// Copyright 2006 The RE2 Authors.  All Rights Reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

#ifndef RE2_REGEXP_H_

#define RE2_REGEXP_H_

// --- SPONSORED LINK --------------------------------------------------

// If you want to use this library for regular expression matching,

// you should use re2/re2.h, which provides a class RE2 that

// mimics the PCRE interface provided by PCRE's C++ wrappers.

// This header describes the low-level interface used to implement RE2

// and may change in backwards-incompatible ways from time to time.

// In contrast, RE2's interface will not.

// ---------------------------------------------------------------------

// Regular expression library: parsing, execution, and manipulation

// of regular expressions.

//

// Any operation that traverses the Regexp structures should be written

// using Regexp::Walker (see walker-inl.h), not recursively, because deeply nested

// regular expressions such as x++++++++++++++++++++... might cause recursive

// traversals to overflow the stack.

//

// It is the caller's responsibility to provide appropriate mutual exclusion

// around manipulation of the regexps.  RE2 does this.

//

// PARSING

//

// Regexp::Parse parses regular expressions encoded in UTF-8.

// The default syntax is POSIX extended regular expressions,

// with the following changes:

//

//   1.  Backreferences (optional in POSIX EREs) are not supported.

//         (Supporting them precludes the use of DFA-based

//          matching engines.)

//

//   2.  Collating elements and collation classes are not supported.

//         (No one has needed or wanted them.)

//

// The exact syntax accepted can be modified by passing flags to

// Regexp::Parse.  In particular, many of the basic Perl additions

// are available.  The flags are documented below (search for LikePerl).

//

// If parsed with the flag Regexp::Latin1, both the regular expression

// and the input to the matching routines are assumed to be encoded in

// Latin-1, not UTF-8.

//

// EXECUTION

//

// Once Regexp has parsed a regular expression, it provides methods

// to search text using that regular expression.  These methods are

// implemented via calling out to other regular expression libraries.

// (Let's call them the sublibraries.)

//

// To call a sublibrary, Regexp does not simply prepare a

// string version of the regular expression and hand it to the

// sublibrary.  Instead, Regexp prepares, from its own parsed form, the

// corresponding internal representation used by the sublibrary.

// This has the drawback of needing to know the internal representation

// used by the sublibrary, but it has two important benefits:

//

//   1. The syntax and meaning of regular expressions is guaranteed

//      to be that used by Regexp's parser, not the syntax expected

//      by the sublibrary.  Regexp might accept a restricted or

//      expanded syntax for regular expressions as compared with

//      the sublibrary.  As long as Regexp can translate from its

//      internal form into the sublibrary's, clients need not know

//      exactly which sublibrary they are using.

//

//   2. The sublibrary parsers are bypassed.  For whatever reason,

//      sublibrary regular expression parsers often have security

//      problems.  For example, plan9grep's regular expression parser

//      has a buffer overflow in its handling of large character

//      classes, and PCRE's parser has had buffer overflow problems

//      in the past.  Security-team requires sandboxing of sublibrary

//      regular expression parsers.  Avoiding the sublibrary parsers

//      avoids the sandbox.

//

// The execution methods we use now are provided by the compiled form,

// Prog, described in prog.h

//

// MANIPULATION

//

// Unlike other regular expression libraries, Regexp makes its parsed

// form accessible to clients, so that client code can analyze the

// parsed regular expressions.

#include <stddef.h>

#include <stdint.h>

#include <map>

#include <set>

#include <string>

#include "absl/log/absl_check.h"

#include "absl/log/absl_log.h"

#include "absl/strings/string_view.h"

#include "util/utf.h"

namespace re2 {

// Keep in sync with string list kOpcodeNames[] in testing/dump.cc

enum RegexpOp {

  // Matches no strings.

  kRegexpNoMatch = 1,

  // Matches empty string.

  kRegexpEmptyMatch,

  // Matches rune_.

  kRegexpLiteral,

  // Matches runes_.

  kRegexpLiteralString,

  // Matches concatenation of sub_[0..nsub-1].

  kRegexpConcat,

  // Matches union of sub_[0..nsub-1].

  kRegexpAlternate,

  // Matches sub_[0] zero or more times.

  kRegexpStar,

  // Matches sub_[0] one or more times.

  kRegexpPlus,

  // Matches sub_[0] zero or one times.

  kRegexpQuest,

  // Matches sub_[0] at least min_ times, at most max_ times.

