src/util/pcre.cc

// Copyright 2003-2009 Google Inc.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This is a variant of PCRE's pcrecpp.cc, originally written at Google.
// The main changes are the addition of the HitLimit method and
// compilation as PCRE in namespace re2.

#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <limits>
#include <string>
#include <utility>

#include "absl/flags/flag.h"
#include "absl/strings/str_format.h"
#include "util/logging.h"
#include "util/pcre.h"

// Silence warnings about the wacky formatting in the operator() functions.
#if defined(__GNUC__)
#pragma GCC diagnostic ignored "-Wmisleading-indentation"
#endif

#define PCREPORT(level) LOG(level)

// Default PCRE limits.
// Defaults chosen to allow a plausible amount of CPU and
// not exceed main thread stacks.  Note that other threads
// often have smaller stacks, and therefore tightening
// regexp_stack_limit may frequently be necessary.
ABSL_FLAG(int, regexp_stack_limit, 256 << 10,
          "default PCRE stack limit (bytes)");
ABSL_FLAG(int, regexp_match_limit, 1000000,
          "default PCRE match limit (function calls)");

#ifndef USEPCRE

// Fake just enough of the PCRE API to allow this file to build. :)

struct pcre_extra {
  int flags;
  int match_limit;
  int match_limit_recursion;
};

#define PCRE_EXTRA_MATCH_LIMIT 0
#define PCRE_EXTRA_MATCH_LIMIT_RECURSION 0
#define PCRE_ANCHORED 0
#define PCRE_NOTEMPTY 0
#define PCRE_ERROR_NOMATCH 1
#define PCRE_ERROR_MATCHLIMIT 2
#define PCRE_ERROR_RECURSIONLIMIT 3
#define PCRE_INFO_CAPTURECOUNT 0

void pcre_free(void*) {
}

pcre* pcre_compile(const char*, int, const char**, int*, const unsigned char*) {
  return NULL;
}

int pcre_exec(const pcre*, const pcre_extra*, const char*, int, int, int, int*, int) {
  return 0;
}

int pcre_fullinfo(const pcre*, const pcre_extra*, int, void*) {
  return 0;
}

#endif

namespace re2 {

// Maximum number of args we can set
static const int kMaxArgs = 16;
static const int kVecSize = (1 + kMaxArgs) * 3;  // results + PCRE workspace

// Approximate size of a recursive invocation of PCRE's
// internal "match()" frame.  This varies depending on the
// compiler and architecture, of course, so the constant is
// just a conservative estimate.  To find the exact number,
// run regexp_unittest with --regexp_stack_limit=0 under
// a debugger and look at the frames when it crashes.
// The exact frame size was 656 in production on 2008/02/03.
static const int kPCREFrameSize = 700;

// Special name for missing C++ arguments.
PCRE::Arg PCRE::no_more_args((void*)NULL);

const PCRE::PartialMatchFunctor PCRE::PartialMatch = { };
const PCRE::FullMatchFunctor PCRE::FullMatch = { } ;
const PCRE::ConsumeFunctor PCRE::Consume = { };
const PCRE::FindAndConsumeFunctor PCRE::FindAndConsume = { };

// If a regular expression has no error, its error_ field points here
static const std::string empty_string;

void PCRE::Init(const char* pattern, Option options, int match_limit,
              int stack_limit, bool report_errors) {
  pattern_ = pattern;
  options_ = options;
  match_limit_ = match_limit;
  stack_limit_ = stack_limit;
  hit_limit_ = false;
  error_ = &empty_string;
  report_errors_ = report_errors;
  re_full_ = NULL;
  re_partial_ = NULL;

  if (options & ~(EnabledCompileOptions | EnabledExecOptions)) {
    error_ = new std::string("illegal regexp option");
    PCREPORT(ERROR)
        << "Error compiling '" << pattern << "': illegal regexp option";
  } else {
    re_partial_ = Compile(UNANCHORED);
    if (re_partial_ != NULL) {
      re_full_ = Compile(ANCHOR_BOTH);
    }
  }
}

PCRE::PCRE(const char* pattern) {
  Init(pattern, None, 0, 0, true);
}
PCRE::PCRE(const char* pattern, Option option) {
  Init(pattern, option, 0, 0, true);
}
PCRE::PCRE(const std::string& pattern) {
  Init(pattern.c_str(), None, 0, 0, true);
}
PCRE::PCRE(const std::string& pattern, Option option) {
  Init(pattern.c_str(), option, 0, 0, true);
}
PCRE::PCRE(const std::string& pattern, const PCRE_Options& re_option) {
  Init(pattern.c_str(), re_option.option(), re_option.match_limit(),
       re_option.stack_limit(), re_option.report_errors());
}

