refactor(server): Introduce pluggable interface for storage backends

This abstracts over the functionality of Google Cloud Storage and
other potential underlying storage backends to make it possible to
replace these in Nixery.

The GCS backend is not yet reimplemented.

1 files changed, 9 insertions, 57 deletions

diff --git a/tools/nixery/server/main.go b/tools/nixery/server/main.go
index f38fab2f2abd..22ed6f1a5e2c 100644
--- a/tools/nixery/server/main.go
+++ b/tools/nixery/server/main.go
@@ -32,9 +32,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"regexp"
-	"time"
 
-	"cloud.google.com/go/storage"
 	"github.com/google/nixery/server/builder"
 	"github.com/google/nixery/server/config"
 	"github.com/google/nixery/server/layers"
@@ -59,49 +57,6 @@ var (
 	layerRegex    = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/blobs/sha256:(\w+)$`)
 )
 
-// layerRedirect constructs the public URL of the layer object in the Cloud
-// Storage bucket, signs it and redirects the user there.
-//
-// Signing the URL allows unauthenticated clients to retrieve objects from the
-// bucket.
-//
-// The Docker client is known to follow redirects, but this might not be true
-// for all other registry clients.
-func constructLayerUrl(cfg *config.Config, digest string) (string, error) {
-	log.WithField("layer", digest).Info("redirecting layer request to bucket")
-	object := "layers/" + digest
-
-	if cfg.Signing != nil {
-		opts := *cfg.Signing
-		opts.Expires = time.Now().Add(5 * time.Minute)
-		return storage.SignedURL(cfg.Bucket, object, &opts)
-	} else {
-		return ("https://storage.googleapis.com/" + cfg.Bucket + "/" + object), nil
-	}
-}
-
-// 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, cfg *config.Config) *storage.BucketHandle {
-	client, err := storage.NewClient(ctx)
-	if err != nil {
-		log.WithError(err).Fatal("failed to set up Cloud Storage client")
-	}
-
-	bkt := client.Bucket(cfg.Bucket)
-
-	if _, err := bkt.Attrs(ctx); err != nil {
-		log.WithError(err).WithField("bucket", cfg.Bucket).Fatal("could not access configured bucket")
-	}
-
-	return bkt
-}
-
 // Downloads the popularity information for the package set from the
 // URL specified in Nixery's configuration.
 func downloadPopularity(url string) (layers.Popularity, error) {
@@ -218,16 +173,15 @@ func (h *registryHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	layerMatches := layerRegex.FindStringSubmatch(r.RequestURI)
 	if len(layerMatches) == 3 {
 		digest := layerMatches[2]
-		url, err := constructLayerUrl(&h.state.Cfg, digest)
-
+		storage := h.state.Storage
+		err := storage.ServeLayer(digest, w)
 		if err != nil {
-			log.WithError(err).WithField("layer", digest).Error("failed to sign GCS URL")
-			writeError(w, 500, "UNKNOWN", "could not serve layer")
-			return
+			log.WithError(err).WithFields(log.Fields{
+				"layer":   digest,
+				"backend": storage.Name(),
+			}).Error("failed to serve layer from storage backend")
 		}
 
-		w.Header().Set("Location", url)
-		w.WriteHeader(303)
 		return
 	}
 
@@ -243,7 +197,6 @@ func main() {
 	}
 
 	ctx := context.Background()
-	bucket := prepareBucket(ctx, &cfg)
 	cache, err := builder.NewCache()
 	if err != nil {
 		log.WithError(err).Fatal("failed to instantiate build cache")
@@ -259,10 +212,9 @@ func main() {
 	}
 
 	state := builder.State{
-		Bucket: bucket,
-		Cache:  &cache,
-		Cfg:    cfg,
-		Pop:    pop,
+		Cache: &cache,
+		Cfg:   cfg,
+		Pop:   pop,
 	}
 
 	log.WithFields(log.Fields{