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      1 // Copyright 2009 The RE2 Authors.  All Rights Reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 // The PrefilterTree class is used to form an AND-OR tree of strings
      6 // that would trigger each regexp. The 'prefilter' of each regexp is
      7 // added tp PrefilterTree, and then PrefilterTree is used to find all
      8 // the unique strings across the prefilters. During search, by using
      9 // matches from a string matching engine, PrefilterTree deduces the
     10 // set of regexps that are to be triggered. The 'string matching
     11 // engine' itself is outside of this class, and the caller can use any
     12 // favorite engine. PrefilterTree provides a set of strings (called
     13 // atoms) that the user of this class should use to do the string
     14 // matching.
     15 //
     16 #ifndef RE2_PREFILTER_TREE_H_
     17 #define RE2_PREFILTER_TREE_H_
     18 
     19 #include "util/util.h"
     20 #include "util/sparse_array.h"
     21 
     22 namespace re2 {
     23 
     24 typedef SparseArray<int> IntMap;
     25 
     26 class Prefilter;
     27 
     28 class PrefilterTree {
     29  public:
     30   PrefilterTree();
     31   ~PrefilterTree();
     32 
     33   // Adds the prefilter for the next regexp. Note that we assume that
     34   // Add called sequentially for all regexps. All Add calls
     35   // must precede Compile.
     36   void Add(Prefilter* prefilter);
     37 
     38   // The Compile returns a vector of string in atom_vec.
     39   // Call this after all the prefilters are added through Add.
     40   // No calls to Add after Compile are allowed.
     41   // The caller should use the returned set of strings to do string matching.
     42   // Each time a string matches, the corresponding index then has to be
     43   // and passed to RegexpsGivenStrings below.
     44   void Compile(vector<string>* atom_vec);
     45 
     46   // Given the indices of the atoms that matched, returns the indexes
     47   // of regexps that should be searched.  The matched_atoms should
     48   // contain all the ids of string atoms that were found to match the
     49   // content. The caller can use any string match engine to perform
     50   // this function. This function is thread safe.
     51   void RegexpsGivenStrings(const vector<int>& matched_atoms,
     52                            vector<int>* regexps) const;
     53 
     54   // Print debug prefilter. Also prints unique ids associated with
     55   // nodes of the prefilter of the regexp.
     56   void PrintPrefilter(int regexpid);
     57 
     58 
     59   // Each unique node has a corresponding Entry that helps in
     60   // passing the matching trigger information along the tree.
     61   struct Entry {
     62    public:
     63     // How many children should match before this node triggers the
     64     // parent. For an atom and an OR node, this is 1 and for an AND
     65     // node, it is the number of unique children.
     66     int propagate_up_at_count;
     67 
     68     // When this node is ready to trigger the parent, what are the indices
     69     // of the parent nodes to trigger. The reason there may be more than
     70     // one is because of sharing. For example (abc | def) and (xyz | def)
     71     // are two different nodes, but they share the atom 'def'. So when
     72     // 'def' matches, it triggers two parents, corresponding to the two
     73     // different OR nodes.
     74     IntMap* parents;
     75 
     76     // When this node is ready to trigger the parent, what are the
     77     // regexps that are triggered.
     78     vector<int> regexps;
     79   };
     80 
     81  private:
     82   // This function assigns unique ids to various parts of the
     83   // prefilter, by looking at if these nodes are already in the
     84   // PrefilterTree.
     85   void AssignUniqueIds(vector<string>* atom_vec);
     86 
     87   // Given the matching atoms, find the regexps to be triggered.
     88   void PropagateMatch(const vector<int>& atom_ids,
     89                       IntMap* regexps) const;
     90 
     91   // Returns the prefilter node that has the same NodeString as this
     92   // node. For the canonical node, returns node.
     93   Prefilter* CanonicalNode(Prefilter* node);
     94 
     95   // A string that uniquely identifies the node. Assumes that the
     96   // children of node has already been assigned unique ids.
     97   string NodeString(Prefilter* node) const;
     98 
     99   // Recursively constructs a readable prefilter string.
    100   string DebugNodeString(Prefilter* node) const;
    101 
    102   // Used for debugging.
    103   void PrintDebugInfo();
    104 
    105   // These are all the nodes formed by Compile. Essentially, there is
    106   // one node for each unique atom and each unique AND/OR node.
    107   vector<Entry> entries_;
    108 
    109   // Map node string to canonical Prefilter node.
    110   map<string, Prefilter*> node_map_;
    111 
    112   // indices of regexps that always pass through the filter (since we
    113   // found no required literals in these regexps).
    114   vector<int> unfiltered_;
    115 
    116   // vector of Prefilter for all regexps.
    117   vector<Prefilter*> prefilter_vec_;
    118 
    119   // Atom index in returned strings to entry id mapping.
    120   vector<int> atom_index_to_id_;
    121 
    122   // Has the prefilter tree been compiled.
    123   bool compiled_;
    124 
    125   DISALLOW_EVIL_CONSTRUCTORS(PrefilterTree);
    126 };
    127 
    128 }  // namespace
    129 
    130 #endif  // RE2_PREFILTER_TREE_H_
    131