server/queue/queue-rabbitmq/src/main/java/org/apache/james/queue/rabbitmq/RabbitMQMailQueueDeadLetterQueueHealthCheck.java

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package org.apache.james.queue.rabbitmq;

import static org.apache.james.queue.api.MailQueueFactory.SPOOL;

import jakarta.inject.Inject;

import org.apache.james.backends.rabbitmq.RabbitMQConfiguration;
import org.apache.james.backends.rabbitmq.RabbitMQManagementAPI;
import org.apache.james.core.healthcheck.ComponentName;
import org.apache.james.core.healthcheck.HealthCheck;
import org.apache.james.core.healthcheck.Result;

import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;

public class RabbitMQMailQueueDeadLetterQueueHealthCheck implements HealthCheck {
    public static final MailQueueName JAMES_MAIL_QUEUE_NAME = MailQueueName.fromString(SPOOL.asString());
    public static final ComponentName COMPONENT_NAME = new ComponentName("RabbitMQMailQueueDeadLetterQueueHealthCheck");
    private static final String DEFAULT_VHOST = "/";

    private final RabbitMQConfiguration configuration;
    private final RabbitMQManagementAPI api;

    @Inject
    public RabbitMQMailQueueDeadLetterQueueHealthCheck(RabbitMQConfiguration configuration) {
        this.configuration = configuration;
        this.api = RabbitMQManagementAPI.from(configuration);
    }

    @Override
    public ComponentName componentName() {
        return COMPONENT_NAME;
    }

    @Override
    public Mono<Result> check() {
        return Mono.fromCallable(() -> api.queueDetails(configuration.getVhost().orElse(DEFAULT_VHOST), JAMES_MAIL_QUEUE_NAME.toDeadLetterQueueName()))
            .map(queueDetails -> {
                if (queueDetails.getQueueLength() != 0) {
                    return Result.degraded(COMPONENT_NAME, "RabbitMQ dead letter queue of the mail queue contain messages. This might indicate transient failure on mail processing.");
                }
                return Result.healthy(COMPONENT_NAME);
            })
            .onErrorResume(e -> Mono.just(Result.unhealthy(COMPONENT_NAME, "Error checking RabbitMQMailQueueDeadLetterQueueHealthCheck", e)))
            .subscribeOn(Schedulers.boundedElastic());
    }
}