Add 'best available' QoS enum values and methods

If users set a policy as 'best available', then the middleware will pick a policy
that is most compatible with the current set of discovered endpoints while maintaining
the highest level of service possible.

For details about the expected behavior, see connected changes:

- ros2/rmw#320
- ros2/rmw_dds_common#60

Signed-off-by: Jacob Perron <[email protected]>

Author: jacobperron

rclcpp/include/rclcpp/qos.hpp

@@ -44,6 +44,7 @@ enum class ReliabilityPolicy
   BestEffort = RMW_QOS_POLICY_RELIABILITY_BEST_EFFORT,
   Reliable = RMW_QOS_POLICY_RELIABILITY_RELIABLE,
   SystemDefault = RMW_QOS_POLICY_RELIABILITY_SYSTEM_DEFAULT,
+  BestAvailable = RMW_QOS_POLICY_RELIABILITY_BEST_AVAILABLE,
   Unknown = RMW_QOS_POLICY_RELIABILITY_UNKNOWN,
 };
 
@@ -52,6 +53,7 @@ enum class DurabilityPolicy
   Volatile = RMW_QOS_POLICY_DURABILITY_VOLATILE,
   TransientLocal = RMW_QOS_POLICY_DURABILITY_TRANSIENT_LOCAL,
   SystemDefault = RMW_QOS_POLICY_DURABILITY_SYSTEM_DEFAULT,
+  BestAvailable = RMW_QOS_POLICY_DURABILITY_BEST_AVAILABLE,
   Unknown = RMW_QOS_POLICY_DURABILITY_UNKNOWN,
 };
 
@@ -60,6 +62,7 @@ enum class LivelinessPolicy
   Automatic = RMW_QOS_POLICY_LIVELINESS_AUTOMATIC,
   ManualByTopic = RMW_QOS_POLICY_LIVELINESS_MANUAL_BY_TOPIC,
   SystemDefault = RMW_QOS_POLICY_LIVELINESS_SYSTEM_DEFAULT,
+  BestAvailable = RMW_QOS_POLICY_LIVELINESS_BEST_AVAILABLE,
   Unknown = RMW_QOS_POLICY_LIVELINESS_UNKNOWN,
 };
 
@@ -180,6 +183,10 @@ class RCLCPP_PUBLIC QoS
   QoS &
   best_effort();
 
+  /// Set the reliability setting to best available.
+  QoS &
+  reliability_best_available();
+
   /// Set the durability setting.
   QoS &
   durability(rmw_qos_durability_policy_t durability);
@@ -199,6 +206,10 @@ class RCLCPP_PUBLIC QoS
   QoS &
   transient_local();
 
+  /// Set the durability setting to best available.
+  QoS &
+  durability_best_available();
+
   /// Set the deadline setting.
   QoS &
   deadline(rmw_time_t deadline);
@@ -488,6 +499,36 @@ class RCLCPP_PUBLIC SystemDefaultsQoS : public QoS
   ));
 };
 
+/**
+ * Best available QoS class
+ *
+ * Match majority of endpoints currently available while maintaining the highest level of service.
+ * Policies are chosen at the time of creating a subscription or publisher.
+ * The middleware is not expected to update policies after creating a subscription or publisher,
+ * even if one or more policies are incompatible with newly discovered endpoints.
+ * Therefore, this profile should be used with care since non-deterministic behavior can occur due
+ * to races with discovery.
+ *
+ *    - History: Keep last,
+ *    - Depth: 10,
+ *    - Reliability: Best available,
+ *    - Durability: Best available,
+ *    - Deadline: Best available,
+ *    - Lifespan: Default,
+ *    - Liveliness: Best available,
+ *    - Liveliness lease duration: Best available,
+ *    - avoid ros namespace conventions: false
+ */
+class RCLCPP_PUBLIC BestAvailableQoS : public QoS
+{
+public:
+  explicit
+  BestAvailableQoS(
+    const QoSInitialization & qos_initialization = (
+      QoSInitialization::from_rmw(rmw_qos_profile_best_available)
+  ));
+};
+
 }  // namespace rclcpp
 
 #endif  // RCLCPP__QOS_HPP_

rclcpp/src/rclcpp/qos.cpp

@@ -150,6 +150,12 @@ QoS::best_effort()
   return this->reliability(RMW_QOS_POLICY_RELIABILITY_BEST_EFFORT);
 }
 
+QoS &
+QoS::reliability_best_available()
+{
+  return this->reliability(RMW_QOS_POLICY_RELIABILITY_BEST_AVAILABLE);
+}
+
 QoS &
 QoS::durability(rmw_qos_durability_policy_t durability)
 {
@@ -176,6 +182,12 @@ QoS::transient_local()
   return this->durability(RMW_QOS_POLICY_DURABILITY_TRANSIENT_LOCAL);
 }
 
+QoS &
+QoS::durability_best_available()
+{
+  return this->durability(RMW_QOS_POLICY_DURABILITY_BEST_AVAILABLE);
+}
+
 QoS &
 QoS::deadline(rmw_time_t deadline)
 {
@@ -380,4 +392,8 @@ SystemDefaultsQoS::SystemDefaultsQoS(const QoSInitialization & qos_initializatio
 : QoS(qos_initialization, rmw_qos_profile_system_default)
 {}
 
+BestAvailableQoS::BestAvailableQoS(const QoSInitialization & qos_initialization)
+: QoS(qos_initialization, rmw_qos_profile_best_available)
+{}
+
 }  // namespace rclcpp

rclcpp/test/rclcpp/test_qos.cpp

@@ -93,6 +93,9 @@ TEST(TestQoS, setters_and_getters) {
   qos.reliable();
   EXPECT_EQ(rclcpp::ReliabilityPolicy::Reliable, qos.reliability());
 
+  qos.reliability_best_available();
+  EXPECT_EQ(rclcpp::ReliabilityPolicy::BestAvailable, qos.reliability());
+
   qos.reliability(rclcpp::ReliabilityPolicy::BestEffort);
   EXPECT_EQ(rclcpp::ReliabilityPolicy::BestEffort, qos.reliability());
 
@@ -102,6 +105,9 @@ TEST(TestQoS, setters_and_getters) {
   qos.transient_local();
   EXPECT_EQ(rclcpp::DurabilityPolicy::TransientLocal, qos.durability());
 
+  qos.durability_best_available();
+  EXPECT_EQ(rclcpp::DurabilityPolicy::BestAvailable, qos.durability());
+
   qos.durability(rclcpp::DurabilityPolicy::Volatile);
   EXPECT_EQ(rclcpp::DurabilityPolicy::Volatile, qos.durability());
 
@@ -183,6 +189,9 @@ TEST(TestQoS, DerivedTypes) {
   const rclcpp::KeepLast expected_initialization(RMW_QOS_POLICY_DEPTH_SYSTEM_DEFAULT);
   const rclcpp::QoS expected_default(expected_initialization);
   EXPECT_EQ(expected_default.get_rmw_qos_profile(), system_default_qos.get_rmw_qos_profile());
+
+  rclcpp::BestAvailableQoS best_available_qos;
+  EXPECT_EQ(rmw_qos_profile_best_available, best_available_qos.get_rmw_qos_profile());
 }
 
 TEST(TestQoS, policy_name_from_kind) {