C# : System.Net.WebException: The underlying conne

Question

I have the following code :

String url = // a valid url
String requestXml = File.ReadAllText(filePath);//opens file , reads all text and closes it
byte[] bytes = System.Text.Encoding.ASCII.GetBytes(requestXml);
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Credentials = new NetworkCredential("DEFAULT\\Admin", "Admin"); 
request.ContentType = "application/xml";
request.ContentLength = bytes.Length;
request.Method = "POST";
request.KeepAlive = false;
Stream requestStream = request.GetRequestStream();
requestStream.Write(bytes, 0, bytes.Length);
requestStream.Close();
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream responseStream = response.GetResponseStream();
return new StreamReader(responseStream).ReadToEnd();

During run-time, I'm getting the following exception while trying to read the HTTPWebResponse :

System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a receive.
---> System.IO.IOException: Unable to read data from the transport connection: An established connection was aborted by the software in your host machine.
---> System.Net.Sockets.SocketException: An established connection was aborted by the software in your host machine
at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.PooledStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.Connection.SyncRead(HttpWebRequest request, Boolean userRetrievedStream, Boolean probeRead)

Answer 1

Don't close the stream before reading from it. This should work:

String url = // a valid url
String requestXml = File.ReadAllText(filePath);//opens file , reads all text and closes it
byte[] bytes = System.Text.Encoding.ASCII.GetBytes(requestXml);
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Credentials = new NetworkCredential("DEFAULT\\Admin", "Admin"); 
request.ContentType = "application/xml";
request.ContentLength = bytes.Length;
request.Method = "POST";
request.KeepAlive = false;
using (Stream requestStream = request.GetRequestStream())
{
    requestStream.Write(bytes, 0, bytes.Length);
    using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
    {
        using (Stream responseStream = response.GetResponseStream())
        {
            using (StreamReader streamReader = new StreamReader(responseStream))
            {
                return streamReader.ReadToEnd();
            }
        }
    }
}

Answer 2

Adding this line of code solved the problem for me:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

This was taken from: https://our.umbraco.com/forum/using-umbraco-and-getting-started/74628-the-underlying-connection-was-closed-an-unexpected-error-occurred-on-a-send