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How to effectively capture GET and POST to a WinForms c# through IIS?

I have my own WinForms c# application and want to add some API functionality. I also have up and running Windows Server 2012 with IIS that is used for third-party application.
The problem is I can't wrap my mind what would be the most effective (= scalable, secure, manageable, powerful but simple enough) way to grab GET and POST requests in my desktop c# app (and respond to them). There're too many options range from c# web-server embedded library (simplest solution) to the newest ASP.net-based frameworks (most complex ones require too much learning).
I think it would be reasonable to avoid setup another c#-based server just to deal with HTTP requests and use the power of existing IIS instead.
Could you please advise specific library, sample code or walkthrough how to deal with HTTP requests in WinForms through IIS but without overwhelmingly complex ASP solutions?

IIS only listen to http.sys so IIS application pool will only handle the request delivered from http.sys.
This link is about how IIS handle these requests
[What is request-processing pipeline?
The special IIS pipeline decide that you can't force IIS listen to your Winform application directly.
Now that http client is not capable, may I know how did your winform application receive http request?
I think you could host an web app in IIS then proxy these request to IIS web app. You need make some code change in winform application so that IIS would help you handle the incoming GET/POST http requests.

I ended up with ASP.NET app with regular API controller, that is how to those things are supposed to be built. Works great. Adding API to WinForm was definitely bad idea.

Using WebSockets to communicate between Java and C# desktop applications?

I am interested in deploying a server to GoDaddy as a C# web application, then have desktop clients developed in C# and Java be able to subscribe/publish to the server using WebSockets (RFC 6455).
WebSocket supported libraries I am looking at are XSockets.Net and SignalR.
I am not able to find anything on using XSockets.Net (not to be confused with XSocket.org) in Java. I understand that XSockets targets MS .Net framework and Mono environments. However, looking at SignalR, there is also SignalA which is a Java based SignalR client for Android.
Thinking-out-loud... I understand there are many WebSocket libraries for Java, which suggests the idea that if I am able to publish a message (using WebSocket) from a Java application to a server, then I should be able to read it and processes it in C#, since WebSocket protocol is a standard.
Thus far, I believe a SignalR solution will satisfy my requirement to allow C# & Java applications to talk on the Web, but due to transport requirments of SignalR, my communication will not utilize WebSockets. Reading through SignalR requirements, to get WebSockets transport activated I must use Windows8+ with .Net Framework for 4.5+. GoDaddy does not use Windows8 for windows hosting, and even if it did, then all my clients must also use Windows8, which is not a guarentee.
So the question is: How can I get C# & Java desktop clients to talk on the web via WebSockets, othan than using SignalR and XSockets.Net?
Any help is very much appreciated!
EDIT: I will now look into deploying a C# XSockets.NET Server and have a C# XSockets.NET client and a Java JWebSocket client since both JWebSockets and XSockets support the WebSocket RFC6455 protocol. I will post my findings here and close this question if that was a successful effort.

You can implement a RFC6455 client in any language and use XSockets. However do note that XSockets uses a publish/subscribe pattern that you will have to implement as well to take benefit of the platform.
The upside is that you actually wont have to implement RFC6455 since you can implement a custom (non websocket protocol) and use that when communicating from desktop (or anything else). Since everything in XSockets is a plugin you can add custom protocols and still communicate with client talking RFC6455 since XSockets will offer cross-protocol communication.
So the thing you have to implement is actually only the publish/subscribe functionality in the java client.
There are probably not any Java clients out there that implements the IXSocketClient interface today, and we focused on Mono instead of Java when covering multi-platform support.
We will help you out in any way we can if you decide to write your own java implementation.
Note: as of the next version (not far away) it will be very easy to implement your custom protocol and connect from any device talking TCP/IP

In my humble opinion, you have misunderstood some things.
XSockets and SignalR are libraries which are totally oriented to a specific platform, .NET. They both wrap the functionality of WebSockets, a platform independent standard, to ease its use. This does not by anyway mean that you could use XSocket, or SignalR libraries in all platforms.
I suppose that creating a java client for XSockets or SignalR would be an overkill and would lead you to heavily depend on a 3rd party library. In your situation, I would go on with using WebSockets directly on my server side. Then I would use a library handling the WebSockets standard for each client, which could be different for each client development platform. Therefore, you would depend on one universal standard and you would minimize dependencies on 3rd party libraries.
Hope I helped!

Simple client / server concept for .NET

I want to implement a simple cardgame in silverlight that can be played together via a server.
My question is, what concept for communication between client and server I should use.
Is it possible to use WCF to
implement the server ? I guess no because its more like a dataprovider right ?
or do I need to use .NET Remoting ? Haven't read much about it yet, but
I'm not quite sure if it is maybe out
of date ?
Maybe there are newer approaches that I don't know yet ?
Maybe someone has a good tutorial link for the beginning that is not a bad coded sample from year 2002

WCF and .NET Remoting define communication protocols, that is, they define the plumbing between client and server.
When writing a client/server application, you should use WCF as .NET Remoting is deprecated.
See this code project article and code for a simple client/server implementation using WCF. The code is for uni-directional communication, where the server responds to the client.
Here is another article, with a more complicated sample (chat client), using bi-directional communications between client(s) and server. It also uses WPF as the UI layer, so you may need to read around that if using winforms.

