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<section id='main' class="content mod">
<h1 class='fqn'><span class='in-band'>Crate <a class='mod' href=''>aho_corasick</a></span><span class='out-of-band'><span id='render-detail'>
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<div class='docblock'><p>An implementation of the
<a href="https://en.wikipedia.org/wiki/Aho%E2%80%93Corasick_string_matching_algorithm">Aho-Corasick string search algorithm</a>.</p>
<p>The Aho-Corasick algorithm is principally useful when you need to search many
large texts for a fixed (possibly large) set of keywords. In particular, the
Aho-Corasick algorithm preprocesses the set of keywords by constructing a
finite state machine. The search phase is then a quick linear scan through the
text. Each character in the search text causes a state transition in the
automaton. Matches are reported when the automaton enters a match state.</p>
<h1 id="examples" class='section-header'><a
href="#examples">Examples</a></h1>
<p>The main type exposed by this crate is <code>AcAutomaton</code>, which can be constructed
from an iterator of pattern strings:</p>
<pre class='rust rust-example-rendered'>
<span class='kw'>use</span> <span class='ident'>aho_corasick</span>::{<span class='ident'>Automaton</span>, <span class='ident'>AcAutomaton</span>};
<span class='kw'>let</span> <span class='ident'>aut</span> <span class='op'>=</span> <span class='ident'>AcAutomaton</span>::<span class='ident'>new</span>(<span class='macro'>vec</span><span class='macro'>!</span>[<span class='string'>"apple"</span>, <span class='string'>"maple"</span>]);
<span class='comment'>// AcAutomaton also implements `FromIterator`:</span>
<span class='kw'>let</span> <span class='ident'>aut</span>: <span class='ident'>AcAutomaton</span> <span class='op'>=</span> [<span class='string'>"apple"</span>, <span class='string'>"maple"</span>].<span class='ident'>iter</span>().<span class='ident'>cloned</span>().<span class='ident'>collect</span>();
</pre>
<p>Finding matches can be done with <code>find</code>:</p>
<pre class='rust rust-example-rendered'>
<span class='kw'>use</span> <span class='ident'>aho_corasick</span>::{<span class='ident'>Automaton</span>, <span class='ident'>AcAutomaton</span>, <span class='ident'>Match</span>};
<span class='kw'>let</span> <span class='ident'>aut</span> <span class='op'>=</span> <span class='ident'>AcAutomaton</span>::<span class='ident'>new</span>(<span class='macro'>vec</span><span class='macro'>!</span>[<span class='string'>"apple"</span>, <span class='string'>"maple"</span>]);
<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>it</span> <span class='op'>=</span> <span class='ident'>aut</span>.<span class='ident'>find</span>(<span class='string'>"I like maple apples."</span>);
<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>it</span>.<span class='ident'>next</span>(), <span class='prelude-val'>Some</span>(<span class='ident'>Match</span> {
<span class='ident'>pati</span>: <span class='number'>1</span>,
<span class='ident'>start</span>: <span class='number'>7</span>,
<span class='ident'>end</span>: <span class='number'>12</span>,
}));
<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>it</span>.<span class='ident'>next</span>(), <span class='prelude-val'>Some</span>(<span class='ident'>Match</span> {
<span class='ident'>pati</span>: <span class='number'>0</span>,
<span class='ident'>start</span>: <span class='number'>13</span>,
<span class='ident'>end</span>: <span class='number'>18</span>,
}));
<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>it</span>.<span class='ident'>next</span>(), <span class='prelude-val'>None</span>);
</pre>
<p>Use <code>find_overlapping</code> if you want to report all matches, even if they
overlap with each other.</p>
<pre class='rust rust-example-rendered'>
<span class='kw'>use</span> <span class='ident'>aho_corasick</span>::{<span class='ident'>Automaton</span>, <span class='ident'>AcAutomaton</span>, <span class='ident'>Match</span>};
<span class='kw'>let</span> <span class='ident'>aut</span> <span class='op'>=</span> <span class='ident'>AcAutomaton</span>::<span class='ident'>new</span>(<span class='macro'>vec</span><span class='macro'>!</span>[<span class='string'>"abc"</span>, <span class='string'>"a"</span>]);
