Srt: Wrapping srt library in other programming language

[newbeewan]

Hi,

We are using SRT commands in shell scripts call by Python and Java programs...

But it would be interesting to have a binding (or a native implementation !) in both this languages, it should offer better integration and direct usage of stream connection, statistics...

Thanks to take this in consideration,

Best regards

C. Mourad Jaber

[alexpokotilo]

Java has JNI support so you can easily load SRT libs and call srt functions from srt.h.
I'm sure you can do the same from python

[lewk2]

Not that you asked for this language, but the title might make other walk down this road - I made an experimental wrapper for C# - you can see this here:

https://github.com/Cinegy/Cinegy.SRT

It was never taken to production levels, but would be a great start for anyone that is trying to use this from .NET

[NickDrouin]

Has anyone gone down the road of attempting to use SWIG or CppSharp to auto-gen srt.h into C#/PInvoke targeting .Net Core (or Standard)?

[lewk2]

I went the hard way and made a managed c++ wrapper around the library.

Check out GitHub.com/cinegy and you should see my c# 'SRTAnalyser' project
that uses the library (and the library, but I forget what I called it).

It not very fully featured, but it lets you catch a stream :)

Lewis

On Fri, 3 May 2019, 17:57 Nick Drouin, [e-mail] wrote:

Has anyone gone down the road of attempting to use SWIG
http://www.swig.org or CppSharp https://github.com/mono/CppSharp to
auto-gen srt.h into C#/PInvoke targeting .Net Core (or Standard)?

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[NickDrouin]

Thanks Lewis, I did have a look prior to going down the auto-gen road, however, I was looking for cross platform: .Net Core (versus .Net Framework). I was also a bit weary of my ability to getting the type marshaling correct. ;)

Reporting back my progress: I was able to create a SWIG binding for CSharp.
From that, I create a .Net Standard dll, which I was able to include in a .Net Core project. From there I can call into LibSrt on both linux and windows.

To do this, the following was added after the SRT_API definition in srt.h (currently line 65):

#ifdef SWIG
   /*
   To automatically generate bindings via SWIG (http://www.swig.org)
   Install swig via the following (or use Windows instructions from the link above):
      sudo apt install swig    
   Generate the bindings using:
      mkdir srtcore/bindings/csharp -p
      swig -v -csharp -outdir ./srtcore/bindings/csharp/ ./srtcore/srt.h
   Create a .Net Standard class library with:
      cd srtcore/bindings/csharp
      dotnet new classlib -n srtsharp
   You can now reference the srtsharp lib in your .Net Core projects.  Ensure the srtlib.so (or srt.dll) is in the binary path of your .NetCore project.
   */
   %module srt
   %{
   // BUG: The generated file SRT_ERRNO.cs has errors, it does not prefix the referenced enums from CodeMajor.cs and CodeMinor.cs
   // BUG: The generated code has no namespace.
   #include "srt.h"
   %}
   // Remove SRT_API definition when using SWIG
   #undef SRT_API
   #define SRT_API
#endif

As you will read, the SWIG auto-gen is not (yet) clean, but it was very straight-forward. When I have it auto-generating bug-free, I'll propose a PR with the above. I do question if the ./bindings/csharp/[files] should be part of the PR as well -- which is more of a philosophical question for the SRT project.

In addition to the code above, libsrt (srt.dll) needs to include the generated srt_wrap.c: it is added to filelist.maf. The new srt_wrap.c publicly exposes it's own functions, these work with the srt.cs that is generated to correctly marshal objects across the language boundary.

@newbeewan : The above should work with Python.

[lewk2]

Apologies for opening an old thread - but i decided to finally review this strategy to look for a solid cross-platform story.

Thanks to the helpful information above, i have got this working - however, i'm not very happy with my implementation.

I hand-crafted a few adjustments on the P/Invokes - but to create the SWIGTYPE_p_sockaddr that is used to pass in address information for the socket, i had to use Marshal.StructureToPtr - which is marked obsolete and I can't easily see what is supposed to replace it.

@NickDrouin did you get much further with this? You comment mentioned everything was a bit of a WIP - I would certainly like to help push this up to 'production' level, and would be happy to get rid of my dead-end managed C++