base/files/file.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_FILES_FILE_H_
   6 #define BASE_FILES_FILE_H_
   7
   8 #include "build/build_config.h"
   9 #if defined(OS_WIN)
  10 #include <windows.h>
  11 #endif
  12
  13 #if defined(OS_POSIX)
  14 #include <sys/stat.h>
  15 #endif
  16
  17 #include <string>
  18
  19 #include "base/base_export.h"
  20 #include "base/basictypes.h"
  21 #include "base/files/scoped_file.h"
  22 #include "base/move.h"
  23 #include "base/time/time.h"
  24
  25 #if defined(OS_WIN)
  26 #include "base/win/scoped_handle.h"
  27 #endif
  28
  29 namespace base {
  30
  31 class FilePath;
  32
  33 #if defined(OS_WIN)
  34 typedef HANDLE PlatformFile;
  35 #elif defined(OS_POSIX)
  36 typedef int PlatformFile;
  37
  38 #if defined(OS_BSD) || defined(OS_MACOSX) || defined(OS_NACL)
  39 typedef struct stat stat_wrapper_t;
  40 #else
  41 typedef struct stat64 stat_wrapper_t;
  42 #endif
  43 #endif  // defined(OS_POSIX)
  44
  45 // Thin wrapper around an OS-level file.
  46 // Note that this class does not provide any support for asynchronous IO, other
  47 // than the ability to create asynchronous handles on Windows.
  48 //
  49 // Note about const: this class does not attempt to determine if the underlying
  50 // file system object is affected by a particular method in order to consider
  51 // that method const or not. Only methods that deal with member variables in an
  52 // obvious non-modifying way are marked as const. Any method that forward calls
  53 // to the OS is not considered const, even if there is no apparent change to
  54 // member variables.
  55 class BASE_EXPORT File {
  56   MOVE_ONLY_TYPE_FOR_CPP_03(File, RValue)
  57
  58  public:
  59   // FLAG_(OPEN|CREATE).* are mutually exclusive. You should specify exactly one
  60   // of the five (possibly combining with other flags) when opening or creating
  61   // a file.
  62   // FLAG_(WRITE|APPEND) are mutually exclusive. This is so that APPEND behavior
  63   // will be consistent with O_APPEND on POSIX.
  64   // FLAG_EXCLUSIVE_(READ|WRITE) only grant exclusive access to the file on
  65   // creation on POSIX; for existing files, consider using Lock().
  66   enum Flags {
  67     FLAG_OPEN = 1 << 0,             // Opens a file, only if it exists.
  68     FLAG_CREATE = 1 << 1,           // Creates a new file, only if it does not
  69                                     // already exist.
  70     FLAG_OPEN_ALWAYS = 1 << 2,      // May create a new file.
  71     FLAG_CREATE_ALWAYS = 1 << 3,    // May overwrite an old file.
  72     FLAG_OPEN_TRUNCATED = 1 << 4,   // Opens a file and truncates it, only if it
  73                                     // exists.
  74     FLAG_READ = 1 << 5,
  75     FLAG_WRITE = 1 << 6,
  76     FLAG_APPEND = 1 << 7,
  77     FLAG_EXCLUSIVE_READ = 1 << 8,   // EXCLUSIVE is opposite of Windows SHARE.
  78     FLAG_EXCLUSIVE_WRITE = 1 << 9,
  79     FLAG_ASYNC = 1 << 10,
  80     FLAG_TEMPORARY = 1 << 11,       // Used on Windows only.
  81     FLAG_HIDDEN = 1 << 12,          // Used on Windows only.
  82     FLAG_DELETE_ON_CLOSE = 1 << 13,
  83     FLAG_WRITE_ATTRIBUTES = 1 << 14,  // Used on Windows only.
  84     FLAG_SHARE_DELETE = 1 << 15,      // Used on Windows only.
  85     FLAG_TERMINAL_DEVICE = 1 << 16,   // Serial port flags.
  86     FLAG_BACKUP_SEMANTICS = 1 << 17,  // Used on Windows only.
  87     FLAG_EXECUTE = 1 << 18,           // Used on Windows only.
  88   };
  89
  90   // This enum has been recorded in multiple histograms. If the order of the
  91   // fields needs to change, please ensure that those histograms are obsolete or
  92   // have been moved to a different enum.
