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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.28/src/io/buf_reader.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>buf_reader.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../source-script.js"></script><script defer src="../../../source-files.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../futures_util/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../futures_util/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span>
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</pre><pre class="rust"><code><span class="kw">use </span><span class="kw">super</span>::DEFAULT_BUF_SIZE;
<span class="kw">use </span>futures_core::future::Future;
<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::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSliceMut, SeekFrom};
<span class="kw">use </span>pin_project_lite::pin_project;
<span class="kw">use </span>std::io::{<span class="self">self</span>, Read};
<span class="kw">use </span>std::pin::Pin;
<span class="kw">use </span>std::{cmp, fmt};
<span class="macro">pin_project! </span>{
<span class="doccomment">/// The `BufReader` struct adds buffering to any reader.
///
/// It can be excessively inefficient to work directly with a [`AsyncRead`]
/// instance. A `BufReader` performs large, infrequent reads on the underlying
/// [`AsyncRead`] and maintains an in-memory buffer of the results.
///
/// `BufReader` can improve the speed of programs that make *small* and
/// *repeated* read calls to the same file or network socket. It does not
/// help when reading very large amounts at once, or reading just one or a few
/// times. It also provides no advantage when reading from a source that is
/// already in memory, like a `Vec&lt;u8&gt;`.
///
/// When the `BufReader` is dropped, the contents of its buffer will be
/// discarded. Creating multiple instances of a `BufReader` on the same
/// stream can cause data loss.
///
/// [`AsyncRead`]: futures_io::AsyncRead
///
</span><span class="comment">// TODO: Examples
</span><span class="kw">pub struct </span>BufReader&lt;R&gt; {
<span class="attribute">#[pin]
</span>inner: R,
buffer: Box&lt;[u8]&gt;,
pos: usize,
cap: usize,
}
}
<span class="kw">impl</span>&lt;R: AsyncRead&gt; BufReader&lt;R&gt; {
<span class="doccomment">/// Creates a new `BufReader` with a default buffer capacity. The default is currently 8 KB,
/// but may change in the future.
</span><span class="kw">pub fn </span>new(inner: R) -&gt; <span class="self">Self </span>{
<span class="self">Self</span>::with_capacity(DEFAULT_BUF_SIZE, inner)
}
<span class="doccomment">/// Creates a new `BufReader` with the specified buffer capacity.
</span><span class="kw">pub fn </span>with_capacity(capacity: usize, inner: R) -&gt; <span class="self">Self </span>{
<span class="kw">unsafe </span>{
<span class="kw">let </span><span class="kw-2">mut </span>buffer = Vec::with_capacity(capacity);
buffer.set_len(capacity);
<span class="kw">super</span>::initialize(<span class="kw-2">&amp;</span>inner, <span class="kw-2">&amp;mut </span>buffer);
<span class="self">Self </span>{ inner, buffer: buffer.into_boxed_slice(), pos: <span class="number">0</span>, cap: <span class="number">0 </span>}
}
}
<span class="macro">delegate_access_inner!</span>(inner, R, ());
<span class="doccomment">/// Returns a reference to the internally buffered data.
///
/// Unlike `fill_buf`, this will not attempt to fill the buffer if it is empty.
</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="kw-2">&amp;</span><span class="self">self</span>.buffer[<span class="self">self</span>.pos..<span class="self">self</span>.cap]
}
<span class="doccomment">/// Invalidates all data in the internal buffer.
</span><span class="attribute">#[inline]
</span><span class="kw">fn </span>discard_buffer(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;) {
<span class="kw">let </span>this = <span class="self">self</span>.project();
<span class="kw-2">*</span>this.pos = <span class="number">0</span>;
<span class="kw-2">*</span>this.cap = <span class="number">0</span>;
}
}
<span class="kw">impl</span>&lt;R: AsyncRead + AsyncSeek&gt; BufReader&lt;R&gt; {
<span class="doccomment">/// Seeks relative to the current position. If the new position lies within the buffer,
/// the buffer will not be flushed, allowing for more efficient seeks.
