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Error 502 (Bad Gateway) when sending a request with HttpWebRequest over SSL

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误落风尘
误落风尘 2020-12-13 14:08

I have the following snippet in classic ASP, to send a command and retrieve the response over SSL:

Dim xmlHTTP
Set xmlHTTP = Server.CreateObject(\"Msxml2.Ser
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5条回答
  • 野的像风
    2020-12-13 14:43

    This was happening for me because a Java proxy on the remote machine was timing out requests if the Java application did not respond in time, rendering the .NET default timeouts kind of useless. The following code loops through all exceptions and writes out responses which helped me determine it was actually coming from the proxy:

    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);
}

    The response body from the proxy looked something like this:

    <!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>
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  • 有刺的猬
    2020-12-13 14:49

    UserAgent is missing

    for example : request.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1)";

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  • 醉梦人生
    2020-12-13 14:50

    Read the entity body of the error response. It might have a hint as to what is happening.

    The code to do that is as follows:

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

    That should show the full contents of the error response.

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  • 眼角桃花
    2020-12-13 15:01

    With the help of this I got a more detailed description of the problem: The proxy was returning the message: "The user agent is not recognized." So I set it manually. Also, I changed the code to use GlobalProxySelection.GetEmptyWebProxy(), as described here. The final working code is included below.

    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;
}
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  • 佛祖请我去吃肉
    2020-12-13 15:01

    It is possible that the wsdl for the web service is "arguing" with the domain name and the SSL certificate. IIS will autogenerate a web service's WSDL using the IIS registered domain name (which by default is the machine name on the local domain, not necessarily your web domain). If the certificate domain doesn't match the domain in the SOAP12 Address you will receive communication errors.

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