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</pre><pre class="rust"><code><span class="kw">use </span><span class="kw">super</span>::buf_writer::BufWriter;
<span class="kw">use </span>futures_core::ready;
<span class="kw">use </span>futures_core::task::{Context, Poll};
<span class="kw">use </span>futures_io::AsyncWrite;
<span class="kw">use </span>futures_io::IoSlice;
<span class="kw">use </span>pin_project_lite::pin_project;
<span class="kw">use </span>std::io;
<span class="kw">use </span>std::pin::Pin;
<span class="macro">pin_project! </span>{
<span class="doccomment">/// Wrap a writer, like [`BufWriter`] does, but prioritizes buffering lines
///
/// This was written based on `std::io::LineWriter` which goes into further details
/// explaining the code.
///
/// Buffering is actually done using `BufWriter`. This class will leverage `BufWriter`
/// to write on-each-line.
</span><span class="attribute">#[derive(Debug)]
</span><span class="kw">pub struct </span>LineWriter&lt;W: AsyncWrite&gt; {
<span class="attribute">#[pin]
</span>buf_writer: BufWriter&lt;W&gt;,
}
}
<span class="kw">impl</span>&lt;W: AsyncWrite&gt; LineWriter&lt;W&gt; {
<span class="doccomment">/// Create a new `LineWriter` with default buffer capacity. The default is currently 1KB
/// which was taken from `std::io::LineWriter`
</span><span class="kw">pub fn </span>new(inner: W) -&gt; LineWriter&lt;W&gt; {
LineWriter::with_capacity(<span class="number">1024</span>, inner)
}
<span class="doccomment">/// Creates a new `LineWriter` with the specified buffer capacity.
</span><span class="kw">pub fn </span>with_capacity(capacity: usize, inner: W) -&gt; LineWriter&lt;W&gt; {
LineWriter { buf_writer: BufWriter::with_capacity(capacity, inner) }
}
<span class="doccomment">/// Flush `buf_writer` if last char is &quot;new line&quot;
</span><span class="kw">fn </span>flush_if_completed_line(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;io::Result&lt;()&gt;&gt; {
<span class="kw">let </span>this = <span class="self">self</span>.project();
<span class="kw">match </span>this.buf_writer.buffer().last().copied() {
<span class="prelude-val">Some</span>(<span class="string">b&#39;\n&#39;</span>) =&gt; this.buf_writer.flush_buf(cx),
<span class="kw">_ </span>=&gt; Poll::Ready(<span class="prelude-val">Ok</span>(())),
}
}
<span class="doccomment">/// Returns a reference to `buf_writer`&#39;s internally buffered data.
</span><span class="kw">pub fn </span>buffer(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>[u8] {
<span class="self">self</span>.buf_writer.buffer()
}
<span class="doccomment">/// Acquires a reference to the underlying sink or stream that this combinator is
/// pulling from.
</span><span class="kw">pub fn </span>get_ref(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>W {
<span class="self">self</span>.buf_writer.get_ref()
}
}
<span class="kw">impl</span>&lt;W: AsyncWrite&gt; AsyncWrite <span class="kw">for </span>LineWriter&lt;W&gt; {
<span class="kw">fn </span>poll_write(
<span class="kw-2">mut </span><span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;,
cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;,
buf: <span class="kw-2">&amp;</span>[u8],
) -&gt; Poll&lt;io::Result&lt;usize&gt;&gt; {
<span class="kw">let </span><span class="kw-2">mut </span>this = <span class="self">self</span>.as_mut().project();
<span class="kw">let </span>newline_index = <span class="kw">match </span>memchr::memrchr(<span class="string">b&#39;\n&#39;</span>, buf) {
<span class="prelude-val">None </span>=&gt; {
<span class="macro">ready!</span>(<span class="self">self</span>.as_mut().flush_if_completed_line(cx)<span class="question-mark">?</span>);
<span class="kw">return </span><span class="self">self</span>.project().buf_writer.poll_write(cx, buf);
}
<span class="prelude-val">Some</span>(newline_index) =&gt; newline_index + <span class="number">1</span>,
};
<span class="macro">ready!</span>(this.buf_writer.as_mut().poll_flush(cx)<span class="question-mark">?</span>);
<span class="kw">let </span>lines = <span class="kw-2">&amp;</span>buf[..newline_index];
<span class="kw">let </span>flushed = { <span class="macro">ready!</span>(this.buf_writer.as_mut().inner_poll_write(cx, lines))<span class="question-mark">? </span>};
<span class="kw">if </span>flushed == <span class="number">0 </span>{
<span class="kw">return </span>Poll::Ready(<span class="prelude-val">Ok</span>(<span class="number">0</span>));
}
<span class="kw">let </span>tail = <span class="kw">if </span>flushed &gt;= newline_index {
<span class="kw-2">&amp;</span>buf[flushed..]
