[Freeswitch-dev] mod managed, cant receive events thru EventReceivedFunction callback

Michael Giagnocavo mgg at giagnocavo.net
Mon Nov 2 04:34:05 PST 2009

Basically, if you want to do something that's not "made easy" for language plugins, you just do it the C way, like any other FreeSWITCH C module. The mod_managed swig wrappers expose nearly every function.

The difficult part is that some of the indirect types (pointers to types and function pointers) aren't swig'd very nicely, and just have a wrapper class such as "SWIGTYPE_p_foo_t". In this case, you're required to create the backing structure however required, then get a pointer to that structure and wrap it in the SWIGTYPE_p_xxx class. If your backing structure is a .NET type, you can use GCHandle to get an IntPtr to it. Or you can directly allocate memory via the Marshal class and use that IntPtr. This is likely to be annoying and a lot of work.

It's only really easy for function pointers, as all you need to do is declare a delegate, attribute it [UnmanagedFunctionPointer(CallingConvention.Cdecl)], then call Marshal.GetFunctionPointerForDelegate. The runtime will emit unmanaged stubs that will handle unmanaged-managed transitioning and give you a nice C compatible function pointer you can wrap and pass around. You can see some examples in ManagedSession.cs.

Additionally, the SWIGTYPE_p_xxx classes don't have public constructors, so the FSUtil class provides this extension method on IntPtr:

public static T CreateSwigTypePointer<T>(this IntPtr cPtr)

That way you can create the wrapper classes as needed after you've created the structures and wrapped them up.

In summary, it's possible to create an endpoint module from C#, but a major PITA. You should consider either using a mixed-mode language such as C++/CLI or write a helper library in C/C++ and export that via swig. We'd welcome contributions to mod_managed that simplify access to a set of the FS APIs.


From: freeswitch-dev-bounces at lists.freeswitch.org [mailto:freeswitch-dev-bounces at lists.freeswitch.org] On Behalf Of Alex To
Sent: Monday, November 02, 2009 5:19 AM
To: freeswitch-dev at lists.freeswitch.org
Subject: Re: [Freeswitch-dev] mod managed, cant receive events thru EventReceivedFunction callback

Hi, I would like to raise this question again since it doesn't seem to have an answer yet.

I built a .NET module which implements IAppPlugin and IApiPlugin. I looked at the /contrib/verifier/eventsocket and it is actually the client to connect to FS through mod_event_socket (correct me if I'm wrong here).

I believe Andrew's concern was how to receive events through EventReceivedFunctionCallback but not connect to FS and receive event via TCP/IP.

I would want to implement a .NET module that acts like an endpoint. Could someone show me the direction of how to hook up handlers like it is done in native C++?

How would I read the incoming audio data and how would I send audio as an outgoing stream.

I setup the .NET module and dial plan so that the Run() method in my module is invoked whenever a call is bridged to my endpoint. The ParkingLot and Demo script sample does enlighten me a little but I still have no clue how would I go about the audio stream after I call session.Answer().

Any help would be greatly appreciated.

Best Regards

Alex To

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