Creating Solid APIs with Lua

Chapter 1. Running a Lua Script from C

In the first part of this book, the focus is on understanding the data and control flows between Lua and C. After those ideas have been established, we’ll be ready to tackle security in the second part, which begins with Chapter 5.

An Overview of the C/Lua Interface

Many programming languages are distributed in the form of a language-specific compiler or interpreter. Lua, on the other hand, is essentially distributed as a C API. Many users interact with Lua by using the official interpreter, but even this interpreter is built on top of the C API, without any special access to the language’s implementation. In other words, Lua is not only written in C; it is also written to be used from C.

Lua’s C API can create or destroy entire runtime environments, which are referred to as Lua states. A Lua state is a C pointer to an opaque data structure. This structure knows everything about a running Lua environment, including all global values, closures, coroutines, and loaded modules. Virtually every function in Lua’s C API accepts a Lua state as its first parameter.

Because Lua states are opaque structures, we need to use API functions to access the Lua values stored within a state. To this end, every Lua state has a Lua stack, which is a container for Lua values such as Lua strings or tables. You can think of the Lua stack as a window into the set of Lua values currently relevant to your C code. We’ll dive into all the relevant details of this stack ...