  93   //
  94   // FILE_ERROR_ACCESS_DENIED is returned when a call fails because of a
  95   // filesystem restriction. FILE_ERROR_SECURITY is returned when a browser
  96   // policy doesn't allow the operation to be executed.
  97   enum Error {
  98     FILE_OK = 0,
  99     FILE_ERROR_FAILED = -1,
 100     FILE_ERROR_IN_USE = -2,
 101     FILE_ERROR_EXISTS = -3,
 102     FILE_ERROR_NOT_FOUND = -4,
 103     FILE_ERROR_ACCESS_DENIED = -5,
 104     FILE_ERROR_TOO_MANY_OPENED = -6,
 105     FILE_ERROR_NO_MEMORY = -7,
 106     FILE_ERROR_NO_SPACE = -8,
 107     FILE_ERROR_NOT_A_DIRECTORY = -9,
 108     FILE_ERROR_INVALID_OPERATION = -10,
 109     FILE_ERROR_SECURITY = -11,
 110     FILE_ERROR_ABORT = -12,
 111     FILE_ERROR_NOT_A_FILE = -13,
 112     FILE_ERROR_NOT_EMPTY = -14,
 113     FILE_ERROR_INVALID_URL = -15,
 114     FILE_ERROR_IO = -16,
 115     // Put new entries here and increment FILE_ERROR_MAX.
 116     FILE_ERROR_MAX = -17
 117   };
 118
 119   // This explicit mapping matches both FILE_ on Windows and SEEK_ on Linux.
 120   enum Whence {
 121     FROM_BEGIN   = 0,
 122     FROM_CURRENT = 1,
 123     FROM_END     = 2
 124   };
 125
 126   // Used to hold information about a given file.
 127   // If you add more fields to this structure (platform-specific fields are OK),
 128   // make sure to update all functions that use it in file_util_{win|posix}.cc
 129   // too, and the ParamTraits<base::PlatformFileInfo> implementation in
 130   // chrome/common/common_param_traits.cc.
 131   struct BASE_EXPORT Info {
 132     Info();
 133     ~Info();
 134 #if defined(OS_POSIX)
 135     // Fills this struct with values from |stat_info|.
 136     void FromStat(const stat_wrapper_t& stat_info);
 137 #endif
 138
 139     // The size of the file in bytes.  Undefined when is_directory is true.
 140     int64 size;
 141
 142     // True if the file corresponds to a directory.
 143     bool is_directory;
 144
 145     // True if the file corresponds to a symbolic link.
 146     bool is_symbolic_link;
 147
 148     // The last modified time of a file.
 149     base::Time last_modified;
 150
 151     // The last accessed time of a file.
 152     base::Time last_accessed;
 153
 154     // The creation time of a file.
 155     base::Time creation_time;
 156   };
 157
 158   File();
 159
 160   // Creates or opens the given file. This will fail with 'access denied' if the
 161   // |name| contains path traversal ('..') components.
 162   File(const FilePath& name, uint32 flags);
 163
 164   // Takes ownership of |platform_file|.
 165   explicit File(PlatformFile platform_file);
 166
 167   // Creates an object with a specific error_details code.
 168   explicit File(Error error_details);
 169
 170   // Move constructor for C++03 move emulation of this type.
 171   File(RValue other);
 172
 173   ~File();
 174
 175   // Move operator= for C++03 move emulation of this type.
 176   File& operator=(RValue other);
 177
 178   // Creates or opens the given file.
 179   void Initialize(const FilePath& name, uint32 flags);
 180
 181   // Creates or opens the given file, allowing paths with traversal ('..')
 182   // components. Use only with extreme care.
 183   void InitializeUnsafe(const FilePath& name, uint32 flags);
 184
 185   bool IsValid() const;
 186
 187   // Returns true if a new file was created (or an old one truncated to zero
 188   // length to simulate a new file, which can happen with
 189   // FLAG_CREATE_ALWAYS), and false otherwise.
 190   bool created() const { return created_; }
 191
 192   // Returns the OS result of opening this file. Note that the way to verify
 193   // the success of the operation is to use IsValid(), not this method:
 194   //   File file(name, flags);
 195   //   if (!file.IsValid())
 196   //     return;
 197   Error error_details() const { return error_details_; }
 198
 199   PlatformFile GetPlatformFile() const;
 200   PlatformFile TakePlatformFile();
 201
 202   // Destroying this object closes the file automatically.