PCRE::PCRE(const char *pattern, const PCRE_Options& re_option) {
  Init(pattern, re_option.option(), re_option.match_limit(),
       re_option.stack_limit(), re_option.report_errors());
}

PCRE::~PCRE() {
  if (re_full_ != NULL)         pcre_free(re_full_);
  if (re_partial_ != NULL)      pcre_free(re_partial_);
  if (error_ != &empty_string)  delete error_;
}

pcre* PCRE::Compile(Anchor anchor) {
  // Special treatment for anchoring.  This is needed because at
  // runtime pcre only provides an option for anchoring at the
  // beginning of a string.
  //
  // There are three types of anchoring we want:
  //    UNANCHORED      Compile the original pattern, and use
  //                    a pcre unanchored match.
  //    ANCHOR_START    Compile the original pattern, and use
  //                    a pcre anchored match.
  //    ANCHOR_BOTH     Tack a "\z" to the end of the original pattern
  //                    and use a pcre anchored match.

  const char* error = "";
  int eoffset;
  pcre* re;
  if (anchor != ANCHOR_BOTH) {
    re = pcre_compile(pattern_.c_str(),
                      (options_ & EnabledCompileOptions),
                      &error, &eoffset, NULL);
  } else {
    // Tack a '\z' at the end of PCRE.  Parenthesize it first so that
    // the '\z' applies to all top-level alternatives in the regexp.
    std::string wrapped = "(?:";  // A non-counting grouping operator
    wrapped += pattern_;
    wrapped += ")\\z";
    re = pcre_compile(wrapped.c_str(),
                      (options_ & EnabledCompileOptions),
                      &error, &eoffset, NULL);
  }
  if (re == NULL) {
    if (error_ == &empty_string) error_ = new std::string(error);
    PCREPORT(ERROR) << "Error compiling '" << pattern_ << "': " << error;
  }
  return re;
}

/***** Convenience interfaces *****/

bool PCRE::FullMatchFunctor::operator()(
    absl::string_view text, const PCRE& re, const Arg& a0, const Arg& a1,
    const Arg& a2, const Arg& a3, const Arg& a4, const Arg& a5, const Arg& a6,
    const Arg& a7, const Arg& a8, const Arg& a9, const Arg& a10, const Arg& a11,
    const Arg& a12, const Arg& a13, const Arg& a14, const Arg& a15) const {
  const Arg* args[kMaxArgs];
  int n = 0;
  if (&a0 == &no_more_args)  goto done; args[n++] = &a0;
  if (&a1 == &no_more_args)  goto done; args[n++] = &a1;
  if (&a2 == &no_more_args)  goto done; args[n++] = &a2;
  if (&a3 == &no_more_args)  goto done; args[n++] = &a3;
  if (&a4 == &no_more_args)  goto done; args[n++] = &a4;
  if (&a5 == &no_more_args)  goto done; args[n++] = &a5;
  if (&a6 == &no_more_args)  goto done; args[n++] = &a6;
  if (&a7 == &no_more_args)  goto done; args[n++] = &a7;
  if (&a8 == &no_more_args)  goto done; args[n++] = &a8;
  if (&a9 == &no_more_args)  goto done; args[n++] = &a9;
  if (&a10 == &no_more_args) goto done; args[n++] = &a10;
  if (&a11 == &no_more_args) goto done; args[n++] = &a11;
  if (&a12 == &no_more_args) goto done; args[n++] = &a12;
  if (&a13 == &no_more_args) goto done; args[n++] = &a13;
  if (&a14 == &no_more_args) goto done; args[n++] = &a14;
  if (&a15 == &no_more_args) goto done; args[n++] = &a15;
done:

  size_t consumed;
  int vec[kVecSize] = {};
  return re.DoMatchImpl(text, ANCHOR_BOTH, &consumed, args, n, vec, kVecSize);
}

