A Clean Build of OpenSSL using Zig

openssl-zig is a working compilation of OpenSSL using the Zig build system that I've been working on for the past couple of weeks. There are a few advantages of using Zig to compile:

• Fast compile times
• Zig build scripts are easy to hack/modify
• Integration with Zig projects as a package

While there are other packages that aim to do the same thing, my goal for this project was to build OpenSSL is the cleanest way possible, without hacky workarounds or anything of that sort.

In this blog post, I'll go over what I learned and my thoughts on the Zig build system as a whole. If you just want to read about the project, check out the GitHub repository.

Learning Zig Build

I came into this project knowing nothing about how to write Zig build scripts. It took a while to know what was going on, especially given the lack of up-to-date documentation.

The Zig docs do have a tutorial of sorts, but given how vast the possibilities are, it doesn't cover a lot of ground.¹ I ended up learning how to do things in two ways:

1. Trial and error
2. Reading other build scripts

For the latter, I read the build.zig file of a different Zig compilation of OpenSSL. While that project does a few things that I wanted to avoid in my compilation, it was a fantastic starting place. I also read the Ghostty project's build.zig. It's quite complex, but it showed me examples of more advanced things, like using the Run build step.

Lazy Paths

The LazyPath is one of the most important concepts in the Zig build system. Getting comfortable with them is the best way to get good at Zig build, in my opinion.

A LazyPath is the path of a file or directory that may or may not exist yet. To understand why we need them, it helps to know about the design of Zig build scripts. Zig builds are declarative, so there are two phases:

1. Telling Zig how to build the project, in steps
2. Executing the steps in the specified manner

For example, in my project, one step of the build process is generating C files to be included in the compilation.² Another step (the C compilation step) depends on those files being built. This is where LazyPath comes in. At the time of specifying the build steps (phase 1), the generated files do not exist yet. So, in order to properly describe the compilation step, we need to reference their future locations.

Closing Thoughts

Writing my first Zig build script was an enjoyable experience after I got over the first few hurdles. Until the language stabilizes, I suspect that this will continue to be the case for newcomers.

I think it's a very viable replacement for CMake (and similar meta-build tools), on account of how much more programmatic everything feels.

Make sure to check out openssl-zig if you're at all interested! I also wrote a HOW.md in case you want to learn more about the design of the project. I hope you enjoyed this post!