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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="Decoding of frames via buffers."><title>Decoder in actix_codec - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-b778ab399e080a4b.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="actix_codec" data-themes="" data-resource-suffix="" data-rustdoc-version="1.83.0-nightly (7608018cb 2024-09-29)" data-channel="nightly" data-search-js="search-e056c65ede92db13.js" data-settings-js="settings-805db61a62df4bd2.js" ><script src="../static.files/storage-1d39b6787ed640ff.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-54bc299d2a5e4e43.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-0111fcff984fae8f.css"></noscript><link rel="icon" href="https://actix.rs/favicon.ico"></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" title="show sidebar"></button><a class="logo-container" href="../actix_codec/index.html"><img src="https://actix.rs/img/logo.png" alt=""></a></nav><nav class="sidebar"><div class="sidebar-crate"><a class="logo-container" href="../actix_codec/index.html"><img src="https://actix.rs/img/logo.png" alt="logo"></a><h2><a href="../actix_codec/index.html">actix_<wbr>codec</a><span class="version">0.5.2</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">Decoder</a></h2><h3><a href="#required-associated-types">Required Associated Types</a></h3><ul class="block"><li><a href="#associatedtype.Error" title="Error">Error</a></li><li><a href="#associatedtype.Item" title="Item">Item</a></li></ul><h3><a href="#required-methods">Required Methods</a></h3><ul class="block"><li><a href="#tymethod.decode" title="decode">decode</a></li></ul><h3><a href="#provided-methods">Provided Methods</a></h3><ul class="block"><li><a href="#method.decode_eof" title="decode_eof">decode_eof</a></li><li><a href="#method.framed" title="framed">framed</a></li></ul><h3><a href="#implementors">Implementors</a></h3></section><div id="rustdoc-modnav"><h2 class="in-crate"><a href="index.html">In crate actix_<wbr>codec</a></h2></div></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><span class="rustdoc-breadcrumbs"><a href="index.html">actix_codec</a></span><h1>Trait <span class="trait">Decoder</span><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"></span></div><pre class="rust item-decl"><code>pub trait Decoder {
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type <a href="#associatedtype.Item" class="associatedtype">Item</a>;
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type <a href="#associatedtype.Error" class="associatedtype">Error</a>: <a class="trait" href="https://doc.rust-lang.org/nightly/core/convert/trait.From.html" title="trait core::convert::From">From</a><<a class="struct" href="https://doc.rust-lang.org/nightly/std/io/error/struct.Error.html" title="struct std::io::error::Error">Error</a>>;
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// Required method
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fn <a href="#tymethod.decode" class="fn">decode</a>(
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&mut self,
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src: &mut BytesMut,
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) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><Self::<a class="associatedtype" href="trait.Decoder.html#associatedtype.Item" title="type actix_codec::Decoder::Item">Item</a>>, Self::<a class="associatedtype" href="trait.Decoder.html#associatedtype.Error" title="type actix_codec::Decoder::Error">Error</a>>;
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// Provided methods
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fn <a href="#method.decode_eof" class="fn">decode_eof</a>(
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&mut self,
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buf: &mut BytesMut,
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) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><Self::<a class="associatedtype" href="trait.Decoder.html#associatedtype.Item" title="type actix_codec::Decoder::Item">Item</a>>, Self::<a class="associatedtype" href="trait.Decoder.html#associatedtype.Error" title="type actix_codec::Decoder::Error">Error</a>> { ... }
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<span class="item-spacer"></span> fn <a href="#method.framed" class="fn">framed</a><T>(self, io: T) -> Framed<T, Self>
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<span class="where">where T: <a class="trait" href="trait.AsyncRead.html" title="trait actix_codec::AsyncRead">AsyncRead</a> + <a class="trait" href="trait.AsyncWrite.html" title="trait actix_codec::AsyncWrite">AsyncWrite</a>,
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Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span> { ... }
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}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Decoding of frames via buffers.</p>
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<p>This trait is used when constructing an instance of <a href="crate::codec::Framed"><code>Framed</code></a> or
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<a href="crate::codec::FramedRead"><code>FramedRead</code></a>. An implementation of <code>Decoder</code> takes a byte stream that has
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already been buffered in <code>src</code> and decodes the data into a stream of
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<code>Self::Item</code> frames.</p>
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<p>Implementations are able to track state on <code>self</code>, which enables
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implementing stateful streaming parsers. In many cases, though, this type
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will simply be a unit struct (e.g. <code>struct HttpDecoder</code>).</p>
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<p>For some underlying data-sources, namely files and FIFOs,
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it’s possible to temporarily read 0 bytes by reaching EOF.</p>
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<p>In these cases <code>decode_eof</code> will be called until it signals
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fulfillment of all closing frames by returning <code>Ok(None)</code>.
