gcs: check if all files exist (#1274)

pkg/storage/gcp/checker.go

@@ -7,6 +7,7 @@ import (
 	"github.com/gomods/athens/pkg/config"
 	"github.com/gomods/athens/pkg/errors"
 	"github.com/gomods/athens/pkg/observ"
+	"google.golang.org/api/iterator"
 )
 
 // Exists implements the (./pkg/storage).Checker interface
@@ -15,15 +16,26 @@ func (s *Storage) Exists(ctx context.Context, module, version string) (bool, err
 	const op errors.Op = "gcp.Exists"
 	ctx, span := observ.StartSpan(ctx, op.String())
 	defer span.End()
-	_, err := s.bucket.Object(config.PackageVersionedName(module, version, "mod")).Attrs(ctx)
 
-	if err == storage.ErrObjectNotExist {
-		return false, nil
+	it := s.bucket.Objects(ctx, &storage.Query{Prefix: config.PackageVersionedName(module, version, "")})
+	var count int
+	for {
+		attrs, err := it.Next()
+		if err == iterator.Done {
+			break
+		}
+		if err != nil {
+			return false, errors.E(op, err, errors.M(module), errors.V(version))
+		}
+		switch attrs.Name {
+		case config.PackageVersionedName(module, version, "info"):
+			count++
+		case config.PackageVersionedName(module, version, "mod"):
+			count++
+		case config.PackageVersionedName(module, version, "zip"):
+			count++
+		}
 	}
 
-	if err != nil {
-		return false, errors.E(op, err, errors.M(module), errors.V(version))
-	}
-
-	return true, nil
+	return count == 3, nil
 }