SnmpNull.java

/*******************************************************************************
 * This file is part of OpenNMS(R).
 *
 * Copyright (C) 2011 The OpenNMS Group, Inc.
 * OpenNMS(R) is Copyright (C) 1999-2011 The OpenNMS Group, Inc.
 *
 * OpenNMS(R) is a registered trademark of The OpenNMS Group, Inc.
 *
 * OpenNMS(R) is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published
 * by the Free Software Foundation, either version 3 of the License,
 * or (at your option) any later version.
 *
 * OpenNMS(R) is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with OpenNMS(R).  If not, see:
 *      http://www.gnu.org/licenses/
 *
 * For more information contact:
 *     OpenNMS(R) Licensing <license@opennms.org>
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package org.opennms.protocols.snmp;

import java.io.Serializable;

import org.opennms.protocols.snmp.asn1.AsnDecodingException;
import org.opennms.protocols.snmp.asn1.AsnEncoder;
import org.opennms.protocols.snmp.asn1.AsnEncodingException;

/**
 * Implements the SNMP Null object as defined by the SNMPv1 and SNMPv2 SMI. The
 * object has no data or length, but is encoded with a specific header. Often
 * used as the value portion of an SnmpVarBind when sending a GET, GETNEXT, etc
 * to a remote agent.
 * 
 * This class manages no internal data, but is derived to provide the proper
 * encoding and handling of SNMP Null datatypes.
 * 
 * @author <a href="mailto:weave@oculan.com">Brian Weaver </a>
 * 
 */
public class SnmpNull extends Object implements SnmpSyntax, Cloneable, Serializable {
    /**
     * Used to allow the serialization format to evolve.
     * 
     */
    static final long serialVersionUID = 441279481529521581L;

    /**
     * Defines the ASN.1 value for the SnmpNull class.
     * 
     */
    public static final byte ASNTYPE = SnmpSMI.SMI_NULL;

    /**
     * Constructs a default SnmpNull class
     * 
     */
    public SnmpNull() {
        // do nothing
    }

    /**
     * Copy constructor. Provided so that if the class is extended or should at
     * some point manage internal data, the data could be meaningfully copied
     * from the passed object.
     * 
     * @param second
     *            The class object to set data from.
     * 
     */
    public SnmpNull(SnmpNull second) {
        // do nothing
    }

    /**
     * Used to retreive the ASN.1 type for this object.
     * 
     * @return The ASN.1 value for the SnmpNull
     * 
     */
    public byte typeId() {
        return ASNTYPE;
    }

    /**
     * Used to encode the null value into an ASN.1 buffer. The passed encoder
     * defines the method for encoding the data.
     * 
     * @param buf
     *            The location to write the encoded data
     * @param offset
     *            The start of the encoded buffer.
     * @param encoder
     *            The ASN.1 encoder object
     * 
     * @return The byte immediantly after the last encoded byte.
     * 
     */
    public int encodeASN(byte[] buf, int offset, AsnEncoder encoder) throws AsnEncodingException {
        return encoder.buildNull(buf, offset, typeId());
    }

    /**
     * Used to decode the null value from the ASN.1 buffer. The passed encoder
     * is used to decode the ASN.1 information.
     * 
     * @param buf
     *            The encoded ASN.1 data
     * @param offset
     *            The offset of the first byte of data
     * @param encoder
     *            The ASN.1 decoder object.
     * 
     * @return The byte immediantly after the last decoded byte of information.
     * 
     */
    public int decodeASN(byte[] buf, int offset, AsnEncoder encoder) throws AsnDecodingException {
        Object[] rVals = encoder.parseNull(buf, offset);

        if (((Byte) rVals[1]).byteValue() != typeId())
            throw new AsnDecodingException("Invalid ASN.1 type");

        return ((Integer) rVals[0]).intValue();
    }

    /**
     * Used to get a duplicate of the current object so that it can be modified
     * without affecting the creating object.
     * 
     * @return A duplicate of the current object.
     * 
     */
    public SnmpSyntax duplicate() {
        return new SnmpNull(this);
    }

    /**
     * Used to get a duplicate of the current object so that it can be modified
     * without affecting the creating object.
     * 
     * @return A duplicate of the current object.
     * 
     */
    public Object clone() {
        return new SnmpNull(this);
    }

    /**
     * Returns a string representation of the SNMP Null object
     * 
     */
    public String toString() {
        return "";
    }
}