396 lines
No EOL
23 KiB
HTML
396 lines
No EOL
23 KiB
HTML
<!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="API documentation for the Rust `length_delimited` mod in crate `tokio_io`.">
|
||
<meta name="keywords" content="rust, rustlang, rust-lang, length_delimited">
|
||
|
||
<title>tokio_io::codec::length_delimited - Rust</title>
|
||
|
||
<link rel="stylesheet" type="text/css" href="../../../normalize.css">
|
||
<link rel="stylesheet" type="text/css" href="../../../rustdoc.css" id="mainThemeStyle">
|
||
|
||
<link rel="stylesheet" type="text/css" href="../../../dark.css">
|
||
<link rel="stylesheet" type="text/css" href="../../../main.css" id="themeStyle">
|
||
<script src="../../../storage.js"></script>
|
||
|
||
|
||
|
||
|
||
</head>
|
||
<body class="rustdoc mod">
|
||
<!--[if lte IE 8]>
|
||
<div class="warning">
|
||
This old browser is unsupported and will most likely display funky
|
||
things.
|
||
</div>
|
||
<![endif]-->
|
||
|
||
|
||
|
||
<nav class="sidebar">
|
||
<div class="sidebar-menu">☰</div>
|
||
|
||
<p class='location'>Module length_delimited</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li></ul></div><p class='location'><a href='../../index.html'>tokio_io</a>::<wbr><a href='../index.html'>codec</a></p><script>window.sidebarCurrent = {name: 'length_delimited', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div>
|
||
</nav>
|
||
|
||
<div class="theme-picker">
|
||
<button id="theme-picker" aria-label="Pick another theme!">
|
||
<img src="../../../brush.svg" width="18" alt="Pick another theme!">
|
||
</button>
|
||
<div id="theme-choices"></div>
|
||
</div>
|
||
<script src="../../../theme.js"></script>
|
||
<nav class="sub">
|
||
<form class="search-form js-only">
|
||
<div class="search-container">
|
||
<input class="search-input" name="search"
|
||
autocomplete="off"
|
||
placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
|
||
type="search">
|
||
</div>
|
||
</form>
|
||
</nav>
|
||
|
||
<section id='main' class="content">
|
||
<h1 class='fqn'><span class='in-band'>Module <a href='../../index.html'>tokio_io</a>::<wbr><a href='../index.html'>codec</a>::<wbr><a class="mod" href=''>length_delimited</a></span><span class='out-of-band'><span id='render-detail'>
|
||
<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
|
||
[<span class='inner'>−</span>]
|
||
</a>
|
||
</span><a class='srclink' href='../../../src/tokio_io/codec/mod.rs.html#27-368' title='goto source code'>[src]</a></span></h1>
|
||
<div class='docblock'><p>Frame a stream of bytes based on a length prefix</p>
|
||
<p>Many protocols delimit their frames by prefacing frame data with a
|
||
frame head that specifies the length of the frame. The
|
||
<code>length_delimited</code> module provides utilities for handling the length
|
||
based framing. This allows the consumer to work with entire frames
|
||
without having to worry about buffering or other framing logic.</p>
|
||
<h1 id="getting-started" class="section-header"><a href="#getting-started">Getting started</a></h1>
|
||
<p>If implementing a protocol from scratch, using length delimited framing
|
||
is an easy way to get started. [<code>Framed::new()</code>] will adapt a
|
||
full-duplex byte stream with a length delimited framer using default
|
||
configuration values.</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="kw">use</span> <span class="ident">tokio_io</span>::{<span class="ident">AsyncRead</span>, <span class="ident">AsyncWrite</span>};
|
||
<span class="kw">use</span> <span class="ident">tokio_io</span>::<span class="ident">codec</span>::<span class="ident">length_delimited</span>;
|
||
|
||
<span class="kw">fn</span> <span class="ident">bind_transport</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">AsyncRead</span> <span class="op">+</span> <span class="ident">AsyncWrite</span><span class="op">></span>(<span class="ident">io</span>: <span class="ident">T</span>)
|
||
<span class="op">-></span> <span class="ident">length_delimited</span>::<span class="ident">Framed</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>
|
||
{
|
||
<span class="ident">length_delimited</span>::<span class="ident">Framed</span>::<span class="ident">new</span>(<span class="ident">io</span>)
|
||
}</pre>
|
||
<p>The returned transport implements <code>Sink + Stream</code> for <code>BytesMut</code>. It
|
||
encodes the frame with a big-endian <code>u32</code> header denoting the frame
|
||
payload length:</p>
|
||
<pre><code class="language-text">+----------+--------------------------------+
|
||
