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   struct stat final_stat;
 189   int res;
 190
 191   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 192
 193   if (file->priv->tmp_filename)
 194     {
 195       /* We need to move the temp file to its final place,
 196        * and possibly create the backup file
 197        */
 198
 199       if (file->priv->backup_filename)
 200         {
 201           if (g_cancellable_set_error_if_cancelled (cancellable, error))
 202             goto err_out;
 203
 204 #ifdef HAVE_LINK
 205           /* create original -> backup link, the original is then renamed over */
 206           if (g_unlink (file->priv->backup_filename) != 0 &&
 207               errno != ENOENT)
 208             {
 209               int errsv = errno;
 210
 211               g_set_error (error, G_IO_ERROR,
 212                            G_IO_ERROR_CANT_CREATE_BACKUP,
 213                            _("Error removing old backup link: %s"),
 214                            g_strerror (errsv));
 215               goto err_out;
 216             }
 217
 218           if (link (file->priv->original_filename, file->priv->backup_filename) != 0)
 219             {
 220               /*  link failed or is not supported, try rename  */
 221               if (g_rename (file->priv->original_filename, file->priv->backup_filename) != 0)
 222                 {
 223                   int errsv = errno;
 224
 225                   g_set_error (error, G_IO_ERROR,
 226                                G_IO_ERROR_CANT_CREATE_BACKUP,
 227                                _("Error creating backup copy: %s"),
 228                                g_strerror (errsv));
 229                   goto err_out;
 230                 }
 231             }
 232 #else
 233             /* If link not supported, just rename... */
 234           if (g_rename (file->priv->original_filename, file->priv->backup_filename) != 0)
 235             {
 236               int errsv = errno;
 237
 238               g_set_error (error, G_IO_ERROR,
 239                            G_IO_ERROR_CANT_CREATE_BACKUP,
 240                            _("Error creating backup copy: %s"),
 241                            g_strerror (errsv));
 242               goto err_out;
 243             }
 244 #endif
 245         }
 246
 247
 248       if (g_cancellable_set_error_if_cancelled (cancellable, error))
 249         goto err_out;
 250
 251       /* tmp -> original */
 252       if (g_rename (file->priv->tmp_filename, file->priv->original_filename) != 0)
 253         {
 254           int errsv = errno;
 255
 256           g_set_error (error, G_IO_ERROR,
 257                        g_io_error_from_errno (errno),
 258                        _("Error renaming temporary file: %s"),
 259                        g_strerror (errsv));
 260           goto err_out;
 261         }
 262     }
 263
 264   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 265     goto err_out;
 266
 267   if (fstat (file->priv->fd, &final_stat) == 0)
 268     file->priv->etag = _g_local_file_info_create_etag (&final_stat);
 269
 270   while (1)
 271     {
 272       res = close (file->priv->fd);
 273       if (res == -1)
 274         {
 275           int errsv = errno;
 276
 277           g_set_error (error, G_IO_ERROR,
 278                        g_io_error_from_errno (errsv),
 279                        _("Error closing file: %s"),
 280                        g_strerror (errsv));
 281         }
 282       break;
 283     }
 284
 285   return res != -1;
 286
 287  err_out:
 288   /* A simple try to close the fd in case we fail before the actual close */
 289   close (file->priv->fd);
 290   return FALSE;
 291 }
 292
 293 static char *
 294 g_local_file_output_stream_get_etag (GFileOutputStream *stream)
 295 {
 296   GLocalFileOutputStream *file;
 297
 298   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 299
 300   return g_strdup (file->priv->etag);
 301 }
 302
 303 static goffset
 304 g_local_file_output_stream_tell (GFileOutputStream *stream)
 305 {
 306   GLocalFileOutputStream *file;
 307   off_t pos;
 308
 309   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 310
 311   pos = lseek (file->priv->fd, 0, SEEK_CUR);
 312
 313   if (pos == (off_t)-1)
 314     return 0;
 315
 316   return pos;
 317 }
 318
 319 static gboolean
 320 g_local_file_output_stream_can_seek (GFileOutputStream *stream)
 321 {
 322   GLocalFileOutputStream *file;
 323   off_t pos;
 324
 325   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 326
 327   pos = lseek (file->priv->fd, 0, SEEK_CUR);
