1 files changed, 80 insertions, 0 deletions
diff --git a/src/main/java/org/openslx/imagemaster/crcchecker/CrcChecker.java b/src/main/java/org/openslx/imagemaster/crcchecker/CrcChecker.java
new file mode 100644
index 0000000..882f565
--- /dev/null
+++ b/src/main/java/org/openslx/imagemaster/crcchecker/CrcChecker.java
@@ -0,0 +1,80 @@
+package org.openslx.imagemaster.crcchecker;
+
+import java.io.IOException;
+import java.util.zip.CRC32;
+
+public class CrcChecker
+{
+	private static final int blockSize = 16 * 1024 * 1024;
+
+	private ImageFile imageFile;
+	private CrcFile crcFile;
+
+	private byte[] block = new byte[ blockSize ];	// array that is used to read the blocks
+
+	/**
+	 * Initialize a crc checker with an image file and a crc file.
+	 * 
+	 * @param imageFile The image file to check
+	 * @param crcFile The crc file to check against
+	 */
+	public CrcChecker( ImageFile imageFile, CrcFile crcFile )
+	{
+		this.imageFile = imageFile;
+		this.crcFile = crcFile;
+	}
+
+	public void done()
+	{
+		imageFile.close();
+	}
+
+	public boolean hasValidCrcFile()
+	{
+		try {
+			return crcFile.isValid();
+		} catch ( IOException e ) {
+			return false;
+		}
+	}
+
+	/**
+	 * Checks a chosen block against the crc file.
+	 * 
+	 * @param block The block to check
+	 * @return Whether the block was valid or not
+	 * @throws IOException When image or crc file could not be read.
+	 */
+	public boolean checkBlock( int blockNumber ) throws IOException
+	{
+		if ( !this.hasValidCrcFile() )
+			return false;
+
+		int length;
+		try {
+			length = imageFile.getBlock( blockNumber, block );
+		} catch ( IOException e ) {
+			throw new IOException( "image", e );
+		}
+
+		if ( length <= 0 )
+			return false;
+
+		CRC32 crcCalc = new CRC32();
+		if ( length == blockSize ) {
+			crcCalc.update( block );
+		} else {
+			crcCalc.update( block, 0, length );
+		}
+
+		int crcSum = Integer.reverseBytes( (int)crcCalc.getValue() );
+		int crcSumFromFile;
+		try {
+			crcSumFromFile = crcFile.getCRCSum( blockNumber );
+		} catch ( IOException e ) {
+			throw new IOException( "crc", e );
+		}
+
+		return ( crcSum == crcSumFromFile );
+	}
+}