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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="Seek bytes asynchronously."><title>AsyncSeek in futures::prelude - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-ac92e1bbe349e143.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="futures" data-themes="" data-resource-suffix="" data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)" data-channel="1.76.0" data-search-js="search-2b6ce74ff89ae146.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-f2adc0d6ca4d09fb.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-305769736d49e732.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-feafe1bb7466e4bd.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc trait"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">&#9776;</button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../futures/index.html">futures</a><span class="version">0.3.28</span></h2></div><h2 class="location"><a href="#">AsyncSeek</a></h2><div class="sidebar-elems"><section><h3><a href="#required-methods">Required Methods</a></h3><ul class="block"><li><a href="#tymethod.poll_seek">poll_seek</a></li></ul><h3><a href="#foreign-impls">Implementations on Foreign Types</a></h3><ul class="block"><li><a href="#impl-AsyncSeek-for-%26mut+T">&amp;mut T</a></li><li><a href="#impl-AsyncSeek-for-Box%3CT%3E">Box&lt;T&gt;</a></li><li><a href="#impl-AsyncSeek-for-Pin%3CP%3E">Pin&lt;P&gt;</a></li></ul><h3><a href="#implementors">Implementors</a></h3></section><h2><a href="index.html">In futures::prelude</a></h2></div></nav><div class="sidebar-resizer"></div>
<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../futures/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press S to search, ? for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Trait <a href="../index.html">futures</a>::<wbr><a href="index.html">prelude</a>::<wbr><a class="trait" href="#">AsyncSeek</a><button id="copy-path" title="Copy item path to clipboard"><img src="../../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../../src/futures_io/lib.rs.html#217">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><pre class="rust item-decl"><code>pub trait AsyncSeek {
// Required method
fn <a href="#tymethod.poll_seek" class="fn">poll_seek</a>(
self: <a class="struct" href="https://doc.rust-lang.org/1.76.0/core/pin/struct.Pin.html" title="struct core::pin::Pin">Pin</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.reference.html">&amp;mut Self</a>&gt;,
cx: &amp;mut <a class="struct" href="../task/struct.Context.html" title="struct futures::task::Context">Context</a>&lt;'_&gt;,
pos: <a class="enum" href="../io/enum.SeekFrom.html" title="enum futures::io::SeekFrom">SeekFrom</a>
) -&gt; <a class="enum" href="../task/enum.Poll.html" title="enum futures::task::Poll">Poll</a>&lt;<a class="enum" href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.u64.html">u64</a>, <a class="struct" href="../io/struct.Error.html" title="struct futures::io::Error">Error</a>&gt;&gt;;
}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Seek bytes asynchronously.</p>
<p>This trait is analogous to the <code>std::io::Seek</code> trait, but integrates
with the asynchronous task system. In particular, the <code>poll_seek</code>
method, unlike <code>Seek::seek</code>, will automatically queue the current task
for wakeup and return if data is not yet available, rather than blocking
the calling thread.</p>
</div></details><h2 id="required-methods" class="section-header">Required Methods<a href="#required-methods" class="anchor">§</a></h2><div class="methods"><details class="toggle method-toggle" open><summary><section id="tymethod.poll_seek" class="method"><a class="src rightside" href="../../src/futures_io/lib.rs.html#237-241">source</a><h4 class="code-header">fn <a href="#tymethod.poll_seek" class="fn">poll_seek</a>(
self: <a class="struct" href="https://doc.rust-lang.org/1.76.0/core/pin/struct.Pin.html" title="struct core::pin::Pin">Pin</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.reference.html">&amp;mut Self</a>&gt;,
cx: &amp;mut <a class="struct" href="../task/struct.Context.html" title="struct futures::task::Context">Context</a>&lt;'_&gt;,
pos: <a class="enum" href="../io/enum.SeekFrom.html" title="enum futures::io::SeekFrom">SeekFrom</a>
) -&gt; <a class="enum" href="../task/enum.Poll.html" title="enum futures::task::Poll">Poll</a>&lt;<a class="enum" href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.u64.html">u64</a>, <a class="struct" href="../io/struct.Error.html" title="struct futures::io::Error">Error</a>&gt;&gt;</h4></section></summary><div class="docblock"><p>Attempt to seek to an offset, in bytes, in a stream.</p>
<p>A seek beyond the end of a stream is allowed, but behavior is defined
by the implementation.</p>
<p>If the seek operation completed successfully,
this method returns the new position from the start of the stream.
