Question

I want to add a public (externally callable) JSON data feed to my ASP.net (4) Forms web site. To this end, I have created the following Web Service:

[WebService(Namespace = "http://localtest.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.ComponentModel.ToolboxItem(false)]
[System.Web.Script.Services.ScriptService]
public class BlogWebService : System.Web.Service.WebService
{
   [WebMethod]
   [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
   public List<Blog> GetLatestBlogs(int noBlogs)
   {
      return GetLatestBlogs(noBlogs)
         .Select(b => b.ToWebServiceModel())
         .ToList();
   }
}

I have tested this on the local server by opening

http://localhost:55671/WebServices/BlogWebService.asmx?op=GetLatestBlogs

and it works correctly.

When I try to access this service remotely and get an Internal Server Error. For example, I have run the following code using LinqPad (based on some script from http://geekswithblogs.net/JuanDoNeblo/archive/2007/10/24/json_in_aspnetajax_part2.aspx):

void Main()
{
   GetLatestBlogs().Dump();
}

private readonly static string BlogServiceUrl =
   "http://localhost:55671/BlogWebService.asmx/GetLatestBlogs?noBlogs={0}";

public static string GetLatestBlogs(int noBlogs = 5)
{
   string formattedUri = String.Format(CultureInfo.InvariantCulture,
      BlogServiceUrl, noBlogs);

   HttpWebRequest webRequest = GetWebRequest(formattedUri);
   HttpWebResponse response = (HttpWebResponse)webRequest.GetResponse();
   string jsonResponse = string.Empty;
   using (StreamReader sr = new StreamReader(response.GetResponseStream()))
   {
      jsonResponse = sr.ReadToEnd();
   }
   return jsonResponse;
}

private static HttpWebRequest GetWebRequest(string formattedUri)
{
   Uri serviceUri = new Uri(formattedUri, UriKind.Absolute);
   return (HttpWebRequest)System.Net.WebRequest.Create(serviceUri);
}

I have a number of questions/doubts:

1. How should the call to the web service be formatted? I’m not sure the construction of my BlogServiceUrl in the LinqPad test code is correct.
2. Are my BlogWebService class and GetBlogs() method defined and attributed correctly?
3. Do I need to to add anything to my web site configuration to make this work?

Any advice would be much appreciated.

Answer 1

I was unable to find a way to get the HttpHandler (.ashx) mechanism working for remote JavaScript calls – I always received the ‘Invalid referrer’ error in the remote jQuery call. I’m not saying it is not possible, but I could not find any documentation on how to do it – not that worked anyway.

In the end, I converted the code to a WCF service guided by this article by Ben Dewey – which was very helpful – make sure you apply the class and method attributes carefully – I didn’t and spent a happy hour or so trying to figure out what was wrong!

Here’s the code:

IBlogService.cs

[ServiceContract]
public interface IBlogService
{
   [OperationContract]
   List<WebServiceModels.Blog> GetLatestBlogs(int noItems);
}

BlogService.svc

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class BlogService 
   : Ninject.Web.WebServiceBase, IBlogService
{

   private readonly IScoRepository ScoDb;       // Data repository


   public BlogService(IScoRepository scoDb)
   {
      this.ScoDb = scoDb;
   }


   [WebGet(ResponseFormat = WebMessageFormat.Json)]
   public List<WebServiceModels.Blog> GetLatestBlogs(int noItems)
   {
      return ScoDb
         .GetLatestBlogs(noItems)
         .Select(b => b.ToWebServiceModel(hostAddress))
         .ToList();
   }
}

Web.config

<system.serviceModel>
   <serviceHostingEnvironment multipleSiteBindingsEnabled="true"  aspNetCompatibilityEnabled="true" />
   <behaviors>
      <endpointBehaviors>
         <behavior name="webHttpBehavior">
            <webHttp />
         </behavior>
      </endpointBehaviors>
      <serviceBehaviors>
         <behavior name="">
            <serviceMetadata httpGetEnabled="true" />
            <serviceDebug includeExceptionDetailInFaults="false" />
         </behavior>
      </serviceBehaviors>
   </behaviors>
   <bindings>
      <webHttpBinding>
         <binding name="webHttpBindingWithJsonP" crossDomainScriptAccessEnabled="true" />
      </webHttpBinding>
   </bindings>
   <services>
      <service name="WebServices.JSON.BlogService">
         <endpoint name="WebServices.JSON.IBlogService" address="" binding="webHttpBinding" bindingConfiguration="webHttpBindingWithJsonP" contract="WebServices.JSON.IBlogService" behaviorConfiguration="webHttpBehavior" />
      </service>
   </services>
</system.serviceModel>

Test JavaScript

$.ajax({
   type: "GET",
   url: "http://localhost:55671/WebServices/JSON/BlogService.svc/GetLatestBlogs",
   data: {
      noItems: 3
   },
   dataType: "jsonp",
   cache: false,
   success: function(result) {
      alert(result[0].Title + " (" + result.length + " Blogs returned)");
   },
   error: function(jqXHR, textStatus, errorThrown) {
     alert(errorThrown);
   }
});

As you can see, I also used Ninject DI. This was problematical until I came across the Ninject.Extension.Wcf module which made life very easy. Couple of gotchyas though.

• I couldn’t find much documentation

• Add the ‘factory’ attribute to the WCF page:

  Factory=”Ninject.Extensions.Wcf.NinjectWebServiceHostFactory”

  • Adjust the Web.config to reference the service interface else the binding magic won’t happen.

I hope it helps.