Complement for #3656

changelog.d/3656.bugfix

@@ -0,0 +1 @@
+Avoid incomplete downloads in cache

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/DefaultFileService.kt

@@ -33,6 +33,7 @@ import org.matrix.android.sdk.internal.di.SessionDownloadsDirectory
 import org.matrix.android.sdk.internal.di.UnauthenticatedWithCertificateWithProgress
 import org.matrix.android.sdk.internal.session.download.DownloadProgressInterceptor.Companion.DOWNLOAD_PROGRESS_INTERCEPTOR_HEADER
 import org.matrix.android.sdk.internal.util.MatrixCoroutineDispatchers
+import org.matrix.android.sdk.internal.util.file.AtomicFileCreator
 import org.matrix.android.sdk.internal.util.md5
 import org.matrix.android.sdk.internal.util.writeToFile
 import timber.log.Timber
@@ -96,6 +97,9 @@ internal class DefaultFileService @Inject constructor(
             }
         }
 
+        var atomicFileDownload: AtomicFileCreator? = null
+        var atomicFileDecrypt: AtomicFileCreator? = null
+
         if (existingDownload != null) {
             // FIXME If the first downloader cancels then we'll unfortunately be cancelled too.
             return existingDownload.await()
@@ -131,8 +135,11 @@ internal class DefaultFileService @Inject constructor(
                     Timber.v("Response size ${response.body?.contentLength()} - Stream available: ${!source.exhausted()}")
 
                     // Write the file to cache (encrypted version if the file is encrypted)
-                    writeToFile(source.inputStream(), cachedFiles.file)
+                    // Write to a part file first, so if we abort before done, we don't have a broken cached file
+                    val atomicFileCreator = AtomicFileCreator(cachedFiles.file).also { atomicFileDownload = it }
+                    writeToFile(source.inputStream(), atomicFileCreator.partFile)
                     response.close()
+                    atomicFileCreator.commit()
                 } else {
                     Timber.v("## FileService: cache hit for $url")
                 }
@@ -145,15 +152,18 @@ internal class DefaultFileService @Inject constructor(
                     Timber.v("## FileService: decrypt file")
                     // Ensure the parent folder exists
                     cachedFiles.decryptedFile.parentFile?.mkdirs()
+                    // Write to a part file first, so if we abort before done, we don't have a broken cached file
+                    val atomicFileCreator = AtomicFileCreator(cachedFiles.decryptedFile).also { atomicFileDecrypt = it }
                     val decryptSuccess = cachedFiles.file.inputStream().use { inputStream ->
-                        cachedFiles.decryptedFile.outputStream().buffered().use { outputStream ->
+                        atomicFileCreator.partFile.outputStream().buffered().use { outputStream ->
                             MXEncryptedAttachments.decryptAttachment(
                                     inputStream,
                                     elementToDecrypt,
                                     outputStream
                             )
                         }
                     }
+                    atomicFileCreator.commit()
                     if (!decryptSuccess) {
                         throw IllegalStateException("Decryption error")
                     }
@@ -174,6 +184,11 @@ internal class DefaultFileService @Inject constructor(
         }
         toNotify?.completeWith(result)
 
+        result.onFailure {
+            atomicFileDownload?.cancel()
+            atomicFileDecrypt?.cancel()
+        }
+
         return result.getOrThrow()
     }
 

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/util/file/AtomicFileCreator.kt

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2021 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.internal.util.file
+
+import timber.log.Timber
+import java.io.File
+
+internal class AtomicFileCreator(private val file: File) {
+    val partFile = File(file.parentFile, "${file.name}.part")
+
+    init {
+        if (file.exists()) {
+            Timber.w("## AtomicFileCreator: target file ${file.path} exists, it should not happen.")
+        }
+        if (partFile.exists()) {
+            Timber.d("## AtomicFileCreator: discard aborted part file ${partFile.path}")
+            // No need to delete the file, we will overwrite it
+        }
+    }
+
+    fun cancel() {
+        partFile.delete()
+    }
+
+    fun commit() {
+        partFile.renameTo(file)
+    }
+}