  // max_ == -1 means no upper limit.

  kRegexpRepeat,

  // Parenthesized (capturing) subexpression.  Index is cap_.

  // Optionally, capturing name is name_.

  kRegexpCapture,

  // Matches any character.

  kRegexpAnyChar,

  // Matches any byte [sic].

  kRegexpAnyByte,

  // Matches empty string at beginning of line.

  kRegexpBeginLine,

  // Matches empty string at end of line.

  kRegexpEndLine,

  // Matches word boundary "\b".

  kRegexpWordBoundary,

  // Matches not-a-word boundary "\B".

  kRegexpNoWordBoundary,

  // Matches empty string at beginning of text.

  kRegexpBeginText,

  // Matches empty string at end of text.

  kRegexpEndText,

  // Matches character class given by cc_.

  kRegexpCharClass,

  // Forces match of entire expression right now,

  // with match ID match_id_ (used by RE2::Set).

  kRegexpHaveMatch,

  kMaxRegexpOp = kRegexpHaveMatch,

};

// Keep in sync with string list in regexp.cc

enum RegexpStatusCode {

  // No error

  kRegexpSuccess = 0,

  // Unexpected error

  kRegexpInternalError,

  // Parse errors

  kRegexpBadEscape,          // bad escape sequence

  kRegexpBadCharClass,       // bad character class

  kRegexpBadCharRange,       // bad character class range

  kRegexpMissingBracket,     // missing closing ]

  kRegexpMissingParen,       // missing closing )

  kRegexpUnexpectedParen,    // unexpected closing )

  kRegexpTrailingBackslash,  // at end of regexp

  kRegexpRepeatArgument,     // repeat argument missing, e.g. "*"

  kRegexpRepeatSize,         // bad repetition argument

  kRegexpRepeatOp,           // bad repetition operator

  kRegexpBadPerlOp,          // bad perl operator

  kRegexpBadUTF8,            // invalid UTF-8 in regexp

  kRegexpBadNamedCapture,    // bad named capture

};

// Error status for certain operations.

class RegexpStatus {

 public:

  RegexpStatus() : code_(kRegexpSuccess), tmp_(NULL) {}

  ~RegexpStatus() { delete tmp_; }

  void set_code(RegexpStatusCode code) { code_ = code; }

  void set_error_arg(absl::string_view error_arg) { error_arg_ = error_arg; }

  void set_tmp(std::string* tmp) { delete tmp_; tmp_ = tmp; }

  RegexpStatusCode code() const { return code_; }

  absl::string_view error_arg() const { return error_arg_; }

  bool ok() const { return code() == kRegexpSuccess; }

  // Copies state from status.

  void Copy(const RegexpStatus& status);

  // Returns text equivalent of code, e.g.:

  //   "Bad character class"

  static std::string CodeText(RegexpStatusCode code);

  // Returns text describing error, e.g.:

  //   "Bad character class: [z-a]"

  std::string Text() const;

 private:

  RegexpStatusCode code_;        // Kind of error.

  absl::string_view error_arg_;  // Piece of regexp containing syntax error.

  std::string* tmp_;             // Temporary storage, possibly for error_arg_.

  RegexpStatus(const RegexpStatus&) = delete;

  RegexpStatus& operator=(const RegexpStatus&) = delete;

};

// Compiled form; see prog.h

class Prog;

struct RuneRange {

  RuneRange() : lo(0), hi(0) { }

  RuneRange(int l, int h) : lo(l), hi(h) { }

  Rune lo;

  Rune hi;

};

// Less-than on RuneRanges treats a == b if they overlap at all.

