How Cloudflare Lost Six Weeks to a Rust Bug That Lied '200 OK'
Imagine your server proudly shouting that everything is absolutely fine while silently throwing half of your data into a digital abyss. The brilliant minds at Cloudflare spent a month and a half dealing with exactly this nightmare.
The whole mess started when customers of Cloudflare noticed that some files, specifically larger ones like images or logs, were mysteriously arriving half-empty. The server logs, however, painted a picture of absolute perfection, showing a flawless HTTP 200 OK status code for every single request.
Engineers initially suspected their own image optimization tools or custom business logic. After tearing their own code apart and finding absolutely nothing, they had to dig deeper into the network stack, where they found that the data truncation was happening directly on the active network connection.
The culprit turned out to be hyper, a highly praised HTTP library written in Rust, which is supposed to be the holy grail of memory safety and reliability. Under specific conditions, the library was closing the socket before flushing its internal buffer, leaving the client with only the first few hundred kilobytes of a multi-megabyte file.
The legendary compiler-guaranteed safety of modern programming languages clearly has its limits. It turns out that even when the code is mathematically incapable of crashing, it can still happily lie to everyone's face while quietly deleting user data in the background.
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