bool PCRE::PartialMatchFunctor::operator()(
    absl::string_view text, const PCRE& re, const Arg& a0, const Arg& a1,
    const Arg& a2, const Arg& a3, const Arg& a4, const Arg& a5, const Arg& a6,
    const Arg& a7, const Arg& a8, const Arg& a9, const Arg& a10, const Arg& a11,
    const Arg& a12, const Arg& a13, const Arg& a14, const Arg& a15) const {
  const Arg* args[kMaxArgs];
  int n = 0;
  if (&a0 == &no_more_args)  goto done; args[n++] = &a0;
  if (&a1 == &no_more_args)  goto done; args[n++] = &a1;
  if (&a2 == &no_more_args)  goto done; args[n++] = &a2;
  if (&a3 == &no_more_args)  goto done; args[n++] = &a3;
  if (&a4 == &no_more_args)  goto done; args[n++] = &a4;
  if (&a5 == &no_more_args)  goto done; args[n++] = &a5;
  if (&a6 == &no_more_args)  goto done; args[n++] = &a6;
  if (&a7 == &no_more_args)  goto done; args[n++] = &a7;
  if (&a8 == &no_more_args)  goto done; args[n++] = &a8;
  if (&a9 == &no_more_args)  goto done; args[n++] = &a9;
  if (&a10 == &no_more_args) goto done; args[n++] = &a10;
  if (&a11 == &no_more_args) goto done; args[n++] = &a11;
  if (&a12 == &no_more_args) goto done; args[n++] = &a12;
  if (&a13 == &no_more_args) goto done; args[n++] = &a13;
  if (&a14 == &no_more_args) goto done; args[n++] = &a14;
  if (&a15 == &no_more_args) goto done; args[n++] = &a15;
done:

  size_t consumed;
  int vec[kVecSize] = {};
  return re.DoMatchImpl(text, UNANCHORED, &consumed, args, n, vec, kVecSize);
}

bool PCRE::ConsumeFunctor::operator()(
    absl::string_view* input, const PCRE& pattern, const Arg& a0, const Arg& a1,
    const Arg& a2, const Arg& a3, const Arg& a4, const Arg& a5, const Arg& a6,
    const Arg& a7, const Arg& a8, const Arg& a9, const Arg& a10, const Arg& a11,
    const Arg& a12, const Arg& a13, const Arg& a14, const Arg& a15) const {
  const Arg* args[kMaxArgs];
  int n = 0;
  if (&a0 == &no_more_args)  goto done; args[n++] = &a0;
  if (&a1 == &no_more_args)  goto done; args[n++] = &a1;
  if (&a2 == &no_more_args)  goto done; args[n++] = &a2;
  if (&a3 == &no_more_args)  goto done; args[n++] = &a3;
  if (&a4 == &no_more_args)  goto done; args[n++] = &a4;
  if (&a5 == &no_more_args)  goto done; args[n++] = &a5;
  if (&a6 == &no_more_args)  goto done; args[n++] = &a6;
  if (&a7 == &no_more_args)  goto done; args[n++] = &a7;
  if (&a8 == &no_more_args)  goto done; args[n++] = &a8;
  if (&a9 == &no_more_args)  goto done; args[n++] = &a9;
  if (&a10 == &no_more_args) goto done; args[n++] = &a10;
  if (&a11 == &no_more_args) goto done; args[n++] = &a11;
  if (&a12 == &no_more_args) goto done; args[n++] = &a12;
  if (&a13 == &no_more_args) goto done; args[n++] = &a13;
  if (&a14 == &no_more_args) goto done; args[n++] = &a14;
  if (&a15 == &no_more_args) goto done; args[n++] = &a15;
done:

  size_t consumed;
  int vec[kVecSize] = {};
  if (pattern.DoMatchImpl(*input, ANCHOR_START, &consumed,
                          args, n, vec, kVecSize)) {
    input->remove_prefix(consumed);
    return true;
  } else {
    return false;
  }
}

bool PCRE::FindAndConsumeFunctor::operator()(
    absl::string_view* input, const PCRE& pattern, const Arg& a0, const Arg& a1,
    const Arg& a2, const Arg& a3, const Arg& a4, const Arg& a5, const Arg& a6,
    const Arg& a7, const Arg& a8, const Arg& a9, const Arg& a10, const Arg& a11,
    const Arg& a12, const Arg& a13, const Arg& a14, const Arg& a15) const {
  const Arg* args[kMaxArgs];
  int n = 0;
  if (&a0 == &no_more_args)  goto done; args[n++] = &a0;
  if (&a1 == &no_more_args)  goto done; args[n++] = &a1;
  if (&a2 == &no_more_args)  goto done; args[n++] = &a2;
  if (&a3 == &no_more_args)  goto done; args[n++] = &a3;
  if (&a4 == &no_more_args)  goto done; args[n++] = &a4;
  if (&a5 == &no_more_args)  goto done; args[n++] = &a5;
  if (&a6 == &no_more_args)  goto done; args[n++] = &a6;
  if (&a7 == &no_more_args)  goto done; args[n++] = &a7;
  if (&a8 == &no_more_args)  goto done; args[n++] = &a8;
  if (&a9 == &no_more_args)  goto done; args[n++] = &a9;
  if (&a10 == &no_more_args) goto done; args[n++] = &a10;
  if (&a11 == &no_more_args) goto done; args[n++] = &a11;
  if (&a12 == &no_more_args) goto done; args[n++] = &a12;
  if (&a13 == &no_more_args) goto done; args[n++] = &a13;
  if (&a14 == &no_more_args) goto done; args[n++] = &a14;
  if (&a15 == &no_more_args) goto done; args[n++] = &a15;
done:

