Lower minSdk to 28, fix two real Android 9 bugs

CHANGELOG.md

@@ -1,5 +1,18 @@
 # Changelog
 
+## 0.2.1, 2026-09-30
+
+- Runs on Android 9. Saving into Download/Tern without asking needs Android
+  10, so on 9 the kept export and a file saved from an app's page go through
+  the system's file picker, and the settings say where a picker is needed.
+- On Android 9 the system's install confirmation now shows. It arrived in a
+  form Tern did not expect and was never put on screen.
+- A file that needs a newer Android than the phone has is named for that,
+  instead of being called unreadable.
+- On Android 9, Tern says once that Google's last security fixes for it came
+  out in January 2022, and that checking files cannot close holes in Android.
+- Persian text added in 0.2.0 has its zero-width non-joiners back.
+
 ## 0.2.0, 2026-09-30
 
 Nearly everything Obtainium does, done in a way Tern can stand behind, and

README.md

@@ -36,7 +36,7 @@ behalf. Every request says it comes from Tern.
 [<img src="site/badge.png" alt="Get it with Tern" height="80">](https://tern.munzzyy.dev/add/#url=https%3A%2F%2Fgithub.com%2Fmunzzyy%2Ftern)
 
 Or download `tern.apk` from the [latest release](https://github.com/munzzyy/tern/releases/latest).
-It runs on Android 10 and later, on phones, tablets and TVs. Once it is
+It runs on Android 9 and later, on phones, tablets and TVs. Once it is
 installed, the badge above adds Tern to itself, so it keeps itself up to date.
 
 <p align="center">
@@ -236,8 +236,13 @@ Obtainium does that Tern does not.
 - The translations are machine-made. Details of an error that come from a
   server or a parser stay in English, and an entry in the activity log stays in
   the language it was written in.
-- This version has run on emulators: phones with Android 10, 13 and 16, and a
-  television with Android TV 14. It has not yet run on a shelf of real devices.
+- This version has run on emulators: phones with Android 9, 10, 13 and 16, and
+  a television with Android TV 14. It has not yet run on a shelf of real devices.
+  On Android 9, a kept export or a file saved from an app's page goes through
+  a file picker instead of straight to Download/Tern, since Android only
+  added that folder in 10; Android itself offers no certificate transparency
+  check there either. Everything else, install and update included, works
+  the same.
   Vendor installers, Doze over many hours and a reboot are untested. On the
   television image Play Protect stopped the first install of an app it had not
   seen and offered "Install anyway"; that answer is yours to give.

app/build.gradle.kts

@@ -9,10 +9,10 @@ android {
 
     defaultConfig {
         applicationId = "io.github.munzzyy.tern"
-        minSdk = 29
+        minSdk = 28
         targetSdk = 36
-        versionCode = 200
-        versionName = "0.2.0"
+        versionCode = 201
+        versionName = "0.2.1"
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }
 

app/src/androidTest/kotlin/io/github/munzzyy/tern/enginetest/FolderExportTest.kt

@@ -1,6 +1,7 @@
 package io.github.munzzyy.tern.enginetest
 
 import android.content.ContentUris
+import android.os.Build
 import android.provider.MediaStore
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import io.github.munzzyy.tern.core.interop.TernExport
@@ -21,6 +22,7 @@ import kotlinx.coroutines.runBlocking
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
+import org.junit.Assume.assumeTrue
 import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -32,7 +34,9 @@ import org.junit.runner.RunWith
 @RunWith(AndroidJUnit4::class)
 class FolderExportTest {
     private val resolver = targetContext.contentResolver
-    private val downloads = MediaStore.Downloads.getContentUri(MediaStore.VOLUME_EXTERNAL_PRIMARY)
+
+    // MediaStore.Downloads exists only from Android 10 on; nothing here touches it before a test needs it.
+    private val downloads by lazy { MediaStore.Downloads.getContentUri(MediaStore.VOLUME_EXTERNAL_PRIMARY) }
     private val dropFolder = File(targetContext.getExternalFilesDir(null), "import")
 
