connectors/iot/src/main/java/org/apache/edgent/connectors/iot/QoS.java

/*
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regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
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with the License.  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

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*/
package org.apache.edgent.connectors.iot;

/**
 * Device event quality of service levels.
 * The QoS levels match the MQTT specification.
 * <BR>
 * An implementation of {@link IotDevice} may not
 * support all QoS levels.
 * 
 * @see <a href="http://mqtt.org/">mqtt.org</a>
 * @see IotDevice#events(org.apache.edgent.topology.TStream, String, int)
 * @see IotDevice#events(org.apache.edgent.topology.TStream, org.apache.edgent.function.Function, org.apache.edgent.function.UnaryOperator, org.apache.edgent.function.Function)

 */
public interface QoS {
    
    /**
     * The message containing the event arrives at the message hub either once or not at all.
     * <BR>
     * Value is {@code 0}.
     */
    Integer AT_MOST_ONCE = 0;
    
    /**
     * Fire and forget the event. Synonym for {@link #AT_MOST_ONCE}.
     * <BR>
     * Value is {@code 0}.
     */
    Integer FIRE_AND_FORGET = 0;
    
    /**
     * The message containing the event arrives at the message hub at least once.
     * The message may be seen at the hub multiple times.
     * <BR>
     * Value is {@code 1}.
     */
    Integer AT_LEAST_ONCE = 1;
    
    /**
     * The message containing the event arrives at the message hub exactly once.
     * <BR>
     * Value is {@code 2}.
     */ 
    Integer EXACTLY_ONCE = 2;
}