[active-active] Fix extra toggle after default route N/A (#279)

Approach
What is the motivation for this PR?
Fixes #278

Fix the extra toggle after the default route N/A.

(active, active, up), ok                        <- default route n/a
                                                -> toggle to standby
(active, standby, up), n/a                      <- mux probe active from the periodically probe
(active, active, up), n/a                       <- mux state standby returned from the toggle to standby
(active, standby, up), n/a                      -> toggle to active
(active, active, up), n/a                       <- mux state active returned from the toggle to active
(active, active, up), n/a                       <- link prober unknown
(unknown, active, up), n/a                      -> toggle to standby
(unknown, standby, up), n/a                     <- mux state standby returned from toggle to standby
Signed-off-by: Longxiang Lyu [email protected]

Work item tracking
Microsoft ADO (number only): 30186968
How did you do it?
Let's check the default route state when the mux transits into (active, standby, up), if the default route state is N/A, skip the toggle to active.

How did you verify/test it?
UT

Author: lolyu

src/link_manager/LinkManagerStateMachineActiveActive.cpp

@@ -780,7 +780,7 @@ void ActiveActiveStateMachine::LinkProberActiveMuxStandbyLinkUpTransitionFunctio
             // last siwtch mux state to standby failed, try again
             switchMuxState(nextState, mux_state::MuxState::Label::Standby, true);
         }
-    } else {
+    } else if (mDefaultRouteState != DefaultRoute::NA) {
         switchMuxState(nextState, mux_state::MuxState::Label::Active);
     }
 }

test/LinkManagerStateMachineActiveActiveTest.cpp

@@ -500,6 +500,35 @@ TEST_F(LinkManagerStateMachineActiveActiveTest, MuxActivDefaultRouteState)
     EXPECT_EQ(mFakeMuxPort.mFakeLinkProber->mRestartTxProbeCallCount, 3);
 }
 
+TEST_F(LinkManagerStateMachineActiveActiveTest, MuxActivDefaultRouteStateNALMuxProbeActiveAfterToggle)
+{
+    setMuxActive();
+
+    mMuxConfig.enableDefaultRouteFeature(true);
+    postDefaultRouteEvent("na", 1);
+    EXPECT_EQ(mFakeMuxPort.mFakeLinkProber->mShutdownTxProbeCallCount, 1);
+    EXPECT_EQ(mFakeMuxPort.mFakeLinkProber->mRestartTxProbeCallCount, 0);
+    EXPECT_EQ(mDbInterfacePtr->mSetMuxStateInvokeCount, 2);
+    EXPECT_EQ(mDbInterfacePtr->mLastSetMuxState, mux_state::MuxState::Label::Standby);
+    VALIDATE_STATE(Active, Standby, Up);
+
+    // misleading mux state active from periodically probe
+    handleProbeMuxState("active", 3);
+    EXPECT_EQ(mDbInterfacePtr->mSetMuxStateInvokeCount, 2);
+    EXPECT_EQ(mDbInterfacePtr->mLastSetMuxState, mux_state::MuxState::Label::Standby);
+    VALIDATE_STATE(Active, Active, Up);
+
+    handleMuxState("standby", 3);
+    EXPECT_EQ(mDbInterfacePtr->mSetMuxStateInvokeCount, 2);
+    EXPECT_EQ(mDbInterfacePtr->mLastSetMuxState, mux_state::MuxState::Label::Standby);
+    VALIDATE_STATE(Active, Standby, Up);
+
+    postLinkProberEvent(link_prober::LinkProberState::Unknown, 3);
+    EXPECT_EQ(mDbInterfacePtr->mSetMuxStateInvokeCount, 2);
+    EXPECT_EQ(mDbInterfacePtr->mLastSetMuxState, mux_state::MuxState::Label::Standby);
+    VALIDATE_STATE(Unknown, Standby, Up);
+}
+
 TEST_F(LinkManagerStateMachineActiveActiveTest, MuxActivDefaultRouteStateMuxConfigActive)
 {
     setMuxActive();