refactor(nixery): Modernise structure of binaries r/4106

Nixery is going to gain a new binary (used for building images without
a registry server); to prepare for this the server binary has moved to
cmd/server and the Nix build logic has been updated to wrap this
binary and set the required environment variables.

Change-Id: I9b4f49f47872ae76430463e2fcb8f68114070f72
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5603
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

1 files changed, 281 insertions, 0 deletions

diff --git a/tools/nixery/cmd/server/main.go b/tools/nixery/cmd/server/main.go
new file mode 100644
index 0000000000..8fe1679cfa
--- /dev/null
+++ b/tools/nixery/cmd/server/main.go
@@ -0,0 +1,281 @@
+// Copyright 2022 The TVL Contributors
+// SPDX-License-Identifier: Apache-2.0
+
+// The nixery server implements 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.
+package main
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"regexp"
+
+	"github.com/google/nixery/builder"
+	"github.com/google/nixery/config"
+	"github.com/google/nixery/layers"
+	"github.com/google/nixery/logs"
+	mf "github.com/google/nixery/manifest"
+	"github.com/google/nixery/storage"
+	log "github.com/sirupsen/logrus"
+)
+
+// ManifestMediaType is 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"
+
+// This variable will be initialised during the build process and set
+// to the hash of the entire Nixery source tree.
+var version string = "devel"
+
+// Regexes matching the V2 Registry API routes. This only includes the
+// routes required for serving images, since pushing and other such
+// functionality is not available.
+var (
+	manifestRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/manifests/([\w|\-|\.|\_]+)$`)
+	blobRegex     = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/(blobs|manifests)/sha256:(\w+)$`)
+)
+
+// Downloads the popularity information for the package set from the
+// URL specified in Nixery's configuration.
+func downloadPopularity(url string) (layers.Popularity, error) {
+	resp, err := http.Get(url)
+	if err != nil {
+		return nil, err
+	}
+
+	if resp.StatusCode != 200 {
+		return nil, fmt.Errorf("popularity download from '%s' returned status: %s\n", url, resp.Status)
+	}
+
+	j, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var pop layers.Popularity
+	err = json.Unmarshal(j, &pop)
+	if err != nil {
+		return nil, err
+	}
+
+	return pop, nil
+}
+
+// Error format corresponding to the registry protocol V2 specification. This
+// allows feeding back errors to clients in a way that can be presented to
+// users.
+type registryError struct {
+	Code    string `json:"code"`
+	Message string `json:"message"`
+}
+
+type registryErrors struct {
+	Errors []registryError `json:"errors"`
+}
+
+func writeError(w http.ResponseWriter, status int, code, message string) {
+	err := registryErrors{
+		Errors: []registryError{
+			{code, message},
+		},
+	}
+	json, _ := json.Marshal(err)
+
+	w.WriteHeader(status)
+	w.Header().Add("Content-Type", "application/json")
+	w.Write(json)
+}
+
+type registryHandler struct {
+	state *builder.State
+}
+
+// Serve a manifest by tag, building it via Nix and populating caches
+// if necessary.
+func (h *registryHandler) serveManifestTag(w http.ResponseWriter, r *http.Request, name string, tag string) {
+	log.WithFields(log.Fields{
+		"image": name,
+		"tag":   tag,
+	}).Info("requesting image manifest")
+
+	image := builder.ImageFromName(name, tag)
+	buildResult, err := builder.BuildImage(r.Context(), h.state, &image)
+
+	if err != nil {
+		writeError(w, 500, "UNKNOWN", "image build failure")
+
+		log.WithError(err).WithFields(log.Fields{
+			"image": name,
+			"tag":   tag,
+		}).Error("failed to build image manifest")
+
+		return
+	}
+
+	// Some error types have special handling, which is applied
+	// here.
+	if buildResult.Error == "not_found" {
+		s := fmt.Sprintf("Could not find Nix packages: %v", buildResult.Pkgs)
+		writeError(w, 404, "MANIFEST_UNKNOWN", s)
+
+		log.WithFields(log.Fields{
+			"image":    name,
