[BackupRestorer] Handle uncompressed backups (#8988)

[Backups] Handle uncompressed backups

app/src/main/java/eu/kanade/tachiyomi/util/BackupUtil.kt

@@ -0,0 +1,32 @@
+package eu.kanade.tachiyomi.util
+
+import android.content.Context
+import android.net.Uri
+import eu.kanade.tachiyomi.data.backup.BackupManager
+import eu.kanade.tachiyomi.data.backup.models.Backup
+import eu.kanade.tachiyomi.data.backup.models.BackupSerializer
+import okio.buffer
+import okio.gzip
+import okio.source
+
+object BackupUtil {
+    /**
+     * Decode a potentially-gzipped backup.
+     */
+    fun decodeBackup(context: Context, uri: Uri): Backup {
+        val backupManager = BackupManager(context)
+
+        val backupStringSource = context.contentResolver.openInputStream(uri)!!.source().buffer()
+
+        val peeked = backupStringSource.peek()
+        peeked.require(2)
+        val id1id2 = peeked.readShort()
+        val backupString = if (id1id2.toInt() == 0x1f8b) { // 0x1f8b is gzip magic bytes
+            backupStringSource.gzip().buffer()
+        } else {
+            backupStringSource
+        }.use { it.readByteArray() }
+
+        return backupManager.parser.decodeFromByteArray(BackupSerializer, backupString)
+    }
+}