OperationFormatter could not serialize error with WCF

I was working with calling WCF from iPhone, I have posted one post on “how can you call WCF from iPhone” you can find here. While I was working with this, I faced this issue and after doing some research I found solution! Here is what I did.

Following operation contract works fine.

[OperationContract]
public Dictionary<string, string> GetDictionary()

Note that I have only put operation contract not decoration which needed to work WCF with iPhone and Json.
But if we change this that operation contract to following...

[OperationContract]
public string GetDictionary()

After doing this I started getting follwoing error.

The OperationFormatter could not serialize any information from the Message because the Message is empty

I was wondering as it was issue with primitive type string! where it was working find with complex type. I searched a lot but did not get any solution for this. The service was retuning Serialized Json data; but not sure what was wrong there. I was searching for workaround to this but didn’t find any then I wrap that string into concert class and and return that class object, and you don’t believe it works fine! Error is gone I fixed The OperationFormatter could not serialize any information from the Message because the Message is empty error, wow!!!!!

I have modified operation and now it looks like following.

[DataContract]
public class Response
{
    [DataMember]
    public string Data { get; set; }
}

[OperationContract]
public Response GetDictionary()
{
    return new Response() { Data = "success" };
}

It still open question why it was not working in only string, however it was working with Dictionary object and then with Abstract type! I assume that at the time of serializing request its not able to create object of string as its primitive type! Not sure its true but it works fine with wrapper.

Calling WCF service from iPhone

WCF changes way of communication between application-to-application and intra-application. This post will help you to call WCF from iPhone application. First we will see what we have to do on WCF to let iPhone application call service. And the sample code which call WCF from iPhone.

First let’s create simple WCF service.

[ServiceContract(Namespace = "")]
[DataContractFormat]
public class MultiEndPointsService
{
    [OperationContract]
    public string GetDictionary()
    {
        Dictionary<string, string> dict = new Dictionary<string, string>();
        dict.Add("IB", "Imran Bhadelia");
        dict.Add("DO", "David Oliver");
        dict.Add("NA", "Nick Althoff");
        dict.Add("JJ", "Jay Joshi");
        dict.Add("DL", "Dave Larson");
        dict.Add("BA", "Brenda Ayong-Chee");
        dict.Add("JP", "Jay Parikh");

        StringBuilder sbJson = new StringBuilder();
        new JavaScriptSerializer().Serialize(dict, sbJson);
        return sbJson.ToString();

    }
}

This is simple WCF Service. We need to add some decoration for enabling web script and handle POST method. We are going to send http post form iPhone application and send Json string as response. Doing so we also need to decorate our operation contract to set request and response format.

[ServiceContract(Namespace = "")]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
[ServiceBehaviorAttribute(IncludeExceptionDetailInFaults = true)]
[DataContractFormat(Style = OperationFormatStyle.Document)]
public class MultiEndPointsService
{
    [WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.WrappedRequest,
        RequestFormat = WebMessageFormat.Xml, ResponseFormat = WebMessageFormat.Json)]
    [OperationContract]
    public string GetDictionary()
    {
        Dictionary<string, string> dict = new Dictionary<string, string>();
        dict.Add("IB", "Imran Bhadelia");
        dict.Add("DO", "David Oliver");
        dict.Add("NA", "Nick Althoff");
        dict.Add("JJ", "Jay Joshi");
        dict.Add("DL", "Dave Larson");
        dict.Add("BA", "Brenda Ayong-Chee");
        dict.Add("JP", "Jay Parikh");
           
        StringBuilder sbJson = new StringBuilder();
        new JavaScriptSerializer().Serialize(dict, sbJson);
        return sbJson.ToString();
    }
}

And following are the configuration settings

<system.serviceModel>
    <services>
      <service name="Demo.Service.MultiEndPointsService" behaviorConfiguration="serviceBehaviour">
        <endpoint address="basic" binding="basicHttpBinding" bindingConfiguration="basicBinding" contract="Demo.Service.MultiEndPointsService" />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="serviceBehaviour">
          <serviceMetadata httpGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="false" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <bindings>
      <basicHttpBinding>
        <binding name="basicBinding" maxBufferSize="2147483647" maxReceivedMessageSize="2147483647">
          <security mode="None"></security>
          <readerQuotas maxStringContentLength="2147483647" />
        </binding>
      </basicHttpBinding>    
    </bindings>
  </system.serviceModel>

We need to create basicHttpBinding so it get called form iPhone application, we haven’t sent security to call this method; and following is the Objective-C code which call WCF from iPhone.

NSString *soapMessage = [NSString stringWithFormat:@"<SOAP-ENV:Envelope xmlns:SOAP-ENV=\"http://schemas.xmlsoap.org/soap/envelope/\"><SOAP-ENV:Body><GetDictionary></GetDictionary></SOAP-ENV:Body></SOAP-ENV:Envelope>"];
   
NSURL *url = [NSURL URLWithString:@http://localhost/Demo.Service/MultiEndPointsService.svc/basic];
NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:url];                        
NSString *msgLength = [NSString stringWithFormat:@"%d", [soapMessage length]];             
   
[theRequest addValue: @"text/xml; charset=utf-8" forHTTPHeaderField:@"Content-Type"];
[theRequest addValue: @"urn:MultiEndPointsService/GetDictionary" forHTTPHeaderField:@"SOAPAction"];
[theRequest addValue: msgLength forHTTPHeaderField:@"Content-Length"];
[theRequest setHTTPMethod:@"POST"];    
[theRequest setHTTPBody: [soapMessage dataUsingEncoding:NSUTF8StringEncoding]];

NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];

Once you parse the response it will look like following.

You can also call operation contract having parameters, for that need to create proper message and then add it in SOAP-BODY that will work.