Issue 5870 - Implement the new ElemHideEmulation filter type

compiled/filter/ElemHideBase.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include <cstring>
 
 #include "ElemHideBase.h"
 #include "../StringScanner.h"
+#include "../Utils.h"
+
+ABP_NS_USING
 
 namespace
 {
   void NormalizeWhitespace(DependentString& text, String::size_type& domainsEnd,
       String::size_type& selectorStart)
   {
     // For element hiding filters we only want to remove spaces preceding the
     // selector part. The positions we've determined already have to be adjusted
     // accordingly.
 
@@ skipping 11 matching lines @@
       if (pos < selectorStart && text[pos] == ' ')
         delta++;
       else
         text[pos - delta] = text[pos];
     }
     selectorStart -= delta;
 
     text.reset(text, 0, len - delta);
   }
 
-  // Convert filter from the old syntax to the new.
-  OwnedString ConvertFilter(const String& text, String::size_type at)

[sergei, 2018/01/30 19:02:40]

I'm not sure that we need to build OwnedString for each filter, perhaps the
contructor of base classes should just support OwnedString&&. What do you think
about it? If we decide to add support of OwnedString&& in the Filter constructor
then IMO it should be in a separate commit and with the issue.

[hub, 2018/01/30 22:53:13]

Since we copy the string at the end in the Filter constructor we could have
chain of constructors that take an OwnedString&& so that ConvertFilter does the
copy or the conversion.

-  {
-    static const auto propsSelector = u"[-abp-properties="_str;
-    static const auto newPropsSelector = u":-abp-properties("_str;
-    auto selectorPos = text.find(propsSelector, at);
-    if (selectorPos != text.npos)
-    {
-      auto length = text.length();
-      auto properties = selectorPos + propsSelector.length();
-      String::value_type quote = 0;
-      bool escape = false;
-      String::size_type removed = 0; // how many chars we remove
-      String::size_type end = properties;
-      String::size_type quote_start = 0;
-      String::size_type quote_end = 0;
-      for (auto index = properties;
-           index < length && end == properties; index++)
-      {
-        if (escape)
-        {
-          escape = false;
-          continue;
-        }
-
-        auto c = text[index];
-        switch (c)
-        {
-        case '\\':
-          escape = true;
-          break;
-        case '"':
-        case '\'':
-          if (quote == 0)
-          {
-            quote = c;
-            quote_start = index + 1;
-          }
-          else if (quote == c)
-          {
-            // end of quoted.
-            quote = 0;
-            removed += 2;
-            quote_end = index;
-          }
-          break;
-        case ']':
-          if (quote == 0)
-            end = index + 1; // end of properties (after ])
-          break;
-        default:
-          break;
-        }
-      }
-
-      if (quote != 0)
-        quote_end = end - 1;
-      else if (quote_end <= quote_start)
-      {
-        // we likely didn't find a quoted content so we just take it as is.
-        quote_start = properties;
-        quote_end = end - 1;
-      }
-
-      OwnedString converted(length - removed);
-      String::size_type offset = 0;
-      std::memcpy(converted.data(), text.data(),
-                  selectorPos * sizeof(String::value_type));
-      offset += selectorPos;
-
-      std::memcpy(converted.data() + offset, newPropsSelector.data(),
-                  newPropsSelector.length() * sizeof(String::value_type));
-      offset += newPropsSelector.length();
-
-      std::memcpy(converted.data() + offset, text.data() + quote_start,
-                  (quote_end - quote_start) * sizeof(String::value_type));
-      offset += quote_end - quote_start;
-
-      std::memcpy(converted.data() + offset, u")", sizeof(String::value_type));
-      offset++;
-
-      std::memcpy(converted.data() + offset, text.data() + end,
-                  (length - end) * sizeof(String::value_type));
-      offset += (length - end) * sizeof(String::value_type);
-
-      return converted;
-    }
-
-    return OwnedString(text);
-  }
+  static constexpr String::value_type ELEM_HIDE_DELIMITER[] = u"##";
+  static constexpr String::size_type ELEM_HIDE_DELIMITER_LEN = str_length_of(ELEM_HIDE_DELIMITER);
+
+  static constexpr String::value_type ELEM_HIDE_EMULATION_DELIMITER[] = u"#?#";
+  static constexpr String::size_type ELEM_HIDE_EMULATION_DELIMITER_LEN = str_length_of(ELEM_HIDE_EMULATION_DELIMITER);
+
+  static constexpr String::value_type OLD_PROPS_SELECTOR[] = u"[-abp-properties=";
+  static constexpr String::size_type OLD_PROPS_SELECTOR_LEN = str_length_of(OLD_PROPS_SELECTOR);
+
+  static constexpr String::value_type PROPS_SELECTOR[] = u":-abp-properties(";
+  static constexpr String::size_type PROPS_SELECTOR_LEN = str_length_of(PROPS_SELECTOR);
 }
 
