consumer_component_base.hpp

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#pragma once
 
/// @file userver/urabbitmq/consumer_component_base.hpp
/// @brief Base component for your consumers.
 
#include <memory>
#include <userver/components/component_base.hpp>
#include <userver/urabbitmq/typedefs.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace urabbitmq {
 
// clang-format off
/// @ingroup userver_base_classes
///
/// @brief Base component for your consumers.
/// Basically a `ConsumerBase` but in a nice component-ish way
///
/// You should derive from it and override `Process` method, which gets called
/// when a new message arrives from the broker.
/// The consumer will be automatically started after all components are loaded
/// and stopped before all components are beginning to stop.
///
/// Library takes care of handling start failures and runtime failures
/// (connection breakage/broker node downtime etc.) and will try it's best to
/// restart the consumer.
///
/// @note Library guarantees `at least once` delivery, hence some deduplication
/// might be needed ou your side.
///
/// ## Static configuration example:
///
/// @snippet samples/rabbitmq_service/static_config.yaml  RabbitMQ consumer sample - static config
///
/// ## Static options:
/// Name             | Description
/// rabbit_name      | Name of the RabbitMQ component to use for consumption
/// queue            | Name of the queue to consume from
/// prefetch_count   | prefetch_count for the consumer, limits the amount of in-flight messages
///
// clang-format on
class ConsumerComponentBase : public components::ComponentBase {
public:
    ConsumerComponentBase(const components::ComponentConfig& config, const components::ComponentContext& context);
    ~ConsumerComponentBase() override;
 
    static yaml_config::Schema GetStaticConfigSchema();
 
protected:
    void OnAllComponentsLoaded() final;
 
    void OnAllComponentsAreStopping() final;
 
    /// @brief You may override this method in derived class and implement
    /// message handling logic. By default it does nothing.
    ///
    /// If this method returns successfully message would be acked (best effort)
    /// to the broker, if this method throws the message would be requeued.
    ///
    /// Please keep in mind that it is possible for the message to be delivered
    /// again even if `Process` returns successfully: sadly we can't guarantee
    /// that `ack` ever reached the broker (network issues or unexpected shutdown,
    /// for example).
    /// It is however guaranteed for message to be requeued if `Process` fails.
    virtual void Process(std::string) { /* do nothing */
    }
 
    /// @brief You may override this method in derived class and implement
    /// message handling logic. By default it just calls `Process` with message
    /// body.
    ///
    virtual void Process(ConsumedMessage msg) { Process(std::move(msg.message)); }
 
private:
    // This is actually just a subclass of `ConsumerBase`
    class Impl;
    std::unique_ptr<Impl> impl_;
};
 
}  // namespace urabbitmq
 
namespace components {
 
template <>
inline constexpr bool kHasValidate<urabbitmq::ConsumerComponentBase> = true;
 
}
 
USERVER_NAMESPACE_END