Keep only one CMD_EVALUATE_PRIVATE_DNS in the queue

If a user changes the private DNS setting while NetworkMonitor
are in EvaluatingPrivateDnsState, new failure caused by
recongiguration will put into the message queue. State machine
will get multiple CMD_EVALUATE_PRIVATE_DNS events with different
delay timer which may not work as expected.

Test: atest NetworkStackTests:\
com.android.server.connectivity.NetworkMonitorTest
Bug: 139797781

Change-Id: I7f4e5642b9734daddfefc9c5ef25890aa8d3d64b

2 files changed, 11 insertions, 12 deletions

diff --git a/src/com/android/server/connectivity/NetworkMonitor.java b/src/com/android/server/connectivity/NetworkMonitor.java
index 7cabb1e..e08170a 100644
--- a/src/com/android/server/connectivity/NetworkMonitor.java
+++ b/src/com/android/server/connectivity/NetworkMonitor.java
@@ -681,6 +681,8 @@ public class NetworkMonitor extends StateMachine {
                     //         no resolved IP addresses, IPs unreachable,
                     //         port 853 unreachable, port 853 is not running a
                     //         DNS-over-TLS server, et cetera).
+                    // Cancel any outstanding CMD_EVALUATE_PRIVATE_DNS.
+                    removeMessages(CMD_EVALUATE_PRIVATE_DNS);
                     sendMessage(CMD_EVALUATE_PRIVATE_DNS);
                     break;
                 }
@@ -1042,6 +1044,11 @@ public class NetworkMonitor extends StateMachine {
                     // All good!
                     transitionTo(mValidatedState);
                     break;
+                case CMD_PRIVATE_DNS_SETTINGS_CHANGED:
+                    // When settings change the reevaluation timer must be reset.
+                    mPrivateDnsReevalDelayMs = INITIAL_REEVALUATE_DELAY_MS;
+                    // Let the message bubble up and be handled by parent states as usual.
+                    return NOT_HANDLED;
                 default:
                     return NOT_HANDLED;
             }
@@ -1094,10 +1101,6 @@ public class NetworkMonitor extends StateMachine {
             // transitioning back to EvaluatingState, to perhaps give ourselves
             // the opportunity to (re)detect a captive portal or something.
             //
-            // TODO: distinguish between CMD_EVALUATE_PRIVATE_DNS messages that are caused by server
-            // lookup failures (which should continue to do exponential backoff) and
-            // CMD_EVALUATE_PRIVATE_DNS messages that are caused by user reconfiguration (which
-            // should be processed immediately.
             sendMessageDelayed(CMD_EVALUATE_PRIVATE_DNS, mPrivateDnsReevalDelayMs);
             mPrivateDnsReevalDelayMs *= 2;
             if (mPrivateDnsReevalDelayMs > MAX_REEVALUATE_DELAY_MS) {
diff --git a/tests/unit/src/com/android/server/connectivity/NetworkMonitorTest.java b/tests/unit/src/com/android/server/connectivity/NetworkMonitorTest.java
index 6eeadf5..49a2ce3 100644
--- a/tests/unit/src/com/android/server/connectivity/NetworkMonitorTest.java
+++ b/tests/unit/src/com/android/server/connectivity/NetworkMonitorTest.java
@@ -868,10 +868,8 @@ public class NetworkMonitorTest {
         WrappedNetworkMonitor wnm = makeNotMeteredNetworkMonitor();
         wnm.notifyPrivateDnsSettingsChanged(new PrivateDnsConfig("dns.google", new InetAddress[0]));
         wnm.notifyNetworkConnected(TEST_LINK_PROPERTIES, NOT_METERED_CAPABILITIES);
-        verify(mCallbacks, timeout(HANDLER_TIMEOUT_MS).atLeastOnce())
-                .notifyNetworkTested(
-                        eq(NETWORK_VALIDATION_PROBE_DNS | NETWORK_VALIDATION_PROBE_HTTPS),
-                        eq(null));
+        verify(mCallbacks, timeout(HANDLER_TIMEOUT_MS)).notifyNetworkTested(
+                eq(NETWORK_VALIDATION_PROBE_DNS | NETWORK_VALIDATION_PROBE_HTTPS), eq(null));
         verify(mCallbacks, timeout(HANDLER_TIMEOUT_MS).times(1)).notifyProbeStatusChanged(
                 eq(VALIDATION_RESULT_PRIVDNS_VALID), eq(NETWORK_VALIDATION_PROBE_DNS
                 | NETWORK_VALIDATION_PROBE_HTTPS));
@@ -907,10 +905,8 @@ public class NetworkMonitorTest {
         mFakeDns.setNonBypassPrivateDnsWorking(false);
         wnm.notifyPrivateDnsSettingsChanged(new PrivateDnsConfig("dns.google",
                 new InetAddress[0]));
-        verify(mCallbacks, timeout(HANDLER_TIMEOUT_MS).atLeastOnce())
-                .notifyNetworkTested(
-                        eq(NETWORK_VALIDATION_PROBE_DNS | NETWORK_VALIDATION_PROBE_HTTPS),
-                        eq(null));
+        verify(mCallbacks, timeout(HANDLER_TIMEOUT_MS)).notifyNetworkTested(
+                eq(NETWORK_VALIDATION_PROBE_DNS | NETWORK_VALIDATION_PROBE_HTTPS), eq(null));
         // NetworkMonitor will check if the probes has changed or not, if the probes has not
         // changed, the callback won't be fired.
         verify(mCallbacks, never()).notifyProbeStatusChanged(