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</pre><pre class="rust"><code><span class="kw">use </span>std::marker::Unpin;
<span class="kw">use </span>std::{cmp, io};
<span class="kw">use </span>bytes::{Buf, Bytes};
<span class="kw">use </span>tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
<span class="kw">use </span><span class="kw">crate</span>::common::{task, Pin, Poll};
<span class="doccomment">/// Combine a buffer with an IO, rewinding reads to use the buffer.
</span><span class="attribute">#[derive(Debug)]
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Rewind&lt;T&gt; {
pre: <span class="prelude-ty">Option</span>&lt;Bytes&gt;,
inner: T,
}
<span class="kw">impl</span>&lt;T&gt; Rewind&lt;T&gt; {
<span class="attribute">#[cfg(any(all(feature = <span class="string">&quot;http2&quot;</span>, feature = <span class="string">&quot;server&quot;</span>), test))]
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>new(io: T) -&gt; <span class="self">Self </span>{
Rewind {
pre: <span class="prelude-val">None</span>,
inner: io,
}
}
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>new_buffered(io: T, buf: Bytes) -&gt; <span class="self">Self </span>{
Rewind {
pre: <span class="prelude-val">Some</span>(buf),
inner: io,
}
}
<span class="attribute">#[cfg(any(all(feature = <span class="string">&quot;http1&quot;</span>, feature = <span class="string">&quot;http2&quot;</span>, feature = <span class="string">&quot;server&quot;</span>), test))]
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>rewind(<span class="kw-2">&amp;mut </span><span class="self">self</span>, bs: Bytes) {
<span class="macro">debug_assert!</span>(<span class="self">self</span>.pre.is_none());
<span class="self">self</span>.pre = <span class="prelude-val">Some</span>(bs);
}
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>into_inner(<span class="self">self</span>) -&gt; (T, Bytes) {
(<span class="self">self</span>.inner, <span class="self">self</span>.pre.unwrap_or_else(Bytes::new))
}
<span class="comment">// pub(crate) fn get_mut(&amp;mut self) -&gt; &amp;mut T {
// &amp;mut self.inner
// }
</span>}
<span class="kw">impl</span>&lt;T&gt; AsyncRead <span class="kw">for </span>Rewind&lt;T&gt;
<span class="kw">where
</span>T: AsyncRead + Unpin,
{
<span class="kw">fn </span>poll_read(
<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>task::Context&lt;<span class="lifetime">&#39;_</span>&gt;,
buf: <span class="kw-2">&amp;mut </span>ReadBuf&lt;<span class="lifetime">&#39;_</span>&gt;,
) -&gt; Poll&lt;io::Result&lt;()&gt;&gt; {
<span class="kw">if let </span><span class="prelude-val">Some</span>(<span class="kw-2">mut </span>prefix) = <span class="self">self</span>.pre.take() {
<span class="comment">// If there are no remaining bytes, let the bytes get dropped.
</span><span class="kw">if </span>!prefix.is_empty() {
<span class="kw">let </span>copy_len = cmp::min(prefix.len(), buf.remaining());
<span class="comment">// TODO: There should be a way to do following two lines cleaner...
