[Vala] How to include C headers into Vala code?

[Андрей Игоревич Кучеров <zox xakep ru>]

Hello,

I have the simple question. Imagine That we have a vala CLI
application... for example like this:

//----- Main.vala -------
using GLib;
class cli_hello : Glib.Object {
  void print_default_hello () {
    stdout.printf("Hello world!\n");
  }

  static int main (string[] args)
  {
    var hello = new cli_hello();
    hello.print_default_hello();
    return 0;
  }
}

And I wand to add new method to my cli_hello class. And this method
needs the C header file... for example <sys/socket.h>, and use C
function in my Vala application.
Is it possible, how could i do that? How the code will be changed?