[PR] fix(core): Respect logical length in Buffer vectored views [opendal]

["codeAnqiang-ma (via GitHub)" <gi...@apache.org>]

codeAnqiang-ma opened a new pull request, #8064:
URL: https://github.com/apache/opendal/pull/8064

   # Which issue does this PR close?
   
   Closes #8063.
   
   # Rationale for this change
   
   For a non-contiguous `Buffer`, `to_io_slice()` and the `bytes::Buf::chunks_vectored()` impl destructure `Inner::NonContiguous` with `..`, dropping the logical `size` field, and then walk each part to its **physical** end. Because `truncate` / `slice` / `split_to` / `split_off` shrink `size` without dropping `parts`, both methods then hand back more bytes than `remaining()` — for a 2-byte view of `["abc", "def"]` they expose all 6 bytes.
   
   That violates the documented `bytes::Buf::chunks_vectored` contract ("the sum of the lengths of all the buffers written to `dst` will be less than or equal to `Buf::remaining()`"), and it contradicts `chunk()` and `Iterator::next` in the same type, which both clamp with `.min(*size)` to honor the `Inner::NonContiguous` invariant ("the logic view … spans `size` bytes").
   
   #4481 already fixed the `offset` half of this problem in these same two methods; the `size` clamp was not added then.
   
   # What changes are included in this PR?
   
   Both non-contiguous branches now bind `size`, track it as a running `remaining`, clamp each slice with `.min(remaining)`, and stop once it reaches zero — mirroring what `chunk()` already does. Nothing else changes.
   
   Regression tests `test_vectored_views_after_slice`, `test_vectored_views_after_split_to` and `test_vectored_views_after_split_off` assert that both vectored views yield exactly the logical content. They fail on `main` and pass here.
   
   <details>
   <summary>Test evidence</summary>
   
   Before the fix (tests applied to unmodified `main`), all three fail — the vectored views expose the whole physical buffer:
   
   ```
   ---- types::buffer::tests::test_vectored_views_after_slice stdout ----
   assertion failed: `(left == right)`
    (
   <    b"abcdef",
   <    b"abcdef",
   >    b"ab",
   >    b"ab",
    )
   
   failures:
       types::buffer::tests::test_vectored_views_after_slice
       types::buffer::tests::test_vectored_views_after_split_off
       types::buffer::tests::test_vectored_views_after_split_to
   
   test result: FAILED. 0 passed; 3 failed
   ```
   
   After the fix:
   
   ```
   $ cargo test -p opendal-core --lib --features "tokio/time"
   test result: ok. 182 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
   
   $ cargo fmt --all -- --check                                              # clean
   $ cargo clippy -p opendal-core --all-targets --features "tokio/time" -- -D warnings   # clean
   ```
   
   `--features "tokio/time"` is only needed to compile `opendal-core`'s `#[cfg(test)]` code when the package is tested in isolation; it is unrelated to this change. The full-workspace `--all-features` clippy/nextest gate and the behavior tests were not run locally.
   
   </details>
   
   # Are there any user-facing changes?
   
   Yes — a bug fix; no signature or API change. A shortened non-contiguous `Buffer` passed to a vectored write now yields only its logical bytes instead of also emitting the truncated tail.
   
   To be precise about the blast radius: there is **no active data corruption in-tree**. The only in-tree vectored write backend, `compfs`, takes its bytes via `Buffer::by_ref().collect()` — the `Iterator` impl, which already respects `size` — so it never reached this path. The defect matters at the public API and trait-contract level: `to_io_slice` is `pub` and documented for vectored writes, and `chunks_vectored` is a `bytes::Buf` impl, so downstream users and any future in-tree consumer doing a vectored write over a shortened view are affected.
   
   # AI Usage Statement
   
   Prepared with AI assistance: Cursor, using Anthropic Claude Opus 5. The AI drafted the patch, the regression tests and this description; I reproduced the defect locally, verified the tests fail before the change and pass after it, and reviewed every line of the diff.
   


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Re: [PR] fix(core): Respect logical length in Buffer vectored views [opendal]

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

Xuanwo merged PR #8064:
URL: https://github.com/apache/opendal/pull/8064


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