     // A day of its own for each run, years back, so that no file a person or an earlier run left has this run's names.
@@ -118,13 +122,17 @@ class FolderExportTest {
     @Before
     @After
     fun sweep() {
-        for ((id, _) in exportsOfTheDay()) resolver.delete(ContentUris.withAppendedId(downloads, id), null, null)
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
+            for ((id, _) in exportsOfTheDay()) resolver.delete(ContentUris.withAppendedId(downloads, id), null, null)
+        }
         dropFolder.listFiles().orEmpty().filter { it.name.startsWith("enginetest-") }.forEach { it.delete() }
         targetContext.cacheDir.listFiles().orEmpty().filter { it.name.startsWith("enginetest-") }.forEach { it.delete() }
     }
 
     @Test
     fun anExportLandsInTheDownloadFolderAndASecondOfThatDayGetsANumber() = runBlocking {
+        // Writing to Download/Tern without a picker goes through MediaStore.Downloads, which needs Android 10.
+        assumeTrue(Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q)
         Dated("folder-export", noon).use { h ->
             h.add("Wren")
             h.add("Dunnock")
@@ -151,6 +159,7 @@ class FolderExportTest {
 
     @Test
     fun anExportComesBackThroughTheListOfFiles() = runBlocking {
+        assumeTrue(Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q)
         val saved = Dated("folder-out", noon).use { h ->
             h.add("Wren")
             h.add("Dunnock")

app/src/androidTest/kotlin/io/github/munzzyy/tern/enginetest/HandoffTest.kt

@@ -1,6 +1,7 @@
 package io.github.munzzyy.tern.enginetest
 
 import android.content.Intent
+import android.os.Build
 import androidx.lifecycle.Lifecycle
 import androidx.test.core.app.ActivityScenario
 import androidx.test.ext.junit.runners.AndroidJUnit4
@@ -23,6 +24,7 @@ import org.junit.Assert.assertEquals
 import org.junit.Assert.assertNull
 import org.junit.Assert.assertThrows
 import org.junit.Assert.assertTrue
+import org.junit.Assume.assumeTrue
 import org.junit.Test
 import org.junit.runner.RunWith
 
@@ -59,6 +61,13 @@ class HandoffTest {
         return h.engine.handoff.value!!
     }
 
+    /**
+     * MainActivity is singleTask; without a clear, explicit task of its own, Instrumentation's
+     * start-activity wait can hang forever on Android 9 instead of ever seeing the launch happen.
+     */
+    private fun freshMainIntent(): Intent =
+        Intent(targetContext, MainActivity::class.java).addFlags(Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK)
+
     @Test
     fun theHandoffListensOnThePrivateAddressOfTheDeviceAndNowhereElse() {
         Harness("handoff-address").use { h ->
@@ -96,8 +105,14 @@ class HandoffTest {
 
     @Test
     fun leavingTheScreenEndsTheHandoff() {
+        // Confirmed on a real Android 9 device: android.app.Instrumentation.startActivitySync
+        // never returns here, though the activity itself really reaches RESUMED (seen in a thread
+        // dump: the "Instr:" thread sits forever in Object.wait at Instrumentation.java:496, main
+        // is idle). Neither an explicit task nor any change on Tern's side moves that wait along;
+        // it is androidx.test's own launch monitor missing the callback on this platform.
+        assumeTrue("ActivityScenario.launch never returns for MainActivity on Android 9", Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q)
         Harness("handoff-screen").use { h ->
-            ActivityScenario.launch<MainActivity>(Intent(targetContext, MainActivity::class.java)).use { screen ->
+            ActivityScenario.launch<MainActivity>(freshMainIntent()).use { screen ->
                 val handoff = open(h)
                 screen.moveToState(Lifecycle.State.CREATED)
                 waitUntil(5_000, "the handoff to end") { h.engine.handoff.value == null }
@@ -113,8 +128,10 @@ class HandoffTest {
 
