How can I set User-Agent and Referer headers when using ClientWebSocket in .net 4.5?

Question

The obvious answer of using ClientWebSocket.SetHeader throws an exception because it's a protected header:

System.ArgumentException occurred
  Message=The 'User-Agent' header must be modified using the appropriate property or method.
Parameter name: name
  ParamName=name
  StackTrace:
       at System.Net.WebHeaderCollection.ThrowOnRestrictedHeader(String headerName)

The exception string suggests using a property/method on the ClientWebSocket itself but I can't find any such property/method. It seems this exception was designed for the HttpWebRequest class, which actually has such property.

The code, which doesn't work:

ClientWebSocket socket = new ClientWebSocket();
// Will throw
socket.Options.SetRequestHeader("User-Agent", "SomeUserAgentString");
// Will throw
socket.Options.SetRequestHeader("Referer", "SomeReferer"]);

Answer 1

It doesn't look like you'll be able to set those properties, at least not right now. You might be able to do it via reflection.

If you look closely at your stack trace, you'll see that the throwing method is System.Net.WebHeaderCollection.ThrowOnRestrictedHeader. System.Net.WebHeaderCollection is a specialized name value collection designed to deal with HTTP headers. If you look at the remarks section, you'll see the following:

Some common headers are considered restricted and are either exposed directly by the API (such as Content-Type) or protected by the system and cannot be changed.

The list has both the User-Agent and Referer properties listed as protected headers and cannot be set since the ClientWebSocket does not expose it.

All that being said, though, if you absolutely need to set those headers, you'll need to find the private reference WebHeaderCollection of your ClientWebSocketOptions (exposed as the Options property on your ClientWebSocket) and call the protected AddWithoutValidate method to set the headers.

Answer 2

Looks like this is a bug in .NET Framework:

https://github.com/dotnet/corefx/issues/26627#issuecomment-391472613

And unfortunately, it seems that even the reflection hack suggested by Joshua won't work, as the validation is performed again as part of the HTTP exchange when the websocket connection is established:

https://github.com/dotnet/corefx/issues/26627#issuecomment-361234413

Answer 3

I think i have found a "easy" solution

If you build with ".NET Core 2.2" (on windows 10) instead then:

"socket.Options.SetRequestHeader("User-Agent", "SomeUserAgentString");"

Will not throw. Same with all the other restricted headers.

So either it works, or it just fails silently. I haven't been able to test and verify that it works, as I don't know how to log or view the request headers. (Anyone know?)

Answer 4

very simple:

The referrer header should be written like so:

HttpWebRequest objRequest()... objRequest.Referer = "http://microsoft.com/simpleApp/