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After that, repeated attempts to read from the <a href="crate::codec::Framed"><code>Framed</code></a> or <a href="crate::codec::FramedRead"><code>FramedRead</code></a>
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will not invoke <code>decode</code> or <code>decode_eof</code> again, until data can be read
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during a retry.</p>
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<p>It is up to the Decoder to keep track of a restart after an EOF,
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and to decide how to handle such an event by, for example,
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allowing frames to cross EOF boundaries, re-emitting opening frames, or
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resetting the entire internal state.</p>
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</div></details><h2 id="required-associated-types" class="section-header">Required Associated Types<a href="#required-associated-types" class="anchor">§</a></h2><div class="methods"><details class="toggle" open><summary><section id="associatedtype.Item" class="method"><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a></h4></section></summary><div class="docblock"><p>The type of decoded frames.</p>
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</div></details><details class="toggle" open><summary><section id="associatedtype.Error" class="method"><h4 class="code-header">type <a href="#associatedtype.Error" class="associatedtype">Error</a>: <a class="trait" href="https://doc.rust-lang.org/nightly/core/convert/trait.From.html" title="trait core::convert::From">From</a><<a class="struct" href="https://doc.rust-lang.org/nightly/std/io/error/struct.Error.html" title="struct std::io::error::Error">Error</a>></h4></section></summary><div class="docblock"><p>The type of unrecoverable frame decoding errors.</p>
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<p>If an individual message is ill-formed but can be ignored without
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interfering with the processing of future messages, it may be more
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useful to report the failure as an <code>Item</code>.</p>
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<p><code>From<io::Error></code> is required in the interest of making <code>Error</code> suitable
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for returning directly from a <a href="crate::codec::FramedRead"><code>FramedRead</code></a>, and to enable the default
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implementation of <code>decode_eof</code> to yield an <code>io::Error</code> when the decoder
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fails to consume all available data.</p>
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<p>Note that implementors of this trait can simply indicate <code>type Error = io::Error</code> to use I/O errors as this type.</p>
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</div></details></div><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.decode" class="method"><h4 class="code-header">fn <a href="#tymethod.decode" class="fn">decode</a>(
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&mut self,
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src: &mut BytesMut,
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) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><Self::<a class="associatedtype" href="trait.Decoder.html#associatedtype.Item" title="type actix_codec::Decoder::Item">Item</a>>, Self::<a class="associatedtype" href="trait.Decoder.html#associatedtype.Error" title="type actix_codec::Decoder::Error">Error</a>></h4></section></summary><div class="docblock"><p>Attempts to decode a frame from the provided buffer of bytes.</p>
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<p>This method is called by <a href="crate::codec::FramedRead"><code>FramedRead</code></a> whenever bytes are ready to be
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parsed. The provided buffer of bytes is what’s been read so far, and
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this instance of <code>Decode</code> can determine whether an entire frame is in
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the buffer and is ready to be returned.</p>
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<p>If an entire frame is available, then this instance will remove those
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bytes from the buffer provided and return them as a decoded
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frame. Note that removing bytes from the provided buffer doesn’t always
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necessarily copy the bytes, so this should be an efficient operation in
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most circumstances.</p>
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<p>If the bytes look valid, but a frame isn’t fully available yet, then
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<code>Ok(None)</code> is returned. This indicates to the <a href="crate::codec::Framed"><code>Framed</code></a> instance that
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it needs to read some more bytes before calling this method again.</p>
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<p>Note that the bytes provided may be empty. If a previous call to
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<code>decode</code> consumed all the bytes in the buffer then <code>decode</code> will be
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called again until it returns <code>Ok(None)</code>, indicating that more bytes need to
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be read.</p>
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<p>Finally, if the bytes in the buffer are malformed then an error is
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returned indicating why. This informs <a href="crate::codec::Framed"><code>Framed</code></a> that the stream is now
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corrupt and should be terminated.</p>
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<h5 id="buffer-management"><a class="doc-anchor" href="#buffer-management">§</a>Buffer management</h5>
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<p>Before returning from the function, implementations should ensure that
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the buffer has appropriate capacity in anticipation of future calls to
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<code>decode</code>. Failing to do so leads to inefficiency.</p>
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<p>For example, if frames have a fixed length, or if the length of the
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current frame is known from a header, a possible buffer management
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strategy is:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">impl </span>Decoder <span class="kw">for </span>MyCodec {
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<span class="comment">// ...
