Use microsecond precision for last modification time

When the file system allows it, this prevents Tumbler from believing
that the original file has not been modified since the last time the
thumbnail was created, when in fact modifications have taken place in
the second that the thumbnail was created.

The time of last modification is stored internally in a `gdouble`, and
written to the PNG thumbnail in `%.6f` format. This complies well with
the Freedesktop specification [1], as the stat command returns this
format when invoked as `stat -c%.6Y file`, although it is likely that
the specification was written with the idea that this value be an
integer.

The extraction of the thumbnail information is done via
`g_ascii_strtod()`, so an integer or less precision is not a problem. As
for a code expecting to find an integer, it is likely to simply ignore
the decimal part, as Tumbler used to do by extracting the information
via `atol()`. It is possible, however, that an error will be found if a
more complete extractor is used, such as `strtol()`.

The changes this causes to the exposed Tumbler APIs should also be
inconsequential, as it is a conversion to a higher type. This should
therefore result in implicit conversions, except perhaps for
`tumbler_file_info_get_mtime()`, if its return value is explicitly
stored in a `gint64`.

[1] https://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html#CREATION

Fixes #15, see !20 for more details.

1 files changed, 12 insertions, 9 deletions

diff --git a/tumbler/tumbler-file-info.c b/tumbler/tumbler-file-info.c
index 7116658..9a32983 100644
--- a/tumbler/tumbler-file-info.c
+++ b/tumbler/tumbler-file-info.c
@@ -70,7 +70,7 @@ struct _TumblerFileInfo
   TumblerThumbnailFlavor *flavor;
   TumblerThumbnail       *thumbnail;
 
-  guint64                 mtime; 
+  gdouble                 mtime;
   gchar                  *uri;
   gchar                  *mime_type;
 };
@@ -93,10 +93,10 @@ tumbler_file_info_class_init (TumblerFileInfoClass *klass)
   gobject_class->set_property = tumbler_file_info_set_property;
 
   g_object_class_install_property (gobject_class, PROP_MTIME,
-                                   g_param_spec_uint64 ("mtime",
+                                   g_param_spec_double ("mtime",
                                                         "mtime",
                                                         "mtime",
-                                                        0, G_MAXUINT64, 0,
+                                                        0, G_MAXDOUBLE, 0,
                                                         G_PARAM_READABLE));
 
   g_object_class_install_property (gobject_class, PROP_URI,
@@ -167,7 +167,7 @@ tumbler_file_info_get_property (GObject    *object,
   switch (prop_id)
     {
     case PROP_MTIME:
-      g_value_set_uint64 (value, info->mtime);
+      g_value_set_double (value, info->mtime);
       break;
     case PROP_URI:
       g_value_set_string (value, info->uri);
@@ -197,7 +197,7 @@ tumbler_file_info_set_property (GObject      *object,
   switch (prop_id)
     {
     case PROP_MTIME:
-      info->mtime = g_value_get_uint64 (value);
+      info->mtime = g_value_get_double (value);
       break;
     case PROP_URI:
       info->uri = g_value_dup_string (value);
@@ -249,7 +249,9 @@ tumbler_file_info_load (TumblerFileInfo *info,
   file = g_file_new_for_uri (info->uri);
 
   /* query the modified time from the file */
-  file_info = g_file_query_info (file, G_FILE_ATTRIBUTE_TIME_MODIFIED, 
+  file_info = g_file_query_info (file,
+                                 G_FILE_ATTRIBUTE_TIME_MODIFIED
+                                   "," G_FILE_ATTRIBUTE_TIME_MODIFIED_USEC,
                                  G_FILE_QUERY_INFO_NONE, cancellable, &err);
 
   /* destroy the GFile */
@@ -263,8 +265,9 @@ tumbler_file_info_load (TumblerFileInfo *info,
     }
 
   /* read and remember the modified time */
-  info->mtime = g_file_info_get_attribute_uint64 (file_info,
-                                                        G_FILE_ATTRIBUTE_TIME_MODIFIED);
+  info->mtime = g_file_info_get_attribute_uint64 (file_info, G_FILE_ATTRIBUTE_TIME_MODIFIED)
+                + 1e-6 * g_file_info_get_attribute_uint32 (file_info,
+                                                           G_FILE_ATTRIBUTE_TIME_MODIFIED_USEC);
 
   /* we no longer need the file information */
   g_object_unref (file_info);
@@ -341,7 +344,7 @@ tumbler_file_info_get_mime_type (TumblerFileInfo *info)
 
 
 
-guint64
+gdouble
 tumbler_file_info_get_mtime (TumblerFileInfo *info)
 {
   g_return_val_if_fail (TUMBLER_IS_FILE_INFO (info), 0);