下载时，Offline Fairplay AVAssetDownloadTask收到未知错误回调(仅在iOS 10.2上发生)

Question

我们正在为我们的客户端应用程序构建离线公平播放内容；我们通过引用HLSCatalog演示应用程序中的苹果示例下载管理器AssetPersistenceManager类来实现该功能。在AssetPersistenceManager类中有一个函数和两个回调，我想在这里突出显示，它是

    /
    func downloadStream(for asset: Asset) {
        /
         For the initial download, we ask the URLSession for an AVAssetDownloadTask
         with a minimum bitrate corresponding with one of the lower bitrate variants
         in the asset.
         */
        guard let task = assetDownloadURLSession.makeAssetDownloadTask(asset: asset.urlAsset, assetTitle: asset.name, assetArtworkData: nil, options: [AVAssetDownloadTaskMinimumRequiredMediaBitrateKey: 265000]) else { return }

        /
        task.taskDescription = asset.name

        activeDownloadsMap[task] = asset

        task.resume()

        var userInfo = [String: Any]()
        userInfo[Asset.Keys.name] = asset.name
        userInfo[Asset.Keys.downloadState] = Asset.DownloadState.downloading.rawValue

        NotificationCenter.default.post(name: AssetDownloadStateChangedNotification, object: nil, userInfo:  userInfo)
    }

并在下载完流后回调

func urlSession(_ session: URLSession, assetDownloadTask: AVAssetDownloadTask, didFinishDownloadingTo location: URL) {
    let userDefaults = UserDefaults.standard

    /
     This delegate callback should only be used to save the location URL
     somewhere in your application. Any additional work should be done in
     `URLSessionTaskDelegate.urlSession(_:task:didCompleteWithError:)`.
     */
    if let asset = activeDownloadsMap[assetDownloadTask] {

        userDefaults.set(location.relativePath, forKey: asset.name)
    }
}

最后一个是didCompleteWithError回调

func urlSession(_ session: URLSession, task: URLSessionTask,
didCompleteWithError error: Error?)

在iOS < 10.2上似乎一切正常，但在一些运行最新iOS 10.2的设备上测试后，应用程序总是得到didFinishDownloadTo委托的回调，而只有13-15%的完成百分比，在调用didCompleteWithError之后，我们收到了以下错误

> "=======> completed percent 11.2888760669556" .
> "=======> completed percent 11.44566601233" 
> "=======> completed percent 11.7592459030787"
> "=======> completed percent 12.0728257938275" 
> "=======> completed percent 12.5431956299506" 
> "=======> completed percent 13.0135654660738" 
> "=======> completed percent 13.3271453568226" 
> "=======> completed percent 13.6407252475713" 
> "=======> completed percent 13.9543051383201" 
> "=======> completed percent 14.1110950836945" 
> "=======> completed percent 14.2678850290689" 
> "Error Domain=AVFoundationErrorDomain Code=-11800 \"The operation could not
> be completed\" UserInfo={NSLocalizedDescription=The operation could
> not be completed, NSLocalizedFailureReason=An unknown error occurred
> (-12667)}"

检查代理调试应用程序，指出应用程序在整个接收响应之前关闭连接。

Status
Complete
Failure
Client closed connection before receiving entire response
Response Code
206 Partial Content

只有iOS 10.2有这个错误，在该版本以下的其他操作系统上测试的相同流仍然工作正常。尝试查找有关此部分的iOS 10.2的一些changelog，但一无所获？你们有什么建议吗？