如何更改 .NET WebClient 对象的超时时间

Question

我正在尝试将客户端的数据下载到我的本地机器（以编程方式），并且他们的网络服务器非常非常慢，这导致我的WebClient对象超时。

这是我的代码：

WebClient webClient = new WebClient();

webClient.Encoding = Encoding.UTF8;
webClient.DownloadFile(downloadUrl, downloadFile);

有没有办法在这个对象上设置无限超时？ 或者，如果没有，任何人都可以帮助我举一个替代方法的例子吗？

该 URL 在浏览器中运行良好 - 显示只需大约 3 分钟。

Answer 1

您可以扩展超时：继承原始 WebClient 类并覆盖 webrequest getter 以设置您自己的超时，如下例所示。

在我的例子中，MyWebClient 是一个私有类：

private class MyWebClient : WebClient
{
    protected override WebRequest GetWebRequest(Uri uri)
    {
        WebRequest w = base.GetWebRequest(uri);
        w.Timeout = 20 * 60 * 1000;
        return w;
    }
}

Answer 2

第一个解决方案对我不起作用，但这里有一些代码对我有用。

    private class WebClient : System.Net.WebClient
    {
        public int Timeout { get; set; }

        protected override WebRequest GetWebRequest(Uri uri)
        {
            WebRequest lWebRequest = base.GetWebRequest(uri);
            lWebRequest.Timeout = Timeout;
            ((HttpWebRequest)lWebRequest).ReadWriteTimeout = Timeout;
            return lWebRequest;
        }
    }

    private string GetRequest(string aURL)
    {
        using (var lWebClient = new WebClient())
        {
            lWebClient.Timeout = 600 * 60 * 1000;
            return lWebClient.DownloadString(aURL);
        }
    }

Answer 3

您需要使用HttpWebRequest而不是WebClient因为您无法在WebClient上设置超时而不扩展它（即使它使用HttpWebRequest ）。 改用HttpWebRequest将允许您设置超时。

Answer 4

拔出网络电缆时无法使 w.Timeout 代码工作，它只是没有超时，转移到使用 HttpWebRequest 并立即完成工作。

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(downloadUrl);
request.Timeout = 10000;
request.ReadWriteTimeout = 10000;
var wresp = (HttpWebResponse)request.GetResponse();

using (Stream file = File.OpenWrite(downloadFile))
{
    wresp.GetResponseStream().CopyTo(file);
}

Answer 5

对于需要适用于异步/任务方法的超时 WebClient 的任何人，建议的解决方案将不起作用。 这是有效的方法：

public class WebClientWithTimeout : WebClient
{
    //10 secs default
    public int Timeout { get; set; } = 10000;

    //for sync requests
    protected override WebRequest GetWebRequest(Uri uri)
    {
        var w = base.GetWebRequest(uri);
        w.Timeout = Timeout; //10 seconds timeout
        return w;
    }

    //the above will not work for async requests :(
    //let's create a workaround by hiding the method
    //and creating our own version of DownloadStringTaskAsync
    public new async Task<string> DownloadStringTaskAsync(Uri address)
    {
        var t = base.DownloadStringTaskAsync(address);
        if(await Task.WhenAny(t, Task.Delay(Timeout)) != t) //time out!
        {
            CancelAsync();
        }
        return await t;
    }
}

我在这里写了关于完整解决方法的博客

Answer 6

为了完整起见，这里是移植到 VB 的 kisp 解决方案（不能在注释中添加代码）

Namespace Utils

''' <summary>
''' Subclass of WebClient to provide access to the timeout property
''' </summary>
Public Class WebClient
    Inherits System.Net.WebClient

    Private _TimeoutMS As Integer = 0

    Public Sub New()
        MyBase.New()
    End Sub
    Public Sub New(ByVal TimeoutMS As Integer)
        MyBase.New()
        _TimeoutMS = TimeoutMS
    End Sub
    ''' <summary>
    ''' Set the web call timeout in Milliseconds
    ''' </summary>
    ''' <value></value>
    Public WriteOnly Property setTimeout() As Integer
        Set(ByVal value As Integer)
            _TimeoutMS = value
        End Set
    End Property


    Protected Overrides Function GetWebRequest(ByVal address As System.Uri) As System.Net.WebRequest
        Dim w As System.Net.WebRequest = MyBase.GetWebRequest(address)
        If _TimeoutMS <> 0 Then
            w.Timeout = _TimeoutMS
        End If
        Return w
    End Function

End Class

End Namespace

Answer 7

'CORRECTED VERSION OF LAST FUNCTION IN VISUAL BASIC BY GLENNG

Protected Overrides Function GetWebRequest(ByVal address As System.Uri) As System.Net.WebRequest
            Dim w As System.Net.WebRequest = MyBase.GetWebRequest(address)
            If _TimeoutMS <> 0 Then
                w.Timeout = _TimeoutMS
            End If
            Return w  '<<< NOTICE: MyBase.GetWebRequest(address) DOES NOT WORK >>>
        End Function

