chore: Import Nixery from experimental

Moves the existing Nixery code base to a git repository and switches
to public equivalents of libraries used.

5 files changed, 679 insertions, 0 deletions

diff --git a/tools/nixery/README.md b/tools/nixery/README.md
new file mode 100644
index 0000000000..6b1db46964
--- /dev/null
+++ b/tools/nixery/README.md
@@ -0,0 +1,99 @@
+# Nixery
+
+This package implements a Docker-compatible container registry that is capable
+of transparently building and serving container images using [Nix][].
+
+The project started out with the intention of becoming a Kubernetes controller
+that can serve declarative image specifications specified in CRDs as container
+images. The design for this is outlined in [a public gist][gist].
+
+Currently it focuses on the ad-hoc creation of container images as outlined
+below with an example instance available at
+[nixery.appspot.com](https://nixery.appspot.com).
+
+This is not an officially supported Google project.
+
+## Ad-hoc container images
+
+Nixery supports building images on-demand based on the *image name*. Every
+package that the user intends to include in the image is specified as a path
+component of the image name.
+
+The path components refer to top-level keys in `nixpkgs` and are used to build a
+container image using Nix's [buildLayeredImage][] functionality.
+
+The special meta-package `shell` provides an image base with many core
+components (such as `bash` and `coreutils`) that users commonly expect in
+interactive images.
+
+## Usage example
+
+Using the publicly available Nixery instance at `nixery.appspot.com`, one could
+retrieve a container image containing `curl` and an interactive shell like this:
+
+```shell
+tazjin@tazbox:~$ sudo docker run -ti nixery.appspot.com/shell/curl bash
+Unable to find image 'nixery.appspot.com/shell/curl:latest' locally
+latest: Pulling from shell/curl
+7734b79e1ba1: Already exists
+b0d2008d18cd: Pull complete
+< ... some layers omitted ...>
+Digest: sha256:178270bfe84f74548b6a43347d73524e5c2636875b673675db1547ec427cf302
+Status: Downloaded newer image for nixery.appspot.com/shell/curl:latest
+bash-4.4# curl --version
+curl 7.64.0 (x86_64-pc-linux-gnu) libcurl/7.64.0 OpenSSL/1.0.2q zlib/1.2.11 libssh2/1.8.0 nghttp2/1.35.1
+```
+
+## Known issues
+
+*   Initial build times for an image can be somewhat slow while Nixery retrieves
+    the required derivations from the Nix cache under-the-hood.
+
+    Due to how the Docker Registry API works, there is no way to provide
+    feedback to the user during this period - hence the UX (in interactive mode)
+    is currently that "nothing is happening" for a while after the `Unable to
+    find image` message is printed.
+
+*   For some reason these images do not currently work in GKE clusters.
+    Launching a Kubernetes pod that uses a Nixery image results in an error
+    stating `unable to convert a nil pointer to a runtime API image:
+    ImageInspectError`.
+
+    This error comes from
+    [here](https://github.com/kubernetes/kubernetes/blob/master/pkg/kubelet/dockershim/convert.go#L35)
+    and it occurs *after* the Kubernetes node has retrieved the image from
+    Nixery (as per the Nixery logs).
+
+## Kubernetes integration (in the future)
+
+**Note**: The Kubernetes integration is not yet implemented.
+
+The basic idea of the Kubernetes integration is to provide a way for users to
+specify the contents of a container image as an API object in Kubernetes which
+will be transparently built by Nix when the container is started up.
+
+For example, given a resource that looks like this:
+
+```yaml
+---
+apiVersion: k8s.nixos.org/v1alpha
+kind: NixImage
+metadata:
+  name: curl-and-jq
+data:
+  tag: v1
+  contents:
+    - curl
+    - jq
+    - bash
+```
+
+One could create a container that references the `curl-and-jq` image, which will
+then be created by Nix when the container image is pulled.
+
+The controller itself runs as a daemonset on every node in the cluster,
+providing a host-mounted `/nix/store`-folder for caching purposes.
