Any way to get OWIN to host a SOAP service?

Question

How do I get OWIN to host a SOAP endpoint (do not care if WCF is or isn't involved, SOAP gives WSDL which makes services easier to consume by certain clients, that's why I want SOAP and REST)

I suspect the answer is: Implement your own middleware that hosts a SOAP endpoint. If that's the answer so be it, but that's a lot of work so I'll probably just end up sticking with WCF and avoiding OWIN if that's the case. I find it hard to believe no one has implemented a SOAP hosting middleware yet...

---

As a rule we like to do both REST and SOAP endpoints on our services; currently we use IIS and the WCF restful bits to host the SOAP with [ServiceContract]/[OperationContract] attributes, and the rest is defined with [WebInvoke] attributes, with these attributes the services need no reimplementation for the different endpoint types.

We just use the ASP.NET routes to add new ServiceRoutes which add a rest binding to URI/REST with the same service as a soap binding to URI/SOAP.

Now we're looking at doing some new services work and I'd like to move forward to using OWIN so we can implement our new services with hosting agnosticism as some services will be better served by windows service hosting and some better served by IIS service hosting.

All of my fiddling with things and so far I can come up with no way of getting a SOAP endpoint hosted by OWIN. I have the rest handled fine by making my service inherit from ApiController and then using this little snippet of code in the OWIN app's Configuration method:

    public void Configuration(IAppBuilder app)
    {
        HttpConfiguration config = new HttpConfiguration();
        config.MapHttpAttributeRoutes();
        app.UseWebApi(config);
        [...]

Answer 1

There is a custom OWIN middleware example on MSDN that shows how to support SOAP requests. It is not a general purpose WCF host but may be enough to expose your existing WCF Services (i.e. [ServiceContract/OperationContract]) within an ASP.NET Core app. The example does not include support for [WebGet/WebInvoke] but may be enough to get you started.

https://blogs.msdn.microsoft.com/dotnet/2016/09/19/custom-asp-net-core-middleware-example/

If your primary goal is simply to begin writing new services using OWIN and you still plan to host them in IIS using Microsoft.Owin.Host.SystemWeb. You could ignore the WCF requests within the OWIN pipeline and allow the IIS ASP.NET pipeline to handle them. This would enable you to write services that are a combination of OWIN middleware and traditional WCF endpoints.

public static class WCFAppBuilderExtensions
{
    public static IAppBuilder IgnoreWCFRequests(this IAppBuilder builder)
    {
        return builder.MapWhen(context => IsWCFRequest(context), appBuilder =>
        {
            // Do nothing and allow the IIS ASP.NET pipeline to process the request
        });
    }

    private static bool IsWCFRequest(IOwinContext context)
    {
        // Determine whether the request is to a WCF endpoint
        return context.Request.Path.Value.EndsWith(".svc", StringComparison.OrdinalIgnoreCase);
    }
}

Then call the IgnoreWCFRequests extension method when configuring your app.

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        var config = new HttpConfiguration();
        WebApiConfig.Register(config);
        app
            .IgnoreWCFRequests()
            .UseWebApi(config)
            .Run(context =>
            {
                return context.Response.WriteAsync("Default Response");
            });
    }
}

Answer 2

It's not so easy to host a WCF infrastructure over an OWIN one, sure it can be possible, with a bit of work it's clear possible to adapt, or proxy the owing request-response layer to the WCF infrastructure; WCF provides a not so easy but a complete infrastructure to do something like that.

Answer 3

cpowers answer may work for some, but didn't for me because I have other Filesystems setup within Owin, and I couldn't get both behaviors (fallback to other handlers when needed and also go through OWIN pipelines).

This was the configuration which made it work for me:

1. Use Owin automatic startup (Remove any appSettings named owin:AutomaticAppStartup)
2. Do not manually add its handlers in your web.config (or Startup will run twice) (Remove OwinHttpHandlerfrom from <handlers> in you web.config)
3. Add appBuilder.UseStageMarker(PipelineStage.MapHandler) after builder.UseFileServer()
   • UseFileServer must happen after all pipelines you setup, otherwise the ones setup after it will not work and you'll get 404
4. Optionally Fork the pipeline like cpower mentioned

If your OWIN pipelines does not register middlewares for the paths where your legacy stuff is you don't even need to fork your pipeline (my case).