fix(core): Return Ok(0) instead of panicking on zero-length write - #8162
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Xuanwo merged 1 commit intoAug 26, 2026
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`FuturesAsyncWriter::poll_write` panicked with `frozen buffer must be valid` when called with an empty buffer, even though both `std::io::Write::write` and `futures::AsyncWrite::poll_write` allow a zero-length input and specify `Ok(0)` as the result. `FlexBuf::put` returns 0 both when the buffer is already frozen and when the input slice is empty. The loop in `poll_write` assumed only the first case, so on an empty input it called `get()` on a buffer that was never frozen and hit the `expect`. `BufferSink` already guards this case, so add the same guard to the adapter. The blocking `StdWriter` path is fixed transitively, since it forwards to `FuturesAsyncWriter::write`. Closes apache#8161
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FuturesAsyncWriter::poll_writepanicked withfrozen buffer must be validwhen called with an empty buffer, even though bothstd::io::Write::writeandfutures::AsyncWrite::poll_writeallow a zero-length input and specifyOk(0)as the result.FlexBuf::putreturns 0 both when the buffer is already frozen and when the input slice is empty. The loop inpoll_writeassumed only the first case, so on an empty input it calledget()on a buffer that was never frozen and hit theexpect.BufferSinkalready guards this case, so add the same guard to the adapter.The blocking
StdWriterpath is fixed transitively, since it forwards toFuturesAsyncWriter::write.Closes #8161
Which issue does this PR close?
Closes #8161
What changes are included in this PR?
core/core/src/types/write/futures_async_writer.rs: returnPoll::Ready(Ok(0))frompoll_writewhen the input buffer is empty, before entering the drain loop.after a non-empty one, and asserting the surrounding payload still commits and reads back
intact.
Are there any user-facing changes?
Yes but nothing breaking. The zero length previously panicked and now returns
Ok(0). No API signaturechanges, and no behavior change for any non-empty write.
AI Usage Statement
AI identified this bug when using opendal in my project and identified this as a potential fix.
The fix is pretty simple though!