// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/url_matcher/substring_set_matcher.h"
#include <algorithm>
#include <queue>
#include "base/logging.h"
#include "base/stl_util.h"
namespace url_matcher {
namespace {
// Compare StringPattern instances based on their string patterns.
bool ComparePatterns(const StringPattern* a, const StringPattern* b) {
return a->pattern() < b->pattern();
}
// Given the set of patterns, compute how many nodes will the corresponding
// Aho-Corasick tree have. Note that |patterns| need to be sorted.
uint32 TreeSize(const std::vector<const StringPattern*>& patterns) {
uint32 result = 1u; // 1 for the root node.
if (patterns.empty())
return result;
std::vector<const StringPattern*>::const_iterator last = patterns.begin();
std::vector<const StringPattern*>::const_iterator current = last + 1;
// For the first pattern, each letter is a label of an edge to a new node.
result += (*last)->pattern().size();
// For the subsequent patterns, only count the edges which were not counted
// yet. For this it suffices to test against the previous pattern, because the
// patterns are sorted.
for (; current != patterns.end(); ++last, ++current) {
const std::string& last_pattern = (*last)->pattern();
const std::string& current_pattern = (*current)->pattern();
const uint32 prefix_bound =
std::min(last_pattern.size(), current_pattern.size());
uint32 common_prefix = 0;
while (common_prefix < prefix_bound &&
last_pattern[common_prefix] == current_pattern[common_prefix])
++common_prefix;
result += current_pattern.size() - common_prefix;
}
return result;
}
} // namespace
//
// SubstringSetMatcher
//
SubstringSetMatcher::SubstringSetMatcher() {
RebuildAhoCorasickTree(SubstringPatternVector());
}
SubstringSetMatcher::~SubstringSetMatcher() {}
void SubstringSetMatcher::RegisterPatterns(
const std::vector<const StringPattern*>& patterns) {
RegisterAndUnregisterPatterns(patterns,
std::vector<const StringPattern*>());
}
void SubstringSetMatcher::UnregisterPatterns(
const std::vector<const StringPattern*>& patterns) {
RegisterAndUnregisterPatterns(std::vector<const StringPattern*>(),
patterns);
}
void SubstringSetMatcher::RegisterAndUnregisterPatterns(
const std::vector<const StringPattern*>& to_register,
const std::vector<const StringPattern*>& to_unregister) {
// Register patterns.
for (std::vector<const StringPattern*>::const_iterator i =
to_register.begin(); i != to_register.end(); ++i) {
DCHECK(patterns_.find((*i)->id()) == patterns_.end());
patterns_[(*i)->id()] = *i;
}
// Unregister patterns
for (std::vector<const StringPattern*>::const_iterator i =
to_unregister.begin(); i != to_unregister.end(); ++i) {
patterns_.erase((*i)->id());
}
// Now we compute the total number of tree nodes needed.
SubstringPatternVector sorted_patterns;
sorted_patterns.resize(patterns_.size());
size_t next = 0;
for (SubstringPatternMap::const_iterator i = patterns_.begin();
i != patterns_.end();
++i, ++next) {
sorted_patterns[next] = i->second;
}
std::sort(sorted_patterns.begin(), sorted_patterns.end(), ComparePatterns);
tree_.reserve(TreeSize(sorted_patterns));
RebuildAhoCorasickTree(sorted_patterns);
}
bool SubstringSetMatcher::Match(const std::string& text,
std::set<StringPattern::ID>* matches) const {
const size_t old_number_of_matches = matches->size();
// Handle patterns matching the empty string.
matches->insert(tree_[0].matches().begin(), tree_[0].matches().end());
uint32 current_node = 0;
for (std::string::const_iterator i = text.begin(); i != text.end(); ++i) {
uint32 edge_from_current = tree_[current_node].GetEdge(*i);
while (edge_from_current == AhoCorasickNode::kNoSuchEdge &&
current_node != 0) {
current_node = tree_[current_node].failure();
edge_from_current = tree_[current_node].GetEdge(*i);
}
if (edge_from_current != AhoCorasickNode::kNoSuchEdge) {
current_node = edge_from_current;
matches->insert(tree_[current_node].matches().begin(),
tree_[current_node].matches().end());
} else {
DCHECK_EQ(0u, current_node);
}
}
return old_number_of_matches != matches->size();
}
bool SubstringSetMatcher::IsEmpty() const {
// An empty tree consists of only the root node.
return patterns_.empty() && tree_.size() == 1u;
}
void SubstringSetMatcher::RebuildAhoCorasickTree(
const SubstringPatternVector& sorted_patterns) {
tree_.clear();
// Initialize root note of tree.
