WCF REST read URL-encoded response - wcf

Question

I'm trying to use WCF to consume a 3rd-party REST service which responds with URL-encoded data:
a=1&b=2&c=3
I have this now:
[DataContract]
class Response {
[DataMember(Name="a")]
public int A { get;set;}
[DataMember(Name="b")]
public int B { get;set;}
[DataMember(Name="c")]
public int C { get;set;}
}
[ServiceContract]
interface IService
{
[OperationContract]
Response Foo();
}
But it comes back with:
There was an error checking start element of object of type Response. The data at the root level is invalid. Line 1, position 1.

Answer 1

WCF does not "understand" forms-data content type (application/x-www-forms-urlencoded), so it won't be able to read that response directly. You can either implement a message formatter which will be able to convert that format into your contract, or you can receive the response as a Stream (which will give you the full bytes of the response), which you can decode into your class.
The code below shows how you could implement a formatter for this operation. It's not generic, but you should get the picture of what needs to be done.
public class StackOverflow_16493746
{
[ServiceContract]
public class Service
{
[WebGet(UriTemplate = "*")]
public Stream GetData()
{
WebOperationContext.Current.OutgoingResponse.ContentType = "application/x-www-form-urlencoded";
return new MemoryStream(Encoding.UTF8.GetBytes("a=1&b=2&c=3"));
}
}
[ServiceContract]
interface IService
{
[WebGet]
Response Foo();
}
[DataContract]
class Response
{
[DataMember(Name = "a")]
public int A { get; set; }
[DataMember(Name = "b")]
public int B { get; set; }
[DataMember(Name = "c")]
public int C { get; set; }
}
public class MyResponseFormatter : IClientMessageFormatter
{
private IClientMessageFormatter originalFormatter;
public MyResponseFormatter(IClientMessageFormatter originalFormatter)
{
this.originalFormatter = originalFormatter;
}
public object DeserializeReply(Message message, object[] parameters)
{
HttpResponseMessageProperty httpResp = (HttpResponseMessageProperty)
message.Properties[HttpResponseMessageProperty.Name];
if (httpResp.Headers[HttpResponseHeader.ContentType] == "application/x-www-form-urlencoded")
{
if (parameters.Length > 0)
{
throw new InvalidOperationException("out/ref parameters not supported in this formatter");
}
byte[] bodyBytes = message.GetReaderAtBodyContents().ReadElementContentAsBase64();
NameValueCollection pairs = HttpUtility.ParseQueryString(Encoding.UTF8.GetString(bodyBytes));
Response result = new Response();
foreach (var key in pairs.AllKeys)
{
string value = pairs[key];
switch (key)
{
case "a":
result.A = int.Parse(value);
break;
case "b":
result.B = int.Parse(value);
break;
case "c":
result.C = int.Parse(value);
break;
}
}
return result;
}
else
{
return this.originalFormatter.DeserializeReply(message, parameters);
}
}
public Message SerializeRequest(MessageVersion messageVersion, object[] parameters)
{
throw new NotSupportedException("This is a reply-only formatter");
}
}
public class MyClientBehavior : WebHttpBehavior
{
protected override IClientMessageFormatter GetReplyClientFormatter(OperationDescription operationDescription, ServiceEndpoint endpoint)
{
return new MyResponseFormatter(base.GetReplyClientFormatter(operationDescription, endpoint));
}
}
public static void Test()
{
string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
WebServiceHost host = new WebServiceHost(typeof(Service), new Uri(baseAddress));
host.Open();
Console.WriteLine("Host opened");
ChannelFactory<IService> factory = new ChannelFactory<IService>(new WebHttpBinding(), new EndpointAddress(baseAddress));
factory.Endpoint.Behaviors.Add(new MyClientBehavior());
IService proxy = factory.CreateChannel();
Response resp = proxy.Foo();
Console.WriteLine("a={0},b={1},c={2}", resp.A, resp.B, resp.C);
((IClientChannel)proxy).Close();
factory.Close();
Console.Write("Press ENTER to close the host");
Console.ReadLine();
host.Close();
}
}