gio/glocalfileoutputstream.c

   1 /* GIO - GLib Input, Output and Streaming Library
   2  *
   3  * Copyright (C) 2006-2007 Red Hat, Inc.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General
  16  * Public License along with this library; if not, write to the
  17  * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  18  * Boston, MA 02111-1307, USA.
  19  *
  20  * Author: Alexander Larsson <alexl@redhat.com>
  21  */
  22
  23 #include "config.h"
  24
  25 #include <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <fcntl.h>
  28 #ifdef HAVE_UNISTD_H
  29 #include <unistd.h>
  30 #endif
  31 #include <errno.h>
  32 #include <string.h>
  33
  34 #include <glib.h>
  35 #include <glib/gstdio.h>
  36 #include "glibintl.h"
  37 #include "gioerror.h"
  38 #include "gcancellable.h"
  39 #include "glocalfileoutputstream.h"
  40 #include "glocalfileinfo.h"
  41
  42 #ifdef G_OS_WIN32
  43 #include <io.h>
  44 #ifndef S_ISDIR
  45 #define S_ISDIR(m) (((m) & _S_IFMT) == _S_IFDIR)
  46 #endif
  47 #ifndef S_ISREG
  48 #define S_ISREG(m) (((m) & _S_IFMT) == _S_IFREG)
  49 #endif
  50 #endif
  51
  52 #ifndef O_BINARY
  53 #define O_BINARY 0
  54 #endif
  55
  56 #include "gioalias.h"
  57
  58 #define g_local_file_output_stream_get_type _g_local_file_output_stream_get_type
  59 G_DEFINE_TYPE (GLocalFileOutputStream, g_local_file_output_stream, G_TYPE_FILE_OUTPUT_STREAM);
  60
  61 /* Some of the file replacement code was based on the code from gedit,
  62  * relicenced to LGPL with permissions from the authors.
  63  */
  64
  65 #define BACKUP_EXTENSION "~"
  66
  67 struct _GLocalFileOutputStreamPrivate {
  68   char *tmp_filename;
  69   char *original_filename;
  70   char *backup_filename;
  71   char *etag;
  72   int fd;
  73 };
  74
  75 static gssize     g_local_file_output_stream_write        (GOutputStream      *stream,
  76                                                            const void         *buffer,
  77                                                            gsize               count,
  78                                                            GCancellable       *cancellable,
  79                                                            GError            **error);
  80 static gboolean   g_local_file_output_stream_close        (GOutputStream      *stream,
  81                                                            GCancellable       *cancellable,
  82                                                            GError            **error);
  83 static GFileInfo *g_local_file_output_stream_query_info   (GFileOutputStream  *stream,
  84                                                            char               *attributes,
  85                                                            GCancellable       *cancellable,
  86                                                            GError            **error);
  87 static char *     g_local_file_output_stream_get_etag     (GFileOutputStream  *stream);
  88 static goffset    g_local_file_output_stream_tell         (GFileOutputStream  *stream);
  89 static gboolean   g_local_file_output_stream_can_seek     (GFileOutputStream  *stream);
  90 static gboolean   g_local_file_output_stream_seek         (GFileOutputStream  *stream,
  91                                                            goffset             offset,
  92                                                            GSeekType           type,
  93                                                            GCancellable       *cancellable,
  94                                                            GError            **error);
  95 static gboolean   g_local_file_output_stream_can_truncate (GFileOutputStream  *stream);
  96 static gboolean   g_local_file_output_stream_truncate     (GFileOutputStream  *stream,
