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Chapter 11. Intercepting messages

Interceptors give you the ability to intercept packets as they enter or exit the broker, which allows you to audit packets or filter messages. Interceptors can change the packets they intercept, which makes them powerful, but also potentially dangerous.

You can develop interceptors to meet your business requirements. Interceptors are protocol specific and must implement the appropriate interface.

Interceptors must implement the intercept() method, which returns a boolean value. If the value is true, the message packet continues onward. If false, the process is aborted, no other interceptors are called, and the message packet is not processed further.

11.1. Creating interceptors
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You can create custom incoming and outgoing interceptors to meet organizational requirements such as auditing packets. All interceptors are protocol specific and are called for any packet entering or exiting the server.

Interceptors can change the packets they intercept. This makes them powerful and potentially dangerous, so be sure to use them with caution.

You must place interceptors and their dependencies in the Java classpath of the broker. You can use the <broker_instance_dir>/lib directory since it is part of the classpath by default.

The following example shows how to create an interceptor that checks the size of each packet passed to it.

Procedure

  1. Implement the appropriate interface and override its intercept() method.

    1. If you are using the AMQP protocol, implement the org.apache.activemq.artemis.protocol.amqp.broker.AmqpInterceptor interface. 

      package com.example;

import org.apache.activemq.artemis.protocol.amqp.broker.AMQPMessage;
import org.apache.activemq.artemis.protocol.amqp.broker.AmqpInterceptor;
import org.apache.activemq.artemis.spi.core.protocol.RemotingConnection;

public class MyInterceptor implements AmqpInterceptor
{
  private final int ACCEPTABLE_SIZE = 1024;

  @Override
  public boolean intercept(final AMQPMessage message, RemotingConnection connection)
  {
    int size = message.getEncodeSize();
    if (size <= ACCEPTABLE_SIZE) {
      System.out.println("This AMQPMessage has an acceptable size.");
      return true;
    }
    return false;
  }
}
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    2. If you are using Core Protocol, your interceptor must implement the org.apache.artemis.activemq.api.core.Interceptor interface. 

      package com.example;

import org.apache.artemis.activemq.api.core.Interceptor;
import org.apache.activemq.artemis.core.protocol.core.Packet;
import org.apache.activemq.artemis.spi.core.protocol.RemotingConnection;

public class MyInterceptor implements Interceptor
{
  private final int ACCEPTABLE_SIZE = 1024;

  @Override
  boolean intercept(Packet packet, RemotingConnection connection)
  throws ActiveMQException
  {
    int size = packet.getPacketSize();
    if (size <= ACCEPTABLE_SIZE) {
      System.out.println("This Packet has an acceptable size.");
      return true;
    }
    return false;
  }
}
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    3. If you are using the MQTT protocol, implement the org.apache.activemq.artemis.core.protocol.mqtt.MQTTInterceptor interface. 

      package com.example;

import org.apache.activemq.artemis.core.protocol.mqtt.MQTTInterceptor;
import io.netty.handler.codec.mqtt.MqttMessage;
import org.apache.activemq.artemis.spi.core.protocol.RemotingConnection;

public class MyInterceptor implements Interceptor
{
  private final int ACCEPTABLE_SIZE = 1024;

  @Override
  boolean intercept(MqttMessage mqttMessage, RemotingConnection connection)
  throws ActiveMQException
  {
    byte[] msg = (mqttMessage.toString()).getBytes();
    int size = msg.length;
    if (size <= ACCEPTABLE_SIZE) {
      System.out.println("This MqttMessage has an acceptable size.");
      return true;
    }
    return false;
  }
}
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    4. If you are using the STOMP protocol, implement the org.apache.activemq.artemis.core.protocol.stomp.StompFrameInterceptor interface. 

      package com.example;

import org.apache.activemq.artemis.core.protocol.stomp.StompFrameInterceptor;
import org.apache.activemq.artemis.core.protocol.stomp.StompFrame;
import org.apache.activemq.artemis.spi.core.protocol.RemotingConnection;

public class MyInterceptor implements Interceptor
{
  private final int ACCEPTABLE_SIZE = 1024;

  @Override
  boolean intercept(StompFrame stompFrame, RemotingConnection connection)
  throws ActiveMQException
  {
    int size = stompFrame.getEncodedSize();
    if (size <= ACCEPTABLE_SIZE) {
      System.out.println("This StompFrame has an acceptable size.");
      return true;
    }
    return false;
  }
}
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11.2. Configuring the broker to use interceptors
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After you create an interceptor, you must configure the broker to activate the interceptor so it can intercept packets as they enter or exit the broker.

Prerequisites

You must create an interceptor class and add it (and its dependencies) to the Java classpath of the broker before you can configure it for use by the broker. You can use the <broker_instance_dir>/lib directory since it is part of the classpath by default.

Procedure

  1. Configure the broker to use an interceptor by adding configuration to <broker_instance_dir>/etc/broker.xml.

    1. If your interceptor is intended for incoming messages, add its class-name to the list of remoting-incoming-interceptors. 

      <configuration>
  <core>
    ...
    <remoting-incoming-interceptors>
       <class-name>org.example.MyIncomingInterceptor</class-name>
    </remoting-incoming-interceptors>
    ...
  </core>
</configuration>
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    2. If your interceptor is intended for outgoing messages, add its class-name to the list of remoting-outgoing-interceptors. 

      <configuration>
  <core>
    ...
    <remoting-outgoing-interceptors>
       <class-name>org.example.MyOutgoingInterceptor</class-name>
    </remoting-outgoing-interceptors>
  </core>
</configuration>
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