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我们正在为我们的客户端应用程序构建离线公平竞赛内容；我们通过引用 HLSatalog 演示应用程序中的 Apple 示例下载管理器 AssetPersistenceManager 类来实现该功能。我想在这里强调的 AssetPersistenceManager 类中有一个函数和两个回调，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)
    }

并在完成下载流时回调

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)
    }
}

最后是 didCompleteWithError 回调

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

在 iOS < 10.2 上一切似乎都正常，但是在运行最新 iOS 10.2 的某些设备上进行测试后，应用程序总是回调到 didFinishDownloadTo 委托，而只有 13-15% 完成百分比，之后调用 didCompleteWithError 并且我们收到以下错误

> "=======> 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，它指出应用程序在整个接收响应之前关闭了连接。

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，在低于该版本的其他操作系统上测试的相同流仍然可以正常工作。试图找到一些关于这部分的 iOS 10.2 更新日志，但我什么也没找到？你们有什么建议吗？

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1 回答 1

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经过一周的坚持，我们自己找到了答案。原来是 iOS 10.0 - 10.1 而不是 10.2 上的错误。30s 后发生的错误与 DRM 错误有关，它发生在 iOS 10.2 上，在 AVAssetDownloadTask 恢复后，有一个来自 AVAssetResourceLoaderDelegate 的回调，您需要点击服务器密钥来完成 Fairplay DRM 内容密钥

func resourceLoader(_ resourceLoader: AVAssetResourceLoader, 
shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool

否则，下载将被强制停止，您将收到上述未知错误。Apple 示例代码 HLSCatalog 只是非 DRM 流的演示，他们甚至没有提及演示中所需的内容密钥实现。

我们遵循了他们的示例，似乎 iOS 10.0 - 10.1，AVFoundation 在处理下载时没有检查内容密钥，这就是为什么当我们第一次实现我们的下载功能时，我们认为下载时不需要内容密钥，这导致我们在 iOS 10.2 上浪费了一周的时间……

于 2017-01-26T09:08:25.833 回答