We found a bug in the hyper HTTP library

2 days ago

Cloudflare's Images service, built in Rust on Workers, runs on their edge network and uses hyper for HTTP connections.
In late 2025, the Images binding was rearchitected for a more direct connection, but intermittent failures occurred for larger images, returning truncated responses with 200 status codes.
A race condition in hyper caused premature socket shutdowns when the outbound buffer filled, leading to truncated image data being sent.
The bug was triggered by a slower reader in the new intermediary service, which replaced FL, causing occasional buffer backpressure.
Debugging involved strace to trace syscalls, revealing that shutdown was called before all data was flushed from hyper's buffer.
The fix involved ensuring hyper flushes its buffer completely before shutting down the socket, resolved with a four-line code change.
The fix was contributed to hyper upstream and will be included in future releases, while Cloudflare runs an internal patched version.
The Images binding now supports both remote and hosted images, offering a unified media processing API on Cloudflare's platform.

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