use more modern methods to track connectivity changes (#2403)

* use registerDefaultNetworkCallback() instead of deprecated CONNECTIVITY_ACTION

CONNECTIVITY_ACTION is deprecated, see https://developer.android.com/reference/android/net/ConnectivityManager#CONNECTIVITY_ACTION,

instead, we call maybe_network() at ConnectivityManager.NetworkCallback::onAvailable() callback.

* add more debug info

src/org/thoughtcrime/securesms/ApplicationContext.java

@@ -4,6 +4,10 @@ import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
+import android.net.ConnectivityManager;
+import android.net.LinkProperties;
+import android.net.NetworkCapabilities;
+import android.os.Build;
 import android.util.Log;
 
 import androidx.annotation.NonNull;
@@ -16,9 +20,9 @@ import androidx.work.PeriodicWorkRequest;
 import androidx.work.WorkManager;
 
 import com.b44t.messenger.DcAccounts;
-import com.b44t.messenger.DcEventEmitter;
 import com.b44t.messenger.DcContext;
 import com.b44t.messenger.DcEvent;
+import com.b44t.messenger.DcEventEmitter;
 
 import org.thoughtcrime.securesms.components.emoji.EmojiProvider;
 import org.thoughtcrime.securesms.connect.AccountManager;
@@ -54,6 +58,11 @@ public class ApplicationContext extends MultiDexApplication {
   public NotificationCenter     notificationCenter;
   private JobManager            jobManager;
 
+  private int                   debugOnAvailableCount;
+  private int                   debugOnBlockedStatusChangedCount;
+  private int                   debugOnCapabilitiesChangedCount;
+  private int                   debugOnLinkPropertiesChangedCount;
+
   public static ApplicationContext getInstance(@NonNull Context context) {
     return (ApplicationContext)context.getApplicationContext();
   }
@@ -120,6 +129,33 @@ public class ApplicationContext extends MultiDexApplication {
 
     new ForegroundDetector(ApplicationContext.getInstance(this));
 
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
+      ConnectivityManager connectivityManager =
+        (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
+      connectivityManager.registerDefaultNetworkCallback(new ConnectivityManager.NetworkCallback() {
+        @Override
+        public void onAvailable(@NonNull android.net.Network network) {
+          Log.i("DeltaChat", "++++++++++++++++++ NetworkCallback.onAvailable() #" + debugOnAvailableCount++);
+          dcAccounts.maybeNetwork();
+        }
+
+        @Override
+        public void onBlockedStatusChanged(@NonNull android.net.Network network, boolean blocked) {
+          Log.i("DeltaChat", "++++++++++++++++++ NetworkCallback.onBlockedStatusChanged() #" + debugOnBlockedStatusChangedCount++);
+        }
+
+        @Override
+        public void onCapabilitiesChanged(@NonNull android.net.Network network, NetworkCapabilities networkCapabilities) {
+          // usually called after onAvailable(), so a maybeNetwork seems contraproductive
+          Log.i("DeltaChat", "++++++++++++++++++ NetworkCallback.onCapabilitiesChanged() #" + debugOnCapabilitiesChangedCount++);
+        }
+
+        @Override
+        public void onLinkPropertiesChanged(@NonNull android.net.Network network, LinkProperties linkProperties) {
+          Log.i("DeltaChat", "++++++++++++++++++ NetworkCallback.onLinkPropertiesChanged() #" + debugOnLinkPropertiesChangedCount++);
+        }
+      });
+    } // no else: use old method for debugging
     BroadcastReceiver networkStateReceiver = new NetworkStateReceiver();
     registerReceiver(networkStateReceiver, new IntentFilter(android.net.ConnectivityManager.CONNECTIVITY_ACTION));
 

src/org/thoughtcrime/securesms/connect/NetworkStateReceiver.java

@@ -5,12 +5,15 @@ import android.content.Context;
 import android.content.Intent;
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
+import android.os.Build;
 import android.util.Log;
 
 import com.b44t.messenger.DcContext;
 
 public class NetworkStateReceiver extends BroadcastReceiver {
 
+    private int debugConnectedCount;
+
     @Override
     public void onReceive(Context context, Intent intent) {
 
@@ -19,8 +22,9 @@ public class NetworkStateReceiver extends BroadcastReceiver {
             NetworkInfo ni = manager.getActiveNetworkInfo();
 
             if (ni != null && ni.getState() == NetworkInfo.State.CONNECTED) {
-                Log.i("DeltaChat", "++++++++++++++++++ Connected ++++++++++++++++++");
+                Log.i("DeltaChat", "++++++++++++++++++ Connected #" + debugConnectedCount++);
-                new Thread(() -> {
+                if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N) {
+                  new Thread(() -> {
                     // call dc_maybe_network() from a worker thread.
                     // theoretically, dc_maybe_network() can be called from the main thread and returns at once,
                     // however, in reality, it does currently halt things for some seconds.
@@ -28,7 +32,8 @@ public class NetworkStateReceiver extends BroadcastReceiver {
                     Log.i("DeltaChat", "calling maybeNetwork()");
                     DcHelper.getAccounts(context).maybeNetwork();
                     Log.i("DeltaChat", "maybeNetwork() returned");
-                }).start();
+                  }).start();
+                }
             }
         }
         catch (Exception e) {