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use ahocorasick::MatchKind; use prefilter::{Prefilter, PrefilterState}; use state_id::{StateID, dead_id, fail_id}; use Match; // NOTE: This trait was essentially copied from regex-automata, with some // wording changed since we use this trait for NFAs in addition to DFAs in this // crate. Additionally, we do not export this trait. It's only used internally // to reduce code duplication. The regex-automata crate needs to expose it // because its Regex type is generic over implementations of this trait. In // this crate, we can encapsulate everything behind the AhoCorasick type. /// A trait describing the interface of an Aho-Corasick finite state machine. /// /// Every automaton has exactly one fail state, one dead state and exactly one /// start state. Generally, these correspond to the first, second and third /// states, respectively. The failure state is always treated as a sentinel. /// That is, no correct Aho-Corasick automaton will ever transition into the /// fail state. The dead state, however, can be transitioned into, but only /// when leftmost-first or leftmost-longest match semantics are enabled and /// only when at least one match has been observed. /// /// Every automaton also has one or more match states, such that /// `Automaton::is_match_state_unchecked(id)` returns `true` if and only if /// `id` corresponds to a match state. pub trait Automaton { /// The representation used for state identifiers in this automaton. /// /// Typically, this is one of `u8`, `u16`, `u32`, `u64` or `usize`. type ID: StateID; /// The type of matching that should be done. fn match_kind(&self) -> &MatchKind; /// An optional prefilter for quickly skipping to the next candidate match. /// A prefilter must report at least every match, although it may report /// positions that do not correspond to a match. That is, it must not allow /// false negatives, but can allow false positives. /// /// Currently, a prefilter only runs when the automaton is in the start /// state. That is, the position reported by a prefilter should always /// correspond to the start of a potential match. fn prefilter(&self) -> Option<&Prefilter>; /// Return the identifier of this automaton's start state. fn start_state(&self) -> Self::ID; /// Returns true if and only if the given state identifier refers to a /// valid state. fn is_valid(&self, id: Self::ID) -> bool; /// Returns true if and only if the given identifier corresponds to a match /// state. /// /// The state ID given must be valid, or else implementors may panic. fn is_match_state(&self, id: Self::ID) -> bool; /// Returns true if and only if the given identifier corresponds to a state /// that is either the dead state or a match state. /// /// Depending on the implementation of the automaton, this routine can /// be used to save a branch in the core matching loop. Nevertheless, /// `is_match_state(id) || id == dead_id()` is always a valid /// implementation. Indeed, this is the default implementation. /// /// The state ID given must be valid, or else implementors may panic. fn is_match_or_dead_state(&self, id: Self::ID) -> bool { id == dead_id() || self.is_match_state(id) } /// If the given state is a match state, return the match corresponding /// to the given match index. `end` must be the ending position of the /// detected match. If no match exists or if `match_index` exceeds the /// number of matches in this state, then `None` is returned. /// /// The state ID given must be valid, or else implementors may panic. /// /// If the given state ID is correct and if the `match_index` is less than /// the number of matches for that state, then this is guaranteed to return /// a match. fn get_match( &self, id: Self::ID, match_index: usize, end: usize, ) -> Option<Match>; /// Returns the number of matches for the given state. If the given state /// is not a match state, then this returns 0. /// /// The state ID given must be valid, or else implementors must panic. fn match_count(&self, id: Self::ID) -> usize; /// Given the current state that this automaton is in and the next input /// byte, this method returns the identifier of the next state. The /// identifier returned must always be valid and may never correspond to /// the fail state. The returned identifier may, however, point to the /// dead state. /// /// This is not safe so