chore: Import Nixery from experimental

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

1 files changed, 309 insertions, 0 deletions

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)
+	})))
+}