🐎 daachorse: Double-Array Aho-Corasick

A fast implementation of the Aho-Corasick algorithm using the compact double-array data structure.

Overview

Daachorse is a crate for fast multiple pattern matching using the Aho-Corasick algorithm, running in linear time over the length of the input text. For time- and memory-efficiency, the pattern match automaton is implemented using the compact double-array data structure. The data structure not only supports constant-time state-to-state traversal, but also represents each state in a compact space of only 12 bytes.

For example, compared to the NFA of the aho-corasick crate that is the most poplar Aho-Corasick implementation in Rust, Daachorse can perform pattern matching 3.0~5.1 times faster while consuming 45~55% smaller memory, when using a word dictionary of 675K patterns. Other experimental results can be found in Wiki.

Installation

To use daachorse, depend on it in your Cargo manifest:

# Cargo.toml

[dependencies]
daachorse = "0.4"

Requirements

To compile this crate, Rust 1.58 or higher is required.

Example usage

Daachorse contains some search options, ranging from basic matching with the Aho-Corasick algorithm to trickier matching. All of them will run very fast based on the double-array data structure and can be easily plugged into your application as shown below.

Finding overlapped occurrences

To search for all occurrences of registered patterns that allow for positional overlap in the input text, use find_overlapping_iter(). When you use new() for constraction, unique identifiers are assigned to each pattern in the input order. The match result has the byte positions of the occurrence and its identifier.

use daachorse::DoubleArrayAhoCorasick;

let patterns = vec!["bcd", "ab", "a"];
let pma = DoubleArrayAhoCorasick::new(patterns).unwrap();

let mut it = pma.find_overlapping_iter("abcd");

let m = it.next().unwrap();
assert_eq!((0, 1, 2), (m.start(), m.end(), m.value()));

let m = it.next().unwrap();
assert_eq!((0, 2, 1), (m.start(), m.end(), m.value()));

let m = it.next().unwrap();
assert_eq!((1, 4, 0), (m.start(), m.end(), m.value()));

assert_eq!(None, it.next());

Finding non-overlapped occurrences with shortest matching

If you do not want to allow positional overlap, use find_iter() instead. It reports the first pattern found in each iteration, which is the shortest pattern starting from each search position.

use daachorse::DoubleArrayAhoCorasick;

let patterns = vec!["bcd", "ab", "a"];
let pma = DoubleArrayAhoCorasick::new(patterns).unwrap();

let mut it = pma.find_iter("abcd");

let m = it.next().unwrap();
assert_eq!((0, 1, 2), (m.start(), m.end(), m.value()));

let m = it.next().unwrap();
assert_eq!((1, 4, 0), (m.start(), m.end(), m.value()));

assert_eq!(None, it.next());

Finding non-overlapped occurrences with longest matching

If you want to search for the longest pattern without positional overlap in each iteration, use leftmost_find_iter() with specifying MatchKind::LeftmostLongest in the construction.

use daachorse::{DoubleArrayAhoCorasickBuilder, MatchKind};

let patterns = vec!["ab", "a", "abcd"];
let pma = DoubleArrayAhoCorasickBuilder::new()
          .match_kind(MatchKind::LeftmostLongest)
          .build(&patterns)
          .unwrap();

let mut it = pma.leftmost_find_iter("abcd");

let m = it.next().unwrap();
assert_eq!((0, 4, 2), (m.start(), m.end(), m.value()));

assert_eq!(None, it.next());

Finding non-overlapped occurrences with leftmost-first matching

If you want to find the the earliest registered pattern among ones starting from the search position, use leftmost_find_iter() with specifying MatchKind::LeftmostFirst.

This is so-called the leftmost first match, a bit tricky search option that is also supported in the aho-corasick crate. For example, in the following code, ab is reported because it is the earliest registered one.

use daachorse::{DoubleArrayAhoCorasickBuilder, MatchKind};

let patterns = vec!["ab", "a", "abcd"];
let pma = DoubleArrayAhoCorasickBuilder::new()
          .match_kind(MatchKind::LeftmostFirst)
          .build(&patterns)
          .unwrap();

let mut it = pma.leftmost_find_iter("abcd");

let m = it.next().unwrap();
assert_eq!((0, 2, 0), (m.start(), m.end(), m.value()));

assert_eq!(None, it.next());

Associating arbitrary values with patterns

To build the automaton from pairs of a pattern and integer value instead of assigning identifiers automatically, use with_values().

use daachorse::DoubleArrayAhoCorasick;

let patvals = vec![("bcd", 0), ("ab", 10), ("a", 20)];
let pma = DoubleArrayAhoCorasick::with_values(patvals).unwrap();

let mut it = pma.find_overlapping_iter("abcd");

let m = it.next().unwrap();
assert_eq!((0, 1, 20), (m.start(), m.end(), m.value()));

let m = it.next().unwrap();
assert_eq!((0, 2, 10), (m.start(), m.end(), m.value()));

let m = it.next().unwrap();
assert_eq!((1, 4, 0), (m.start(), m.end(), m.value()));

assert_eq!(None, it.next());

Building faster automaton on multibyte characters

To build a faster automaton on multibyte characters, use CharwiseDoubleArrayAhoCorasick instead.

The standard version DoubleArrayAhoCorasick handles strings as UTF-8 sequences and defines transition labels using byte values. On the other hand, CharwiseDoubleArrayAhoCorasick uses code point values of Unicode, resulting in reducing the number of transitions and faster matching.

use daachorse::charwise::CharwiseDoubleArrayAhoCorasick;

let patterns = vec!["全世界", "世界", "に"];
let pma = CharwiseDoubleArrayAhoCorasick::new(patterns).unwrap();

let mut it = pma.find_iter("全世界中に");

let m = it.next().unwrap();
assert_eq!((0, 9, 0), (m.start(), m.end(), m.value()));

let m = it.next().unwrap();
assert_eq!((12, 15, 2), (m.start(), m.end(), m.value()));

assert_eq!(None, it.next());

CLI

This repository contains a command line interface named daacfind for searching patterns in text files.

% cat ./pat.txt
fn
const fn
pub fn
unsafe fn
% find . -name "*.rs" | xargs cargo run --release -p daacfind -- --color=auto -nf ./pat.txt
...
...
./src/errors.rs:67:    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
./src/errors.rs:81:    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
./src/lib.rs:115:    fn default() -> Self {
./src/lib.rs:126:    pub fn base(&self) -> Option<u32> {
./src/lib.rs:131:    pub const fn check(&self) -> u8 {
./src/lib.rs:136:    pub const fn fail(&self) -> u32 {
...
...

Disclaimer

This software is developed by LegalForce, Inc., but not an officially supported LegalForce product.

License

Licensed under either of

Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

For softwares under bench/data, follow the license terms of each software.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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legalforce-research / daachorse

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