Querying subs to query newly discovered publishers with publication caches

rmw_zenoh_cpp/src/detail/graph_cache.cpp

@@ -341,7 +341,7 @@ void GraphCache::parse_put(
   if (ignore_from_current_session && is_entity_local(*entity)) {
     RMW_ZENOH_LOG_DEBUG_NAMED(
       "rmw_zenoh_cpp",
-      "Ignoring parse_put for %s from the same session.\n", entity->keyexpr().c_str());
+      "Ignoring parse_put for %s from the same session.\n", entity->liveliness_keyexpr().c_str());
     return;
   }
 
@@ -403,6 +403,20 @@ void GraphCache::parse_put(
   // Otherwise, the entity represents a node that already exists in the graph.
   // Update topic info if required below.
   update_topic_maps_for_put(node_it->second, entity);
+
+  // If the newly added entity is a publisher with transient_local qos durability,
+  // we trigger any registered querying subscriber callbacks.
+  if (entity->type() == liveliness::EntityType::Publisher &&
+    entity->topic_info().has_value() &&
+    entity->topic_info()->qos_.durability == RMW_QOS_POLICY_DURABILITY_TRANSIENT_LOCAL)
+  {
+    auto sub_cbs_it = querying_subs_cbs_.find(entity->topic_info()->topic_keyexpr_);
+    if (sub_cbs_it != querying_subs_cbs_.end()) {
+      for (const auto & cb : sub_cbs_it->second) {
+        cb(entity->zid());
+      }
+    }
+  }
 }
 
 ///=============================================================================
@@ -559,7 +573,7 @@ void GraphCache::parse_del(
   if (ignore_from_current_session && is_entity_local(*entity)) {
     RMW_ZENOH_LOG_DEBUG_NAMED(
       "rmw_zenoh_cpp",
-      "Ignoring parse_del for %s from the same session.\n", entity->keyexpr().c_str());
+      "Ignoring parse_del for %s from the same session.\n", entity->liveliness_keyexpr().c_str());
     return;
   }
   // Lock the graph mutex before accessing the graph.
@@ -1315,4 +1329,18 @@ std::unique_ptr<rmw_zenoh_event_status_t> GraphCache::take_event_status(
   status_to_take.current_count_change = 0;
   return result;
 }
+
+///=============================================================================
+void GraphCache::set_querying_subscriber_callback(
+  const std::string & keyexpr,
+  QueryingSubscriberCallback cb)
+{
+  auto cb_it = querying_subs_cbs_.find(keyexpr);
+  if (cb_it == querying_subs_cbs_.end()) {
+    querying_subs_cbs_[keyexpr] = std::move(std::vector<QueryingSubscriberCallback>{});
+    cb_it = querying_subs_cbs_.find(keyexpr);
+  }
+  cb_it->second.push_back(std::move(cb));
+}
+
 }  // namespace rmw_zenoh_cpp

rmw_zenoh_cpp/src/detail/graph_cache.hpp

@@ -99,6 +99,12 @@ using GraphNodePtr = std::shared_ptr<GraphNode>;
 class GraphCache final
 {
 public:
+  /// @brief Signature for a function that will be invoked by the GraphCache when a QoS
+  ///   event is detected.
+  using GraphCacheEventCallback = std::function<void (std::unique_ptr<rmw_zenoh_event_status_t>)>;
+  /// Callback to be triggered when a publication cache is detected in the ROS Graph.
+  using QueryingSubscriberCallback = std::function<void (const std::string & queryable_prefix)>;
+
   /// @brief Constructor
   /// @param id The id of the zenoh session that is building the graph cache.
   ///   This is used to infer which entities originated from the current session
@@ -169,10 +175,6 @@ class GraphCache final
     const char * service_type,
     bool * is_available) const;
 
-  /// @brief Signature for a function that will be invoked by the GraphCache when a QoS
-  ///   event is detected.
-  using GraphCacheEventCallback = std::function<void (std::unique_ptr<rmw_zenoh_event_status_t>)>;
-
   /// Set a qos event callback for an entity from the current session.
   /// @note The callback will be removed when the entity is removed from the graph.
   void set_qos_event_callback(
@@ -183,6 +185,10 @@ class GraphCache final
   /// Returns true if the entity is a publisher or client. False otherwise.
   static bool is_entity_pub(const liveliness::Entity & entity);
 
