Removed SharedFileChannel transferTo and corresponding methods

* Removed from SharedFileChannel and Test
* Refactored Copier#copy(File,File) to sequence of truncated, followed
by looping read and write till EOF
* Changed tests accordingly
* Implemented CryptoWritableFile#truncate to make things work

main/filesystem-crypto/src/main/java/org/cryptomator/crypto/engine/FileContentEncryptor.java

@@ -27,6 +27,11 @@ public interface FileContentEncryptor extends Destroyable, Closeable {
 	 */
 	ByteBuffer getHeader();
 
+	/**
+	 * @return the size of headers created by this {@code FileContentCryptor}. The length of headers returned by {@link #getHeader()} equals this value.
+	 */
+	int getHeaderSize();
+
 	/**
 	 * Appends further cleartext to this encryptor. This method might block until space becomes available.
 	 * 

main/filesystem-crypto/src/main/java/org/cryptomator/crypto/engine/impl/FileContentEncryptorImpl.java

@@ -60,6 +60,11 @@ class FileContentEncryptorImpl implements FileContentEncryptor {
 		return header.toByteBuffer(headerKey, hmacSha256);
 	}
 
+	@Override
+	public int getHeaderSize() {
+		return FileHeader.HEADER_SIZE;
+	}
+
 	@Override
 	public void append(ByteBuffer cleartext) throws InterruptedException {
 		cleartextBytesEncrypted.add(cleartext.remaining());

main/filesystem-crypto/src/main/java/org/cryptomator/filesystem/crypto/CryptoReadableFile.java

@@ -18,7 +18,6 @@ import java.util.concurrent.Future;
 import org.cryptomator.crypto.engine.FileContentCryptor;
 import org.cryptomator.crypto.engine.FileContentDecryptor;
 import org.cryptomator.filesystem.ReadableFile;
-import org.cryptomator.filesystem.WritableFile;
 import org.cryptomator.io.ByteBuffers;
 
 class CryptoReadableFile implements ReadableFile {
@@ -90,16 +89,6 @@ class CryptoReadableFile implements ReadableFile {
 		return ByteBuffers.copy(bufferedCleartext, target);
 	}
 
-	@Override
-	public void copyTo(WritableFile other) {
-		if (other instanceof CryptoWritableFile) {
-			CryptoWritableFile dst = (CryptoWritableFile) other;
-			file.copyTo(dst.file);
-		} else {
-			throw new IllegalArgumentException("Can not move CryptoFile to conventional File.");
-		}
-	}
-
 	@Override
 	public boolean isOpen() {
 		return file.isOpen();

main/filesystem-crypto/src/main/java/org/cryptomator/filesystem/crypto/CryptoWritableFile.java

@@ -28,14 +28,21 @@ class CryptoWritableFile implements WritableFile {
 
 	final WritableFile file;
 	private final ExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
-	private final FileContentEncryptor encryptor;
-	private final Future<Void> writeTask;
+	private final FileContentCryptor cryptor;
+
+	private FileContentEncryptor encryptor;
+	private Future<Void> writeTask;
 
 	public CryptoWritableFile(FileContentCryptor cryptor, WritableFile file) {
 		this.file = file;
-		this.encryptor = cryptor.createFileContentEncryptor(Optional.empty(), 0);
+		this.cryptor = cryptor;
+		initialize(0);
+	}
+
+	private void initialize(long firstCleartextByte) {
+		encryptor = cryptor.createFileContentEncryptor(Optional.empty(), firstCleartextByte);
 		writeHeader();
-		this.writeTask = executorService.submit(new CiphertextWriter(file, encryptor));
+		writeTask = executorService.submit(new CiphertextWriter(file, encryptor));
 	}
 
 	private void writeHeader() {
@@ -87,11 +94,9 @@ class CryptoWritableFile implements WritableFile {
 
 	@Override
 	public void truncate() {
-		/*
-		 * TODO kill writer thread (EOF) and reinitialize CryptoWritableFile
-		 * after truncating the file
-		 */
-		throw new UnsupportedOperationException("Truncate not supported yet");
+		terminateAndWaitForWriteTask();
+		file.truncate();
+		initialize(0);
 	}
 
 	@Override
@@ -108,11 +113,20 @@ class CryptoWritableFile implements WritableFile {
 	public void close() {
 		try {
 			if (file.isOpen()) {
-				encryptor.append(FileContentCryptor.EOF);
-				writeTask.get();
+				terminateAndWaitForWriteTask();
 				writeHeader();
 				// TODO append padding
 			}
+		} finally {
+			executorService.shutdownNow();
+			file.close();
+		}
+	}
+
+	private void terminateAndWaitForWriteTask() {
+		try {
+			encryptor.append(FileContentCryptor.EOF);
+			writeTask.get();
 		} catch (ExecutionException e) {
 			if (e.getCause() instanceof UncheckedIOException || e.getCause() instanceof IOException) {
 				throw new UncheckedIOException(new IOException(e));
@@ -121,9 +135,6 @@ class CryptoWritableFile implements WritableFile {
 			}
 		} catch (InterruptedException e) {
 			throw new UncheckedIOException(new InterruptedIOException("Task interrupted while flushing encrypted content"));
-		} finally {
-			executorService.shutdownNow();
-			file.close();
 		}
 	}
 

main/filesystem-crypto/src/test/java/org/cryptomator/crypto/engine/NoFileContentCryptor.java

@@ -100,6 +100,11 @@ class NoFileContentCryptor implements FileContentCryptor {
 			return buf;
 		}
 
+		@Override
+		public int getHeaderSize() {
+			return Long.BYTES;
+		}
+
 		@Override
 		public void append(ByteBuffer cleartext) {
 			try {