[subresource_filter] Replace KMP by std::search.

components/subresource_filter/core/common/url_pattern.cc

 // Copyright 2016 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.
 
+// The matching logic distinguishes between the terms URL pattern and
+// subpattern. A URL pattern usually stands for the full thing, e.g.
+// "example.com^*path*par=val^", whereas subpattern denotes a maximal substring
+// of a pattern not containing the wildcard '*' character. For the example above
+// the subpatterns are: "example.com^", "path" and "par=val^".
+//
+// The separator placeholder '^' symbol is used in subpatterns to match any
+// separator character, which is any ASCII symbol except letters, digits, and
+// the following: '_', '-', '.', '%'. Note that the separator placeholder
+// character '^' is itself a separator, as well as '\0'.
+
 #include "components/subresource_filter/core/common/url_pattern.h"
 
+#include <stddef.h>
+
+#include <ostream>
+
+#include "base/logging.h"
 #include "components/subresource_filter/core/common/flat/rules_generated.h"
+#include "components/subresource_filter/core/common/fuzzy_pattern_matching.h"
+#include "components/subresource_filter/core/common/string_splitter.h"
+#include "url/gurl.h"
+#include "url/third_party/mozilla/url_parse.h"
 
 namespace subresource_filter {
 
 namespace {
 
+class IsWildcard {
+ public:
+  bool operator()(char c) const { return c == '*'; }
+};
+
 proto::UrlPatternType ConvertUrlPatternType(flat::UrlPatternType type) {
   switch (type) {
     case flat::UrlPatternType_SUBSTRING:
       return proto::URL_PATTERN_TYPE_SUBSTRING;
     case flat::UrlPatternType_WILDCARDED:
       return proto::URL_PATTERN_TYPE_WILDCARDED;
     case flat::UrlPatternType_REGEXP:
       return proto::URL_PATTERN_TYPE_REGEXP;
     default:
       return proto::URL_PATTERN_TYPE_UNSPECIFIED;
@@ skipping 11 matching lines @@
     default:
       return proto::ANCHOR_TYPE_UNSPECIFIED;
   }
 }
 
 base::StringPiece ConvertString(const flatbuffers::String* string) {
   return string ? base::StringPiece(string->data(), string->size())
                 : base::StringPiece();
 }
 
+// Returns whether |position| within the |url| belongs to its |host| component
+// and corresponds to the beginning of a (sub-)domain.
+inline bool IsSubdomainAnchored(base::StringPiece url,
+                                url::Component host,
+                                size_t position) {
+  DCHECK_LE(position, url.size());
+  const size_t host_begin = static_cast<size_t>(host.begin);
+  const size_t host_end = static_cast<size_t>(host.end());
+  DCHECK_LE(host_end, url.size());
+
+  return position == host_begin ||
+         (position > host_begin && position <= host_end &&
+          url[position - 1] == '.');
+}
+
+// Returns the position of the leftmost occurrence of a |subpattern| in the
+// |text|, starting |from| a certain position. If the |subpattern| has separator
+// placeholders, searches for a fuzzy occurrence.
+size_t FindSubpattern(base::StringPiece text,
+                      base::StringPiece subpattern,
+                      size_t from = 0) {
+  const bool is_fuzzy =
+      (subpattern.find(kSeparatorPlaceholder) != base::StringPiece::npos);
+  return is_fuzzy ? FindFuzzy(text, subpattern, from)
+                  : text.find(subpattern, from);
+}
+
+// Same as FindSubpattern(url, subpattern), but searches for an occurrence that
+// starts at the beginning of a (sub-)domain within the url's |host| component.
+size_t FindSubdomainAnchoredSubpattern(base::StringPiece url,
+                                       url::Component host,
+                                       base::StringPiece subpattern) {
+  const bool is_fuzzy =
+      (subpattern.find(kSeparatorPlaceholder) != base::StringPiece::npos);
+
+  for (size_t position = 0; position <= url.size(); ++position) {
+    position = is_fuzzy ? FindFuzzy(url, subpattern, position)
+                        : url.find(subpattern, position);
+    if (position == base::StringPiece::npos ||

[engedy, 2017/04/05 13:41:33]

Shouldn't we return npos in case the first term is true?

