ChecksumSyslogMessageModifier.java

package org.graylog2.syslog4j.impl.message.modifier.checksum;

import org.graylog2.syslog4j.SyslogIF;
import org.graylog2.syslog4j.SyslogRuntimeException;
import org.graylog2.syslog4j.impl.message.modifier.AbstractSyslogMessageModifier;
import org.graylog2.syslog4j.util.SyslogUtility;

/**
 * ChecksumSyslogMessageModifier is an implementation of SyslogMessageModifierIF
 * that provides support for Java Checksum algorithms (java.util.zip.Checksum).
 * <p/>
 * <p>Syslog4j is licensed under the Lesser GNU Public License v2.1.  A copy
 * of the LGPL license is available in the META-INF folder in all
 * distributions of Syslog4j and in the base directory of the "doc" ZIP.</p>
 *
 * @author <syslog4j@productivity.org>
 * @version $Id: ChecksumSyslogMessageModifier.java,v 1.5 2010/10/28 05:10:57 cvs Exp $
 */
public class ChecksumSyslogMessageModifier extends AbstractSyslogMessageModifier {
    private static final long serialVersionUID = -3268914290497005065L;

    protected ChecksumSyslogMessageModifierConfig config = null;

    public static final ChecksumSyslogMessageModifier createCRC32() {
        ChecksumSyslogMessageModifier crc32 = new ChecksumSyslogMessageModifier(ChecksumSyslogMessageModifierConfig.createCRC32());

        return crc32;
    }

    public static final ChecksumSyslogMessageModifier createADLER32() {
        ChecksumSyslogMessageModifier adler32 = new ChecksumSyslogMessageModifier(ChecksumSyslogMessageModifierConfig.createADLER32());

        return adler32;
    }

    public ChecksumSyslogMessageModifier(ChecksumSyslogMessageModifierConfig config) {
        super(config);

        this.config = config;

        if (this.config == null) {
            throw new SyslogRuntimeException("Checksum config object cannot be null");
        }

        if (this.config.getChecksum() == null) {
            throw new SyslogRuntimeException("Checksum object cannot be null");
        }
    }

    public ChecksumSyslogMessageModifierConfig getConfig() {
        return this.config;
    }

    protected void continuousCheckForVerify() {
        if (this.config.isContinuous()) {
            throw new SyslogRuntimeException(this.getClass().getName() + ".verify(..) does not work with isContinuous() returning true");
        }

    }

    public boolean verify(String message, String hexChecksum) {
        continuousCheckForVerify();

        long checksum = Long.parseLong(hexChecksum, 16);

        return verify(message, checksum);
    }

    public boolean verify(String message, long checksum) {
        continuousCheckForVerify();

        synchronized (this.config.getChecksum()) {
            this.config.getChecksum().reset();

            byte[] messageBytes = SyslogUtility.getBytes(this.config, message);

            this.config.getChecksum().update(messageBytes, 0, message.length());

            return this.config.getChecksum().getValue() == checksum;
        }
    }

    public String modify(SyslogIF syslog, int facility, int level, String message) {
        synchronized (this.config.getChecksum()) {
            StringBuffer messageBuffer = new StringBuffer(message);

            byte[] messageBytes = SyslogUtility.getBytes(syslog.getConfig(), message);

            if (!this.config.isContinuous()) {
                this.config.getChecksum().reset();
            }

            this.config.getChecksum().update(messageBytes, 0, message.length());

            messageBuffer.append(this.config.getPrefix());
            messageBuffer.append(Long.toHexString(this.config.getChecksum().getValue()).toUpperCase());
            messageBuffer.append(this.config.getSuffix());

            return messageBuffer.toString();
        }
    }
}