Ignore errors when untethering

Sometimes the interface is removed before we can untether leading to
errors when cleanup up various rules (iptables).  Do as much as we can
and then let a re-tether result in error if needed.

bug:5536516
Change-Id: Ib1d064ecc8e9022566f9b0e4678b33144906971c

Author: Robert Greenwalt

services/java/com/android/server/connectivity/Tethering.java

@@ -73,7 +73,7 @@ public class Tethering extends INetworkManagementEventObserver.Stub {
     private Context mContext;
     private final static String TAG = "Tethering";
     private final static boolean DBG = true;
-    private final static boolean VDBG = false;
+    private final static boolean VDBG = true;
 
     // TODO - remove both of these - should be part of interface inspection/selection stuff
     private String[] mTetherableUsbRegexs;
@@ -920,6 +920,29 @@ public void enter() {
                 setTethered(true);
                 sendTetherStateChangedBroadcast();
             }
+
+            void cleanupUpstream() {
+                if (mMyUpstreamIfaceName != null) {
+                    // note that we don't care about errors here.
+                    // sometimes interfaces are gone before we get
+                    // to remove their rules, which generates errors.
+                    // just do the best we can.
+                    try {
+                        // about to tear down NAT; gather remaining statistics
+                        mStatsService.forceUpdate();
+                    } catch (Exception e) {
+                        if (VDBG) Log.e(TAG, "Exception in forceUpdate: " + e.toString());
+                    }
+                    try {
+                        mNMService.disableNat(mIfaceName, mMyUpstreamIfaceName);
+                    } catch (Exception e) {
+                        if (VDBG) Log.e(TAG, "Exception in disableNat: " + e.toString());
+                    }
+                    mMyUpstreamIfaceName = null;
+                }
+                return;
+            }
+
             @Override
             public boolean processMessage(Message message) {
                 if (VDBG) Log.d(TAG, "TetheredState.processMessage what=" + message.what);
@@ -928,23 +951,7 @@ public boolean processMessage(Message message) {
                 switch (message.what) {
                     case CMD_TETHER_UNREQUESTED:
                     case CMD_INTERFACE_DOWN:
-                        if (mMyUpstreamIfaceName != null) {
-                            try {
-                                // about to tear down NAT; gather remaining statistics
-                                mStatsService.forceUpdate();
-
-                                mNMService.disableNat(mIfaceName, mMyUpstreamIfaceName);
-                                mMyUpstreamIfaceName = null;
-                            } catch (Exception e) {
-                                try {
-                                    mNMService.untetherInterface(mIfaceName);
-                                } catch (Exception ee) {}
-
-                                setLastErrorAndTransitionToInitialState(
-                                        ConnectivityManager.TETHER_ERROR_DISABLE_NAT_ERROR);
-                                break;
-                            }
-                        }
+                        cleanupUpstream();
                         try {
                             mNMService.untetherInterface(mIfaceName);
                         } catch (Exception e) {
@@ -975,23 +982,7 @@ public boolean processMessage(Message message) {
                             if (VDBG) Log.d(TAG, "Connection changed noop - dropping");
                             break;
                         }
-                        if (mMyUpstreamIfaceName != null) {
-                            try {
-                                // about to tear down NAT; gather remaining statistics
-                                mStatsService.forceUpdate();
-
-                                mNMService.disableNat(mIfaceName, mMyUpstreamIfaceName);
-                                mMyUpstreamIfaceName = null;
-                            } catch (Exception e) {
-                                try {
-                                    mNMService.untetherInterface(mIfaceName);
-                                } catch (Exception ee) {}
-
-                                setLastErrorAndTransitionToInitialState(
-                                        ConnectivityManager.TETHER_ERROR_DISABLE_NAT_ERROR);
-                                break;
-                            }
-                        }
+                        cleanupUpstream();
                         if (newUpstreamIfaceName != null) {
                             try {
                                 mNMService.enableNat(mIfaceName, newUpstreamIfaceName);
@@ -1016,23 +1007,7 @@ public boolean processMessage(Message message) {
                         error = true;
                         // fall through
                     case CMD_TETHER_MODE_DEAD:
-                        if (mMyUpstreamIfaceName != null) {
-                            try {
-                                // about to tear down NAT; gather remaining statistics
-                                mStatsService.forceUpdate();
-
-                                mNMService.disableNat(mIfaceName, mMyUpstreamIfaceName);
-                                mMyUpstreamIfaceName = null;
-                            } catch (Exception e) {
-                                try {
-                                    mNMService.untetherInterface(mIfaceName);
-                                } catch (Exception ee) {}
-
-                                setLastErrorAndTransitionToInitialState(
-                                        ConnectivityManager.TETHER_ERROR_DISABLE_NAT_ERROR);
-                                break;
-                            }
-                        }
+                        cleanupUpstream();
                         try {
                             mNMService.untetherInterface(mIfaceName);
                         } catch (Exception e) {