+
+[Nix]: https://nixos.org/
+[gist]: https://gist.github.com/tazjin/08f3d37073b3590aacac424303e6f745
+[buildLayeredImage]: https://grahamc.com/blog/nix-and-layered-docker-images
diff --git a/tools/nixery/app.yaml b/tools/nixery/app.yaml
new file mode 100644
index 0000000000..223fa75829
--- /dev/null
+++ b/tools/nixery/app.yaml
@@ -0,0 +1,14 @@
+env: flex
+runtime: custom
+
+resources:
+  cpu: 2
+  memory_gb: 4
+  disk_size_gb: 50
+
+automatic_scaling:
+  max_num_instances: 3
+  cool_down_period_sec: 60
+
+env_variables:
+  BUCKET: "nixery-layers"
diff --git a/tools/nixery/build-registry-image.nix b/tools/nixery/build-registry-image.nix
new file mode 100644
index 0000000000..11030d38a5
--- /dev/null
+++ b/tools/nixery/build-registry-image.nix
@@ -0,0 +1,167 @@
+# This file contains a modified version of dockerTools.buildImage that, instead
+# of outputting a single tarball which can be imported into a running Docker
+# daemon, builds a manifest file that can be used for serving the image over a
+# registry API.
+
+{
+  # Image Name
+  name,
+  # Image tag, the Nix's output hash will be used if null
+  tag ? null,
+  # Files to put on the image (a nix store path or list of paths).
+  contents ? [],
+  # Packages to install by name (which must refer to top-level attributes of
+  # nixpkgs). This is passed in as a JSON-array in string form.
+  packages ? "[]",
+  # Optional bash script to run on the files prior to fixturizing the layer.
+  extraCommands ? "", uid ? 0, gid ? 0,
+  # Docker's lowest maximum layer limit is 42-layers for an old
+  # version of the AUFS graph driver. We pick 24 to ensure there is
+  # plenty of room for extension. I believe the actual maximum is
+  # 128.
+  maxLayers ? 24,
+  # Nix package set to use
+  pkgs ? (import <nixpkgs> {})
+}:
+
+# Since this is essentially a re-wrapping of some of the functionality that is
+# implemented in the dockerTools, we need all of its components in our top-level
+# namespace.
+with pkgs;
+with dockerTools;
+
+let
+  tarLayer = "application/vnd.docker.image.rootfs.diff.tar";
+  baseName = baseNameOf name;
+
+  # deepFetch traverses the top-level Nix package set to retrieve an item via a
+  # path specified in string form.
+  #
+  # For top-level items, the name of the key yields the result directly. Nested
+  # items are fetched by using dot-syntax, as in Nix itself.
+  #
+  # For example, `deepFetch pkgs "xorg.xev"` retrieves `pkgs.xorg.xev`.
+  deepFetch = s: n:
+    let path = lib.strings.splitString "." n;
+        err = builtins.throw "Could not find '${n}' in package set";
+    in lib.attrsets.attrByPath path err s;
+
+  # allContents is the combination of all derivations and store paths passed in
+  # directly, as well as packages referred to by name.
+  allContents = contents ++ (map (deepFetch pkgs) (builtins.fromJSON packages));
+
+  contentsEnv = symlinkJoin {
+    name = "bulk-layers";
+    paths = allContents;
+  };
+
+  # The image build infrastructure expects to be outputting a slightly different
+  # format than the one we serve over the registry protocol. To work around its
+  # expectations we need to provide an empty JSON file that it can write some
+  # fun data into.
+  emptyJson = writeText "empty.json" "{}";
+
+  bulkLayers = mkManyPureLayers {
+    name = baseName;
+    configJson = emptyJson;
+    closure = writeText "closure" "${contentsEnv} ${emptyJson}";
+    # One layer will be taken up by the customisationLayer, so
+    # take up one less.
+    maxLayers = maxLayers - 1;
+  };
+
+  customisationLayer = mkCustomisationLayer {
+    name = baseName;
+    contents = contentsEnv;
+    baseJson = emptyJson;
+    inherit uid gid extraCommands;
+  };
+
+  # Inspect the returned bulk layers to determine which layers belong to the
+  # image and how to serve them.
+  #
+  # This computes both an MD5 and a SHA256 hash of each layer, which are used
+  # for different purposes. See the registry server implementation for details.
+  #
+  # Some of this logic is copied straight from `buildLayeredImage`.
+  allLayersJson = runCommand "fs-layer-list.json" {
+    buildInputs = [ coreutils findutils jq openssl ];
+  } ''
+      find ${bulkLayers} -mindepth 1 -maxdepth 1 | sort -t/ -k5 -n > layer-list
+      echo ${customisationLayer} >> layer-list
+
+      for layer in $(cat layer-list); do
+        layerPath="$layer/layer.tar"
+        layerSha256=$(sha256sum $layerPath | cut -d ' ' -f1)
+        # The server application compares binary MD5 hashes and expects base64
+        # encoding instead of hex.
