| <!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="Asynchronously copies the entire contents of a reader into a writer."><meta name="keywords" content="rust, rustlang, rust-lang, copy"><title>copy in tokio::io - Rust</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 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href="../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2><a href="index.html">In tokio::io</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><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="main-heading"><h1 class="fqn">Function <a href="../index.html">tokio</a>::<wbr><a href="index.html">io</a>::<wbr><a class="fn" href="#">copy</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../src/tokio/io/util/copy.rs.html#193-203">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust fn"><code>pub async fn copy<'a, R, W>(reader: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&'a mut </a>R, writer: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&'a mut </a>W) -> <a class="type" href="https://doc.rust-lang.org/nightly/std/io/error/type.Result.html" title="type std::io::error::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u64.html">u64</a>><span class="where fmt-newline">where<br> R: <a class="trait" href="trait.AsyncRead.html" title="trait tokio::io::AsyncRead">AsyncRead</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Unpin.html" title="trait core::marker::Unpin">Unpin</a> + ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,<br> W: <a class="trait" href="trait.AsyncWrite.html" title="trait tokio::io::AsyncWrite">AsyncWrite</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Unpin.html" title="trait core::marker::Unpin">Unpin</a> + ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</span></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Asynchronously copies the entire contents of a reader into a writer.</p> |
| <p>This function returns a future that will continuously read data from |
| <code>reader</code> and then write it into <code>writer</code> in a streaming fashion until |
| <code>reader</code> returns EOF or fails.</p> |
| <p>On success, the total number of bytes that were copied from <code>reader</code> to |
| <code>writer</code> is returned.</p> |
| <p>This is an asynchronous version of <a href="https://doc.rust-lang.org/nightly/std/io/copy/fn.copy.html"><code>std::io::copy</code></a>.</p> |
| <p>A heap-allocated copy buffer with 8 KB is created to take data from the |
| reader to the writer, check <a href="fn.copy_buf.html"><code>copy_buf</code></a> if you want an alternative for |
| <a href="trait.AsyncBufRead.html"><code>AsyncBufRead</code></a>. You can use <code>copy_buf</code> with <a href="struct.BufReader.html"><code>BufReader</code></a> to change the |
| buffer capacity.</p> |
| <h2 id="errors"><a href="#errors">Errors</a></h2> |
| <p>The returned future will return an error immediately if any call to |
| <code>poll_read</code> or <code>poll_write</code> returns an error.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::io; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>reader: <span class="kw-2">&</span>[u8] = <span class="string">b"hello"</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>writer: Vec<u8> = <span class="macro">vec!</span>[]; |
| |
| io::copy(<span class="kw-2">&mut </span>reader, <span class="kw-2">&mut </span>writer).<span class="kw">await</span><span class="question-mark">?</span>; |
| |
| <span class="macro">assert_eq!</span>(<span class="kw-2">&</span><span class="string">b"hello"</span>[..], <span class="kw-2">&</span>writer[..]);</code></pre></div> |
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