ArgumentException when setting httpWebRequest.Connection to "Closed"

Question

I am trying to connect to a php apache 2.2.1 webservice like this:

        protected override WebRequest GetWebRequest(Uri uri)
        {
            var req = base.GetWebRequest(uri);
            var http = req as HttpWebRequest;
            if (http != null)
            {
                http.Connection = "Close";
                http.ServicePoint.Expect100Continue = false;
            }
            return req;
        }

But I received an System.ArgumentException mean as following "Keep-Alive and Close cannot be set"(This message has been translated from Japanese).

I have no idea why this exception is thrown. I have searched in MSDN and there is an explanation like this Exception Condition: The value of Connection is set to Keep-alive or Close.. In this case my httpWebRequest.Connection is null.

Do you have any idea about the reason of this exception?

Answer 1

I cannot explain why setting HttpWebRequest.Connection to Close or Keep-alive throw an ArgumentException. But we can set the Connection header to Close via the setting HttpWebRequest.KeepAlive to false.

More infos here : https://learn.microsoft.com/en-us/dotnet/api/system.net.httpwebrequest.connection?view=netframework-4.7.2