 ElemHideBase::ElemHideBase(Type type, const String& text, const ElemHideData& data)
-    : ActiveFilter(type, ConvertFilter(text, data.mSelectorStart), false),
-      mData(data)
+    : ActiveFilter(type, text, false), mData(data)
 {
   if (mData.HasDomains())
     ParseDomains(mData.GetDomainsSource(mText), u',');
 }
 
-Filter::Type ElemHideBase::Parse(DependentString& text, ElemHideData& data)
-{
+Filter::Type ElemHideBase::Parse(DependentString& text, ElemHideData& data, bool& needConversion)
+{
+  needConversion = false;
+
   StringScanner scanner(text);
 
   // Domains part
   bool seenSpaces = false;
   while (!scanner.done())
   {
     String::value_type next = scanner.next();
     if (next == u'#')
     {
       data.mDomainsEnd = scanner.position();
@@ skipping 14 matching lines @@
         break;
     }
   }
 
   seenSpaces |= scanner.skip(u' ');
   bool emulation = false;
   bool exception = scanner.skipOne(u'@');
   if (exception)
     seenSpaces |= scanner.skip(u' ');
   else
     emulation = scanner.skipOne(u'?');

[sergei, 2018/01/30 19:02:40]

It's actually different from "Filter.elemhideRegExp =
/^([^/*|@"!]*?)#([@?])?#(.+)$/;"
https://github.com/adblockplus/adblockpluscore/blob/ec65d0a80470fc2eacd9ef83e...
where it allows only one character @ or ? but here we allow "#@?#". I think it
should be fixed.

[hub, 2018/01/30 22:53:13]

#@?# is "rejected". actually according to issue 6234 it is made to a blocking
filter. But this is correct. Same as the regexp.

Adding a test.

 
   String::value_type next = scanner.next();
   if (next != u'#')
     return Type::UNKNOWN;
 
   // Selector part
 
   // Selector shouldn't be empty
   seenSpaces |= scanner.skip(u' ');
   if (scanner.done())
     return Type::UNKNOWN;
 
   data.mSelectorStart = scanner.position() + 1;
 
   // We are done validating, now we can normalize whitespace and the domain part
   if (seenSpaces)
     NormalizeWhitespace(text, data.mDomainsEnd, data.mSelectorStart);
   DependentString(text, 0, data.mDomainsEnd).toLower();
 
+  // We still need to check the old syntax. It will be converted when
+  // we instantiate the filter.
+  if (!emulation &&
+      text.find(OLD_PROPS_SELECTOR, data.mSelectorStart, OLD_PROPS_SELECTOR_LEN) != text.npos)
+  {
+    needConversion = true;
+    emulation = !exception;
+  }
+
   if (exception)
     return Type::ELEMHIDEEXCEPTION;
 
   if (emulation)
     return Type::ELEMHIDEEMULATION;
 
