Question

At the moment I have an C# console application that exposes Web Services through WebServiceHost those web services are being used by an website but now I’m trying to add SSE to the site.

The code at the client is:

var source = new EventSource(server+'eventSource');
source.onmessage = function (event) {
  alert(event.data);
};  

But on the server side, when I try to define the contract:

[OperationContract]
[WebGet]
String EventSource();

What the service is returning service is a xml with a String.

What should I do on the server side to create a document available for SSE?

Thanks in advace

Answer 1

If you have an OperationContract, the return Type is always serialized as XML or optionaly as JSON. If you do not want the return value to be serialized define it as Stream.

[OperationContract] 
[WebGet] 
Stream EventSource(); 

// Implementation Example for returning an unserialized string.
Stream EventSource()
{
   // These 4 lines are optional but can spare you a lot of trouble ;)
   OutgoingWebResponseContext context = WebOperationContext.Current.OutgoingResponse;
   context.Headers.Clear();
   context.Headers.Add("cache-control", "no-cache");
   context.ContentType = "text/event-stream"; // change to whatever content type you want to serve.

   return new System.IO.MemoryStream(Encoding.ASCII.GetBytes("Some String you want to return without the WCF serializer interfering.")); 
}

If you build the stream yourself remember to exectute .Seek(0, SeekOrigin.Begin); before you return it.

EDIT:
Changed the command order to set the ContentType AFTER the Header gets cleard. Otherwise you would clear the freshly set ContentType too 😉