Type Alias InvokeFn 

pub type InvokeFn = unsafe extern "C" fn(name: *const c_char, input_json: *const c_char, host: *const Host, out: *mut *mut c_char) -> i32;

Handles one request. Writes a NUL-terminated string to *out and returns OK, ERR_REQUEST or ERR_INTERNAL. Must not unwind or longjmp.