gst: deviceprodiver: Sort devices by session priority

Applications using the device provider typically list devices in the
order they were added. In order to ensure that apps pick nodes like cameras
with the highest priority by default, sort devices accordingly.

This unfortunately does not not have an effect on nodes added later,
e.g. on hotplug.

Closes https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/3072

src/gst/gstpipewiredeviceprovider.c

@@ -210,6 +210,7 @@ new_node (GstPipeWireDeviceProvider *self, struct node_data *data)
   const struct pw_node_info *info = data->info;
   const gchar *element = NULL;
   GstPipeWireDevice *gstdev;
+  int priority = 0;
 
   if (info->max_input_ports > 0 && info->max_output_ports == 0) {
     type = GST_PIPEWIRE_DEVICE_TYPE_SINK;
@@ -224,11 +225,16 @@ new_node (GstPipeWireDeviceProvider *self, struct node_data *data)
   props = gst_structure_new_empty ("pipewire-proplist");
   if (info->props) {
     const struct spa_dict_item *item;
+    const char *str;
+
     spa_dict_for_each (item, info->props)
       gst_structure_set (props, item->key, G_TYPE_STRING, item->value, NULL);
 
     klass = spa_dict_lookup (info->props, PW_KEY_MEDIA_CLASS);
     name = spa_dict_lookup (info->props, PW_KEY_NODE_DESCRIPTION);
+
+    if ((str = spa_dict_lookup(info->props, PW_KEY_PRIORITY_SESSION)))
+      priority = atoi(str);
   }
   if (klass == NULL)
     klass = "unknown/unknown";
@@ -244,26 +250,56 @@ new_node (GstPipeWireDeviceProvider *self, struct node_data *data)
   gstdev->serial = data->serial;
   gstdev->type = type;
   gstdev->element = element;
+  gstdev->priority = priority;
   if (props)
     gst_structure_free (props);
 
   return GST_DEVICE (gstdev);
 }
 
+static int
+compare_device_session_priority (const void *a,
+                                 const void *b)
+{
+  const GstPipeWireDevice *dev_a = a;
+  const GstPipeWireDevice *dev_b = b;
+
+  if (dev_a->priority < dev_b->priority)
+    return 1;
+  else if (dev_a->priority > dev_b->priority)
+    return -1;
+  else
+    return 0;
+}
+
 static void do_add_nodes(GstPipeWireDeviceProvider *self)
 {
   struct node_data *nd;
+  GList *new_devices = NULL;
+  GList *l;
 
   spa_list_for_each(nd, &self->nodes, link) {
     if (nd->dev != NULL)
 	    continue;
     pw_log_info("add node %d", nd->id);
     nd->dev = new_node (self, nd);
-    if (nd->dev) {
-      if(self->list_only)
-        self->devices = g_list_prepend (self->devices, gst_object_ref_sink (nd->dev));
-      else
-        gst_device_provider_device_add (GST_DEVICE_PROVIDER (self), nd->dev);
+    if (nd->dev)
+      new_devices = g_list_prepend (new_devices, nd->dev);
+  }
+  if (!new_devices)
+    return;
+
+  new_devices = g_list_sort (new_devices,
+                             compare_device_session_priority);
+  for (l = new_devices; l != NULL; l = l->next) {
+    GstDevice *device = l->data;
+
+    if(self->list_only) {
+      self->devices = g_list_insert_sorted (self->devices,
+                                            gst_object_ref_sink (device),
+                                            compare_device_session_priority);
+    } else {
+      gst_device_provider_device_add (GST_DEVICE_PROVIDER (self), device);
     }
   }
 }

src/gst/gstpipewiredeviceprovider.h

@@ -39,6 +39,7 @@ struct _GstPipeWireDevice {
   uint64_t            serial;
   int                 fd;
   const gchar        *element;
+  int                 priority;
 };
 
 struct _GstPipeWireDeviceClass {