android/ui: prompt for write external storage permission and show error if necessary

Updates #ENG-2948

Signed-off-by: Percy Wegmann <percy@tailscale.com>

android/build.gradle

@@ -87,6 +87,7 @@ dependencies {
     implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.7.0'
     implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.7.0'
     implementation 'androidx.activity:activity-compose:1.8.2'
+    implementation "com.google.accompanist:accompanist-permissions:0.34.0"
 
     // Navigation dependencies.
     def nav_version = "2.7.7"

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

@@ -36,7 +36,6 @@ import androidx.browser.customtabs.CustomTabsIntent
 import androidx.core.app.ActivityCompat
 import androidx.core.app.NotificationCompat
 import androidx.core.app.NotificationManagerCompat
-import androidx.core.content.ContextCompat
 import androidx.security.crypto.EncryptedSharedPreferences
 import androidx.security.crypto.MasterKey
 import com.tailscale.ipn.mdm.AlwaysNeverUserDecidesSetting
@@ -314,20 +313,6 @@ class App : Application(), libtailscale.AppContext {
       return null
     }
 
-  fun requestWriteStoragePermission(act: Activity) {
-    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q ||
-        Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
-      // We can write files without permission.
-      return
-    }
-    if (ContextCompat.checkSelfPermission(act, Manifest.permission.WRITE_EXTERNAL_STORAGE) ==
-        PackageManager.PERMISSION_GRANTED) {
-      return
-    }
-    act.requestPermissions(
-        arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE), IPNActivity.WRITE_STORAGE_RESULT)
-  }
-
   @Throws(IOException::class)
   fun insertMedia(name: String?, mimeType: String): String {
     return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {

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

@@ -5,7 +5,6 @@ package com.tailscale.ipn;
 
 import android.app.Activity;
 import android.content.Intent;
-import android.content.pm.PackageManager;
 import android.content.res.Configuration;
 import android.database.Cursor;
 import android.net.Uri;
@@ -14,11 +13,7 @@ import android.provider.OpenableColumns;
 
 import java.util.List;
 
-import libtailscale.Libtailscale;
-
 public final class IPNActivity extends Activity {
-    final static int WRITE_STORAGE_RESULT = 1000;
-
     @Override
     public void onCreate(Bundle state) {
         super.onCreate(state);
@@ -88,15 +83,6 @@ public final class IPNActivity extends Activity {
 //        App.onShareIntent(nfiles, types, mimes, items, names, sizes);
     }
 
-    @Override
-    public void onRequestPermissionsResult(int reqCode, String[] perms, int[] grants) {
-        if (reqCode == WRITE_STORAGE_RESULT) {
-            if (grants.length > 0 && grants[0] == PackageManager.PERMISSION_GRANTED) {
-                Libtailscale.onWriteStorageGranted();
-            }
-        }
-    }
-
     @Override
     public void onDestroy() {
         super.onDestroy();

android/src/main/java/com/tailscale/ipn/ui/view/ErrorDialog.kt

@@ -37,7 +37,7 @@ fun ErrorDialog(type: ErrorDialogType, action: () -> Unit = {}) {
 
 @Composable
 fun ErrorDialog(
-    @StringRes title: Int,
+    @StringRes title: Int = R.string.error,
     @StringRes message: Int,
     @StringRes buttonText: Int = R.string.ok,
     onDismiss: () -> Unit = {}

android/src/main/java/com/tailscale/ipn/ui/view/MainView.kt

@@ -3,6 +3,9 @@
 
 package com.tailscale.ipn.ui.view
 
+import android.Manifest
+import androidx.activity.compose.rememberLauncherForActivityResult
+import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
@@ -36,8 +39,10 @@ import androidx.compose.material3.SearchBar
 import androidx.compose.material3.SearchBarDefaults
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
@@ -49,6 +54,10 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
+import com.google.accompanist.permissions.ExperimentalPermissionsApi
+import com.google.accompanist.permissions.isGranted
+import com.google.accompanist.permissions.rememberPermissionState
+import com.google.accompanist.permissions.shouldShowRationale
 import com.tailscale.ipn.R
 import com.tailscale.ipn.ui.model.Ipn
 import com.tailscale.ipn.ui.model.IpnLocal
@@ -60,6 +69,7 @@ import com.tailscale.ipn.ui.util.PeerSet
 import com.tailscale.ipn.ui.util.flag
 import com.tailscale.ipn.ui.util.itemsWithDividers
 import com.tailscale.ipn.ui.viewModel.MainViewModel
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 
 // Navigation actions for the MainView
@@ -69,6 +79,7 @@ data class MainViewNavigation(
     val onNavigateToExitNodes: () -> Unit
 )
 
+@OptIn(ExperimentalPermissionsApi::class)
 @Composable
 fun MainView(navigation: MainViewNavigation, viewModel: MainViewModel = viewModel()) {
   LoadingIndicator.Wrap {
@@ -108,6 +119,8 @@ fun MainView(navigation: MainViewNavigation, viewModel: MainViewModel = viewMode
             when (state.value) {
               Ipn.State.Running -> {
 
+                PromptWriteStoragePermissionsIfNecessary()
+
                 val selfPeerId = viewModel.selfPeerId.collectAsState(initial = "")
                 Row(
                     modifier =
@@ -395,3 +408,34 @@ fun PeerList(
         }
       }
 }
+
+@OptIn(ExperimentalPermissionsApi::class)
+@Composable
+fun PromptWriteStoragePermissionsIfNecessary() {
+  val writeStoragePermissionState =
+      rememberPermissionState(Manifest.permission.WRITE_EXTERNAL_STORAGE)
+
+  val showDialog = remember { MutableStateFlow(false) }
+
+  val requestPermissionLauncher =
+      rememberLauncherForActivityResult(ActivityResultContracts.RequestPermission()) { granted ->
+        if (!granted) {
+          showDialog.value = true
+        }
+      }
+
+  LaunchedEffect(writeStoragePermissionState) {
+    if (!writeStoragePermissionState.status.isGranted &&
+        writeStoragePermissionState.status.shouldShowRationale) {
+      showDialog.value = true
+    } else {
+      requestPermissionLauncher.launch(Manifest.permission.WRITE_EXTERNAL_STORAGE)
+    }
+  }
+
+  if (showDialog.collectAsState().value) {
+    ErrorDialog(title = R.string.permission_required, message = R.string.taildrop_requires_write) {
+      showDialog.value = false
+    }
+  }
+}

android/src/main/res/values/strings.xml

@@ -160,4 +160,7 @@
     <string name="shows_or_hides_the_ui_to_run_the_android_device_as_an_exit_node">Shows or hides the UI to run the Android device as an exit node.</string>
     <string name="run_as_exit_node_visibility">Run As Exit Node visibility</string>
 
+    <!-- Permissions Management -->
+    <string name="permission_required">Permission Required</string>
+    <string name="taildrop_requires_write">Please grant access to write to external storage to be able to receive files with Taildrop.</string>
 </resources>