Example usage for java.nio.channels SeekableByteChannel truncate

Introduction

In this page you can find the example usage for java.nio.channels SeekableByteChannel truncate.

Prototype

SeekableByteChannel truncate(long size) throws IOException;

Source Link

Document

Truncates the entity, to which this channel is connected, to the given size.

Usage

From source file:org.cryptomator.crypto.aes256.Aes256Cryptor.java

@Override
public Long encryptFile(InputStream plaintextFile, SeekableByteChannel encryptedFile) throws IOException {
    // truncate file
    encryptedFile.truncate(0);

    // use an IV, whose last 8 bytes store a long used in counter mode and write initial value to file.
    final ByteBuffer countingIv = ByteBuffer.wrap(randomData(AES_BLOCK_LENGTH));
    countingIv.putLong(AES_BLOCK_LENGTH - Long.BYTES, 0l);
    countingIv.position(0);/*from   w  w w.j  a v  a 2s. c o  m*/
    encryptedFile.write(countingIv);

    // init crypto stuff:
    final Mac mac = this.hmacSha256(hMacMasterKey);
    final Cipher cipher = this.aesCtrCipher(primaryMasterKey, countingIv.array(), Cipher.ENCRYPT_MODE);

    // init mac buffer and skip 32 bytes
    final ByteBuffer macBuffer = ByteBuffer.allocate(mac.getMacLength());
    encryptedFile.write(macBuffer);

    // init filesize buffer and skip 16 bytes
    final ByteBuffer encryptedFileSizeBuffer = ByteBuffer.allocate(AES_BLOCK_LENGTH);
    encryptedFile.write(encryptedFileSizeBuffer);

    // write content:
    final OutputStream out = new SeekableByteChannelOutputStream(encryptedFile);
    final OutputStream macOut = new MacOutputStream(out, mac);
    final OutputStream cipheredOut = new CipherOutputStream(macOut, cipher);
    final OutputStream blockSizeBufferedOut = new BufferedOutputStream(cipheredOut, AES_BLOCK_LENGTH);
    final Long plaintextSize = IOUtils.copyLarge(plaintextFile, blockSizeBufferedOut);

    // ensure total byte count is a multiple of the block size, in CTR mode:
    final int remainderToFillLastBlock = AES_BLOCK_LENGTH - (int) (plaintextSize % AES_BLOCK_LENGTH);
    blockSizeBufferedOut.write(new byte[remainderToFillLastBlock]);

    // append a few blocks of fake data:
    final int numberOfPlaintextBlocks = (int) Math.ceil(plaintextSize / AES_BLOCK_LENGTH);
    final int upToTenPercentFakeBlocks = (int) Math.ceil(Math.random() * 0.1 * numberOfPlaintextBlocks);
    final byte[] emptyBytes = new byte[AES_BLOCK_LENGTH];
    for (int i = 0; i < upToTenPercentFakeBlocks; i += AES_BLOCK_LENGTH) {
        blockSizeBufferedOut.write(emptyBytes);
    }
    blockSizeBufferedOut.flush();

    // write MAC of total ciphertext:
    macBuffer.position(0);
    macBuffer.put(mac.doFinal());
    macBuffer.position(0);
    encryptedFile.position(16); // right behind the IV
    encryptedFile.write(macBuffer); // 256 bit MAC

    // encrypt and write plaintextSize
    try {
        final ByteBuffer fileSizeBuffer = ByteBuffer.allocate(Long.BYTES);
        fileSizeBuffer.putLong(plaintextSize);
        final Cipher sizeCipher = aesEcbCipher(primaryMasterKey, Cipher.ENCRYPT_MODE);
        final byte[] encryptedFileSize = sizeCipher.doFinal(fileSizeBuffer.array());
        encryptedFileSizeBuffer.position(0);
        encryptedFileSizeBuffer.put(encryptedFileSize);
        encryptedFileSizeBuffer.position(0);
        encryptedFile.position(48); // right behind the IV and MAC
        encryptedFile.write(encryptedFileSizeBuffer);
    } catch (IllegalBlockSizeException | BadPaddingException e) {
        throw new IllegalStateException(
                "Block size must be valid, as padding is requested. BadPaddingException not possible in encrypt mode.",
                e);
    }

    return plaintextSize;
}

---

From source file:org.neo4j.io.fs.FileUtils.java

public static void truncateFile(SeekableByteChannel fileChannel, long position) throws IOException {
    int count = 0;
    boolean success = false;
    IOException cause = null;//from   ww  w.jav a 2  s.  co  m
    do {
        count++;
        try {
            fileChannel.truncate(position);
            success = true;
        } catch (IOException e) {
            cause = e;
        }

    } while (!success && count <= WINDOWS_RETRY_COUNT);
    if (!success) {
        throw cause;
    }
}

---