// This lets us look in a set to find the range covering a particular Rune.

struct RuneRangeLess {

  bool operator()(const RuneRange& a, const RuneRange& b) const {

    return a.hi < b.lo;

  }

};

class CharClassBuilder;

class CharClass {

 public:

  void Delete();

  typedef RuneRange* iterator;

  iterator begin() { return ranges_; }

  iterator end() { return ranges_ + nranges_; }

  int size() { return nrunes_; }

  bool empty() { return nrunes_ == 0; }

  bool full() { return nrunes_ == Runemax+1; }

  bool FoldsASCII() { return folds_ascii_; }

  bool Contains(Rune r) const;

  CharClass* Negate();

 private:

  CharClass();  // not implemented

  ~CharClass();  // not implemented

  static CharClass* New(size_t maxranges);

  friend class CharClassBuilder;

  bool folds_ascii_;

  int nrunes_;

  RuneRange *ranges_;

  int nranges_;

  CharClass(const CharClass&) = delete;

  CharClass& operator=(const CharClass&) = delete;

};

class Regexp {

 public:

  // Flags for parsing.  Can be ORed together.

  enum ParseFlags {

    NoParseFlags  = 0,

    FoldCase      = 1<<0,   // Fold case during matching (case-insensitive).

    Literal       = 1<<1,   // Treat s as literal string instead of a regexp.

    ClassNL       = 1<<2,   // Allow char classes like [^a-z] and \D and \s

                            // and [[:space:]] to match newline.

    DotNL         = 1<<3,   // Allow . to match newline.

    MatchNL       = ClassNL | DotNL,

    OneLine       = 1<<4,   // Treat ^ and $ as only matching at beginning and

                            // end of text, not around embedded newlines.

                            // (Perl's default)

    Latin1        = 1<<5,   // Regexp and text are in Latin1, not UTF-8.

    NonGreedy     = 1<<6,   // Repetition operators are non-greedy by default.

    PerlClasses   = 1<<7,   // Allow Perl character classes like \d.

    PerlB         = 1<<8,   // Allow Perl's \b and \B.

    PerlX         = 1<<9,   // Perl extensions:

                            //   non-capturing parens - (?: )

                            //   non-greedy operators - *? +? ?? {}?

                            //   flag edits - (?i) (?-i) (?i: )

                            //     i - FoldCase

                            //     m - !OneLine

                            //     s - DotNL

                            //     U - NonGreedy

                            //   line ends: \A \z

                            //   \Q and \E to disable/enable metacharacters

                            //   (?P<name>expr) for named captures

                            //   \C to match any single byte

    UnicodeGroups = 1<<10,  // Allow \p{Han} for Unicode Han group

                            //   and \P{Han} for its negation.

    NeverNL       = 1<<11,  // Never match NL, even if the regexp mentions

                            //   it explicitly.

    NeverCapture  = 1<<12,  // Parse all parens as non-capturing.

    // As close to Perl as we can get.

    LikePerl      = ClassNL | OneLine | PerlClasses | PerlB | PerlX |

                    UnicodeGroups,

    // Internal use only.

    WasDollar     = 1<<13,  // on kRegexpEndText: was $ in regexp text

    AllParseFlags = (1<<14)-1,

  };

  // Get.  No set, Regexps are logically immutable once created.

  RegexpOp op() { return static_cast<RegexpOp>(op_); }

  int nsub() { return nsub_; }

  bool simple() { return simple_ != 0; }

  ParseFlags parse_flags() { return static_cast<ParseFlags>(parse_flags_); }

  int Ref();  // For testing.

  Regexp** sub() {

    if(nsub_ <= 1)

      return &subone_;

    else

      return submany_;

  }

  int min() {

    ABSL_DCHECK_EQ(op_, kRegexpRepeat);

    return min_;

  }

  int max() {

    ABSL_DCHECK_EQ(op_, kRegexpRepeat);

    return max_;

  }

  Rune rune() {

    ABSL_DCHECK_EQ(op_, kRegexpLiteral);

    return rune_;

  }

  CharClass* cc() {

    ABSL_DCHECK_EQ(op_, kRegexpCharClass);

    return cc_;

  }

  int cap() {

    ABSL_DCHECK_EQ(op_, kRegexpCapture);

    return cap_;

  }

  const std::string* name() {

    ABSL_DCHECK_EQ(op_, kRegexpCapture);

    return name_;

  }

  Rune* runes() {

    ABSL_DCHECK_EQ(op_, kRegexpLiteralString);

    return runes_;

  }

  int nrunes() {

    ABSL_DCHECK_EQ(op_, kRegexpLiteralString);

    return nrunes_;

  }

  int match_id() {

    ABSL_DCHECK_EQ(op_, kRegexpHaveMatch);

    return match_id_;

  }

  // Increments reference count, returns object as convenience.