+        layerMd5=$(openssl dgst -md5 -binary $layerPath | openssl enc -base64)
+        layerSize=$(wc -c $layerPath | cut -d ' ' -f1)
+
+        jq -n -c --arg sha256 $layerSha256 --arg md5 $layerMd5 --arg size $layerSize --arg path $layerPath \
+          '{ size: ($size | tonumber), sha256: $sha256, md5: $md5, path: $path }' >> fs-layers
+      done
+
+      cat fs-layers | jq -s -c '.' > $out
+  '';
+  allLayers = builtins.fromJSON (builtins.readFile allLayersJson);
+
+  # Image configuration corresponding to the OCI specification for the file type
+  # 'application/vnd.oci.image.config.v1+json'
+  config = {
+    architecture = "amd64";
+    os = "linux";
+    rootfs.type = "layers";
+    rootfs.diff_ids = map (layer: "sha256:${layer.sha256}") allLayers;
+  };
+  configJson = writeText "${baseName}-config.json" (builtins.toJSON config);
+  configMetadata = with builtins; fromJSON (readFile (runCommand "config-meta" {
+    buildInputs = [ jq openssl ];
+  } ''
+    size=$(wc -c ${configJson} | cut -d ' ' -f1)
+    sha256=$(sha256sum ${configJson} | cut -d ' ' -f1)
+    md5=$(openssl dgst -md5 -binary $layerPath | openssl enc -base64)
+    jq -n -c --arg size $size --arg sha256 $sha256 --arg md5 $md5 \
+      '{ size: ($size | tonumber), sha256: $sha256, md5: $md5 }' \
+      >> $out
+  ''));
+
+  # Corresponds to the manifest JSON expected by the Registry API.
+  #
+  # This is Docker's "Image Manifest V2, Schema 2":
+  #   https://docs.docker.com/registry/spec/manifest-v2-2/
+  manifest = {
+    schemaVersion = 2;
+    mediaType = "application/vnd.docker.distribution.manifest.v2+json";
+
+    config = {
+      mediaType = "application/vnd.docker.container.image.v1+json";
+      size = configMetadata.size;
+      digest = "sha256:${configMetadata.sha256}";
+    };
+
+    layers = map (layer: {
+      mediaType = tarLayer;
+      digest = "sha256:${layer.sha256}";
+      size = layer.size;
+    }) allLayers;
+  };
+
+  # This structure maps each layer digest to the actual tarball that will need
+  # to be served. It is used by the controller to cache the paths during a pull.
+  layerLocations = {
+      "${configMetadata.sha256}" = {
+        path = configJson;
+        md5 = configMetadata.md5;
+      };
+    } // (builtins.listToAttrs (map (layer: {
+      name  = "${layer.sha256}";
+      value = {
+        path = layer.path;
+        md5 = layer.md5;
+      };
+    }) allLayers));
+
+in writeText "manifest-output.json" (builtins.toJSON {
+  inherit manifest layerLocations;
+})
diff --git a/tools/nixery/index.html b/tools/nixery/index.html
new file mode 100644
index 0000000000..ebec9968c0
--- /dev/null
+++ b/tools/nixery/index.html
@@ -0,0 +1,90 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+    <title>Nixery</title>
+    <style>
+      body {
+        margin: 40px auto;
+        max-width: 650px;
+        line-height: 1.6;
+        font-size: 18px;
+        color: #444;
+        padding: 010px
+      }
+
+      h1, h2, h3 {
+        line-height: 1.2
+      }
+    </style>
+  </head>
+  <body>
+    <header>
+      <h1>Nixery</h1>
+      <aside>ad-hoc container images - powered by <a href="https://nixos.org/nix/">Nix</a></aside>
+    </header>
+    <h3>What is this?</h3>
+    <p>
+      Nixery provides the ability to pull ad-hoc container images from a Docker-compatible registry
+      server. The image names specify the contents the image should contain, which are then
+      retrieved and built by the Nix package manager.
+    </p>
+    <p>
+      Nix is also responsible for the creation of the container images themselves. To do this it
+      uses an interesting layering strategy described in
+      <a href="https://grahamc.com/blog/nix-and-layered-docker-images">this blog post</a>.
