[#478] *: Fix funlen linter warnings

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/services/tree/signature.go

@@ -51,20 +51,10 @@ func (s *Service) verifyClient(req message, cid cidSDK.ID, rawBearer []byte, op
 	if err != nil {
 		return err
 	}
-	if op == acl.OpObjectGet {
-		// verify if the request for a client operation
-		// was signed by a key from authorized list.
-		// Operation must be one of READ.
-		sign := req.GetSignature()
-		if sign == nil {
-			return errors.New("missing signature")
-		}
-		var key = sign.GetKey()
-		for i := range s.authorizedKeys {
-			if bytes.Equal(s.authorizedKeys[i], key) {
-				return nil
-			}
-		}
+
+	isAuthorized, err := s.isAuthorized(req, op)
+	if isAuthorized || err != nil {
+		return err
 	}
 
 	cnr, err := s.cnrSource.Get(cid)
@@ -74,18 +64,9 @@ func (s *Service) verifyClient(req message, cid cidSDK.ID, rawBearer []byte, op
 
 	eaclOp := eACLOp(op)
 
-	var bt *bearer.Token
-	if len(rawBearer) > 0 {
-		bt = new(bearer.Token)
-		if err = bt.Unmarshal(rawBearer); err != nil {
-			return eACLErr(eaclOp, fmt.Errorf("invalid bearer token: %w", err))
-		}
-		if !bt.AssertContainer(cid) {
-			return eACLErr(eaclOp, errBearerWrongContainer)
-		}
-		if !bt.VerifySignature() {
-			return eACLErr(eaclOp, errBearerSignature)
-		}
+	bt, err := parseBearer(rawBearer, cid, eaclOp)
+	if err != nil {
+		return err
 	}
 
 	role, err := roleFromReq(cnr, req, bt)
@@ -117,32 +98,65 @@ func (s *Service) verifyClient(req message, cid cidSDK.ID, rawBearer []byte, op
 
 	var tb eacl.Table
 	signer := req.GetSignature().GetKey()
-	if tableFromBearer {
-		if bt.Impersonate() {
-			tbCore, err := s.eaclSource.GetEACL(cid)
-			if err != nil {
-				return handleGetEACLError(err)
-			}
-			tb = *tbCore.Value
-			signer = bt.SigningKeyBytes()
-		} else {
-			if !bearer.ResolveIssuer(*bt).Equals(cnr.Value.Owner()) {
-				return eACLErr(eaclOp, errBearerWrongOwner)
-			}
-			tb = bt.EACLTable()
+	if tableFromBearer && !bt.Impersonate() {
+		if !bearer.ResolveIssuer(*bt).Equals(cnr.Value.Owner()) {
+			return eACLErr(eaclOp, errBearerWrongOwner)
 		}
+		tb = bt.EACLTable()
 	} else {
 		tbCore, err := s.eaclSource.GetEACL(cid)
 		if err != nil {
 			return handleGetEACLError(err)
 		}
-
 		tb = *tbCore.Value
+
+		if bt.Impersonate() {
+			signer = bt.SigningKeyBytes()
+		}
 	}
 
 	return checkEACL(tb, signer, eACLRole(role), eaclOp)
 }
 
+// Returns true iff the operation is read-only and request was signed
+// with one of the authorized keys.
+func (s *Service) isAuthorized(req message, op acl.Op) (bool, error) {
+	if op != acl.OpObjectGet {
+		return false, nil
+	}
+
+	sign := req.GetSignature()
+	if sign == nil {
+		return false, errors.New("missing signature")
+	}
+
+	key := sign.GetKey()
+	for i := range s.authorizedKeys {
+		if bytes.Equal(s.authorizedKeys[i], key) {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+func parseBearer(rawBearer []byte, cid cidSDK.ID, eaclOp eacl.Operation) (*bearer.Token, error) {
+	if len(rawBearer) == 0 {
+		return nil, nil
+	}
+
+	bt := new(bearer.Token)
+	if err := bt.Unmarshal(rawBearer); err != nil {
+		return nil, eACLErr(eaclOp, fmt.Errorf("invalid bearer token: %w", err))
+	}
+	if !bt.AssertContainer(cid) {
+		return nil, eACLErr(eaclOp, errBearerWrongContainer)
+	}
+	if !bt.VerifySignature() {
+		return nil, eACLErr(eaclOp, errBearerSignature)
+	}
+	return bt, nil
+}
+
 func handleGetEACLError(err error) error {
 	if client.IsErrEACLNotFound(err) {
 		return nil