We found a bug in the hyper HTTP library

Post by watt » Mon, Jun 29, 2026, 8:39 AM UTC

lifthrasiir wrote: post #6

logicchains wrote: post #3

[flagged]

It is an explicit way to discard return values; `self.poll_read(cx)?` etc. alone would warn. Or in this case, `Poll >` is unwrapped once and `Result ` is being discarded. The decision to discard `Result ` should have been intentional, albeit turned out to be not always the case.

Post by a_cul » Mon, Jun 29, 2026, 9:24 AM UTC

watt wrote: post #11

lifthrasiir wrote: post #6

Earlier quoted context omitted.

It is an explicit way to discard return values; `self.poll_read(cx)?` etc. alone would warn. Or in this case, `Poll >` is unwrapped once and `Result ` is being discarded. The decision to discard `Result ` should have been intentional, albeit turned out to be not always the case.

If they're not going to handle the return values, they should change the function signature to reflect this aspirational contract, that that function "never fails". I see in the article they did change the poll_flush to run just-in-time at poll_shutdown. So they definitely can make a "best effort" poll_flush version that just does not return any errors for use in that loop. But all in all? Amateur hour.

  let _, err = function_call();
  if err {
    return err
  }
  ...

Post by algoth1 » Mon, Jun 29, 2026, 10:26 AM UTC

Post by watt » Mon, Jun 29, 2026, 10:50 AM UTC

a_cul wrote: post #13

watt wrote: post #11

Earlier quoted context omitted.

If they're not going to handle the return values, they should change the function signature to reflect this aspirational contract, that that function "never fails". I see in the article they did change the poll_flush to run just-in-time at poll_shutdown. So they definitely can make a "best effort" poll_flush version that just does not return any errors for use in that loop. But all in all? Amateur hour.

You're missing how rust works. The function is explicitly allowed to fail, which is why it returns a Result . They're using the function calls within for their side effects. The ? at the end of each line signals that the function will short-circuit return with an error if the function call fails, and only if it is successful it returns the actual value: they just don't care about this value, hence the let _ =. Basica…

Post by michalc » Mon, Jun 29, 2026, 10:51 AM UTC

100ms wrote: post #12

> The failure was caused by a timing-dependent race condition in hyper’s HTTP/1 connection handling. When the reader was slower and the socket buffer filled, poll_flush returned Poll::Pending, but the dispatch loop discarded that result. Hyper then treated the response as complete and shut down the socket while data remained buffered internally, causing the client to receive an EOF before the full body arrived. https…