[#221] node: Allow using vector copies_number

Also, take into account that value in general (it was not used before at
all).

Signed-off-by: Pavel Karpy <p.karpy@yadro.com>

pkg/services/object_manager/placement/traverser.go

@@ -38,6 +38,7 @@ type Traverser struct {
 
 type cfg struct {
 	trackCopies bool
+	copyNumbers []uint32
 
 	flatSuccess *uint32
 
@@ -84,19 +85,23 @@ func NewTraverser(opts ...Option) (*Traverser, error) {
 		return nil, fmt.Errorf("could not build placement: %w", err)
 	}
 
+	// backward compatibility for scalar `copies_number`
+	if len(cfg.copyNumbers) == 1 {
+		cfg.flatSuccess = &cfg.copyNumbers[0]
+	}
+
 	var rem []int
 	if cfg.flatSuccess != nil {
 		ns = flatNodes(ns)
 		rem = []int{int(*cfg.flatSuccess)}
 	} else {
-		replNum := cfg.policy.NumberOfReplicas()
-		rem = make([]int, 0, replNum)
+		rem = defaultCopiesVector(cfg.policy)
 
-		for i := 0; i < replNum; i++ {
-			if cfg.trackCopies {
-				rem = append(rem, int(cfg.policy.ReplicaNumberByIndex(i)))
-			} else {
-				rem = append(rem, -1)
+		for i := range rem {
+			if !cfg.trackCopies {
+				rem[i] = -1
+			} else if len(cfg.copyNumbers) > i {
+				rem[i] = int(cfg.copyNumbers[i])
 			}
 		}
 	}
@@ -108,6 +113,17 @@ func NewTraverser(opts ...Option) (*Traverser, error) {
 	}, nil
 }
 
+func defaultCopiesVector(policy netmap.PlacementPolicy) []int {
+	replNum := policy.NumberOfReplicas()
+	copyVector := make([]int, 0, replNum)
+
+	for i := 0; i < replNum; i++ {
+		copyVector = append(copyVector, int(policy.ReplicaNumberByIndex(i)))
+	}
+
+	return copyVector
+}
+
 func flatNodes(ns [][]netmap.NodeInfo) [][]netmap.NodeInfo {
 	sz := 0
 	for i := range ns {
@@ -265,3 +281,9 @@ func WithoutSuccessTracking() Option {
 		c.trackCopies = false
 	}
 }
+
+func WithCopyNumbers(v []uint32) Option {
+	return func(c *cfg) {
+		c.copyNumbers = v
+	}
+}