/// This method does not return the location of the underlying reader, so the caller
/// must track this information themselves if it is required.
</span><span class="kw">pub fn </span>seek_relative(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, offset: i64) -&gt; SeeKRelative&lt;<span class="lifetime">&#39;_</span>, R&gt; {
SeeKRelative { inner: <span class="self">self</span>, offset, first: <span class="bool-val">true </span>}
}
<span class="doccomment">/// Attempts to seek relative to the current position. If the new position lies within the buffer,
/// the buffer will not be flushed, allowing for more efficient seeks.
/// This method does not return the location of the underlying reader, so the caller
/// must track this information themselves if it is required.
</span><span class="kw">pub fn </span>poll_seek_relative(
<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;,
offset: i64,
) -&gt; Poll&lt;io::Result&lt;()&gt;&gt; {
<span class="kw">let </span>pos = <span class="self">self</span>.pos <span class="kw">as </span>u64;
<span class="kw">if </span>offset &lt; <span class="number">0 </span>{
<span class="kw">if let </span><span class="prelude-val">Some</span>(new_pos) = pos.checked_sub((-offset) <span class="kw">as </span>u64) {
<span class="kw-2">*</span><span class="self">self</span>.project().pos = new_pos <span class="kw">as </span>usize;
<span class="kw">return </span>Poll::Ready(<span class="prelude-val">Ok</span>(()));
}
} <span class="kw">else if let </span><span class="prelude-val">Some</span>(new_pos) = pos.checked_add(offset <span class="kw">as </span>u64) {
<span class="kw">if </span>new_pos &lt;= <span class="self">self</span>.cap <span class="kw">as </span>u64 {
<span class="kw-2">*</span><span class="self">self</span>.project().pos = new_pos <span class="kw">as </span>usize;
<span class="kw">return </span>Poll::Ready(<span class="prelude-val">Ok</span>(()));
}
}
<span class="self">self</span>.poll_seek(cx, SeekFrom::Current(offset)).map(|res| res.map(|<span class="kw">_</span>| ()))
}
}
<span class="kw">impl</span>&lt;R: AsyncRead&gt; AsyncRead <span class="kw">for </span>BufReader&lt;R&gt; {
<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>Context&lt;<span class="lifetime">&#39;_</span>&gt;,
buf: <span class="kw-2">&amp;mut </span>[u8],
) -&gt; Poll&lt;io::Result&lt;usize&gt;&gt; {
<span class="comment">// If we don&#39;t have any buffered data and we&#39;re doing a massive read
// (larger than our internal buffer), bypass our internal buffer
// entirely.
</span><span class="kw">if </span><span class="self">self</span>.pos == <span class="self">self</span>.cap &amp;&amp; buf.len() &gt;= <span class="self">self</span>.buffer.len() {
<span class="kw">let </span>res = <span class="macro">ready!</span>(<span class="self">self</span>.as_mut().project().inner.poll_read(cx, buf));
<span class="self">self</span>.discard_buffer();
<span class="kw">return </span>Poll::Ready(res);
}
<span class="kw">let </span><span class="kw-2">mut </span>rem = <span class="macro">ready!</span>(<span class="self">self</span>.as_mut().poll_fill_buf(cx))<span class="question-mark">?</span>;
<span class="kw">let </span>nread = rem.read(buf)<span class="question-mark">?</span>;
<span class="self">self</span>.consume(nread);
Poll::Ready(<span class="prelude-val">Ok</span>(nread))
}
<span class="kw">fn </span>poll_read_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;mut </span>[IoSliceMut&lt;<span class="lifetime">&#39;_</span>&gt;],
) -&gt; Poll&lt;io::Result&lt;usize&gt;&gt; {
<span class="kw">let </span>total_len = bufs.iter().map(|b| b.len()).sum::&lt;usize&gt;();
