HttpClient & HttpWebRequest Confusion with HTTP POST

A developer came to me and need my help to troubleshoot a problem with HttpClient and HttpWebRequest. Imagine that I have a WCF REST service, the operation contract is a logical invoke operation which expect POST method and accepting a string parameter.

[OperationContract]

[WebInvoke(UriTemplate="Push", Method="POST", BodyStyle=WebMessageBodyStyle.Bare)]

string PushPost(string input);

The developer tried to invoke the web method by using HttpClient. It is a success with the following code:

HttpClient client = new HttpClient();

var post = client.PostAsync<string>("http://localhost:58072/ResearchAPI.aspx/push",

    "input1=abc&input2=cde", new XmlMediaTypeFormatter()).Result;

string result = post.Content.ReadAsStringAsync().Result;

However, the developer tried to invoke the same web method by using HttpWebRequest and it failed and getting HTTP400 bad request error with the following code:

string input = "input1=abc&input2=cde";

var request = (HttpWebRequest)WebRequest.Create("http://localhost:58072/ResearchAPI.aspx/push");

request.Method = "POST";

byte[] data = Encoding.UTF8.GetBytes(input);

request.ContentLength = input.Length;

request.ContentType = "application/xml";

Stream newStream = request.GetRequestStream();

newStream.Write(data, 0, data.Length);

newStream.Close();

newStream.Flush();

var response = (HttpWebResponse)request.GetResponse();

var stream = response.GetResponseStream();

StreamReader reader = new StreamReader(stream);

string result = reader.ReadToEnd();

So, I tried to play around with the RAW data by using SOAP UI. I am posting same RAW data to the service and I get the same HTTP400 error too.

I find something is not right here. The WCF service is accepting the same HTTP request, why would HttpClient success but not HttpWebRequest and posting raw HTTP with SOAP UI. Therefore, I proceed to checkout what are the HTTP header and content difference between HttpClient and HttpWebRequest by using Fiddler.

This is what I got from HttpClient:

POST http://ipv4.fiddler:58072/ResearchAPI.aspx/push HTTP/1.1

Content-Type: application/xml; charset=utf-8

Host: ipv4.fiddler:58072

Content-Length: 102

Expect: 100-continue

Connection: Keep-Alive

<string xmlns="http://schemas.microsoft.com/2003/10/Serialization/">input1=abc&amp;input2=cde</string>

This is what I got from HttpWebRequest:

POST http://ipv4.fiddler:58072/ResearchAPI.aspx/push HTTP/1.1

Content-Type: application/xml

Host: ipv4.fiddler:58072

Content-Length: 21

Expect: 100-continue

Connection: Keep-Alive

input1=abc&input2=cde

Ha! So, you notice the missing charset=utf-8 header in the HttpWebRequest. And then, the content is different as highlighted above.

I suppose the reason why serialized <string> content is working fine while calling my WCF service is because the operation contract parameter is a string data type. If we want to post RAW content to the service, we have to make sure the service input parameter data type is a Stream type. Otherwise, I actually can use HttpWebRequest post the same content as HttpClient did, and then I will get HTTP200.

The following HttpClient will post the string content with serialized <string> which I do not want:

HttpClient client = new HttpClient();

var post = client.PostAsync<string>("http://localhost:58072/ResearchAPI.aspx/push",

    "input1=abc&input2=cde", new XmlMediaTypeFormatter()).Result;

In order to post the exact string or RAW content to the service like what I did with HttpWebRequest or SOAP UI, I need to modify the HttpClient code as follow:

HttpClient client = new HttpClient();

var post = client.PostAsync("http://localhost:58072/ResearchAPI.aspx/push",

    new StringContent("input1=abc&input2=cde")).Result;

In summary, there was a little confusion with the HttpClient.PostAsync method. The PostAsync<string> method does not post the same content as StringContent.