</span>buf.put_slice(<span class="kw-2">&amp;</span>prefix[..copy_len]);
prefix.advance(copy_len);
<span class="comment">// Put back what&#39;s left
</span><span class="kw">if </span>!prefix.is_empty() {
<span class="self">self</span>.pre = <span class="prelude-val">Some</span>(prefix);
}
<span class="kw">return </span>Poll::Ready(<span class="prelude-val">Ok</span>(()));
}
}
Pin::new(<span class="kw-2">&amp;mut </span><span class="self">self</span>.inner).poll_read(cx, buf)
}
}
<span class="kw">impl</span>&lt;T&gt; AsyncWrite <span class="kw">for </span>Rewind&lt;T&gt;
<span class="kw">where
</span>T: AsyncWrite + Unpin,
{
<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>task::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; {
Pin::new(<span class="kw-2">&amp;mut </span><span class="self">self</span>.inner).poll_write(cx, buf)
}
<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>task::Context&lt;<span class="lifetime">&#39;_</span>&gt;,
bufs: <span class="kw-2">&amp;</span>[io::IoSlice&lt;<span class="lifetime">&#39;_</span>&gt;],
) -&gt; Poll&lt;io::Result&lt;usize&gt;&gt; {
Pin::new(<span class="kw-2">&amp;mut </span><span class="self">self</span>.inner).poll_write_vectored(cx, bufs)
}
<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>task::Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;io::Result&lt;()&gt;&gt; {
Pin::new(<span class="kw-2">&amp;mut </span><span class="self">self</span>.inner).poll_flush(cx)
}
<span class="kw">fn </span>poll_shutdown(<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>task::Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;io::Result&lt;()&gt;&gt; {
Pin::new(<span class="kw-2">&amp;mut </span><span class="self">self</span>.inner).poll_shutdown(cx)
}
<span class="kw">fn </span>is_write_vectored(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; bool {
<span class="self">self</span>.inner.is_write_vectored()
}
}
<span class="attribute">#[cfg(test)]
</span><span class="kw">mod </span>tests {
<span class="comment">// FIXME: re-implement tests with `async/await`, this import should
// trigger a warning to remind us
</span><span class="kw">use </span><span class="kw">super</span>::Rewind;
<span class="kw">use </span>bytes::Bytes;
<span class="kw">use </span>tokio::io::AsyncReadExt;
<span class="attribute">#[tokio::test]
</span><span class="kw">async fn </span>partial_rewind() {
<span class="kw">let </span>underlying = [<span class="number">104</span>, <span class="number">101</span>, <span class="number">108</span>, <span class="number">108</span>, <span class="number">111</span>];
<span class="kw">let </span>mock = tokio_test::io::Builder::new().read(<span class="kw-2">&amp;</span>underlying).build();
<span class="kw">let </span><span class="kw-2">mut </span>stream = Rewind::new(mock);
<span class="comment">// Read off some bytes, ensure we filled o1
</span><span class="kw">let </span><span class="kw-2">mut </span>buf = [<span class="number">0</span>; <span class="number">2</span>];
stream.read_exact(<span class="kw-2">&amp;mut </span>buf).<span class="kw">await</span>.expect(<span class="string">&quot;read1&quot;</span>);
<span class="comment">// Rewind the stream so that it is as if we never read in the first place.
</span>stream.rewind(Bytes::copy_from_slice(<span class="kw-2">&amp;</span>buf[..]));
<span class="kw">let </span><span class="kw-2">mut </span>buf = [<span class="number">0</span>; <span class="number">5</span>];
stream.read_exact(<span class="kw-2">&amp;mut </span>buf).<span class="kw">await</span>.expect(<span class="string">&quot;read1&quot;</span>);
<span class="comment">// At this point we should have read everything that was in the MockStream
</span><span class="macro">assert_eq!</span>(<span class="kw-2">&amp;</span>buf, <span class="kw-2">&amp;</span>underlying);
}
<span class="attribute">#[tokio::test]
</span><span class="kw">async fn </span>full_rewind() {
<span class="kw">let </span>underlying = [<span class="number">104</span>, <span class="number">101</span>, <span class="number">108</span>, <span class="number">108</span>, <span class="number">111</span>];
<span class="kw">let </span>mock = tokio_test::io::Builder::new().read(<span class="kw-2">&amp;</span>underlying).build();
<span class="kw">let </span><span class="kw-2">mut </span>stream = Rewind::new(mock);
<span class="kw">let </span><span class="kw-2">mut </span>buf = [<span class="number">0</span>; <span class="number">5</span>];
stream.read_exact(<span class="kw-2">&amp;mut </span>buf).<span class="kw">await</span>.expect(<span class="string">&quot;read1&quot;</span>);
<span class="comment">// Rewind the stream so that it is as if we never read in the first place.
</span>stream.rewind(Bytes::copy_from_slice(<span class="kw-2">&amp;</span>buf[..]));
<span class="kw">let </span><span class="kw-2">mut </span>buf = [<span class="number">0</span>; <span class="number">5</span>];
stream.read_exact(<span class="kw-2">&amp;mut </span>buf).<span class="kw">await</span>.expect(<span class="string">&quot;read1&quot;</span>);
}
}
</code></pre></div>
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