android: make foreground notification call synchronous, and use exped… (#736)

android: make foreground notification call synchronous, and use expedited work

-Stop using Dispatchers.IO for showing foreground notifications, since the scheduling can introduce delays for work that we want done immediately
-Make WorkManager expedited to avoid delaying/losing tasks scheduled when the app is backgrounded/immediately

Updates tailscale/tailscale#14148

Signed-off-by: kari-ts <kari@tailscale.com>

Author: kari-ts

android/src/main/java/com/tailscale/ipn/IPNReceiver.java

@@ -6,9 +6,11 @@
 import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.Intent;
-import androidx.work.Data;
 
+import androidx.work.Data;
+import androidx.work.ExistingWorkPolicy;
 import androidx.work.OneTimeWorkRequest;
+import androidx.work.OutOfQuotaPolicy;
 import androidx.work.WorkManager;
 
 import java.util.Objects;
@@ -20,26 +22,56 @@ public class IPNReceiver extends BroadcastReceiver {
 
     public static final String INTENT_CONNECT_VPN = "com.tailscale.ipn.CONNECT_VPN";
     public static final String INTENT_DISCONNECT_VPN = "com.tailscale.ipn.DISCONNECT_VPN";
-
     private static final String INTENT_USE_EXIT_NODE = "com.tailscale.ipn.USE_EXIT_NODE";
 
+    // Unique work names prevent connect/disconnect flapping from enqueuing a long backlog.
+    private static final String WORK_CONNECT = "ipn-connect-vpn";
+    private static final String WORK_DISCONNECT = "ipn-disconnect-vpn";
+    private static final String WORK_USE_EXIT_NODE = "ipn-use-exit-node";
+
     @Override
     public void onReceive(Context context, Intent intent) {
-        WorkManager workManager = WorkManager.getInstance(context);
+        if (intent == null) return;
 
-        // On the relevant action, start the relevant worker, which can stay active for longer than this receiver can.
-        if (Objects.equals(intent.getAction(), INTENT_CONNECT_VPN)) {
-            workManager.enqueue(new OneTimeWorkRequest.Builder(StartVPNWorker.class).build());
-        } else if (Objects.equals(intent.getAction(), INTENT_DISCONNECT_VPN)) {
-            workManager.enqueue(new OneTimeWorkRequest.Builder(StopVPNWorker.class).build());
-        }
-        else if (Objects.equals(intent.getAction(), INTENT_USE_EXIT_NODE)) {
+        final WorkManager workManager = WorkManager.getInstance(context);
+        final String action = intent.getAction();
+
+        if (Objects.equals(action, INTENT_CONNECT_VPN)) {
+            OneTimeWorkRequest req =
+                    new OneTimeWorkRequest.Builder(StartVPNWorker.class)
+                            .setExpedited(OutOfQuotaPolicy.RUN_AS_NON_EXPEDITED_WORK_REQUEST)
+                            .addTag(WORK_CONNECT)
+                            .build();
+
+            workManager.enqueueUniqueWork(WORK_CONNECT, ExistingWorkPolicy.REPLACE, req);
+
+        } else if (Objects.equals(action, INTENT_DISCONNECT_VPN)) {
+            OneTimeWorkRequest req =
+                    new OneTimeWorkRequest.Builder(StopVPNWorker.class)
+                            .setExpedited(OutOfQuotaPolicy.RUN_AS_NON_EXPEDITED_WORK_REQUEST)
+                            .addTag(WORK_DISCONNECT)
+                            .build();
+
+            workManager.enqueueUniqueWork(WORK_DISCONNECT, ExistingWorkPolicy.REPLACE, req);
+
+        } else if (Objects.equals(action, INTENT_USE_EXIT_NODE)) {
             String exitNode = intent.getStringExtra("exitNode");
             boolean allowLanAccess = intent.getBooleanExtra("allowLanAccess", false);
-            Data.Builder workData = new Data.Builder();
-            workData.putString(UseExitNodeWorker.EXIT_NODE_NAME, exitNode);
-            workData.putBoolean(UseExitNodeWorker.ALLOW_LAN_ACCESS, allowLanAccess);
-            workManager.enqueue(new OneTimeWorkRequest.Builder(UseExitNodeWorker.class).setInputData(workData.build()).build());
+
+            Data input =
+                    new Data.Builder()
+                            .putString(UseExitNodeWorker.EXIT_NODE_NAME, exitNode)
+                            .putBoolean(UseExitNodeWorker.ALLOW_LAN_ACCESS, allowLanAccess)
+                            .build();
+
+            OneTimeWorkRequest req =
+                    new OneTimeWorkRequest.Builder(UseExitNodeWorker.class)
+                            .setInputData(input)
+                            .setExpedited(OutOfQuotaPolicy.RUN_AS_NON_EXPEDITED_WORK_REQUEST)
+                            .addTag(WORK_USE_EXIT_NODE)
+                            .build();
+
+            workManager.enqueueUniqueWork(WORK_USE_EXIT_NODE, ExistingWorkPolicy.REPLACE, req);
         }
     }
 }

android/src/main/java/com/tailscale/ipn/IPNService.kt

@@ -54,7 +54,7 @@ open class IPNService : VpnService(), libtailscale.IPNService {
           START_NOT_STICKY
         }
         ACTION_START_VPN -> {
-          scope.launch { showForegroundNotification() }
+          showForegroundNotification()
           app.setWantRunning(true)
           Libtailscale.requestVPN(this)
           START_STICKY
@@ -78,7 +78,7 @@ open class IPNService : VpnService(), libtailscale.IPNService {
           // This means that we were restarted after the service was killed
           // (potentially due to OOM).
           if (UninitializedApp.get().isAbleToStartVPN()) {
-            scope.launch { showForegroundNotification() }
+            showForegroundNotification() 
             App.get()
             Libtailscale.requestVPN(this)
             START_STICKY