Merge branch '3144-file-set-contents-truncation' into 'main'

gfileutils: Add a missing ftruncate() call when writing files

Closes #3144

See merge request GNOME/glib!3650

glib/gfileutils.c

@@ -1139,6 +1139,36 @@ fd_should_be_fsynced (int                    fd,
 #endif  /* !HAVE_FSYNC */
 }
 
+static gboolean
+truncate_file (int          fd,
+               off_t        length,
+               const char  *dest_file,
+               GError     **error)
+{
+  while (
+#ifdef G_OS_WIN32
+    g_win32_ftruncate (fd, length) < 0
+#else
+    ftruncate (fd, length) < 0
+#endif
+    )
+    {
+      int saved_errno = errno;
+
+      if (saved_errno == EINTR)
+        continue;
+
+      if (error != NULL)
+        set_file_error (error,
+                        dest_file,
+                        _("Failed to write file “%s”: ftruncate() failed: %s"),
+                        saved_errno);
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
 /* closes @fd once it’s finished (on success or error) */
 static gboolean
 write_to_file (const gchar  *contents,
@@ -1475,6 +1505,8 @@ consistent_out:
         }
 
       do_fsync = fd_should_be_fsynced (direct_fd, filename, flags);
+      if (!truncate_file (direct_fd, 0, filename, error))
+        return FALSE;
       if (!write_to_file (contents, length, g_steal_fd (&direct_fd), filename,
                           do_fsync, error))
         return FALSE;

glib/tests/fileutils.c

@@ -1603,6 +1603,8 @@ test_set_contents_full (void)
           gsize len;
           gboolean ret;
           GStatBuf statbuf;
+          const gchar *original_contents = "a string which is longer than what will be overwritten on it";
+          size_t original_contents_len = strlen (original_contents);
 
           g_test_message ("Flags %d and test %" G_GSIZE_FORMAT, flags, i);
 
@@ -1617,7 +1619,7 @@ test_set_contents_full (void)
 
                 fd = g_file_open_tmp (NULL, &file_name, &error);
                 g_assert_no_error (error);
-                g_assert_cmpint (write (fd, "a", 1), ==, 1);
+                g_assert_cmpint (write (fd, original_contents, original_contents_len), ==, original_contents_len);
                 g_assert_no_errno (g_fsync (fd));
                 close (fd);
 
@@ -1713,7 +1715,7 @@ test_set_contents_full (void)
 
                   g_file_get_contents (file_name, &target_contents, NULL, &error);
                   g_assert_no_error (error);
-                  g_assert_cmpstr (target_contents, ==, "a");
+                  g_assert_cmpstr (target_contents, ==, original_contents);
 
                   g_free (target_contents);
                 }