  97                                                            goffset             size,
  98                                                            GCancellable       *cancellable,
  99                                                            GError            **error);
 100
 101 static void
 102 g_local_file_output_stream_finalize (GObject *object)
 103 {
 104   GLocalFileOutputStream *file;
 105
 106   file = G_LOCAL_FILE_OUTPUT_STREAM (object);
 107
 108   g_free (file->priv->tmp_filename);
 109   g_free (file->priv->original_filename);
 110   g_free (file->priv->backup_filename);
 111   g_free (file->priv->etag);
 112
 113   G_OBJECT_CLASS (g_local_file_output_stream_parent_class)->finalize (object);
 114 }
 115
 116 static void
 117 g_local_file_output_stream_class_init (GLocalFileOutputStreamClass *klass)
 118 {
 119   GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
 120   GOutputStreamClass *stream_class = G_OUTPUT_STREAM_CLASS (klass);
 121   GFileOutputStreamClass *file_stream_class = G_FILE_OUTPUT_STREAM_CLASS (klass);
 122
 123   g_type_class_add_private (klass, sizeof (GLocalFileOutputStreamPrivate));
 124
 125   gobject_class->finalize = g_local_file_output_stream_finalize;
 126
 127   stream_class->write_fn = g_local_file_output_stream_write;
 128   stream_class->close_fn = g_local_file_output_stream_close;
 129   file_stream_class->query_info = g_local_file_output_stream_query_info;
 130   file_stream_class->get_etag = g_local_file_output_stream_get_etag;
 131   file_stream_class->tell = g_local_file_output_stream_tell;
 132   file_stream_class->can_seek = g_local_file_output_stream_can_seek;
 133   file_stream_class->seek = g_local_file_output_stream_seek;
 134   file_stream_class->can_truncate = g_local_file_output_stream_can_truncate;
 135   file_stream_class->truncate_fn = g_local_file_output_stream_truncate;
 136 }
 137
 138 static void
 139 g_local_file_output_stream_init (GLocalFileOutputStream *stream)
 140 {
 141   stream->priv = G_TYPE_INSTANCE_GET_PRIVATE (stream,
 142                                               G_TYPE_LOCAL_FILE_OUTPUT_STREAM,
 143                                               GLocalFileOutputStreamPrivate);
 144 }
 145
 146 static gssize
 147 g_local_file_output_stream_write (GOutputStream  *stream,
 148                                   const void     *buffer,
 149                                   gsize           count,
 150                                   GCancellable   *cancellable,
 151                                   GError        **error)
 152 {
 153   GLocalFileOutputStream *file;
 154   gssize res;
 155
 156   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 157
 158   while (1)
 159     {
 160       if (g_cancellable_set_error_if_cancelled (cancellable, error))
 161         return -1;
 162       res = write (file->priv->fd, buffer, count);
 163       if (res == -1)
 164         {
 165           int errsv = errno;
 166
 167           if (errsv == EINTR)
 168             continue;
 169
 170           g_set_error (error, G_IO_ERROR,
 171                        g_io_error_from_errno (errsv),
 172                        _("Error writing to file: %s"),
 173                        g_strerror (errsv));
 174         }
 175
 176       break;
 177     }
 178
 179   return res;
 180 }
 181
 182 static gboolean
 183 g_local_file_output_stream_close (GOutputStream  *stream,
 184                                   GCancellable   *cancellable,
 185                                   GError        **error)
 186 {
 187   GLocalFileOutputStream *file;
 188   GLocalFileStat final_stat;
 189   int res;
 190
 191   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 192
 193 #ifdef G_OS_WIN32
 194
 195   /* Must close before renaming on Windows, so just do the close first
 196    * in all cases for now.
