Avoid adding charset to Content-Type header

[samrat]

Hello! 👋

I'm trying to use the OpenAI Realtime API and need to send Content-Type: application/sdp as one of the headers.

Here's what my Dart code looks like

      final response = await http.post(
        Uri.parse('$baseUrl?model=$model'),
        headers: {
          'Authorization': 'Bearer $ephemeralKey',
          'Content-Type': 'application/sdp',
        },
        body: sdp,
        encoding: null
      );

Even though I'm setting the header to application/sdp the request sent has the header set to application/sdp; charset=utf-8(I tested this with iOS, macOS and Web debug targets)

And looks like the OpenAI endpoint is very strict about the value it accepts for this header:

Response body: {"error":{"message":"Unsupported content type. This API method only accepts 'application/sdp' requests, but you specified the header 'Content-Type: application/sdp; charset=utf-8'. Please try again with a supported content type.","type":"invalid_request_error","param":null,"code":"unsupported_content_type"}}

Is there any way to prevent the http library from modifying headers before the request is made?