*`Updated: 2023/08/08`*

## Block Diagram

## QoS Update Detail
The QoS update process can be simply separated in three steps:
1. Get update signal from QoS server via topic
2. Send request to QoS server to get `topic name`'s QoS profile
3. Response QoS profile for `topic name` and update QoS

For **initial state** QoS setting, **ignore** first step and request QoS profile just once. Otherwise, for **dynamic QoS updating**, several rules need to be followed:
1. The QoS server must have a QoS ID (`qid`) to describe the current status of all QoS profile settings, and the `qid` must be unique. The `qid` changes **if and only if** some of QoS profile changes.
2. The QoS publisher (server side) sends QoS ID (`qid`) and string array (`topic_table`) as the update signal. The `topic_table` shows the specific topics which QoS profile had been changed, and `qid` describes the whole current QoS profiles in QoS server. Subscriber (client side) can easily identify `qid` to prevent updating the same QoS profile.
3. While the device (client) finished the QoS update process, remember to record the `qid`, the QoS server can also record which client finish the QoS update process, to decrease the publish times.

## Service Interface
- File in `vehicle_interfaces/srv/QosReq.srv`

# Get topic_name QoS setting
string topic_name

# Device type corresponds to vehicle_interfaces header DEVTYPE_XXX definitions (preserve)
uint8 dev_type

---
# response is true if value accepted, otherwise server ignore the request and response false
bool response

# Unique ID describes current qos profile
uint64 qid

# Ref to enum rmw_qos_history_policy_t
int8 history

# Ref to size_t depth
int64 depth

# Ref to enum rmw_qos_reliability_policy_t
int8 reliability

# Ref to enum rmw_qos_durability_policy_t
int8 durability

# Ref to struct rmw_time_t deadline
float64 deadline_ms

# Ref to struct rmw_time_t lifespan
float64 lifespan_ms

# Ref to enum rmw_qos_liveliness_policy_t
int8 liveliness

# Ref to struct rmw_time_t liveliness_lease_duration
float64 liveliness_lease_duration_ms

## Topic Interface
- File in `vehicle_interfaces/msg/QosUpdate.msg`

vehicle_interfaces/Header header
uint64 qid
string[] topic_table

## Rclcpp QoS Members (Additional)
- **QoS Profile**

/*
 * QoS definition in rclcpp/qos.hpp
 * QoS private member: rmw_qos_profile_t (rmw/types.h)
 * */

typedef struct rmw_qos_profile_t
{
    enum rmw_qos_history_policy_t history;
    size_t depth;
    enum rmw_qos_reliability_policy_t reliability;
    enum rmw_qos_durability_policy_t durability;
    struct rmw_time_t deadline;
    struct rmw_time_t lifespan;
    enum rmw_qos_liveliness_policy_t liveliness;
    struct rmw_time_t liveliness_lease_duration;


    bool avoid_ros_namespace_conventions;
} rmw_qos_profile_t;

- **Enumerators in QoS Profile**

enum rmw_qos_history_policy_t
{
    RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT,
    RMW_QOS_POLICY_HISTORY_KEEP_LAST,
    RMW_QOS_POLICY_HISTORY_KEEP_ALL,
    RMW_QOS_POLICY_HISTORY_UNKNOWN
};

enum rmw_qos_reliability_policy_t
{
    RMW_QOS_POLICY_RELIABILITY_SYSTEM_DEFAULT,
    RMW_QOS_POLICY_RELIABILITY_RELIABLE,
    RMW_QOS_POLICY_RELIABILITY_BEST_EFFORT,
    RMW_QOS_POLICY_RELIABILITY_UNKNOWN
};

enum rmw_qos_durability_policy_t
{
    RMW_QOS_POLICY_DURABILITY_SYSTEM_DEFAULT,
    RMW_QOS_POLICY_DURABILITY_TRANSIENT_LOCAL,
    RMW_QOS_POLICY_DURABILITY_VOLATILE,
    RMW_QOS_POLICY_DURABILITY_UNKNOWN
};

enum rmw_qos_liveliness_policy_t
{
    RMW_QOS_POLICY_LIVELINESS_SYSTEM_DEFAULT = 0,
    RMW_QOS_POLICY_LIVELINESS_AUTOMATIC = 1,
    RMW_DECLARE_DEPRECATED(
        RMW_QOS_POLICY_LIVELINESS_MANUAL_BY_NODE,
        RMW_QOS_POLICY_LIVELINESS_MANUAL_BY_NODE_DEPRECATED_MSG) = 2,
    // Using `3` for backwards compatibility.
    RMW_QOS_POLICY_LIVELINESS_MANUAL_BY_TOPIC = 3,
    RMW_QOS_POLICY_LIVELINESS_UNKNOWN = 4
};