base/files/file_util_win.cc

// 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.

#include "base/files/file_util.h"

// windows.h includes winsock.h which isn't compatible with winsock2.h. To use
// winsock2.h you have to include it first.
// clang-format off
#include <winsock2.h>
#include <windows.h>
// clang-format on

#include <io.h>
#include <psapi.h>
#include <share.h>
#include <shellapi.h>
#include <shlobj.h>
#include <stddef.h>
#include <stdint.h>
#include <time.h>

#include <algorithm>
#include <iterator>
#include <limits>
#include <string>
#include <string_view>

#include "base/files/file_enumerator.h"
#include "base/files/file_path.h"
#include "base/logging.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/strings/utf_string_conversions.h"
#include "base/win/scoped_handle.h"
#include "base/win/win_util.h"

// #define needed to link in RtlGenRandom(), a.k.a. SystemFunction036.  See the
// "Community Additions" comment on MSDN here:
// http://msdn.microsoft.com/en-us/library/windows/desktop/aa387694.aspx
#define SystemFunction036 NTAPI SystemFunction036
#include <ntsecapi.h>
#undef SystemFunction036

namespace base {

namespace {

const DWORD kFileShareAll =
    FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;

// Deletes all files and directories in a path.
// Returns ERROR_SUCCESS on success or the Windows error code corresponding to
// the first error encountered.
DWORD DeleteFileRecursive(const FilePath& path,
                          const FilePath::StringType& pattern,
                          bool recursive) {
  FileEnumerator traversal(path, false,
                           FileEnumerator::FILES | FileEnumerator::DIRECTORIES,
                           pattern);
  DWORD result = ERROR_SUCCESS;
  for (FilePath current = traversal.Next(); !current.empty();
       current = traversal.Next()) {
    // Try to clear the read-only bit if we find it.
    FileEnumerator::FileInfo info = traversal.GetInfo();
    if ((info.find_data().dwFileAttributes & FILE_ATTRIBUTE_READONLY) &&
        (recursive || !info.IsDirectory())) {
      ::SetFileAttributes(
          ToWCharT(&current.value()),
          info.find_data().dwFileAttributes & ~FILE_ATTRIBUTE_READONLY);
    }

    DWORD this_result = ERROR_SUCCESS;
    if (info.IsDirectory()) {
      if (recursive) {
        this_result = DeleteFileRecursive(current, pattern, true);
        if (this_result == ERROR_SUCCESS &&
            !::RemoveDirectory(ToWCharT(&current.value()))) {
          this_result = ::GetLastError();
        }
      }
    } else if (!::DeleteFile(ToWCharT(&current.value()))) {
      this_result = ::GetLastError();
    }
    if (result == ERROR_SUCCESS)
      result = this_result;
  }
  return result;
}

// Appends |mode_char| to |mode| before the optional character set encoding; see
// https://msdn.microsoft.com/library/yeby3zcb.aspx for details.
void AppendModeCharacter(char16_t mode_char, std::u16string* mode) {
  size_t comma_pos = mode->find(L',');
  mode->insert(comma_pos == std::u16string::npos ? mode->length() : comma_pos,
               1, mode_char);
}

// Returns ERROR_SUCCESS on success, or a Windows error code on failure.
DWORD DoDeleteFile(const FilePath& path, bool recursive) {
  if (path.empty())
    return ERROR_SUCCESS;

  if (path.value().length() >= MAX_PATH)
    return ERROR_BAD_PATHNAME;

  // Handle any path with wildcards.
  if (path.BaseName().value().find_first_of(u"*?") !=
      FilePath::StringType::npos) {
    return DeleteFileRecursive(path.DirName(), path.BaseName().value(),
                               recursive);
  }

  // Report success if the file or path does not exist.
  const DWORD attr = ::GetFileAttributes(ToWCharT(&path.value()));
  if (attr == INVALID_FILE_ATTRIBUTES) {
    const DWORD error_code = ::GetLastError();
    return (error_code == ERROR_FILE_NOT_FOUND ||
            error_code == ERROR_PATH_NOT_FOUND)
               ? ERROR_SUCCESS
               : error_code;
  }

  // Clear the read-only bit if it is set.
  if ((attr & FILE_ATTRIBUTE_READONLY) &&
      !::SetFileAttributes(ToWCharT(&path.value()),
                           attr & ~FILE_ATTRIBUTE_READONLY)) {
    return ::GetLastError();
  }

