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.i18n.Msg;
023import ca.uhn.fhir.rest.server.messaging.IMessage;
024
025/**
026 * Receives messages from a Message Broker.
027 *
028 * @param <T> The type of messages received by this consumer
029 */
030public interface IChannelConsumer<T> extends AutoCloseable {
031        /**
032         * @return the name of the topic or queue that this consumer is consuming from
033         */
034        String getChannelName();
035
036        /**
037         * Start the thread(s) that will be consuming messages
038         * @throws ChannelConsumerStartFailureException if the consumer fails to start (e.g. if it fails to connect to the broker)
039         */
040        void start();
041        /**
042         * Close this consumer's listener and this consumer, releasing any resources.
043         */
044        void close();
045
046        /**
047         * @return true if this consumer is closed
048         */
049        boolean isClosed();
050
051        /**
052         * @return the type of messages that will be delivered to this consumer
053         */
054        Class<? extends IMessage<T>> getMessageType();
055
056        /**
057         * @return the {@link IMessageListener} this consumer is sending messages to (i.e. the one it was created with).
058         */
059        IMessageListener<T> getMessageListener();
060
061        /**
062         * Pause requesting new messages from the broker until resume() is called.
063         */
064        default void pause() {
065                throw new UnsupportedOperationException(Msg.code(2655));
066        }
067
068        /**
069         * Resume requesting messages from the broker.
070         */
071        default void resume() {
072                throw new UnsupportedOperationException(Msg.code(2656));
073        }
074
075        /**
076         * Consumers should call this method at the top of any method that attempts to use the consumer
077         */
078        default void checkState() {
079                if (isClosed()) {
080                        throw new BrokerConsumerClosedException(Msg.code(2657) + "Attempted to use a closed "
081                                        + this.getClass().getSimpleName() + ": " + this);
082                }
083        }
084}