Meta’s messaging apps have undergone a quiet but significant transformation—moving from a decade-old C codebase riddled with memory bugs to the safety and stability of Rust. In a Meta Tech Podcast episode, engineers Eliane W, Buping W, and Pascal Hartig detailed how C’s manual memory management, massive functions, and lack of modern abstractions created weeks-long debugging marathons. “It took maybe half of the people working on this whole big project to really spend weeks to debug that,” recalled Buping, describing elusive use-after-free and double-free errors.
The shift to Rust has been a game-changer. Its ownership system and compile-time memory safety have eliminated the very bugs that triggered Meta’s most severe incidents. “Since a lot of the issues that we face in the day-to-day are related to memory management, it doesn’t make sense that we wouldn’t choose a language that combats that most effectively,” said Eliane. The team also embraced Rust’s tooling—real-time type hints, autocompletion, and rustfmt—making collaboration smoother and coding standards more uniform.
Beyond safety, Rust has unified Meta’s cross-platform development. Problems once unique to Windows, Android emulators, or Apple Silicon now get resolved in one place. “We can get to a point where you can just land the Rust code everywhere our code is linked, which is pretty much also everywhere,” Buping noted. Debugging has also improved, with breakpoints, stack traces, and variable inspection working seamlessly across C and Rust.
While the migration is still ongoing, early results show a cleaner codebase, fewer production incidents, and a shared sense of standards across the team. As Eliane put it, Rust’s relatively new ecosystem puts everyone “on an even playing field,” making it easier to fight bloat and keep code maintainable.
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