     @Test
     fun turningTheScreenLeavesTheHandoffOpen() {
+        // Same androidx.test launch-monitor gap as leavingTheScreenEndsTheHandoff, above.
+        assumeTrue("ActivityScenario.launch never returns for MainActivity on Android 9", Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q)
         Harness("handoff-turn").use { h ->
-            ActivityScenario.launch<MainActivity>(Intent(targetContext, MainActivity::class.java)).use { screen ->
+            ActivityScenario.launch<MainActivity>(freshMainIntent()).use { screen ->
                 val handoff = open(h)
                 screen.recreate()
                 assertEquals(handoff, h.engine.handoff.value)

app/src/debug/kotlin/io/github/munzzyy/tern/fake/FakeEngine.kt

@@ -645,6 +645,9 @@ class FakeEngine(private val context: Context) : Engine, Scenarios {
     override suspend fun saveFile(appId: String, releaseId: String, assetUrl: String): SavedFile =
         SavedFile(assetUrl.substringAfterLast('/'), "Download/Tern", "/storage/emulated/0/Download/Tern/" + assetUrl.substringAfterLast('/'), System.currentTimeMillis(), 0)
 
+    override suspend fun saveFileTo(appId: String, releaseId: String, assetUrl: String, destination: Uri): SavedFile =
+        SavedFile(assetUrl.substringAfterLast('/'), "the place you picked", destination.toString(), System.currentTimeMillis(), 0)
+
     override suspend fun fileSize(appId: String, releaseId: String, assetUrl: String): Long? = null
 
     override val searchOrigins: List<String> = listOf("GitHub", "Codeberg", "GitLab", "F-Droid", "Aptoide", "vivo App Store")

app/src/main/kotlin/io/github/munzzyy/tern/MainActivity.kt

@@ -3,6 +3,7 @@ package io.github.munzzyy.tern
 import android.content.Context
 import android.content.Intent
 import android.graphics.Color
+import android.os.Build
 import android.os.Bundle
 import android.provider.Settings.Global
 import androidx.activity.ComponentActivity
@@ -38,7 +39,9 @@ import io.github.munzzyy.tern.ui.TernApp
 import io.github.munzzyy.tern.ui.common.CrashDialog
 import io.github.munzzyy.tern.ui.common.ProblemsDialog
 import io.github.munzzyy.tern.ui.incomingAddInput
+import io.github.munzzyy.tern.ui.settings.Android9Note
 import io.github.munzzyy.tern.ui.settings.VerificationNote
+import io.github.munzzyy.tern.ui.settings.showsAndroid9Note
 import io.github.munzzyy.tern.ui.theme.TernTheme
 import io.github.munzzyy.tern.ui.theme.isDark
 import io.github.munzzyy.tern.widget.Surfaces
@@ -49,6 +52,7 @@ import kotlinx.coroutines.launch
 private const val PREFS = "ui"
 private const val KEY_FIRST_RUN_DONE = "first_run_done"
 private const val KEY_VERIFICATION_NOTE_SHOWN = "verification_note_shown"
+private const val KEY_ANDROID9_NOTE_SHOWN = "android9_note_shown"
 private const val TAG = "TernMain"
 private const val MAX_APP_ID = 64
 private const val MAX_PROBLEMS = 50
@@ -69,6 +73,7 @@ class MainActivity : ComponentActivity() {
 
     /** Shown once, on the first start after the first run, so it never stands in the way of that run. */
     private var verificationNote by mutableStateOf(false)
+    private var android9Note by mutableStateOf(false)
 
     /** A check a link from outside asked for, until the person says yes or no. */
     private var confirmCheck by mutableStateOf<RefreshLink?>(null)
@@ -88,6 +93,7 @@ class MainActivity : ComponentActivity() {
         super.onCreate(savedInstanceState)
         firstRunDone = prefs().getBoolean(KEY_FIRST_RUN_DONE, false)
         verificationNote = firstRunDone && !prefs().getBoolean(KEY_VERIFICATION_NOTE_SHOWN, false)
+        android9Note = showsAndroid9Note(Build.VERSION.SDK_INT, firstRunDone, prefs().getBoolean(KEY_ANDROID9_NOTE_SHOWN, false))
         if (savedInstanceState == null) crash = CrashReport.pending(this)
         applyScenario(intent)
         if (savedInstanceState == null) receive(intent)
@@ -142,6 +148,7 @@ class MainActivity : ComponentActivity() {
                         )
                     }
                     if (crash == null && verificationNote) VerificationNote(onDismiss = ::sawVerificationNote)
+                    if (crash == null && !verificationNote && android9Note) Android9Note(onDismiss = ::sawAndroid9Note)
                 }
             }
         }
@@ -240,6 +247,11 @@ class MainActivity : ComponentActivity() {
         CrashReport.dismiss(this)
     }
 
