[PR] fix(core): Return Ok(0) instead of panicking on zero-length write [opendal]

["bavardage (via GitHub)" <gi...@apache.org>]

bavardage opened a new pull request, #8162:
URL: https://github.com/apache/opendal/pull/8162

   `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 #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`: return `Poll::Ready(Ok(0))` from
   `poll_write` when the input buffer is empty, before entering the drain loop.
   - A unit test in the same file’s existing mod tests, covering an empty write before and
   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 signature
   changes, 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!
   
   


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Re: [PR] fix(core): Return Ok(0) instead of panicking on zero-length write [opendal]

["Xuanwo (via GitHub)" <gi...@apache.org>]

Xuanwo merged PR #8162:
URL: https://github.com/apache/opendal/pull/8162


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