Use truncate mode to replace the contents of existing files

`ContentResolver.openOutputStream(Uri)` does not truncate existing files. If the amount of data written is smaller than the file size, you end up with new data at the beginning of the file followed by old data at the end of the file.

changelog.d/5663.bugfix

@@ -0,0 +1 @@
+Fixed key export when overwriting existing files

vector/src/main/java/im/vector/app/features/crypto/keys/KeysExporter.kt

@@ -34,7 +34,7 @@ class KeysExporter @Inject constructor(
     suspend fun export(password: String, uri: Uri) {
         withContext(dispatchers.io) {
             val data = session.cryptoService().exportRoomKeys(password)
-            context.contentResolver.openOutputStream(uri)
+            context.contentResolver.openOutputStream(uri, "wt")
                     ?.use { it.write(data) }
                     ?: throw IllegalStateException("Unable to open file for writing")
             verifyExportedKeysOutputFileSize(uri, expectedSize = data.size.toLong())

vector/src/main/java/im/vector/app/features/crypto/keysbackup/setup/KeysBackupSetupStep3Fragment.kt

@@ -165,7 +165,7 @@ class KeysBackupSetupStep3Fragment @Inject constructor() : VectorBaseFragment<Fr
         lifecycleScope.launch(Dispatchers.Main) {
             Try {
                 withContext(Dispatchers.IO) {
-                    requireContext().contentResolver.openOutputStream(uri)
+                    requireContext().contentResolver.openOutputStream(uri, "wt")
                             ?.use { os ->
                                 os.write(data.toByteArray())
                                 os.flush()

vector/src/main/java/im/vector/app/features/crypto/recover/BootstrapSaveRecoveryKeyFragment.kt

@@ -81,7 +81,7 @@ class BootstrapSaveRecoveryKeyFragment @Inject constructor(
             val uri = activityResult.data?.data ?: return@registerStartForActivityResult
             lifecycleScope.launch(Dispatchers.IO) {
                 try {
-                    sharedViewModel.handle(BootstrapActions.SaveKeyToUri(requireContext().contentResolver!!.openOutputStream(uri)!!))
+                    sharedViewModel.handle(BootstrapActions.SaveKeyToUri(requireContext().contentResolver!!.openOutputStream(uri, "wt")!!))
                 } catch (failure: Throwable) {
                     sharedViewModel.handle(BootstrapActions.SaveReqFailed)
                 }

vector/src/main/java/im/vector/app/features/settings/devtools/KeyRequestsFragment.kt

@@ -106,7 +106,7 @@ class KeyRequestsFragment @Inject constructor() : VectorBaseFragment<FragmentDev
             when (it) {
                 is KeyRequestEvents.SaveAudit -> {
                     tryOrNull {
-                        requireContext().contentResolver?.openOutputStream(it.uri)
+                        requireContext().contentResolver?.openOutputStream(it.uri, "wt")
                                 ?.use { os -> os.write(it.raw.toByteArray()) }
                     }
                 }

vector/src/test/java/im/vector/app/features/crypto/keys/KeysExporterTest.kt

@@ -53,7 +53,7 @@ class KeysExporterTest {
     @Test
     fun `when exporting then writes exported keys to context output stream`() {
         givenFileDescriptorWithSize(size = A_ROOM_KEYS_EXPORT.size.toLong())
-        val outputStream = context.givenOutputStreamFor(A_URI)
+        val outputStream = context.givenOutputStreamFor(A_URI, mode = "wt")
 
         runTest { keysExporter.export(A_PASSWORD, A_URI) }
 
@@ -63,7 +63,7 @@ class KeysExporterTest {
     @Test
     fun `given different file size returned for export when exporting then throws UnexpectedExportKeysFileSizeException`() {
         givenFileDescriptorWithSize(size = 110)
-        context.givenOutputStreamFor(A_URI)
+        context.givenOutputStreamFor(A_URI, mode = "wt")
 
         assertFailsWith<UnexpectedExportKeysFileSizeException> {
             runTest { keysExporter.export(A_PASSWORD, A_URI) }
@@ -72,7 +72,7 @@ class KeysExporterTest {
 
     @Test
     fun `given output stream is unavailable for exporting to when exporting then throws IllegalStateException`() {
-        context.givenMissingOutputStreamFor(A_URI)
+        context.givenMissingOutputStreamFor(A_URI, mode = "wt")
 
         assertFailsWith<IllegalStateException>(message = "Unable to open file for writing") {
             runTest { keysExporter.export(A_PASSWORD, A_URI) }
@@ -82,7 +82,7 @@ class KeysExporterTest {
     @Test
     fun `given exported file is missing after export when exporting then throws IllegalStateException`() {
         context.givenFileDescriptor(A_URI, mode = "r") { null }
-        context.givenOutputStreamFor(A_URI)
+        context.givenOutputStreamFor(A_URI, mode = "wt")
 
         assertFailsWith<IllegalStateException>(message = "Exported file not found") {
             runTest { keysExporter.export(A_PASSWORD, A_URI) }

vector/src/test/java/im/vector/app/test/fakes/FakeContext.kt

@@ -39,13 +39,13 @@ class FakeContext(
         every { contentResolver.openFileDescriptor(uri, mode, null) } returns fileDescriptor
     }
 
-    fun givenOutputStreamFor(uri: Uri): OutputStream {
+    fun givenOutputStreamFor(uri: Uri, mode: String): OutputStream {
         val outputStream = mockk<OutputStream>(relaxed = true)
-        every { contentResolver.openOutputStream(uri) } returns outputStream
+        every { contentResolver.openOutputStream(uri, mode) } returns outputStream
         return outputStream
     }
 
-    fun givenMissingOutputStreamFor(uri: Uri) {
+    fun givenMissingOutputStreamFor(uri: Uri, mode: String) {
-        every { contentResolver.openOutputStream(uri) } returns null
+        every { contentResolver.openOutputStream(uri, mode) } returns null
     }
 }