  // Perform a simple delete on anything that isn't a directory.
  if (!(attr & FILE_ATTRIBUTE_DIRECTORY)) {
    return ::DeleteFile(ToWCharT(&path.value())) ? ERROR_SUCCESS
                                                 : ::GetLastError();
  }

  if (recursive) {
    const DWORD error_code = DeleteFileRecursive(path, u"*", true);
    if (error_code != ERROR_SUCCESS)
      return error_code;
  }
  return ::RemoveDirectory(ToWCharT(&path.value())) ? ERROR_SUCCESS
                                                    : ::GetLastError();
}

std::string RandomDataToGUIDString(const uint64_t bytes[2]) {
  return base::StringPrintf(
      "%08x-%04x-%04x-%04x-%012llx", static_cast<unsigned int>(bytes[0] >> 32),
      static_cast<unsigned int>((bytes[0] >> 16) & 0x0000ffff),
      static_cast<unsigned int>(bytes[0] & 0x0000ffff),
      static_cast<unsigned int>(bytes[1] >> 48),
      bytes[1] & 0x0000ffff'ffffffffULL);
}

void RandBytes(void* output, size_t output_length) {
  char* output_ptr = static_cast<char*>(output);
  while (output_length > 0) {
    const ULONG output_bytes_this_pass = static_cast<ULONG>(std::min(
        output_length, static_cast<size_t>(std::numeric_limits<ULONG>::max())));
    const bool success =
        RtlGenRandom(output_ptr, output_bytes_this_pass) != FALSE;
    CHECK(success);
    output_length -= output_bytes_this_pass;
    output_ptr += output_bytes_this_pass;
  }
}

std::string GenerateGUID() {
  uint64_t sixteen_bytes[2];
  // Use base::RandBytes instead of crypto::RandBytes, because crypto calls the
  // base version directly, and to prevent the dependency from base/ to crypto/.
  RandBytes(&sixteen_bytes, sizeof(sixteen_bytes));

  // Set the GUID to version 4 as described in RFC 4122, section 4.4.
  // The format of GUID version 4 must be xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx,
  // where y is one of [8, 9, A, B].

  // Clear the version bits and set the version to 4:
  sixteen_bytes[0] &= 0xffffffff'ffff0fffULL;
  sixteen_bytes[0] |= 0x00000000'00004000ULL;

  // Set the two most significant bits (bits 6 and 7) of the
  // clock_seq_hi_and_reserved to zero and one, respectively:
  sixteen_bytes[1] &= 0x3fffffff'ffffffffULL;
  sixteen_bytes[1] |= 0x80000000'00000000ULL;

  return RandomDataToGUIDString(sixteen_bytes);
}

}  // namespace

FilePath MakeAbsoluteFilePath(const FilePath& input) {
  char16_t file_path[MAX_PATH];
  if (!_wfullpath(ToWCharT(file_path), ToWCharT(&input.value()), MAX_PATH))
    return FilePath();
  return FilePath(file_path);
}

bool DeleteFile(const FilePath& path, bool recursive) {
  static constexpr char kRecursive[] = "DeleteFile.Recursive";
  static constexpr char kNonRecursive[] = "DeleteFile.NonRecursive";
  const std::string_view operation(recursive ? kRecursive : kNonRecursive);

  // Metrics for delete failures tracked in https://crbug.com/599084. Delete may
  // fail for a number of reasons. Log some metrics relating to failures in the
  // current code so that any improvements or regressions resulting from
  // subsequent code changes can be detected.
  const DWORD error = DoDeleteFile(path, recursive);
  return error == ERROR_SUCCESS;
}

bool DeleteFileAfterReboot(const FilePath& path) {
  if (path.value().length() >= MAX_PATH)
    return false;

  return MoveFileEx(ToWCharT(&path.value()), NULL,
                    MOVEFILE_DELAY_UNTIL_REBOOT | MOVEFILE_REPLACE_EXISTING) !=
         FALSE;
}

bool ReplaceFile(const FilePath& from_path,
                 const FilePath& to_path,
                 File::Error* error) {
  // Try a simple move first.  It will only succeed when |to_path| doesn't
  // already exist.
  if (::MoveFile(ToWCharT(&from_path.value()), ToWCharT(&to_path.value())))
    return true;
  File::Error move_error = File::OSErrorToFileError(GetLastError());

