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|
use aho_corasick::{AhoCorasick, AhoCorasickBuilder, MatchKind};
use grep_matcher::{Matcher, Match, NoError};
use regex_syntax::hir::Hir;
use error::Error;
use matcher::RegexCaptures;
/// A matcher for an alternation of literals.
///
/// Ideally, this optimization would be pushed down into the regex engine, but
/// making this work correctly there would require quite a bit of refactoring.
/// Moreover, doing it one layer above lets us do thing like, "if we
/// specifically only want to search for literals, then don't bother with
/// regex parsing at all."
#[derive(Clone, Debug)]
pub struct MultiLiteralMatcher {
/// The Aho-Corasick automaton.
ac: AhoCorasick,
}
impl MultiLiteralMatcher {
/// Create a new multi-literal matcher from the given literals.
pub fn new<B: AsRef<[u8]>>(
literals: &[B],
) -> Result<MultiLiteralMatcher, Error> {
let ac = AhoCorasickBuilder::new()
.match_kind(MatchKind::LeftmostFirst)
.auto_configure(literals)
.build_with_size::<usize, _, _>(literals)
.map_err(Error::regex)?;
Ok(MultiLiteralMatcher { ac })
}
}
impl Matcher for MultiLiteralMatcher {
type Captures = RegexCaptures;
type Error = NoError;
fn find_at(
&self,
haystack: &[u8],
at: usize,
) -> Result<Option<Match>, NoError> {
match self.ac.find(&haystack[at..]) {
None => Ok(None),
Some(m) => Ok(Some(Match::new(at + m.start(), at + m.end()))),
}
}
fn new_captures(&self) -> Result<RegexCaptures, NoError> {
Ok(RegexCaptures::simple())
}
fn capture_count(&self) -> usize {
1
}
fn capture_index(&self, _: &str) -> Option<usize> {
None
}
fn captures_at(
&self,
haystack: &[u8],
at: usize,
caps: &mut RegexCaptures,
) -> Result<bool, NoError> {
caps.set_simple(None);
let mat = self.find_at(haystack, at)?;
caps.set_simple(mat);
Ok(mat.is_some())
}
// We specifically do not implement other methods like find_iter. Namely,
// the iter methods are guaranteed to be correct by virtue of implementing
// find_at above.
}
/// Alternation literals checks if the given HIR is a simple alternation of
/// literals, and if so, returns them. Otherwise, this returns None.
pub fn alternation_literals(expr: &Hir) -> Option<Vec<Vec<u8>>> {
use regex_syntax::hir::{HirKind, Literal};
// This is pretty hacky, but basically, if `is_alternation_literal` is
// true, then we can make several assumptions about the structure of our
// HIR. This is what justifies the `unreachable!` statements below.
if !expr.is_alternation_literal() {
return None;
}
let alts = match *expr.kind() {
HirKind::Alternation(ref alts) => alts,
_ => return None, // one literal isn't worth it
};
let extendlit = |lit: &Literal, dst: &mut Vec<u8>| {
match *lit {
Literal::Unicode(c) => {
let mut buf = [0; 4];
dst.extend_from_slice(c.encode_utf8(&mut buf).as_bytes());
}
Literal::Byte(b) => {
dst.push(b);
}
}
};
let mut lits = vec![];
for alt in alts {
let mut lit = vec![];
match *alt.kind() {
HirKind::Empty => {}
HirKind::Literal(ref x) => extendlit(x, &mut lit),
HirKind::Concat(ref exprs) => {
for e in exprs {
match *e.kind() {
HirKind::Literal(ref x) => extendlit(x, &mut lit),
_ => unreachable!("expected literal, got {:?}", e),
}
}
}
_ => unreachable!("expected literal or concat, got {:?}", alt),
}
lits.push(lit);
}
Some(lits)
}
|
