Packt first contacted me about writing this book nearly a year ago. It's been a long journey, harder than I anticipated at times, and I've learned a lot. The book you hold now is the culmination of many long days, and I'm proud to finally present it.
I think C is a beautiful programming language. No other language in everyday use gets you as close to the machine as C does. I've used C to program 8-bit microcontrollers with only 16 bytes of RAM, just the same as I've used it to program modern desktops with multi-core, multi-GHz processors. It's truly remarkable that C works efficiently in both contexts.
Network programming is a fun topic, but it's also a very deep one; a lot is going on at many levels. Some programming languages hide these abstractions. In the Python programming language, for example, you can download an entire web page using only one line of code. This isn't the case in C! In C, if you want to download a web page, you have to know how everything works. You need to know sockets, you need to know Transfer Control Protocol (TCP), and you need to know HTTP. In C network programming, nothing is hidden.
C is a great language to learn network programming in. This is not only because we get to see all the details, but also because the popular operating systems all use kernels written in C. No other language gives you the same first-class access as C does. In C, everything is under your control – you can lay out your data structures exactly how you want, manage memory precisely as you please, and even shoot yourself in the foot just the way you want.
When I first began writing this book, I surveyed other resources related to learning network programming with C. I found much misinformation – not only on the web, but even in print. There is a lot of C networking code that is done wrong. Internet tutorials about C sockets often use deprecated functions and ignore memory safety completely. When it comes to network programming, you can't take the it works so it's good enough programming-by-coincidence approach. You have to use reasoning.
In this book, I take care to approach network programming in a modern and safe way. The example programs are carefully designed to work with both IPv4 and IPv6, and they are all written in a portable, operating system-independent way, whenever possible. Wherever there is an opportunity for memory errors, I try to take notice and point out these concerns. Security is too often left as an afterthought. I believe security is important, and it should be planned in the system from the beginning. Therefore, in addition to teaching network basics, this book spends a lot of time working with secure protocols, such as TLS.
I hope you enjoy reading this book as much as I enjoyed writing it.