  // Try the full-blown replace if the move fails, as ReplaceFile will only
  // succeed when |to_path| does exist. When writing to a network share, we may
  // not be able to change the ACLs. Ignore ACL errors then
  // (REPLACEFILE_IGNORE_MERGE_ERRORS).
  if (::ReplaceFile(ToWCharT(&to_path.value()), ToWCharT(&from_path.value()),
                    NULL, REPLACEFILE_IGNORE_MERGE_ERRORS, NULL, NULL)) {
    return true;
  }
  // In the case of FILE_ERROR_NOT_FOUND from ReplaceFile, it is likely that
  // |to_path| does not exist. In this case, the more relevant error comes
  // from the call to MoveFile.
  if (error) {
    File::Error replace_error = File::OSErrorToFileError(GetLastError());
    *error = replace_error == File::FILE_ERROR_NOT_FOUND ? move_error
                                                         : replace_error;
  }
  return false;
}

bool PathExists(const FilePath& path) {
  return (GetFileAttributes(ToWCharT(&path.value())) !=
          INVALID_FILE_ATTRIBUTES);
}

bool PathIsWritable(const FilePath& path) {
  HANDLE dir =
      CreateFile(ToWCharT(&path.value()), FILE_ADD_FILE, kFileShareAll, NULL,
                 OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);

  if (dir == INVALID_HANDLE_VALUE)
    return false;

  CloseHandle(dir);
  return true;
}

bool DirectoryExists(const FilePath& path) {
  DWORD fileattr = GetFileAttributes(ToWCharT(&path.value()));
  if (fileattr != INVALID_FILE_ATTRIBUTES)
    return (fileattr & FILE_ATTRIBUTE_DIRECTORY) != 0;
  return false;
}

bool GetTempDir(FilePath* path) {
  char16_t temp_path[MAX_PATH + 1];
  DWORD path_len = ::GetTempPath(MAX_PATH, ToWCharT(temp_path));
  if (path_len >= MAX_PATH || path_len <= 0)
    return false;
  // TODO(evanm): the old behavior of this function was to always strip the
  // trailing slash.  We duplicate this here, but it shouldn't be necessary
  // when everyone is using the appropriate FilePath APIs.
  *path = FilePath(temp_path).StripTrailingSeparators();
  return true;
}

File CreateAndOpenTemporaryFileInDir(const FilePath& dir, FilePath* temp_file) {
  constexpr uint32_t kFlags =
      File::FLAG_CREATE | File::FLAG_READ | File::FLAG_WRITE;

  // Use GUID instead of ::GetTempFileName() to generate unique file names.
  // "Due to the algorithm used to generate file names, GetTempFileName can
  // perform poorly when creating a large number of files with the same prefix.
  // In such cases, it is recommended that you construct unique file names based
  // on GUIDs."
  // https://msdn.microsoft.com/library/windows/desktop/aa364991.aspx

  FilePath temp_name;
  File file;

  // Although it is nearly impossible to get a duplicate name with GUID, we
  // still use a loop here in case it happens.
  for (int i = 0; i < 100; ++i) {
    temp_name = dir.Append(
        FilePath(UTF8ToUTF16(GenerateGUID()) + FILE_PATH_LITERAL(".tmp")));
    file.Initialize(temp_name, kFlags);
    if (file.IsValid())
      break;
  }

  if (!file.IsValid()) {
    DPLOG(WARNING) << "Failed to get temporary file name in "
                   << UTF16ToUTF8(dir.value());
    return file;
  }

  char16_t long_temp_name[MAX_PATH + 1];
  const DWORD long_name_len = GetLongPathName(
      ToWCharT(temp_name.value().c_str()), ToWCharT(long_temp_name), MAX_PATH);
  if (long_name_len != 0 && long_name_len <= MAX_PATH) {
    *temp_file =
        FilePath(FilePath::StringViewType(long_temp_name, long_name_len));
  } else {
    // GetLongPathName() failed, but we still have a temporary file.
    *temp_file = std::move(temp_name);
  }

  return file;
}

bool CreateTemporaryDirInDir(const FilePath& base_dir,
                             const FilePath::StringType& prefix,
                             FilePath* new_dir) {
  FilePath path_to_create;

  for (int count = 0; count < 50; ++count) {
    // Try create a new temporary directory with random generated name. If
    // the one exists, keep trying another path name until we reach some limit.
    std::u16string new_dir_name;
    new_dir_name.assign(prefix);
    new_dir_name.append(IntToString16(::GetCurrentProcessId()));
    new_dir_name.push_back('_');
    new_dir_name.append(UTF8ToUTF16(GenerateGUID()));