 197    */
 198   if (_fstati64 (file->priv->fd, &final_stat) == 0)
 199     file->priv->etag = _g_local_file_info_create_etag (&final_stat);
 200
 201   res = close (file->priv->fd);
 202   if (res == -1)
 203     {
 204       int errsv = errno;
 205
 206       g_set_error (error, G_IO_ERROR,
 207                    g_io_error_from_errno (errsv),
 208                    _("Error closing file: %s"),
 209                    g_strerror (errsv));
 210       return FALSE;
 211     }
 212
 213 #endif
 214
 215   if (file->priv->tmp_filename)
 216     {
 217       /* We need to move the temp file to its final place,
 218        * and possibly create the backup file
 219        */
 220
 221       if (file->priv->backup_filename)
 222         {
 223           if (g_cancellable_set_error_if_cancelled (cancellable, error))
 224             goto err_out;
 225
 226 #ifdef HAVE_LINK
 227           /* create original -> backup link, the original is then renamed over */
 228           if (g_unlink (file->priv->backup_filename) != 0 &&
 229               errno != ENOENT)
 230             {
 231               int errsv = errno;
 232
 233               g_set_error (error, G_IO_ERROR,
 234                            G_IO_ERROR_CANT_CREATE_BACKUP,
 235                            _("Error removing old backup link: %s"),
 236                            g_strerror (errsv));
 237               goto err_out;
 238             }
 239
 240           if (link (file->priv->original_filename, file->priv->backup_filename) != 0)
 241             {
 242               /*  link failed or is not supported, try rename  */
 243               if (g_rename (file->priv->original_filename, file->priv->backup_filename) != 0)
 244                 {
 245                   int errsv = errno;
 246
 247                   g_set_error (error, G_IO_ERROR,
 248                                G_IO_ERROR_CANT_CREATE_BACKUP,
 249                                _("Error creating backup copy: %s"),
 250                                g_strerror (errsv));
 251                   goto err_out;
 252                 }
 253             }
 254 #else
 255             /* If link not supported, just rename... */
 256           if (g_rename (file->priv->original_filename, file->priv->backup_filename) != 0)
 257             {
 258               int errsv = errno;
 259
 260               g_set_error (error, G_IO_ERROR,
 261                            G_IO_ERROR_CANT_CREATE_BACKUP,
 262                            _("Error creating backup copy: %s"),
 263                            g_strerror (errsv));
 264               goto err_out;
 265             }
 266 #endif
 267         }
 268
 269
 270       if (g_cancellable_set_error_if_cancelled (cancellable, error))
 271         goto err_out;
 272
 273       /* tmp -> original */
 274       if (g_rename (file->priv->tmp_filename, file->priv->original_filename) != 0)
 275         {
 276           int errsv = errno;
 277
 278           g_set_error (error, G_IO_ERROR,
 279                        g_io_error_from_errno (errno),
 280                        _("Error renaming temporary file: %s"),
 281                        g_strerror (errsv));
 282           goto err_out;
 283         }
 284     }
 285
 286   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 287     goto err_out;
 288
 289 #ifndef G_OS_WIN32              /* Already did the fstat() and close() above on Win32 */
 290
 291   if (fstat (file->priv->fd, &final_stat) == 0)
 292     file->priv->etag = _g_local_file_info_create_etag (&final_stat);
 293
 294   while (1)
 295     {
 296       res = close (file->priv->fd);
 297       if (res == -1)
 298         {
 299           int errsv = errno;
 300
 301           g_set_error (error, G_IO_ERROR,
 302                        g_io_error_from_errno (errsv),
 303                        _("Error closing file: %s"),
 304                        g_strerror (errsv));
 305         }
 306       break;
 307     }
 308
 309   return res != -1;
 310
 311 #else
 312
 313   return TRUE;
 314
 315 #endif
 316
 317  err_out:
 318
 319 #ifndef G_OS_WIN32
 320   /* A simple try to close the fd in case we fail before the actual close */
 321   close (file->priv->fd);
 322 #endif
 323   return FALSE;
 324 }
 325
 326 static char *
 327 g_local_file_output_stream_get_etag (GFileOutputStream *stream)
 328 {
 329   GLocalFileOutputStream *file;
 330
 331   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 332
 333   return g_strdup (file->priv->etag);
 334 }
 335
 336 static goffset
 337 g_local_file_output_stream_tell (GFileOutputStream *stream)
 338 {
 339   GLocalFileOutputStream *file;
 340   off_t pos;
 341
 342   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 343
 344   pos = lseek (file->priv->fd, 0, SEEK_CUR);
 345