| len: u32 | frame payload |
|
||
+----------+--------------------------------+
|
||
</code></pre>
|
||
<p>Specifically, given the following:</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="kw">use</span> <span class="ident">tokio_io</span>::{<span class="ident">AsyncRead</span>, <span class="ident">AsyncWrite</span>};
|
||
<span class="kw">use</span> <span class="ident">tokio_io</span>::<span class="ident">codec</span>::<span class="ident">length_delimited</span>;
|
||
<span class="kw">use</span> <span class="ident">bytes</span>::<span class="ident">BytesMut</span>;
|
||
<span class="kw">use</span> <span class="ident">futures</span>::{<span class="ident">Sink</span>, <span class="ident">Future</span>};
|
||
|
||
<span class="kw">fn</span> <span class="ident">write_frame</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">AsyncRead</span> <span class="op">+</span> <span class="ident">AsyncWrite</span><span class="op">></span>(<span class="ident">io</span>: <span class="ident">T</span>) {
|
||
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">transport</span> <span class="op">=</span> <span class="ident">length_delimited</span>::<span class="ident">Framed</span>::<span class="ident">new</span>(<span class="ident">io</span>);
|
||
<span class="kw">let</span> <span class="ident">frame</span> <span class="op">=</span> <span class="ident">BytesMut</span>::<span class="ident">from</span>(<span class="string">"hello world"</span>);
|
||
|
||
<span class="ident">transport</span>.<span class="ident">send</span>(<span class="ident">frame</span>).<span class="ident">wait</span>().<span class="ident">unwrap</span>();
|
||
}</pre>
|
||
<p>The encoded frame will look like this:</p>
|
||
<pre><code class="language-text">+---- len: u32 ----+---- data ----+
|
||
| \x00\x00\x00\x0b | hello world |
|
||
+------------------+--------------+
|
||
</code></pre>
|
||
<h1 id="decoding" class="section-header"><a href="#decoding">Decoding</a></h1>
|
||
<p><a href="struct.FramedRead.html"><code>FramedRead</code></a> adapts an <a href="../../trait.AsyncRead.html"><code>AsyncRead</code></a> into a <code>Stream</code> of <a href="https://docs.rs/bytes/%7E0.4/bytes/struct.BytesMut.html"><code>BytesMut</code></a>,
|
||
such that each yielded <a href="https://docs.rs/bytes/%7E0.4/bytes/struct.BytesMut.html"><code>BytesMut</code></a> value contains the contents of an
|
||
entire frame. There are many configuration parameters enabling
|
||
[<code>FrameRead</code>] to handle a wide range of protocols. Here are some
|
||
examples that will cover the various options at a high level.</p>
|
||
<h2 id="example-1" class="section-header"><a href="#example-1">Example 1</a></h2>
|
||
<p>The following will parse a <code>u16</code> length field at offset 0, including the
|
||
frame head in the yielded <code>BytesMut</code>.</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="ident">length_delimited</span>::<span class="ident">Builder</span>::<span class="ident">new</span>()
|
||
.<span class="ident">length_field_offset</span>(<span class="number">0</span>) <span class="comment">// default value</span>
|
||
.<span class="ident">length_field_length</span>(<span class="number">2</span>)
|
||
.<span class="ident">length_adjustment</span>(<span class="number">0</span>) <span class="comment">// default value</span>
|
||
.<span class="ident">num_skip</span>(<span class="number">0</span>) <span class="comment">// Do not strip frame header</span>
|
||
.<span class="ident">new_read</span>(<span class="ident">io</span>);</pre>
|
||
<p>The following frame will be decoded as such:</p>
|
||
<pre><code class="language-text"> INPUT DECODED
|
||
+-- len ---+--- Payload ---+ +-- len ---+--- Payload ---+
|
||
| \x00\x0B | Hello world | --> | \x00\x0B | Hello world |
|
||
+----------+---------------+ +----------+---------------+
|
||
</code></pre>
|
||
<p>The value of the length field is 11 (<code>\x0B</code>) which represents the length
|
||
of the payload, <code>hello world</code>. By default, <a href="struct.FramedRead.html"><code>FramedRead</code></a> assumes that
|
||
the length field represents the number of bytes that <strong>follows</strong> the
|
||
length field. Thus, the entire frame has a length of 13: 2 bytes for the
|
||
frame head + 11 bytes for the payload.</p>
|
||
<h2 id="example-2" class="section-header"><a href="#example-2">Example 2</a></h2>
|
||
<p>The following will parse a <code>u16</code> length field at offset 0, omitting the
|
||
