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I have a standalone C# WCF service running as a Windows service. I have the requirement to add custom headers like X-Frame-Options to all responses. I have tried to use Message Inspector but it not invoking the "BeforeSendReply" method of "CustomHeaderMessageInspector" class. Following is the code I have implemented.

What I have tried:

public class CustomHeaderMessageInspector : IDispatchMessageInspector
        Dictionary<string, string=""> requiredHeaders;

        public CustomHeaderMessageInspector(Dictionary<string, string=""> headers)
            requiredHeaders = headers ?? new Dictionary<string, string="">();
        public object AfterReceiveRequest(ref Message request, IClientChannel channel, InstanceContext instanceContext)
            string displayText = $"Server has received the following message:\n{request}\n";
            return null;

        public void BeforeSendReply(ref Message reply, object correlationState)

            var httpHeader = reply.Properties["httpResponse"] as HttpResponseMessageProperty;

            foreach (var item in requiredHeaders)
                httpHeader.Headers.Add(item.Key, item.Value);

            string displayText = $"Server has replied the following message:\n{reply}\n";

Calling the above class from the below code snippet

public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
           var requiredHeaders = new Dictionary<string, string>();
           requiredHeaders.Add("Access-Control-Allow", "*");
           requiredHeaders.Add("Access-Control-Allow-Headers", "X-Requested-With,Content-Type");
           requiredHeaders.Add("Access-Control-Request-Method", "POST,GET,DELET,OPTION");

           #pragma warning disable CA1062 // Validate arguments of public methods
           endpointDispatcher.DispatchRuntime.MessageInspectors.Add(new CustomHeaderMessageInspector(requiredHeaders));
           #pragma warning restore CA1062 // Validate arguments of public methods
Updated 12-May-21 22:52pm

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