Cxx11BindingsSharp 1.6.0

Cxx11BindingsSharp

Introduction

P/Invoke provides a set of marshaling capabilities for C-style APIs, but it does not support C++ Stream/APIs directly.

This library provides a thin layer to wrap a System.IO.Stream in C# to a portable C++ stream (std::streambuf). The intermediate C layer is exposed and can be used directly in a C11 project. The custom std::streambuf implementation simply uses the portable C layer to call back into the concrete C# stream implementation.

This is somewhat related to System.Runtime.InteropServices.ComTypes.IStream on windows.

Typical usage in your library

Installation is:

dotnet add package Cxx11BindingsSharp

In your C# library, you can now write something like:

using Cxx11BindingsSharp;
public void AcmeConvert(System.IO.Stream src, System.IO.Stream dst)
{
  var srcWrap = new ManagedC11Stream(src);
  var dstWrap = new ManagedC11Stream(dst);
  if (NativeService.acme_convert(srcWrap, dstWrap)<0)
  {
    throw new ArgumentException($"Cannot convert");
  }
}

This will expose a C# Stream-like interface to your C11 library.

The only requirement is the following P/Invoke declaration in your C# code:

[DllImport(NativeLibraryName, CallingConvention = CallingConvention.Cdecl)]
internal static extern int acme_convert(C11StreamHandle src, C11StreamHandle dst);

On the C11 side, export your function as:

ACME_EXPORT int acme_convert(c11_stream* src, c11_stream* dst);

At this point you can either re-use one of the existing std::streambuf wrappers, or directly use the c11_stream interface if you prefer to work with C-style APIs.

Implementation details

The stream abstraction is simply defined with a set of five function pointers:

struct c11_stream {
  read_fn read;
  write_fn write;
  seek_fn seek;
  flush_fn flush;
  trunc_fn trunc;
};

Where function declarations are:

typedef int32_t (*read_fn)(struct c11_stream* self, byte* buffer, int32_t count);
typedef int32_t (*write_fn)(struct c11_stream* self, const byte* buffer, int32_t count);
typedef int64_t (*seek_fn)(struct c11_stream* self, int64_t off, int dir);
typedef int (*flush_fn)(struct c11_stream* self);
typedef int64_t (*trunc_fn)(struct c11_stream* self, int64_t size);

See:

• https://learn.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.comtypes.istream
• https://learn.microsoft.com/en-us/dotnet/framework/interop/marshalling-classes-structures-and-unions
• https://stackoverflow.com/questions/6601355/passing-an-fstream-or-equivalent-from-c-sharp-to-c-through-cli

References:

• https://github.com/dicomstudio/Cxx11Bindings
• https://www.nuget.org/packages/Cxx11BindingsSharp/