frame head in the yielded <code>BytesMut</code>.</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="ident">length_delimited</span>::<span class="ident">Builder</span>::<span class="ident">new</span>()
|
||
.<span class="ident">length_field_offset</span>(<span class="number">0</span>) <span class="comment">// default value</span>
|
||
.<span class="ident">length_field_length</span>(<span class="number">2</span>)
|
||
.<span class="ident">length_adjustment</span>(<span class="number">0</span>) <span class="comment">// default value</span>
|
||
<span class="comment">// `num_skip` is not needed, the default is to skip</span>
|
||
.<span class="ident">new_read</span>(<span class="ident">io</span>);</pre>
|
||
<p>The following frame will be decoded as such:</p>
|
||
<pre><code class="language-text"> INPUT DECODED
|
||
+-- len ---+--- Payload ---+ +--- Payload ---+
|
||
| \x00\x0B | Hello world | --> | Hello world |
|
||
+----------+---------------+ +---------------+
|
||
</code></pre>
|
||
<p>This is similar to the first example, the only difference is that the
|
||
frame head is <strong>not</strong> included in the yielded <code>BytesMut</code> value.</p>
|
||
<h2 id="example-3" class="section-header"><a href="#example-3">Example 3</a></h2>
|
||
<p>The following will parse a <code>u16</code> length field at offset 0, including the
|
||
frame head in the yielded <code>BytesMut</code>. In this case, the length field
|
||
<strong>includes</strong> the frame head length.</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="ident">length_delimited</span>::<span class="ident">Builder</span>::<span class="ident">new</span>()
|
||
.<span class="ident">length_field_offset</span>(<span class="number">0</span>) <span class="comment">// default value</span>
|
||
.<span class="ident">length_field_length</span>(<span class="number">2</span>)
|
||
.<span class="ident">length_adjustment</span>(<span class="op">-</span><span class="number">2</span>) <span class="comment">// size of head</span>
|
||
.<span class="ident">num_skip</span>(<span class="number">0</span>)
|
||
.<span class="ident">new_read</span>(<span class="ident">io</span>);</pre>
|
||
<p>The following frame will be decoded as such:</p>
|
||
<pre><code class="language-text"> INPUT DECODED
|
||
+-- len ---+--- Payload ---+ +-- len ---+--- Payload ---+
|
||
| \x00\x0D | Hello world | --> | \x00\x0D | Hello world |
|
||
+----------+---------------+ +----------+---------------+
|
||
</code></pre>
|
||
<p>In most cases, the length field represents the length of the payload
|
||
only, as shown in the previous examples. However, in some protocols the
|
||
length field represents the length of the whole frame, including the
|
||
head. In such cases, we specify a negative <code>length_adjustment</code> to adjust
|
||
the value provided in the frame head to represent the payload length.</p>
|
||
<h2 id="example-4" class="section-header"><a href="#example-4">Example 4</a></h2>
|
||
<p>The following will parse a 3 byte length field at offset 0 in a 5 byte
|
||
frame head, including the frame head in the yielded <code>BytesMut</code>.</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="ident">length_delimited</span>::<span class="ident">Builder</span>::<span class="ident">new</span>()
|
||
.<span class="ident">length_field_offset</span>(<span class="number">0</span>) <span class="comment">// default value</span>
|
||
.<span class="ident">length_field_length</span>(<span class="number">3</span>)
|
||
.<span class="ident">length_adjustment</span>(<span class="number">2</span>) <span class="comment">// remaining head</span>
|
||
.<span class="ident">num_skip</span>(<span class="number">0</span>)
|
||
.<span class="ident">new_read</span>(<span class="ident">io</span>);</pre>
|
||
<p>The following frame will be decoded as such:</p>
|
||
<pre><code class="language-text"> INPUT
|
||
+---- len -----+- head -+--- Payload ---+
|
||
| \x00\x00\x0B | \xCAFE | Hello world |
|
||
+--------------+--------+---------------+
|
||
|
||
DECODED
|
||
+---- len -----+- head -+--- Payload ---+
|
||
| \x00\x00\x0B | \xCAFE | Hello world |
|
||
+--------------+--------+---------------+
|
||
</code></pre>
|
||
<p>A more advanced example that shows a case where there is extra frame
|
||
head data between the length field and the payload. In such cases, it is
|
||
usually desirable to include the frame head as part of the yielded
|
||
<code>BytesMut</code>. This lets consumers of the length delimited framer to
|
||
process the frame head as needed.</p>
|
||
<p>The positive <code>length_adjustment</code> value lets <code>FramedRead</code> factor in the