 328
 329   if (pos == (off_t)-1 && errno == ESPIPE)
 330     return FALSE;
 331
 332   return TRUE;
 333 }
 334
 335 static int
 336 seek_type_to_lseek (GSeekType type)
 337 {
 338   switch (type)
 339     {
 340     default:
 341     case G_SEEK_CUR:
 342       return SEEK_CUR;
 343
 344     case G_SEEK_SET:
 345       return SEEK_SET;
 346
 347     case G_SEEK_END:
 348       return SEEK_END;
 349     }
 350 }
 351
 352 static gboolean
 353 g_local_file_output_stream_seek (GFileOutputStream  *stream,
 354                                  goffset             offset,
 355                                  GSeekType           type,
 356                                  GCancellable       *cancellable,
 357                                  GError            **error)
 358 {
 359   GLocalFileOutputStream *file;
 360   off_t pos;
 361
 362   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 363
 364   pos = lseek (file->priv->fd, offset, seek_type_to_lseek (type));
 365
 366   if (pos == (off_t)-1)
 367     {
 368       int errsv = errno;
 369
 370       g_set_error (error, G_IO_ERROR,
 371                    g_io_error_from_errno (errsv),
 372                    _("Error seeking in file: %s"),
 373                    g_strerror (errsv));
 374       return FALSE;
 375     }
 376
 377   return TRUE;
 378 }
 379
 380 static gboolean
 381 g_local_file_output_stream_can_truncate (GFileOutputStream *stream)
 382 {
 383   /* We can't truncate pipes and stuff where we can't seek */
 384   return g_local_file_output_stream_can_seek (stream);
 385 }
 386
 387 static gboolean
 388 g_local_file_output_stream_truncate (GFileOutputStream  *stream,
 389                                      goffset             size,
 390                                      GCancellable       *cancellable,
 391                                      GError            **error)
 392 {
 393   GLocalFileOutputStream *file;
 394   int res;
 395
 396   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 397
 398  restart:
 399 #ifdef G_OS_WIN32
 400   res = g_win32_ftruncate (file->priv->fd, size);
 401 #else
 402   res = ftruncate (file->priv->fd, size);
 403 #endif
 404
 405   if (res == -1)
 406     {
 407       int errsv = errno;
 408
 409       if (errsv == EINTR)
 410         {
 411           if (g_cancellable_set_error_if_cancelled (cancellable, error))
 412             return FALSE;
 413           goto restart;
 414         }
 415
 416       g_set_error (error, G_IO_ERROR,
 417                    g_io_error_from_errno (errsv),
 418                    _("Error truncating file: %s"),
 419                    g_strerror (errsv));
 420       return FALSE;
 421     }
 422
 423   return TRUE;
 424 }
 425
 426
 427 static GFileInfo *
 428 g_local_file_output_stream_query_info (GFileOutputStream  *stream,
 429                                        char               *attributes,
 430                                        GCancellable       *cancellable,
 431                                        GError            **error)
 432 {
 433   GLocalFileOutputStream *file;
 434
 435   file = G_LOCAL_FILE_OUTPUT_STREAM (stream);
 436
 437   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 438     return NULL;
 439
 440   return _g_local_file_info_get_from_fd (file->priv->fd,
 441                                          attributes,
 442                                          error);
 443 }
 444
 445 GFileOutputStream *
 446 _g_local_file_output_stream_create  (const char        *filename,
 447                                      GFileCreateFlags   flags,
 448                                      GCancellable      *cancellable,
 449                                      GError           **error)
 450 {
 451   GLocalFileOutputStream *stream;
 452   int mode;
 453   int fd;
 454
 455   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 456     return NULL;
 457
 458   if (flags & G_FILE_CREATE_PRIVATE)
 459     mode = 0600;
 460   else
 461     mode = 0666;
 462
 463   fd = g_open (filename, O_CREAT | O_EXCL | O_WRONLY | O_BINARY, mode);
 464   if (fd == -1)
 465     {
 466       int errsv = errno;
 467
 468       if (errsv == EINVAL)
 469         /* This must be an invalid filename, on e.g. FAT */
 470         g_set_error_literal (error, G_IO_ERROR,
 471                              G_IO_ERROR_INVALID_FILENAME,
 472                              _("Invalid filename"));
 473       else
 474         {
 475           char *display_name = g_filename_display_name (filename);
 476           g_set_error (error, G_IO_ERROR,