<span class="kw">if </span><span class="self">self</span>.pos == <span class="self">self</span>.cap &amp;&amp; total_len &gt;= <span class="self">self</span>.buffer.len() {
<span class="kw">let </span>res = <span class="macro">ready!</span>(<span class="self">self</span>.as_mut().project().inner.poll_read_vectored(cx, bufs));
<span class="self">self</span>.discard_buffer();
<span class="kw">return </span>Poll::Ready(res);
}
<span class="kw">let </span><span class="kw-2">mut </span>rem = <span class="macro">ready!</span>(<span class="self">self</span>.as_mut().poll_fill_buf(cx))<span class="question-mark">?</span>;
<span class="kw">let </span>nread = rem.read_vectored(bufs)<span class="question-mark">?</span>;
<span class="self">self</span>.consume(nread);
Poll::Ready(<span class="prelude-val">Ok</span>(nread))
}
}
<span class="kw">impl</span>&lt;R: AsyncRead&gt; AsyncBufRead <span class="kw">for </span>BufReader&lt;R&gt; {
<span class="kw">fn </span>poll_fill_buf(<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;<span class="kw-2">&amp;</span>[u8]&gt;&gt; {
<span class="kw">let </span>this = <span class="self">self</span>.project();
<span class="comment">// If we&#39;ve reached the end of our internal buffer then we need to fetch
// some more data from the underlying reader.
// Branch using `&gt;=` instead of the more correct `==`
// to tell the compiler that the pos..cap slice is always valid.
</span><span class="kw">if </span><span class="kw-2">*</span>this.pos &gt;= <span class="kw-2">*</span>this.cap {
<span class="macro">debug_assert!</span>(<span class="kw-2">*</span>this.pos == <span class="kw-2">*</span>this.cap);
<span class="kw-2">*</span>this.cap = <span class="macro">ready!</span>(this.inner.poll_read(cx, this.buffer))<span class="question-mark">?</span>;
<span class="kw-2">*</span>this.pos = <span class="number">0</span>;
}
Poll::Ready(<span class="prelude-val">Ok</span>(<span class="kw-2">&amp;</span>this.buffer[<span class="kw-2">*</span>this.pos..<span class="kw-2">*</span>this.cap]))
}
<span class="kw">fn </span>consume(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, amt: usize) {
<span class="kw-2">*</span><span class="self">self</span>.project().pos = cmp::min(<span class="self">self</span>.pos + amt, <span class="self">self</span>.cap);
}
}
<span class="kw">impl</span>&lt;R: AsyncWrite&gt; AsyncWrite <span class="kw">for </span>BufReader&lt;R&gt; {
<span class="macro">delegate_async_write!</span>(inner);
}
<span class="kw">impl</span>&lt;R: fmt::Debug&gt; fmt::Debug <span class="kw">for </span>BufReader&lt;R&gt; {
<span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
f.debug_struct(<span class="string">&quot;BufReader&quot;</span>)
.field(<span class="string">&quot;reader&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.inner)
.field(<span class="string">&quot;buffer&quot;</span>, <span class="kw-2">&amp;</span><span class="macro">format_args!</span>(<span class="string">&quot;{}/{}&quot;</span>, <span class="self">self</span>.cap - <span class="self">self</span>.pos, <span class="self">self</span>.buffer.len()))
.finish()
}
}
<span class="kw">impl</span>&lt;R: AsyncRead + AsyncSeek&gt; AsyncSeek <span class="kw">for </span>BufReader&lt;R&gt; {
<span class="doccomment">/// Seek to an offset, in bytes, in the underlying reader.
///
/// The position used for seeking with `SeekFrom::Current(_)` is the
/// position the underlying reader would be at if the `BufReader` had no
/// internal buffer.
///
/// Seeking always discards the internal buffer, even if the seek position
/// would otherwise fall within it. This guarantees that calling
/// `.into_inner()` immediately after a seek yields the underlying reader
/// at the same position.