AhoCorasickNode root;
root.set_failure(0);
tree_.push_back(root);
// Insert all patterns.
for (SubstringPatternVector::const_iterator i = sorted_patterns.begin();
i != sorted_patterns.end();
++i) {
InsertPatternIntoAhoCorasickTree(*i);
}
CreateFailureEdges();
}
void SubstringSetMatcher::InsertPatternIntoAhoCorasickTree(
const StringPattern* pattern) {
const std::string& text = pattern->pattern();
const std::string::const_iterator text_end = text.end();
// Iterators on the tree and the text.
uint32 current_node = 0;
std::string::const_iterator i = text.begin();
// Follow existing paths for as long as possible.
while (i != text_end) {
uint32 edge_from_current = tree_[current_node].GetEdge(*i);
if (edge_from_current == AhoCorasickNode::kNoSuchEdge)
break;
current_node = edge_from_current;
++i;
}
// Create new nodes if necessary.
while (i != text_end) {
tree_.push_back(AhoCorasickNode());
tree_[current_node].SetEdge(*i, tree_.size() - 1);
current_node = tree_.size() - 1;
++i;
}
// Register match.
tree_[current_node].AddMatch(pattern->id());
}
void SubstringSetMatcher::CreateFailureEdges() {
typedef AhoCorasickNode::Edges Edges;
std::queue<uint32> queue;
AhoCorasickNode& root = tree_[0];
root.set_failure(0);
const Edges& root_edges = root.edges();
for (Edges::const_iterator e = root_edges.begin(); e != root_edges.end();
++e) {
const uint32& leads_to = e->second;
tree_[leads_to].set_failure(0);
queue.push(leads_to);
}
while (!queue.empty()) {
AhoCorasickNode& current_node = tree_[queue.front()];
queue.pop();
for (Edges::const_iterator e = current_node.edges().begin();
e != current_node.edges().end(); ++e) {
const char& edge_label = e->first;
const uint32& leads_to = e->second;
queue.push(leads_to);
uint32 failure = current_node.failure();
uint32 edge_from_failure = tree_[failure].GetEdge(edge_label);
while (edge_from_failure == AhoCorasickNode::kNoSuchEdge &&
failure != 0) {
failure = tree_[failure].failure();
edge_from_failure = tree_[failure].GetEdge(edge_label);
}
const uint32 follow_in_case_of_failure =
edge_from_failure != AhoCorasickNode::kNoSuchEdge
? edge_from_failure
: 0;
tree_[leads_to].set_failure(follow_in_case_of_failure);
tree_[leads_to].AddMatches(tree_[follow_in_case_of_failure].matches());
}
}
}
const uint32 SubstringSetMatcher::AhoCorasickNode::kNoSuchEdge = ~0;
SubstringSetMatcher::AhoCorasickNode::AhoCorasickNode()
: failure_(kNoSuchEdge) {}
SubstringSetMatcher::AhoCorasickNode::~AhoCorasickNode() {}
SubstringSetMatcher::AhoCorasickNode::AhoCorasickNode(
const SubstringSetMatcher::AhoCorasickNode& other)
: edges_(other.edges_),
failure_(other.failure_),
matches_(other.matches_) {}
SubstringSetMatcher::AhoCorasickNode&
SubstringSetMatcher::AhoCorasickNode::operator=(
const SubstringSetMatcher::AhoCorasickNode& other) {
edges_ = other.edges_;
failure_ = other.failure_;
matches_ = other.matches_;
return *this;
}
uint32 SubstringSetMatcher::AhoCorasickNode::GetEdge(char c) const {
Edges::const_iterator i = edges_.find(c);
return i == edges_.end() ? kNoSuchEdge : i->second;
}
void SubstringSetMatcher::AhoCorasickNode::SetEdge(char c, uint32 node) {
edges_[c] = node;
}
void SubstringSetMatcher::AhoCorasickNode::AddMatch(StringPattern::ID id) {
matches_.insert(id);
}
void SubstringSetMatcher::AhoCorasickNode::AddMatches(
const SubstringSetMatcher::AhoCorasickNode::Matches& matches) {
matches_.insert(matches.begin(), matches.end());
}
} // namespace url_matcher