 477                        g_io_error_from_errno (errsv),
 478                        _("Error opening file '%s': %s"),
 479                        display_name, g_strerror (errsv));
 480           g_free (display_name);
 481         }
 482       return NULL;
 483     }
 484
 485   stream = g_object_new (G_TYPE_LOCAL_FILE_OUTPUT_STREAM, NULL);
 486   stream->priv->fd = fd;
 487   return G_FILE_OUTPUT_STREAM (stream);
 488 }
 489
 490 GFileOutputStream *
 491 _g_local_file_output_stream_append  (const char        *filename,
 492                                      GFileCreateFlags   flags,
 493                                      GCancellable      *cancellable,
 494                                      GError           **error)
 495 {
 496   GLocalFileOutputStream *stream;
 497   int mode;
 498   int fd;
 499
 500   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 501     return NULL;
 502
 503   if (flags & G_FILE_CREATE_PRIVATE)
 504     mode = 0600;
 505   else
 506     mode = 0666;
 507
 508   fd = g_open (filename, O_CREAT | O_APPEND | O_WRONLY | O_BINARY, mode);
 509   if (fd == -1)
 510     {
 511       int errsv = errno;
 512
 513       if (errsv == EINVAL)
 514         /* This must be an invalid filename, on e.g. FAT */
 515         g_set_error_literal (error, G_IO_ERROR,
 516                              G_IO_ERROR_INVALID_FILENAME,
 517                              _("Invalid filename"));
 518       else
 519         {
 520           char *display_name = g_filename_display_name (filename);
 521           g_set_error (error, G_IO_ERROR,
 522                        g_io_error_from_errno (errsv),
 523                        _("Error opening file '%s': %s"),
 524                        display_name, g_strerror (errsv));
 525           g_free (display_name);
 526         }
 527       return NULL;
 528     }
 529
 530   stream = g_object_new (G_TYPE_LOCAL_FILE_OUTPUT_STREAM, NULL);
 531   stream->priv->fd = fd;
 532
 533   return G_FILE_OUTPUT_STREAM (stream);
 534 }
 535
 536 static char *
 537 create_backup_filename (const char *filename)
 538 {
 539   return g_strconcat (filename, BACKUP_EXTENSION, NULL);
 540 }
 541
 542 #define BUFSIZE 8192 /* size of normal write buffer */
 543
 544 static gboolean
 545 copy_file_data (gint     sfd,
 546                 gint     dfd,
 547                 GError **error)
 548 {
 549   gboolean ret = TRUE;
 550   gpointer buffer;
 551   const gchar *write_buffer;
 552   gssize bytes_read;
 553   gssize bytes_to_write;
 554   gssize bytes_written;
 555
 556   buffer = g_malloc (BUFSIZE);
 557
 558   do
 559     {
 560       bytes_read = read (sfd, buffer, BUFSIZE);
 561       if (bytes_read == -1)
 562         {
 563           int errsv = errno;
 564
 565           if (errsv == EINTR)
 566             continue;
 567
 568           g_set_error (error, G_IO_ERROR,
 569                        g_io_error_from_errno (errsv),
 570                        _("Error reading from file: %s"),
 571                        g_strerror (errsv));
 572           ret = FALSE;
 573           break;
 574         }
 575
 576       bytes_to_write = bytes_read;
 577       write_buffer = buffer;
 578
 579       do
 580         {
 581           bytes_written = write (dfd, write_buffer, bytes_to_write);
 582           if (bytes_written == -1)
 583             {
 584               int errsv = errno;
 585
 586               if (errsv == EINTR)
 587                 continue;
 588
 589               g_set_error (error, G_IO_ERROR,
 590                            g_io_error_from_errno (errsv),
 591                            _("Error writing to file: %s"),
 592                            g_strerror (errsv));
 593               ret = FALSE;
 594               break;
 595             }
 596
 597           bytes_to_write -= bytes_written;
 598           write_buffer += bytes_written;
 599         }
 600       while (bytes_to_write > 0);
 601
 602     } while ((bytes_read != 0) && (ret == TRUE));
 603
 604   g_free (buffer);
 605
 606   return ret;
 607 }
 608
 609 static int
 610 handle_overwrite_open (const char    *filename,
 611                        const char    *etag,
 612                        gboolean       create_backup,
 613                        char         **temp_filename,
 614                        GCancellable  *cancellable,
 615                        GError       **error)
 616 {
 617   int fd = -1;
 618   struct stat original_stat;
 619   char *current_etag;
 620   gboolean is_symlink;
 621   int open_flags;
 622
 623   /* We only need read access to the original file if we are creating a backup.