  Regexp* Incref();

  // Decrements reference count and deletes this object if count reaches 0.

  void Decref();

  // Parses string s to produce regular expression, returned.

  // Caller must release return value with re->Decref().

  // On failure, sets *status (if status != NULL) and returns NULL.

  static Regexp* Parse(absl::string_view s, ParseFlags flags,

                       RegexpStatus* status);

  // Returns a _new_ simplified version of the current regexp.

  // Does not edit the current regexp.

  // Caller must release return value with re->Decref().

  // Simplified means that counted repetition has been rewritten

  // into simpler terms and all Perl/POSIX features have been

  // removed.  The result will capture exactly the same

  // subexpressions the original did, unless formatted with ToString.

  Regexp* Simplify();

  friend class CoalesceWalker;

  friend class SimplifyWalker;

  // Parses the regexp src and then simplifies it and sets *dst to the

  // string representation of the simplified form.  Returns true on success.

  // Returns false and sets *status (if status != NULL) on parse error.

  static bool SimplifyRegexp(absl::string_view src, ParseFlags flags,

                             std::string* dst, RegexpStatus* status);

  // Returns the number of capturing groups in the regexp.

  int NumCaptures();

  friend class NumCapturesWalker;

  // Returns a map from names to capturing group indices,

  // or NULL if the regexp contains no named capture groups.

  // The caller is responsible for deleting the map.

  std::map<std::string, int>* NamedCaptures();

  // Returns a map from capturing group indices to capturing group

  // names or NULL if the regexp contains no named capture groups. The

  // caller is responsible for deleting the map.

  std::map<int, std::string>* CaptureNames();

  // Returns a string representation of the current regexp,

  // using as few parentheses as possible.

  std::string ToString();

  // Convenience functions.  They consume the passed reference,

  // so in many cases you should use, e.g., Plus(re->Incref(), flags).

  // They do not consume allocated arrays like subs or runes.

  static Regexp* Plus(Regexp* sub, ParseFlags flags);

  static Regexp* Star(Regexp* sub, ParseFlags flags);

  static Regexp* Quest(Regexp* sub, ParseFlags flags);

  static Regexp* Concat(Regexp** subs, int nsubs, ParseFlags flags);

  static Regexp* Alternate(Regexp** subs, int nsubs, ParseFlags flags);

  static Regexp* Capture(Regexp* sub, ParseFlags flags, int cap);

  static Regexp* Repeat(Regexp* sub, ParseFlags flags, int min, int max);

  static Regexp* NewLiteral(Rune rune, ParseFlags flags);

  static Regexp* NewCharClass(CharClass* cc, ParseFlags flags);

  static Regexp* LiteralString(Rune* runes, int nrunes, ParseFlags flags);

  static Regexp* HaveMatch(int match_id, ParseFlags flags);

  // Like Alternate but does not factor out common prefixes.

  static Regexp* AlternateNoFactor(Regexp** subs, int nsubs, ParseFlags flags);

  // Debugging function.  Returns string format for regexp

  // that makes structure clear.  Does NOT use regexp syntax.

  std::string Dump();

  // Helper traversal class, defined fully in walker-inl.h.

  template<typename T> class Walker;

  // Compile to Prog.  See prog.h

  // Reverse prog expects to be run over text backward.

  // Construction and execution of prog will

  // stay within approximately max_mem bytes of memory.

  // If max_mem <= 0, a reasonable default is used.

  Prog* CompileToProg(int64_t max_mem);

  Prog* CompileToReverseProg(int64_t max_mem);

  // Whether to expect this library to find exactly the same answer as PCRE

  // when running this regexp.  Most regexps do mimic PCRE exactly, but a few

  // obscure cases behave differently.  Technically this is more a property

  // of the Prog than the Regexp, but the computation is much easier to do

  // on the Regexp.  See mimics_pcre.cc for the exact conditions.

  bool MimicsPCRE();

  // Benchmarking function.

  void NullWalk();

  // Whether every match of this regexp must be anchored and

  // begin with a non-empty fixed string (perhaps after ASCII

  // case-folding).  If so, returns the prefix and the sub-regexp that

  // follows it.