  size_t consumed;
  int vec[kVecSize] = {};
  if (pattern.DoMatchImpl(*input, UNANCHORED, &consumed,
                          args, n, vec, kVecSize)) {
    input->remove_prefix(consumed);
    return true;
  } else {
    return false;
  }
}

bool PCRE::Replace(std::string* str, const PCRE& pattern,
                   absl::string_view rewrite) {
  int vec[kVecSize] = {};
  int matches = pattern.TryMatch(*str, 0, UNANCHORED, true, vec, kVecSize);
  if (matches == 0)
    return false;

  std::string s;
  if (!pattern.Rewrite(&s, rewrite, *str, vec, matches))
    return false;

  assert(vec[0] >= 0);
  assert(vec[1] >= 0);
  str->replace(vec[0], vec[1] - vec[0], s);
  return true;
}

int PCRE::GlobalReplace(std::string* str, const PCRE& pattern,
                        absl::string_view rewrite) {
  int count = 0;
  int vec[kVecSize] = {};
  std::string out;
  size_t start = 0;
  bool last_match_was_empty_string = false;

  while (start <= str->size()) {
    // If the previous match was for the empty string, we shouldn't
    // just match again: we'll match in the same way and get an
    // infinite loop.  Instead, we do the match in a special way:
    // anchored -- to force another try at the same position --
    // and with a flag saying that this time, ignore empty matches.
    // If this special match returns, that means there's a non-empty
    // match at this position as well, and we can continue.  If not,
    // we do what perl does, and just advance by one.
    // Notice that perl prints '@@@' for this;
    //    perl -le '$_ = "aa"; s/b*|aa/@/g; print'
    int matches;
    if (last_match_was_empty_string) {
      matches = pattern.TryMatch(*str, start, ANCHOR_START, false,
                                 vec, kVecSize);
      if (matches <= 0) {
        if (start < str->size())
          out.push_back((*str)[start]);
        start++;
        last_match_was_empty_string = false;
        continue;
      }
    } else {
      matches = pattern.TryMatch(*str, start, UNANCHORED, true,
                                 vec, kVecSize);
      if (matches <= 0)
        break;
    }
    size_t matchstart = vec[0], matchend = vec[1];
    assert(matchstart >= start);
    assert(matchend >= matchstart);

    out.append(*str, start, matchstart - start);
    pattern.Rewrite(&out, rewrite, *str, vec, matches);
    start = matchend;
    count++;
    last_match_was_empty_string = (matchstart == matchend);
  }

  if (count == 0)
    return 0;

  if (start < str->size())
    out.append(*str, start, str->size() - start);
  using std::swap;
  swap(out, *str);
  return count;
}

bool PCRE::Extract(absl::string_view text, const PCRE& pattern,
                   absl::string_view rewrite, std::string* out) {
  int vec[kVecSize] = {};
  int matches = pattern.TryMatch(text, 0, UNANCHORED, true, vec, kVecSize);
  if (matches == 0)
    return false;
  out->clear();
  return pattern.Rewrite(out, rewrite, text, vec, matches);
}

std::string PCRE::QuoteMeta(absl::string_view unquoted) {
  std::string result;
  result.reserve(unquoted.size() << 1);

