerPath | cut -d ' ' -f1)
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jq -n -c --arg sha256 $layerSha256 --arg md5 $layerMd5 --arg size $layerSize --arg path $layerPath \
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'{ size: ($size | tonumber), sha256: $sha256, md5: $md5, path: $path }' >> fs-layers
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done
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cat fs-layers | jq -s -c '.' > $out
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'';
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allLayers = fromJSON (readFile allLayersJson);
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# Image configuration corresponding to the OCI specification for the file type
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# 'application/vnd.oci.image.config.v1+json'
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config = {
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architecture = "amd64";
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os = "linux";
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rootfs.type = "layers";
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rootfs.diff_ids = map (layer: "sha256:${layer.sha256}") allLayers;
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# Required to let Kubernetes import Nixery images
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config = {};
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};
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configJson = writeText "${baseName}-config.json" (toJSON config);
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configMetadata = fromJSON (readFile (runCommand "config-meta" {
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buildInputs = [ jq openssl ];
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} ''
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size=$(wc -c ${configJson} | cut -d ' ' -f1)
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sha256=$(sha256sum ${configJson} | cut -d ' ' -f1)
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md5=$(openssl dgst -md5 -binary ${configJson} | openssl enc -base64)
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jq -n -c --arg size $size --arg sha256 $sha256 --arg md5 $md5 \
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'{ size: ($size | tonumber), sha256: $sha256, md5: $md5 }' \
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>> $out
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''));
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# Corresponds to the manifest JSON expected by the Registry API.
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#
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# This is Docker's "Image Manifest V2, Schema 2":
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# https://docs.docker.com/registry/spec/manifest-v2-2/
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manifest = {
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schemaVersion = 2;
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mediaType = "application/vnd.docker.distribution.manifest.v2+json";
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config = {
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mediaType = "application/vnd.docker.container.image.v1+json";
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size = configMetadata.size;
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digest = "sha256:${configMetadata.sha256}";
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};
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layers = map (layer: {
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mediaType = tarLayer;
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digest = "sha256:${layer.sha256}";
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size = layer.size;
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}) allLayers;
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};
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# This structure maps each layer digest to the actual tarball that will need
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# to be served. It is used by the controller to cache the paths during a pull.
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layerLocations = {
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"${configMetadata.sha256}" = {
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path = configJson;
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md5 = configMetadata.md5;
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};
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} // (listToAttrs (map (layer: {
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name = "${layer.sha256}";
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value = {
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path = layer.path;
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md5 = layer.md5;
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};
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}) allLayers));
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# Final output structure returned to the controller in the case of a
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# successful build.
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manifestOutput = {
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inherit manifest layerLocations;
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};
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# Output structure returned if errors occured during the build. Currently the
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# only error type that is returned in a structured way is 'not_found'.
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errorOutput = {
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error = "not_found";
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pkgs = map (err: err.pkg) allContents.errors;
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};
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in writeText "manifest-output.json" (if (length allContents.errors) == 0
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then toJSON (trace manifestOutput manifestOutput)
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else toJSON (trace errorOutput errorOutput)
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)
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