 346   if (pos == (off_t)-1)
 347     return 0;
 348
 349   return pos;
 350 }
 351
 352 static gboolean
 353 g_local_file_output_stream_can_seek (GFileOutputStream *stream)
 354 {
 355   GLocalFileOutputStream *file;
 356   off_t pos;
 357
 358   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 359
 360   pos = lseek (file->priv->fd, 0, SEEK_CUR);
 361
 362   if (pos == (off_t)-1 && errno == ESPIPE)
 363     return FALSE;
 364
 365   return TRUE;
 366 }
 367
 368 static int
 369 seek_type_to_lseek (GSeekType type)
 370 {
 371   switch (type)
 372     {
 373     default:
 374     case G_SEEK_CUR:
 375       return SEEK_CUR;
 376
 377     case G_SEEK_SET:
 378       return SEEK_SET;
 379
 380     case G_SEEK_END:
 381       return SEEK_END;
 382     }
 383 }
 384
 385 static gboolean
 386 g_local_file_output_stream_seek (GFileOutputStream  *stream,
 387                                  goffset             offset,
 388                                  GSeekType           type,
 389                                  GCancellable       *cancellable,
 390                                  GError            **error)
 391 {
 392   GLocalFileOutputStream *file;
 393   off_t pos;
 394
 395   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 396
 397   pos = lseek (file->priv->fd, offset, seek_type_to_lseek (type));
 398
 399   if (pos == (off_t)-1)
 400     {
 401       int errsv = errno;
 402
 403       g_set_error (error, G_IO_ERROR,
 404                    g_io_error_from_errno (errsv),
 405                    _("Error seeking in file: %s"),
 406                    g_strerror (errsv));
 407       return FALSE;
 408     }
 409
 410   return TRUE;
 411 }
 412
 413 static gboolean
 414 g_local_file_output_stream_can_truncate (GFileOutputStream *stream)
 415 {
 416   /* We can't truncate pipes and stuff where we can't seek */
 417   return g_local_file_output_stream_can_seek (stream);
 418 }
 419
 420 static gboolean
 421 g_local_file_output_stream_truncate (GFileOutputStream  *stream,
 422                                      goffset             size,
 423                                      GCancellable       *cancellable,
 424                                      GError            **error)
 425 {
 426   GLocalFileOutputStream *file;
 427   int res;
 428
 429   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 430
 431  restart:
 432 #ifdef G_OS_WIN32
 433   res = g_win32_ftruncate (file->priv->fd, size);
 434 #else
 435   res = ftruncate (file->priv->fd, size);
 436 #endif
 437
 438   if (res == -1)
 439     {
 440       int errsv = errno;
 441
 442       if (errsv == EINTR)
 443         {
 444           if (g_cancellable_set_error_if_cancelled (cancellable, error))
 445             return FALSE;
 446           goto restart;
 447         }
 448
 449       g_set_error (error, G_IO_ERROR,
 450                    g_io_error_from_errno (errsv),
 451                    _("Error truncating file: %s"),
 452                    g_strerror (errsv));
 453       return FALSE;
 454     }
 455
 456   return TRUE;
 457 }
 458
 459
 460 static GFileInfo *
 461 g_local_file_output_stream_query_info (GFileOutputStream  *stream,
 462                                        char               *attributes,
 463                                        GCancellable       *cancellable,
 464                                        GError            **error)
 465 {
 466   GLocalFileOutputStream *file;
 467
 468   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 469
 470   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 471     return NULL;
 472
 473   return _g_local_file_info_get_from_fd (file->priv->fd,
 474                                          attributes,
 475                                          error);
 476 }
 477
 478 GFileOutputStream *
 479 _g_local_file_output_stream_create  (const char        *filename,
 480                                      GFileCreateFlags   flags,
 481                                      GCancellable      *cancellable,
 482                                      GError           **error)
 483 {
 484   GLocalFileOutputStream *stream;
 485   int mode;
 486   int fd;
 487
 488   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 489     return NULL;
 490
 491   if (flags & G_FILE_CREATE_PRIVATE)
 492     mode = 0600;
 493   else
 494     mode = 0666;
 495
 496   fd = g_open (filename, O_CREAT | O_EXCL | O_WRONLY | O_BINARY, mode);
 497   if (fd == -1)
 498     {
 499       int errsv = errno;
 500
 501       if (errsv == EINVAL)
 502         /* This must be an invalid filename, on e.g. FAT */
 503         g_set_error_literal (error, G_IO_ERROR,
 504                              G_IO_ERROR_INVALID_FILENAME,
 505                              _("Invalid filename"));