[pkalinnikov, 2017/04/05 13:48:47]

If the first term is true, then "return position" returns npos.

[engedy, 2017/04/05 13:55:40]

Oh, of course. :)

+        IsSubdomainAnchored(url, host, position)) {
+      return position;
+    }
+  }
+  return base::StringPiece::npos;
+}
+
 }  // namespace
 
 UrlPattern::UrlPattern() = default;
 
 UrlPattern::UrlPattern(base::StringPiece url_pattern,
                        proto::UrlPatternType type)
-    : type(type), url_pattern(url_pattern) {}
+    : type_(type), url_pattern_(url_pattern) {}
 
 UrlPattern::UrlPattern(base::StringPiece url_pattern,
                        proto::AnchorType anchor_left,
                        proto::AnchorType anchor_right)
-    : type(proto::URL_PATTERN_TYPE_WILDCARDED),
-      url_pattern(url_pattern),
-      anchor_left(anchor_left),
-      anchor_right(anchor_right) {}
+    : type_(proto::URL_PATTERN_TYPE_WILDCARDED),
+      url_pattern_(url_pattern),
+      anchor_left_(anchor_left),
+      anchor_right_(anchor_right) {}
 
 UrlPattern::UrlPattern(const flat::UrlRule& rule)
-    : type(ConvertUrlPatternType(rule.url_pattern_type())),
-      url_pattern(ConvertString(rule.url_pattern())),
-      anchor_left(ConvertAnchorType(rule.anchor_left())),
-      anchor_right(ConvertAnchorType(rule.anchor_right())),
-      match_case(!!(rule.options() & flat::OptionFlag_IS_MATCH_CASE)) {}
+    : type_(ConvertUrlPatternType(rule.url_pattern_type())),
+      url_pattern_(ConvertString(rule.url_pattern())),
+      anchor_left_(ConvertAnchorType(rule.anchor_left())),
+      anchor_right_(ConvertAnchorType(rule.anchor_right())),
+      match_case_(!!(rule.options() & flat::OptionFlag_IS_MATCH_CASE)) {}
 
 UrlPattern::UrlPattern(const proto::UrlRule& rule)
-    : type(rule.url_pattern_type()),
-      url_pattern(rule.url_pattern()),
-      anchor_left(rule.anchor_left()),
-      anchor_right(rule.anchor_right()),
-      match_case(rule.match_case()) {}
+    : type_(rule.url_pattern_type()),
+      url_pattern_(rule.url_pattern()),
+      anchor_left_(rule.anchor_left()),
+      anchor_right_(rule.anchor_right()),
+      match_case_(rule.match_case()) {}
 
 UrlPattern::~UrlPattern() = default;
 
