[#220] netmap: process REP X policies correctly

For `REP X` select X nodes from the default filter
and fail if it cannot be done.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/netmap/netmap.go

@@ -71,6 +71,19 @@ func (m *Netmap) GetContainerNodes(p *PlacementPolicy, pivot []byte) (ContainerN
 		}
 
 		if r.Selector() == "" {
+			if len(p.Selectors()) == 0 {
+				s := new(Selector)
+				s.SetCount(r.Count())
+				s.SetFilter(MainFilterName)
+
+				nodes, err := c.getSelection(p, s)
+				if err != nil {
+					return nil, err
+				}
+
+				result[i] = flattenNodes(nodes)
+			}
+
 			for _, s := range p.Selectors() {
 				result[i] = append(result[i], flattenNodes(c.Selections[s.Name()])...)
 			}

pkg/netmap/selector_test.go

@@ -31,6 +31,43 @@ func TestPlacementPolicy_UnspecifiedClause(t *testing.T) {
 	require.Equal(t, 4, len(v.Flatten()))
 }
 
+func TestPlacementPolicy_Minimal(t *testing.T) {
+	nodes := []NodeInfo{
+		nodeInfoFromAttributes("City", "Saint-Petersburg"),
+		nodeInfoFromAttributes("City", "Moscow"),
+		nodeInfoFromAttributes("City", "Berlin"),
+		nodeInfoFromAttributes("City", "Paris"),
+	}
+	nm, err := NewNetmap(NodesFromInfo(nodes))
+	require.NoError(t, err)
+
+	runTest := func(t *testing.T, rep uint32, expectError bool) {
+		p := newPlacementPolicy(0,
+			[]*Replica{newReplica(rep, "")},
+			nil, nil)
+
+		v, err := nm.GetContainerNodes(p, nil)
+
+		if expectError {
+			require.Error(t, err)
+			return
+		}
+
+		require.NoError(t, err)
+		require.EqualValues(t, rep, len(v.Flatten()))
+	}
+
+	t.Run("REP 1", func(t *testing.T) {
+		runTest(t, 1, false)
+	})
+	t.Run("REP 3", func(t *testing.T) {
+		runTest(t, 3, false)
+	})
+	t.Run("REP 5", func(t *testing.T) {
+		runTest(t, 5, true)
+	})
+}
+
 // Issue #215.
 func TestPlacementPolicy_MultipleREP(t *testing.T) {
 	p := newPlacementPolicy(1,