Acquire MulticastLock for local discovery to work on Android 11 (fixes …

…#735) (#800)
Catfriend1 · May 16, 2021 · ee2642b · ee2642b
1 parent 6ba250c
commit ee2642b
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diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
@@ -33,6 +33,8 @@
     <uses-permission android:name="android.permission.CAMERA" />
     <!-- MANAGE_EXTERNAL_STORAGE is required on Android 11 "R" -->
     <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
+    <!-- CHANGE_WIFI_MULTICAST_STATE is required for local discovery to work on Android 11 "R" -->
+    <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE"/>
 
     <application
         android:allowBackup="false"

diff --git a/app/src/main/java/com/nutomic/syncthingandroid/service/SyncthingRunnable.java b/app/src/main/java/com/nutomic/syncthingandroid/service/SyncthingRunnable.java
@@ -4,6 +4,8 @@
 import android.content.Context;
 import android.content.Intent;
 import android.content.SharedPreferences;
+import android.net.wifi.WifiManager;
+import android.net.wifi.WifiManager.MulticastLock;
 import android.os.Build;
 import android.os.Environment;
 import android.os.PowerManager;
@@ -158,12 +160,19 @@ public String run(boolean returnStdOut) throws ExecutableNotFoundException {
             );
         }
 
+        MulticastLock multicastLock = null;
         Process process = null;
         try {
             if (wakeLock != null) {
                 wakeLock.acquire();
             }
 
+            // See issue #735: Android 11 blocks local discovery if we did not acquire MulticastLock.
+            WifiManager wifi = (WifiManager) mContext.getApplicationContext().getSystemService(Context.WIFI_SERVICE);
+            multicastLock = wifi.createMulticastLock("multicastLock");
+            multicastLock.setReferenceCounted(true);
+            multicastLock.acquire();
+
             /**
              * Setup and run a new syncthing instance
              */
@@ -250,6 +259,10 @@ public String run(boolean returnStdOut) throws ExecutableNotFoundException {
             if (wakeLock != null) {
                 wakeLock.release();
             }
+            if (multicastLock != null) {
+                multicastLock.release();
+                multicastLock = null;
+            }
             if (process != null) {
                 process.destroy();
             }