Answer 8

正如 Sohnee 所说，使用System.Net.HttpWebRequest并设置Timeout属性而不是使用System.Net.WebClient 。

但是，您不能设置无限超时值（它不受支持并且尝试这样做会抛出ArgumentOutOfRangeException ）。

我建议首先执行HEAD HTTP请求并检查返回的Content-Length标头值以确定您正在下载的文件中的字节数，然后为后续GET请求相应地设置超时值或简单地指定一个很长的超时您永远不会期望超过的价值。

Answer 9

用法：

using (var client = new TimeoutWebClient(TimeSpan.FromSeconds(10)))
{
    return await client.DownloadStringTaskAsync(url).ConfigureAwait(false);
}

班级：

using System;
using System.Net;

namespace Utilities
{
    public class TimeoutWebClient : WebClient
    {
        public TimeSpan Timeout { get; set; }

        public TimeoutWebClient(TimeSpan timeout)
        {
            Timeout = timeout;
        }

        protected override WebRequest GetWebRequest(Uri uri)
        {
            var request = base.GetWebRequest(uri);
            if (request == null)
            {
                return null;
            }

            var timeoutInMilliseconds = (int) Timeout.TotalMilliseconds;

            request.Timeout = timeoutInMilliseconds;
            if (request is HttpWebRequest httpWebRequest)
            {
                httpWebRequest.ReadWriteTimeout = timeoutInMilliseconds;
            }

            return request;
        }
    }
}

但我推荐一个更现代的解决方案：

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

public static async Task<string> ReadGetRequestDataAsync(Uri uri, TimeSpan? timeout = null, CancellationToken cancellationToken = default)
{
    using var source = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
    if (timeout != null)
    {
        source.CancelAfter(timeout.Value);
    }

    using var client = new HttpClient();
    using var response = await client.GetAsync(uri, source.Token).ConfigureAwait(false);

    return await response.Content.ReadAsStringAsync().ConfigureAwait(false);
}

它会在超时后抛出OperationCanceledException 。

Answer 10

昨天我不得不与这个问题作斗争，我也最终编写了我的自定义扩展类。

正如您通过查看下面的代码并将其与接受的答案进行比较所看到的，我尝试对建议进行更多调整，以便拥有一个更通用的类：通过这种方式，您可以在实例化对象时设置精确的超时或在使用使用内部WebRequest处理程序的方法之前。

using System;
using System.Net;

namespace Ryadel.Components.Web
{
    /// <summary>
    /// An extension of the standard System.Net.WebClient
    /// featuring a customizable constructor and [Timeout] property.
    /// </summary>
    public class RyadelWebClient : WebClient
    {
        /// <summary>
        /// Default constructor (30000 ms timeout)
        /// NOTE: timeout can be changed later on using the [Timeout] property.
        /// </summary>
        public RyadelWebClient() : this(30000) { }

        /// <summary>
        /// Constructor with customizable timeout
        /// </summary>
        /// <param name="timeout">
        /// Web request timeout (in milliseconds)
        /// </param>
        public RyadelWebClient(int timeout)
        {
            Timeout = timeout;
        }

        #region Methods
        protected override WebRequest GetWebRequest(Uri uri)
        {
            WebRequest w = base.GetWebRequest(uri);
            w.Timeout = Timeout;
            ((HttpWebRequest)w).ReadWriteTimeout = Timeout;
            return w;
        }
        #endregion

        /// <summary>
        /// Web request timeout (in milliseconds)
        /// </summary>
        public int Timeout { get; set; }
    }
}

当我在那里时，我也借此机会将默认Timeout值降低到30秒，因为100对我来说似乎太多了。

如果您需要更多关于这个类或如何使用它的其他信息，请查看这篇文章我在我的博客中写道。

Answer 11

根据 kisp 解决方案，这是我编辑的异步工作版本：

类WebConnection.cs

internal class WebConnection : WebClient
{
    internal int Timeout { get; set; }

    protected override WebRequest GetWebRequest(Uri Address)
    {
        WebRequest WebReq = base.GetWebRequest(Address);
        WebReq.Timeout = Timeout * 1000 // Seconds
        return WebReq;
    }
}

异步任务

private async Task GetDataAsyncWithTimeout()
{
    await Task.Run(() =>
    {
        using (WebConnection webClient = new WebConnection())
        {
            webClient.Timeout = 5; // Five seconds
            webClient.DownloadData("https://www.yourwebsite.com");
        }
    });
} // await GetDataAsyncWithTimeout()

否则，如果您不想使用异步：

private void GetDataSyncWithTimeout()
{
    using (WebConnection webClient = new WebConnection())
    {
        webClient.Timeout = 5; // Five seconds
        webClient.DownloadData("https://www.yourwebsite.com");
    }
} // GetDataSyncWithTimeout()

Answer 12

在某些情况下，需要将用户代理添加到标头中：

WebClient myWebClient = new WebClient();
myWebClient.DownloadFile(myStringWebResource, fileName);
myWebClient.Headers["User-Agent"] = "Mozilla/4.0 (Compatible; Windows NT 5.1; MSIE 6.0) (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)";

这是我的情况的解决方案。

信用：

http://genjurosdojo.blogspot.com/2012/10/the-remote-server-returned-error-504.html