That position can be used later with <a href="../io/enum.SeekFrom.html#variant.Start" title="variant futures::io::SeekFrom::Start"><code>SeekFrom::Start</code></a>.</p>
<h5 id="errors"><a href="#errors">Errors</a></h5>
<p>Seeking to a negative offset is considered an error.</p>
<h5 id="implementation"><a href="#implementation">Implementation</a></h5>
<p>This function may not return errors of kind <code>WouldBlock</code> or
<code>Interrupted</code>. Implementations must convert <code>WouldBlock</code> into
<code>Poll::Pending</code> and either internally retry or convert
<code>Interrupted</code> into another error kind.</p>
</div></details></div><h2 id="foreign-impls" class="section-header">Implementations on Foreign Types<a href="#foreign-impls" class="anchor">§</a></h2><details class="toggle implementors-toggle"><summary><section id="impl-AsyncSeek-for-Pin%3CP%3E" class="impl"><a class="src rightside" href="../../src/futures_io/lib.rs.html#492-495">source</a><a href="#impl-AsyncSeek-for-Pin%3CP%3E" class="anchor">§</a><h3 class="code-header">impl&lt;P&gt; <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> for <a class="struct" href="https://doc.rust-lang.org/1.76.0/core/pin/struct.Pin.html" title="struct core::pin::Pin">Pin</a>&lt;P&gt;<div class="where">where
P: <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/ops/deref/trait.DerefMut.html" title="trait core::ops::deref::DerefMut">DerefMut</a> + <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Unpin.html" title="trait core::marker::Unpin">Unpin</a>,
&lt;P as <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/ops/deref/trait.Deref.html" title="trait core::ops::deref::Deref">Deref</a>&gt;::<a class="associatedtype" href="https://doc.rust-lang.org/1.76.0/core/ops/deref/trait.Deref.html#associatedtype.Target" title="type core::ops::deref::Deref::Target">Target</a>: <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a>,</div></h3></section></summary><div class="impl-items"><section id="method.poll_seek" class="method trait-impl"><a class="src rightside" href="../../src/futures_io/lib.rs.html#497-501">source</a><a href="#method.poll_seek" class="anchor">§</a><h4 class="code-header">fn <a href="#tymethod.poll_seek" class="fn">poll_seek</a>(
self: <a class="struct" href="https://doc.rust-lang.org/1.76.0/core/pin/struct.Pin.html" title="struct core::pin::Pin">Pin</a>&lt;&amp;mut <a class="struct" href="https://doc.rust-lang.org/1.76.0/core/pin/struct.Pin.html" title="struct core::pin::Pin">Pin</a>&lt;P&gt;&gt;,
cx: &amp;mut <a class="struct" href="../task/struct.Context.html" title="struct futures::task::Context">Context</a>&lt;'_&gt;,
pos: <a class="enum" href="../io/enum.SeekFrom.html" title="enum futures::io::SeekFrom">SeekFrom</a>
) -&gt; <a class="enum" href="../task/enum.Poll.html" title="enum futures::task::Poll">Poll</a>&lt;<a class="enum" href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.u64.html">u64</a>, <a class="struct" href="../io/struct.Error.html" title="struct futures::io::Error">Error</a>&gt;&gt;</h4></section></div></details><details class="toggle implementors-toggle"><summary><section id="impl-AsyncSeek-for-%26mut+T" class="impl"><a class="src rightside" href="../../src/futures_io/lib.rs.html#488">source</a><a href="#impl-AsyncSeek-for-%26mut+T" class="anchor">§</a><h3 class="code-header">impl&lt;T&gt; <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> for <a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.reference.html">&amp;mut T</a><div class="where">where
T: <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> + <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Unpin.html" title="trait core::marker::Unpin">Unpin</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h3></section></summary><div class="impl-items"><section id="method.poll_seek-1" class="method trait-impl"><a class="src rightside" href="../../src/futures_io/lib.rs.html#489">source</a><a href="#method.poll_seek-1" class="anchor">§</a><h4 class="code-header">fn <a href="#tymethod.poll_seek" class="fn">poll_seek</a>(
self: <a class="struct" href="https://doc.rust-lang.org/1.76.0/core/pin/struct.Pin.html" title="struct core::pin::Pin">Pin</a>&lt;&amp;mut <a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.reference.html">&amp;mut T</a>&gt;,
cx: &amp;mut <a class="struct" href="../task/struct.Context.html" title="struct futures::task::Context">Context</a>&lt;'_&gt;,
pos: <a class="enum" href="../io/enum.SeekFrom.html" title="enum futures::io::SeekFrom">SeekFrom</a>
) -&gt; <a class="enum" href="../task/enum.Poll.html" title="enum futures::task::Poll">Poll</a>&lt;<a class="enum" href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.u64.html">u64</a>, <a class="struct" href="../io/struct.Error.html" title="struct futures::io::Error">Error</a>&gt;&gt;</h4></section></div></details><details class="toggle implementors-toggle"><summary><section id="impl-AsyncSeek-for-Box%3CT%3E" class="impl"><a class="src rightside" href="../../src/futures_io/lib.rs.html#484">source</a><a href="#impl-AsyncSeek-for-Box%3CT%3E" class="anchor">§</a><h3 class="code-header">impl&lt;T&gt; <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> for <a class="struct" href="https://doc.rust-lang.org/1.76.0/alloc/boxed/struct.Box.html" title="struct alloc::boxed::Box">Box</a>&lt;T&gt;<div class="where">where
