WebClient挂起直到超时

本文介绍了WebClient挂起直到超时的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我尝试使用WebClient下载网页，但该网页会一直挂起，直到达到WebClient中的超时为止，然后失败并出现异常。

I try do download a web page using the WebClient, but it hangs until the timeout in WebClient is reached, and then fails with an Exception.

以下代码

WebClient client = new WebClient(); string url = "www.nasdaq/de/symbol/aapl/dividend-history"; string page = client.DownloadString(url);

使用其他URL，传输可以正常进行。例如，

Using a different URL, the transfer works fine. For example

WebClient client = new WebClient(); string url = "www.ariva.de/apple-aktie"; string page = client.DownloadString(url);

完成非常快，并且整个html都在页面变量中。

completes very quick and has the whole html in the page variable.

使用HttpClient或WebRequest / WebResponse在第一个URL上产生相同的结果：阻止直到超时异常。

Using a HttpClient or WebRequest/WebResponse gives the same result on the first URL: block until timeout exception.

两个URL在浏览器中均可正常加载，大约需要2-5秒。 任何想法，问题出在哪里，什么解决方案可用？

Both URLs load fine in a browser, in roughly 2-5 seconds. Any idea what the problem is, and what solution is available?

我注意到在Windows窗体对话框上使用WebBrowser控件时，第一个URL会加载带有20多个javascript错误，需要确认点击。当访问第一个URL时，在浏览器中打开开发人员工具时，也会观察到同样的情况。

I noticed that when using a WebBrowser control on a Windows Forms dialog, the first URL loads with 20+ javascript errors that need to be confirm-clicked. Same can be observed when developer tools are open in a browser when accessing the first URL.

但是，WebClient不会对它获得的返回值起作用。它不会运行javascript，也不会加载引用的图片，css或其他脚本，因此这应该不是问题。

However, WebClient does NOT act on the return it gets. It does not run the javascript, and does not load referenced pictures, css or other scripts, so this should not be a problem.

谢谢！

Ralf

推荐答案

第一个站点， https：// www.nasdaq/de/symbol/aapl/dividend-history； ，要求：

• ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
• ServicePointManager.ServerCertificateValidationCallback
• 一组用户代理标头
• A CookieContainer 显然不是必需的。

• ServicePointManager.SecurityProtocol= SecurityProtocolType.Tls12
• ServicePointManager.ServerCertificateValidationCallback
• A set User-Agent Header
• A CookieContainer is, apparently, not required. It should be set anyway.

此处的 User-agent 很重要。如果在User-agent 。 httpwebrequest.useragent？view = netframework-4.7.2 rel = nofollow noreferrer> WebRequest.UserAgent ，网站将激活 Http 2.0 协议和 HSTS （ HTTP严格传输安全性 ）），只有最近的浏览器（作为参考，FireFox 56或更高版本）才支持/理解。

The User-agent here is important. If a recent User-agent is specified in the WebRequest.UserAgent, the WebSite will activate the Http 2.0 protocol and HSTS (HTTP Strict Transport Security)) that are supported/understood only by recent Browsers (as a reference, FireFox 56 or newer).

必须使用较新的浏览器作为 User-agent ，否则WebSite会期望（并等待）动态响应。使用较旧 用户代理，网站将激活 Http 1.1 协议。

Using a less recent Browser as User-agent is necessary, otherwise the WebSite will expect (and wait for) a dynamic response. Using an older User-agent, the WebSite will activate the Http 1.1 protocol.

第二个站点 www.ariva.de/apple-aktie; ：

• ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
• 不需要服务器证书验证
• 不需要特定的用户代理

我建议通过以下方式设置WebRequest（或相应的HttpClient设置）： （WebClient 可能可以工作，但可能需要派生的自定义控件）

I suggest to setup a WebRequest (or a correspnding HttpClient setup) this way: (WebClient could work, but it'ld probably require a derived Custom Control)

private async void button1_Click(object sender, EventArgs e) { button1.Enabled = false; Uri uri = new Uri("www.nasdaq/de/symbol/aapl/dividend-history"); string destinationFile = "[Some Local File]"; await HTTPDownload(uri, destinationFile); button1.Enabled = true; } CookieContainer httpCookieJar = new CookieContainer(); //The 32bit IE11 header is the User-agent used here public async Task HTTPDownload(Uri resourceURI, string filePath) { ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12; ServicePointManager.ServerCertificateValidationCallback += (s, cert, ch, sec) => { return true; }; ServicePointManager.DefaultConnectionLimit = 50; HttpWebRequest httpRequest = WebRequest.CreateHttp(resourceURI); try { httpRequest.CookieContainer = httpCookieJar; httpRequest.Timeout = (int)TimeSpan.FromSeconds(15).TotalMilliseconds; httpRequest.AllowAutoRedirect = true; httpRequest.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate; httpRequest.ServicePoint.Expect100Continue = false; httpRequest.UserAgent = "Mozilla / 5.0(Windows NT 6.1; WOW32; Trident / 7.0; rv: 11.0) like Gecko"; httpRequest.Accept = "ext/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"; httpRequest.Headers.Add(HttpRequestHeader.AcceptEncoding, "gzip, deflate;q=0.8"); httpRequest.Headers.Add(HttpRequestHeader.CacheControl, "no-cache"); using (HttpWebResponse httpResponse = (HttpWebResponse)await httpRequest.GetResponseAsync()) using (Stream responseStream = httpResponse.GetResponseStream()) { if (httpResponse.StatusCode == HttpStatusCode.OK) { try { int buffersize = 132072; using (FileStream fileStream = File.Create(filePath, buffersize, FileOptions.Asynchronous)) { int read; byte[] buffer = new byte[buffersize]; while ((read = await responseStream.ReadAsync(buffer, 0, buffer.Length)) > 0) { await fileStream.WriteAsync(buffer, 0, read); } }; } catch (DirectoryNotFoundException) { /* Log or throw */} catch (PathTooLongException) { /* Log or throw */} catch (IOException) { /* Log or throw */} } }; } catch (WebException) { /* Log and message */} catch (Exception) { /* Log and message */} }

返回的第一个网站（ nasdaq ）的有效载荷长度为 101.562 个字节 返回的第二个网站（ www.ariva.de ）的有效载荷长度为 56.919 字节

The first WebSite (nasdaq) returned payload length is 101.562 bytes The second WebSite (www.ariva.de) returned payload length is 56.919 bytes