Introspection returns bogus child paths

[mriemensberger]

Describe the bug

I see the following path hierarchy when showing the object tree with busctl tree com.example.Service

└─/com
  └─/com/example
    └─/com/example/service
      ├─/com/example/service/item
      │ ├─/com/example/service/item/0
      │ ├─/com/example/service/item/1
      │ │ ├─/com/example/service/item/1/0
      │ │ └─/com/example/service/item/1/1
      │ ├─/com/example/service/item/10
      │ ├─/com/example/service/item/11
      │ └─/com/example/service/item/2
...

I would expect to see only

└─/com
  └─/com/example
    └─/com/example/service
      ├─/com/example/service/item
      │ ├─/com/example/service/item/0
      │ ├─/com/example/service/item/1
      │ ├─/com/example/service/item/10
      │ ├─/com/example/service/item/11
      │ └─/com/example/service/item/2
...

The /com/example/service/item/1/0 and /com/example/service/item/1/1 are bogus and have never been exported by the service. They also show up without any interfaces when being introspected with busctl introspect.

It looks like that the computation of the children nodes in https://github.com/Bluetooth-Devices/dbus-fast/blob/f0fc6668b9543bd81e2438fe78a54c31702a4bc5/src/dbus_fast/message_bus.py#L650 is wrong if some paths are prefixes for other paths. For example, /com/example/service/item/1 is a prefix of /com/example/service/item/10, but the latter is not a child of the former.

To Reproduce

• Expose object paths where one path is a prefix of another path but they have no parent-child relationship.
• Introspect with busctl tree

Additional context

Suggested fix: Replace https://github.com/Bluetooth-Devices/dbus-fast/blob/f0fc6668b9543bd81e2438fe78a54c31702a4bc5/src/dbus_fast/message_bus.py#L663 with

            if not export_path.startswith(path + '/'):

[bdraco]

That looks like a reasonable fix. It might need an equality check as well for the exact path (but not sure on that one without a test)

[mriemensberger]

I ended up with this fix:

--- a/src/dbus_fast/message_bus.py  2024-05-01 00:20:01.242137424 +0000
+++ b/src/dbus_fast/message_bus.py  2024-05-01 00:20:17.490082951 +0000
@@ -665,6 +665,9 @@

             child_path = export_path.split(path, maxsplit=1)[1]
+            if path and path[-1] != "/" and child_path and child_path[0] != "/":
+                continue
+
             child_path = child_path.lstrip("/")
             child_name = child_path.split("/", maxsplit=1)[0]

             children.add(child_name)

[mriemensberger]

Otherwise the root path introspection (path = "/" doesn't work).

[mriemensberger]

But there is probably a prettier way to fix it.

[bdraco]

If you open a PR with a test, I can do a proper review this weekend assuming the Home Assistant release tomorrow doesn't eat up all my available time

[mriemensberger]

PR #280 created. Please review.

[mriemensberger]

@bdraco Thanks for handling this so quickly.

[bdraco]

Thank you for your contributions!