  // Callers should expect *prefix, *foldcase and *suffix to be "zeroed"

  // regardless of the return value.

  bool RequiredPrefix(std::string* prefix, bool* foldcase,

                      Regexp** suffix);

  // Whether every match of this regexp must be unanchored and

  // begin with a non-empty fixed string (perhaps after ASCII

  // case-folding).  If so, returns the prefix.

  // Callers should expect *prefix and *foldcase to be "zeroed"

  // regardless of the return value.

  bool RequiredPrefixForAccel(std::string* prefix, bool* foldcase);

  // Controls the maximum repeat count permitted by the parser.

  // FOR FUZZING ONLY.

  static void FUZZING_ONLY_set_maximum_repeat_count(int i);

 private:

  // Constructor allocates vectors as appropriate for operator.

  explicit Regexp(RegexpOp op, ParseFlags parse_flags);

  // Use Decref() instead of delete to release Regexps.

  // This is private to catch deletes at compile time.

  ~Regexp();

  void Destroy();

  bool QuickDestroy();

  // Helpers for Parse.  Listed here so they can edit Regexps.

  class ParseState;

  friend class ParseState;

  friend bool ParseCharClass(absl::string_view* s, Regexp** out_re,

                             RegexpStatus* status);

  // Helper for testing [sic].

  friend bool RegexpEqualTestingOnly(Regexp*, Regexp*);

  // Computes whether Regexp is already simple.

  bool ComputeSimple();

  // Constructor that generates a Star, Plus or Quest,

  // squashing the pair if sub is also a Star, Plus or Quest.

  static Regexp* StarPlusOrQuest(RegexpOp op, Regexp* sub, ParseFlags flags);

  // Constructor that generates a concatenation or alternation,

  // enforcing the limit on the number of subexpressions for

  // a particular Regexp.

  static Regexp* ConcatOrAlternate(RegexpOp op, Regexp** subs, int nsubs,

                                   ParseFlags flags, bool can_factor);

  // Returns the leading string that re starts with.

  // The returned Rune* points into a piece of re,

  // so it must not be used after the caller calls re->Decref().

  static Rune* LeadingString(Regexp* re, int* nrune, ParseFlags* flags);

  // Removes the first n leading runes from the beginning of re.

  // Edits re in place.

  static void RemoveLeadingString(Regexp* re, int n);

  // Returns the leading regexp in re's top-level concatenation.

  // The returned Regexp* points at re or a sub-expression of re,

  // so it must not be used after the caller calls re->Decref().

  static Regexp* LeadingRegexp(Regexp* re);

  // Removes LeadingRegexp(re) from re and returns the remainder.

  // Might edit re in place.

  static Regexp* RemoveLeadingRegexp(Regexp* re);

  // Simplifies an alternation of literal strings by factoring out

  // common prefixes.

  static int FactorAlternation(Regexp** sub, int nsub, ParseFlags flags);

  friend class FactorAlternationImpl;

  // Is a == b?  Only efficient on regexps that have not been through

  // Simplify yet - the expansion of a kRegexpRepeat will make this

  // take a long time.  Do not call on such regexps, hence private.

  static bool Equal(Regexp* a, Regexp* b);

  // Allocate space for n sub-regexps.

  void AllocSub(int n) {

    ABSL_DCHECK(n >= 0 && static_cast<uint16_t>(n) == n);

    if (n > 1)

      submany_ = new Regexp*[n];

    nsub_ = static_cast<uint16_t>(n);

  }

  // Add Rune to LiteralString

  void AddRuneToString(Rune r);

  // Swaps this with that, in place.

  void Swap(Regexp *that);

  // Operator.  See description of operators above.

  // uint8_t instead of RegexpOp to control space usage.

  uint8_t op_;

  // Is this regexp structure already simple

  // (has it been returned by Simplify)?

  // uint8_t instead of bool to control space usage.

  uint8_t simple_;

  // Flags saved from parsing and used during execution.

  // (Only FoldCase is used.)

  // uint16_t instead of ParseFlags to control space usage.

  uint16_t parse_flags_;

  // Reference count.  Exists so that SimplifyRegexp can build

  // regexp structures that are dags rather than trees to avoid

  // exponential blowup in space requirements.