|
||
additional head into the frame length calculation.</p>
|
||
<h2 id="example-5" class="section-header"><a href="#example-5">Example 5</a></h2>
|
||
<p>The following will parse a <code>u16</code> length field at offset 1 of a 4 byte
|
||
frame head. The first byte and the length field will be omitted from the
|
||
yielded <code>BytesMut</code>, but the trailing 2 bytes of the frame head will be
|
||
included.</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="ident">length_delimited</span>::<span class="ident">Builder</span>::<span class="ident">new</span>()
|
||
.<span class="ident">length_field_offset</span>(<span class="number">1</span>) <span class="comment">// length of hdr1</span>
|
||
.<span class="ident">length_field_length</span>(<span class="number">2</span>)
|
||
.<span class="ident">length_adjustment</span>(<span class="number">1</span>) <span class="comment">// length of hdr2</span>
|
||
.<span class="ident">num_skip</span>(<span class="number">3</span>) <span class="comment">// length of hdr1 + LEN</span>
|
||
.<span class="ident">new_read</span>(<span class="ident">io</span>);</pre>
|
||
<p>The following frame will be decoded as such:</p>
|
||
<pre><code class="language-text"> INPUT
|
||
+- hdr1 -+-- len ---+- hdr2 -+--- Payload ---+
|
||
| \xCA | \x00\x0B | \xFE | Hello world |
|
||
+--------+----------+--------+---------------+
|
||
|
||
DECODED
|
||
+- hdr2 -+--- Payload ---+
|
||
| \xFE | Hello world |
|
||
+--------+---------------+
|
||
</code></pre>
|
||
<p>The length field is situated in the middle of the frame head. In this
|
||
case, the first byte in the frame head could be a version or some other
|
||
identifier that is not needed for processing. On the other hand, the
|
||
second half of the head is needed.</p>
|
||
<p><code>length_field_offset</code> indicates how many bytes to skip before starting
|
||
to read the length field. <code>length_adjustment</code> is the number of bytes to
|
||
skip starting at the end of the length field. In this case, it is the
|
||
second half of the head.</p>
|
||
<h2 id="example-6" class="section-header"><a href="#example-6">Example 6</a></h2>
|
||
<p>The following will parse a <code>u16</code> length field at offset 1 of a 4 byte
|
||
frame head. The first byte and the length field will be omitted from the
|
||
yielded <code>BytesMut</code>, but the trailing 2 bytes of the frame head will be
|
||
included. In this case, the length field <strong>includes</strong> the frame head
|
||
length.</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="ident">length_delimited</span>::<span class="ident">Builder</span>::<span class="ident">new</span>()
|
||
.<span class="ident">length_field_offset</span>(<span class="number">1</span>) <span class="comment">// length of hdr1</span>
|
||
.<span class="ident">length_field_length</span>(<span class="number">2</span>)
|
||
.<span class="ident">length_adjustment</span>(<span class="op">-</span><span class="number">3</span>) <span class="comment">// length of hdr1 + LEN, negative</span>
|
||
.<span class="ident">num_skip</span>(<span class="number">3</span>)
|
||
.<span class="ident">new_read</span>(<span class="ident">io</span>);</pre>
|
||
<p>The following frame will be decoded as such:</p>
|
||
<pre><code class="language-text"> INPUT
|
||
+- hdr1 -+-- len ---+- hdr2 -+--- Payload ---+
|
||
| \xCA | \x00\x0F | \xFE | Hello world |
|
||
+--------+----------+--------+---------------+
|
||
|
||
DECODED
|
||
+- hdr2 -+--- Payload ---+
|
||
| \xFE | Hello world |
|
||
+--------+---------------+
|
||
</code></pre>
|
||
<p>Similar to the example above, the difference is that the length field
|
||
represents the length of the entire frame instead of just the payload.
|
||
The length of <code>hdr1</code> and <code>len</code> must be counted in <code>length_adjustment</code>.
|
||
Note that the length of <code>hdr2</code> does <strong>not</strong> need to be explicitly set
|
||
anywhere because it already is factored into the total frame length that
|
||
is read from the byte stream.</p>
|
||
<h1 id="encoding" class="section-header"><a href="#encoding">Encoding</a></h1>
|
||
<p><a href="struct.FramedWrite.html"><code>FramedWrite</code></a> adapts an <a href="../../trait.AsyncWrite.html"><code>AsyncWrite</code></a> into a <code>Sink</code> of <a href="https://docs.rs/bytes/%7E0.4/bytes/struct.BytesMut.html"><code>BytesMut</code></a>,
|
||
such that each submitted <a href="https://docs.rs/bytes/%7E0.4/bytes/struct.BytesMut.html"><code>BytesMut</code></a> is prefaced by a length field.