WCF (Windows Communication Foundation) is the .NET technology for communication. It includes simple client / server scenarios, as well as publish / subscribe and peer to peer.
Ignore .NET Remoting. It has been replaced by WCF.
I have no idea why you thought that WCF was a data provider, but you're mistaken. See the WCF Developers Center for more on WCF.

Can I interact with .NET libraries through Javascript?

We've built a set of .NET libraries (in C#) which are used to interact with an outside resource. The outside resource provide bindings in Java and .NET, so it was necessary to build our libraries in one of those languages and we're officially a Windows shop.
We also use PHP/Javascript for a lot of our front-end web applications. Is it possible for these PHP/Javascript web applications to interact with our .NET libraries? We have both IIS and Apache web servers if that makes a difference. Communication would need to go in both directions.

The most obvious approach is exposing your .NET libraries as web services on a web server (either IIS or Apache/Mono). This allows both JS and PHP to consume the same service endpoints (JS via AJAX, PHP vs web service calls).
If extreme performance is a concern - for example, your PHP apps need to make heavy calls into the .NET libraries as if they are native, then web services are probably not the best approach. For that, you might want to look into making COM Callable Wrappers for your .NET libraries and consuming them from PHP.

Although Ajax is the usual approach, another idea for you, in case it might help, would be to use Silverlight on the client side. That way, you would embed your .NET classes into a Silverlight application, which would then be downloaded to the client where it would run inside the browser. Silverlight apps can easily interact bi-directionaly with JavaScript, as well as with remote resources.
For example, you can mark a .NET method with the [ScriptableMember] attribute, which will expose it to JavaScript.

You can pass data via AJAX calls where you communicate to and from the client via JSON. For client side data set manipulation jLinq is a great library for performing Linq queries on JSON objects.
If you are looking for a good place to start with web services, JSON and ASP.Net webforms Dave Ward's posts on Encosia are really top notch.

How are server side applications created, how is client - server communication done?

I would like to have a client-server application written in .NET which would do following:
server is running Linux
on the server there is SQL database (mySQL) containing document URLs
What we want:
- server side would regularly crawl all URLs and create a full text index for them
- client side would be able to perform a query into this index using GUI
The client application is written in .NET using C#. Besides of searching in documents it will be able to do a lot of other things which are not described here and which are done client-side very well.
We would like to use C# for the server side as well, but we have no experience in this area. How are things like this usually done?
Clarifying question now based on some answers:
The thing which is most unclear to me is how client-server communication is usually handled. Is client and server usually using sockets, caring about details like IP addresses, ports or NAT traversal? Or are there some common frameworks and patters, which would make this transparent, and make client-server messaging or procedure calling easy? Any examples or good starting points for this? Are there some common techniques how to handle the fact a single server is required to server multiple clients at the same time?

To use c# on Linux you will need to use Mono. This is an open source implementation of the CLR specification.
Next you need to decide on how to communicate between server and client, from the lowest level of just opening a TCP/IP socket and sending bits up and down, to .Net remoting, to WCF, to exposing webservices on the server. I do not know how compleat WCF implementation is on mono, also I think you may have issue with binary remoting between mono and MS .Net .
I would suggest RPC style WebServices offer a very good solution. WebServices also have the advantage of alowing clients from other platforms to connect easily.
EDIT
In response to the clarification of the question.
I would suggest using mono/ASP.NET/WebServices on the server, if you wish to use c# on both server and client.
One assumption I have made is that you can do a client pull model, where every message is initiated by the client. Using another approach could allow the server to push events to the client. Given the client has the ability to pole the server regularly I don't consider this much of a draw back but it may be depending on the type of application you are developing.
Mono allow execution of c# (compiled to IL) on a Linux box. Mono ASP.NET allows you to use the standard ASP.NET and integrate into Apache see http://www.mono-project.com/ASP.NET and finally WebServices allow you to communicate robustly in a strongly typed manner between you client and your server.
Using this approach negates most of the issues raised in your clarification and makes them someone else's problem.
Sockets/SSL - is taken care of by standard .Net runtime on the client and Apache on the server.
IPAddress/ports/NAT traversal - Is all taken care of. DNS look up will get the servers IP. Open socket will allow the server to respond through any firewall and NAT setup.
Multiple Clients - Apache is built to handle multiple clients processing at the same time as is ASP.NET, so you should not encounter any problems there.

As many have already mentioned there are a number of thing that you have mentioned which are going to cause you pain. I'm not going to go into those, instead I will answer your original question about communication.
The current popular choice in this kind of communication is web services. These allow you to make remote calls using the HTTP protocol, and encoding the requests and responses in XML. While this method has its critics I have found it incredibly simple to get up and running, and works fine for nearly all applications.
The .NET framework has built in support for web services which can definitely be called by your client. A brief look at the mono website indicates that it has support for web services also, so writing your server in C# and running it under mono should be fine. Googling for "C# Web Service Tutorial" shows many sites which have information about how to get started, here is a random pick from those results:
http://www.codeguru.com/Csharp/Csharp/cs_webservices/tutorials/article.php/c5477

have a look at Grasshopper:
"With Grasshopper, you can use your favorite development environment from Microsoft® to deploy applications on Java-enabled platforms such as Linux"
Or see here
The ideea is to convert your app to Java and then run it on Tomcat or JBoss.

Another approach: use the Mod_AspDotNet module for Apache, as described here.

This Basic Client/Server Chat Application in C# looks like a kind of example which might be a starting point for me. Relevant .NET classes are TcpClient and TcpListener