Enabling OPTIONS method in CORS during REST request from AJAX on WCF Service

Question

I have scratched my head for 7 hours trying to figure this out. I have searched all over the web but no luck. I have an Angular App that is making requests to a WCF command-line hosted service application. I managed to get by CORS by using these two classes:

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, 
    System.ServiceModel.IClientChannel channel, 
    System.ServiceModel.InstanceContext instanceContext)
    {
        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);
        }
    }
}

And:

public class EnableCorsBehavior : BehaviorExtensionElement, IEndpointBehavior
{
    public void AddBindingParameters(ServiceEndpoint endpoint, System.ServiceModel.Channels.BindingParameterCollection bindingParameters)
    { }

    public void ApplyClientBehavior(ServiceEndpoint endpoint, System.ServiceModel.Dispatcher.ClientRuntime clientRuntime)
    { }

    public void ApplyDispatchBehavior(ServiceEndpoint endpoint, System.ServiceModel.Dispatcher.EndpointDispatcher endpointDispatcher)
    {
        var requiredHeaders = new Dictionary<string, string>();

        requiredHeaders.Add("Access-Control-Allow-Origin", "*");
        requiredHeaders.Add("Access-Control-Request-Method", "POST,GET,PUT,DELETE,OPTIONS");
        requiredHeaders.Add("Access-Control-Allow-Headers", "X-Requested-With,Content-Type");

        endpointDispatcher.DispatchRuntime.MessageInspectors.Add(new CustomHeaderMessageInspector(requiredHeaders));
    }

    public void Validate(ServiceEndpoint endpoint) { }

    public override Type BehaviorType
    {
        get { return typeof(EnableCorsBehavior); }
    }

    protected override object CreateBehavior()
    {
        return new EnableCorsBehavior();
    }
}

Adding this custom extension to the app.config file solved my CORS problem. My current problem is whenever I make a POST request, I get the error:

Request Method:OPTIONS
Status Code:405 Method Not Allowed

I am quite new to C# and I can't seem to find where to place the code that will allow me to get past this. I have an idea that it should be placed somewhere in the BeforeSendReply() method. Please help me! I will really really appreciate it!

Regards!

Answer 1

In addition to realnsleo answer:

I had problems to use (dynamic)correlationState because my project has to be in Framework 3.5

I tried to simplify some lines, too:

private class CORSHeaderInjectingMessageInspector : IDispatchMessageInspector
{
    private static IDictionary<string, string> _headersToInject = new Dictionary<string, string>
    {
        { "Access-Control-Allow-Origin", "*" },
        { "Access-Control-Request-Method", "POST,GET,PUT,DELETE,OPTIONS" },
        { "Access-Control-Allow-Headers", "X-Requested-With,Content-Type,Origin,Accept" },
        { "Access-Control-Request-Headers", "POST" }
    };


    public object AfterReceiveRequest( ref Message request, IClientChannel channel, InstanceContext instanceContext)
    {
        var httpRequest = (HttpRequestMessageProperty)request.Properties[HttpRequestMessageProperty.Name];       
        return httpRequest.Method.Equals("OPTIONS", StringComparison.InvariantCulture);   
    }


    public void BeforeSendReply(ref Message reply, object correlationState)
    {
        if ((bool) correlationState)
        {
            var httpResponse = (HttpResponseMessageProperty)reply.Properties[HttpResponseMessageProperty.Name];
            httpResponse.SuppressEntityBody = true;
            httpResponse.StatusCode = HttpStatusCode.OK;
        }

        var httpHeader = reply.Properties["httpResponse"] as HttpResponseMessageProperty;
        foreach (var item in _headersToInject)
        {
            httpHeader.Headers.Add(item.Key, item.Value);
        }
    }

Answer 2

I figured out the solution to this and i hope this helps everyone who comes across this same issue. In the CustomHeaderMessageInspector class that I posted in the question, I edited the following code in the AfterReceiveRequest method as follows:

// return null;
var httpRequest = (HttpRequestMessageProperty)request
    .Properties[HttpRequestMessageProperty.Name];
return new
{
    origin = httpRequest.Headers["Origin"],
    handlePreflight = httpRequest.Method.Equals("OPTIONS",
    StringComparison.InvariantCultureIgnoreCase)
};

What I hoped that code did is monitor any request with the OPTIONS method and "tag" it with a preflight state. Then I modified the code in the BeforeSendReply to look as follows:

var state = (dynamic)correlationState;
if (state.handlePreflight)
{
    reply = Message.CreateMessage(MessageVersion.None, "PreflightReturn");

    var httpResponse = new HttpResponseMessageProperty();
    reply.Properties.Add(HttpResponseMessageProperty.Name, httpResponse);

    httpResponse.SuppressEntityBody = true;
    httpResponse.StatusCode = HttpStatusCode.OK;
}

var httpHeader = reply.Properties["httpResponse"] as HttpResponseMessageProperty;
foreach (var item in requiredHeaders)
{
    httpHeader.Headers.Add(item.Key, item.Value);
}

What that does (i hope) is get any request tagged with OPTIONS and handle it by returning a 200 status code. This got it finally working and I hope it helps someone!