+    </p>
+    <h3>How does it work?</h3>
+    <p>
+      Simply point your local Docker installation (or other compatible registry client) at Nixery
+      and ask for an image with the contents you desire. Image contents are path separated in the
+      name, so for example if you needed an image that contains a shell and <code>emacs</code> you
+      could pull it as such:
+    </p>
+    <p>
+      <code>nixery.appspot.com/shell/emacs25-nox</code>
+    </p>
+    <p>
+      Image tags are currently <i>ignored</i>. Every package name needs to correspond to a key in the
+      <a href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/all-packages.nix">nixpkgs package set</a>.
+    </p>
+    <p>
+      There are some special <i>meta-packages</i> which you <strong>must</strong> specify as the
+      first package in an image. These are:
+    </p>
+    <ul>
+      <li><code>shell</code>: Provides default packages you would expect in an interactive environment</li>
+      <li><code>builder</code>: Provides the above as well as Nix's standard build environment</li>
+    </ul>
+    <p>
+      Hence if you needed an interactive image with, for example, <code>htop</code> installed you
+      could run <code>docker run -ti nixery.appspot.com/shell/htop bash</code>.
+    </p>
+    <h3>FAQ</h3>
+    <p>
+      Technically speaking none of these are frequently-asked questions (because no questions have
+      been asked so far), but I'm going to take a guess at a few anyways:
+    </p>
+    <ul>
+      <li>
+        <strong>Where is the source code for this?</strong>
+        <br>
+        Not yet public, sorry. Check back later(tm).
+      </li>
+      <li>
+        <strong>Which revision of <code>nixpkgs</code> is used?</strong>
+        <br>
+        Currently whatever was <code>HEAD</code> at the time I deployed this. One idea I've had is
+        to let users specify tags on images that correspond to commits in nixpkgs, however there is
+        some potential for abuse there (e.g. by triggering lots of builds on commits that have
+        broken Hydra builds) and I don't want to deal with that yet.
+      </li>
+      <li>
+        <strong>Who made this?</strong>
+        <br>
+        <a href="https://twitter.com/tazjin">@tazjin</a>
+      </li>
+    </ul>
+  </body>
+</html>
diff --git a/tools/nixery/main.go b/tools/nixery/main.go
new file mode 100644
index 0000000000..29b22f3018
--- /dev/null
+++ b/tools/nixery/main.go
@@ -0,0 +1,309 @@
+// Package main provides the implementation of a container registry that
+// transparently builds container images based on Nix derivations.
+//
+// The Nix derivation used for image creation is responsible for creating
+// objects that are compatible with the registry API. The targeted registry
+// protocol is currently Docker's.
+//
+// When an image is requested, the required contents are parsed out of the
+// request and a Nix-build is initiated that eventually responds with the
+// manifest as well as information linking each layer digest to a local
+// filesystem path.
+//
+// Nixery caches the filesystem paths and returns the manifest to the client.
+// Subsequent requests for layer content per digest are then fulfilled by
+// serving the files from disk.
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"regexp"
+	"strings"
+
+	"cloud.google.com/go/storage"
+)
+
+// ManifestMediaType stores the Content-Type used for the manifest itself. This
+// corresponds to the "Image Manifest V2, Schema 2" described on this page:
+//
+// https://docs.docker.com/registry/spec/manifest-v2-2/
+const ManifestMediaType string = "application/vnd.docker.distribution.manifest.v2+json"
+
+// Image represents the information necessary for building a container image. This can
+// be either a list of package names (corresponding to keys in the nixpkgs set) or a
+// Nix expression that results in a *list* of derivations.
+type image struct {
+	// Name of the container image.
+	name string
+
+	// Names of packages to include in the image. These must correspond directly to
+	// top-level names of Nix packages in the nixpkgs tree.
+	packages []string
+}
+
+// BuildResult represents the output of calling the Nix derivation responsible for building
+// registry images.
+//
+// The `layerLocations` field contains the local filesystem paths to each individual image layer
+// that will need to be served, while the `manifest` field contains the JSON-representation of
+// the manifest that needs to be served to the client.
+//
+// The later field is simply treated as opaque JSON and passed through.
+type BuildResult struct {
+	Manifest       json.RawMessage `json:"manifest"`
+	LayerLocations map[string]struct {
+		Path string `json:"path"`
+		Md5  []byte `json:"md5"`
+	} `json:"layerLocations"`
+}
+
+// imageFromName parses an image name into the corresponding structure which can
+// be used to invoke Nix.