 506       else
 507         {
 508           char *display_name = g_filename_display_name (filename);
 509           g_set_error (error, G_IO_ERROR,
 510                        g_io_error_from_errno (errsv),
 511                        _("Error opening file '%s': %s"),
 512                        display_name, g_strerror (errsv));
 513           g_free (display_name);
 514         }
 515       return NULL;
 516     }
 517
 518   stream = g_object_new (G_TYPE_LOCAL_FILE_OUTPUT_STREAM, NULL);
 519   stream->priv->fd = fd;
 520   return G_FILE_OUTPUT_STREAM (stream);
 521 }
 522
 523 GFileOutputStream *
 524 _g_local_file_output_stream_append  (const char        *filename,
 525                                      GFileCreateFlags   flags,
 526                                      GCancellable      *cancellable,
 527                                      GError           **error)
 528 {
 529   GLocalFileOutputStream *stream;
 530   int mode;
 531   int fd;
 532
 533   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 534     return NULL;
 535
 536   if (flags & G_FILE_CREATE_PRIVATE)
 537     mode = 0600;
 538   else
 539     mode = 0666;
 540
 541   fd = g_open (filename, O_CREAT | O_APPEND | O_WRONLY | O_BINARY, mode);
 542   if (fd == -1)
 543     {
 544       int errsv = errno;
 545
 546       if (errsv == EINVAL)
 547         /* This must be an invalid filename, on e.g. FAT */
 548         g_set_error_literal (error, G_IO_ERROR,
 549                              G_IO_ERROR_INVALID_FILENAME,
 550                              _("Invalid filename"));
 551       else
 552         {
 553           char *display_name = g_filename_display_name (filename);
 554           g_set_error (error, G_IO_ERROR,
 555                        g_io_error_from_errno (errsv),
 556                        _("Error opening file '%s': %s"),
 557                        display_name, g_strerror (errsv));
 558           g_free (display_name);
 559         }
 560       return NULL;
 561     }
 562
 563   stream = g_object_new (G_TYPE_LOCAL_FILE_OUTPUT_STREAM, NULL);
 564   stream->priv->fd = fd;
 565
 566   return G_FILE_OUTPUT_STREAM (stream);
 567 }
 568
 569 static char *
 570 create_backup_filename (const char *filename)
 571 {
 572   return g_strconcat (filename, BACKUP_EXTENSION, NULL);
 573 }
 574
 575 #define BUFSIZE 8192 /* size of normal write buffer */
 576
 577 static gboolean
 578 copy_file_data (gint     sfd,
 579                 gint     dfd,
 580                 GError **error)
 581 {
 582   gboolean ret = TRUE;
 583   gpointer buffer;
 584   const gchar *write_buffer;
 585   gssize bytes_read;
 586   gssize bytes_to_write;
 587   gssize bytes_written;
 588
 589   buffer = g_malloc (BUFSIZE);
 590
 591   do
 592     {
 593       bytes_read = read (sfd, buffer, BUFSIZE);
 594       if (bytes_read == -1)
 595         {
 596           int errsv = errno;
 597
 598           if (errsv == EINTR)
 599             continue;
 600
 601           g_set_error (error, G_IO_ERROR,
 602                        g_io_error_from_errno (errsv),
 603                        _("Error reading from file: %s"),
 604                        g_strerror (errsv));
 605           ret = FALSE;
 606           break;
 607         }
 608
 609       bytes_to_write = bytes_read;
 610       write_buffer = buffer;
 611
 612       do
 613         {
 614           bytes_written = write (dfd, write_buffer, bytes_to_write);
 615           if (bytes_written == -1)
 616             {
 617               int errsv = errno;
 618
 619               if (errsv == EINTR)
 620                 continue;
 621
 622               g_set_error (error, G_IO_ERROR,
 623                            g_io_error_from_errno (errsv),
 624                            _("Error writing to file: %s"),
 625                            g_strerror (errsv));
 626               ret = FALSE;
 627               break;
 628             }
 629
 630           bytes_to_write -= bytes_written;
 631           write_buffer += bytes_written;
 632         }
 633       while (bytes_to_write > 0);
 634
 635     } while ((bytes_read != 0) && (ret == TRUE));
 636
 637   g_free (buffer);
 638
 639   return ret;
 640 }
 641
 642 static int
 643 handle_overwrite_open (const char    *filename,
 644                        const char    *etag,
 645                        gboolean       create_backup,
 646                        char         **temp_filename,
 647                        GCancellable  *cancellable,
 648                        GError       **error)
 649 {
 650   int fd = -1;
 651   GLocalFileStat original_stat;
 652   char *current_etag;
 653   gboolean is_symlink;
 654   int open_flags;
 655   int res;
 656
 657   /* We only need read access to the original file if we are creating a backup.
