I have a Go program that starts a C/Lua process. Now I'd like to communicate between those two. For example, in the middle of the run of the child (the c/lua process), I'd like to ask the parent (the Go program) to do some calculations and wait for the result. I am not keen to use stdin/stdout for communication, as this is already used for regular output. Now I am thinking of using sockets for the communication, but I don't want to reinvent the wheel.
I now talk to the subprocess via regular tcp sockets. The child process (Lua) has luasocket built in and this seems to work on Windows, Mac and Linux without problems.
Also, I have (for now) defined my own very simple protocol which looks OK in the first steps.
Just in case anybody is interested: https://github.com/speedata/publisher/commit/ea253382c1096274bca2d4124867c39cd0d512e5 and the child commits implement the tcp connection.
Besides all the usual IPC methods you've mentioned (yeah, a unix socket with protobuf should do it, and stdin/stdout as well), if you run the C/Lua code embedded in your program, and not start it as a process, you can actually communicate between the languages directly.
Using the cgo module, Go code can call C functions, and embedded C code can call Go functions. See here: http://golang.org/cmd/cgo/#hdr-C_references_to_Go
Also, you have a couple embeddable Lua binding libraries for Go which you can try, that let you call Lua code and let your Lua code call Go. see https://github.com/aarzilli/golua and https://github.com/stevedonovan/luar/