001/*-
002 * #%L
003 * HAPI FHIR Storage api
004 * %%
005 * Copyright (C) 2014 - 2025 Smile CDR, Inc.
006 * %%
007 * Licensed under the Apache License, Version 2.0 (the "License");
008 * you may not use this file except in compliance with the License.
009 * You may obtain a copy of the License at
010 *
011 *      http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing, software
014 * distributed under the License is distributed on an "AS IS" BASIS,
015 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
016 * See the License for the specific language governing permissions and
017 * limitations under the License.
018 * #L%
019 */
020package ca.uhn.fhir.broker.api;
021
022import ca.uhn.fhir.rest.server.messaging.IMessage;
023
024/**
025 * Receives messages from a Message Broker.
026 *
027 * @param <T> The type of messages received by this consumer
028 */
029public interface IChannelConsumer<T> extends AutoCloseable {
030        /**
031         * @return the name of the topic or queue that this consumer is consuming from
032         */
033        String getChannelName();
034
035        /**
036         * Start the thread(s) that will be consuming messages
037         * @throws ChannelConsumerStartFailureException if the consumer fails to start (e.g. if it fails to connect to the broker)
038         */
039        void start();
040        /**
041         * Close this consumer's listener and this consumer, releasing any resources.
042         */
043        void close();
044
045        /**
046         * @return true if this consumer is closed
047         */
048        boolean isClosed();
049
050        /**
051         * @return the type of messages that will be delivered to this consumer
052         */
053        Class<? extends IMessage<T>> getMessageType();
054
055        /**
056         * @return the {@link IMessageListener} this consumer is sending messages to (i.e. the one it was created with).
057         */
058        IMessageListener<T> getMessageListener();
059
060        /**
061         * Pause requesting new messages from the broker until resume() is called.
062         */
063        default void pause() {
064                throw new UnsupportedOperationException();
065        }
066
067        /**
068         * Resume requesting messages from the broker.
069         */
070        default void resume() {
071                throw new UnsupportedOperationException();
072        }
073
074        /**
075         * Consumers should call this method at the top of any method that attempts to use the consumer
076         */
077        default void checkState() {
078                if (isClosed()) {
079                        throw new BrokerConsumerClosedException(
080                                        "Attempted to use a closed " + this.getClass().getSimpleName() + ": " + this);
081                }
082        }
083}