commit	47b1892936eb272555873fd6ba3c483bedfa936c	[log] [tgz]
author	Luca Milanesio <luca.milanesio@gmail.com>	Fri May 19 13:37:44 2023 +0100
committer	Luca Milanesio <luca.milanesio@gmail.com>	Fri May 19 13:37:44 2023 +0100
tree	87d96c56451e5b9da2a0af114bce82ce9487a941
parent	55baed4a3cd2d419a4b66e5bb97194d0ea084778 [diff]

tree: 87d96c56451e5b9da2a0af114bce82ce9487a941

README.md

Events Broker API for Gerrit Code Review

API of a generic events broker for use with Gerrit Code Review.

Enables the de-coupling between Gerrit, plugins and the different implementations of a generic events broker.

Stream Events Publisher

It is a quite common use case for consumers of this library to listen for Gerrit events and to stream them on a specific topic.

Since the implementation of such logic is always the same, this library provides a generic stream events publisher which will perform the relevant operations.

In order to listen and stream gerrit events, consumers of this API need to provide a binding for the StreamEventPublisherConfig configuration and java.util.concurrent.Executor binding annotated with StreamEventPublisherExecutor annotation. A default single threaded implementation (StreamEventPublisherExecutor) is provided by the library. The last step is to explicitly bind the Stream Events Publisher, as such:

import java.util.concurrent.Executor;

import com.gerritforge.gerrit.eventbroker.publisher.StreamEventPublisher;
import com.gerritforge.gerrit.eventbroker.publisher.StreamEventPublisherConfig;
import com.gerritforge.gerrit.eventbroker.publisher.executor.StreamEventPublisherExecutor;
import com.gerritforge.gerrit.eventbroker.publisher.executor.StreamEventPublisherExecutorProvider;
import com.google.gerrit.extensions.registration.DynamicSet;
import com.google.gerrit.server.events.EventListener;
import com.google.inject.AbstractModule;

public class SomeModule extends AbstractModule {
    @Override
    protected void configure() {
        long messagePublishingTimeout = 1000L;

        bind(StreamEventPublisherConfig.class)
                .toInstance(new StreamEventPublisherConfig(
                    "name_of_the_stream_events_topic",
                    messagePublishingTimeout));

        bind(Executor.class).annotatedWith(StreamEventPublisherExecutor.class).toProvider(StreamEventPublisherExecutorProvider.class);
        DynamicSet.bind(binder(), EventListener.class).to(StreamEventPublisher.class);
    }
}

Alternative way to setup Stream Event Publisher is to use default Guice module StreamEventPublisherModule:

import com.gerritforge.gerrit.eventbroker.publisher.StreamEventPublisherConfig;
import com.gerritforge.gerrit.eventbroker.publisher.StreamEventPublisherModule;
import com.google.inject.AbstractModule;
import com.google.inject.TypeLiteral;
import com.google.inject.name.Names;

public class SomeModule extends AbstractModule {
    @Override
    protected void configure() {
        long messagePublishingTimeout = 1000L;
        bind(StreamEventPublisherConfig.class)
                .toInstance(new StreamEventPublisherConfig(
                    "name_of_the_stream_events_topic",
                    messagePublishingTimeout));
        install(new StreamEventPublisherModule());
    }
}

Note: To avoid message duplication Stream Events Publisher uses gerrit.instanceId and Event.instanceId to filter out forwarded events.

Broker Metrics

When StreamEventPublisher is used user can optionally bind an implementation of the BrokerMetrics` interface. This will allow to collect metrics about successful/failure stream events publishing. If no binding is provided default implementation will skip collecting metrics:

import com.google.gerrit.extensions.registration.DynamicItem;
import com.google.inject.AbstractModule;

public class SomeModule extends AbstractModule {
    @Override
    protected void configure() {
        DynamicItem.bind(binder(), BrokerMetrics.class)
            .to(BrokerMetricsImpl.class)
            .in(Scopes.SINGLETON);
    }
}

Note: BrokerMetrics implementation must be bound in a plugin module.