discoverer: Add APIs to simply get installer details for missing plugins

Currently the API is far from optimal and the user has to work around
our badly defined API to simply install missing plugins.

API:
  new:
    gst_discoverer_info_get_missing_elements_installer_details

  deprecated:
    gst_discoverer_info_get_misc
    gst_discoverer_stream_info_get_misc

https://bugzilla.gnome.org/show_bug.cgi?id=720596

docs/libs/gst-plugins-base-libs-sections.txt

@@ -2761,6 +2761,7 @@ gst_discoverer_stream_info_ref
 gst_discoverer_stream_info_unref
 gst_discoverer_stream_info_list_free
 gst_discoverer_stream_info_get_stream_type_nick
+gst_discoverer_info_get_missing_elements_installer_details
 gst_discoverer_info_get_audio_streams
 gst_discoverer_info_get_container_streams
 gst_discoverer_info_get_streams

gst-libs/gst/pbutils/gstdiscoverer-types.c

@@ -353,7 +353,7 @@ G_DEFINE_TYPE (GstDiscovererInfo, gst_discoverer_info, G_TYPE_OBJECT);
 static void
 gst_discoverer_info_init (GstDiscovererInfo * info)
 {
-  /* Nothing needs initialization */
+  info->missing_elements_details = g_ptr_array_new_with_free_func (g_free);
 }
 
 static void
@@ -375,6 +375,8 @@ gst_discoverer_info_finalize (GObject * object)
 
   if (info->toc)
     gst_toc_unref (info->toc);
+
+  g_ptr_array_unref (info->missing_elements_details);
 }
 
 static GstDiscovererInfo *
@@ -687,6 +689,9 @@ gst_discoverer_stream_info_get_stream_id (GstDiscovererStreamInfo * info)
  * gst_discoverer_stream_info_get_misc:
  * @info: a #GstDiscovererStreamInfo
  *
+ * Deprecated: This functions is deprecated since version 1.4, use
+ * gst_discoverer_stream_get_missing_elements_installer_details
+ *
  * Returns: (transfer none): additional information regarding the stream (for
  * example codec version, profile, etc..). If you wish to use the #GstStructure
  * after the life-time of @info you will need to copy it.
@@ -1010,6 +1015,9 @@ DISCOVERER_INFO_ACCESSOR_CODE (seekable, gboolean, FALSE);
  * gst_discoverer_info_get_misc:
  * @info: a #GstDiscovererInfo
  *
+ * Deprecated: This functions is deprecated since version 1.4, use
+ * gst_discoverer_info_get_missing_elements_installer_details
+ *
  * Returns: (transfer none): Miscellaneous information stored as a #GstStructure
  * (for example: information about missing plugins). If you wish to use the
  * #GstStructure after the life-time of @info, you will need to copy it.
@@ -1068,3 +1076,38 @@ DISCOVERER_INFO_ACCESSOR_CODE (toc, const GstToc *, NULL);
  *
  * Decrements the reference count of @info.
  */
+
+
+/**
+ * gst_discoverer_info_get_missing_elements_installer_details:
+ * @info: a #GstDiscovererStreamInfo to retrieve installer detail
+ * for the missing element
+ *
+ * Get the installer details for missing elements
+ *
+ * Returns: (transfer full): (array zero-terminated=1): An array of strings
+ * containing informations about how to install the various missing elements
+ * for @info to be usable. Free with g_strfreev.
+ *
+ * Since: 1.4
+ */
+const gchar **
+gst_discoverer_info_get_missing_elements_installer_details (const
+    GstDiscovererInfo * info)
+{
+
+  if (info->result != GST_DISCOVERER_MISSING_PLUGINS) {
+    GST_WARNING_OBJECT (info, "Trying to get missing element installed details "
+        "but result is not 'MISSING_PLUGINS'");
+
+    return NULL;
+  }
+
+  if (info->missing_elements_details->pdata[info->missing_elements_details->
+          len]) {
+    GST_DEBUG ("Adding NULL pointer to the end of missing_elements_details");
+    g_ptr_array_add (info->missing_elements_details, NULL);
+  }
+
+  return (const gchar **) info->missing_elements_details->pdata;
+}

gst-libs/gst/pbutils/gstdiscoverer.c

@@ -1383,9 +1383,13 @@ handle_message (GstDiscoverer * dc, GstMessage * msg)
         GST_DEBUG_OBJECT (GST_MESSAGE_SRC (msg),
             "Setting result to MISSING_PLUGINS");
         dc->priv->current_info->result = GST_DISCOVERER_MISSING_PLUGINS;
+        /* FIXME 2.0 Remove completely the ->misc
+         * Keep the old behaviour for now.
+         */
         if (dc->priv->current_info->misc)
           gst_structure_free (dc->priv->current_info->misc);
-        dc->priv->current_info->misc = gst_structure_copy (structure);
+        g_ptr_array_add (dc->priv->current_info->missing_elements_details,
+            gst_missing_plugin_message_get_installer_detail (msg));
       } else if (sttype == _STREAM_TOPOLOGY_QUARK) {
         if (dc->priv->current_topology)
           gst_structure_free (dc->priv->current_topology);

gst-libs/gst/pbutils/gstdiscoverer.h

@@ -204,6 +204,7 @@ gboolean                  gst_discoverer_info_get_seekable(const GstDiscovererIn
 const GstStructure*       gst_discoverer_info_get_misc(const GstDiscovererInfo* info);
 const GstTagList*         gst_discoverer_info_get_tags(const GstDiscovererInfo* info); 
 const GstToc*             gst_discoverer_info_get_toc(const GstDiscovererInfo* info);
+const gchar**             gst_discoverer_info_get_missing_elements_installer_details(const GstDiscovererInfo* info);
 
 GList *                   gst_discoverer_info_get_streams (GstDiscovererInfo *info,
 							   GType streamtype);

gst-libs/gst/pbutils/pbutils-private.h

@@ -100,6 +100,7 @@ struct _GstDiscovererInfo {
   GstTagList *tags;
   GstToc *toc;
   gboolean seekable;
+  GPtrArray *missing_elements_details;
 
   gpointer _gst_reserved[GST_PADDING];
 };

tools/gst-discoverer.c

@@ -409,10 +409,15 @@ print_info (GstDiscovererInfo * info, GError * err)
     {
       g_print ("Missing plugins\n");
       if (verbose) {
-        gchar *tmp =
-            gst_structure_to_string (gst_discoverer_info_get_misc (info));
-        g_print (" (%s)\n", tmp);
-        g_free (tmp);
+        gint i = 0;
+        const gchar **installer_details =
+            gst_discoverer_info_get_missing_elements_installer_details (info);
+
+        while (installer_details[i]) {
+          g_print (" (%s)\n", installer_details[i]);
+
+          i++;
+        }
       }
       break;
     }