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</span><span class="kw">fn </span>decode(<span class="kw-2">&mut </span><span class="self">self</span>, src: <span class="kw-2">&mut </span>BytesMut) -> <span class="prelude-ty">Result</span><<span class="prelude-ty">Option</span><<span class="self">Self</span>::Item>, <span class="self">Self</span>::Error> {
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<span class="comment">// ...
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// Reserve enough to complete decoding of the current frame.
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</span><span class="kw">let </span>current_frame_len: usize = <span class="number">1000</span>; <span class="comment">// Example.
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// And to start decoding the next frame.
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</span><span class="kw">let </span>next_frame_header_len: usize = <span class="number">10</span>; <span class="comment">// Example.
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</span>src.reserve(current_frame_len + next_frame_header_len);
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<span class="kw">return </span><span class="prelude-val">Ok</span>(<span class="prelude-val">None</span>);
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}
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}</code></pre></div>
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<p>An optimal buffer management strategy minimizes reallocations and
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over-allocations.</p>
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</div></details></div><h2 id="provided-methods" class="section-header">Provided Methods<a href="#provided-methods" class="anchor">§</a></h2><div class="methods"><details class="toggle method-toggle" open><summary><section id="method.decode_eof" class="method"><h4 class="code-header">fn <a href="#method.decode_eof" class="fn">decode_eof</a>(
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&mut self,
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buf: &mut BytesMut,
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) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><Self::<a class="associatedtype" href="trait.Decoder.html#associatedtype.Item" title="type actix_codec::Decoder::Item">Item</a>>, Self::<a class="associatedtype" href="trait.Decoder.html#associatedtype.Error" title="type actix_codec::Decoder::Error">Error</a>></h4></section></summary><div class="docblock"><p>A default method available to be called when there are no more bytes
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available to be read from the underlying I/O.</p>
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<p>This method defaults to calling <code>decode</code> and returns an error if
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<code>Ok(None)</code> is returned while there is unconsumed data in <code>buf</code>.
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Typically this doesn’t need to be implemented unless the framing
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protocol differs near the end of the stream, or if you need to construct
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frames <em>across</em> eof boundaries on sources that can be resumed.</p>
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<p>Note that the <code>buf</code> argument may be empty. If a previous call to
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<code>decode_eof</code> consumed all the bytes in the buffer, <code>decode_eof</code> will be
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called again until it returns <code>None</code>, indicating that there are no more
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frames to yield. This behavior enables returning finalization frames
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that may not be based on inbound data.</p>
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<p>Once <code>None</code> has been returned, <code>decode_eof</code> won’t be called again until
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an attempt to resume the stream has been made, where the underlying stream
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actually returned more data.</p>
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</div></details><details class="toggle method-toggle" open><summary><section id="method.framed" class="method"><h4 class="code-header">fn <a href="#method.framed" class="fn">framed</a><T>(self, io: T) -> Framed<T, Self><div class="where">where
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T: <a class="trait" href="trait.AsyncRead.html" title="trait actix_codec::AsyncRead">AsyncRead</a> + <a class="trait" href="trait.AsyncWrite.html" title="trait actix_codec::AsyncWrite">AsyncWrite</a>,
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Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Provides a <a href="futures_core::Stream"><code>Stream</code></a> and <a href="futures_sink::Sink"><code>Sink</code></a> interface for reading and writing to this
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<code>Io</code> object, using <code>Decode</code> and <code>Encode</code> to read and write the raw data.</p>
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<p>Raw I/O objects work with byte sequences, but higher-level code usually
