Always check off-link connectivity in NetworkDiagnostics.

Currently, NetworkDiagnostics only checks off-link connectivity if
one of the DNS servers is off-link. Make it check off-link
connectivity in all cases by sending probes to Google Public DNS
if off-link DNS servers are not specified.

Bug: 22569331
Bug: 22641669
Bug: 22748900
Change-Id: I6cb0dd8491bc0c1a488631deca56722b9c1d2b3f

Author: lcolitti

core/java/android/net/LinkProperties.java

@@ -661,6 +661,17 @@ public boolean hasIPv4Address() {
         return false;
     }
 
+    /**
+     * Returns true if this link or any of its stacked interfaces has an IPv4 address.
+     *
+     * @return {@code true} if there is an IPv4 address, {@code false} otherwise.
+     */
+    private boolean hasIPv4AddressOnInterface(String iface) {
+        return (mIfaceName.equals(iface) && hasIPv4Address()) ||
+                (iface != null && mStackedLinks.containsKey(iface) &&
+                        mStackedLinks.get(iface).hasIPv4Address());
+    }
+
     /**
      * Returns true if this link has a global preferred IPv6 address.
      *
@@ -792,7 +803,7 @@ public boolean isReachable(InetAddress ip) {
 
         if (ip instanceof Inet4Address) {
             // For IPv4, it suffices for now to simply have any address.
-            return hasIPv4Address();
+            return hasIPv4AddressOnInterface(bestRoute.getInterface());
         } else if (ip instanceof Inet6Address) {
             if (ip.isLinkLocalAddress()) {
                 // For now, just make sure link-local destinations have

services/core/java/com/android/server/ConnectivityService.java

@@ -1772,7 +1772,7 @@ protected void dump(FileDescriptor fd, PrintWriter writer, String[] args) {
                 // Start gathering diagnostic information.
                 netDiags.add(new NetworkDiagnostics(
                         nai.network,
-                        new LinkProperties(nai.linkProperties),
+                        new LinkProperties(nai.linkProperties),  // Must be a copy.
                         DIAG_TIME_MS));
             }
 

services/core/java/com/android/server/connectivity/NetworkDiagnostics.java

@@ -20,6 +20,7 @@
 
 import android.net.LinkProperties;
 import android.net.Network;
+import android.net.NetworkUtils;
 import android.net.RouteInfo;
 import android.os.SystemClock;
 import android.system.ErrnoException;
@@ -79,6 +80,10 @@
 public class NetworkDiagnostics {
     private static final String TAG = "NetworkDiagnostics";
 
+    private static final InetAddress TEST_DNS4 = NetworkUtils.numericToInetAddress("8.8.8.8");
+    private static final InetAddress TEST_DNS6 = NetworkUtils.numericToInetAddress(
+            "2001:4860:4860::8888");
+
     // For brevity elsewhere.
     private static final long now() {
         return SystemClock.elapsedRealtime();
@@ -156,6 +161,21 @@ public NetworkDiagnostics(Network network, LinkProperties lp, long timeoutMs) {
         mStartTime = now();
         mDeadlineTime = mStartTime + mTimeoutMs;
 
+        // Hardcode measurements to TEST_DNS4 and TEST_DNS6 in order to test off-link connectivity.
+        // We are free to modify mLinkProperties with impunity because ConnectivityService passes us
+        // a copy and not the original object. It's easier to do it this way because we don't need
+        // to check whether the LinkProperties already contains these DNS servers because
+        // LinkProperties#addDnsServer checks for duplicates.
+        if (mLinkProperties.isReachable(TEST_DNS4)) {
+            mLinkProperties.addDnsServer(TEST_DNS4);
+        }
+        // TODO: we could use mLinkProperties.isReachable(TEST_DNS6) here, because we won't set any
+        // DNS servers for which isReachable() is false, but since this is diagnostic code, be extra
+        // careful.
+        if (mLinkProperties.hasGlobalIPv6Address() || mLinkProperties.hasIPv6DefaultRoute()) {
+            mLinkProperties.addDnsServer(TEST_DNS6);
+        }
+
         for (RouteInfo route : mLinkProperties.getRoutes()) {
             if (route.hasGateway()) {
                 prepareIcmpMeasurement(route.getGateway());