Re: Compiling for netcore targeting Linux (Ubuntu)

Just for the record, there was a Github issue for this at
https://github.com/swig/swig/issues/1233 and I see you found it.

William


On Sat, 22 Feb 2020 at 21:32, Jason Daly <[email protected]> wrote:

> Hi,
> We are using SWIG to wrap some C++ libraries with C#, and compiling the
> wrapper code in an aspnetcore service, which runs in a Docker container,
> targeting Linux. So, .net, running on Linux, calling in to some native
> linux .so libs.
>
> We have been having problems with string marshalling.
> Ubuntu uses 32-bit chars, and the libs we are wrapping make use of the
> std::wstring type.
>
> We had to implement a custom marshaller for marshalling the C# strings
> to/from std::wstring using UTF32 encoding (see below).
>
> Then we had to swap out the SWIG std_wstring.i script with our own custom
> one for ubuntu, which uses our custom marshaller.
>
> We still have one more issue to resolve - the
> generated SWIGWStringHelper's, CreateWString method incorrectly marshalls
> strings using LPWStr. We need this to use our custom UTF32 marshalling.
>
> I think what I need to do is write my own SWIGWStringHelper, and decorate
> CreateWString to use my UTF32 marshaller. But I am not sure how to 'wire
> this in'.
>
> Please advise.
>
> Also, I am wondering if the SWIG .NET contributors are doing any work to
> better support this case (netcore apps, interoperating with Linex .so libs,
> running on Ubuntu or equivalent Docker containers)?
>
> Regards,
> Jason Daly
>
>     public class UTC32StringMarshaller : ICustomMarshaler
>     {
>         static UTC32StringMarshaller singleton;
>
>         public IntPtr MarshalManagedToNative(object managedObj)
>         {
>             if (managedObj == null)
>                 return IntPtr.Zero;
>             if (!(managedObj is string))
>                 throw new MarshalDirectiveException("UTC32StringMarshaller
> must be used on a string.");
>
>             var nullTerminated =
> $"{(string)managedObj}{Convert.ToChar(0x0).ToString()}";
>             byte[] strbuf = Encoding.UTF32.GetBytes(nullTerminated);
>             IntPtr buffer = Marshal.AllocHGlobal(strbuf.Length);
>             Marshal.Copy(strbuf, 0, buffer, strbuf.Length);
>             return buffer;
>         }
>
>         public unsafe object MarshalNativeToManaged(IntPtr pNativeData)
>         {
>             int pos = 0;
>             while (Marshal.ReadInt32(pNativeData, pos) != 0)
>                 pos += 4;
>
>             byte[] strbuf = new byte[pos];
>             Marshal.Copy((IntPtr)pNativeData, strbuf, 0, pos);
>             return Encoding.UTF32.GetString(strbuf);
>         }
>
>         public void CleanUpNativeData(IntPtr pNativeData)
>         {
>             Marshal.FreeHGlobal(pNativeData);
>         }
>
>         public void CleanUpManagedData(object managedObj)
>         {
>         }
>
>         public int GetNativeDataSize()
>         {
>             return -1;
>         }
>
>         public static ICustomMarshaler GetInstance(string cookie)
>         {
>             if (singleton == null)
>                 return singleton = new UTC32StringMarshaller();
>
>             return singleton;
>         }
>     }
>
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>

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