<span class='kw'>let</span> <span class='ident'>matches</span>: <span class='ident'>Vec</span><span class='op'><</span>_<span class='op'>></span> <span class='op'>=</span> <span class='ident'>aut</span>.<span class='ident'>find_overlapping</span>(<span class='string'>"abc"</span>).<span class='ident'>collect</span>();
<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>matches</span>, <span class='macro'>vec</span><span class='macro'>!</span>[
<span class='ident'>Match</span> { <span class='ident'>pati</span>: <span class='number'>1</span>, <span class='ident'>start</span>: <span class='number'>0</span>, <span class='ident'>end</span>: <span class='number'>1</span>}, <span class='ident'>Match</span> { <span class='ident'>pati</span>: <span class='number'>0</span>, <span class='ident'>start</span>: <span class='number'>0</span>, <span class='ident'>end</span>: <span class='number'>3</span> },
]);
<span class='comment'>// Regular `find` will report only one match:</span>
<span class='kw'>let</span> <span class='ident'>matches</span>: <span class='ident'>Vec</span><span class='op'><</span>_<span class='op'>></span> <span class='op'>=</span> <span class='ident'>aut</span>.<span class='ident'>find</span>(<span class='string'>"abc"</span>).<span class='ident'>collect</span>();
<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>matches</span>, <span class='macro'>vec</span><span class='macro'>!</span>[<span class='ident'>Match</span> { <span class='ident'>pati</span>: <span class='number'>1</span>, <span class='ident'>start</span>: <span class='number'>0</span>, <span class='ident'>end</span>: <span class='number'>1</span>}]);
</pre>
<p>Finally, there are also methods for finding matches on <em>streams</em>. Namely, the
search text does not have to live in memory. It's useful to run this on files
that can't fit into memory:</p>
<pre class='rust rust-example-rendered'>
<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>fs</span>::<span class='ident'>File</span>;
<span class='kw'>use</span> <span class='ident'>aho_corasick</span>::{<span class='ident'>Automaton</span>, <span class='ident'>AcAutomaton</span>};
<span class='kw'>let</span> <span class='ident'>aut</span> <span class='op'>=</span> <span class='ident'>AcAutomaton</span>::<span class='ident'>new</span>(<span class='macro'>vec</span><span class='macro'>!</span>[<span class='string'>"foo"</span>, <span class='string'>"bar"</span>, <span class='string'>"baz"</span>]);
<span class='kw'>let</span> <span class='ident'>rdr</span> <span class='op'>=</span> <span class='ident'>File</span>::<span class='ident'>open</span>(<span class='string'>"search.txt"</span>).<span class='ident'>unwrap</span>();
<span class='kw'>for</span> <span class='ident'>m</span> <span class='kw'>in</span> <span class='ident'>aut</span>.<span class='ident'>stream_find</span>(<span class='ident'>rdr</span>) {
<span class='kw'>let</span> <span class='ident'>m</span> <span class='op'>=</span> <span class='ident'>m</span>.<span class='ident'>unwrap</span>(); <span class='comment'>// could be an IO error</span>
<span class='macro'>println</span><span class='macro'>!</span>(<span class='string'>"Pattern '{}' matched at: ({}, {})"</span>,
<span class='ident'>aut</span>.<span class='ident'>pattern</span>(<span class='ident'>m</span>.<span class='ident'>pati</span>), <span class='ident'>m</span>.<span class='ident'>start</span>, <span class='ident'>m</span>.<span class='ident'>end</span>);
}
</pre>
<p>There is also <code>stream_find_overlapping</code>, which is just like <code>find_overlapping</code>,
but it operates on streams.</p>
<p>Please see <code>dict-search.rs</code> in this crate's <code>examples</code> directory for a more
complete example. It creates a large automaton from a dictionary and can do a
streaming match over arbitrarily large data.</p>
<h1 id="memory-usage" class='section-header'><a
href="#memory-usage">Memory usage</a></h1>
<p>A key aspect of an Aho-Corasick implementation is how the state transitions
are represented. The easiest way to make the automaton fast is to store a
sparse 256-slot map in each state. It maps an input byte to a state index.
