Only apply VPN isolation if it's fully routed

VPN is considered fully routed if both IPv4 and IPv6 have
either a default route or a prohibit route.

Bug: 145332510
Test: atest FrameworksNetTests
Change-Id: I59cf48552bca98092d1212e3d718fd420add5458

core/java/android/net/LinkProperties.java

@@ -1073,6 +1073,21 @@ public final class LinkProperties implements Parcelable {
         return false;
     }
 
+    /**
+     * Returns true if this link has an IPv4 unreachable default route.
+     *
+     * @return {@code true} if there is an IPv4 unreachable default route, {@code false} otherwise.
+     * @hide
+     */
+    public boolean hasIpv4UnreachableDefaultRoute() {
+        for (RouteInfo r : mRoutes) {
+            if (r.isIPv4UnreachableDefault()) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     /**
      * For backward compatibility.
      * This was annotated with @UnsupportedAppUsage in P, so we can't remove the method completely
@@ -1101,6 +1116,21 @@ public final class LinkProperties implements Parcelable {
         return false;
     }
 
+    /**
+     * Returns true if this link has an IPv6 unreachable default route.
+     *
+     * @return {@code true} if there is an IPv6 unreachable default route, {@code false} otherwise.
+     * @hide
+     */
+    public boolean hasIpv6UnreachableDefaultRoute() {
+        for (RouteInfo r : mRoutes) {
+            if (r.isIPv6UnreachableDefault()) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     /**
      * For backward compatibility.
      * This was annotated with @UnsupportedAppUsage in P, so we can't remove the method completely

core/java/android/net/RouteInfo.java

@@ -425,6 +425,16 @@ public final class RouteInfo implements Parcelable {
         return mType == RTN_UNICAST && mDestination.getPrefixLength() == 0;
     }
 
+    /**
+     * Indicates if this route is an unreachable default route.
+     *
+     * @return {@code true} if it's an unreachable route with prefix length of 0.
+     * @hide
+     */
+    private boolean isUnreachableDefaultRoute() {
+        return mType == RTN_UNREACHABLE && mDestination.getPrefixLength() == 0;
+    }
+
     /**
      * Indicates if this route is an IPv4 default route.
      * @hide
@@ -433,6 +443,14 @@ public final class RouteInfo implements Parcelable {
         return isDefaultRoute() && mDestination.getAddress() instanceof Inet4Address;
     }
 
+    /**
+     * Indicates if this route is an IPv4 unreachable default route.
+     * @hide
+     */
+    public boolean isIPv4UnreachableDefault() {
+        return isUnreachableDefaultRoute() && mDestination.getAddress() instanceof Inet4Address;
+    }
+
     /**
      * Indicates if this route is an IPv6 default route.
      * @hide
@@ -441,6 +459,14 @@ public final class RouteInfo implements Parcelable {
         return isDefaultRoute() && mDestination.getAddress() instanceof Inet6Address;
     }
 
+    /**
+     * Indicates if this route is an IPv6 unreachable default route.
+     * @hide
+     */
+    public boolean isIPv6UnreachableDefault() {
+        return isUnreachableDefaultRoute() && mDestination.getAddress() instanceof Inet6Address;
+    }
+
     /**
      * Indicates if this route is a host route (ie, matches only a single host address).
      *