[#268] client: Make PayloadPatch correctly receive empty patch payload

* Make the method `PatchPayload` send a patch with empty
  payload patch if range's length is non-zero and if it's the
  first call.
* Empty payload patches just cut original object payload. So, these
  patches are also valid.

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

client/object_patch.go

@@ -175,6 +175,21 @@ func (x *objectPatcher) PatchPayload(_ context.Context, rng *object.Range, paylo
 			return false
 		}
 		if n == 0 {
+			if patchIter == 0 {
+				if rng.GetLength() == 0 {
+					x.err = errors.New("zero-length empty payload patch can't be applied")
+					return false
+				}
+				if !x.patch(&object.Patch{
+					Address: x.addr,
+					PayloadPatch: &object.PayloadPatch{
+						Range: rng,
+						Chunk: []byte{},
+					},
+				}) {
+					return false
+				}
+			}
 			break
 		}
 

client/object_patch_test.go

@@ -193,6 +193,93 @@ func TestObjectPatcher(t *testing.T) {
 	}
 }
 
+func TestRepeatPayloadPatch(t *testing.T) {
+	t.Run("no payload patch partioning", func(t *testing.T) {
+		m := &mockPatchStream{}
+
+		pk, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+
+		const maxChunkLen = 20
+
+		patcher := objectPatcher{
+			client:      &Client{},
+			stream:      m,
+			addr:        oidtest.Address(),
+			key:         pk,
+			maxChunkLen: maxChunkLen,
+		}
+
+		for _, pp := range []struct {
+			patchPayload string
+			rng          *object.Range
+		}{
+			{
+				patchPayload: "xxxxxxxxxx",
+				rng:          newRange(1, 6),
+			},
+			{
+				patchPayload: "yyyyyyyyyy",
+				rng:          newRange(5, 9),
+			},
+			{
+				patchPayload: "zzzzzzzzzz",
+				rng:          newRange(10, 0),
+			},
+		} {
+			success := patcher.PatchPayload(context.Background(), pp.rng, bytes.NewReader([]byte(pp.patchPayload)))
+			require.True(t, success)
+		}
+
+		requireRangeChunk(t, m.streamedPayloadPatches[0], 1, 6, "xxxxxxxxxx")
+		requireRangeChunk(t, m.streamedPayloadPatches[1], 5, 9, "yyyyyyyyyy")
+		requireRangeChunk(t, m.streamedPayloadPatches[2], 10, 0, "zzzzzzzzzz")
+	})
+
+	t.Run("payload patch partioning", func(t *testing.T) {
+		m := &mockPatchStream{}
+
+		pk, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+
+		const maxChunkLen = 5
+
+		patcher := objectPatcher{
+			client:      &Client{},
+			stream:      m,
+			addr:        oidtest.Address(),
+			key:         pk,
+			maxChunkLen: maxChunkLen,
+		}
+
+		for _, pp := range []struct {
+			patchPayload string
+			rng          *object.Range
+		}{
+			{
+				patchPayload: "xxxxxxxxxx",
+				rng:          newRange(1, 6),
+			},
+			{
+				patchPayload: "yyyyyyyyyy",
+				rng:          newRange(5, 9),
+			},
+			{
+				patchPayload: "zzzzzzzzzz",
+				rng:          newRange(10, 0),
+			},
+		} {
+			success := patcher.PatchPayload(context.Background(), pp.rng, bytes.NewReader([]byte(pp.patchPayload)))
+			require.True(t, success)
+		}
+
+		requireRangeChunk(t, m.streamedPayloadPatches[0], 1, 6, "xxxxx")
+		requireRangeChunk(t, m.streamedPayloadPatches[1], 7, 0, "xxxxx")
+		requireRangeChunk(t, m.streamedPayloadPatches[2], 5, 9, "yyyyy")
+		requireRangeChunk(t, m.streamedPayloadPatches[3], 14, 0, "yyyyy")
+		requireRangeChunk(t, m.streamedPayloadPatches[4], 10, 0, "zzzzz")
+		requireRangeChunk(t, m.streamedPayloadPatches[5], 10, 0, "zzzzz")
+	})
+}
+
 func requireRangeChunk(t *testing.T, pp *object.PayloadPatch, offset, length int, chunk string) {
 	require.NotNil(t, pp)
 	require.Equal(t, uint64(offset), pp.Range.GetOffset())