Cloudflare Fixes Race Condition in Rust HTTP Library Hyper

• •Cloudflare fixed a race condition in the hyper library affecting large image responses.
• •The bug caused HTTP 200 responses to return truncated data under specific timing conditions.
• •The issue has been resolved upstream, improving the reliability of the hyper library.

Cloudflare identified a race condition in the hyper library affecting its Images service. The bug caused large image transformation requests to intermittently return truncated data while still reporting a 200 OK status. This issue was difficult to diagnose as it only occurred under specific timing conditions. After receiving customer reports of truncated images, Cloudflare's team spent six weeks isolating the root cause. They discovered that hyper was prematurely closing connections before fully transmitting buffered response data. The bug has now been fixed upstream in the hyper library, which is widely used in Rust applications. The fix involved adding a deterministic test and modifying hyper to ensure complete data flushing before connection closure. This incident has prompted discussions within the Rust community regarding the reliability of the hyper library.