  // Escape any ascii character not in [A-Za-z_0-9].
  //
  // Note that it's legal to escape a character even if it has no
  // special meaning in a regular expression -- so this function does
  // that.  (This also makes it identical to the perl function of the
  // same name except for the null-character special case;
  // see `perldoc -f quotemeta`.)
  for (size_t ii = 0; ii < unquoted.size(); ++ii) {
    // Note that using 'isalnum' here raises the benchmark time from
    // 32ns to 58ns:
    if ((unquoted[ii] < 'a' || unquoted[ii] > 'z') &&
        (unquoted[ii] < 'A' || unquoted[ii] > 'Z') &&
        (unquoted[ii] < '0' || unquoted[ii] > '9') &&
        unquoted[ii] != '_' &&
        // If this is the part of a UTF8 or Latin1 character, we need
        // to copy this byte without escaping.  Experimentally this is
        // what works correctly with the regexp library.
        !(unquoted[ii] & 128)) {
      if (unquoted[ii] == '\0') {  // Special handling for null chars.
        // Can't use "\\0" since the next character might be a digit.
        result += "\\x00";
        continue;
      }
      result += '\\';
    }
    result += unquoted[ii];
  }

  return result;
}

/***** Actual matching and rewriting code *****/

bool PCRE::HitLimit() {
  return hit_limit_ != 0;
}

void PCRE::ClearHitLimit() {
  hit_limit_ = 0;
}

int PCRE::TryMatch(absl::string_view text, size_t startpos, Anchor anchor,
                   bool empty_ok, int* vec, int vecsize) const {
  pcre* re = (anchor == ANCHOR_BOTH) ? re_full_ : re_partial_;
  if (re == NULL) {
    PCREPORT(ERROR) << "Matching against invalid re: " << *error_;
    return 0;
  }

  int match_limit = match_limit_;
  if (match_limit <= 0) {
    match_limit = absl::GetFlag(FLAGS_regexp_match_limit);
  }

  int stack_limit = stack_limit_;
  if (stack_limit <= 0) {
    stack_limit = absl::GetFlag(FLAGS_regexp_stack_limit);
  }

  pcre_extra extra = { 0 };
  if (match_limit > 0) {
    extra.flags |= PCRE_EXTRA_MATCH_LIMIT;
    extra.match_limit = match_limit;
  }
  if (stack_limit > 0) {
    extra.flags |= PCRE_EXTRA_MATCH_LIMIT_RECURSION;
    extra.match_limit_recursion = stack_limit / kPCREFrameSize;
  }

  int options = 0;
  if (anchor != UNANCHORED)
    options |= PCRE_ANCHORED;
  if (!empty_ok)
    options |= PCRE_NOTEMPTY;

  int rc = pcre_exec(re,              // The regular expression object
                     &extra,
                     (text.data() == NULL) ? "" : text.data(),
                     static_cast<int>(text.size()),
                     static_cast<int>(startpos),
                     options,
                     vec,
                     vecsize);

  // Handle errors
  if (rc == 0) {
    // pcre_exec() returns 0 as a special case when the number of
    // capturing subpatterns exceeds the size of the vector.
    // When this happens, there is a match and the output vector
    // is filled, but we miss out on the positions of the extra subpatterns.
    rc = vecsize / 2;
  } else if (rc < 0) {
    switch (rc) {
      case PCRE_ERROR_NOMATCH:
        return 0;
      case PCRE_ERROR_MATCHLIMIT:
        // Writing to hit_limit is not safe if multiple threads
        // are using the PCRE, but the flag is only intended
        // for use by unit tests anyway, so we let it go.
        hit_limit_ = true;
        PCREPORT(WARNING) << "Exceeded match limit of " << match_limit
                        << " when matching '" << pattern_ << "'"
                        << " against text that is " << text.size() << " bytes.";
        return 0;
      case PCRE_ERROR_RECURSIONLIMIT:
        // See comment about hit_limit above.
        hit_limit_ = true;
        PCREPORT(WARNING) << "Exceeded stack limit of " << stack_limit
                        << " when matching '" << pattern_ << "'"
                        << " against text that is " << text.size() << " bytes.";
        return 0;
      default:
        // There are other return codes from pcre.h :
        // PCRE_ERROR_NULL           (-2)
        // PCRE_ERROR_BADOPTION      (-3)
        // PCRE_ERROR_BADMAGIC       (-4)
        // PCRE_ERROR_UNKNOWN_NODE   (-5)
        // PCRE_ERROR_NOMEMORY       (-6)
        // PCRE_ERROR_NOSUBSTRING    (-7)
        // ...
        PCREPORT(ERROR) << "Unexpected return code: " << rc
                      << " when matching '" << pattern_ << "'"
                      << ", re=" << re
                      << ", text=" << text
                      << ", vec=" << vec
                      << ", vecsize=" << vecsize;
        return 0;
    }
  }

  return rc;
}

bool PCRE::DoMatchImpl(absl::string_view text, Anchor anchor, size_t* consumed,
                       const Arg* const* args, int n, int* vec,
                       int vecsize) const {
  assert((1 + n) * 3 <= vecsize);  // results + PCRE workspace
  if (NumberOfCapturingGroups() < n) {
    // RE has fewer capturing groups than number of Arg pointers passed in.
    return false;
  }

  int matches = TryMatch(text, 0, anchor, true, vec, vecsize);
  assert(matches >= 0);  // TryMatch never returns negatives
  if (matches == 0)
    return false;

