feat: name the subscriber (node + topic) in the UDS send-drop warning…

[benaliabderrahmane]

Names the offending subscriber (fully-qualified node name + topic) in the UDS send-drop warning and clarifies that the byte count is the dropped message's size, not the buffer fill level. Before/after:

UDS send to '/tmp/ros2_uds/200/sub_1_159bd.sock' dropped: subscriber recv buffer full (89 bytes, errno=Resource temporarily unavailable). ...
UDS send to node '/test_ns/test_node' on topic '/pull_stress' (socket '/tmp/ros2_uds/200/sub_1_159bd.sock') dropped: subscriber recv queue full — dropped a 89-byte message (recv buf configured 48 MB, errno=Resource temporarily unavailable). ...

How

• make_peer_label(ns, name, topic) in transport.cpp (unit-tested, incl. root-namespace collapse and null tolerance).
• The publisher's copy-on-write cache holds CachedSubscriber {socket_path, label}; labels are built once per graph change inside refresh_subscribers, so the publish hot path still copies one refcount and never formats a string.
• send_to gains an optional peer_label (default null). The three publisher fan-out paths supply it; request/response callers are unchanged.

Rebased and retargeted onto devel

Rewritten against current devel (single commit): the wake-side TRANSIENT_LOCAL replay this originally also patched in rmw_wait.cpp no longer exists (#60 made replay pull-based, so the wait path no longer sends), and the three cache-refresh sites it edited are now devel's single refresh_subscribers helper — the feature got smaller by landing after those changes.

Verified: 14/14 ctest in the jazzy container; the churn stress test triggers a real drop and prints the new labeled warning.

[Copilot]

Pull request overview

This PR improves slow-subscriber drop diagnostics for the Unix Domain Socket (UDS) transport by attaching a human-readable subscriber identity (fully-qualified node name + topic) to ENOBUFS/EAGAIN send-drop warnings, while keeping the publish hot path allocation-free by caching the formatted label on graph changes.

Changes:

• Add make_peer_label() to format node '/ns/name' on topic '/topic' (with sensible null/root handling) and test coverage for it.
• Extend the publisher subscriber cache from socket paths to {socket_path, label} entries and plumb labels into send_to() from publish and TRANSIENT_LOCAL replay paths.
• Update the ENOBUFS/EAGAIN warning to clarify the dropped byte count and include the configured receive buffer size for reference.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
rmw_unix_socket_cpp/test/test_transport.cpp	Adds unit tests validating peer label formatting edge cases.
rmw_unix_socket_cpp/src/types.hpp	Introduces CachedSubscriber and updates publisher cache to store {path,label} entries.
rmw_unix_socket_cpp/src/transport.hpp	Extends send_to() with optional peer_label and declares make_peer_label().
rmw_unix_socket_cpp/src/transport.cpp	Implements make_peer_label() and improves ENOBUFS/EAGAIN drop warning content.
rmw_unix_socket_cpp/src/rmw_wait.cpp	Populates and uses cached subscriber labels for TRANSIENT_LOCAL replay sends.
rmw_unix_socket_cpp/src/rmw_publisher.cpp	Populates and uses cached subscriber labels for publish and replay sends.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

Suppressed comments (1)

rmw_unix_socket_cpp/src/transport.cpp:196

• The drop warning reports total = sizeof(WireHeader) + payload_size, but the message text says “dropped a %zu-byte message”, which reads like the serialized ROS message size. Either log payload_size instead, or clarify that the count is the on-wire datagram size (incl. header) to avoid confusion when users compare against their message size.

        "UDS send to %s (socket '%s') dropped: subscriber recv queue full — "
        "dropped a %zu-byte message (recv buf configured %d MB, errno=%s). "
        "Slow subscriber or undersized SO_RCVBUF.",
        peer_label ? peer_label : "peer", dest_path.c_str(), total,
        RECV_BUF_SIZE / (1024 * 1024), std::strerror(err));