download method

Implementation

Future<File?> download(
  String url,
  String filename,
  int? size, {
  String? path,
  String? checksum,
  Function(int count, int total)? onReceiveProgress,
  CancelToken? cancelToken,
  bool temporary = false,
  int retries = 5,
}) async {
  dynamic completeWith;
  int tries = 0;

  CancelableOperation<File?>? operation;
  operation = CancelableOperation.fromFuture(
    Future(() async {
      // Rethrows the [exception], if any other than `404` is thrown.
      void onError(dynamic exception) {
        if (exception is! DioException ||
            exception.response?.statusCode != 404) {
          completeWith = exception;
          operation?.cancel();
        } else {
          ++tries;

          if (tries <= retries) {
            // Continue the [Backoff.run] re-trying.
            throw exception;
          }
        }
      }

      if (PlatformUtils.isWeb) {
        await Backoff.run(() async {
          try {
            await WebUtils.downloadFile(url, filename);
          } catch (e) {
            onError(e);
          }
        }, cancelToken);
      } else {
        File? file;

        if (path == null) {
          // Retry fetching the size unless any other that `404` error is
          // thrown.
          file = await Backoff.run(() async {
            try {
              return await fileExists(
                filename,
                size: size,
                url: url,
                temporary: temporary,
              );
            } catch (e) {
              onError(e);
            }

            return null;
          }, cancelToken);
        }

        if (file == null) {
          Uint8List? data;
          if (checksum != null && CacheWorker.instance.exists(checksum)) {
            data = (await CacheWorker.instance.get(checksum: checksum)).bytes;
          }

          if (path == null) {
            final String name = p.basenameWithoutExtension(filename);
            final String extension = p.extension(filename);
            final Directory directory =
                temporary
                    ? await temporaryDirectory
                    : await downloadsDirectory;

            file = File('${directory.path}/$filename');
            for (int i = 1; await file!.exists(); ++i) {
              file = File('${directory.path}/$name ($i)$extension');
            }
          } else {
            file = File(path);
          }

          if (data == null) {
            // Retry the downloading unless any other that `404` error is
            // thrown.
            await Backoff.run(() async {
              try {
                // TODO: Cache the response.
                await (await dio).download(
                  url,
                  file!.path,
                  onReceiveProgress: onReceiveProgress,
                  cancelToken: cancelToken,
                );
              } catch (e) {
                onError(e);
              }
            }, cancelToken);
          } else {
            await file.writeAsBytes(data);
          }
        }

        return file;
      }

      return null;
    }),
  );

  cancelToken?.whenCancel.whenComplete(operation.cancel);

  final File? result = await operation.valueOrCancellation();
  if (completeWith != null) {
    throw completeWith;
  }

  return result;
}