} <span class="kw">else if </span>newline_index - flushed &lt;= this.buf_writer.capacity() {
<span class="kw-2">&amp;</span>buf[flushed..newline_index]
} <span class="kw">else </span>{
<span class="kw">let </span>scan_area = <span class="kw-2">&amp;</span>buf[flushed..];
<span class="kw">let </span>scan_area = <span class="kw-2">&amp;</span>scan_area[..this.buf_writer.capacity()];
<span class="kw">match </span>memchr::memrchr(<span class="string">b&#39;\n&#39;</span>, scan_area) {
<span class="prelude-val">Some</span>(newline_index) =&gt; <span class="kw-2">&amp;</span>scan_area[..newline_index + <span class="number">1</span>],
<span class="prelude-val">None </span>=&gt; scan_area,
}
};
<span class="kw">let </span>buffered = this.buf_writer.as_mut().write_to_buf(tail);
Poll::Ready(<span class="prelude-val">Ok</span>(flushed + buffered))
}
<span class="kw">fn </span>poll_write_vectored(
<span class="kw-2">mut </span><span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;,
cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;,
bufs: <span class="kw-2">&amp;</span>[IoSlice&lt;<span class="lifetime">&#39;_</span>&gt;],
) -&gt; Poll&lt;io::Result&lt;usize&gt;&gt; {
<span class="kw">let </span><span class="kw-2">mut </span>this = <span class="self">self</span>.as_mut().project();
<span class="comment">// `is_write_vectored()` is handled in original code, but not in this crate
// see https://github.com/rust-lang/rust/issues/70436
</span><span class="kw">let </span>last_newline_buf_idx = bufs
.iter()
.enumerate()
.rev()
.find_map(|(i, buf)| memchr::memchr(<span class="string">b&#39;\n&#39;</span>, buf).map(|<span class="kw">_</span>| i));
<span class="kw">let </span>last_newline_buf_idx = <span class="kw">match </span>last_newline_buf_idx {
<span class="prelude-val">None </span>=&gt; {
<span class="macro">ready!</span>(<span class="self">self</span>.as_mut().flush_if_completed_line(cx)<span class="question-mark">?</span>);
<span class="kw">return </span><span class="self">self</span>.project().buf_writer.poll_write_vectored(cx, bufs);
}
<span class="prelude-val">Some</span>(i) =&gt; i,
};
<span class="macro">ready!</span>(this.buf_writer.as_mut().poll_flush(cx)<span class="question-mark">?</span>);
<span class="kw">let </span>(lines, tail) = bufs.split_at(last_newline_buf_idx + <span class="number">1</span>);
<span class="kw">let </span>flushed = { <span class="macro">ready!</span>(this.buf_writer.as_mut().inner_poll_write_vectored(cx, lines))<span class="question-mark">? </span>};
<span class="kw">if </span>flushed == <span class="number">0 </span>{
<span class="kw">return </span>Poll::Ready(<span class="prelude-val">Ok</span>(<span class="number">0</span>));
}
<span class="kw">let </span>lines_len = lines.iter().map(|buf| buf.len()).sum();
<span class="kw">if </span>flushed &lt; lines_len {
<span class="kw">return </span>Poll::Ready(<span class="prelude-val">Ok</span>(flushed));
}
<span class="kw">let </span>buffered: usize = tail
.iter()
.filter(|buf| !buf.is_empty())
.map(|buf| this.buf_writer.as_mut().write_to_buf(buf))
.take_while(|<span class="kw-2">&amp;</span>n| n &gt; <span class="number">0</span>)
.sum();
Poll::Ready(<span class="prelude-val">Ok</span>(flushed + buffered))
}
<span class="doccomment">/// Forward to `buf_writer` &#39;s `BufWriter::poll_flush()`
</span><span class="kw">fn </span>poll_flush(<span class="kw-2">mut </span><span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;io::Result&lt;()&gt;&gt; {
<span class="self">self</span>.as_mut().project().buf_writer.poll_flush(cx)
}
<span class="doccomment">/// Forward to `buf_writer` &#39;s `BufWriter::poll_close()`
</span><span class="kw">fn </span>poll_close(<span class="kw-2">mut </span><span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;io::Result&lt;()&gt;&gt; {
<span class="self">self</span>.as_mut().project().buf_writer.poll_close(cx)
}
}
</code></pre></div>
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