 624    * We also add O_CREATE to avoid a race if the file was just removed */
 625   if (create_backup)
 626     open_flags = O_RDWR | O_CREAT | O_BINARY;
 627   else
 628     open_flags = O_WRONLY | O_CREAT | O_BINARY;
 629
 630   /* Some systems have O_NOFOLLOW, which lets us avoid some races
 631    * when finding out if the file we opened was a symlink */
 632 #ifdef O_NOFOLLOW
 633   is_symlink = FALSE;
 634   fd = g_open (filename, open_flags | O_NOFOLLOW, 0666);
 635   if (fd == -1 && errno == ELOOP)
 636     {
 637       /* Could be a symlink, or it could be a regular ELOOP error,
 638        * but then the next open will fail too. */
 639       is_symlink = TRUE;
 640       fd = g_open (filename, open_flags, 0666);
 641     }
 642 #else
 643   fd = g_open (filename, open_flags, 0666);
 644   /* This is racy, but we do it as soon as possible to minimize the race */
 645   is_symlink = g_file_test (filename, G_FILE_TEST_IS_SYMLINK);
 646 #endif
 647
 648   if (fd == -1)
 649     {
 650       int errsv = errno;
 651       char *display_name = g_filename_display_name (filename);
 652       g_set_error (error, G_IO_ERROR,
 653                    g_io_error_from_errno (errsv),
 654                    _("Error opening file '%s': %s"),
 655                    display_name, g_strerror (errsv));
 656       g_free (display_name);
 657       return -1;
 658     }
 659
 660   if (fstat (fd, &original_stat) != 0)
 661     {
 662       int errsv = errno;
 663       char *display_name = g_filename_display_name (filename);
 664       g_set_error (error, G_IO_ERROR,
 665                    g_io_error_from_errno (errsv),
 666                    _("Error stating file '%s': %s"),
 667                    display_name, g_strerror (errsv));
 668       g_free (display_name);
 669       goto err_out;
 670     }
 671
 672   /* not a regular file */
 673   if (!S_ISREG (original_stat.st_mode))
 674     {
 675       if (S_ISDIR (original_stat.st_mode))
 676         g_set_error_literal (error,
 677                              G_IO_ERROR,
 678                              G_IO_ERROR_IS_DIRECTORY,
 679                              _("Target file is a directory"));
 680       else
 681         g_set_error_literal (error,
 682                              G_IO_ERROR,
 683                              G_IO_ERROR_NOT_REGULAR_FILE,
 684                              _("Target file is not a regular file"));
 685       goto err_out;
 686     }
 687
 688   if (etag != NULL)
 689     {
 690       current_etag = _g_local_file_info_create_etag (&original_stat);
 691       if (strcmp (etag, current_etag) != 0)
 692         {
 693           g_set_error_literal (error,
 694                                G_IO_ERROR,
 695                                G_IO_ERROR_WRONG_ETAG,
 696                                _("The file was externally modified"));
 697           g_free (current_etag);
 698           goto err_out;
 699         }
 700       g_free (current_etag);
 701     }
 702
 703   /* We use two backup strategies.
 704    * The first one (which is faster) consist in saving to a
 705    * tmp file then rename the original file to the backup and the
 706    * tmp file to the original name. This is fast but doesn't work
 707    * when the file is a link (hard or symbolic) or when we can't
 708    * write to the current dir or can't set the permissions on the
 709    * new file.
