[client.keyset] added 'Rescue()' method to keyset

src/git.xdrm.io/schastsp/client/keyset/keyset.go

@@ -206,3 +206,45 @@ func (s T) MigrationCode(optional... uint8) uint8 {
 	return s.mcode
 
 }
+
+
+
+/* (7) Updates depth for rescuing from desynchroisation
+*
+* @lastHash<[]byte>					Last received hash
+*
+* @return error<err>				Error or NIL if not
+*
+* @description						We must update @depth so the next sent hash h_depth(k)
+*										hashed MIN times equals the received hash @lastHash
+*									We must find depth = i-MIN+1
+*									with i so that h_MIN( h_i(k) ) = lastHash
+*
+---------------------------------------------------------*/
+func (s *T) Rescue(lastHash []byte) error {
+
+	/* (1) Browse possible values
+	---------------------------------------------------------*/
+	for i := s.depth ; i <= s.depth+s.ctx.MinDepth() ; i++ {
+
+		/* (1) Process hash */
+		currentHash, err := s.Hash();
+		if err != nil { return err }
+
+		/* (2) If not found -> try again */
+		if string(currentHash) != string(lastHash) { continue }
+
+		/* (3) Store new depth */
+		s.depth = i - s.ctx.MinDepth() + 1
+
+		/* (4) Update migration code */
+		s.mcode = 2
+
+		return nil
+
+	}
+
+	return errors.New("Cannot find an available rescue depth");
+
+
+}