+			"tag":      tag,
+			"packages": buildResult.Pkgs,
+		}).Warn("could not find Nix packages")
+
+		return
+	}
+
+	// This marshaling error is ignored because we know that this
+	// field represents valid JSON data.
+	manifest, _ := json.Marshal(buildResult.Manifest)
+	w.Header().Add("Content-Type", manifestMediaType)
+
+	// The manifest needs to be persisted to the blob storage (to become
+	// available for clients that fetch manifests by their hash, e.g.
+	// containerd) and served to the client.
+	//
+	// Since we have no stable key to address this manifest (it may be
+	// uncacheable, yet still addressable by blob) we need to separate
+	// out the hashing, uploading and serving phases. The latter is
+	// especially important as clients may start to fetch it by digest
+	// as soon as they see a response.
+	sha256sum := fmt.Sprintf("%x", sha256.Sum256(manifest))
+	path := "layers/" + sha256sum
+	ctx := context.TODO()
+
+	_, _, err = h.state.Storage.Persist(ctx, path, mf.ManifestType, func(sw io.Writer) (string, int64, error) {
+		// We already know the hash, so no additional hash needs to be
+		// constructed here.
+		written, err := sw.Write(manifest)
+		return sha256sum, int64(written), err
+	})
+
+	if err != nil {
+		writeError(w, 500, "MANIFEST_UPLOAD", "could not upload manifest to blob store")
+
+		log.WithError(err).WithFields(log.Fields{
+			"image": name,
+			"tag":   tag,
+		}).Error("could not upload manifest")
+
+		return
+	}
+
+	w.Write(manifest)
+}
+
+// serveBlob serves a blob from storage by digest
+func (h *registryHandler) serveBlob(w http.ResponseWriter, r *http.Request, blobType, digest string) {
+	storage := h.state.Storage
+	err := storage.Serve(digest, r, w)
+	if err != nil {
+		log.WithError(err).WithFields(log.Fields{
+			"type":    blobType,
+			"digest":  digest,
+			"backend": storage.Name(),
+		}).Error("failed to serve blob from storage backend")
+	}
+}
+
+// ServeHTTP dispatches HTTP requests to the matching handlers.
+func (h *registryHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Acknowledge that we speak V2 with an empty response
+	if r.RequestURI == "/v2/" {
+		return
+	}
+
+	// Build & serve a manifest by tag
+	manifestMatches := manifestRegex.FindStringSubmatch(r.RequestURI)
+	if len(manifestMatches) == 3 {
+		h.serveManifestTag(w, r, manifestMatches[1], manifestMatches[2])
+		return
+	}
+
+	// Serve a blob by digest
+	layerMatches := blobRegex.FindStringSubmatch(r.RequestURI)
+	if len(layerMatches) == 4 {
+		h.serveBlob(w, r, layerMatches[2], layerMatches[3])
+		return
+	}
+
+	log.WithField("uri", r.RequestURI).Info("unsupported registry route")
+
+	w.WriteHeader(404)
+}
+
+func main() {
+	logs.Init(version)
+	cfg, err := config.FromEnv()
+	if err != nil {
+		log.WithError(err).Fatal("failed to load configuration")
+	}
+
+	var s storage.Backend
+
+	switch cfg.Backend {
+	case config.GCS:
+		s, err = storage.NewGCSBackend()
+	case config.FileSystem:
+		s, err = storage.NewFSBackend()
+	}
+	if err != nil {
+		log.WithError(err).Fatal("failed to initialise storage backend")
+	}
+
+	log.WithField("backend", s.Name()).Info("initialised storage backend")
+
+	cache, err := builder.NewCache()
+	if err != nil {
+		log.WithError(err).Fatal("failed to instantiate build cache")
+	}
+
+	var pop layers.Popularity
+	if cfg.PopUrl != "" {
+		pop, err = downloadPopularity(cfg.PopUrl)
+		if err != nil {
+			log.WithError(err).WithField("popURL", cfg.PopUrl).
+				Fatal("failed to fetch popularity information")
+		}
+	}
+
+	state := builder.State{
+		Cache:   &cache,
+		Cfg:     cfg,
+		Pop:     pop,
+		Storage: s,
+	}
+
+	log.WithFields(log.Fields{
+		"version": version,
+		"port":    cfg.Port,
+	}).Info("starting Nixery")
+
+	// All /v2/ requests belong to the registry handler.
+	http.Handle("/v2/", &registryHandler{
+		state: &state,
+	})
+
+	// All other roots are served by the static file server.
+	webDir := http.Dir(cfg.WebDir)
+	http.Handle("/", http.FileServer(webDir))
+
+	log.Fatal(http.ListenAndServe(":"+cfg.Port, nil))
+}