  // uint16_t to control space usage.

  // The standard regexp routines will never generate a

  // ref greater than the maximum repeat count (kMaxRepeat),

  // but even so, Incref and Decref consult an overflow map

  // when ref_ reaches kMaxRef.

  uint16_t ref_;

  static const uint16_t kMaxRef = 0xffff;

  // Subexpressions.

  // uint16_t to control space usage.

  // Concat and Alternate handle larger numbers of subexpressions

  // by building concatenation or alternation trees.

  // Other routines should call Concat or Alternate instead of

  // filling in sub() by hand.

  uint16_t nsub_;

  static const uint16_t kMaxNsub = 0xffff;

  union {

    Regexp** submany_;  // if nsub_ > 1

    Regexp* subone_;  // if nsub_ == 1

  };

  // Extra space for parse and teardown stacks.

  Regexp* down_;

  // Arguments to operator.  See description of operators above.

  union {

    struct {  // Repeat

      int max_;

      int min_;

    };

    struct {  // Capture

      int cap_;

      std::string* name_;

    };

    struct {  // LiteralString

      int nrunes_;

      Rune* runes_;

    };

    struct {  // CharClass

      // These two could be in separate union members,

      // but it wouldn't save any space (there are other two-word structs)

      // and keeping them separate avoids confusion during parsing.

      CharClass* cc_;

      CharClassBuilder* ccb_;

    };

    Rune rune_;  // Literal

    int match_id_;  // HaveMatch

    void *the_union_[2];  // as big as any other element, for memset

  };

  Regexp(const Regexp&) = delete;

  Regexp& operator=(const Regexp&) = delete;

};

// Character class set: contains non-overlapping, non-abutting RuneRanges.

typedef std::set<RuneRange, RuneRangeLess> RuneRangeSet;

class CharClassBuilder {

 public:

  CharClassBuilder();

  typedef RuneRangeSet::iterator iterator;

  iterator begin() { return ranges_.begin(); }

  iterator end() { return ranges_.end(); }

  int size() { return nrunes_; }

  bool empty() { return nrunes_ == 0; }

  bool full() { return nrunes_ == Runemax+1; }

  bool Contains(Rune r);

  bool FoldsASCII();

  bool AddRange(Rune lo, Rune hi);  // returns whether class changed

  CharClassBuilder* Copy();

  void AddCharClass(CharClassBuilder* cc);

  void Negate();

  void RemoveAbove(Rune r);

  CharClass* GetCharClass();

  void AddRangeFlags(Rune lo, Rune hi, Regexp::ParseFlags parse_flags);

 private:

  static const uint32_t AlphaMask = (1<<26) - 1;

  uint32_t upper_;  // bitmap of A-Z

  uint32_t lower_;  // bitmap of a-z

  int nrunes_;

  RuneRangeSet ranges_;

  CharClassBuilder(const CharClassBuilder&) = delete;

  CharClassBuilder& operator=(const CharClassBuilder&) = delete;

};

// Bitwise ops on ParseFlags produce ParseFlags.

inline Regexp::ParseFlags operator|(Regexp::ParseFlags a,

                                    Regexp::ParseFlags b) {

  return static_cast<Regexp::ParseFlags>(

      static_cast<int>(a) | static_cast<int>(b));

}

inline Regexp::ParseFlags operator^(Regexp::ParseFlags a,

                                    Regexp::ParseFlags b) {

  return static_cast<Regexp::ParseFlags>(

      static_cast<int>(a) ^ static_cast<int>(b));

}

inline Regexp::ParseFlags operator&(Regexp::ParseFlags a,

                                    Regexp::ParseFlags b) {

  return static_cast<Regexp::ParseFlags>(

      static_cast<int>(a) & static_cast<int>(b));

}

inline Regexp::ParseFlags operator~(Regexp::ParseFlags a) {

  // Attempting to produce a value out of enum's range has undefined behaviour.

  return static_cast<Regexp::ParseFlags>(

      ~static_cast<int>(a) & static_cast<int>(Regexp::AllParseFlags));

}

}  // namespace re2

#endif  // RE2_REGEXP_H_