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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.
use std::mem;
use derivative::Derivative;
use regex::{Regex, RegexBuilder};
use serde::{Deserialize, Serialize};
use crate::scalar::EvalError;
use lowertest::MzReflect;
// This implementation supports a couple of different methods of matching
// text against a SQL LIKE pattern.
//
// The most general approach is to convert the LIKE pattern into a
// regular expression and use the well-tested Regex library to perform the
// match. This works well with complex patterns and case-insensitive matches
// that are hard to get right.
//
// That said, regular expressions aren't that efficient. For most patterns
// we can do better using built-in string matching.
/// An object that can test whether a string matches a LIKE pattern.
#[derive(Debug, Clone, Deserialize, Serialize, Derivative, MzReflect)]
#[derivative(Eq, PartialEq, Ord, PartialOrd, Hash)]
pub struct Matcher {
pub pattern: String,
pub case_insensitive: bool,
#[derivative(
PartialEq = "ignore",
Hash = "ignore",
Ord = "ignore",
PartialOrd = "ignore"
)]
matcher_impl: MatcherImpl,
}
impl Matcher {
pub fn is_match(&self, text: &str) -> bool {
match &self.matcher_impl {
MatcherImpl::String(subpatterns) => is_match_subpatterns(subpatterns, text),
MatcherImpl::Regex(r) => r.is_match(text),
}
}
}
#[derive(Debug, Clone, Deserialize, Serialize, MzReflect)]
enum MatcherImpl {
String(Vec<Subpattern>),
Regex(#[serde(with = "serde_regex")] Regex),
}
/// Builds a Matcher that matches a SQL LIKE pattern.
pub fn compile(pattern: &str, case_insensitive: bool, escape: char) -> Result<Matcher, EvalError> {
// We would like to have a consistent, documented limit to the size of
// supported LIKE patterns. The real limiting factor is the number of states
// that can be handled by the Regex library. In testing, I was able to
// create an adversarial pattern "%a%b%c%d%e..." that started failing around
// 9 KiB, so we chose 8 KiB as the limit. This is consistent with limits
// set by other databases, like SQL Server.
// On the other hand, PostgreSQL does not have a documented limit.
if pattern.len() > 8 << 10 {
return Err(EvalError::LikePatternTooLong);
}
// TODO: Fall back to regex if the chain of sub-patterns is too long?
let matcher_impl = match case_insensitive {
false => MatcherImpl::String(build_subpatterns(pattern, escape)?),
true => MatcherImpl::Regex(build_regex(pattern, case_insensitive, escape)?),
};
Ok(Matcher {
pattern: String::from(pattern),
case_insensitive,
matcher_impl,
})
}
/// Builds a regular expression that matches the same strings as a SQL
/// LIKE pattern.
fn build_regex(pattern: &str, case_insensitive: bool, escape: char) -> Result<Regex, EvalError> {
// LIKE patterns always cover the whole string, so we anchor the regex on
// both sides. An underscore (`_`) in a LIKE pattern matches any single
// character and a percent sign (`%`) matches any sequence of zero or more
// characters, so we translate those operators to their equivalent regex
// operators, `.` and `.*`, respectively. Other characters match themselves
// and are copied directly, unless they have special meaning in a regex, in
// which case they are escaped in the regex with a backslash (`\`).
//
// Note that characters in LIKE patterns may also be escaped by preceding
// them with a backslash. This has no effect on most characters, but it
// removes the special meaning from the underscore and percent sign
// operators, and means that matching a literal backslash requires doubling
// the backslash.
let mut regex = String::from("^");
let mut in_escape = false;
for c in pattern.chars() {
match c {
c if !in_escape && c == escape => {
in_escape = true;
}
'_' if !in_escape => regex.push('.'),
'%' if !in_escape => regex.push_str(".*"),
c => {
if regex_syntax::is_meta_character(c) {
regex.push('\\');
}
regex.push(c);
in_escape = false;
}
}
}
regex.push('$');
if in_escape {
return Err(EvalError::UnterminatedLikeEscapeSequence);
}
let mut regex = RegexBuilder::new(®ex);
regex.dot_matches_new_line(true);
regex.case_insensitive(case_insensitive);
match regex.build() {
Ok(regex) => Ok(regex),
Err(regex::Error::CompiledTooBig(_)) => Err(EvalError::LikePatternTooLong),
Err(e) => Err(EvalError::Internal(format!(
"build_regex produced invalid regex: {}",
e
))),
}
}
// The algorithm below is based on the observation that any LIKE pattern can be
// decomposed into multiple parts:
// <PATTERN> := <SUB-PATTERN> (<SUB-PATTERN> ...)
// <SUB-PATTERN> := <WILDCARDS> <SUFFIX>
//
// The sub-patterns start with zero or more wildcard characters, eventually
// followed by (non-wildcard) literal characters. The last sub-pattern may
// have an empty SUFFIX.
