[#607] network: Implement AddressGroup type

Define `network.AddressGroup` type which represents group of network
addresses. This type is going to be used to support group-address of the
storage node.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/network/group.go

@@ -0,0 +1,105 @@
+package network
+
+import (
+	"errors"
+
+	"github.com/nspcc-dev/neofs-api-go/pkg/netmap"
+)
+
+// AddressGroup represents list of network addresses of the node.
+//
+// List is sorted by priority of use.
+type AddressGroup []Address
+
+// IterateAddresses iterates over all network addresses of the node.
+//
+// Breaks iterating on handler's true return.
+//
+// Handler should not be nil.
+func (x AddressGroup) IterateAddresses(f func(Address) bool) {
+	for i := range x {
+		if f(x[i]) {
+			break
+		}
+	}
+}
+
+// MultiAddressIterator is an interface of network address group.
+type MultiAddressIterator interface {
+	// Must iterate over network addresses and pass each one
+	// to the handler until it returns true.
+	IterateAddresses(func(string) bool)
+
+	// Must return number of addresses in group.
+	NumberOfAddresses() int
+}
+
+// FromIterator forms AddressGroup from MultiAddressIterator structure.
+//
+// Returns an error in the absence of addresses or if any of the addresses are incorrect.
+func (x *AddressGroup) FromIterator(iter MultiAddressIterator) (err error) {
+	as := *x
+
+	addrNum := iter.NumberOfAddresses()
+	if addrNum <= 0 {
+		err = errors.New("missing network addresses")
+		return
+	}
+
+	if cap(as) >= addrNum {
+		as = as[:0]
+	} else {
+		as = make(AddressGroup, 0, addrNum)
+	}
+
+	iter.IterateAddresses(func(s string) bool {
+		var a Address
+
+		err = a.FromString(s)
+
+		fail := err != nil
+		if !fail {
+			as = append(as, a)
+		}
+
+		return fail
+	})
+
+	if err == nil {
+		*x = as
+	}
+
+	return
+}
+
+// GroupFromAddress wraps single Address into AddressGroup.
+//
+// Deprecated: use AddressGroup.FromIterator method.
+func GroupFromAddress(addr Address) AddressGroup {
+	return AddressGroup{addr}
+}
+
+// WriteToNodeInfo writes AddressGroup to netmap.NodeInfo structure.
+func (x AddressGroup) WriteToNodeInfo(ni *netmap.NodeInfo) {
+	addrs := make([]string, len(x))
+
+	for i := range x {
+		addrs[i] = x[i].String()
+	}
+
+	ni.SetAddresses(addrs...)
+}
+
+// Intersects checks if two AddressGroup have
+// at least one common address.
+func (x AddressGroup) Intersects(x2 AddressGroup) bool {
+	for i := range x {
+		for j := range x2 {
+			if x[i].Equal(x2[j]) {
+				return true
+			}
+		}
+	}
+
+	return false
+}