Getting error: HttpRequestException: Received an invalid header name: 'Content=Transfer-Encoding'. when using MVC Core to download a file - model-view-controller

Question

I'm trying to have a controller in MVC core (3.1) download an audio file to present to the user but everything I try ends up with the error:
HttpRequestException: Received an invalid header name: 'Content=Transfer-Encoding'.
I have tried webclient, httpclient and just lately webrequest/webresponse. My code looks like this right now (specifics removed for security):
WebRequest downloadRequest = WebRequest.Create({url here});
downloadRequest.Headers.Add("Cookie", "{cookie data here};");
downloadRequest.Headers.Add("Accept", "application/json, text/javascript, */*; q=0.01");
downloadRequest.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:73.0) Gecko/20100101 Firefox/73.0");
downloadRequest.Headers.Add("Sec-Fetch-Dest", "empty");
downloadRequest.Headers.Add("X-Requested-With", "XMLHttpRequest");
using (WebResponse webResponse = await downloadRequest.GetResponseAsync())
{
return File(webResponse.GetResponseStream(), "audio/wav", wavFile + ".txt");
}
The error is on the line
using (WebResponse webResponse = await downloadRequest.GetResponseAsync())
Using fiddler the request looks good and the header it is complaining about is: Content=Transfer-Encoding: binary, it has the file in the content-disposition as an attachement. I have no control at all over the sending server unfortunately but this works fine in a browser. Can anyone tell me what i'm doing wrong please?
Thanks

Answer 1

The incoming request looks malformed. Transfer-Encoding is its own header name. You cannot assign it to the value of another header. And AFAIK, Content isn't even a standard HTTP header name.
Refer to the list at https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers#Message_body_information for valid Content-* headers. The Transfer-Encoding header is documented at https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Transfer-Encoding.
Edit for framework 4.8 and below
I had to add the following lines to app.config to let the client process invalid responses from the server.
<system.net>
<settings>
<httpWebRequest useUnsafeHeaderParsing="true" />
</settings>
</system.net>
The program itself is shown below.
try
{
var httpclient = new HttpClient();
var response = await httpclient.GetAsync("http://localhost:9091");
var attachment = new byte[1024];
foreach (var h in response.Content.Headers)
{
var e = h.Value.GetEnumerator();
e.MoveNext();
attachment = Encoding.UTF8.GetBytes(e.Current); // Convert UTF-8 encoded string into raw bytes
Console.WriteLine($"{h.Key}, {Encoding.UTF8.GetString(attachment)}"); // Save raw bytes to disk instead of converting back to string and writing to Console
}
}
catch (Exception exception)
{
Console.WriteLine(exception.Message);
}
Edit for dotnet core
try
{
var s = new Socket(SocketType.Stream, ProtocolType.Tcp);
var a = IPAddress.Parse("127.0.0.1");
await s.ConnectAsync(a, 9091);
var request = "GET http://localhost:9091/";
var outBytes = Encoding.UTF8.GetBytes(request);
var outBuffer = new ArraySegment<byte>(outBytes);
await s.SendAsync(outBuffer, SocketFlags.None);
var inBytes = new byte[1024];
var inBuffer = new ArraySegment<byte>(inBytes);
await s.ReceiveAsync(inBuffer, SocketFlags.None);
var r = Encoding.UTF8.GetString(inBuffer.Array);
}
catch (SocketException exception)
{
Console.WriteLine($"Error: {exception.Message}");
}