WCF responds with HTTP 400 to serialized JSON string from Razor Pages app - wcf

Question

I'm trying to POST a request containing JSON from a Razor Pages app to a WCF service endpoint expecting a Json WebMessageFormat and Bare BodyStyle.The JSON passes just fine via Postman, but not when I send it through http-client. Wireshark also shows some extra bytes around JSON in the http-client produced packet that are not present in the Postman packet. Wireshark also reports this as line-based text data: application/json for the Postman packet. The .Net packet is JavaScript Object Notation: application/json.
Here's my C# code to send the JSON to the WCF endpoint:
var client = new HttpClient();
client.BaseAddress = new Uri("http://localhost:8000");
dynamic foo = new ExpandoObject();
foo.position = 1;
var content = new StringContent(Newtonsoft.Json.JsonConvert.SerializeObject(foo), System.Text.Encoding.UTF8, "application/json");
var request = new HttpRequestMessage(HttpMethod.Post, "http://localhost:8000/WCFService/ControllerV1/PostJSON");
request.Headers.Add("cache-control", "no-cache");
request.Headers.Add("Accept", "*/*");
request.Headers.Add("Connection", "keep-alive");
request.Content = content;
try
{
var response = await client.SendAsync(request);
response.EnsureSuccessStatusCode();
string responseBody = await response.Content.ReadAsStringAsync();
}
catch (HttpRequestException e)
{
Console.WriteLine(e.Message);
}
And here's my WCF endpoint declaration:
[OperationContract, WebInvoke(Method="POST", RequestFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.Bare)]
void PostJSON(string jsonString);
I would expect the packets to produce the same response from the server, but, what appears to be the same string produces a response 200 when the packet is built by postman and a response 400 when built by .Net. I'm clearly missing something subtle here, but I can't seem to tease it out.

Answer 1

There are 2 possible BodyStyle for request and response, wrapped or bare. When you specify wrapped body style the WCF service expects a valid json to be passed which in your case would be
//note that property name is case sensitive and must match service parameter name
{
"jsonString": "some value"
}
And when you specify bare format the service expects only plain string value (in case of primitive type as yours) as the request like this
"some value"
When you serialize your object like this
dynamic foo = new ExpandoObject();
foo.position = 1;
string result = JsonConvert.SerializeObject(foo);
the result contains the following json
{
"position":1
}
which corresponds to wrapped format and the service returns 400: Bad Request. All you need to do is to turn this json into valid json string value like this
"{\"position\":1}"
It can be done by repeated JsonConvert.SerializeObject call
dynamic foo = new ExpandoObject();
foo.position = 1;
string wrapped = JsonConvert.SerializeObject(foo);
string bare = JsonConvert.SerializeObject(wrapped);
var content = new StringContent(bare, System.Text.Encoding.UTF8, "application/json");