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Client library for working with the NATS messaging system.
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// Copyright 2022 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at:
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package io.nats.client;

import java.time.Duration;

/**
 * This interface provides a simple iterative access to a pull consumer.
 * Note: This interface is superseded by  {@link ConsumerContext ConsumerContext}. For examples for recommended usage see {@link JetStream JetStream}.
 */
public interface JetStreamReader {
    /**
     * Read the next message. Return null if the calls times out.
     * Use a timeout of 0 to wait indefinitely. This could still be interrupted if
     * the subscription is unsubscribed or the client connection is closed.
     * @param timeout the maximum time to wait
     * @return the next message for this subscriber or null if there is a timeout
     * @throws InterruptedException if one is thrown, in order to propagate it up
     * @throws IllegalStateException if the subscription belongs to a dispatcher, or is not active
     */
    Message nextMessage(Duration timeout) throws InterruptedException;

    /**
     * Read the next message. Return null if the calls times out.
     * Use a timeout of 0 to wait indefinitely. This could still be interrupted if
     * the subscription is unsubscribed or the client connection is closed.
     * @param timeoutMillis the maximum time to wait
     * @return the next message for this subscriber or null if there is a timeout
     * @throws InterruptedException if one is thrown, in order to propagate it up
     * @throws IllegalStateException if the subscription belongs to a dispatcher, or is not active
     */
    Message nextMessage(long timeoutMillis) throws InterruptedException;

    /**
     * Stop getting more messages from the server. Some messages may have already arrived and
     * are in the buffer, so continue to call nextMessage until a null is returned.
     */
    void stop();
}