Chapter 4: Making Direct C-Language Calls

This chapter introduces the Foreign Function Interface (FFI). In this chapter, you will learn what FFI is all about, what it's good for, and how to use it. This information in this chapter is important for developers interested in rapid custom prototyping using direct C-language calls.

In this chapter, not only do you learn about the background behind introducing FFI into the PHP language, but you also learn how to incorporate C-language structures and functions directly into your code. Although—as you will learn—this should not be done to achieve greater speed, it does give you the ability to incorporate any C-language libraries directly into your PHP application. This ability opens the doors to an entire world of functionality hitherto unavailable to PHP.

Topics covered in this chapter include the following:

• Understanding FFI
• Learning where to use FFI
• Examining the FFI class
• Using FFI in an application...

Technical requirements

To examine and run the code examples provided in this chapter, the minimum recommended hardware is listed here:

• X86_64-based desktop PC or laptop
• 1 gigabyte (GB) free disk space
• 4 GB of random-access memory (RAM)
• 500 kilobits per second (Kbps) or faster internet connection

In addition, you will need to install the following software:

• Docker
• Docker Compose

Please refer to the Technical requirements section of Chapter 1, Introducing New PHP 8 OOP Features, for more information on Docker and Docker Compose installation, as well as how to build the Docker container used to demonstrate code explained in this book. In this book, we refer to the directory in which you restored the sample code as /repo.

The source code for this chapter is located here:

https://github.com/PacktPublishing/PHP-8-Programming-Tips-Tricks-and-Best-Practices

We can now begin our discussion by gaining an understanding of FFI.

Understanding FFI

The main purpose of a FFI is to allow any given programming language the ability to incorporate code and function calls from external libraries written in other languages. An early example of this was the ability of 1980s microcomputers to incorporate assembler language into otherwise sluggish Beginners' All-purpose Symbolic Instruction Code (BASIC) programming language scripts using the PEEK and POKE commands. Unlike many other languages, PHP did not have this capability prior to PHP 7.4, although it had been under discussion since 2004.

In order to gain a full understanding of FFI in PHP 8, it's necessary to digress and have a look at why it took so long for FFI to be fully adopted into the PHP language. It's also necessary to take a quick look at PHP extensions in general, and the ability to work with C-language code. We first examine the relationship between PHP and the C language.

Relationship between PHP and the C language

The C language...

Learning where to use FFI

The potential for importing C libraries directly into PHP is truly staggering. One of the PHP core developers actually used the FFI extension to bind PHP to the C-language TensorFlow machine learning platform!

Tip

For information on the TensorFlow machine learning platform, head over to this web page: https://www.tensorflow.org/. To see how PHP can be bound to this library, have a look here: https://github.com/dstogov/php-tensorflow.

As we show you in this section, the FFI extension is not a magic solution for all of your needs. This section discusses the main strengths and weaknesses of the FFI extension, as well as giving you guidelines for its use. A myth we debunk in this section is that making direct C-language calls using the FFI extension speeds up PHP 8 program execution. First, let's have a look at what took so long to get the FFI extension into PHP.

Adopting FFI into PHP

The first FFI extension was actually introduced for PHP...

Examining the FFI class

As you learned in this chapter, not every developer has a need to use the FFI extension. Having direct experience with the FFI extension deepens your understanding of the internals of the PHP language, and this deepened understanding can have a beneficial impact on your career as a PHP developer: it's quite possible that at some point in the future, you will be employed by a company that has developed a custom PHP extension. Knowing how to operate the FFI extension in this situation allows you to develop new features for a custom PHP extension, as well as helping you to troubleshoot extension problems.

The FFI class consists of 20 methods that fall into four broad categories, outlined as follows:

• Creational: Methods in this category create instances of classes available from the FFI extension application programming interface (API).
• Comparison: Comparison methods are designed to compare C data values.
• Informational: This set of methods...

Using FFI in an application

Any shared C library (generally with a *.so extension) can be included in a PHP application using the FFI extension. If you plan to work with any of the core PHP libraries or libraries produced when PHP extensions are installed, it's important to note that you have the ability to modify the behavior of the PHP language itself.

Before we examine how that works, let's first have a look at incorporating an external C library into a PHP script using the FFI extension.

Integrating an external C library into a PHP script

For the purposes of illustration, we use a simple function that might have originated from a Computer Science 101 (CS101) class: the famous bubble sort. This algorithm is widely used in beginner's computer science classes because it's easy to follow.

Important note

The bubble sort is an extremely inefficient sort algorithm and has long been superseded by faster sorting algorithms such as the shell sort, quick...

Summary

In this chapter, you learned about the FFI, its history, and how it can be used to facilitate rapid PHP extension prototyping. You also learned that although the FFI extension should not be used to improve speed, it also serves the purpose of allowing your PHP application to directly call native C functions from an external C library. The power of this ability was demonstrated through an example that called a bubble-sort function from an external C library. This same capability can be extended to encompass any of the thousands of C libraries available, including machine learning, optical character recognition, communications, encryption; ad infinitum.

In this chapter, you acquired a deeper understanding of how PHP itself operates at the C- language level. You learned how to create and directly use C-language data structures, giving you the ability to interact, and even override, the PHP language itself. In addition, you now have an idea how to incorporate the functionality...