//
// Example: the PATTERN "n__dl%" can be broken into the following parts:
// 1. SUB-PATTERN = <WILDCARDS ""> <SUFFIX "n">
// 2. SUB-PATTERN = <WILDCARDS "__"> <SUFFIX "dl">
// 3. SUB-PATTERN = <WILDCARDS "%"> <SUFFIX "">
//
// The WILDCARDS can be any combination of '_', which matches exactly 1 char,
// and '%' which matches zero or more chars. These wildcards can be simplified
// down to the (min, max) of characters they might consume:
// "" = (0, 0) // doesn't consume any characters
// "_" = (1, 1) // consumes exactly one
// "%" = (0, many) // zero or more
// These are additive, so:
// "_%" = (1, many)
// "__%__" = (4, many)
// "%%%_" = (1, many)
#[derive(Debug, Default, Clone, Deserialize, Serialize, MzReflect)]
struct Subpattern {
/// The minimum number of characters that can be consumed by the wildcard expression.
consume: usize,
/// Whether the wildcard expression can consume an arbitrary number of characters.
many: bool,
/// A string literal that is expected after the wildcards.
suffix: String,
}
fn is_match_subpatterns(subpatterns: &[Subpattern], mut text: &str) -> bool {
let (subpattern, subpatterns) = match subpatterns {
[] => return text.is_empty(),
[subpattern, subpatterns @ ..] => (subpattern, subpatterns),
};
// Go ahead and skip the minimum number of characters the sub-pattern consumes:
if subpattern.consume > 0 {
let mut chars = text.chars();
if chars.nth(subpattern.consume - 1).is_none() {
return false;
}
text = chars.as_str();
}
if subpattern.many {
// The sub-pattern might consume any number of characters, but we need to find
// where it terminates so we can match any subsequent sub-patterns. We do this
// by searching for the suffix string using str::find.
//
// We could investigate using a fancier substring search like Boyer-Moore:
// https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_string-search_algorithm
//
// .. but it's likely not worth it. It's slower for small strings,
// and doesn't really start outperforming the naive approach until
// haystack sizes of 1KB or greater. See benchmarking results from:
// https://github.com/killerswan/boyer-moore-search/blob/master/README.md
//
// Another approach that may be interesteing to look at is a
// hardware-optimized search:
// http://0x80.pl/articles/simd-strfind.html
if subpattern.suffix.len() == 0 {
// Nothing to find... This should only happen in the last sub-pattern.
assert!(
subpatterns.is_empty(),
"empty suffix in middle of a pattern"
);
return true;
}
// Use rfind so we perform a greedy capture, like Regex.
let mut found = text.rfind(&subpattern.suffix);
loop {
match found {
None => return false,
Some(offset) => {
let end = offset + subpattern.suffix.len();
if is_match_subpatterns(subpatterns, &text[end..]) {
return true;
}
// Didn't match, look for the next rfind.
if offset == 0 {
return false;
}
found = text[..(end - 1)].rfind(&subpattern.suffix);
}
}
}
}
// No string search needed, we just use a prefix match on rest.
if !text.starts_with(&subpattern.suffix) {
return false;
}
is_match_subpatterns(subpatterns, &text[subpattern.suffix.len()..])
}
/// Breaks a LIKE pattern into a chain of sub-patterns.
fn build_subpatterns(pattern: &str, escape: char) -> Result<Vec<Subpattern>, EvalError> {
let mut subpatterns = vec![];
let mut current = Subpattern::default();
let mut in_wildcard = true;
let mut in_escape = false;
for c in pattern.chars() {
match c {
c if !in_escape && c == escape => {
in_escape = true;
in_wildcard = false;
}
'_' if !in_escape => {
if !in_wildcard {
subpatterns.push(mem::take(&mut current));
in_wildcard = true;
}
current.consume += 1;
}
'%' if !in_escape => {
if !in_wildcard {
subpatterns.push(mem::take(&mut current));
in_wildcard = true;
}
current.many = true;
}
c => {
current.suffix.push(c);
in_escape = false;
in_wildcard = false;
}
}
}
if in_escape {
return Err(EvalError::UnterminatedLikeEscapeSequence);
}
subpatterns.push(mem::take(&mut current));
Ok(subpatterns)
}
// Unit Tests
//
// Most of the unit tests for LIKE and ILIKE can be found in:
// test/sqllogictest/cockroach/like.slt
// These tests are here as a convenient place to run quick tests while
// actively working on changes to the implementation. Make sure you
// run the full test suite before submitting any changes.
#[cfg(test)]
mod test {
use super::*;
use ore::str::StrExt;
#[test]
fn test_like() {
struct Input<'a> {
haystack: &'a str,
matches: bool,
}
let input = |haystack, matches| Input { haystack, matches };
struct Pattern<'a> {
needle: &'a str,
case_insensitive: bool,
escape: char,
inputs: Vec<Input<'a>>,
}
let test_cases = vec![
Pattern {
needle: "ban%na!",
case_insensitive: false,
escape: '\\',
inputs: vec![input("banana!", true)],
},
Pattern {
needle: "ban%na!",
case_insensitive: false,
escape: 'n',
inputs: vec![input("banana!", false), input("ba%a!", true)],
},
Pattern {
needle: "ban%%%na!",
case_insensitive: false,
escape: '%',
inputs: vec![input("banana!", false), input("ban%na!", true)],
},
Pattern {
needle: "foo",
case_insensitive: true,
escape: '\\',
inputs: vec![
input("", false),
input("f", false),
input("fo", false),
input("foo", true),
input("FOO", true),
input("Foo", true),
input("fOO", true),
input("food", false),
],
},
];
for tc in test_cases {
let matcher = compile(tc.needle, tc.case_insensitive, tc.escape).unwrap();
for input in tc.inputs {
let actual = matcher.is_match(input.haystack);
assert!(
actual == input.matches,
"{} {} {}:\n\tactual: {}\n\texpected: {}\n",
input.haystack.quoted(),
match tc.case_insensitive {
true => "ILIKE",
false => "LIKE",
},
tc.needle.quoted(),
actual,
input.matches,
);
}
}
}
}