You must write ContentLength bytes to the request stream before calling [Begin]GetResponse

Question

Error: You must write ContentLength bytes to the request stream before calling [Begin]GetResponse.

Can anyone advise why I am getting the above error when running the following code

        Dim xml As New System.Xml.XmlDocument()

        Dim root As XmlElement
        root = xml.CreateElement("root")
        xml.AppendChild(root)

        Dim username As XmlElement
        username = xml.CreateElement("UserName")
        username.InnerText = "xxxxx"
        root.AppendChild(username)

        Dim password As XmlElement
        password = xml.CreateElement("Password")
        password.InnerText = "xxxx"
        root.AppendChild(password)

        Dim shipmenttype As XmlElement
        shipmenttype = xml.CreateElement("ShipmentType")
        shipmenttype.InnerText = "DELIVERY"
        root.AppendChild(shipmenttype)


        Dim url = "xxxxxx"
        Dim req As WebRequest = WebRequest.Create(url)
        req.Method = "POST"
        req.ContentType = "application/xml"
        req.Headers.Add("Custom: API_Method")
        req.ContentLength = xml.InnerXml.Length

        Dim newStream As Stream = req.GetRequestStream()
        xml.Save(newStream)

        Dim response As WebResponse = req.GetResponse()


        Console.Write(response.ToString())

Answer 1

Probably a length mismatch between the character length of xml.InnerXml and what is actually written to the stream in xml.Save(newStream). Check if InnerXml includes the xml version node, for example. Also, I don't see you specifying a character encoding, which definitely affects the size on the wire. Perhaps you need to save to a temporary memory stream, get the length of that, and then send that in the request.

Answer 2

In short: newStream.Length != xml.InnerXml.Length.

• First of all, XmlDocument.Save(Stream) will encode the response, which may result in a different number of bytes than are chars in the .InnerXml string.
• .InnerXML does not necessarily contain other stuff, such as the XML preamble.

Here is a complete example. (Sorry, my VB is a bit rusty, so C# instead):

using System;
using System.IO;
using System.Net;
using System.Xml;

namespace xmlreq
{
  class Program
  {
    static void Main(string[] args)
    {
      var xml = new XmlDocument();
      var root = xml.CreateElement("root");
      xml.AppendChild(root);

      var req = WebRequest.Create("http://stackoverflow.com/");
      req.Method = "POST";
      req.ContentType = "application/xml";

      using (var ms = new MemoryStream()) {
        xml.Save(ms);
        req.ContentLength = ms.Length;
        ms.WriteTo(req.GetRequestStream());
      }
      Console.WriteLine(req.GetResponse().Headers.ToString());
    }
  }
}

Answer 3

I had this error today and the issue was that the endpoint provider had been redirecting http requests to https for years, but changed their policy. So updating my code from

request = WebRequest.Create("http://api.myfaxservice.net/fax.php") 

to

request = WebRequest.Create("https://api.myfaxservice.net/fax.php")

did the trick. If the provider would have just shut off http, I think it would have been an easier problem to run down as this error was putting me on the wrong track.