Disable IPv6 stack when IPv6 provisioning is lost but IPv4 is still alive.

When IPv6 provisioning loss happens due to the default route has
gone, however, if IPv4 network is still provisioned, we can consider
to disable IPv6 stack and still keep the current connection without
disconnecting from wifi, applications will be able to reconnect over
IPv4 network.

Bug: 131781810
Test: atest NetworkStackTests NetworkStackNextTests
Test: atest NetworkStackIntegrationTests
Merged-In: I8f56a05b38c8387c91306c0dc2bdf4430ec3bd00
Change-Id: I8f56a05b38c8387c91306c0dc2bdf4430ec3bd00

1 files changed, 22 insertions, 4 deletions

diff --git a/src/android/net/ip/IpClient.java b/src/android/net/ip/IpClient.java
index 018d6ab..629d216 100644
--- a/src/android/net/ip/IpClient.java
+++ b/src/android/net/ip/IpClient.java
@@ -482,6 +482,7 @@ public class IpClient extends StateMachine {
     private boolean mMulticastFiltering;
     private long mStartTimeMillis;
     private MacAddress mCurrentBssid;
+    private boolean mHasDisabledIPv6OnProvLoss;
 
     /**
      * Reading the snapshot is an asynchronous operation initiated by invoking
@@ -1137,9 +1138,9 @@ public class IpClient extends StateMachine {
         // Note that we can still be disconnected by IpReachabilityMonitor
         // if the IPv6 default gateway (but not the IPv6 DNS servers; see
         // accompanying code in IpReachabilityMonitor) is unreachable.
-        final boolean ignoreIPv6ProvisioningLoss =
-                mConfiguration != null && mConfiguration.mUsingMultinetworkPolicyTracker
-                && !mCm.shouldAvoidBadWifi();
+        final boolean ignoreIPv6ProvisioningLoss = mHasDisabledIPv6OnProvLoss
+                || (mConfiguration != null && mConfiguration.mUsingMultinetworkPolicyTracker
+                        && !mCm.shouldAvoidBadWifi());
 
         // Additionally:
         //
@@ -1163,7 +1164,23 @@ public class IpClient extends StateMachine {
         // IPv6 default route then also consider the loss of that default route
         // to be a loss of provisioning. See b/27962810.
         if (oldLp.hasGlobalIpv6Address() && (lostIPv6Router && !ignoreIPv6ProvisioningLoss)) {
-            delta = PROV_CHANGE_LOST_PROVISIONING;
+            // Although link properties have lost IPv6 default route in this case, if IPv4 is still
+            // working with appropriate routes and DNS servers, we can keep the current connection
+            // without disconnecting from the network, just disable IPv6 on that given network until
+            // to the next provisioning. Disabling IPv6 will result in all IPv6 connectivity torn
+            // down and all IPv6 sockets being closed, the non-routable IPv6 DNS servers will be
+            // stripped out, so applications will be able to reconnect immediately over IPv4. See
+            // b/131781810.
+            if (newLp.isIpv4Provisioned()) {
+                mInterfaceCtrl.disableIPv6();
+                mHasDisabledIPv6OnProvLoss = true;
+                delta = PROV_CHANGE_STILL_PROVISIONED;
+                if (DBG) {
+                    mLog.log("Disable IPv6 stack completely when the default router has gone");
+                }
+            } else {
+                delta = PROV_CHANGE_LOST_PROVISIONING;
+            }
         }
 
         return delta;
@@ -1591,6 +1608,7 @@ public class IpClient extends StateMachine {
         @Override
         public void enter() {
             stopAllIP();
+            mHasDisabledIPv6OnProvLoss = false;
 
             mLinkObserver.clearInterfaceParams();
             resetLinkProperties();