[#36] Add attribute parser

Attribute parser converts strings of attribute chain into
one-dimension array of NodeInfo attributes, that used
in network map.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/util/attributes/parser.go

@@ -0,0 +1,77 @@
+package attributes
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/netmap"
+)
+
+const (
+	pairSeparator     = "/"
+	keyValueSeparator = ":"
+)
+
+var (
+	errEmptyChain      = errors.New("empty attribute chain")
+	errNonUniqueBucket = errors.New("attributes must contain unique keys")
+	errUnexpectedKey   = errors.New("attributes contain unexpected key")
+)
+
+// ParseV2Attributes parses strings like "K1:V1/K2:V2/K3:V3" into netmap
+// attributes.
+func ParseV2Attributes(attrs []string, excl []string) ([]*netmap.Attribute, error) {
+	restricted := make(map[string]struct{}, len(excl))
+	for i := range excl {
+		restricted[excl[i]] = struct{}{}
+	}
+
+	cache := make(map[string]*netmap.Attribute, len(attrs))
+
+	for i := range attrs {
+		line := strings.Trim(attrs[i], pairSeparator)
+		chain := strings.Split(line, pairSeparator)
+		if len(chain) == 0 {
+			return nil, errEmptyChain
+		}
+
+		var parentKey string // backtrack parents in next pairs
+
+		for j := range chain {
+			pair := strings.Split(chain[j], keyValueSeparator)
+			if len(pair) != 2 {
+				return nil, fmt.Errorf("incorrect attribute pair %s", chain[j])
+			}
+
+			key := pair[0]
+			value := pair[1]
+
+			if at, ok := cache[key]; ok && at.GetValue() != value {
+				return nil, errNonUniqueBucket
+			}
+
+			if _, ok := restricted[key]; ok {
+				return nil, errUnexpectedKey
+			}
+
+			attribute := new(netmap.Attribute)
+			attribute.SetKey(key)
+			attribute.SetValue(value)
+
+			if parentKey != "" {
+				attribute.SetParents([]string{parentKey})
+			}
+
+			parentKey = key
+			cache[key] = attribute
+		}
+	}
+
+	result := make([]*netmap.Attribute, 0, len(cache))
+	for _, v := range cache {
+		result = append(result, v)
+	}
+
+	return result, nil
+}