You can get the raw data by calling ReadAsStringAsAsync on the Request.Content property.
string result = await Request.Content.ReadAsStringAsync();
There are various overloads if you want it in a byte or in a stream. Since these are async-methods you need to make sure your controller is async:
public async Task<IHttpActionResult> GetSomething()
{
var rawMessage = await Request.Content.ReadAsStringAsync();
// ...
return Ok();
}
EDIT: if you're receiving an empty string from this method, it means something else has already read it. When it does that, it leaves the pointer at the end. An alternative method of doing this is as follows:
public IHttpActionResult GetSomething()
{
var reader = new StreamReader(Request.Body);
reader.BaseStream.Seek(0, SeekOrigin.Begin);
var rawMessage = reader.ReadToEnd();
return Ok();
}
In this case, your endpoint doesn't need to be async (unless you have other async-methods)