This makes the matching loop extremely fast, since it translates to a simple
pointer read.</p>
<p>The problem is that as the automaton accumulates more states, you end up paying
a <code>256 * 4</code> (<code>4</code> is for the <code>u32</code> state index) byte penalty for every state
regardless of how many transitions it has.</p>
<p>To solve this, only states near the root of the automaton have this sparse
map representation. States near the leaves of the automaton use a dense mapping
that requires a linear scan.</p>
<p>(The specific limit currently set is <code>3</code>, so that states with a depth less than
or equal to <code>3</code> are less memory efficient. The result is that the memory usage
of the automaton stops growing rapidly past ~60MB, even for automatons with
thousands of patterns.)</p>
<p>If you'd like to opt for the less-memory-efficient-but-faster version, then
you can construct an <code>AcAutomaton</code> with a <code>Sparse</code> transition strategy:</p>
<pre class='rust rust-example-rendered'>
<span class='kw'>use</span> <span class='ident'>aho_corasick</span>::{<span class='ident'>Automaton</span>, <span class='ident'>AcAutomaton</span>, <span class='ident'>Match</span>, <span class='ident'>Sparse</span>};
<span class='kw'>let</span> <span class='ident'>aut</span> <span class='op'>=</span> <span class='ident'>AcAutomaton</span>::<span class='op'><</span><span class='ident'>Sparse</span><span class='op'>></span>::<span class='ident'>with_transitions</span>(<span class='macro'>vec</span><span class='macro'>!</span>[<span class='string'>"abc"</span>, <span class='string'>"a"</span>]);
<span class='kw'>let</span> <span class='ident'>matches</span>: <span class='ident'>Vec</span><span class='op'><</span>_<span class='op'>></span> <span class='op'>=</span> <span class='ident'>aut</span>.<span class='ident'>find</span>(<span class='string'>"abc"</span>).<span class='ident'>collect</span>();
<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>matches</span>, <span class='macro'>vec</span><span class='macro'>!</span>[<span class='ident'>Match</span> { <span class='ident'>pati</span>: <span class='number'>1</span>, <span class='ident'>start</span>: <span class='number'>0</span>, <span class='ident'>end</span>: <span class='number'>1</span>}]);
</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.AcAutomaton.html'
title='aho_corasick::AcAutomaton'>AcAutomaton</a></td>
<td class='docblock short'>
<p>An Aho-Corasick finite automaton.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='struct' href='struct.Dense.html'
title='aho_corasick::Dense'>Dense</a></td>
<td class='docblock short'>
<p>State transitions that can be stored either sparsely or densely.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='struct' href='struct.FullAcAutomaton.html'
title='aho_corasick::FullAcAutomaton'>FullAcAutomaton</a></td>
<td class='docblock short'>
<p>A complete Aho-Corasick automaton.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='struct' href='struct.Match.html'
title='aho_corasick::Match'>Match</a></td>
<td class='docblock short'>
<p>Records a match in the search text.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='struct' href='struct.Matches.html'
title='aho_corasick::Matches'>Matches</a></td>
<td class='docblock short'>
<p>An iterator of non-overlapping matches for in-memory text.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='struct' href='struct.MatchesOverlapping.html'
title='aho_corasick::MatchesOverlapping'>MatchesOverlapping</a></td>
<td class='docblock short'>
<p>An iterator of overlapping matches for in-memory text.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='struct' href='struct.Sparse.html'
title='aho_corasick::Sparse'>Sparse</a></td>
<td class='docblock short'>
<p>State transitions that are always sparse.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='struct' href='struct.StreamMatches.html'
title='aho_corasick::StreamMatches'>StreamMatches</a></td>
<td class='docblock short'>
<p>An iterator of non-overlapping matches for streaming text.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='struct' href='struct.StreamMatchesOverlapping.html'
title='aho_corasick::StreamMatchesOverlapping'>StreamMatchesOverlapping</a></td>
<td class='docblock short'>
<p>An iterator of overlapping matches for streaming text.</p>
</td>
</tr>
</table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
<table>
<tr class=' module-item'>
<td><a class='trait' href='trait.Automaton.html'
title='aho_corasick::Automaton'>Automaton</a></td>
<td class='docblock short'>
<p>An abstraction over automatons and their corresponding iterators.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class='trait' href='trait.Transitions.html'
title='aho_corasick::Transitions'>Transitions</a></td>
<td class='docblock short'>
<p>An abstraction over state transition strategies.</p>
</td>
</tr>
</table><h2 id='types' class='section-header'><a href="#types">Type Definitions</a></h2>
<table>
<tr class=' module-item'>
<td><a class='type' href='type.StateIdx.html'
title='aho_corasick::StateIdx'>StateIdx</a></td>
<td class='docblock short'>
<p>The integer type used for the state index.</p>
</td>
</tr>
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