///
/// To seek without discarding the internal buffer, use
/// [`BufReader::seek_relative`](BufReader::seek_relative) or
/// [`BufReader::poll_seek_relative`](BufReader::poll_seek_relative).
///
/// See [`AsyncSeek`](futures_io::AsyncSeek) for more details.
///
/// Note: In the edge case where you&#39;re seeking with `SeekFrom::Current(n)`
/// where `n` minus the internal buffer length overflows an `i64`, two
/// seeks will be performed instead of one. If the second seek returns
/// `Err`, the underlying reader will be left at the same position it would
/// have if you called `seek` with `SeekFrom::Current(0)`.
</span><span class="kw">fn </span>poll_seek(
<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;,
pos: SeekFrom,
) -&gt; Poll&lt;io::Result&lt;u64&gt;&gt; {
<span class="kw">let </span>result: u64;
<span class="kw">if let </span>SeekFrom::Current(n) = pos {
<span class="kw">let </span>remainder = (<span class="self">self</span>.cap - <span class="self">self</span>.pos) <span class="kw">as </span>i64;
<span class="comment">// it should be safe to assume that remainder fits within an i64 as the alternative
// means we managed to allocate 8 exbibytes and that&#39;s absurd.
// But it&#39;s not out of the realm of possibility for some weird underlying reader to
// support seeking by i64::min_value() so we need to handle underflow when subtracting
// remainder.
</span><span class="kw">if let </span><span class="prelude-val">Some</span>(offset) = n.checked_sub(remainder) {
result =
<span class="macro">ready!</span>(<span class="self">self</span>.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(offset)))<span class="question-mark">?</span>;
} <span class="kw">else </span>{
<span class="comment">// seek backwards by our remainder, and then by the offset
</span><span class="macro">ready!</span>(<span class="self">self</span>.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(-remainder)))<span class="question-mark">?</span>;
<span class="self">self</span>.as_mut().discard_buffer();
result = <span class="macro">ready!</span>(<span class="self">self</span>.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(n)))<span class="question-mark">?</span>;
}
} <span class="kw">else </span>{
<span class="comment">// Seeking with Start/End doesn&#39;t care about our buffer length.
</span>result = <span class="macro">ready!</span>(<span class="self">self</span>.as_mut().project().inner.poll_seek(cx, pos))<span class="question-mark">?</span>;
}
<span class="self">self</span>.discard_buffer();
Poll::Ready(<span class="prelude-val">Ok</span>(result))
}
}
<span class="doccomment">/// Future for the [`BufReader::seek_relative`](self::BufReader::seek_relative) method.
</span><span class="attribute">#[derive(Debug)]
#[must_use = <span class="string">&quot;futures do nothing unless polled&quot;</span>]
</span><span class="kw">pub struct </span>SeeKRelative&lt;<span class="lifetime">&#39;a</span>, R&gt; {
inner: Pin&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span><span class="kw-2">mut </span>BufReader&lt;R&gt;&gt;,
offset: i64,
first: bool,
}
<span class="kw">impl</span>&lt;R&gt; Future <span class="kw">for </span>SeeKRelative&lt;<span class="lifetime">&#39;_</span>, R&gt;
<span class="kw">where
</span>R: AsyncRead + AsyncSeek,
{
<span class="kw">type </span>Output = io::Result&lt;()&gt;;
<span class="kw">fn </span>poll(<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;<span class="self">Self</span>::Output&gt; {
<span class="kw">let </span>offset = <span class="self">self</span>.offset;
<span class="kw">if </span><span class="self">self</span>.first {
<span class="self">self</span>.first = <span class="bool-val">false</span>;
<span class="self">self</span>.inner.as_mut().poll_seek_relative(cx, offset)
} <span class="kw">else </span>{
<span class="self">self</span>.inner
.as_mut()
.as_mut()
.poll_seek(cx, SeekFrom::Current(offset))
.map(|res| res.map(|<span class="kw">_</span>| ()))
}
}
}
</code></pre></div>
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