multi: add AddActionReq MacaroonId helper func

Add helper method to `AddActionReq` returns the 4 byte macaroon ID that
is derived from the MacaroonRootKeyID. Using the helper removes some
code repetition at call sites, and makes the intended usage clearer.

firewalldb/actions.go

@@ -84,6 +84,18 @@ type AddActionReq struct {
 	RPCParamsJson []byte
 }
 
+// MacaroonId returns the 4 byte macaroon ID that is derived from the
+// MacaroonRootKeyID. If the MacaroonRootKeyID is not set, then this will return
+// an empty 4 byte array.
+func (a *AddActionReq) MacaroonId() [4]byte {
+	var macID [4]byte
+	a.MacaroonRootKeyID.WhenSome(func(rootID uint64) {
+		macID = session.IDFromMacRootKeyID(rootID)
+	})
+
+	return macID
+}
+
 // Action represents an RPC call made through the firewall.
 type Action struct {
 	AddActionReq

firewalldb/actions_kvdb.go

@@ -61,10 +61,7 @@ func (db *BoltDB) AddAction(ctx context.Context,
 	// If no macaroon is provided, then an empty 4-byte array is used as the
 	// macaroon ID. Note that the kvdb implementation only stores the last
 	// 4 bytes of the macaroon root key ID.
-	var macaroonID [4]byte
-	req.MacaroonRootKeyID.WhenSome(func(rootID uint64) {
-		macaroonID = session.IDFromMacRootKeyID(rootID)
-	})
+	macaroonID := req.MacaroonId()
 
 	// If the new action links to a session, the session must exist.
 	// For the bbolt impl of the store, this is our best effort attempt

firewalldb/actions_test.go

@@ -243,12 +243,8 @@ func TestListActions(t *testing.T) {
 	assertActions := func(dbActions []*Action, al []*action) {
 		require.Len(t, dbActions, len(al))
 		for i, a := range al {
-			rID, err := dbActions[i].MacaroonRootKeyID.UnwrapOrErr(
-				fmt.Errorf("macaroon root key is none"),
-			)
-			require.NoError(t, err)
 			require.EqualValues(
-				t, a.sessionID, session.IDFromMacRootKeyID(rID),
+				t, a.sessionID, dbActions[i].MacaroonId(),
 			)
 			require.Equal(t, a.actionID, dbActions[i].FeatureName)
 		}

session_rpcserver.go

@@ -817,10 +817,7 @@ func (s *sessionRpcServer) ListActions(ctx context.Context,
 			sessionID = id
 		})
 
-		var macID [4]byte
-		a.MacaroonRootKeyID.WhenSome(func(rootID uint64) {
-			macID = session.IDFromMacRootKeyID(rootID)
-		})
+		macID := a.MacaroonId()
 
 		resp[i] = &litrpc.Action{
 			SessionId:          sessionID[:],