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<meta name="description" content="API documentation for the Rust `untrusted` crate.">
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<meta name="keywords" content="rust, rustlang, rust-lang, untrusted">
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<title>untrusted - Rust</title>
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This old browser is unsupported and will most likely display funky
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things.
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<nav class="sidebar">
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<p class='location'>Crate untrusted</p><div class="block items"><ul><li><a href="#structs">Structs</a></li><li><a href="#functions">Functions</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'untrusted', ty: 'mod', relpath: '../'};</script>
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autocomplete="off"
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placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
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type="search">
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</div>
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<section id='main' class="content">
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<h1 class='fqn'><span class='in-band'>Crate <a class="mod" href=''>untrusted</a></span><span class='out-of-band'><span id='render-detail'>
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<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
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[<span class='inner'>−</span>]
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</a>
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</span><a class='srclink' href='../src/untrusted/untrusted.rs.html#15-400' title='goto source code'>[src]</a></span></h1>
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<div class='docblock'><p>untrusted.rs: Safe, fast, zero-panic, zero-crashing, zero-allocation
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parsing of untrusted inputs in Rust.</p>
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<p><code>git clone <a href="https://github.com/briansmith/untrusted">https://github.com/briansmith/untrusted</a></code></p>
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<p>untrusted.rs goes beyond Rust's normal safety guarantees by also
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guaranteeing that parsing will be panic-free, as long as
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<code>untrusted::Input::as_slice_less_safe()</code> is not used. It avoids copying
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data and heap allocation and strives to prevent common pitfalls such as
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accidentally parsing input bytes multiple times. In order to meet these
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goals, untrusted.rs is limited in functionality such that it works best for
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input languages with a small fixed amount of lookahead such as ASN.1, TLS,
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TCP/IP, and many other networking, IPC, and related protocols. Languages
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that require more lookahead and/or backtracking require some significant
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contortions to parse using this framework. It would not be realistic to use
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it for parsing programming language code, for example.</p>
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<p>The overall pattern for using untrusted.rs is:</p>
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<ol>
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<li><p>Write a recursive-descent-style parser for the input language, where the
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input data is given as a <code>&mut untrusted::Reader</code> parameter to each
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function. Each function should have a return type of <code>Result<V, E></code> for
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some value type <code>V</code> and some error type <code>E</code>, either or both of which may
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be <code>()</code>. Functions for parsing the lowest-level language constructs
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should be defined. Those lowest-level functions will parse their inputs
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using <code>::read_byte()</code>, <code>Reader::peek()</code>, and similar functions.
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Higher-level language constructs are then parsed by calling the
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lower-level functions in sequence.</p></li>
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<li><p>Wrap the top-most functions of your recursive-descent parser in
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functions that take their input data as an <code>untrusted::Input</code>. The
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wrapper functions should call the <code>Input</code>'s <code>read_all</code> (or a variant
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thereof) method. The wrapper functions are the only ones that should be
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exposed outside the parser's module.</p></li>
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<li><p>After receiving the input data to parse, wrap it in an <code>untrusted::Input</code>
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using <code>untrusted::Input::from()</code> as early as possible. Pass the
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<code>untrusted::Input</code> to the wrapper functions when they need to be parsed.</p></li>
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</ol>
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<p>In general parsers built using <code>untrusted::Reader</code> do not need to explicitly
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check for end-of-input unless they are parsing optional constructs, because
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<code>Reader::read_byte()</code> will return <code>Err(EndOfInput)</code> on end-of-input.
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Similarly, parsers using <code>untrusted::Reader</code> generally don't need to check
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for extra junk at the end of the input as long as the parser's API uses the
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pattern described above, as <code>read_all</code> and its variants automatically check
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for trailing junk. <code>Reader::skip_to_end()</code> must be used when any remaining
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unread input should be ignored without triggering an error.</p>
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<p>untrusted.rs works best when all processing of the input data is done
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through the <code>untrusted::Input</code> and <code>untrusted::Reader</code> types. In
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particular, avoid trying to parse input data using functions that take
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byte slices. However, when you need to access a part of the input data as
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a slice to use a function that isn't written using untrusted.rs,
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<code>Input::as_slice_less_safe()</code> can be used.</p>
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<p>It is recommend to use <code>use untrusted;</code> and then <code>untrusted::Input</code>,
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<code>untrusted::Reader</code>, etc., instead of using <code>use untrusted::*</code>. Qualifying
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the names with <code>untrusted</code> helps remind the reader of the code that it is
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dealing with <em>untrusted</em> input.</p>
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<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
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<p><a href="https://github.com/briansmith/ring"><em>ring</em></a>'s parser for the subset of
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ASN.1 DER it needs to understand,
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<a href="https://github.com/briansmith/ring/blob/master/src/der.rs"><code>ring::der</code></a>,
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is built on top of untrusted.rs. <em>ring</em> also uses untrusted.rs to parse ECC
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public keys, RSA PKCS#1 1.5 padding, and for all other parsing it does.</p>
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<p>All of <a href="https://github.com/briansmith/webpki">webpki</a>'s parsing of X.509
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certificates (also ASN.1 DER) is done using untrusted.rs.</p>
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</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.EndOfInput.html"
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title='struct untrusted::EndOfInput'>EndOfInput</a></td>
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<td class='docblock-short'>
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<p>The error type used to indicate the end of the input was reached before the
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operation could be completed.</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.Input.html"
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title='struct untrusted::Input'>Input</a></td>
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<td class='docblock-short'>
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<p>A wrapper around <code>&'a [u8]</code> that helps in writing panic-free code.</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.Mark.html"
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title='struct untrusted::Mark'>Mark</a></td>
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<td class='docblock-short'>
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<p>An index into the already-parsed input of a <code>Reader</code>.</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.Reader.html"
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title='struct untrusted::Reader'>Reader</a></td>
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<td class='docblock-short'>
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<p>A read-only, forward-only* cursor into the data in an <code>Input</code>.</p>
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</td>
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</tr></table><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="fn" href="fn.read_all_optional.html"
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title='fn untrusted::read_all_optional'>read_all_optional</a></td>
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<td class='docblock-short'>
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<p>Calls <code>read</code> with the given input as a <code>Reader</code>, ensuring that <code>read</code>
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consumed the entire input. When <code>input</code> is <code>None</code>, <code>read</code> will be
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called with <code>None</code>.</p>
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</td>
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</tr></table></section>
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<section id='search' class="content hidden"></section>
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<div class="infos">
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<h2>Search Tricks</h2>
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<p>
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Prefix searches with a type followed by a colon (e.g.
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<code>fn:</code>) to restrict the search to a given type.
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Accepted types are: <code>fn</code>, <code>mod</code>,
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<code>struct</code>, <code>enum</code>,
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<code>trait</code>, <code>type</code>, <code>macro</code>,
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and <code>const</code>.
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Search functions by type signature (e.g.
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window.rootPath = "../";
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