  *consumed = vec[1];

  if (n == 0 || args == NULL) {
    // We are not interested in results
    return true;
  }

  // If we got here, we must have matched the whole pattern.
  // We do not need (can not do) any more checks on the value of 'matches' here
  // -- see the comment for TryMatch.
  for (int i = 0; i < n; i++) {
    const int start = vec[2*(i+1)];
    const int limit = vec[2*(i+1)+1];

    // Avoid invoking undefined behavior when text.data() happens
    // to be null and start happens to be -1, the latter being the
    // case for an unmatched subexpression. Even if text.data() is
    // not null, pointing one byte before was a longstanding bug.
    const char* addr = NULL;
    if (start != -1) {
      addr = text.data() + start;
    }

    if (!args[i]->Parse(addr, limit-start)) {
      // TODO: Should we indicate what the error was?
      return false;
    }
  }

  return true;
}

bool PCRE::DoMatch(absl::string_view text, Anchor anchor, size_t* consumed,
                   const Arg* const args[], int n) const {
  assert(n >= 0);
  const int vecsize = (1 + n) * 3;  // results + PCRE workspace
                                    // (as for kVecSize)
  int* vec = new int[vecsize];
  bool b = DoMatchImpl(text, anchor, consumed, args, n, vec, vecsize);
  delete[] vec;
  return b;
}

bool PCRE::Rewrite(std::string* out, absl::string_view rewrite,
                   absl::string_view text, int* vec, int veclen) const {
  int number_of_capturing_groups = NumberOfCapturingGroups();
  for (const char *s = rewrite.data(), *end = s + rewrite.size();
       s < end; s++) {
    int c = *s;
    if (c == '\\') {
      c = *++s;
      if (isdigit(c)) {
        int n = (c - '0');
        if (n >= veclen) {
          if (n <= number_of_capturing_groups) {
            // unmatched optional capturing group. treat
            // its value as empty string; i.e., nothing to append.
          } else {
            PCREPORT(ERROR) << "requested group " << n
                          << " in regexp " << rewrite.data();
            return false;
          }
        }
        int start = vec[2 * n];
        if (start >= 0)
          out->append(text.data() + start, vec[2 * n + 1] - start);
      } else if (c == '\\') {
        out->push_back('\\');
      } else {
        PCREPORT(ERROR) << "invalid rewrite pattern: " << rewrite.data();
        return false;
      }
    } else {
      out->push_back(c);
    }
  }
  return true;
}

bool PCRE::CheckRewriteString(absl::string_view rewrite,
                              std::string* error) const {
  int max_token = -1;
  for (const char *s = rewrite.data(), *end = s + rewrite.size();
       s < end; s++) {
    int c = *s;
    if (c != '\\') {
      continue;
    }
    if (++s == end) {
      *error = "Rewrite schema error: '\\' not allowed at end.";
      return false;
    }
    c = *s;
    if (c == '\\') {
      continue;
    }
    if (!isdigit(c)) {
      *error = "Rewrite schema error: "
               "'\\' must be followed by a digit or '\\'.";
      return false;
    }
    int n = (c - '0');
    if (max_token < n) {
      max_token = n;
    }
  }

  if (max_token > NumberOfCapturingGroups()) {
    *error = absl::StrFormat(
        "Rewrite schema requests %d matches, but the regexp only has %d "
        "parenthesized subexpressions.",
        max_token, NumberOfCapturingGroups());
    return false;
  }
  return true;
}

// Return the number of capturing subpatterns, or -1 if the
// regexp wasn't valid on construction.
int PCRE::NumberOfCapturingGroups() const {
  if (re_partial_ == NULL) return -1;

  int result;
  int rc = pcre_fullinfo(re_partial_,       // The regular expression object
                         NULL,              // We did not study the pattern
                         PCRE_INFO_CAPTURECOUNT,
                         &result);
  if (rc != 0) {
    PCREPORT(ERROR) << "Unexpected return code: " << rc;
    return -1;
  }
  return result;
}


