如何使用HttpClient在（HTTP GET）Rest请求头集合中添加'Content-Type'头？

Question

I am using HttpClient for rest service . At at one point I have a problem when I try to add "Content-Type" in my 'Get' request header .

I know "Content-Type" is suitable for content send in request body part But It's my need i have to send "Content-Type" with request header part.

I also try to remove "Content-Type" header from Invalid Header list of HttpRequestHeaders

I find link How do you set the Content-Type header for an HttpClient request?

        Dim field = GetType(System.Net.Http.Headers.HttpRequestHeaders).GetField("invalidHeaders", System.Reflection.BindingFlags.NonPublic Or System.Reflection.BindingFlags.[Static])

        If field IsNot Nothing Then
            Dim invalidFields = DirectCast(field.GetValue(Nothing), HashSet(Of String))
            invalidFields.Remove("Content-Type")
        End If

But my issue not resolved I have exception

InnerException:

Message=The 'content-type' header must be modified using the appropriate property or method.

   StackTrace:
        at System.Net.WebHeaderCollection.ThrowOnRestrictedHeader(String headerName)
        at System.Net.WebHeaderCollection.Add(String name, String value)
        at System.Net.Http.HttpClientHandler.SetRequestHeaders(HttpWebRequest webRequest, HttpRequestMessage request)
        at System.Net.Http.HttpClientHandler.CreateAndPrepareWebRequest(HttpRequestMessage request)
        at System.Net.Http.HttpClientHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   InnerException:

I find some tools like Postman or SoupUI allow this .

Please help me to find some solution .

Thanks

Answer 1

HttpWebRequest may come to your rescue.

private static string CallService(string url)
{
    WebRequest req = WebRequest.Create(url);
    req.Method = "GET";
    String json;
    req.ContentType = "application/json; charset=utf-8";
    var resp = req.GetResponse();
    using (varstream = resp.GetResponseStream())
    {
        var re = new StreamReader(stream);

            json = re.ReadToEnd();
        }

        return json; 
    }
}

Async implementation of this can be found from Getting the Response of a Asynchronous HttpWebRequest