[PATCH] dbus: emit DBus.Introspectable for real objects only

[PATCH] dbus: emit DBus.Introspectable for real objects only

[Arseny Maslennikov]

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From: Arseny Maslennikov <arseny@altlinux.org>

In a similar vein to GDBus, we now explicitly declare
org.freedesktop.DBus.Introspectable in the introspection output for
registered objects only, not for every node. This removes clutter from
introspection trees.

For example, if a service exports the following object paths on the bus:
* /org/freedesktop/LogControl1
* /org/bluez
* /org/bluez/hci0
then /org is now described in the introspection output as a node
containing two subnodes "bluez" and "freedesktop" and no interface
elements.
Inspection tools like d-feet only list the objects themselves, while
before this change they would uselessly list:
* /
* /org
* /org/bluez
* /org/bluez/hci0
* /org/freedesktop
* /org/freedesktop/LogControl1

We still conform to the spec by responding to
org.freedesktop.DBus.Introspectable.Introspect calls on every node — we
just don't advertise the interface in the xml response.
---
 ell/dbus-service.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/ell/dbus-service.c b/ell/dbus-service.c
index 84fca3a..94afc14 100644
--- a/ell/dbus-service.c
+++ b/ell/dbus-service.c
@@ -1709,16 +1709,28 @@ void _dbus_object_tree_introspect(struct _dbus_object_tree *tree,
 {
 	struct object_node *node;
 	struct child_node *child;
+	bool path_is_object = true;
 
 	node = l_hashmap_lookup(tree->objects, path);
-	if (!node)
+	if (!node) {
+		path_is_object = false;
 		node = _dbus_object_tree_lookup(tree, path);
+	}
 
 	l_string_append(buf, XML_HEAD);
 	l_string_append(buf, "<node>\n");
 
 	if (node) {
-		l_string_append(buf, static_introspectable);
+		/* We emit org.freedesktop.DBus.Introspectable only in case the
+		 * object node corresponds to a registered object, i. e.
+		 * exposes anything other than:
+		 * - org.freedesktop.DBus.Introspectable
+		 * - org.freedesktop.DBus.Peer
+		 * - org.freedesktop.DBus.Properties
+		 */
+		if (path_is_object)
+			l_string_append(buf, static_introspectable);
+
 		l_queue_foreach(node->instances,
 					generate_interface_instance, buf);
 
-- 
2.31.0

Re: [PATCH] dbus: emit DBus.Introspectable for real objects only

[Denis Kenzior]

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Hi Arseny,

On 4/19/21 2:11 AM, Arseny Maslennikov wrote:
> From: Arseny Maslennikov <arseny@altlinux.org>
> 
> In a similar vein to GDBus, we now explicitly declare
> org.freedesktop.DBus.Introspectable in the introspection output for
> registered objects only, not for every node. This removes clutter from
> introspection trees.
> 
> For example, if a service exports the following object paths on the bus:
> * /org/freedesktop/LogControl1
> * /org/bluez
> * /org/bluez/hci0
> then /org is now described in the introspection output as a node
> containing two subnodes "bluez" and "freedesktop" and no interface
> elements.
> Inspection tools like d-feet only list the objects themselves, while
> before this change they would uselessly list:
> * /
> * /org
> * /org/bluez
> * /org/bluez/hci0
> * /org/freedesktop
> * /org/freedesktop/LogControl1
> 
> We still conform to the spec by responding to
> org.freedesktop.DBus.Introspectable.Introspect calls on every node — we
> just don't advertise the interface in the xml response.
> ---
>   ell/dbus-service.c | 16 ++++++++++++++--
>   1 file changed, 14 insertions(+), 2 deletions(-)
> 

For some reason this patch came through base64 encoded and with <CR><LF> endings 
in the payload.  This confused git am and I had to do some post-processing to 
fix it up.  Not sure why this occurred..?

> diff --git a/ell/dbus-service.c b/ell/dbus-service.c
> index 84fca3a..94afc14 100644
> --- a/ell/dbus-service.c
> +++ b/ell/dbus-service.c
> @@ -1709,16 +1709,28 @@ void _dbus_object_tree_introspect(struct _dbus_object_tree *tree,
>   {
>   	struct object_node *node;
>   	struct child_node *child;
> +	bool path_is_object = true;
>   
>   	node = l_hashmap_lookup(tree->objects, path);
> -	if (!node)
> +	if (!node) {
> +		path_is_object = false;
>   		node = _dbus_object_tree_lookup(tree, path);
> +	}
>   
>   	l_string_append(buf, XML_HEAD);
>   	l_string_append(buf, "<node>\n");
>   
>   	if (node) {
> -		l_string_append(buf, static_introspectable);
> +		/* We emit org.freedesktop.DBus.Introspectable only in case the

Nit: multiline comments should follow doc/coding-style.txt item M2.  I fixed 
this up for you.

> +		 * object node corresponds to a registered object, i. e.
> +		 * exposes anything other than:
> +		 * - org.freedesktop.DBus.Introspectable
> +		 * - org.freedesktop.DBus.Peer
> +		 * - org.freedesktop.DBus.Properties
> +		 */
> +		if (path_is_object)
> +			l_string_append(buf, static_introspectable);
> +
>   		l_queue_foreach(node->instances,
>   					generate_interface_instance, buf);
>   
> 

Applied, thanks.

Regards,
-Denis