This is a good codebase to browse if you’re interested in high-quality C. The style was heavily influenced by the way C code is written in djb’s codebases.
In particular, notice how a small set of macros were made to do common checks, defer, etc https://github.com/awslabs/s2n/blob/master/utils/s2n_safety.h
And how this leads to extremely legible code with minimal branching and appropriate error checks/cleanup
Also interesting are the handful of core data structures they defined (eg. stuffer) and use pervasively, high ratio of tests to code, and multiple proof engines.