+//
+// It will expand convenience names under the hood (see the `convenienceNames` function below).
+func imageFromName(name string) image {
+	packages := strings.Split(name, "/")
+	return image{
+		name:     name,
+		packages: convenienceNames(packages),
+	}
+}
+
+// convenienceNames expands convenience package names defined by Nixery which let users
+// include commonly required sets of tools in a container quickly.
+//
+// Convenience names must be specified as the first package in an image.
+//
+// Currently defined convenience names are:
+//
+// * `shell`: Includes bash, coreutils and other common command-line tools
+// * `builder`: Includes the standard build environment, as well as everything from `shell`
+func convenienceNames(packages []string) []string {
+	shellPackages := []string{"bashInteractive", "coreutils", "moreutils", "nano"}
+	builderPackages := append(shellPackages, "stdenv")
+
+	if packages[0] == "shell" {
+		return append(packages[1:], shellPackages...)
+	} else if packages[0] == "builder" {
+		return append(packages[1:], builderPackages...)
+	} else {
+		return packages
+	}
+}
+
+// Call out to Nix and request that an image be built. Nix will, upon success, return
+// a manifest for the container image.
+func buildImage(image *image, ctx *context.Context, bucket *storage.BucketHandle) ([]byte, error) {
+	// This file is made available at runtime via Blaze. See the `data` declaration in `BUILD`
+	nixPath := "experimental/users/tazjin/nixery/build-registry-image.nix"
+
+	packages, err := json.Marshal(image.packages)
+	if err != nil {
+		return nil, err
+	}
+
+	cmd := exec.Command("nix-build", "--no-out-link", "--show-trace", "--argstr", "name", image.name, "--argstr", "packages", string(packages), nixPath)
+
+	outpipe, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, err
+	}
+
+	errpipe, err := cmd.StderrPipe()
+	if err != nil {
+		return nil, err
+	}
+
+	if err = cmd.Start(); err != nil {
+		log.Println("Error starting nix-build:", err)
+		return nil, err
+	}
+	log.Printf("Started Nix image build for ''%s'", image.name)
+
+	stdout, _ := ioutil.ReadAll(outpipe)
+	stderr, _ := ioutil.ReadAll(errpipe)
+
+	if err = cmd.Wait(); err != nil {
+		// TODO(tazjin): Propagate errors upwards in a usable format.
+		log.Printf("nix-build execution error: %s\nstdout: %s\nstderr: %s\n", err, stdout, stderr)
+		return nil, err
+	}
+
+	log.Println("Finished Nix image build")
+
+	buildOutput, err := ioutil.ReadFile(strings.TrimSpace(string(stdout)))
+	if err != nil {
+		return nil, err
+	}
+
+	// The build output returned by Nix is deserialised to add all contained layers to the
+	// bucket. Only the manifest itself is re-serialised to JSON and returned.
+	var result BuildResult
+	err = json.Unmarshal(buildOutput, &result)
+	if err != nil {
+		return nil, err
+	}
+
+	for layer, meta := range result.LayerLocations {
+		err = uploadLayer(ctx, bucket, layer, meta.Path, meta.Md5)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return json.Marshal(result.Manifest)
+}
+
+// uploadLayer uploads a single layer to Cloud Storage bucket. Before writing any data
+// the bucket is probed to see if the file already exists.
+//
+// If the file does exist, its MD5 hash is verified to ensure that the stored file is
+// not - for example - a fragment of a previous, incomplete upload.
+func uploadLayer(ctx *context.Context, bucket *storage.BucketHandle, layer string, path string, md5 []byte) error {
+	layerKey := fmt.Sprintf("layers/%s", layer)
+	obj := bucket.Object(layerKey)
+
+	// Before uploading a layer to the bucket, probe whether it already exists.
+	//
+	// If it does and the MD5 checksum matches the expected one, the layer upload
+	// can be skipped.
