Question

我在经典ASP中有以下代码段，用于发送命令并通过SSL检索响应：

Dim xmlHTTP
Set xmlHTTP = Server.CreateObject("Msxml2.ServerXMLHTTP.3.0")
xmlHTTP.open "POST", "https://www.example.com", False
xmlHTTP.setRequestHeader "Content-Type","application/x-www-form-urlencoded"
xmlHTTP.setRequestHeader "Content-Length", Len(postData)
xmlHTTP.Send postData
If xmlHTTP.status = 200 And Len(message) > 0 And Not Err Then
   Print xmlHTTP.responseText
End If

然后我使用this code作为参考，在c＃中重新实现请求：

private static string SendRequest(string url, string postdata)
{
   WebRequest rqst = HttpWebRequest.Create(url);
   // We have a proxy on the domain, so authentication is required.
   WebProxy proxy = new WebProxy("myproxy.mydomain.com", 8080);
   proxy.Credentials = new NetworkCredential("username", "password", "mydomain");
   rqst.Proxy = proxy;
   rqst.Method = "POST";
   if (!String.IsNullOrEmpty(postdata))
   {
       rqst.ContentType = "application/x-www-form-urlencoded";

       byte[] byteData = Encoding.UTF8.GetBytes(postdata);
       rqst.ContentLength = byteData.Length;
       using (Stream postStream = rqst.GetRequestStream())
       {
           postStream.Write(byteData, 0, byteData.Length);
           postStream.Close();
       }
   }
   ((HttpWebRequest)rqst).KeepAlive = false;
   StreamReader rsps = new StreamReader(rqst.GetResponse().GetResponseStream());
   string strRsps = rsps.ReadToEnd();
   return strRsps;
}

问题是，在调用GetRequestStream时，我不断收到带有消息"The remote server returned an error: (502) Bad Gateway."的WebException

起初我认为它与SSL证书验证有关。所以我添加了这一行：

ServicePointManager.CertificatePolicy = new AcceptAllCertificatePolicy();

其中

public class AcceptAllCertificatePolicy : ICertificatePolicy
{
    public bool CheckValidationResult(ServicePoint srvPoint, 
                                      System.Security.Cryptography.X509Certificate certificate,
                                      WebRequest request, 
                                      int certificateProblem)
    {
        return true;
    }
}

我一直得到同样的502错误。有什么想法吗？

Answer 1

读取错误响应的实体主体。它可能会暗示正在发生的事情。

执行此操作的代码如下：

catch(WebException e)
{
if (e.Status == WebExceptionStatus.ProtocolError)
{
    WebResponse resp = e.Response;
    using(StreamReader sr = new StreamReader(resp.GetResponseStream()))
    {
         Response.Write(sr.ReadToEnd());
    }
}
}

那应该显示错误响应的全部内容。

Answer 2

With the help of this我对问题有了更详细的描述：代理正在返回消息：“无法识别用户代理。”所以我手动设置它。另外，我更改了代码以使用GlobalProxySelection.GetEmptyWebProxy（），如here所述。最终的工作代码包含在下面。

private static string SendRequest(string url, string postdata)
{
    if (String.IsNullOrEmpty(postdata))
        return null;
    HttpWebRequest rqst = (HttpWebRequest)HttpWebRequest.Create(url);
    // No proxy details are required in the code.
    rqst.Proxy = GlobalProxySelection.GetEmptyWebProxy();
    rqst.Method = "POST";
    rqst.ContentType = "application/x-www-form-urlencoded";
    // In order to solve the problem with the proxy not recognising the user
    // agent, a default value is provided here.
    rqst.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1)";
    byte[] byteData = Encoding.UTF8.GetBytes(postdata);
    rqst.ContentLength = byteData.Length;

    using (Stream postStream = rqst.GetRequestStream())
    {
        postStream.Write(byteData, 0, byteData.Length);
        postStream.Close();
    }
    StreamReader rsps = new StreamReader(rqst.GetResponse().GetResponseStream());
    string strRsps = rsps.ReadToEnd();
    return strRsps;
}

Answer 3

Web服务的wsdl可能与域名和SSL证书“争论”。 IIS将使用IIS注册的域名自动生成Web服务的WSDL（默认情况下，该域名是本地域中的计算机名称，不一定是您的Web域）。如果证书域与SOAP12地址中的域不匹配，则会收到通信错误。

Answer 4

缺少UserAgent

例如： request.UserAgent =“Mozilla / 4.0（兼容; MSIE 7.0; Windows NT 5.1）”;

Answer 5

我发生这种情况是因为如果Java应用程序没有及时响应，远程计算机上的Java代理会超时请求，这会导致.NET默认超时无用。以下代码遍历所有异常并写出响应，这些响应帮助我确定它实际来自代理：

static void WriteUnderlyingResponse(Exception exception)
{
    do
    {
        if (exception.GetType() == typeof(WebException))
        {
            var webException = (WebException)exception;
            using (var writer = new StreamReader(webException.Response.GetResponseStream()))
                Console.WriteLine(writer.ReadToEnd());
        }
        exception = exception?.InnerException;
    }
    while (exception != null);
}

来自代理的响应主体看起来像这样：

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>502 Proxy Error</title>
</head><body>
<h1>Proxy Error</h1>
<p>The proxy server received an invalid
response from an upstream server.<br />
The proxy server could not handle the request <em><a href="/xxx/xxx/xxx">POST&nbsp;/xxx/xxx/xxx</a></em>.<p>
Reason: <strong>Error reading from remote server</strong></p></p>
</body></html>

通过SSL发送带有HttpWebRequest的请求时出现错误502（错误网关）

5 个答案: