[gnome-software/wip/rancell/apt] Check if a file is a .deb before trying to install it

[Robert Ancell <rancell src gnome org>]

commit 1191f36540a101a953afc589c1229dfe6179d9a4
Author: Robert Ancell <robert ancell canonical com>
Date:   Mon Mar 14 16:39:33 2016 +1300

    Check if a file is a .deb before trying to install it

 src/plugins/gs-plugin-apt.c |   38 ++++++++++++++++++++++++++++++++++++++
 1 files changed, 38 insertions(+), 0 deletions(-)
---
diff --git a/src/plugins/gs-plugin-apt.c b/src/plugins/gs-plugin-apt.c
index f8b2984..7b02631 100644
--- a/src/plugins/gs-plugin-apt.c
+++ b/src/plugins/gs-plugin-apt.c
@@ -869,6 +869,35 @@ gs_plugin_launch (GsPlugin *plugin,
        return gs_plugin_app_launch (plugin, app, error);
 }
 
+static gboolean
+content_type_matches (const gchar *filename,
+                     gboolean *matches,
+                     GCancellable *cancellable,
+                     GError **error)
+{
+       const gchar *content_type;
+       g_autoptr(GFile) file = NULL;
+       g_autoptr(GFileInfo) info = NULL;
+       const gchar *supported_types[] = {
+               "application/vnd.debian.binary-package",
+               NULL };
+
+       /* get content type */
+       file = g_file_new_for_path (filename);
+       info = g_file_query_info (file,
+                                 G_FILE_ATTRIBUTE_STANDARD_CONTENT_TYPE,
+                                 G_FILE_QUERY_INFO_NONE,
+                                 cancellable,
+                                 error);
+       if (info == NULL)
+               return FALSE;
+
+       content_type = g_file_info_get_attribute_string (info, G_FILE_ATTRIBUTE_STANDARD_CONTENT_TYPE);
+       *matches = g_strv_contains (supported_types, content_type);
+
+       return TRUE;
+}
+
 gboolean
 gs_plugin_filename_to_app (GsPlugin      *plugin,
                           GList        **list,
@@ -876,6 +905,7 @@ gs_plugin_filename_to_app (GsPlugin      *plugin,
                           GCancellable  *cancellable,
                           GError       **error)
 {
+       gboolean supported;
        GsApp *app;
        g_autoptr(GFile) file = NULL;
        gchar *argv[5] = { NULL };
@@ -888,6 +918,14 @@ gs_plugin_filename_to_app (GsPlugin      *plugin,
        g_autofree gchar *path = NULL;
        g_auto(GStrv) tokens = NULL;
 
+       if (!content_type_matches (filename,
+                                  &supported,
+                                  cancellable,
+                                  error))
+               return FALSE;
+       if (!supported)
+               return TRUE;
+
        argv[0] = argv0 = g_strdup ("dpkg-deb");
        argv[1] = argv1 = g_strdup ("--showformat=${Package}\\n"
                                    "${Version}\\n"