WinRT/Win8 中的多个 HTTP 请求 [英] Multiple HTTP Requests in WinRT / Win8

问题描述

是否可以在 WinRT 中同时发送两个以上的 HTTP 请求?我正在尝试从服务器加载多个 JSON 文档，第二次调用后 HttpWebRequest 无法响应.以下是说明这一点的示例代码段:

Is it possible to send more than two HTTP requests concurrently in WinRT? I'm trying to load multiple JSON documents from a server and HttpWebRequest fails to respond after the second call. Here is a sample snippet that illustrates this:

protected async override void OnNavigatedTo(NavigationEventArgs e)
{
    const string url = "http://www.bom.gov.au/fwo/IDV60901/IDV60901.94868.json";
    const int iterations = 3;

    var tasks = new List<Task>();
    var ticks = DateTime.Now.Ticks;

    for (var i = 0; i < iterations; i++)
    {
        // Create unique URL by appending a generated number.
        var uniqueUrl = string.Format("{0}?v={1}", url, (i + ticks));

        // Create the request.
        var request = WebRequest.CreateHttp(uniqueUrl);

        // Create the async task and store it for later.
        var task = request.GetResponseAsync();

        tasks.Add(task);
    }

    // Await all tasks in collection.
    await Task.WhenAll(tasks);



    Debugger.Break(); // <----- This will never break when iterations > 2
}

将此代码放在一个空白的MainPage.xaml.cs 中并使用迭代值.如果您将其设置为 2，则它可以工作.高于此值的任何操作都会失败.

Put this code in a blank MainPage.xaml.cs and play around with the iterations value. If you set it to 2, then it works. Anything above that, it will fail.

注意 :: 测试时不要使用 Fiddler.Fiddler 做了一些有趣的事情，它允许所有这些连接通过.我不知道怎么做，也不知道为什么.你可以自己测试一下.如果你在 fiddler 打开的情况下运行上面的代码，那么成功.

NOTE :: Do not use Fiddler when testing this. Fiddler does something funny and it allows all these connections to go through. I don't know how nor why. You can test this yourself. If you run the code above with fiddler open, then success.

注意 :: 这不是真正的代码.我只是用这个例子来说明这个问题.

NOTE :: This is not real code. I'm only using this example to illustrate the issue.

推荐答案

我没有尝试在 WinRT 中使用 WebClient API，我只使用了 HttpClientAPI(我在我的应用程序中广泛使用).

I haven't tried using the WebClient API in WinRT, I've only used the HttpClient API (which I'm using quite extensively in my application).

此代码有效:

const string url = "http://www.bom.gov.au/fwo/IDV60901/IDV60901.94868.json";
const int iterations = 10;

var tasks = new List<Task<HttpResponseMessage>>();
var ticks = DateTime.Now.Ticks;

for (var i = 0; i < iterations; i++)
{
    // Create unique URL by appending a generated number.
    var uniqueUrl = string.Format("{0}?v={1}", url, (i + ticks));

    var handler = new HttpClientHandler();

    var client = new HttpClient(handler)
                        {
                            BaseAddress = new Uri(uniqueUrl)
                        };

    var task = client.GetAsync(client.BaseAddress);

    tasks.Add(task);
}

// Await all tasks in collection.
await Task.WhenAll(tasks);

虽然您需要像这样异步读取所有响应，但取出响应正文有点乏味:

It is a bit more tedious to get out the response body though as you need to do an async read of all the responses like so:

var responseTasks = tasks.Select(task => task.Result.Content.ReadAsStringAsync());

await Task.WhenAll(responseTasks);

然后您可以遍历 responseTask 对象并获取它们的结果.

Then you can iterate through the responseTask objects and take their result.

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