   return Type::ELEMHIDE;
 }
 
 namespace
 {
+  struct Range
+  {
+    String::size_type start;
+    String::size_type end;
+    String::size_type len() const
+    {
+        return end - start;
+    }
+    String::size_type byte_len() const
+    {
+      return len() * sizeof(String::value_type);
+    }
+  };
+}
+
+// Convert filter from the old syntax to the new.
+DependentString ElemHideBase::ConvertFilter(String& text, String::size_type& at)
+{
+  Range prefix = {at, text.find(OLD_PROPS_SELECTOR, at, OLD_PROPS_SELECTOR_LEN)};
+  if (prefix.end == text.npos)
+    return DependentString(text);
+
+  auto length = text.length();
+  Range suffix = {at, length};
+  Range properties = { prefix.end + OLD_PROPS_SELECTOR_LEN, 0 };
+  String::value_type quote = 0;
+  for (auto index = properties.start;
+       index < length && (suffix.start == at); index++)
+  {
+    auto c = text[index];
+    switch (c)
+    {
+    case u'"':
+    case u'\'':
+      if (quote == 0)
+      {
+        // syntax error: we already have a quoted section.
+        if (properties.end)
+          return DependentString();
+
+        if (properties.start != index)
+          return DependentString();
+
+        quote = c;
+        properties.start = index + 1;
+      }
+      else if (quote == c)
+      {
+        // end of quoted.
+        quote = 0;
+        properties.end = index;
+      }
+      break;
+    case u']':
+      if (quote == 0)
+      {
+        if (properties.end == 0)
+          return DependentString();
+        if (properties.end + 1 != index)
+          return DependentString();
+        suffix.start = index + 1;
+      }
+      break;
+    default:
+      break;
+    }
+  }
+
+  if (suffix.start == at)

[sergei, 2018/02/27 10:56:53]

Just for reference, I think it (what the whole for-loop above is doing) can be
written in a simpler form, but since it's some sort of interim function it's
fine.

+    return DependentString();
+
+  String::size_type delimiter = text.find(ELEM_HIDE_DELIMITER, 0,
+                                          ELEM_HIDE_DELIMITER_LEN);
+  // +1 for the replacement of "##" by "#?#"
+  if (delimiter != text.npos)
+    at++;
+  auto new_len = at + prefix.len() + PROPS_SELECTOR_LEN + properties.len() + 1 /* ) */ + suffix.len();
+
+  assert2(new_len + 1 == length || (delimiter == text.npos && new_len + 2 == length), u"Inconsistent length in filter conversion."_str);

[sergei, 2018/02/27 10:56:53]

not important just for reference
length == new_len + (delimiter == text.npos ? 2 : 1)
looks shorted and maybe even more logical.

[hub, 2018/02/27 13:32:30]

Acknowledged.

+
+  DependentString converted(text, 0, new_len);
+
+  if (suffix.len())
+  {
+    new_len -= suffix.len();
+    std::memmove(converted.data() + new_len,
+                 text.data() + suffix.start,
+                 suffix.byte_len());
+  }
+  new_len--;
+  // here we need to move the properties before inserting the ')'
+  auto parens = new_len;
+  if (properties.len())
+  {
+    new_len -= properties.len();
+    std::memmove(converted.data() + new_len,
+                 text.data() + properties.start, properties.byte_len());
+  }
+  converted[parens] = u')';
+
+  new_len -= PROPS_SELECTOR_LEN;
+  std::memcpy(converted.data() + new_len,
+              PROPS_SELECTOR,
+              PROPS_SELECTOR_LEN * sizeof(String::value_type));
+  if (prefix.len())
+  {
+    new_len -= prefix.len();
+    std::memmove(converted.data() + new_len,
+                 text.data() + prefix.start, prefix.byte_len());
+  }
+
+  if (delimiter != String::npos)
+  {
+    std::memcpy(converted.data() + delimiter, ELEM_HIDE_EMULATION_DELIMITER,
+                ELEM_HIDE_EMULATION_DELIMITER_LEN * sizeof(String::value_type));
+  }
+
+  return converted;
+}
+
+namespace
+{
   static constexpr String::value_type OPENING_CURLY_REPLACEMENT[] = u"\\7B ";
   static constexpr String::value_type CLOSING_CURLY_REPLACEMENT[] = u"\\7D ";
-  static constexpr String::size_type CURLY_REPLACEMENT_SIZE = sizeof(OPENING_CURLY_REPLACEMENT) / sizeof(OPENING_CURLY_REPLACEMENT[0]) - 1;
+  static constexpr String::size_type CURLY_REPLACEMENT_SIZE = str_length_of(OPENING_CURLY_REPLACEMENT);
 
   OwnedString EscapeCurlies(String::size_type replacementCount,
                             const DependentString& str)
   {
     OwnedString result(str.length() + replacementCount * (CURLY_REPLACEMENT_SIZE - 1));
 
     String::value_type* current = result.data();
     for (String::size_type i = 0; i < str.length(); i++)
     {
       switch(str[i])
@@ skipping 43 matching lines @@
       if (item.second && !item.first.empty())
       {
         if (!result.empty())
           result.append(u',');
         result.append(item.first);
       }
     }
   }
   return result;
 }