 203   void Close();
 204
 205   // Changes current position in the file to an |offset| relative to an origin
 206   // defined by |whence|. Returns the resultant current position in the file
 207   // (relative to the start) or -1 in case of error.
 208   int64 Seek(Whence whence, int64 offset);
 209
 210   // Reads the given number of bytes (or until EOF is reached) starting with the
 211   // given offset. Returns the number of bytes read, or -1 on error. Note that
 212   // this function makes a best effort to read all data on all platforms, so it
 213   // is not intended for stream oriented files but instead for cases when the
 214   // normal expectation is that actually |size| bytes are read unless there is
 215   // an error.
 216   int Read(int64 offset, char* data, int size);
 217
 218   // Same as above but without seek.
 219   int ReadAtCurrentPos(char* data, int size);
 220
 221   // Reads the given number of bytes (or until EOF is reached) starting with the
 222   // given offset, but does not make any effort to read all data on all
 223   // platforms. Returns the number of bytes read, or -1 on error.
 224   int ReadNoBestEffort(int64 offset, char* data, int size);
 225
 226   // Same as above but without seek.
 227   int ReadAtCurrentPosNoBestEffort(char* data, int size);
 228
 229   // Writes the given buffer into the file at the given offset, overwritting any
 230   // data that was previously there. Returns the number of bytes written, or -1
 231   // on error. Note that this function makes a best effort to write all data on
 232   // all platforms.
 233   // Ignores the offset and writes to the end of the file if the file was opened
 234   // with FLAG_APPEND.
 235   int Write(int64 offset, const char* data, int size);
 236
 237   // Save as above but without seek.
 238   int WriteAtCurrentPos(const char* data, int size);
 239
 240   // Save as above but does not make any effort to write all data on all
 241   // platforms. Returns the number of bytes written, or -1 on error.
 242   int WriteAtCurrentPosNoBestEffort(const char* data, int size);
 243
 244   // Returns the current size of this file, or a negative number on failure.
 245   int64 GetLength();
 246
 247   // Truncates the file to the given length. If |length| is greater than the
 248   // current size of the file, the file is extended with zeros. If the file
 249   // doesn't exist, |false| is returned.
 250   bool SetLength(int64 length);
 251
 252   // Flushes the buffers.
 253   bool Flush();
 254
 255   // Updates the file times.
 256   bool SetTimes(Time last_access_time, Time last_modified_time);
 257
 258   // Returns some basic information for the given file.
 259   bool GetInfo(Info* info);
 260
 261   // Attempts to take an exclusive write lock on the file. Returns immediately
 262   // (i.e. does not wait for another process to unlock the file). If the lock
 263   // was obtained, the result will be FILE_OK. A lock only guarantees
 264   // that other processes may not also take a lock on the same file with the
 265   // same API - it may still be opened, renamed, unlinked, etc.
 266   //
 267   // Common semantics:
 268   //  * Locks are held by processes, but not inherited by child processes.
 269   //  * Locks are released by the OS on file close or process termination.
 270   //  * Locks are reliable only on local filesystems.
 271   //  * Duplicated file handles may also write to locked files.
 272   // Windows-specific semantics:
 273   //  * Locks are mandatory for read/write APIs, advisory for mapping APIs.
 274   //  * Within a process, locking the same file (by the same or new handle)
 275   //    will fail.
 276   // POSIX-specific semantics:
 277   //  * Locks are advisory only.
 278   //  * Within a process, locking the same file (by the same or new handle)
 279   //    will succeed.
 280   //  * Closing any descriptor on a given file releases the lock.
 281   Error Lock();
 282
 283   // Unlock a file previously locked.
 284   Error Unlock();
 285
 286   bool async() const { return async_; }
 287
 288 #if defined(OS_WIN)
 289   static Error OSErrorToFileError(DWORD last_error);
 290 #elif defined(OS_POSIX)
 291   static Error OSErrorToFileError(int saved_errno);
 292 #endif
 293
 294   // Converts an error value to a human-readable form. Used for logging.
 295   static std::string ErrorToString(Error error);
 296
 297  private:
 298   void SetPlatformFile(PlatformFile file);
 299
 300 #if defined(OS_WIN)
 301   win::ScopedHandle file_;
 302 #elif defined(OS_POSIX)
 303   ScopedFD file_;
 304 #endif
 305
 306   Error error_details_;
 307   bool created_;
 308   bool async_;
 309 };
 310
 311 }  // namespace base
 312
 313 #endif  // BASE_FILES_FILE_H_