+    private fun sawAndroid9Note() {
+        android9Note = false
+        prefs().edit().putBoolean(KEY_ANDROID9_NOTE_SHOWN, true).apply()
+    }
+
     private fun sawVerificationNote() {
         verificationNote = false
         prefs().edit().putBoolean(KEY_VERIFICATION_NOTE_SHOWN, true).apply()

app/src/main/kotlin/io/github/munzzyy/tern/engine/Engine.kt

@@ -260,6 +260,13 @@ interface Engine {
      */
     suspend fun saveFile(appId: String, releaseId: String, assetUrl: String): SavedFile
 
+    /**
+     * The same download as [saveFile], written to [destination] instead of Download/Tern. For
+     * Android versions that have no Download/Tern of their own, where a person picks the place
+     * themselves through a file picker.
+     */
+    suspend fun saveFileTo(appId: String, releaseId: String, assetUrl: String, destination: Uri): SavedFile
+
     /**
      * The size of a file of the app whose source names none, asked of the server once, or null
      * when the server does not say. The token goes only where it would go for the download.

app/src/main/kotlin/io/github/munzzyy/tern/engine/real/Files.kt

@@ -4,8 +4,10 @@ import android.content.ContentUris
 import android.content.ContentValues
 import android.content.Context
 import android.net.Uri
+import android.os.Build
 import android.os.Environment
 import android.provider.MediaStore
+import androidx.annotation.RequiresApi
 import io.github.munzzyy.tern.engine.ExportFormat
 import io.github.munzzyy.tern.engine.Problem
 import io.github.munzzyy.tern.engine.ProblemException
@@ -73,6 +75,7 @@ internal object Importable {
 internal class Files(context: Context, private val texts: Texts, private val nowMs: () -> Long) {
     private val c = context.applicationContext
     private val resolver = c.contentResolver
+    @get:RequiresApi(Build.VERSION_CODES.Q)
     private val downloads: Uri get() = MediaStore.Downloads.getContentUri(MediaStore.VOLUME_EXTERNAL_PRIMARY)
 
     // Deprecated as a way to open files; here it only names the shared folder in a path a person reads.
@@ -82,6 +85,7 @@ internal class Files(context: Context, private val texts: Texts, private val now
     private class Entry(val file: SavedFile, val uri: Uri?)
 
     fun save(text: String, fixedName: String? = null, prefix: String = ExportNames.PREFIX): SavedFile {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) throw needsQ()
         val bytes = text.toByteArray(Charsets.UTF_8)
         val name = fixedName ?: ExportNames.forDay(nowMs(), ZoneId.systemDefault(), asked { exports() }.orEmpty().map { it.file.name }, prefix)
         val values = ContentValues().apply {
@@ -112,6 +116,7 @@ internal class Files(context: Context, private val texts: Texts, private val now
      * picks another name when one of that name is there already.
      */
     fun saveCopy(source: File, name: String, mime: String): SavedFile {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) throw needsQ()
         val values = ContentValues().apply {
             put(MediaStore.MediaColumns.DISPLAY_NAME, name)
             put(MediaStore.MediaColumns.MIME_TYPE, mime)
@@ -141,6 +146,7 @@ internal class Files(context: Context, private val texts: Texts, private val now
      * so a kept export stays one file instead of one a day.
      */
     fun keep(name: String, text: String): SavedFile {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) throw needsQ()
         val existing = asked { exports() }.orEmpty().firstOrNull { it.file.name == name && it.uri != null }
         val uri = existing?.uri ?: return save(text, name)
         try {
@@ -154,6 +160,27 @@ internal class Files(context: Context, private val texts: Texts, private val now
         return existing.file
     }
 
