如何复制HttpContent异步和取消？ [英] How to copy HttpContent async and cancelable?

问题描述

我用 HttpClient.PostAsync（）和响应是的Htt presponseMessage 。其内容属性的类型为 HttpContent 具有 CopyToAsync（）方法。不幸的是，这不是取消。 有没有办法让复制到流的响应，并通过的CancellationToken ？

I'm using HttpClient.PostAsync() and the response is an HttpResponseMessage. Its Content property is of type HttpContent which has a CopyToAsync() method. Unfortunately, this is not cancelable. Is there a way to get the response copied into a Stream and pass a CancellationToken?

我不坚持 CopyToAsync（）！如果有一个解决办法，这将是罚款。就像读一对夫妇的字节，检查是否取消，请继续阅读等。

I am not stuck with CopyToAsync()! If there is a workaround, that would be fine. Like read a couple of bytes, check if canceled, continue reading and so on.

在 HttpContent.CreateContentReadStreamAsync（）方法看起来这将是一个候选人。不幸的是，不可用我的选择的配置文件。而且目前还不清楚它是否会阅读所有的数据一气呵成，浪费了大量的内存。

The HttpContent.CreateContentReadStreamAsync() methods looks like it would be a candidate. Unfortunately, it's not available with my selected profile. Also unclear if it would read all data in one go and waste a lot of memory.

注：我用这个针对WP8，Windows应用商店8，.NET 4.5的PCL里面，Xamarin.iOS和Xamarin.Android

Note: I'm using this inside a PCL targeting WP8, Windows Store 8, .NET 4.5, Xamarin.iOS and Xamarin.Android

推荐答案

我认为这应该工作：

public static async Task DownloadToStreamAsync(string uri, HttpContent data, Stream target, CancellationToken token)
{
    using (var client = new HttpClient())
    using (var response = await client.PostAsync(uri, data, token))
    using (var stream = await response.Content.ReadAsStreamAsync())
    {
        await stream.CopyToAsync(target, 4096, token);
    }
}

注意 ReadAsStreamAsync 要求 CreateContentReadStreamAsync ，这对于数据流的反应只是返回相关的内容流无缓存到内存

Note that ReadAsStreamAsync calls CreateContentReadStreamAsync, which for stream responses just returns the underlying content stream without buffering it into memory.

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