that implementors may look up the next state /// without memory safety checks such as bounds checks. As such, callers /// must ensure that the given identifier corresponds to a valid automaton /// state. Implementors must, in turn, ensure that this routine is safe for /// all valid state identifiers and for all possible `u8` values. unsafe fn next_state_unchecked( &self, current: Self::ID, input: u8, ) -> Self::ID; /// Like next_state_unchecked, but debug_asserts that the underlying /// implementation never returns a `fail_id()` for the next state. unsafe fn next_state_unchecked_no_fail( &self, current: Self::ID, input: u8, ) -> Self::ID { let next = self.next_state_unchecked(current, input); // We should never see a transition to the failure state. debug_assert!( next != fail_id(), "automaton should never return fail_id for next state" ); next } /// Execute a search using standard match semantics. /// /// This can be used even when the automaton was constructed with leftmost /// match semantics when you want to find the earliest possible match. This /// can also be used as part of an overlapping search implementation. /// /// N.B. This does not report a match if `state_id` is given as a matching /// state. As such, this should not be used directly. #[inline(always)] fn standard_find_at( &self, prestate: &mut PrefilterState, haystack: &[u8], at: usize, state_id: &mut Self::ID, ) -> Option<Match> { if let Some(pre) = self.prefilter() { self.standard_find_at_imp( prestate, Some(pre), haystack, at, state_id, ) } else { self.standard_find_at_imp( prestate, None, haystack, at, state_id, ) } } // It's important for this to always be inlined. Namely, it's only caller // is standard_find_at, and the inlining should remove the case analysis // for prefilter scanning when there is no prefilter available. #[inline(always)] fn standard_find_at_imp( &self, prestate: &mut PrefilterState, prefilter: Option<&Prefilter>, haystack: &[u8], at: usize, state_id: &mut Self::ID, ) -> Option<Match> { // This is necessary for guaranteeing a safe API, since we use the // state ID below in a function that exhibits UB if called with an // invalid state ID. assert!( self.is_valid(*state_id), "{} is not a valid state ID", state_id.to_usize() ); unsafe { let start = haystack.as_ptr(); let end = haystack[haystack.len()..].as_ptr(); let mut ptr = haystack[at..].as_ptr(); while ptr < end { if let Some(pre) = prefilter { if prestate.is_effective() && *state_id == self.start_state() { let at = ptr as usize - start as usize; match pre.next_candidate(haystack, at) { None => return None, Some(i) => { prestate.update(i - at); ptr = start.offset(i as isize); } } } } // SAFETY: next_state is safe for all possible u8 values, // so the only thing we're concerned about is the validity // of `state_id`. `state_id` either comes from the caller // (in which case, we assert above that it is valid), or it // comes from the return value of next_state, which is also // guaranteed to be valid. *state_id = self.next_state_unchecked_no_fail(*state_id, *ptr); ptr = ptr.offset(1); // This routine always quits immediately after seeing a // match, and since dead states can only come after seeing // a match, seeing a dead state here is impossible. debug_assert!( *state_id != dead_id(), "standard find should never see a dead state" ); let end = ptr as usize - start as usize; if let Some(m) = self.get_match(*state_id, 0, end) { return Some(m); } } None } } /// Execute a search using leftmost (either first or longest) match /// semantics. /// /// The principle difference between searching with standard semantics and /// searching with leftmost semantics is that leftmost searching will /// continue searching even after a match has been found. Once a match /// is found, the search does not stop until either the haystack has been /// exhausted or a dead state is observed in the automaton. (Dead states /// only exist in automatons constructed with leftmost semantics.) That is, /// we rely on the construction of the automaton to tell us when to quit. #[inline(never)] fn leftmost_find_at( &self, prestate: &mut PrefilterState, haystack: &[u8], at: usize, state_id: &mut Self::ID, ) -> Option<Match> { if let Some(pre) = self.prefilter() { self.leftmost_find_at_imp( prestate, Some(pre), haystack, at, state_id, ) } else { self.leftmost_find_at_imp( prestate, None, haystack, at, state_id, ) } } // It's important for this to always be inlined. Namely, it's only caller // is leftmost_find_at, and the inlining should remove the case analysis // for prefilter scanning when there is no prefilter available. #[inline(always)] fn leftmost_find_at_imp( &self, prestate: &mut PrefilterState, prefilter: Option<&Prefilter>, haystack: &[u8], at: usize, state_id: &mut Self::ID, ) -> Option<Match> { debug_assert!