+  void set_querying_subscriber_callback(
+    const std::string & keyexpr,
+    QueryingSubscriberCallback cb);
+
 private:
   // Helper function to convert an Entity into a GraphNode.
   // Note: this will update bookkeeping variables in GraphCache.
@@ -281,6 +287,8 @@ class GraphCache final
   using GraphEventCallbackMap = std::unordered_map<liveliness::ConstEntityPtr, GraphEventCallbacks>;
   // EventCallbackMap for each type of event we support in rmw_zenoh_cpp.
   GraphEventCallbackMap event_callbacks_;
+  // Map keyexpressions to QueryingSubscriberCallback.
+  std::unordered_map<std::string, std::vector<QueryingSubscriberCallback>> querying_subs_cbs_;
   // Counters to track changes to event statues for each topic.
   std::unordered_map<std::string,
     std::array<rmw_zenoh_event_status_t, ZENOH_EVENT_ID_MAX + 1>> event_statuses_;

rmw_zenoh_cpp/src/detail/liveliness_utils.cpp

@@ -49,8 +49,27 @@ NodeInfo::NodeInfo(
   // Do nothing.
 }
 
+namespace
+{
+// Helper function to create a copy of a string after removing any
+// leading or trailing slashes.
+std::string strip_slashes(const std::string & str)
+{
+  std::string ret = str;
+  std::size_t start = 0;
+  std::size_t end = str.length() - 1;
+  if (str[0] == '/') {
+    ++start;
+  }
+  if (str[end] == '/') {
+    --end;
+  }
+  return ret.substr(start, end - start + 1);
+}
+}  // namespace
 ///=============================================================================
 TopicInfo::TopicInfo(
+  std::size_t domain_id,
   std::string name,
   std::string type,
   std::string type_hash,
@@ -60,7 +79,13 @@ TopicInfo::TopicInfo(
   type_hash_(std::move(type_hash)),
   qos_(std::move(qos))
 {
-  // Do nothing.
+  topic_keyexpr_ = std::to_string(domain_id);
+  topic_keyexpr_ += "/";
+  topic_keyexpr_ += strip_slashes(name_);
+  topic_keyexpr_ += "/";
+  topic_keyexpr_ += type_;
+  topic_keyexpr_ += "/";
+  topic_keyexpr_ += type_hash_;
 }
 
 ///=============================================================================
@@ -403,7 +428,7 @@ Entity::Entity(
   for (std::size_t i = 0; i < KEYEXPR_INDEX_MAX + 1; ++i) {
     bool last = false;
     if (!keyexpr_parts[i].empty()) {
-      this->keyexpr_ += std::move(keyexpr_parts[i]);
+      this->liveliness_keyexpr_ += std::move(keyexpr_parts[i]);
     }
     if (i == KEYEXPR_INDEX_MAX || keyexpr_parts[i + 1].empty()) {
       last = true;
@@ -412,9 +437,9 @@ Entity::Entity(
       break;
     }
     // Append the delimiter unless it is the last component.
-    this->keyexpr_ += KEYEXPR_DELIMITER;
+    this->liveliness_keyexpr_ += KEYEXPR_DELIMITER;
   }
-  this->guid_ = std::hash<std::string>{}(this->keyexpr_);
+  this->guid_ = std::hash<std::string>{}(this->liveliness_keyexpr_);
 }
 
 ///=============================================================================
@@ -521,6 +546,7 @@ std::shared_ptr<Entity> Entity::make(const std::string & keyexpr)
       return nullptr;
     }
     topic_info = TopicInfo{
+      domain_id,
       demangle_name(std::move(parts[KeyexprIndex::TopicName])),
       demangle_name(std::move(parts[KeyexprIndex::TopicType])),
       demangle_name(std::move(parts[KeyexprIndex::TopicTypeHash])),
@@ -590,9 +616,9 @@ std::optional<TopicInfo> Entity::topic_info() const
 }
 
 ///=============================================================================
-std::string Entity::keyexpr() const
+std::string Entity::liveliness_keyexpr() const
 {
-  return this->keyexpr_;
+  return this->liveliness_keyexpr_;
 }
 
 ///=============================================================================

rmw_zenoh_cpp/src/detail/liveliness_utils.hpp

@@ -50,9 +50,11 @@ struct TopicInfo
   std::string name_;
   std::string type_;
   std::string type_hash_;
+  std::string topic_keyexpr_;
   rmw_qos_profile_t qos_;
 
   TopicInfo(
+    std::size_t domain_id,
     std::string name,
     std::string type,
     std::string type_hash,
@@ -162,7 +164,7 @@ class Entity
   std::optional<TopicInfo> topic_info() const;
 
   /// Get the liveliness keyexpr for this entity.
-  std::string keyexpr() const;
+  std::string liveliness_keyexpr() const;
 
   // Two entities are equal if their guids are equal.
   bool operator==(const Entity & other) const;
@@ -183,7 +185,7 @@ class Entity
   EntityType type_;
   NodeInfo node_info_;
   std::optional<TopicInfo> topic_info_;
-  std::string keyexpr_;
+  std::string liveliness_keyexpr_;
 };
 
 ///=============================================================================