getObject method

Future<File?> getObject({ required String savePath, required String bucket, required String key, void progress(int downloadedBytes, int totalBytes)?, String? region, Map<String, String>? headers, Map<String, String>? params, int? chunkSize, int? concurrent, })

下载对象 参考文档： https://cloud.tencent.com/document/product/436/7749 savePath 文件下载路径 progress 下载进度 concurrent 同时发起请求数，默认 10 chunkSize 下载分块大小，单位字节，默认 4M

Implementation

Future<File?> getObject({
  required String savePath,
  required String bucket,
  required String key,
  void Function(int downloadedBytes, int totalBytes)? progress,
  String? region,
  Map<String, String>? headers,
  Map<String, String>? params,
  int? chunkSize,
  int? concurrent,
}) async {
  COSLogger.t('getObject: begin');

  File file = File(savePath);

  if (!file.existsSync()) {
    await file.create(recursive: true);
  }

  final randomAccessFile = await file.open(mode: FileMode.writeOnly);

  Future<int?> getContentLength() async {
    return send(COSFetchConfig(
        bucket: bucket,
        key: key,
        method: 'HEAD',
        region: region,
        headers: headers,
        params: params,
        resHandlers: [
          (fetchContext, data) async {
            final res = fetchContext.res;

            if (res != null) {
              if (res.statusCode == HttpStatus.ok) {
                return res.headers.contentLength;
              } else {
                throw await COSException.fromResponse(res);
              }
            } else {
              throw Exception('getObject: getContentLength: res is null');
            }
          },
          (context, data) async {
            COSLogger.t('getObject: getContentLength: end');

            return Future.value(data);
          }
        ]));
  }

  final totalSize = await getContentLength();
  int downloadedSize = 0;

  if (totalSize != null) {
    final fetchConcurrent = COSFetchConcurrent(
      chunkSize: chunkSize ?? 1024 * 1024 * 4,
      concurrent: concurrent ?? 10,
      totalSize: totalSize,
      input: (fetchChunk) async {
        await send(COSFetchConfig(
            bucket: bucket,
            key: key,
            method: 'GET',
            region: region,
            headers: {
              'Range': 'bytes=${fetchChunk.start}-${fetchChunk.end}',
              ...headers ?? {},
            },
            params: params,
            resHandlers: [
              (fetchContext, data) async {
                final res = fetchContext.res;

                if (res != null) {
                  if (res.statusCode == HttpStatus.partialContent) {
                    final controller = StreamController<List<int>>();

                    List<int> buffer = [];

                    controller.stream.listen((chunk) {
                      if (progress != null) {
                        downloadedSize += chunk.length;
                        progress(downloadedSize, totalSize);
                      }

                      buffer.addAll(chunk);
                    });

                    await res.pipe(controller);

                    await controller.close();

                    fetchChunk.setData(buffer);

                    fetchChunk.status = COSFetchChunkStatus.inputFinished;
                  } else {
                    throw await COSException.fromResponse(res);
                  }
                } else {
                  throw Exception('getObject: res is null');
                }

                COSLogger.t('getObject: end');
              }
            ]));
      },
      output: (fetchChunk) async {
        await randomAccessFile.setPosition(fetchChunk.start);
        await randomAccessFile.writeFrom(fetchChunk.data!);

        fetchChunk.status = COSFetchChunkStatus.outputFinished;
      },
    );

    await fetchConcurrent.go();

    await randomAccessFile.close();

    return file;
  } else {
    throw Exception('getObject: getContentLength: totalSize is null');
  }
}