[#64] transformer: Simplify interface

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

object/transformer/channel.go

@@ -4,47 +4,25 @@ import (
 	"context"
 
 	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
-	"github.com/nspcc-dev/neo-go/pkg/util/slice"
 )
 
 type chanTarget struct {
-	header  *objectSDK.Object
-	payload []byte
-	ch      chan<- *objectSDK.Object
+	ch chan<- *objectSDK.Object
 }
 
 // NewChannelTarget returns ObjectTarget which writes
 // object parts to a provided channel.
-func NewChannelTarget(ch chan<- *objectSDK.Object) ObjectTarget {
+func NewChannelTarget(ch chan<- *objectSDK.Object) ObjectWriter {
 	return &chanTarget{
 		ch: ch,
 	}
 }
 
-// WriteHeader implements the ObjectTarget interface.
-func (c *chanTarget) WriteHeader(_ context.Context, object *objectSDK.Object) error {
-	c.header = object
+func (c *chanTarget) WriteObject(ctx context.Context, o *objectSDK.Object) error {
+	select {
+	case c.ch <- o:
+	case <-ctx.Done():
+		return ctx.Err()
+	}
 	return nil
 }
-
-// Write implements the ObjectTarget interface.
-func (c *chanTarget) Write(_ context.Context, p []byte) (n int, err error) {
-	c.payload = append(c.payload, p...)
-	return len(p), nil
-}
-
-// Close implements the ObjectTarget interface.
-func (c *chanTarget) Close(ctx context.Context) (*AccessIdentifiers, error) {
-	if len(c.payload) != 0 {
-		c.header.SetPayload(slice.Copy(c.payload))
-	}
-	select {
-	case c.ch <- c.header:
-	case <-ctx.Done():
-		return nil, ctx.Err()
-	}
-
-	c.header = nil
-	c.payload = nil
-	return new(AccessIdentifiers), nil
-}