de.berlin.magun.nfcmime.core.CrcGenerator.java Source code

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Here is the source code for de.berlin.magun.nfcmime.core.CrcGenerator.java

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/*
 * Licensed 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.
 */
package de.berlin.magun.nfcmime.core;

import java.util.zip.CRC32;
import java.util.zip.Checksum;

import org.apache.commons.lang.ArrayUtils;
import android.nfc.NdefRecord;

/**
 * This class provides methods to generate and verify checksums for NdefRecord arrays.
 * @author Johannes Bolz
 *
 */
public class CrcGenerator {

    /**
     * Generates a CRC32 checksum for an array of NdefRecords.
     * @param records
     * @return CRC32 checksum represented as long.
     */
    public long getChecksum(NdefRecord[] records) {
        byte[] overallBytes = getByteArray(records);
        Checksum cs = new CRC32();
        cs.update(overallBytes, 0, overallBytes.length);
        return cs.getValue();
    }

    /**
     * Checks if the CRC32 checksum of a NdefRecord[] array matches a reference 
     * checksum
     * @param records NdefRecord[] to check against checksum
     * @param checksum long representation of a CRC32 reference checksum
     * @return true if the CRC32 checksum of records matches checksum.
     */
    public boolean checkHash(NdefRecord[] records, long checksum) {
        String chksumStr = String.valueOf(checksum);
        String toValidate = String.valueOf(getChecksum(records));
        return (toValidate.equals(chksumStr));
    }

    /**
     * Creates a single byte array out of a NdefRecord[] array.
     * @param records
     * @return byte[]
     */
    private byte[] getByteArray(NdefRecord[] records) {
        byte[] overallBytes = new byte[0];
        for (int i = 0; i < records.length; i++) {
            overallBytes = ArrayUtils.addAll(overallBytes, records[i].toByteArray());
        }
        return overallBytes;
    }

}