    path_to_create = base_dir.Append(new_dir_name);
    if (::CreateDirectory(ToWCharT(&path_to_create.value()), NULL)) {
      *new_dir = path_to_create;
      return true;
    }
  }

  return false;
}

bool CreateNewTempDirectory(const FilePath::StringType& prefix,
                            FilePath* new_temp_path) {
  FilePath system_temp_dir;
  if (!GetTempDir(&system_temp_dir))
    return false;

  return CreateTemporaryDirInDir(system_temp_dir, prefix, new_temp_path);
}

bool CreateDirectoryAndGetError(const FilePath& full_path, File::Error* error) {
  // If the path exists, we've succeeded if it's a directory, failed otherwise.
  DWORD fileattr = ::GetFileAttributes(ToWCharT(&full_path.value()));
  if (fileattr != INVALID_FILE_ATTRIBUTES) {
    if ((fileattr & FILE_ATTRIBUTE_DIRECTORY) != 0) {
      return true;
    }
    DLOG(WARNING) << "CreateDirectory(" << UTF16ToUTF8(full_path.value())
                  << "), " << "conflicts with existing file.";
    if (error) {
      *error = File::FILE_ERROR_NOT_A_DIRECTORY;
    }
    return false;
  }

  // Invariant:  Path does not exist as file or directory.

  // Attempt to create the parent recursively.  This will immediately return
  // true if it already exists, otherwise will create all required parent
  // directories starting with the highest-level missing parent.
  FilePath parent_path(full_path.DirName());
  if (parent_path.value() == full_path.value()) {
    if (error) {
      *error = File::FILE_ERROR_NOT_FOUND;
    }
    return false;
  }
  if (!CreateDirectoryAndGetError(parent_path, error)) {
    DLOG(WARNING) << "Failed to create one of the parent directories.";
    if (error) {
      DCHECK(*error != File::FILE_OK);
    }
    return false;
  }

  if (!::CreateDirectory(ToWCharT(&full_path.value()), NULL)) {
    DWORD error_code = ::GetLastError();
    if (error_code == ERROR_ALREADY_EXISTS && DirectoryExists(full_path)) {
      // This error code ERROR_ALREADY_EXISTS doesn't indicate whether we
      // were racing with someone creating the same directory, or a file
      // with the same path.  If DirectoryExists() returns true, we lost the
      // race to create the same directory.
      return true;
    } else {
      if (error)
        *error = File::OSErrorToFileError(error_code);
      DLOG(WARNING) << "Failed to create directory "
                    << UTF16ToUTF8(full_path.value()) << ", last error is "
                    << error_code << ".";
      return false;
    }
  } else {
    return true;
  }
}

bool NormalizeFilePath(const FilePath& path, FilePath* real_path) {
  FilePath mapped_file;
  if (!NormalizeToNativeFilePath(path, &mapped_file))
    return false;
  // NormalizeToNativeFilePath() will return a path that starts with
  // "\Device\Harddisk...".  Helper DevicePathToDriveLetterPath()
  // will find a drive letter which maps to the path's device, so
  // that we return a path starting with a drive letter.
  return DevicePathToDriveLetterPath(mapped_file, real_path);
}

bool DevicePathToDriveLetterPath(const FilePath& nt_device_path,
                                 FilePath* out_drive_letter_path) {
  // Get the mapping of drive letters to device paths.
  const int kDriveMappingSize = 1024;
  char16_t drive_mapping[kDriveMappingSize] = {'\0'};
  if (!::GetLogicalDriveStrings(kDriveMappingSize - 1,
                                ToWCharT(drive_mapping))) {
    DLOG(ERROR) << "Failed to get drive mapping.";
    return false;
  }

  // The drive mapping is a sequence of null terminated strings.
  // The last string is empty.
  char16_t* drive_map_ptr = drive_mapping;
  char16_t device_path_as_string[MAX_PATH];
  char16_t drive[] = u" :";

  // For each string in the drive mapping, get the junction that links
  // to it.  If that junction is a prefix of |device_path|, then we
  // know that |drive| is the real path prefix.
  while (*drive_map_ptr) {
    drive[0] = drive_map_ptr[0];  // Copy the drive letter.

