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Posted to commits@opendal.apache.org by "bavardage (via GitHub)" <gi...@apache.org> on 2026/08/26 15:39:39 UTC
[I] bug: FuturesAsyncWriter panics on zero-length write [opendal]
bavardage opened a new issue, #8161:
URL: https://github.com/apache/opendal/issues/8161
### OpenDAL version or commit
v0.58.2, and commit 053739c76bfa8b127e62cdb8efb52b86130a059f (main)
### Affected service or component
core (opendal-core): FuturesAsyncWriter / Writer::into_futures_async_write. Service-independent
### Describe the bug
`FuturesAsyncWriter::poll_write` panics with frozen buffer must be valid when called with
an empty buffer. Both `std::io::Write::write` and `futures::AsyncWrite::poll_write` permit a
zero-length input and specify `Ok(0)` as the result, so this is a panic on legal input.
The panic is service-independent: it happens in the adapter’s own buffering layer, before any
service call. The blocking adapter shares the bug, since
`Writer::into_std_write()` → `StdWriter::write` → `FuturesAsyncWriter::write` (core/core/src/blocking/write/std_writer.rs:63)
### Steps to Reproduce
use futures::AsyncWriteExt;
use opendal::Operator;
use opendal::services::Memory;
#[tokio::main(flavor = "current_thread")]
async fn main() {
let op = Operator::new(Memory::default()).unwrap();
let mut w = op.writer("a").await.unwrap().into_futures_async_write();
assert_eq!(w.write(b"").await.unwrap(), 0); // panics: "frozen buffer must be valid"
w.write_all(b"hello").await.unwrap();
w.close().await.unwrap();
assert_eq!(op.read("a").await.unwrap().to_vec(), b"hello");
}
### Actual Behavior
thread 'types::write::futures_async_writer::tests::test_empty_write' panicked at core/src/types/write/futures_async_writer.rs:67:37:
frozen buffer must be valid
### Expected Behavior
poll_write returns `Poll::Ready(Ok(0))` for an empty input buffer, leaving the internal
buffer untouched, and subsequent non-empty writes commit normally
### Additional Context
_No response_
### Reproduction confirmation
- [x] I reproduced this issue against the affected component. For a service-specific report, I used the actual service rather than only a mock, emulator, or source-code analysis.
### Are you willing to submit a PR to fix this bug?
- [x] Yes, I would like to submit a PR.
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Re: [I] bug: FuturesAsyncWriter panics on zero-length write [opendal]
Posted by "dosubot[bot] (via GitHub)" <gi...@apache.org>.
dosubot[bot] commented on issue #8161:
URL: https://github.com/apache/opendal/issues/8161#issuecomment-5427599022
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<!-- Answer -->
Hi @bavardage! I'm [Dosu](https://go.dosu.dev/dosubot) and I'm helping the Apache OpenDAL team.
I can confirm the bug. Here's the problematic path in [`poll_write`](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/types/write/futures_async_writer.rs#L59-L72):
```rust
loop {
let n = this.buf.put(buf); // buf is empty → n = 0
if n > 0 {
return Poll::Ready(Ok(n)); // skipped because n == 0
}
ready!(this.sink.poll_ready_unpin(cx))...;
let bs = this.buf.get().expect("frozen buffer must be valid"); // PANICS
```
When `buf` is empty, [`FlexBuf::put`](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/raw/oio/buf/flex_buf.rs#L50-L66) returns `0` without freezing the internal buffer — freezing only happens when the buffer reaches capacity or `freeze()` is called explicitly. So the loop falls through to `get().expect(...)`, which panics because `frozen` is `None`.
**The fix** is an early return at the top of `poll_write`:
```rust
fn poll_write(..., buf: &[u8]) -> Poll<io::Result<usize>> {
if buf.is_empty() {
return Poll::Ready(Ok(0));
}
// rest of existing logic…
}
```
This is consistent with how both `std::io::Write` and `futures::AsyncWrite` specify that a zero-length write should return `Ok(0)`. The same guard should be applied to the blocking `StdWriter` path if it doesn't already short-circuit before reaching `FuturesAsyncWriter`.
Looking forward to your PR — the fix is minimal and well-scoped!
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Re: [I] bug: FuturesAsyncWriter panics on zero-length write [opendal]
Posted by "Xuanwo (via GitHub)" <gi...@apache.org>.
Xuanwo closed issue #8161: bug: FuturesAsyncWriter panics on zero-length write
URL: https://github.com/apache/opendal/issues/8161
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