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；我们通过参考HLSCatalog演示应用程序中的Apple示例下载管理器AssetPersistenceManager类来实现该功能。AssetPersistenceManager类中有一个函数和两个回调，我想在这里强调一下，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，但在运行最新iOS 10.2的一些设备上测试后，该应用程序总是回调到didFinishDownloadTo委派，而只有13-15%的人完成了百分比，之后didCompleteWithError被调用，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)}"
通过与代理调试应用程序的检查，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，在该版本以下的其他操作系统上测试的相同流仍然运行良好。试图为iOS 10.2找到一些关于这一部分的更改日志，但我一无所获？你们有什么建议吗？
经过一周的努力，我们自己找到了答案。结果是iOS 10.0-10.1上的错误，而不是10.2。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，AVAssetResourceLoaderDelegate发出回调，您需要点击服务器密钥才能在中完成Fairplay DRM内容密钥
func resourceLoader(_ resourceLoader: AVAssetResourceLoader,
shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool
否则，下载将被迫停止，您将收到如上所述的未知错误。苹果的示例代码HLSCatalog只是非DRM流的演示，他们甚至没有提到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下载功能时，我们认为下载时不需要内容密钥，导致我们在iOS 10.2中浪费了一周…