How to create RPC server for a C# application

Question

I have an existing C# application that I want to use it as a RPC server so a remote RPC client can call its C# functions. I've searched and read the Microsoft RPC architecture in its Windows SDK. It only uses C/C++ to create the RPC server application which requires generation of IDL, ACF files & the use of the MIDL compiler.

Microsoft RPC Server tutorial: http://msdn.microsoft.com/en-us/library/windows/desktop/aa378869(v=vs.85).aspx

Is there a way I can use my existing C# application as a RPC server to work in such RPC architecture? Perhaps RPC server C wrapper code calling my C# code? I'm just thinking out loud.

Thank you for your help, some sample code illustration would be very useful.

Answer 1

Kevin, this is possible, but I would also agree with Kirill, it is very difficult.

The primary issue is that the .idl language is C/C++ specific as is the generated code from the midl compiler. I've done it before by compiling the .idl to the appropriate C/C++ client/server stubs and then translating the code into C# PInvoke. This translation is Painful (with a capital "P"). The structures involved have circular references which makes it rather difficult, but not impossible, in C#.

Instead of fighting with loads of interface methods we chose the easier approach, a single entry-point. To that end our IDL looks like the following:

[ uuid (546B0CE0-C70B-1067-B317-00DD010662DA),
  version(1.0),
  pointer_default(unique)
]
interface IRpcExec
{
    error_status_t Exec(
                    [in] handle_t Binding,
                    [in] long lDataSize,
                    [size_is(lDataSize)] byte arData[*],
                    [out] long *plReturnSize,
                    [out, size_is(,*plReturnSize)] byte **arReturn
                    );
}

The ACF then simply declares this to return errors:

interface IRpcExec
{
    [comm_status, fault_status] 
    Exec();
}

Effectively this allows us to receive a byte[], and return a byte[], thereby turning RPC into a simple transport layer rather than a full-blown protocol. The full project and source are available from:

http://csharptest.net/browse/src/RpcLibrary/

Layered on top of this simple transport is a library to add support for a full-featured RPC mechanism via Google protocol buffers (using Skeet's protobuf-csharp-port):

https://code.google.com/p/protobuf-csharp-rpc/