 658    * We also add O_CREATE to avoid a race if the file was just removed */
 659   if (create_backup)
 660     open_flags = O_RDWR | O_CREAT | O_BINARY;
 661   else
 662     open_flags = O_WRONLY | O_CREAT | O_BINARY;
 663
 664   /* Some systems have O_NOFOLLOW, which lets us avoid some races
 665    * when finding out if the file we opened was a symlink */
 666 #ifdef O_NOFOLLOW
 667   is_symlink = FALSE;
 668   fd = g_open (filename, open_flags | O_NOFOLLOW, 0666);
 669   if (fd == -1 && errno == ELOOP)
 670     {
 671       /* Could be a symlink, or it could be a regular ELOOP error,
 672        * but then the next open will fail too. */
 673       is_symlink = TRUE;
 674       fd = g_open (filename, open_flags, 0666);
 675     }
 676 #else
 677   fd = g_open (filename, open_flags, 0666);
 678   /* This is racy, but we do it as soon as possible to minimize the race */
 679   is_symlink = g_file_test (filename, G_FILE_TEST_IS_SYMLINK);
 680 #endif
 681
 682   if (fd == -1)
 683     {
 684       int errsv = errno;
 685       char *display_name = g_filename_display_name (filename);
 686       g_set_error (error, G_IO_ERROR,
 687                    g_io_error_from_errno (errsv),
 688                    _("Error opening file '%s': %s"),
 689                    display_name, g_strerror (errsv));
 690       g_free (display_name);
 691       return -1;
 692     }
 693
 694 #ifdef G_OS_WIN32
 695   res = _fstati64 (fd, &original_stat);
 696 #else
 697   res = fstat (fd, &original_stat);
 698 #endif
 699
 700   if (res != 0)
 701     {
 702       int errsv = errno;
 703       char *display_name = g_filename_display_name (filename);
 704       g_set_error (error, G_IO_ERROR,
 705                    g_io_error_from_errno (errsv),
 706                    _("Error stating file '%s': %s"),
 707                    display_name, g_strerror (errsv));
 708       g_free (display_name);
 709       goto err_out;
 710     }
 711
 712   /* not a regular file */
 713   if (!S_ISREG (original_stat.st_mode))
 714     {
 715       if (S_ISDIR (original_stat.st_mode))
 716         g_set_error_literal (error,
 717                              G_IO_ERROR,
 718                              G_IO_ERROR_IS_DIRECTORY,
 719                              _("Target file is a directory"));
 720       else
 721         g_set_error_literal (error,
 722                              G_IO_ERROR,
 723                              G_IO_ERROR_NOT_REGULAR_FILE,
 724                              _("Target file is not a regular file"));
 725       goto err_out;
 726     }
 727
 728   if (etag != NULL)
 729     {
 730       current_etag = _g_local_file_info_create_etag (&original_stat);
 731       if (strcmp (etag, current_etag) != 0)
 732         {
 733           g_set_error_literal (error,
 734                                G_IO_ERROR,
 735                                G_IO_ERROR_WRONG_ETAG,
 736                                _("The file was externally modified"));
 737           g_free (current_etag);
 738           goto err_out;
 739         }
 740       g_free (current_etag);
 741     }
 742
 743   /* We use two backup strategies.
 744    * The first one (which is faster) consist in saving to a
 745    * tmp file then rename the original file to the backup and the
 746    * tmp file to the original name. This is fast but doesn't work
 747    * when the file is a link (hard or symbolic) or when we can't
 748    * write to the current dir or can't set the permissions on the
 749    * new file.
