Use "Size" field to describe blobs over "Length"

After consideration, we've changed the main descriptor field name to for number
of bytes to "size" to match convention. While this may be a subjective
argument, commonly we refer to files by their "size" rather than their
"length". This will match other conventions, like `(FileInfo).Size()` and
methods on `io.SizeReaderAt`. Under more broad analysis, this argument doesn't
necessarily hold up. If anything, "size" is shorter than "length".

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/storage/cache/cache.go

@@ -23,8 +23,8 @@ func ValidateDescriptor(desc distribution.Descriptor) error {
 		return err
 	}
 
-	if desc.Length < 0 {
-		return fmt.Errorf("cache: invalid length in descriptor: %v < 0", desc.Length)
+	if desc.Size < 0 {
+		return fmt.Errorf("cache: invalid length in descriptor: %v < 0", desc.Size)
 	}
 
 	if desc.MediaType == "" {

docs/storage/cache/redis/redis.go

@@ -66,17 +66,20 @@ func (rbds *redisBlobDescriptorService) Stat(ctx context.Context, dgst digest.Di
 // stat provides an internal stat call that takes a connection parameter. This
 // allows some internal management of the connection scope.
 func (rbds *redisBlobDescriptorService) stat(ctx context.Context, conn redis.Conn, dgst digest.Digest) (distribution.Descriptor, error) {
-	reply, err := redis.Values(conn.Do("HMGET", rbds.blobDescriptorHashKey(dgst), "digest", "length", "mediatype"))
+	reply, err := redis.Values(conn.Do("HMGET", rbds.blobDescriptorHashKey(dgst), "digest", "size", "mediatype"))
 	if err != nil {
 		return distribution.Descriptor{}, err
 	}
 
-	if len(reply) < 2 || reply[0] == nil || reply[1] == nil { // don't care if mediatype is nil
+	// NOTE(stevvooe): The "size" field used to be "length". We treat a
+	// missing "size" field here as an unknown blob, which causes a cache
+	// miss, effectively migrating the field.
+	if len(reply) < 3 || reply[0] == nil || reply[1] == nil { // don't care if mediatype is nil
 		return distribution.Descriptor{}, distribution.ErrBlobUnknown
 	}
 
 	var desc distribution.Descriptor
-	if _, err := redis.Scan(reply, &desc.Digest, &desc.Length, &desc.MediaType); err != nil {
+	if _, err := redis.Scan(reply, &desc.Digest, &desc.Size, &desc.MediaType); err != nil {
 		return distribution.Descriptor{}, err
 	}
 
@@ -104,7 +107,7 @@ func (rbds *redisBlobDescriptorService) SetDescriptor(ctx context.Context, dgst
 func (rbds *redisBlobDescriptorService) setDescriptor(ctx context.Context, conn redis.Conn, dgst digest.Digest, desc distribution.Descriptor) error {
 	if _, err := conn.Do("HMSET", rbds.blobDescriptorHashKey(dgst),
 		"digest", desc.Digest,
-		"length", desc.Length); err != nil {
+		"size", desc.Size); err != nil {
 		return err
 	}
 

docs/storage/cache/suite.go

@@ -35,14 +35,14 @@ func checkBlobDescriptorCacheEmptyRepository(t *testing.T, ctx context.Context,
 
 	if err := cache.SetDescriptor(ctx, "", distribution.Descriptor{
 		Digest:    "sha384:abc",
-		Length:    10,
+		Size:      10,
 		MediaType: "application/octet-stream"}); err != digest.ErrDigestInvalidFormat {
 		t.Fatalf("expected error with invalid digest: %v", err)
 	}
 
 	if err := cache.SetDescriptor(ctx, "sha384:abc", distribution.Descriptor{
 		Digest:    "",
-		Length:    10,
+		Size:      10,
 		MediaType: "application/octet-stream"}); err == nil {
 		t.Fatalf("expected error setting value on invalid descriptor")
 	}
@@ -60,7 +60,7 @@ func checkBlobDescriptorCacheSetAndRead(t *testing.T, ctx context.Context, provi
 	localDigest := digest.Digest("sha384:abc")
 	expected := distribution.Descriptor{
 		Digest:    "sha256:abc",
-		Length:    10,
+		Size:      10,
 		MediaType: "application/octet-stream"}
 
 	cache, err := provider.RepositoryScoped("foo/bar")