 710    * The second strategy consist simply in copying the old file
 711    * to a backup file and rewrite the contents of the file.
 712    */
 713
 714   if (!(original_stat.st_nlink > 1) && !is_symlink)
 715     {
 716       char *dirname, *tmp_filename;
 717       int tmpfd;
 718
 719       dirname = g_path_get_dirname (filename);
 720       tmp_filename = g_build_filename (dirname, ".goutputstream-XXXXXX", NULL);
 721       g_free (dirname);
 722
 723       tmpfd = g_mkstemp (tmp_filename);
 724       if (tmpfd == -1)
 725         {
 726           g_free (tmp_filename);
 727           goto fallback_strategy;
 728         }
 729
 730       /* try to keep permissions */
 731
 732       if (
 733 #ifdef HAVE_FCHOWN
 734           fchown (tmpfd, original_stat.st_uid, original_stat.st_gid) == -1 ||
 735 #endif
 736 #ifdef HAVE_FCHMOD
 737           fchmod (tmpfd, original_stat.st_mode) == -1 ||
 738 #endif
 739           0
 740           )
 741         {
 742           struct stat tmp_statbuf;
 743
 744           /* Check that we really needed to change something */
 745           if (fstat (tmpfd, &tmp_statbuf) != 0 ||
 746               original_stat.st_uid != tmp_statbuf.st_uid ||
 747               original_stat.st_gid != tmp_statbuf.st_gid ||
 748               original_stat.st_mode != tmp_statbuf.st_mode)
 749             {
 750               close (tmpfd);
 751               g_unlink (tmp_filename);
 752               g_free (tmp_filename);
 753               goto fallback_strategy;
 754             }
 755         }
 756
 757       close (fd);
 758       *temp_filename = tmp_filename;
 759       return tmpfd;
 760     }
 761
 762  fallback_strategy:
 763
 764   if (create_backup)
 765     {
 766       struct stat tmp_statbuf;
 767       char *backup_filename;
 768       int bfd;
 769
 770       backup_filename = create_backup_filename (filename);
 771
 772       if (g_unlink (backup_filename) == -1 && errno != ENOENT)
 773         {
 774           g_set_error_literal (error,
 775                                G_IO_ERROR,
 776                                G_IO_ERROR_CANT_CREATE_BACKUP,
 777                                _("Backup file creation failed"));
 778           g_free (backup_filename);
 779           goto err_out;
 780         }
 781
 782       bfd = g_open (backup_filename,
 783                     O_WRONLY | O_CREAT | O_EXCL | O_BINARY,
 784                     original_stat.st_mode & 0777);
 785
 786       if (bfd == -1)
 787         {
 788           g_set_error_literal (error,
 789                                G_IO_ERROR,
 790                                G_IO_ERROR_CANT_CREATE_BACKUP,
 791                                _("Backup file creation failed"));
 792           g_free (backup_filename);
 793           goto err_out;
 794         }
 795
 796       /* If needed, Try to set the group of the backup same as the
 797        * original file. If this fails, set the protection
 798        * bits for the group same as the protection bits for
 799        * others. */
 800 #if defined(HAVE_FCHOWN) && defined(HAVE_FCHMOD)
 801       if (fstat (bfd, &tmp_statbuf) != 0)
 802         {
 803           g_set_error_literal (error,
 804                                G_IO_ERROR,
 805                                G_IO_ERROR_CANT_CREATE_BACKUP,
 806                                _("Backup file creation failed"));
 807           g_unlink (backup_filename);
 808           g_free (backup_filename);
 809           goto err_out;
 810         }
 811
 812       if ((original_stat.st_gid != tmp_statbuf.st_gid)  &&
 813           fchown (bfd, (uid_t) -1, original_stat.st_gid) != 0)
 814         {
 815           if (fchmod (bfd,
 816                       (original_stat.st_mode & 0707) |
 817                       ((original_stat.st_mode & 07) << 3)) != 0)
 818             {
 819               g_set_error_literal (error,
 820                                    G_IO_ERROR,
 821                                    G_IO_ERROR_CANT_CREATE_BACKUP,
 822                                    _("Backup file creation failed"));