    if (QueryDosDevice(ToWCharT(drive), ToWCharT(device_path_as_string),
                       MAX_PATH)) {
      FilePath device_path(device_path_as_string);
      if (device_path == nt_device_path ||
          device_path.IsParent(nt_device_path)) {
        *out_drive_letter_path =
            FilePath(drive + nt_device_path.value().substr(
                                 wcslen(ToWCharT(device_path_as_string))));
        return true;
      }
    }
    // Move to the next drive letter string, which starts one
    // increment after the '\0' that terminates the current string.
    while (*drive_map_ptr++) {
    }
  }

  // No drive matched.  The path does not start with a device junction
  // that is mounted as a drive letter.  This means there is no drive
  // letter path to the volume that holds |device_path|, so fail.
  return false;
}

bool NormalizeToNativeFilePath(const FilePath& path, FilePath* nt_path) {
  // In Vista, GetFinalPathNameByHandle() would give us the real path
  // from a file handle.  If we ever deprecate XP, consider changing the
  // code below to a call to GetFinalPathNameByHandle().  The method this
  // function uses is explained in the following msdn article:
  // http://msdn.microsoft.com/en-us/library/aa366789(VS.85).aspx
  win::ScopedHandle file_handle(
      ::CreateFile(ToWCharT(&path.value()), GENERIC_READ, kFileShareAll, NULL,
                   OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL));
  if (!file_handle.IsValid())
    return false;

  // Create a file mapping object.  Can't easily use MemoryMappedFile, because
  // we only map the first byte, and need direct access to the handle. You can
  // not map an empty file, this call fails in that case.
  win::ScopedHandle file_map_handle(
      ::CreateFileMapping(file_handle.Get(), NULL, PAGE_READONLY, 0,
                          1,  // Just one byte.  No need to look at the data.
                          NULL));
  if (!file_map_handle.IsValid())
    return false;

  // Use a view of the file to get the path to the file.
  void* file_view =
      MapViewOfFile(file_map_handle.Get(), FILE_MAP_READ, 0, 0, 1);
  if (!file_view)
    return false;

  // The expansion of |path| into a full path may make it longer.
  // GetMappedFileName() will fail if the result is longer than MAX_PATH.
  // Pad a bit to be safe.  If kMaxPathLength is ever changed to be less
  // than MAX_PATH, it would be nessisary to test that GetMappedFileName()
  // not return kMaxPathLength.  This would mean that only part of the
  // path fit in |mapped_file_path|.
  const int kMaxPathLength = MAX_PATH + 10;
  char16_t mapped_file_path[kMaxPathLength];
  bool success = false;
  HANDLE cp = GetCurrentProcess();
  if (::GetMappedFileNameW(cp, file_view, ToWCharT(mapped_file_path),
                           kMaxPathLength)) {
    *nt_path = FilePath(mapped_file_path);
    success = true;
  }
  ::UnmapViewOfFile(file_view);
  return success;
}

// TODO(rkc): Work out if we want to handle NTFS junctions here or not, handle
// them if we do decide to.
bool IsLink(const FilePath& file_path) {
  return false;
}

bool GetFileInfo(const FilePath& file_path, File::Info* results) {
  WIN32_FILE_ATTRIBUTE_DATA attr;
  if (!GetFileAttributesEx(ToWCharT(&file_path.value()), GetFileExInfoStandard,
                           &attr)) {
    return false;
  }

  ULARGE_INTEGER size;
  size.HighPart = attr.nFileSizeHigh;
  size.LowPart = attr.nFileSizeLow;
  results->size = size.QuadPart;

  results->is_directory =
      (attr.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0;
  results->last_modified = *reinterpret_cast<uint64_t*>(&attr.ftLastWriteTime);
  results->last_accessed = *reinterpret_cast<uint64_t*>(&attr.ftLastAccessTime);
  results->creation_time = *reinterpret_cast<uint64_t*>(&attr.ftCreationTime);

  return true;
}

FILE* OpenFile(const FilePath& filename, const char* mode) {
  // 'N' is unconditionally added below, so be sure there is not one already
  // present before a comma in |mode|.
  DCHECK(
      strchr(mode, 'N') == nullptr ||
      (strchr(mode, ',') != nullptr && strchr(mode, 'N') > strchr(mode, ',')));
  std::u16string w_mode = ASCIIToUTF16(mode);
  AppendModeCharacter(L'N', &w_mode);
  return _wfsopen(ToWCharT(&filename.value()), ToWCharT(&w_mode), _SH_DENYNO);
}