|
||
There are fewer configuration options than <a href="struct.FramedRead.html"><code>FramedRead</code></a>. Given
|
||
protocols that have more complex frame heads, an encoder should probably
|
||
be written by hand using <a href="../trait.Encoder.html"><code>Encoder</code></a>.</p>
|
||
<p>Here is a simple example, given a <code>FramedWrite</code> with the following
|
||
configuration:</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="ident">length_delimited</span>::<span class="ident">Builder</span>::<span class="ident">new</span>()
|
||
.<span class="ident">length_field_length</span>(<span class="number">2</span>)
|
||
.<span class="ident">new_write</span>(<span class="ident">io</span>);</pre>
|
||
<p>A payload of <code>hello world</code> will be encoded as:</p>
|
||
<pre><code class="language-text">+- len: u16 -+---- data ----+
|
||
| \x00\x0b | hello world |
|
||
+------------+--------------+
|
||
</code></pre>
|
||
</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class="struct" href="struct.Builder.html"
|
||
title='struct tokio_io::codec::length_delimited::Builder'>Builder</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Configure length delimited <code>FramedRead</code>, <code>FramedWrite</code>, and <code>Framed</code> values.</p>
|
||
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class="struct" href="struct.FrameTooBig.html"
|
||
title='struct tokio_io::codec::length_delimited::FrameTooBig'>FrameTooBig</a></td>
|
||
<td class='docblock-short'>
|
||
<p>An error when the number of bytes read is more than max frame length.</p>
|
||
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class="struct" href="struct.Framed.html"
|
||
title='struct tokio_io::codec::length_delimited::Framed'>Framed</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Adapts a byte stream into a unified <code>Stream</code> and <code>Sink</code> that works over
|
||
entire frame values.</p>
|
||
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class="struct" href="struct.FramedRead.html"
|
||
title='struct tokio_io::codec::length_delimited::FramedRead'>FramedRead</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Adapts a byte stream to a <code>Stream</code> yielding entire frame values.</p>
|
||
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class="struct" href="struct.FramedWrite.html"
|
||
title='struct tokio_io::codec::length_delimited::FramedWrite'>FramedWrite</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Adapts a byte stream to a <code>Sink</code> accepting entire frame values.</p>
|
||
|
||
</td>
|
||
</tr></table></section>
|
||
<section id='search' class="content hidden"></section>
|
||
|
||
<section class="footer"></section>
|
||
|
||
<aside id="help" class="hidden">
|
||
<div>
|
||
<h1 class="hidden">Help</h1>
|
||
|
||
<div class="shortcuts">
|
||
<h2>Keyboard Shortcuts</h2>
|
||
|
||
<dl>
|
||
<dt><kbd>?</kbd></dt>
|
||
<dd>Show this help dialog</dd>
|
||
<dt><kbd>S</kbd></dt>
|
||
<dd>Focus the search field</dd>
|
||
<dt><kbd>↑</kbd></dt>
|
||
<dd>Move up in search results</dd>
|
||
<dt><kbd>↓</kbd></dt>
|
||
<dd>Move down in search results</dd>
|
||
<dt><kbd>↹</kbd></dt>
|
||
<dd>Switch tab</dd>
|
||
<dt><kbd>⏎</kbd></dt>
|
||
<dd>Go to active search result</dd>
|
||
<dt><kbd>+</kbd></dt>
|
||
<dd>Expand all sections</dd>
|
||
<dt><kbd>-</kbd></dt>
|
||
<dd>Collapse all sections</dd>
|
||
</dl>
|
||
</div>
|
||
|
||
<div class="infos">
|
||
<h2>Search Tricks</h2>
|
||
|
||
<p>
|
||
Prefix searches with a type followed by a colon (e.g.
|
||
<code>fn:</code>) to restrict the search to a given type.
|
||
</p>
|
||
|
||
<p>
|
||
Accepted types are: <code>fn</code>, <code>mod</code>,
|
||
<code>struct</code>, <code>enum</code>,
|
||
<code>trait</code>, <code>type</code>, <code>macro</code>,
|
||
and <code>const</code>.
|
||
</p>
|
||
|
||
<p>
|
||
Search functions by type signature (e.g.
|
||
<code>vec -> usize</code> or <code>* -> vec</code>)
|
||
</p>
|
||
</div>
|
||
</div>
|
||
</aside>
|
||
|
||
|
||
|
||
<script>
|
||
window.rootPath = "../../../";
|
||
window.currentCrate = "tokio_io";
|
||
</script>
|
||
<script src="../../../main.js"></script>
|
||
<script defer src="../../../search-index.js"></script>
|
||
</body>
|
||
</html> |