[YuanYuYuan]

Problem

A buffer-aware rmw_zenoh_cpp publisher stops writing the plain topic key for a message with an unbounded uint8[] or char[] field. It writes <topic key>/_buf_cpu for subscribers whose liveliness token ends with backends:cpu:. See ros2/rmw_zenoh#930. This text calls <topic key> the base key and <topic key>/_buf_cpu the group key.

A raw subscriber declared no token and read only the base key. It received nothing from such a publisher, with no error and no log. This is the report in #369.

Part of #372.

What changes

• A raw subscriber joins the CPU group by default. It has no message schema to inspect, so Auto joins it, as it joins a typed subscriber without a schema.
• create_raw_subscriber and create_raw_subscriber_with_qos use Auto. The C and Go bindings call them, so they join too.
• New method ZNode::create_raw_subscriber_with_group, only with the ffi feature. It takes Auto, Cpu or Off. Off stays out and declares no token. The Go bindings have no entry point for it yet.
• A joined raw subscriber declares two exact subscriptions, on the base key and on the group key, and then a token that ends with backends:cpu:. One callback serves both keys.
• It stays out with transient-local QoS or a custom key format, whatever the group. The feedback subscriber of a raw action client reads nothing and stays out.
• RawSubscriber has no public field now. RawSubscriber::undeclare consumes the wrapper and stops the token and both subscriptions. Dropping the wrapper stops the same three handles in the same order.
• The interop guide states the new behaviour, the migration, and the dependency on ros2/rmw_zenoh#1078 for subscribers with no backends: field.
• CI runs the raw test suite as its own cargo nextest run --no-tests=fail step. Without the raw-sub-tests feature the suite compiles to nothing, and the step fails instead of passing with zero tests.

Before and after

case	today	with this PR
default raw subscriber, token	none	ends with backends:cpu:
default raw subscriber, keys	base key	base key and group key
default raw, buffer-aware publisher	receives nothing	receives
default raw, sample for another subscriber	not delivered	not delivered, unchanged
raw subscriber with Off	stays out	stays out, unchanged
transient-local or custom key format	stays out	stays out, unchanged
raw action client feedback	stays out	stays out, unchanged
raw.inner.undeclare() (feature ffi)	compiles; stops one subscription	does not compile; use raw.undeclare()

Compatibility

change	who is affected	action
RawSubscriber.inner is no longer public	Rust code with the ffi feature that calls raw.inner.undeclare() (the field is public in release 0.2.0)	call raw.undeclare()
raw subscriber joins by default	subscribers behind a default-deny router	allow both keys; see below
raw subscriber joins by default	every raw, C and Go subscriber, on every topic	none; use create_raw_subscriber_with_group with Off to stay out (Rust only)

A router that allows only the base key starves a joined raw, C or Go subscriber of a buffer-aware publisher, with no error. Allow both keys. BufferGroup::Off needs no group key. A subscriber with no backends: field gets no buffer message from a buffer-aware publisher. This holds until a release carries ros2/rmw_zenoh#1078, so Off does not bring those messages back.

Design

A raw subscriber has no message schema, so Auto and Cpu do the same for it. A subscriber with no schema joins on every topic, not only on buffer topics. The subscriptions come before the token, as in #384. The token drops first. This sets the order of local undeclaration only. A remote publisher can still count the subscriber, and send to it, for a short time after the drop. The typed subscriber and the cache drop their handles in a different order; this PR leaves them unchanged.

Tests

The raw suite plays the publisher with a plain Zenoh session, so it needs no ROS installation. CI runs it in its own cargo nextest run --no-tests=fail step, so a build without the raw-sub-tests feature fails instead of passing with zero tests.

test (buffer_cpu_group_raw.rs)	checks
raw_subscriber_default_joins_and_announces_backends	the default constructors declare a backends:cpu: token, and one callback serves both keys
raw_subscribers_that_stay_out_announce_no_backends_and_skip_the_group_key	Off, transient-local QoS and a custom key format declare no token and read only the base key
raw_action_client_feedback_subscriber_stays_out	the feedback subscriber of a raw action client stays out
raw_subscriber_declares_two_exact_subscriptions_and_off_declares_one	two exact subscriptions when joined, one for Off
raw_group_subscription_is_declared_before_the_token_is_visible	the group subscription exists before the token
raw_access_control_starves_the_group_key_silently	a router that denies the group key drops buffer messages with no error
raw_denied_group_key_leaves_the_base_key_flowing	the same router still delivers the base key
raw_create_and_teardown_cycles_leave_no_token_and_no_callback	undeclare() and drop remove the token and both callbacks
raw_join_logs_both_keys_at_debug_level	a join logs one debug line with both keys, and an Off subscriber logs none

test (buffer_cpu_group_raw_interop.rs)	checks
raw_default_subscriber_receives_from_a_released_publisher	a default raw subscriber receives every sample from a released rmw_zenoh_cpp publisher, beside a released subscriber and an Off raw subscriber; the Off subscriber receives none. The released subscriber can make the publisher write the group key alone, so this cell does not show that the raw token matched
raw_default_subscriber_alone_matches_a_released_publisher	the default raw subscriber is the only subscriber: its token alone makes the publisher match and write the group key, and it receives every sample

The interop cells publish with ros2 topic pub and count what arrives. They check totals, not per-message identity.

To check that the tests can fail, I added one deliberate bug at a time to the production code. Each bug turned at least one raw test red.

deliberate bug	what it breaks
teardown forgets the token	undeclare() leaves the backends:cpu: token declared
teardown forgets the group subscription	undeclare() leaves the group-key callback running
create_raw_subscriber or _with_qos pass Off	the default raw subscriber stops joining
group subscription declared after the token	a publisher can see the token before the group subscription exists
raw path ignores Off, transient-local, custom key format or the feedback case	a subscriber that must stay out joins
raw join does not log its two keys	no debug line for a raw, C or Go join

#384 has merged. Merge order: this PR, #388, #389, then #386.