FILE* FileToFILE(File file, const char* mode) {
  if (!file.IsValid())
    return NULL;
  int fd =
      _open_osfhandle(reinterpret_cast<intptr_t>(file.GetPlatformFile()), 0);
  if (fd < 0)
    return NULL;
  file.TakePlatformFile();
  FILE* stream = _fdopen(fd, mode);
  if (!stream)
    _close(fd);
  return stream;
}

int ReadFile(const FilePath& filename, char* data, int max_size) {
  win::ScopedHandle file(CreateFile(ToWCharT(&filename.value()), GENERIC_READ,
                                    FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
                                    OPEN_EXISTING, FILE_FLAG_SEQUENTIAL_SCAN,
                                    NULL));
  if (!file.IsValid())
    return -1;

  DWORD read;
  if (::ReadFile(file.Get(), data, max_size, &read, NULL))
    return read;

  return -1;
}

int WriteFile(const FilePath& filename, const char* data, int size) {
  win::ScopedHandle file(CreateFile(ToWCharT(&filename.value()), GENERIC_WRITE,
                                    0, NULL, CREATE_ALWAYS,
                                    FILE_ATTRIBUTE_NORMAL, NULL));
  if (!file.IsValid()) {
    DPLOG(WARNING) << "CreateFile failed for path "
                   << UTF16ToUTF8(filename.value());
    return -1;
  }

  DWORD written;
  BOOL result = ::WriteFile(file.Get(), data, size, &written, NULL);
  if (result && static_cast<int>(written) == size)
    return written;

  if (!result) {
    // WriteFile failed.
    DPLOG(WARNING) << "writing file " << UTF16ToUTF8(filename.value())
                   << " failed";
  } else {
    // Didn't write all the bytes.
    DLOG(WARNING) << "wrote" << written << " bytes to "
                  << UTF16ToUTF8(filename.value()) << " expected " << size;
  }
  return -1;
}

bool AppendToFile(const FilePath& filename, const char* data, int size) {
  win::ScopedHandle file(CreateFile(ToWCharT(&filename.value()),
                                    FILE_APPEND_DATA, 0, NULL, OPEN_EXISTING, 0,
                                    NULL));
  if (!file.IsValid()) {
    return false;
  }

  DWORD written;
  BOOL result = ::WriteFile(file.Get(), data, size, &written, NULL);
  if (result && static_cast<int>(written) == size)
    return true;

  return false;
}

bool GetCurrentDirectory(FilePath* dir) {
  char16_t system_buffer[MAX_PATH];
  system_buffer[0] = 0;
  DWORD len = ::GetCurrentDirectory(MAX_PATH, ToWCharT(system_buffer));
  if (len == 0 || len > MAX_PATH)
    return false;
  // TODO(evanm): the old behavior of this function was to always strip the
  // trailing slash.  We duplicate this here, but it shouldn't be necessary
  // when everyone is using the appropriate FilePath APIs.
  std::u16string dir_str(system_buffer);
  *dir = FilePath(dir_str).StripTrailingSeparators();
  return true;
}

bool SetCurrentDirectory(const FilePath& directory) {
  return ::SetCurrentDirectory(ToWCharT(&directory.value())) != 0;
}

int GetMaximumPathComponentLength(const FilePath& path) {
  char16_t volume_path[MAX_PATH];
  if (!GetVolumePathNameW(ToWCharT(&path.NormalizePathSeparators().value()),
                          ToWCharT(volume_path), std::size(volume_path))) {
    return -1;
  }

  DWORD max_length = 0;
  if (!GetVolumeInformationW(ToWCharT(volume_path), NULL, 0, NULL, &max_length,
                             NULL, NULL, 0)) {
    return -1;
  }

  // Length of |path| with path separator appended.
  size_t prefix = path.StripTrailingSeparators().value().size() + 1;
  // The whole path string must be shorter than MAX_PATH. That is, it must be
  // prefix + component_length < MAX_PATH (or equivalently, <= MAX_PATH - 1).
  int whole_path_limit = std::max(0, MAX_PATH - 1 - static_cast<int>(prefix));
  return std::min(whole_path_limit, static_cast<int>(max_length));
}

bool SetNonBlocking(int fd) {
  unsigned long nonblocking = 1;
  if (ioctlsocket(fd, FIONBIO, &nonblocking) == 0)
    return true;
  return false;
}

}  // namespace base