 750    * The second strategy consist simply in copying the old file
 751    * to a backup file and rewrite the contents of the file.
 752    */
 753
 754   if (!(original_stat.st_nlink > 1) && !is_symlink)
 755     {
 756       char *dirname, *tmp_filename;
 757       int tmpfd;
 758
 759       dirname = g_path_get_dirname (filename);
 760       tmp_filename = g_build_filename (dirname, ".goutputstream-XXXXXX", NULL);
 761       g_free (dirname);
 762
 763       tmpfd = g_mkstemp (tmp_filename);
 764       if (tmpfd == -1)
 765         {
 766           g_free (tmp_filename);
 767           goto fallback_strategy;
 768         }
 769
 770       /* try to keep permissions */
 771
 772       if (
 773 #ifdef HAVE_FCHOWN
 774           fchown (tmpfd, original_stat.st_uid, original_stat.st_gid) == -1 ||
 775 #endif
 776 #ifdef HAVE_FCHMOD
 777           fchmod (tmpfd, original_stat.st_mode) == -1 ||
 778 #endif
 779           0
 780           )
 781         {
 782           struct stat tmp_statbuf;
 783
 784           /* Check that we really needed to change something */
 785           if (fstat (tmpfd, &tmp_statbuf) != 0 ||
 786               original_stat.st_uid != tmp_statbuf.st_uid ||
 787               original_stat.st_gid != tmp_statbuf.st_gid ||
 788               original_stat.st_mode != tmp_statbuf.st_mode)
 789             {
 790               close (tmpfd);
 791               g_unlink (tmp_filename);
 792               g_free (tmp_filename);
 793               goto fallback_strategy;
 794             }
 795         }
 796
 797       close (fd);
 798       *temp_filename = tmp_filename;
 799       return tmpfd;
 800     }
 801
 802  fallback_strategy:
 803
 804   if (create_backup)
 805     {
 806 #if defined(HAVE_FCHOWN) && defined(HAVE_FCHMOD)
 807       struct stat tmp_statbuf;
 808 #endif
 809       char *backup_filename;
 810       int bfd;
 811
 812       backup_filename = create_backup_filename (filename);
 813
 814       if (g_unlink (backup_filename) == -1 && errno != ENOENT)
 815         {
 816           g_set_error_literal (error,
 817                                G_IO_ERROR,
 818                                G_IO_ERROR_CANT_CREATE_BACKUP,
 819                                _("Backup file creation failed"));
 820           g_free (backup_filename);
 821           goto err_out;
 822         }
 823
 824       bfd = g_open (backup_filename,
 825                     O_WRONLY | O_CREAT | O_EXCL | O_BINARY,
 826                     original_stat.st_mode & 0777);
 827
 828       if (bfd == -1)
 829         {
 830           g_set_error_literal (error,
 831                                G_IO_ERROR,
 832                                G_IO_ERROR_CANT_CREATE_BACKUP,
 833                                _("Backup file creation failed"));
 834           g_free (backup_filename);
 835           goto err_out;
 836         }
 837
 838       /* If needed, Try to set the group of the backup same as the
 839        * original file. If this fails, set the protection
 840        * bits for the group same as the protection bits for
 841        * others. */
 842 #if defined(HAVE_FCHOWN) && defined(HAVE_FCHMOD)
 843       if (fstat (bfd, &tmp_statbuf) != 0)
 844         {
 845           g_set_error_literal (error,
 846                                G_IO_ERROR,
 847                                G_IO_ERROR_CANT_CREATE_BACKUP,
 848                                _("Backup file creation failed"));
 849           g_unlink (backup_filename);
 850           g_free (backup_filename);
 851           goto err_out;
 852         }
 853
 854       if ((original_stat.st_gid != tmp_statbuf.st_gid)  &&
 855           fchown (bfd, (uid_t) -1, original_stat.st_gid) != 0)
 856         {
 857           if (fchmod (bfd,
 858                       (original_stat.st_mode & 0707) |
 859                       ((original_stat.st_mode & 07) << 3)) != 0)
 860             {
 861               g_set_error_literal (error,
 862                                    G_IO_ERROR,
 863                                    G_IO_ERROR_CANT_CREATE_BACKUP,
