firefox/security/sandbox/chromium-shim/base/files/file_path.cpp

// Copyright (c) 2012 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.

// This is a partial implementation of Chromium's source file
// base/file/file_path.cc.

#include "base/files/file_path.h"

namespace base {

using StringType = FilePath::StringType;
using StringPieceType = FilePath::StringPieceType;

namespace {

const FilePath::CharType kStringTerminator = FILE_PATH_LITERAL('\0');

// If this FilePath contains a drive letter specification, returns the
// position of the last character of the drive letter specification,
// otherwise returns npos.  This can only be true on Windows, when a pathname
// begins with a letter followed by a colon.  On other platforms, this always
// returns npos.
StringPieceType::size_type FindDriveLetter(StringPieceType path) {
#if defined(FILE_PATH_USES_DRIVE_LETTERS)
  // This is dependent on an ASCII-based character set, but that's a
  // reasonable assumption.  iswalpha can be too inclusive here.
  if (path.length() >= 2 && path[1] == L':' &&
      ((path[0] >= L'A' && path[0] <= L'Z') ||
       (path[0] >= L'a' && path[0] <= L'z'))) {
    return 1;
  }
#endif  // FILE_PATH_USES_DRIVE_LETTERS
  return StringType::npos;
}

bool IsPathAbsolute(StringPieceType path) {
#if defined(FILE_PATH_USES_DRIVE_LETTERS)
  StringType::size_type letter = FindDriveLetter(path);
  if (letter != StringType::npos) {
    // Look for a separator right after the drive specification.
    return path.length() > letter + 1 &&
        FilePath::IsSeparator(path[letter + 1]);
  }
  // Look for a pair of leading separators.
  return path.length() > 1 &&
      FilePath::IsSeparator(path[0]) && FilePath::IsSeparator(path[1]);
#else  // FILE_PATH_USES_DRIVE_LETTERS
  // Look for a separator in the first position.
  return path.length() > 0 && FilePath::IsSeparator(path[0]);
#endif  // FILE_PATH_USES_DRIVE_LETTERS
}

}  // namespace

FilePath::FilePath() = default;

FilePath::FilePath(const FilePath& that) = default;
FilePath::FilePath(FilePath&& that) noexcept = default;

FilePath::FilePath(StringPieceType path) : path_(path) {
  StringType::size_type nul_pos = path_.find(kStringTerminator);
  if (nul_pos != StringType::npos)
    path_.erase(nul_pos, StringType::npos);
}

FilePath::~FilePath() = default;

FilePath& FilePath::operator=(const FilePath& that) = default;

FilePath& FilePath::operator=(FilePath&& that) = default;

// static
bool FilePath::IsSeparator(CharType character) {
  for (size_t i = 0; i < kSeparatorsLength - 1; ++i) {
    if (character == kSeparators[i]) {
      return true;
    }
  }

  return false;
}

// libgen's dirname and basename aren't guaranteed to be thread-safe and aren't
// guaranteed to not modify their input strings, and in fact are implemented
// differently in this regard on different platforms.  Don't use them, but
// adhere to their behavior.
FilePath FilePath::DirName() const {
  FilePath new_path(path_);
  new_path.StripTrailingSeparatorsInternal();

  // The drive letter, if any, always needs to remain in the output.  If there
  // is no drive letter, as will always be the case on platforms which do not
  // support drive letters, letter will be npos, or -1, so the comparisons and
  // resizes below using letter will still be valid.
  StringType::size_type letter = FindDriveLetter(new_path.path_);