+bool UrlPattern::MatchesUrl(const GURL& url) const {
+  // Note: Empty domains are also invalid.
+  DCHECK(url.is_valid());
+  DCHECK(type_ == proto::URL_PATTERN_TYPE_SUBSTRING ||
+         proto::URL_PATTERN_TYPE_WILDCARDED);
+
+  StringSplitter<IsWildcard> subpatterns(url_pattern_);
+  auto subpattern_it = subpatterns.begin();
+  auto subpattern_end = subpatterns.end();
+
+  if (subpattern_it == subpattern_end) {
+    return anchor_left_ == proto::ANCHOR_TYPE_NONE ||
+           anchor_right_ == proto::ANCHOR_TYPE_NONE;
+  }
+
+  const base::StringPiece spec = url.possibly_invalid_spec();
+  const url::Component host_part = url.parsed_for_possibly_invalid_spec().host;
+  DCHECK(!spec.empty());
+
+  base::StringPiece subpattern = *subpattern_it;
+  ++subpattern_it;
+
+  // If there is only one |subpattern|, and it has a right anchor, then simply
+  // check that it is a suffix of the |spec|, and the left anchor is fulfilled.
+  if (subpattern_it == subpattern_end &&
+      anchor_right_ == proto::ANCHOR_TYPE_BOUNDARY) {
+    if (!EndsWithFuzzy(spec, subpattern))
+      return false;
+    if (anchor_left_ == proto::ANCHOR_TYPE_BOUNDARY)
+      return spec.size() == subpattern.size();
+    if (anchor_left_ == proto::ANCHOR_TYPE_SUBDOMAIN) {
+      DCHECK_LE(subpattern.size(), spec.size());
+      return url.has_host() &&
+             IsSubdomainAnchored(spec, host_part,
+                                 spec.size() - subpattern.size());
+    }
+    return true;
+  }
+
+  // Otherwise, the first |subpattern| does not have to be a suffix. But it
+  // still can have a left anchor. Check and handle that.
+  base::StringPiece text = spec;
+  if (anchor_left_ == proto::ANCHOR_TYPE_BOUNDARY) {
+    if (!StartsWithFuzzy(spec, subpattern))
+      return false;
+    if (subpattern_it == subpattern_end) {
+      DCHECK_EQ(anchor_right_, proto::ANCHOR_TYPE_NONE);
+      return true;
+    }
+    text.remove_prefix(subpattern.size());
+  } else if (anchor_left_ == proto::ANCHOR_TYPE_SUBDOMAIN) {
+    if (!url.has_host())
+      return false;
+    const size_t match_begin =
+        FindSubdomainAnchoredSubpattern(spec, host_part, subpattern);
+    if (match_begin == base::StringPiece::npos)
+      return false;
+    if (subpattern_it == subpattern_end) {
+      DCHECK_EQ(anchor_right_, proto::ANCHOR_TYPE_NONE);
+      return true;
+    }
+    text.remove_prefix(match_begin + subpattern.size());
+  } else {
+    DCHECK_EQ(anchor_left_, proto::ANCHOR_TYPE_NONE);
+    // Get back to the initial |subpattern|, process it in the loop below.
+    subpattern_it = subpatterns.begin();
+  }
+
+  // Consecutively find all the remaining subpatterns in the |text|. If the
+  // pattern has a right anchor, don't search for the last subpattern, but
+  // instead check that it is a suffix of the |text|.
+  while (subpattern_it != subpattern_end) {
+    subpattern = *subpattern_it;
+    DCHECK(!subpattern.empty());
+
+    if (++subpattern_it == subpattern_end &&
+        anchor_right_ == proto::ANCHOR_TYPE_BOUNDARY) {
+      break;
+    }
+
+    const size_t match_position = FindSubpattern(text, subpattern);
+    if (match_position == base::StringPiece::npos)
+      return false;
+    text.remove_prefix(match_position + subpattern.size());
+  }
+
+  return anchor_right_ != proto::ANCHOR_TYPE_BOUNDARY ||
+         EndsWithFuzzy(text, subpattern);
+}
+
+std::ostream& operator<<(std::ostream& out, const UrlPattern& pattern) {
+  // Note: Each fall-through in this switch is intentional.
+  switch (pattern.anchor_left()) {
+    case proto::ANCHOR_TYPE_SUBDOMAIN:
+      out << '|';
+    case proto::ANCHOR_TYPE_BOUNDARY:
+      out << '|';
+    default:
+      break;
+  }
+  out << pattern.url_pattern();
+  if (pattern.anchor_right() == proto::ANCHOR_TYPE_BOUNDARY)
+    out << '|';
+  if (pattern.match_case())
+    out << "$match-case";
+
+  return out;
+}
+
 }  // namespace subresource_filter