[#127] Split FrostFS ReadObject to separate methods

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

internal/handler/handler.go

@@ -46,8 +46,26 @@ type PrmAuth struct {
 	BearerToken *bearer.Token
 }
 
-// PrmObjectRead groups parameters of FrostFS.ReadObject operation.
-type PrmObjectRead struct {
+// PrmObjectHead groups parameters of FrostFS.HeadObject operation.
+type PrmObjectHead struct {
+	// Authentication parameters.
+	PrmAuth
+
+	// Address to read the object header from.
+	Address oid.Address
+}
+
+// PrmObjectGet groups parameters of FrostFS.GetObject operation.
+type PrmObjectGet struct {
+	// Authentication parameters.
+	PrmAuth
+
+	// Address to read the object header from.
+	Address oid.Address
+}
+
+// PrmObjectRange groups parameters of FrostFS.RangeObject operation.
+type PrmObjectRange struct {
 	// Authentication parameters.
 	PrmAuth
 
@@ -58,10 +76,10 @@ type PrmObjectRead struct {
 	PayloadRange [2]uint64
 }
 
-// ObjectPart represents partially read FrostFS object.
-type ObjectPart struct {
-	// Object header with optional in-memory payload part.
-	Head *object.Object
+// Object represents FrostFS object.
+type Object struct {
+	// Object header (doesn't contain payload).
+	Header object.Object
 
 	// Object payload part encapsulated in io.Reader primitive.
 	// Returns ErrAccessDenied on read access violation.
@@ -115,7 +133,9 @@ var (
 // FrostFS represents virtual connection to FrostFS network.
 type FrostFS interface {
 	Container(context.Context, PrmContainer) (*container.Container, error)
-	ReadObject(context.Context, PrmObjectRead) (*ObjectPart, error)
+	HeadObject(context.Context, PrmObjectHead) (*object.Object, error)
+	GetObject(context.Context, PrmObjectGet) (*Object, error)
+	RangeObject(context.Context, PrmObjectRange) (io.ReadCloser, error)
 	CreateObject(context.Context, PrmObjectCreate) (oid.ID, error)
 	SearchObjects(context.Context, PrmObjectSearch) (ResObjectSearch, error)
 	utils.EpochInfoFetcher