slicer: Fixed object upload in some cases

The case when the reader returns io.EOF with the last data chunk. Slicer was closing the writer without payload writing

Signed-off-by: Evgenii Baidakov <evgenii@nspcc.io>

object/slicer/slicer.go

@@ -177,9 +177,9 @@ func slice(ctx context.Context, ow ObjectWriter, header object.Object, data io.R
 			if !errors.Is(err, io.EOF) {
 				return rootID, fmt.Errorf("read payload chunk: %w", err)
 			}
+		}
 
-			// no more data to read
-
+		if n == 0 {
 			if err = writer.Close(); err != nil {
 				return rootID, fmt.Errorf("writer close: %w", err)
 			}

object/slicer/slicer_test.go

@@ -269,6 +269,23 @@ func testSlicer(t *testing.T, size, sizeLimit uint64) {
 	}
 }
 
+// eofOnLastChunkReader is a special reader for tests. It returns io.EOF with the last data portion.
+type eofOnLastChunkReader struct {
+	Payload []byte
+	point   int
+}
+
+func (l *eofOnLastChunkReader) Read(p []byte) (int, error) {
+	n := copy(p, l.Payload[l.point:])
+	l.point += n
+
+	if l.point == len(l.Payload) {
+		return n, io.EOF
+	}
+
+	return n, nil
+}
+
 func testSlicerByHeaderType(t *testing.T, checker *slicedObjectChecker, in input, opts slicer.Options) {
 	ctx := context.Background()
 
@@ -296,6 +313,20 @@ func testSlicerByHeaderType(t *testing.T, checker *slicedObjectChecker, in input
 		checker.chainCollector.verify(checker.input, rootID)
 	})
 
+	t.Run("slicer.Put, io.EOF in last chunk", func(t *testing.T) {
+		checker.chainCollector = newChainCollector(t)
+
+		var hdr object.Object
+		hdr.SetSessionToken(opts.Session())
+		hdr.SetContainerID(in.container)
+		hdr.SetOwnerID(&in.owner)
+		hdr.SetAttributes(in.attributes...)
+
+		rootID, err := slicer.Put(ctx, checker, hdr, checker.input.signer, &eofOnLastChunkReader{Payload: in.payload}, opts)
+		require.NoError(t, err)
+		checker.chainCollector.verify(checker.input, rootID)
+	})
+
 	t.Run("Slicer.InitPut", func(t *testing.T) {
 		checker.chainCollector = newChainCollector(t)