Struct DFA

pub struct DFA { /* private fields */ }

A DFA implementation of Aho-Corasick.

When possible, prefer using AhoCorasick instead of this type directly. Using a DFA directly is typically only necessary when one needs access to the Automaton trait implementation.

This DFA can only be built by first constructing a noncontiguous::NFA. Both DFA::new and Builder::build do this for you automatically, but Builder::build_from_noncontiguous permits doing it explicitly.

A DFA provides the best possible search performance (in this crate) via two mechanisms:

• All states use a dense representation for their transitions.
• All failure transitions are pre-computed such that they are never explicitly handled at search time.

These two facts combined mean that every state transition is performed using a constant number of instructions. However, this comes at great cost. The memory usage of a DFA can be quite exorbitant. It is potentially multiple orders of magnitude greater than a contiguous::NFA for example. In exchange, a DFA will typically have better search speed than a contiguous::NFA, but not by orders of magnitude.

Unless you have a small number of patterns or memory usage is not a concern and search performance is critical, a DFA is usually not the best choice.

Moreover, unlike the NFAs in this crate, it is costly for a DFA to support for anchored and unanchored search configurations. Namely, since failure transitions are pre-computed, supporting both anchored and unanchored searches requires a duplication of the transition table, making the memory usage of such a DFA ever bigger. (The NFAs in this crate unconditionally support both anchored and unanchored searches because there is essentially no added cost for doing so.) It is for this reason that a DFA’s support for anchored and unanchored searches can be configured via Builder::start_kind. By default, a DFA only supports unanchored searches.

Example

This example shows how to build an DFA directly and use it to execute Automaton::try_find:

use aho_corasick::{
    automaton::Automaton,
    dfa::DFA,
    Input, Match,
};

let patterns = &["b", "abc", "abcd"];
let haystack = "abcd";

let nfa = DFA::new(patterns).unwrap();
assert_eq!(
    Some(Match::must(0, 1..2)),
    nfa.try_find(&Input::new(haystack))?,
);

It is also possible to implement your own version of try_find. See the Automaton documentation for an example.

Implementations

impl DFA

pub fn new<I, P>(patterns: I) -> Result<DFA, BuildError>

where I: IntoIterator<Item = P>, P: AsRef<[u8]>,

Create a new Aho-Corasick DFA using the default configuration.

Use a Builder if you want to change the configuration.

pub fn builder() -> Builder

A convenience method for returning a new Aho-Corasick DFA builder.

This usually permits one to just import the DFA type.

Trait Implementations

impl Automaton for DFA

fn start_state(&self, anchored: Anchored) -> Result<StateID, MatchError>

Returns the starting state for the given anchor mode.

fn next_state(&self, _anchored: Anchored, sid: StateID, byte: u8) -> StateID

Performs a state transition from sid for byte and returns the next state.

fn is_special(&self, sid: StateID) -> bool

Returns true if the given ID represents a “special” state. A special state is a dead, match or start state.

fn is_dead(&self, sid: StateID) -> bool

Returns true if the given ID represents a dead state.

fn is_match(&self, sid: StateID) -> bool

Returns true if the given ID represents a match state.

fn is_start(&self, sid: StateID) -> bool

Returns true if the given ID represents a start state.

fn match_kind(&self) -> MatchKind

Returns the match semantics that this automaton was built with.

fn patterns_len(&self) -> usize

Returns the total number of patterns compiled into this automaton.

fn pattern_len(&self, pid: PatternID) -> usize

Returns the length of the pattern for the given ID.

fn min_pattern_len(&self) -> usize

Returns the length, in bytes, of the shortest pattern in this automaton.

fn max_pattern_len(&self) -> usize

Returns the length, in bytes, of the longest pattern in this automaton.

fn match_len(&self, sid: StateID) -> usize

Returns the total number of matches for the given state ID.

fn match_pattern(&self, sid: StateID, index: usize) -> PatternID

Returns the pattern ID for the match state given by sid at the index given.

fn memory_usage(&self) -> usize

Returns the heap memory usage, in bytes, used by this automaton.

fn prefilter(&self) -> Option<&Prefilter>

Returns a prefilter, if available, that can be used to accelerate searches for this automaton.

fn try_find(&self, input: &Input<'_>) -> Result<Option<Match>, MatchError>

Executes a non-overlapping search with this automaton using the given configuration.

fn try_find_overlapping( &self, input: &Input<'_>, state: &mut OverlappingState, ) -> Result<(), MatchError>

Executes a overlapping search with this automaton using the given configuration.

fn try_find_iter<'a, 'h>( &'a self, input: Input<'h>, ) -> Result<FindIter<'a, 'h, Self>, MatchError>

where Self: Sized,

Returns an iterator of non-overlapping matches with this automaton using the given configuration.

fn try_find_overlapping_iter<'a, 'h>( &'a self, input: Input<'h>, ) -> Result<FindOverlappingIter<'a, 'h, Self>, MatchError>

where Self: Sized,

Returns an iterator of overlapping matches with this automaton using the given configuration.

fn try_replace_all<B>( &self, haystack: &str, replace_with: &[B], ) -> Result<String, MatchError>

where Self: Sized, B: AsRef<str>,

Replaces all non-overlapping matches in haystack with strings from replace_with depending on the pattern that matched. The replace_with slice must have length equal to Automaton::patterns_len.

fn try_replace_all_bytes<B>( &self, haystack: &[u8], replace_with: &[B], ) -> Result<Vec<u8>, MatchError>

where Self: Sized, B: AsRef<[u8]>,

Replaces all non-overlapping matches in haystack with strings from replace_with depending on the pattern that matched. The replace_with slice must have length equal to Automaton::patterns_len.

fn try_replace_all_with<F>( &self, haystack: &str, dst: &mut String, replace_with: F, ) -> Result<(), MatchError>

where Self: Sized, F: FnMut(&Match, &str, &mut String) -> bool,

Replaces all non-overlapping matches in haystack by calling the replace_with closure given.

fn try_replace_all_with_bytes<F>( &self, haystack: &[u8], dst: &mut Vec<u8>, replace_with: F, ) -> Result<(), MatchError>

where Self: Sized, F: FnMut(&Match, &[u8], &mut Vec<u8>) -> bool,

Replaces all non-overlapping matches in haystack by calling the replace_with closure given.

fn try_stream_find_iter<'a, R: Read>( &'a self, rdr: R, ) -> Result<StreamFindIter<'a, Self, R>, MatchError>

where Self: Sized,

Returns an iterator of non-overlapping matches with this automaton from the stream given.

fn try_stream_replace_all<R, W, B>( &self, rdr: R, wtr: W, replace_with: &[B], ) -> Result<()>

where Self: Sized, R: Read, W: Write, B: AsRef<[u8]>,

Replaces all non-overlapping matches in rdr with strings from replace_with depending on the pattern that matched, and writes the result to wtr. The replace_with slice must have length equal to Automaton::patterns_len.

fn try_stream_replace_all_with<R, W, F>( &self, rdr: R, wtr: W, replace_with: F, ) -> Result<()>

where Self: Sized, R: Read, W: Write, F: FnMut(&Match, &[u8], &mut W) -> Result<()>,

Replaces all non-overlapping matches in rdr by calling the replace_with closure given and writing the result to wtr.

impl Clone for DFA

fn clone(&self) -> DFA

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for DFA

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.