 823               g_unlink (backup_filename);
 824               close (bfd);
 825               g_free (backup_filename);
 826               goto err_out;
 827             }
 828         }
 829 #endif
 830
 831       if (!copy_file_data (fd, bfd, NULL))
 832         {
 833           g_set_error_literal (error,
 834                                G_IO_ERROR,
 835                                G_IO_ERROR_CANT_CREATE_BACKUP,
 836                                _("Backup file creation failed"));
 837           g_unlink (backup_filename);
 838           close (bfd);
 839           g_free (backup_filename);
 840
 841           goto err_out;
 842         }
 843
 844       close (bfd);
 845       g_free (backup_filename);
 846
 847       /* Seek back to the start of the file after the backup copy */
 848       if (lseek (fd, 0, SEEK_SET) == -1)
 849         {
 850           int errsv = errno;
 851
 852           g_set_error (error, G_IO_ERROR,
 853                        g_io_error_from_errno (errsv),
 854                        _("Error seeking in file: %s"),
 855                        g_strerror (errsv));
 856           goto err_out;
 857         }
 858     }
 859
 860   /* Truncate the file at the start */
 861 #ifdef G_OS_WIN32
 862   if (g_win32_ftruncate (fd, 0) == -1)
 863 #else
 864   if (ftruncate (fd, 0) == -1)
 865 #endif
 866     {
 867       int errsv = errno;
 868
 869       g_set_error (error, G_IO_ERROR,
 870                    g_io_error_from_errno (errsv),
 871                    _("Error truncating file: %s"),
 872                    g_strerror (errsv));
 873       goto err_out;
 874     }
 875
 876   return fd;
 877
 878  err_out:
 879   close (fd);
 880   return -1;
 881 }
 882
 883 GFileOutputStream *
 884 _g_local_file_output_stream_replace (const char        *filename,
 885                                      const char        *etag,
 886                                      gboolean           create_backup,
 887                                      GFileCreateFlags   flags,
 888                                      GCancellable      *cancellable,
 889                                      GError           **error)
 890 {
 891   GLocalFileOutputStream *stream;
 892   int mode;
 893   int fd;
 894   char *temp_file;
 895
 896   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 897     return NULL;
 898
 899   temp_file = NULL;
 900
 901   if (flags & G_FILE_CREATE_PRIVATE)
 902     mode = 0600;
 903   else
 904     mode = 0666;
 905
 906   /* If the file doesn't exist, create it */
 907   fd = g_open (filename, O_CREAT | O_EXCL | O_WRONLY | O_BINARY, mode);
 908
 909   if (fd == -1 && errno == EEXIST)
 910     {
 911       /* The file already exists */
 912       fd = handle_overwrite_open (filename, etag, create_backup, &temp_file,
 913                                   cancellable, error);
 914       if (fd == -1)
 915         return NULL;
 916     }
 917   else if (fd == -1)
 918     {
 919       int errsv = errno;
 920
 921       if (errsv == EINVAL)
 922         /* This must be an invalid filename, on e.g. FAT */
 923         g_set_error_literal (error, G_IO_ERROR,
 924                              G_IO_ERROR_INVALID_FILENAME,
 925                              _("Invalid filename"));
 926       else
 927         {
 928           char *display_name = g_filename_display_name (filename);
 929           g_set_error (error, G_IO_ERROR,
 930                        g_io_error_from_errno (errsv),
 931                        _("Error opening file '%s': %s"),
 932                        display_name, g_strerror (errsv));
 933           g_free (display_name);
 934         }
 935       return NULL;
 936     }
 937
 938
 939   stream = g_object_new (G_TYPE_LOCAL_FILE_OUTPUT_STREAM, NULL);
 940   stream->priv->fd = fd;
 941   stream->priv->tmp_filename = temp_file;
 942   if (create_backup)
 943     stream->priv->backup_filename = create_backup_filename (filename);
 944   stream->priv->original_filename =  g_strdup (filename);
 945
 946   return G_FILE_OUTPUT_STREAM (stream);
 947 }