Add download zip page

lib/utils/download_zip.dart

@@ -0,0 +1,36 @@
+import 'package:dio/dio.dart';
+import 'package:flutter/foundation.dart';
+import '../globals.dart';
+import '../platform/save_file.dart';
+
+Future<void> downloadZip(int gid,
+    {bool? jpnTitle, int? maxLength, bool? exportAd}) async {
+  final cancel = CancelToken();
+  final re = await api.exportGalleryZip(gid,
+      jpnTitle: jpnTitle,
+      maxLength: maxLength,
+      exportAd: exportAd,
+      cancel: cancel);
+  final data = re.data as ResponseBody;
+  if (data.statusCode != 200) {
+    throw Exception("${data.statusCode} ${data.statusMessage}.");
+  }
+  final fileName = re.response.headers.value("content-disposition");
+  final filenameWithoutExtension = fileName?.substring(
+          fileName.indexOf("filename=\"") + 10, fileName.lastIndexOf(".")) ??
+      "$gid";
+  try {
+    final f = await platformPath.openFile(
+        Uri.decodeComponent(filenameWithoutExtension), "application/zip");
+    try {
+      await data.stream.forEach((data) {
+        f.write(data);
+      });
+    } finally {
+      await f.dispose();
+    }
+  } catch (e) {
+    cancel.cancel();
+    rethrow;
+  }
+}