Post with HttpClient and custom Accept / Encoding headers

Question

I need to consume a 3rd party api of an internal system, which expects the following headers:

Accept application/json;charset=iso-8859-1
Content-Type application/json;charset=iso-8859-1

In order to do this I've cobbled together the following piece of code:

public async Task<bool> CreateOrDeleteFolder(CreateFolderRequestBody body)
{
   var request = new HttpRequestMessage(HttpMethod.Post, $"{BaseAddress}/testFolder.php");
   request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json")
   {
      CharSet = "iso-8859-1"
   });
   
   var isoEncoding = Encoding.GetEncoding("iso-8859-1");
   var payload = new StringContent(JsonConvert.SerializeObject(body), isoEncoding, "application/json");

   request.Content = payload;
   HttpResponseMessage responseMessage = null;
   
   responseMessage = await _client.SendAsync(request);
  
   responseMessage.EnsureSuccessStatusCode();
   var responseBody = await responseMessage.Content.ReadAsStringAsync();
   //do something with the body
   return true;
}

This produces the following request:

POST http://somewhere.to/testFolder.php HTTP/1.1
Accept: application/json; charset=iso-8859-1
Content-Type: application/json; charset=iso-8859-1
Host: somwhere.to
Content-Length: 57
Expect: 100-continue
Connection: Keep-Alive

Apparently the additional whitespace in the headers between the semicolon and the charset produces a response stating invalid header values.

How can I manipulate those header values to not contain those white spaces?

Ahm, I know that this might sound weird, but can you try adding User-agent to your request and see if that helps, despite the ; space — zaitsman
– zaitsman, Commented Oct 9, 2020 at 12:20
In Postman I have PostmanRuntime/7.26.5 as the user-agent and adding removing the whitespace reproduces the issue consistently. — Marco
– Marco, Commented Oct 9, 2020 at 12:24
So apparently this is a bug in.net core and if you use full .net framework 4.5 it may be avoided. But not later versions of .NETFX. o_O. github.com/dotnet/runtime/issues/30171 It devolved into the usual potato-potato argument with .net devs saying 'we are following RFC' :/ — zaitsman
– zaitsman, Commented Oct 9, 2020 at 12:39
Also, apparently partially addressed in .net 5.0, so wait another month and you should have it :) github.com/dotnet/corefx/pull/41640 — zaitsman
– zaitsman, Commented Oct 9, 2020 at 12:40
I'm on full 4.6.2, and I need it done yesterday - as always. So no luck there ;) — Marco
– Marco, Commented Oct 9, 2020 at 12:42

Marco · Accepted Answer · 2020-10-09 13:01:58Z

1

I've botched a workaround together by inherting from MediaTypeHeaderValue:

public class TrimmedMediaTypeHeaderValue : MediaTypeHeaderValue
{
   public TrimmedMediaTypeHeaderValue(string mediaType) :base(mediaType)
   {

   }

   public override string ToString() 
        => string.IsNullOrEmpty(CharSet)
           ? MediaType
           : $"{MediaType};charset={CharSet}";
}

Since the docs did not specify any method that would build the header string together I just assumed it would be ToString() and indeed - it is. So this now produces a header value, without a whitespace between the ; and the charset.

Be aware, that this class has only one constructor instead of the 2 of the base class. So if you want to use this, you might need to add another one in.

answered Oct 9, 2020 at 13:01

Marco

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