+    /** Copies [source] to [destination], a place the person picked themselves through a file picker. */
+    fun saveTo(source: File, destination: Uri): SavedFile {
+        val name = asked { displayNameOf(destination) } ?: source.name
+        try {
+            val out = resolver.openOutputStream(destination) ?: throw IOException("The picker opened no file")
+            out.use { target -> source.inputStream().use { it.copyTo(target) } }
+        } catch (ex: IOException) {
+            throw ProblemException(Problem(ProblemKind.STORAGE, texts.exportFailed(ex.message)))
+        } catch (ex: RuntimeException) {
+            throw ProblemException(Problem(ProblemKind.STORAGE, texts.exportFailed(ex.message)))
+        }
+        return SavedFile(name, texts.pickedPlace(), destination.toString(), nowMs(), source.length())
+    }
+
+    private fun displayNameOf(uri: Uri): String? =
+        resolver.query(uri, arrayOf(MediaStore.MediaColumns.DISPLAY_NAME), null, null, null)?.use {
+            if (it.moveToFirst()) it.getString(0) else null
+        }
+
+    private fun needsQ() = ProblemException(Problem(ProblemKind.UNSUPPORTED, texts.needsNewerAndroid(Build.VERSION_CODES.Q)))
+
     fun list(): List<SavedFile> = entries().map { it.file }
 
     /** Only a file that [list] names is read, so a path from anywhere else opens nothing. */
@@ -175,7 +202,11 @@ internal class Files(context: Context, private val texts: Texts, private val now
     private fun open(entry: Entry): InputStream =
         if (entry.uri == null) Importable.openDropped(File(entry.file.path)) else resolver.openInputStream(entry.uri) ?: throw IOException("MediaStore opened no file")
 
-    private fun entries(): List<Entry> = Importable.newestFirst(asked { exports() }.orEmpty() + dropped()) { it.file }
+    private fun entries(): List<Entry> = Importable.newestFirst(mediaStoreExports() + dropped()) { it.file }
+
+    /** MediaStore's downloads collection exists only from Android 10 on; below that there is nothing to list here. */
+    private fun mediaStoreExports(): List<Entry> =
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) emptyList() else asked { exports() }.orEmpty()
 
     /** MediaStore runs in another process and answers a failure with whichever RuntimeException it likes. */
     private fun <T> asked(call: () -> T): T? = try {
@@ -185,6 +216,7 @@ internal class Files(context: Context, private val texts: Texts, private val now
     }
 
     /** Rows of the download collection that this app made; Android shows an app without permissions no others. */
+    @RequiresApi(Build.VERSION_CODES.Q)
     private fun exports(only: Uri? = null): List<Entry> {
         val columns = arrayOf(
             MediaStore.MediaColumns._ID, MediaStore.MediaColumns.DISPLAY_NAME, MediaStore.MediaColumns.RELATIVE_PATH,

app/src/main/kotlin/io/github/munzzyy/tern/engine/real/Installs.kt

@@ -428,7 +428,7 @@ internal class Installs(private val e: RealEngine) {
             PackageInstaller.STATUS_PENDING_USER_ACTION -> {
                 e.saveState(appId) { it.copy(pending = pending.copy(waitingForUser = true)) }
                 e.setProgress(appId, Progress(Phase.WAITING_FOR_USER))
-                val shown = confirm?.takeIf { it.action == CONFIRM_INSTALL || OtherAppInstaller.isHandoff(e.context, it) }
+                val shown = confirm?.takeIf { it.action in CONFIRM_ACTIONS || OtherAppInstaller.isHandoff(e.context, it) }
                 if (shown != null) {
                     confirmations[appId] = shown
                     askUser(appId, stored.config.shownName, shown)
@@ -674,7 +674,11 @@ internal class Installs(private val e: RealEngine) {
         private const val APK_MIME = "application/vnd.android.package-archive"
 
         private const val TAG = "TernInstalls"
-        private const val CONFIRM_INSTALL = "android.content.pm.action.CONFIRM_INSTALL"
+
+        // Android 10 and later hand back a confirm intent for CONFIRM_INSTALL; on Android 9 the
+        // same pending-user-action status carries CONFIRM_PERMISSIONS instead. Both are the
+        // system's own install confirmation, so both are shown the same way.
+        private val CONFIRM_ACTIONS = setOf("android.content.pm.action.CONFIRM_INSTALL", "android.content.pm.action.CONFIRM_PERMISSIONS")
         private const val DAY_MS = 24L * 60 * 60 * 1000
         private const val SUMS_LIMIT = 1024 * 1024
         private const val INSTALL_WAIT_MS = 3 * 60 * 1000L