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wants to batch these into meaningful chunks, called “frames”. This
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method layers framing on top of an I/O object, by using the <code>Codec</code>
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traits to handle encoding and decoding of messages frames. Note that
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the incoming and outgoing frame types may be distinct.</p>
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<p>This function returns a <em>single</em> object that is both <code>Stream</code> and
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<code>Sink</code>; grouping this into a single object is often useful for layering
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things like gzip or TLS, which require both read and write access to the
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underlying object.</p>
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<p>If you want to work more directly with the streams and sink, consider
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calling <code>split</code> on the <a href="crate::codec::Framed"><code>Framed</code></a> returned by this method, which will
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break them into separate objects, allowing them to interact more easily.</p>
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</div></details></div><h2 id="implementors" class="section-header">Implementors<a href="#implementors" class="anchor">§</a></h2><div id="implementors-list"><details class="toggle implementors-toggle"><summary><section id="impl-Decoder-for-BytesCodec" class="impl"><a class="src rightside" href="../src/actix_codec/bcodec.rs.html#21-32">source</a><a href="#impl-Decoder-for-BytesCodec" class="anchor">§</a><h3 class="code-header">impl <a class="trait" href="trait.Decoder.html" title="trait actix_codec::Decoder">Decoder</a> for actix_codec::<a class="struct" href="struct.BytesCodec.html" title="struct actix_codec::BytesCodec">BytesCodec</a></h3></section></summary><div class="impl-items"><section id="associatedtype.Item-1" class="associatedtype trait-impl"><a class="src rightside" href="../src/actix_codec/bcodec.rs.html#22">source</a><a href="#associatedtype.Item-1" class="anchor">§</a><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a> = BytesMut</h4></section><section id="associatedtype.Error-1" class="associatedtype trait-impl"><a class="src rightside" href="../src/actix_codec/bcodec.rs.html#23">source</a><a href="#associatedtype.Error-1" class="anchor">§</a><h4 class="code-header">type <a href="#associatedtype.Error" class="associatedtype">Error</a> = <a class="struct" href="https://doc.rust-lang.org/nightly/std/io/error/struct.Error.html" title="struct std::io::error::Error">Error</a></h4></section></div></details><details class="toggle implementors-toggle"><summary><section id="impl-Decoder-for-LinesCodec" class="impl"><a class="src rightside" href="../src/actix_codec/lines.rs.html#29-86">source</a><a href="#impl-Decoder-for-LinesCodec" class="anchor">§</a><h3 class="code-header">impl <a class="trait" href="trait.Decoder.html" title="trait actix_codec::Decoder">Decoder</a> for actix_codec::<a class="struct" href="struct.LinesCodec.html" title="struct actix_codec::LinesCodec">LinesCodec</a></h3></section></summary><div class="impl-items"><section id="associatedtype.Item-2" class="associatedtype trait-impl"><a class="src rightside" href="../src/actix_codec/lines.rs.html#30">source</a><a href="#associatedtype.Item-2" class="anchor">§</a><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a> = <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/string/struct.String.html" title="struct alloc::string::String">String</a></h4></section><section id="associatedtype.Error-2" class="associatedtype trait-impl"><a class="src rightside" href="../src/actix_codec/lines.rs.html#31">source</a><a href="#associatedtype.Error-2" class="anchor">§</a><h4 class="code-header">type <a href="#associatedtype.Error" class="associatedtype">Error</a> = <a class="struct" href="https://doc.rust-lang.org/nightly/std/io/error/struct.Error.html" title="struct std::io::error::Error">Error</a></h4></section></div></details><details class="toggle implementors-toggle"><summary><section id="impl-Decoder-for-AnyDelimiterCodec" class="impl"><a href="#impl-Decoder-for-AnyDelimiterCodec" class="anchor">§</a><h3 class="code-header">impl <a class="trait" href="trait.Decoder.html" title="trait actix_codec::Decoder">Decoder</a> for AnyDelimiterCodec</h3></section></summary><div class="impl-items"><section id="associatedtype.Item-3" class="associatedtype trait-impl"><a href="#associatedtype.Item-3" class="anchor">§</a><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a> = Bytes</h4></section><section id="associatedtype.Error-3" class="associatedtype trait-impl"><a href="#associatedtype.Error-3" class="anchor">§</a><h4 class="code-header">type <a href="#associatedtype.Error" class="associatedtype">Error</a> = AnyDelimiterCodecError</h4></section></div></details><details class="toggle implementors-toggle"><summary><section id="impl-Decoder-for-BytesCodec-1" class="impl"><a href="#impl-Decoder-for-BytesCodec-1" class="anchor">§</a><h3 class="code-header">impl <a class="trait" href="trait.Decoder.html" title="trait actix_codec::Decoder">
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