(self.match_kind().is_leftmost()); // This is necessary for guaranteeing a safe API, since we use the // state ID below in a function that exhibits UB if called with an // invalid state ID. assert!( self.is_valid(*state_id), "{} is not a valid state ID", state_id.to_usize() ); unsafe { let start = haystack.as_ptr(); let end = haystack[haystack.len()..].as_ptr(); let mut ptr = haystack[at..].as_ptr(); let mut last_match = self.get_match(*state_id, 0, at); while ptr < end { if let Some(pre) = prefilter { if prestate.is_effective() && *state_id == self.start_state() { let at = ptr as usize - start as usize; match pre.next_candidate(haystack, at) { None => return None, Some(i) => { prestate.update(i - at); ptr = start.offset(i as isize); } } } } // SAFETY: next_state is safe for all possible u8 values, // so the only thing we're concerned about is the validity // of `state_id`. `state_id` either comes from the caller // (in which case, we assert above that it is valid), or it // comes from the return value of next_state, which is also // guaranteed to be valid. *state_id = self.next_state_unchecked_no_fail(*state_id, *ptr); ptr = ptr.offset(1); if self.is_match_or_dead_state(*state_id) { if *state_id == dead_id() { // The only way to enter into a dead state is if a // match has been found, so we assert as much. This // is different from normal automata, where you might // enter a dead state if you know a subsequent match // will never be found (regardless of whether a match // has already been found). For Aho-Corasick, it is // built so that we can match at any position, so the // possibility of a match always exists. debug_assert!( last_match.is_some(), "failure state should only be seen after match" ); return last_match; } let end = ptr as usize - start as usize; last_match = self.get_match(*state_id, 0, end); } } last_match } } /// Execute an overlapping search. /// /// When executing an overlapping match, the previous state ID in addition /// to the previous match index should be given. If there are more matches /// at the given state, then the match is reported and the given index is /// incremented. #[inline(always)] fn overlapping_find_at( &self, prestate: &mut PrefilterState, haystack: &[u8], at: usize, state_id: &mut Self::ID, match_index: &mut usize, ) -> Option<Match> { let match_count = self.match_count(*state_id); if *match_index < match_count { // This is guaranteed to return a match since // match_index < match_count. let result = self.get_match( *state_id, *match_index, at, ); debug_assert!(result.is_some(), "must be a match"); *match_index += 1; return result; } *match_index = 0; match self.standard_find_at(prestate, haystack, at, state_id) { None => None, Some(m) => { *match_index = 1; Some(m) } } } /// Return the earliest match found. This returns as soon as we know that /// we have a match. As such, this does not necessarily correspond to the /// leftmost starting match, but rather, the leftmost position at which a /// match ends. #[inline(always)] fn earliest_find_at( &self, prestate: &mut PrefilterState, haystack: &[u8], at: usize, state_id: &mut Self::ID, ) -> Option<Match> { if *state_id == self.start_state() { if let Some(m) = self.get_match(*state_id, 0, at) { return Some(m); } } self.standard_find_at(prestate, haystack, at, state_id) } /// A convenience function for finding the next match according to the /// match semantics of this automaton. For standard match semantics, this /// finds the earliest match. Otherwise, the leftmost match is found. #[inline(always)] fn find_at( &self, prestate: &mut PrefilterState, haystack: &[u8], at: usize, state_id: &mut Self::ID, ) -> Option<Match> { match *self.match_kind() { MatchKind::Standard => { self.earliest_find_at(prestate, haystack, at, state_id) } MatchKind::LeftmostFirst | MatchKind::LeftmostLongest => { self.leftmost_find_at(prestate, haystack, at, state_id) } MatchKind::__Nonexhaustive => unreachable!(), } } }