 864                                    _("Backup file creation failed"));
 865               g_unlink (backup_filename);
 866               close (bfd);
 867               g_free (backup_filename);
 868               goto err_out;
 869             }
 870         }
 871 #endif
 872
 873       if (!copy_file_data (fd, bfd, NULL))
 874         {
 875           g_set_error_literal (error,
 876                                G_IO_ERROR,
 877                                G_IO_ERROR_CANT_CREATE_BACKUP,
 878                                _("Backup file creation failed"));
 879           g_unlink (backup_filename);
 880           close (bfd);
 881           g_free (backup_filename);
 882
 883           goto err_out;
 884         }
 885
 886       close (bfd);
 887       g_free (backup_filename);
 888
 889       /* Seek back to the start of the file after the backup copy */
 890       if (lseek (fd, 0, SEEK_SET) == -1)
 891         {
 892           int errsv = errno;
 893
 894           g_set_error (error, G_IO_ERROR,
 895                        g_io_error_from_errno (errsv),
 896                        _("Error seeking in file: %s"),
 897                        g_strerror (errsv));
 898           goto err_out;
 899         }
 900     }
 901
 902   /* Truncate the file at the start */
 903 #ifdef G_OS_WIN32
 904   if (g_win32_ftruncate (fd, 0) == -1)
 905 #else
 906   if (ftruncate (fd, 0) == -1)
 907 #endif
 908     {
 909       int errsv = errno;
 910
 911       g_set_error (error, G_IO_ERROR,
 912                    g_io_error_from_errno (errsv),
 913                    _("Error truncating file: %s"),
 914                    g_strerror (errsv));
 915       goto err_out;
 916     }
 917
 918   return fd;
 919
 920  err_out:
 921   close (fd);
 922   return -1;
 923 }
 924
 925 GFileOutputStream *
 926 _g_local_file_output_stream_replace (const char        *filename,
 927                                      const char        *etag,
 928                                      gboolean           create_backup,
 929                                      GFileCreateFlags   flags,
 930                                      GCancellable      *cancellable,
 931                                      GError           **error)
 932 {
 933   GLocalFileOutputStream *stream;
 934   int mode;
 935   int fd;
 936   char *temp_file;
 937
 938   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 939     return NULL;
 940
 941   temp_file = NULL;
 942
 943   if (flags & G_FILE_CREATE_PRIVATE)
 944     mode = 0600;
 945   else
 946     mode = 0666;
 947
 948   /* If the file doesn't exist, create it */
 949   fd = g_open (filename, O_CREAT | O_EXCL | O_WRONLY | O_BINARY, mode);
 950
 951   if (fd == -1 && errno == EEXIST)
 952     {
 953       /* The file already exists */
 954       fd = handle_overwrite_open (filename, etag, create_backup, &temp_file,
 955                                   cancellable, error);
 956       if (fd == -1)
 957         return NULL;
 958     }
 959   else if (fd == -1)
 960     {
 961       int errsv = errno;
 962
 963       if (errsv == EINVAL)
 964         /* This must be an invalid filename, on e.g. FAT */
 965         g_set_error_literal (error, G_IO_ERROR,
 966                              G_IO_ERROR_INVALID_FILENAME,
 967                              _("Invalid filename"));
 968       else
 969         {
 970           char *display_name = g_filename_display_name (filename);
 971           g_set_error (error, G_IO_ERROR,
 972                        g_io_error_from_errno (errsv),
 973                        _("Error opening file '%s': %s"),
 974                        display_name, g_strerror (errsv));
 975           g_free (display_name);
 976         }
 977       return NULL;
 978     }
 979
 980
 981   stream = g_object_new (G_TYPE_LOCAL_FILE_OUTPUT_STREAM, NULL);
 982   stream->priv->fd = fd;
 983   stream->priv->tmp_filename = temp_file;
 984   if (create_backup)
 985     stream->priv->backup_filename = create_backup_filename (filename);
 986   stream->priv->original_filename =  g_strdup (filename);
 987
 988   return G_FILE_OUTPUT_STREAM (stream);
 989 }