Notes

using System;
using System.Collections.Generic;
using System.Linq;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.ServiceModel.Description;
using System.ServiceModel.Dispatcher;
using System.Text;
using System.Web;
using System.Xml;

namespace _WcfDataServicee
{
public class JSONPSupportInspector: IDispatchMessageInspector
{
// Assume utf-8, note that Data Services supports
// charset negotation, so this needs to be more
// sophisticated (and per-request) if clients will
// use multiple charsets
private static Encoding encoding = Encoding.UTF8;

#region IDispatchMessageInspector Members

public object AfterReceiveRequest(ref System.ServiceModel.Channels.Message request, IClientChannel channel, InstanceContext instanceContext)
{
if (request.Properties.ContainsKey("UriTemplateMatchResults"))
{
HttpRequestMessageProperty httpmsg = (HttpRequestMessageProperty)request.Properties[HttpRequestMessageProperty.Name];
UriTemplateMatch match = (UriTemplateMatch)request.Properties["UriTemplateMatchResults"];

string format = match.QueryParameters["$format"];
if ("json".Equals(format, StringComparison.InvariantCultureIgnoreCase))
{
// strip out $format from the query options to avoid an error
// due to use of a reserved option (starts with "$")
match.QueryParameters.Remove("$format");

// replace the Accept header so that the Data Services runtime
// assumes the client asked for a JSON representation
httpmsg.Headers["Accept"] = "application/json";

string callback = match.QueryParameters["$callback"];
if (!string.IsNullOrEmpty(callback))
{
match.QueryParameters.Remove("$callback");
return callback;
}
}
}
return null;
}

public void BeforeSendReply(ref System.ServiceModel.Channels.Message reply, object correlationState)
{
if (correlationState != null && correlationState is string)
{
// if we have a JSONP callback then buffer the response, wrap it with the
// callback call and then re-create the response message

string callback = (string)correlationState;

XmlDictionaryReader reader = reply.GetReaderAtBodyContents();
reader.ReadStartElement();
string content = JSONPSupportInspector.encoding.GetString(reader.ReadContentAsBase64());

content = callback + "(" + content + ")";

Message newreply = Message.CreateMessage(MessageVersion.None, "", new Writer(content));
newreply.Properties.CopyProperties(reply.Properties);

reply = newreply;
}
}

#endregion

class Writer : BodyWriter
{
private string content;

public Writer(string content)
: base(false)
{
this.content = content;
}

protected override void OnWriteBodyContents(XmlDictionaryWriter writer)
{
writer.WriteStartElement("Binary");
byte[] buffer = JSONPSupportInspector.encoding.GetBytes(this.content);
writer.WriteBase64(buffer, 0, buffer.Length);
writer.WriteEndElement();
}
}


}
// Simply apply this attribute to a DataService-derived class to get
// JSONP support in that service
[AttributeUsage(AttributeTargets.Class)]
public class JSONPSupportBehaviorAttribute : Attribute, IServiceBehavior
{
#region IServiceBehavior Members

void IServiceBehavior.AddBindingParameters(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase, System.Collections.ObjectModel.Collection<ServiceEndpoint> endpoints, System.ServiceModel.Channels.BindingParameterCollection bindingParameters)
{
}

void IServiceBehavior.ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
{
foreach (ChannelDispatcher cd in serviceHostBase.ChannelDispatchers)
{
foreach (EndpointDispatcher ed in cd.Endpoints)
{
ed.DispatchRuntime.MessageInspectors.Add(new JSONPSupportInspector());
}
}
}

void IServiceBehavior.Validate(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
{
}

#endregion
}
}