T: <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> + <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Unpin.html" title="trait core::marker::Unpin">Unpin</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h3></section></summary><div class="impl-items"><section id="method.poll_seek-2" class="method trait-impl"><a class="src rightside" href="../../src/futures_io/lib.rs.html#485">source</a><a href="#method.poll_seek-2" class="anchor">§</a><h4 class="code-header">fn <a href="#tymethod.poll_seek" class="fn">poll_seek</a>(
self: <a class="struct" href="https://doc.rust-lang.org/1.76.0/core/pin/struct.Pin.html" title="struct core::pin::Pin">Pin</a>&lt;&amp;mut <a class="struct" href="https://doc.rust-lang.org/1.76.0/alloc/boxed/struct.Box.html" title="struct alloc::boxed::Box">Box</a>&lt;T&gt;&gt;,
cx: &amp;mut <a class="struct" href="../task/struct.Context.html" title="struct futures::task::Context">Context</a>&lt;'_&gt;,
pos: <a class="enum" href="../io/enum.SeekFrom.html" title="enum futures::io::SeekFrom">SeekFrom</a>
) -&gt; <a class="enum" href="../task/enum.Poll.html" title="enum futures::task::Poll">Poll</a>&lt;<a class="enum" href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.u64.html">u64</a>, <a class="struct" href="../io/struct.Error.html" title="struct futures::io::Error">Error</a>&gt;&gt;</h4></section></div></details><h2 id="implementors" class="section-header">Implementors<a href="#implementors" class="anchor">§</a></h2><div id="implementors-list"><section id="impl-AsyncSeek-for-Either%3CA,+B%3E" class="impl"><a class="src rightside" href="../../src/futures_util/future/either.rs.html#281-284">source</a><a href="#impl-AsyncSeek-for-Either%3CA,+B%3E" class="anchor">§</a><h3 class="code-header">impl&lt;A, B&gt; <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> for <a class="enum" href="../future/enum.Either.html" title="enum futures::future::Either">Either</a>&lt;A, B&gt;<div class="where">where
A: <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a>,
B: <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a>,</div></h3></section><section id="impl-AsyncSeek-for-BufReader%3CR%3E" class="impl"><a class="src rightside" href="../../src/futures_util/io/buf_reader.rs.html#181">source</a><a href="#impl-AsyncSeek-for-BufReader%3CR%3E" class="anchor">§</a><h3 class="code-header">impl&lt;R&gt; <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> for <a class="struct" href="../io/struct.BufReader.html" title="struct futures::io::BufReader">BufReader</a>&lt;R&gt;<div class="where">where
R: <a class="trait" href="../io/trait.AsyncRead.html" title="trait futures::io::AsyncRead">AsyncRead</a> + <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a>,</div></h3></section><section id="impl-AsyncSeek-for-AllowStdIo%3CT%3E" class="impl"><a class="src rightside" href="../../src/futures_util/io/allow_std.rs.html#163-165">source</a><a href="#impl-AsyncSeek-for-AllowStdIo%3CT%3E" class="anchor">§</a><h3 class="code-header">impl&lt;T&gt; <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> for <a class="struct" href="../io/struct.AllowStdIo.html" title="struct futures::io::AllowStdIo">AllowStdIo</a>&lt;T&gt;<div class="where">where
T: <a class="trait" href="https://doc.rust-lang.org/1.76.0/std/io/trait.Seek.html" title="trait std::io::Seek">Seek</a>,</div></h3></section><section id="impl-AsyncSeek-for-Cursor%3CT%3E" class="impl"><a class="src rightside" href="../../src/futures_util/io/cursor.rs.html#146-148">source</a><a href="#impl-AsyncSeek-for-Cursor%3CT%3E" class="anchor">§</a><h3 class="code-header">impl&lt;T&gt; <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> for <a class="struct" href="../io/struct.Cursor.html" title="struct futures::io::Cursor">Cursor</a>&lt;T&gt;<div class="where">where
T: <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/convert/trait.AsRef.html" title="trait core::convert::AsRef">AsRef</a>&lt;[<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.u8.html">u8</a>]&gt; + <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Unpin.html" title="trait core::marker::Unpin">Unpin</a>,</div></h3></section><section id="impl-AsyncSeek-for-BufWriter%3CW%3E" class="impl"><a class="src rightside" href="../../src/futures_util/io/buf_writer.rs.html#212">source</a><a href="#impl-AsyncSeek-for-BufWriter%3CW%3E" class="anchor">§</a><h3 class="code-header">impl&lt;W&gt; <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a> for <a class="struct" href="../io/struct.BufWriter.html" title="struct futures::io::BufWriter">BufWriter</a>&lt;W&gt;<div class="where">where
W: <a class="trait" href="../io/trait.AsyncWrite.html" title="trait futures::io::AsyncWrite">AsyncWrite</a> + <a class="trait" href="../io/trait.AsyncSeek.html" title="trait futures::io::AsyncSeek">AsyncSeek</a>,</div></h3></section></div><script src="../../trait.impl/futures_io/if_std/trait.AsyncSeek.js" data-ignore-extern-crates="futures_util,alloc,core" async></script></section></div></main></body></html>