How to corectly set the ContentType property in HttpWebRequest (or how to fix the missing Content-Type header) - header

Question

I thought I'd share something that took me some time to figure out:
I wrote a simple Post method using HttpWebRequest class.
In HttpWebRequest you can't use HttpWebRequest.Headers collection to set your desired headers when there is a dedicated property for it - you must use that dedicated property. ContentType is one of them. So I created my HttpWebRequest like this:
HttpWebRequest httpWebRequest = (HttpWebRequest)webRequest;
httpWebRequest.Method = "POST";
httpWebRequest.KeepAlive = false;
httpWebRequest.ServicePoint.Expect100Continue = false;
httpWebRequest.ContentType = "application/json";
somewhere below I set the body of my request like this:
using (StreamWriter streamWriter = new StreamWriter(streamWebRequest))
{
streamWriter.Write(sJson);
}
and posted the request using:
WebResponse webResponse = httpWebRequest.GetResponse();
But I kept getting a "400 - Bad Request" error, while the same request worked from Postman. After analyzing the request with Fiddler I found that when I send the request from my app, the Content-Type: application/json header is missing. All the other headers were present, except for Content-Type. I thought I'm setting it wrong, so I googled but didn't find a good answer. After much experimentation I found, that if I move the line:
httpWebRequest.ContentType = "application/json"
after this block:
using (StreamWriter streamWriter = new StreamWriter(streamWebRequest))
{
streamWriter.Write(sJson);
}
then the httpWebRequest.ContentType = "application/json" header finally appears in the request. So, for HttpWebRequest make sure you always set your HttpWebRequest's body/content first, before you set the ContentType property.
Hope it helps

Answer 1

My question above already has the answer, but to mark it as "Answered" I had to add this comment:
Make sure you always set your HttpWebRequest's body/content first, before you set the ContentType property.This way the "Content-Type" header will appear in the request.