  StringType::size_type last_separator =
      new_path.path_.find_last_of(kSeparators, StringType::npos,
                                  kSeparatorsLength - 1);
  if (last_separator == StringType::npos) {
    // path_ is in the current directory.
    new_path.path_.resize(letter + 1);
  } else if (last_separator == letter + 1) {
    // path_ is in the root directory.
    new_path.path_.resize(letter + 2);
  } else if (last_separator == letter + 2 &&
             IsSeparator(new_path.path_[letter + 1])) {
    // path_ is in "//" (possibly with a drive letter); leave the double
    // separator intact indicating alternate root.
    new_path.path_.resize(letter + 3);
  } else if (last_separator != 0) {
    // path_ is somewhere else, trim the basename.
    new_path.path_.resize(last_separator);
  }

  new_path.StripTrailingSeparatorsInternal();
  if (!new_path.path_.length())
    new_path.path_ = kCurrentDirectory;

  return new_path;
}

FilePath FilePath::BaseName() const {
  FilePath new_path(path_);
  new_path.StripTrailingSeparatorsInternal();

  // The drive letter, if any, is always stripped.
  StringType::size_type letter = FindDriveLetter(new_path.path_);
  if (letter != StringType::npos) {
    new_path.path_.erase(0, letter + 1);
  }

  // Keep everything after the final separator, but if the pathname is only
  // one character and it's a separator, leave it alone.
  StringType::size_type last_separator =
      new_path.path_.find_last_of(kSeparators, StringType::npos,
                                  kSeparatorsLength - 1);
  if (last_separator != StringType::npos &&
      last_separator < new_path.path_.length() - 1) {
    new_path.path_.erase(0, last_separator + 1);
  }

  return new_path;
}

FilePath FilePath::Append(StringPieceType component) const {
  StringPieceType appended = component;
  StringType without_nuls;

  StringType::size_type nul_pos = component.find(kStringTerminator);
  if (nul_pos != StringPieceType::npos) {
    without_nuls = StringType(component.substr(0, nul_pos));
    appended = StringPieceType(without_nuls);
  }

  DCHECK(!IsPathAbsolute(appended));

  if (path_.compare(kCurrentDirectory) == 0 && !appended.empty()) {
    // Append normally doesn't do any normalization, but as a special case,
    // when appending to kCurrentDirectory, just return a new path for the
    // component argument.  Appending component to kCurrentDirectory would
    // serve no purpose other than needlessly lengthening the path, and
    // it's likely in practice to wind up with FilePath objects containing
    // only kCurrentDirectory when calling DirName on a single relative path
    // component.
    return FilePath(appended);
  }

  FilePath new_path(path_);
  new_path.StripTrailingSeparatorsInternal();

  // Don't append a separator if the path is empty (indicating the current
  // directory) or if the path component is empty (indicating nothing to
  // append).
  if (!appended.empty() && !new_path.path_.empty()) {
    // Don't append a separator if the path still ends with a trailing
    // separator after stripping (indicating the root directory).
    if (!IsSeparator(new_path.path_.back())) {
      // Don't append a separator if the path is just a drive letter.
      if (FindDriveLetter(new_path.path_) + 1 != new_path.path_.length()) {
        new_path.path_.append(1, kSeparators[0]);
      }
    }
  }

  new_path.path_.append(appended.data(), appended.size());
  return new_path;
}

FilePath FilePath::Append(const FilePath& component) const {
  return Append(component.value());
}

void FilePath::StripTrailingSeparatorsInternal() {
  // If there is no drive letter, start will be 1, which will prevent stripping
  // the leading separator if there is only one separator.  If there is a drive
  // letter, start will be set appropriately to prevent stripping the first
  // separator following the drive letter, if a separator immediately follows
  // the drive letter.
  StringType::size_type start = FindDriveLetter(path_) + 2;

  StringType::size_type last_stripped = StringType::npos;
  for (StringType::size_type pos = path_.length();
       pos > start && IsSeparator(path_[pos - 1]);
       --pos) {
    // If the string only has two separators and they're at the beginning,
    // don't strip them, unless the string began with more than two separators.
    if (pos != start + 1 || last_stripped == start + 2 ||
        !IsSeparator(path_[start - 1])) {
      path_.resize(pos - 1);
      last_stripped = pos;
    }
  }
}

} // namespace base