+	attrs, err := obj.Attrs(*ctx)
+
+	if err == nil && bytes.Equal(attrs.MD5, md5) {
+		log.Printf("Layer sha256:%s already exists in bucket, skipping upload", layer)
+	} else {
+		writer := obj.NewWriter(*ctx)
+		file, err := os.Open(path)
+
+		if err != nil {
+			return fmt.Errorf("failed to open layer %s from path %s: %v", layer, path, err)
+		}
+
+		size, err := io.Copy(writer, file)
+		if err != nil {
+			return fmt.Errorf("failed to write layer %s to Cloud Storage: %v", layer, err)
+		}
+
+		if err = writer.Close(); err != nil {
+			return fmt.Errorf("failed to write layer %s to Cloud Storage: %v", layer, err)
+		}
+
+		log.Printf("Uploaded layer sha256:%s (%v bytes written)\n", layer, size)
+	}
+
+	return nil
+}
+
+// layerRedirect constructs the public URL of the layer object in the Cloud Storage bucket
+// and redirects the client there.
+//
+// The Docker client is known to follow redirects, but this might not be true for all other
+// registry clients.
+func layerRedirect(w http.ResponseWriter, bucket string, digest string) {
+	log.Printf("Redirecting layer '%s' request to bucket '%s'\n", digest, bucket)
+	url := fmt.Sprintf("https://storage.googleapis.com/%s/layers/%s", bucket, digest)
+	w.Header().Set("Location", url)
+	w.WriteHeader(303)
+}
+
+// prepareBucket configures the handle to a Cloud Storage bucket in which individual layers will be
+// stored after Nix builds. Nixery does not directly serve layers to registry clients, instead it
+// redirects them to the public URLs of the Cloud Storage bucket.
+//
+// The bucket is required for Nixery to function correctly, hence fatal errors are generated in case
+// it fails to be set up correctly.
+func prepareBucket(ctx *context.Context, bucket string) *storage.BucketHandle {
+	client, err := storage.NewClient(*ctx)
+	if err != nil {
+		log.Fatalln("Failed to set up Cloud Storage client:", err)
+	}
+
+	bkt := client.Bucket(bucket)
+
+	if _, err := bkt.Attrs(*ctx); err != nil {
+		log.Fatalln("Could not access configured bucket", err)
+	}
+
+	return bkt
+}
+
+var manifestRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/manifests/(\w+)$`)
+var layerRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/blobs/sha256:(\w+)$`)
+
+func main() {
+	bucketName := os.Getenv("BUCKET")
+	if bucketName == "" {
+		log.Fatalln("GCS bucket for layer storage must be specified")
+	}
+
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "5726"
+	}
+
+	ctx := context.Background()
+	bucket := prepareBucket(&ctx, bucketName)
+
+	log.Printf("Starting Kubernetes Nix controller on port %s\n", port)
+
+	log.Fatal(http.ListenAndServe(":"+port, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// When running on AppEngine, HTTP traffic should be redirected to HTTPS.
+		//
+		// This is achieved here by enforcing HSTS (with a one week duration) on responses.
+		if r.Header.Get("X-Forwarded-Proto") == "http" && strings.Contains(r.Host, "appspot.com") {
+			w.Header().Add("Strict-Transport-Security", "max-age=604800")
+		}
+
+		// Serve an index page to anyone who visits the registry's base URL:
+		if r.RequestURI == "/" {
+			index, _ := ioutil.ReadFile("experimental/users/tazjin/nixery/index.html")
+			w.Header().Add("Content-Type", "text/html")
+			w.Write(index)
+			return
+		}
+
+		// Acknowledge that we speak V2
+		if r.RequestURI == "/v2/" {
+			fmt.Fprintln(w)
+			return
+		}
+
+		// Serve the manifest (straight from Nix)
+		manifestMatches := manifestRegex.FindStringSubmatch(r.RequestURI)
+		if len(manifestMatches) == 3 {
+			imageName := manifestMatches[1]
+			log.Printf("Requesting manifest for image '%s'", imageName)
+			image := imageFromName(manifestMatches[1])
+			manifest, err := buildImage(&image, &ctx, bucket)
+
+			if err != nil {
+				log.Println("Failed to build image manifest", err)
+				return
+			}
+
+			w.Header().Add("Content-Type", ManifestMediaType)
+			w.Write(manifest)
+			return
+		}
+
+		// Serve an image layer. For this we need to first ask Nix for the
+		// manifest, then proceed to extract the correct layer from it.
+		layerMatches := layerRegex.FindStringSubmatch(r.RequestURI)
+		if len(layerMatches) == 3 {
+			digest := layerMatches[2]
+			layerRedirect(w, bucketName, digest)
+			return
+		}
+
+		w.WriteHeader(404)
+	})))
+}