/***** Parsers for various types *****/

bool PCRE::Arg::parse_null(const char* str, size_t n, void* dest) {
  // We fail if somebody asked us to store into a non-NULL void* pointer
  return (dest == NULL);
}

bool PCRE::Arg::parse_string(const char* str, size_t n, void* dest) {
  if (dest == NULL) return true;
  reinterpret_cast<std::string*>(dest)->assign(str, n);
  return true;
}

bool PCRE::Arg::parse_string_view(const char* str, size_t n, void* dest) {
  if (dest == NULL) return true;
  *(reinterpret_cast<absl::string_view*>(dest)) = absl::string_view(str, n);
  return true;
}

bool PCRE::Arg::parse_char(const char* str, size_t n, void* dest) {
  if (n != 1) return false;
  if (dest == NULL) return true;
  *(reinterpret_cast<char*>(dest)) = str[0];
  return true;
}

bool PCRE::Arg::parse_schar(const char* str, size_t n, void* dest) {
  if (n != 1) return false;
  if (dest == NULL) return true;
  *(reinterpret_cast<signed char*>(dest)) = str[0];
  return true;
}

bool PCRE::Arg::parse_uchar(const char* str, size_t n, void* dest) {
  if (n != 1) return false;
  if (dest == NULL) return true;
  *(reinterpret_cast<unsigned char*>(dest)) = str[0];
  return true;
}

// Largest number spec that we are willing to parse
static const int kMaxNumberLength = 32;

// PCREQUIPCRES "buf" must have length at least kMaxNumberLength+1
// PCREQUIPCRES "n > 0"
// Copies "str" into "buf" and null-terminates if necessary.
// Returns one of:
//      a. "str" if no termination is needed
//      b. "buf" if the string was copied and null-terminated
//      c. "" if the input was invalid and has no hope of being parsed
static const char* TerminateNumber(char* buf, const char* str, size_t n) {
  if ((n > 0) && isspace(*str)) {
    // We are less forgiving than the strtoxxx() routines and do not
    // allow leading spaces.
    return "";
  }

  // See if the character right after the input text may potentially
  // look like a digit.
  if (isdigit(str[n]) ||
      ((str[n] >= 'a') && (str[n] <= 'f')) ||
      ((str[n] >= 'A') && (str[n] <= 'F'))) {
    if (n > kMaxNumberLength) return ""; // Input too big to be a valid number
    memcpy(buf, str, n);
    buf[n] = '\0';
    return buf;
  } else {
    // We can parse right out of the supplied string, so return it.
    return str;
  }
}

bool PCRE::Arg::parse_long_radix(const char* str,
                                 size_t n,
                                 void* dest,
                                 int radix) {
  if (n == 0) return false;
  char buf[kMaxNumberLength+1];
  str = TerminateNumber(buf, str, n);
  char* end;
  errno = 0;
  long r = strtol(str, &end, radix);
  if (end != str + n) return false;   // Leftover junk
  if (errno) return false;
  if (dest == NULL) return true;
  *(reinterpret_cast<long*>(dest)) = r;
  return true;
}

bool PCRE::Arg::parse_ulong_radix(const char* str,
                                  size_t n,
                                  void* dest,
                                  int radix) {
  if (n == 0) return false;
  char buf[kMaxNumberLength+1];
  str = TerminateNumber(buf, str, n);
  if (str[0] == '-') {
    // strtoul() will silently accept negative numbers and parse
    // them.  This module is more strict and treats them as errors.
    return false;
  }

  char* end;
  errno = 0;
  unsigned long r = strtoul(str, &end, radix);
  if (end != str + n) return false;   // Leftover junk
  if (errno) return false;
  if (dest == NULL) return true;
  *(reinterpret_cast<unsigned long*>(dest)) = r;
  return true;
}

bool PCRE::Arg::parse_short_radix(const char* str,
                                  size_t n,
                                  void* dest,
                                  int radix) {
  long r;
  if (!parse_long_radix(str, n, &r, radix)) return false;  // Could not parse
  if ((short)r != r) return false;                         // Out of range
  if (dest == NULL) return true;
  *(reinterpret_cast<short*>(dest)) = (short)r;
  return true;
}

bool PCRE::Arg::parse_ushort_radix(const char* str,
                                   size_t n,
                                   void* dest,
                                   int radix) {
  unsigned long r;
  if (!parse_ulong_radix(str, n, &r, radix)) return false;  // Could not parse
  if ((unsigned short)r != r) return false;                 // Out of range
  if (dest == NULL) return true;
  *(reinterpret_cast<unsigned short*>(dest)) = (unsigned short)r;
  return true;
}

