如何使来自 BackgroundDownloader 的 DownloadOperation 可恢复 [英] How to make DownloadOperation from BackgroundDownloader resumable

问题描述

我正在添加使用 BackgroundDownloader/DownloadOperation 功能将大文件下载到我的应用程序中的功能.我在 Web Api 控制器中使用 PushStreamContent 来提供使用 GET 操作请求的数据.

I am adding in functionality to download a large file into my application using the BackgroundDownloader/DownloadOperation functionality. I am using a PushStreamContent in a Web Api controller to serve the data that's being requested using a GET operation.

我已将 Accept-Ranges 标头添加到从 Web Api 控制器收到的响应中，但是 BackgroundDownloader 似乎无法识别并尝试恢复下载.如果我调用 DownloadOperation.Pause() 然后 DownloadOperation.Resume() 然后从头开始下载并且不会尝试恢复.

I have added in the Accept-Ranges header to the response that's received from the Web Api controller, however the BackgroundDownloader doesn't seem to be recognising and attempting to resume downloads. If I call DownloadOperation.Pause() then DownloadOperation.Resume() then the download starts again from the start and doesn't attempt to resume.

事实上，如果我查看 AC\BackgroundTransferApi 文件夹，我可以看到 .down_data 在我执行暂停时被删除.查看 down_meta 文件，我可以看到 Accept-Ranges: bytes 标头存在，我可以在查看 Fidder 中的请求时看到它.

In fact if I look in the AC\BackgroundTransferApi folder I can see the .down_data get deleted when I perform the pause. Looking in the down_meta file I can see the Accept-Ranges: bytes header is present and I can see it when looking at the request in Fidder.

我需要在服务器端做什么来向 BackgroundDownloader 表明它支持可恢复传输?MSDN 文档很简单状态 注意暂停或不完整的下载操作只能在服务器接受范围请求时恢复.我相信我已经满足了.

What do I need to do on the server side to indicate to the BackgroundDownloader that it supports a resumable transfer? The MSDN documentation simply states Note Paused or incomplete download operations can only be resumed if the server accepts range-requests. which I believe I have satisfied.

推荐答案

DownloadOperation 类有一个属性可以告诉您操作是否可恢复:DownloadOperation.GetResponseInformation().IsResumable

The DownloadOperation class has a property that tells you if the operations is resumable: DownloadOperation.GetResponseInformation().IsResumable

文件没有从AC\BackgroundTransferApi中删除，而是移动到AC\Temp.

The file is not deleted from AC\BackgroundTransferApi, it is moved to AC\Temp.

第一个 HTTP 响应必须包含 ETag 和 Accept-Ranges 标头:

The first HTTP response must include ETag and Accept-Ranges headers:

ETag: "123ABC"
Accept-Ranges: bytes

恢复操作时，HTTP 请求将包含:

When an operations is resumen, the HTTP request will contain:

Range: bytes=23000000-
If-Range: "123ABC"

下一个 HTTP 响应应包含如下内容:

Next HTTP response should contain something like this:

ETag: "123ABC"
Accept-Ranges: bytes
Content-Range: bytes 23000000-499999999/500000000
Content-Length: 477000000

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