流式解密视频播放方案

func (s *Server) streamFile(c *gin.Context) {
    // 1. 从 S3 下载加密文件
    encryptedData, err := s.s3.Download(ctx, s3Key)
    
    // 2. 派生文件密钥
    fileKey := crypto.DeriveFileKey(s.masterKey, fileID)
    
    // 3. 流式解密（逐块解密并输出）
    c.Header("Content-Type", mimeType)
    c.Header("Accept-Ranges", "bytes")
    
    err = s.encryptor.DecryptStream(
        bytes.NewReader(encryptedData), 
        c.Writer, 
        fileKey,
    )
}

// pubspec.yaml 依赖
dependencies:
  media_kit: ^1.1.11
  media_kit_video: ^1.2.5
  media_kit_libs_video: ^1.0.5
 
// main.dart 初始化
void main() {
  WidgetsFlutterBinding.ensureInitialized();
  MediaKit.ensureInitialized();
  runApp(const MyApp());
}
 
// VideoPlayerPage 实现
class VideoPlayerPage extends StatefulWidget {
  final String fileId;
  final String fileName;
  // ...
}
 
class _VideoPlayerPageState extends State<VideoPlayerPage> {
  late final Player _player;
  late final VideoController _controller;
 
  @override
  void initState() {
    super.initState();
    _player = Player();
    _controller = VideoController(_player);
    
    // 获取流式播放 URL 并打开
    final streamUrl = widget.api.getStreamUrl(widget.fileId);
    _player.open(Media(streamUrl));
  }
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(widget.fileName)),
      body: Video(controller: _controller),
    );
  }
}

func (s *Server) partialFile(c *gin.Context) {
    // 获取最大字节数参数，默认 5MB
    maxBytesStr := c.Query("maxBytes")
    maxBytes := int64(5 * 1024 * 1024)
    if maxBytesStr != "" {
        if mb, err := strconv.ParseInt(maxBytesStr, 10, 64); err == nil && mb > 0 {
            maxBytes = mb
        }
    }
 
    // 下载部分解密数据
    data, mimeType, err := s.downloadPartialDecrypted(ctx, fileID, maxBytes)
    
    c.Data(http.StatusOK, mimeType, data)
}
 
func (s *Server) downloadPartialDecrypted(ctx context.Context, fileID string, maxBytes int64) ([]byte, string, error) {
    // 从 S3 下载完整加密文件
    encryptedData, err := s.s3.Download(ctx, s3Key)
    
    // 逐块解密，直到达到 maxBytes
    var result bytes.Buffer
    for {
        // 解密一个块
        plainBlock, err := s.encryptor.DecryptBlock(...)
        result.Write(plainBlock)
        
        if result.Len() >= int(maxBytes) {
            break
        }
    }
    
    return result.Bytes()[:maxBytes], mimeType, nil
}

func (s *Server) downloadThumbnail(c *gin.Context) {
    // 获取文件元数据
    fileMeta, err := s.getFileMetadata(ctx, fileID)
    
    // 视频文件需要客户端生成缩略图
    if strings.HasPrefix(fileMeta.MimeType, "video/") {
        c.JSON(http.StatusOK, gin.H{
            "needClientGenerate": true, 
            "fileId": fileID, 
            "mimeType": fileMeta.MimeType,
        })
        return
    }
    
    // 其他文件类型...返回已有缩略图或生成
}

Future<Uint8List?> _generateVideoThumbnailLocally(
  ApiClient api,
  String fileId,
) async {
  try {
    // 1. 下载部分视频数据（5MB）
    final partialResult = await api.downloadPartialFile(fileId);
    if (!partialResult.isSuccess || partialResult.data == null) {
      return null;
    }
 
    // 2. 保存到临时文件
    final tempDir = await path_provider.getTemporaryDirectory();
    final tempVideoPath = path.join(tempDir.path, 'video_$fileId.tmp');
    final tempThumbPath = path.join(tempDir.path, 'thumb_$fileId.jpg');
 
    final videoFile = File(tempVideoPath);
    await videoFile.writeAsBytes(partialResult.data!);
 
    // 3. 使用原生 API 生成缩略图
    final plugin = FcNativeVideoThumbnail();
    final success = await plugin.getVideoThumbnail(
      srcFile: tempVideoPath,
      destFile: tempThumbPath,
      width: 256,
      height: 256,
      format: 'jpeg',
      quality: 85,
    );
 
    if (!success) {
      return null;
    }
 
    // 4. 读取生成的缩略图
    final thumbFile = File(tempThumbPath);
    final thumbData = await thumbFile.readAsBytes();
 
    // 5. 清理临时文件
    await videoFile.delete();
    await thumbFile.delete();
 
    // 6. 上传缩略图到后端缓存
    if (thumbData.isNotEmpty) {
      await api.uploadThumbnail(fileId, thumbData);
    }
 
    return thumbData;
  } catch (e) {
    debugPrint('Video thumbnail generation failed: $e');
    return null;
  }
}

Widget _buildLeading(FileMetadata file) {
  final isVideo = file.mimeType.startsWith('video/');
  
  if (_thumbnailCache.containsKey(file.id)) {
    return Stack(
      children: [
        Image.memory(_thumbnailCache[file.id]!, fit: BoxFit.cover),
        if (isVideo)
          Positioned.fill(
            child: Center(
              child: Container(
                padding: const EdgeInsets.all(4),
                decoration: BoxDecoration(
                  color: Colors.black.withOpacity(0.5),
                  shape: BoxShape.circle,
                ),
                child: const Icon(
                  Icons.play_arrow,
                  color: Colors.white,
                  size: 16,
                ),
              ),
            ),
          ),
      ],
    );
  }
  
  // 显示占位图标
  return Icon(isVideo ? Icons.videocam : Icons.insert_drive_file);
}