Xamarin HTTP请求超时 [英] Timeouts in Xamarin HTTP requests

问题描述

晚上好！

我试图清理/改进一些代码，最终发现Xamarin HTTP请求中超时的问题（如在我的原始帖子中描述：异步下载和反序列化。）

I was trying to clean/refine some code and ended up finding issues with timeouts in Xamarin HTTP requests (as described in my original thread: Async Download and Deserialize).

发现问题（仅使用Xamarin.Android测试;不了解iOS）：

当<无法访问strong>主机（例如，脱机本地服务器）， GetAsync 抛出 System.Net.WebException 大致 3分钟后，消息错误：ConnectFailure（连接超时）。内部异常是 System.Net.Sockets.SocketsException （完整记录在这里： http://pastebin.com/MzHyp2FM ）。

When a host cannot be reached (e.g., an offline local server), GetAsync throws a System.Net.WebException after roughly 3 minutes with the message Error: ConnectFailure (Connection timed out). The Inner exception is System.Net.Sockets.SocketsException (full log here: http://pastebin.com/MzHyp2FM).

代码：

internal static class WebUtilities
{
    /// <summary>
    /// Downloads the page of the given url
    /// </summary>
    /// <param name="url">url to download the page from</param>
    /// <param name="cancellationToken">token to cancel the download</param>
    /// <returns>the page content or null when impossible</returns>
    internal static async Task<string> DownloadStringAsync(string url, CancellationToken cancellationToken)
    {
        try
        {
            // create Http Client and dispose of it even if exceptions are thrown (same as using finally statement)
            using (var client = new HttpClient() { Timeout = TimeSpan.FromSeconds(5) })
            {
                // should I always do this?
                client.CancelPendingRequests();

                // Issue here; Timeout of roughly 3 minutes
                using (var response = await client.GetAsync(url, cancellationToken).ConfigureAwait(false))
                {
                    // if response was successful (otherwise return null)
                    if (response.IsSuccessStatusCode)
                    {
                        // return its content
                        return await response.Content.ReadAsStringAsync().ConfigureAwait(false);
                    }
                }
            }
        }
        // TODO: split exceptions?
        catch (Exception ex) when (ex is System.Net.Sockets.SocketException ||
                                    ex is InvalidOperationException ||
                                    ex is OperationCanceledException ||
                                    ex is System.Net.Http.HttpRequestException)
        {
            WriteLine("DownloadStringAsync task has been cancelled.");
            WriteLine(ex.Message);
            return null;
        }

        // return null if response was unsuccessful
        return null;
    }
}

通话方式：

internal static async Task CallAsync(string url)
    {
        using (var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10)))
        {
            var token = cts.Token;
            token.ThrowIfCancellationRequested();

            string result = await WebUtilities.DownloadStringAsync(url, token).ConfigureAwait(false);
        }
    }

设置客户端.Timeout 似乎不起作用。

Setting client.Timeout doesn't seem to work.

无论哪种方式，不应该在10秒后自动取消cancelToken ？

此超时问题发生在：

• 请求离线/无法访问的IP地址（在我的情况下是离线本地服务器
  ，如192.168.1.101:8080）（即使用 GetAsync ， SendAsync ，
  GetResponseAsync ）

• An offline/unreachable IP address (in my case an offline local server such as 192.168.1.101:8080) is requested (i.e., using GetAsync, SendAsync, GetResponseAsync)

代码在以下情况下运作良好：

• 请求来自桌面客户端（例如， WPF ）。如果
  IP离线/无法访问，它会非常快地抛出4个异常（无法建立连接，因为目标计算机主动拒绝它）。

• The request is made from a desktop client (e.g., WPF). If the IP is offline/unreachable it throws 4 exceptions really fast (No connection could be made because the target machine actively refused it).

结论

Xamarin似乎在Http请求中有一些错误（至少有超时？），因为他们没有给出预期的结果。从我所看到的情况来看，它可能已经存在了几年（自2012年或2013年）。

Xamarin seems to have some bugs in Http requests (with Timeouts at least?), as they do not give the expected results. And from what I have read, it could be something that has been around for few a years (since 2012 or 2013).

Xamarin单元测试并没有真正帮助： https ：//github.com/xamarin/xamarin-android/blob/1b3a76c6874853049e89bbc113b22bc632ed5ca4/src/Mono.Android/Test/Xamarin.Android.Net/HttpClientIntegrationTests.cs

Xamarin unit testing doesn't really help either: https://github.com/xamarin/xamarin-android/blob/1b3a76c6874853049e89bbc113b22bc632ed5ca4/src/Mono.Android/Test/Xamarin.Android.Net/HttpClientIntegrationTests.cs

修改

• 超时= TimeSpan.FromMilliseconds（1000） - 作品


• 超时=超时= TimeSpan.FromSeconds（1） - 不起作用（???? ？）


• Timeout = TimeSpan.FromMilliseconds（2000）（及以上） - 不是
  work

• Timeout = TimeSpan.FromMilliseconds(1000) - works
• Timeout = Timeout = TimeSpan.FromSeconds(1) - doesn't work (?????)
• Timeout = TimeSpan.FromMilliseconds(2000) (and above) - doesn't work

有什么想法吗？谢谢！

推荐答案

我发现更改Android的http客户端设置解决了我的问题！我在这里发布了更多详细信息： http://jeremei.com/xamarinvisual-studio-httpclient -request-timeout /

I found that that changing the http client settings for Android resolved my issue! I posted more details here: http://jeremei.com/xamarinvisual-studio-httpclient-request-timeout/

这篇关于Xamarin HTTP请求超时的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！