Let LinkProperties#getRoutes() keeps returning all routes before T

Starting from T, VpnService supports exclude routes, which will
make the caller to get both of include routes and exclude routes
from LinkProperties#getRoutes(), and it's not expected to get the
exclude routes before T in production code even though the code
returns all routes.

But there is a CTS - LinkPropertiesTest#testRouteAddWithSameKey()
will try to add an exclude route and check if the result of
LinkProperties#getRoutes() contains that exclude route or not.
And the test is failed now since LinkProperties#getRoutes() will
only return include route if compat feature - EXCLUDED_ROUTES is
disabled. (EXCLUDED_ROUTES is enabled starting from target SDK T)

To fix this test failure, let LinkProperties#getRoutes() keeps
returning all routes if SDK is before T. This avoids changing
behavior on S, and even though there is still a behavior change
when upgrading to T, apps are unlikely to be relying on such
behavior, especially outside of tests.

Bug: 238061814
Test: Run "atest CtsNetTestCases:LinkPropertiesTest" on S build
      with mainline module which contains this patch.
Change-Id: Iac4362c4fe347ee3f06d5b21b0325fa69a7f27b6
diff --git a/framework/src/android/net/LinkProperties.java b/framework/src/android/net/LinkProperties.java
index a8f707e..76ca061 100644
--- a/framework/src/android/net/LinkProperties.java
+++ b/framework/src/android/net/LinkProperties.java
@@ -29,6 +29,8 @@
 import android.text.TextUtils;
 
 import com.android.internal.annotations.VisibleForTesting;
+import com.android.modules.utils.build.SdkLevel;
+import com.android.net.module.util.CollectionUtils;
 import com.android.net.module.util.LinkPropertiesUtils;
 
 import java.net.Inet4Address;
@@ -42,7 +44,6 @@
 import java.util.List;
 import java.util.Objects;
 import java.util.StringJoiner;
-import java.util.stream.Collectors;
 
 /**
  * Describes the properties of a network link.
@@ -759,20 +760,25 @@
      * @return An unmodifiable {@link List} of {@link RouteInfo} for this link.
      */
     public @NonNull List<RouteInfo> getRoutes() {
-        if (CompatChanges.isChangeEnabled(EXCLUDED_ROUTES)) {
+        // Before T, there's no throw routes because VpnService is not updatable, so no need to
+        // filter them out.
+        if (CompatChanges.isChangeEnabled(EXCLUDED_ROUTES) || !SdkLevel.isAtLeastT()) {
             return Collections.unmodifiableList(mRoutes);
         } else {
-            return Collections.unmodifiableList(getUnicastRoutes());
+            // Apps that added a throw route themselves (not obtaining LinkProperties from the
+            // system) will not see it in getRoutes on T+ if they do not have the compat change
+            // enabled (target SDK < T); but this is expected to be rare and typically only affect
+            // tests creating LinkProperties themselves (like CTS v12, which is only running on S).
+            return Collections.unmodifiableList(getNonThrowRoutes());
         }
     }
 
     /**
-     * Returns all the {@link RouteInfo} of type {@link RouteInfo#RTN_UNICAST} set on this link.
+     * Returns all the {@link RouteInfo} that are not of type {@link RouteInfo#RTN_THROW} set on
+     * this link.
      */
-    private @NonNull List<RouteInfo> getUnicastRoutes() {
-        return mRoutes.stream()
-                .filter(route -> route.getType() == RouteInfo.RTN_UNICAST)
-                .collect(Collectors.toList());
+    private @NonNull List<RouteInfo> getNonThrowRoutes() {
+        return CollectionUtils.filter(mRoutes, route -> route.getType() != RouteInfo.RTN_THROW);
     }
 
     /**
diff --git a/tests/common/java/android/net/LinkPropertiesTest.java b/tests/common/java/android/net/LinkPropertiesTest.java
index 9ed2bb3..319dbf4 100644
--- a/tests/common/java/android/net/LinkPropertiesTest.java
+++ b/tests/common/java/android/net/LinkPropertiesTest.java
@@ -1312,7 +1312,26 @@
         assertEquals(3, lp.getRoutes().size());
     }
 
-    @Test @IgnoreUpTo(Build.VERSION_CODES.R)
+    @Test @IgnoreUpTo(Build.VERSION_CODES.R) @IgnoreAfter(Build.VERSION_CODES.S_V2)
+    @CtsNetTestCasesMaxTargetSdk31(reason = "Compat change cannot be overridden when targeting T+")
+    @DisableCompatChanges({LinkProperties.EXCLUDED_ROUTES})
+    public void testExcludedRoutesDisabled_S() {
+        final LinkProperties lp = new LinkProperties();
+        assertEquals(0, lp.getRoutes().size());
+
+        lp.addRoute(new RouteInfo(new IpPrefix(ADDRV4, 0), RTN_UNREACHABLE));
+        assertEquals(1, lp.getRoutes().size());
+
+        lp.addRoute(new RouteInfo(new IpPrefix(ADDRV6, 5), RTN_THROW));
+        // RTN_THROW routes are visible on S when added by the caller (but they are not added by
+        // the system). This is uncommon usage but was tested by CTSv12.
+        assertEquals(2, lp.getRoutes().size());
+
+        lp.addRoute(new RouteInfo(new IpPrefix(ADDRV6, 2), RTN_UNICAST));
+        assertEquals(3, lp.getRoutes().size());
+    }
+
+    @Test @IgnoreUpTo(Build.VERSION_CODES.S_V2)
     @CtsNetTestCasesMaxTargetSdk31(reason = "Compat change cannot be overridden when targeting T+")
     @DisableCompatChanges({LinkProperties.EXCLUDED_ROUTES})
     public void testExcludedRoutesDisabled() {
@@ -1320,12 +1339,12 @@
         assertEquals(0, lp.getRoutes().size());
 
         lp.addRoute(new RouteInfo(new IpPrefix(ADDRV4, 0), RTN_UNREACHABLE));
-        assertEquals(0, lp.getRoutes().size());
+        assertEquals(1, lp.getRoutes().size());
 
         lp.addRoute(new RouteInfo(new IpPrefix(ADDRV6, 5), RTN_THROW));
-        assertEquals(0, lp.getRoutes().size());
+        assertEquals(1, lp.getRoutes().size());
 
         lp.addRoute(new RouteInfo(new IpPrefix(ADDRV6, 2), RTN_UNICAST));
-        assertEquals(1, lp.getRoutes().size());
+        assertEquals(2, lp.getRoutes().size());
     }
 }