bool PCRE::Arg::parse_int_radix(const char* str,
                                size_t n,
                                void* dest,
                                int radix) {
  long r;
  if (!parse_long_radix(str, n, &r, radix)) return false;  // Could not parse
  if ((int)r != r) return false;                           // Out of range
  if (dest == NULL) return true;
  *(reinterpret_cast<int*>(dest)) = (int)r;
  return true;
}

bool PCRE::Arg::parse_uint_radix(const char* str,
                                 size_t n,
                                 void* dest,
                                 int radix) {
  unsigned long r;
  if (!parse_ulong_radix(str, n, &r, radix)) return false;  // Could not parse
  if ((unsigned int)r != r) return false;                   // Out of range
  if (dest == NULL) return true;
  *(reinterpret_cast<unsigned int*>(dest)) = (unsigned int)r;
  return true;
}

bool PCRE::Arg::parse_longlong_radix(const char* str,
                                     size_t n,
                                     void* dest,
                                     int radix) {
  if (n == 0) return false;
  char buf[kMaxNumberLength+1];
  str = TerminateNumber(buf, str, n);
  char* end;
  errno = 0;
  long long r = strtoll(str, &end, radix);
  if (end != str + n) return false;   // Leftover junk
  if (errno) return false;
  if (dest == NULL) return true;
  *(reinterpret_cast<long long*>(dest)) = r;
  return true;
}

bool PCRE::Arg::parse_ulonglong_radix(const char* str,
                                      size_t n,
                                      void* dest,
                                      int radix) {
  if (n == 0) return false;
  char buf[kMaxNumberLength+1];
  str = TerminateNumber(buf, str, n);
  if (str[0] == '-') {
    // strtoull() will silently accept negative numbers and parse
    // them.  This module is more strict and treats them as errors.
    return false;
  }
  char* end;
  errno = 0;
  unsigned long long r = strtoull(str, &end, radix);
  if (end != str + n) return false;   // Leftover junk
  if (errno) return false;
  if (dest == NULL) return true;
  *(reinterpret_cast<unsigned long long*>(dest)) = r;
  return true;
}

static bool parse_double_float(const char* str, size_t n, bool isfloat,
                               void* dest) {
  if (n == 0) return false;
  static const int kMaxLength = 200;
  char buf[kMaxLength];
  if (n >= kMaxLength) return false;
  memcpy(buf, str, n);
  buf[n] = '\0';
  char* end;
  errno = 0;
  double r;
  if (isfloat) {
    r = strtof(buf, &end);
  } else {
    r = strtod(buf, &end);
  }
  if (end != buf + n) return false;   // Leftover junk
  if (errno) return false;
  if (dest == NULL) return true;
  if (isfloat) {
    *(reinterpret_cast<float*>(dest)) = (float)r;
  } else {
    *(reinterpret_cast<double*>(dest)) = r;
  }
  return true;
}

bool PCRE::Arg::parse_double(const char* str, size_t n, void* dest) {
  return parse_double_float(str, n, false, dest);
}

bool PCRE::Arg::parse_float(const char* str, size_t n, void* dest) {
  return parse_double_float(str, n, true, dest);
}

#define DEFINE_INTEGER_PARSER(name)                                           \
  bool PCRE::Arg::parse_##name(const char* str, size_t n, void* dest) {       \
    return parse_##name##_radix(str, n, dest, 10);                            \
  }                                                                           \
  bool PCRE::Arg::parse_##name##_hex(const char* str, size_t n, void* dest) { \
    return parse_##name##_radix(str, n, dest, 16);                            \
  }                                                                           \
  bool PCRE::Arg::parse_##name##_octal(const char* str, size_t n,             \
                                       void* dest) {                          \
    return parse_##name##_radix(str, n, dest, 8);                             \
  }                                                                           \
  bool PCRE::Arg::parse_##name##_cradix(const char* str, size_t n,            \
                                        void* dest) {                         \
    return parse_##name##_radix(str, n, dest, 0);                             \
  }

DEFINE_INTEGER_PARSER(short);
DEFINE_INTEGER_PARSER(ushort);
DEFINE_INTEGER_PARSER(int);
DEFINE_INTEGER_PARSER(uint);
DEFINE_INTEGER_PARSER(long);
DEFINE_INTEGER_PARSER(ulong);
DEFINE_INTEGER_PARSER(longlong);
DEFINE_INTEGER_PARSER(ulonglong);

#undef DEFINE_INTEGER_PARSER

}  // namespace re2