include/pulsar/ConsumerInterceptor.h

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

#ifndef PULSAR_CPP_CONSUMER_INTERCEPTOR_H
#define PULSAR_CPP_CONSUMER_INTERCEPTOR_H

#include <pulsar/Message.h>
#include <pulsar/Result.h>
#include <pulsar/defines.h>

#include <set>

namespace pulsar {

class Consumer;

/**
 * A plugin interface that allows you to intercept (and possibly mutate)
 * messages received by the consumer.
 *
 * <p>A primary use case is to hook into consumer applications for custom
 * monitoring, logging, etc.
 *
 * <p>Exceptions thrown by interceptor methods will be caught, logged, but
 * not propagated further.
 */
class PULSAR_PUBLIC ConsumerInterceptor {
   public:
    virtual ~ConsumerInterceptor() {}
    /**
     * Close the interceptor
     */
    virtual void close() {}

    /**
     * This is called just before the message is consumed.
     *
     * <p>This method is allowed to modify message, in which case the new message
     * will be returned.
     *
     * <p>Any exception thrown by this method will be caught by the caller, logged,
     * but not propagated to client.
     *
     * <p>Since the consumer may run multiple interceptors, a particular
     * interceptor's <tt>beforeConsume</tt> callback will be called in the order.
     * The first interceptor in the list gets the consumed message, the following interceptor will be passed
     * the message returned by the previous interceptor, and so on. Since
     * interceptors are allowed to modify message, interceptors may potentially
     * get the messages already modified by other interceptors. However building a
     * pipeline of mutable interceptors that depend on the output of the previous interceptor is
     * discouraged, because of potential side-effects caused by interceptors
     * potentially failing to modify the message and throwing an exception.
     * if one of interceptors in the list throws an exception from
     * <tt>beforeConsume</tt>, the exception is caught, logged,
     * and the next interceptor is called with the message returned by the last
     * successful interceptor in the list, or otherwise the original consumed
     * message.
     *
     * @param consumer the consumer which contains the interceptor
     * @param message the message to be consumed by the client
     * @return message that is either modified by the interceptor or same message
     *         passed into the method.
     */
    virtual Message beforeConsume(const Consumer& consumer, const Message& message) = 0;

    /**
     *
     * This is called before consumer sends the acknowledgment to the broker.
     *
     * <p>Any exception thrown by this method will be ignored by the caller.
     *
     * @param consumer the consumer which contains the interceptor
     * @param result the result of the acknowledgement
     * @param messageID the message id to be acknowledged
     */
    virtual void onAcknowledge(const Consumer& consumer, Result result, const MessageId& messageID) = 0;

    /**
     *
     * This is called before consumer sends the cumulative acknowledgment to the broker.
     *
     * <p>Any exception thrown by this method will be ignored by the caller.
     *
     * @param consumer the consumer which contains the interceptor
     * @param result the result of the cumulative acknowledgement
     * @param messageID the message id to be acknowledged cumulatively
     */
    virtual void onAcknowledgeCumulative(const Consumer& consumer, Result result,
                                         const MessageId& messageID) = 0;

    /**
     * This method will be called when a redelivery from a negative acknowledge occurs.
     *
     * <p>Any exception thrown by this method will be ignored by the caller.
     *
     * @param consumer the consumer which contains the interceptor
     * @param messageIds the set of message ids to negative ack
     */
    virtual void onNegativeAcksSend(const Consumer& consumer, const std::set<MessageId>& messageIds) = 0;
};

typedef std::shared_ptr<ConsumerInterceptor> ConsumerInterceptorPtr;
}  // namespace pulsar

#endif  // PULSAR_CPP_CONSUMER_INTERCEPTOR_H