A FreeSWITCH module built with So.

This module is mostly an experiment with So and C interop — it doesn't do anything useful.

This repo includes pre-generated C code in the generated directory, so no So installation is required to build:

make c       # build with gcc
make install # install to /usr/local/freeswitch/mod (override in Makefile if needed)

If you have So installed, build natively:

make
make install

To regenerate the C code:

make gen

load mod_solod                # load the module
solod                         # API command
originate null/1234 &solod    # dialplan application

C constants and enums must be redefined in So. See core.go for examples.

FreeSWITCH uses variadic functions like switch_log_printf and stream->write_function. So cannot call a variadic function from within another variadic function, so helper macros in embed.h are used to bridge this gap.

So can use C types directly, but to export a type from a package it must be capitalized (like Go). For example:

//so:extern
type switch_core_session_t struct {}
type Session switch_core_session_t

So can access C struct members, but you only need to define the members you intend to use.

To export a member for external access, define a getter/setter function. See frame.go for an example.

.h and .c files can be embedded using the so:embed directive. //go:build ignore needs to be added to .c files at the very begining to prevent Go build errors.

FreeSWITCH requires a mod_solod_module_interface struct to be present, which can be defined using the SWITCH_MODULE_DEFINITION macro. So doesn't support exposing structs, so mod_solod.c is used for that purpose.

Also, So doesn't support symbol visibility control — symbols exposed to FreeSWITCH must be in C for now.

It's good practice to hide symbols from the shared library and only expose public APIs. This helps prevent symbol conflicts when you have two or more shared libraries that might use different versions of so_ functions.

So doesn't support visibility control, so you must use a C function marked with __attribute__((visibility("default"))) or __declspec(dllexport), etc., to make it visible.

-f visibility=hidden can be used to hide all symbols.

Alternatively, use Linker Version Scripts might be a better idea.