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BufWriter: improve safety comment

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This commit is contained in:
Tyson Nottingham 2021-04-13 21:09:41 -07:00
parent 0f29dc40f8
commit 01e701828c
1 changed files with 10 additions and 6 deletions
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16
library/std/src/io/buffered/bufwriter.rs
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@ -366,9 +366,11 @@ impl<W: Write> BufWriter<W> {
// exactly. Doing otherwise would mean flushing the buffer, then writing this
// input to the inner writer, which in many cases would be a worse strategy.
// SAFETY: We just called `self.flush_buf()`, so `self.buf.len()` is 0, and
// we entered this else block because `buf.len() < self.buf.capacity()`.
// Therefore, `buf.len() <= self.buf.capacity() - self.buf.len()`.
// SAFETY: There was either enough spare capacity already, or there wasn't and we
// flushed the buffer to ensure that there is. In the latter case, we know that there
// is because flushing ensured that our entire buffer is spare capacity, and we entered
// this block because the input buffer length is less than that capacity. In either
// case, it's safe to write the input buffer to our buffer.
unsafe {
self.write_to_buffer_unchecked(buf);
}
@ -406,9 +408,11 @@ impl<W: Write> BufWriter<W> {
// exactly. Doing otherwise would mean flushing the buffer, then writing this
// input to the inner writer, which in many cases would be a worse strategy.
// SAFETY: We just called `self.flush_buf()`, so `self.buf.len()` is 0, and
// we entered this else block because `buf.len() < self.buf.capacity()`.
// Therefore, `buf.len() <= self.buf.capacity() - self.buf.len()`.
// SAFETY: There was either enough spare capacity already, or there wasn't and we
// flushed the buffer to ensure that there is. In the latter case, we know that there
// is because flushing ensured that our entire buffer is spare capacity, and we entered
// this block because the input buffer length is less than that capacity. In either
// case, it's safe to write the input buffer to our buffer.
unsafe {
self.write_to_buffer_unchecked(buf);
}