[Filetransfer] Add more sanity checks and error handling, remodel class structure, introduce common base class for Uploader and Downloader

5 files changed, 405 insertions, 595 deletions

diff --git a/src/main/java/org/openslx/filetransfer/ClassTest.java b/src/main/java/org/openslx/filetransfer/ClassTest.java
index 998e3c7..4550060 100644
--- a/src/main/java/org/openslx/filetransfer/ClassTest.java
+++ b/src/main/java/org/openslx/filetransfer/ClassTest.java
@@ -79,7 +79,7 @@ public class ClassTest
 		d.setOutputFilename( "output.txt" );
 		d.sendToken( "xyz" );
 		while ( d.readMetaData() )
-			d.readBinary();
+			d.receiveBinary();
 
 		/*
 		String pathToKeyStore =
@@ -145,6 +145,6 @@ class Test implements IncomingEvent
 	{
 		downloader.setOutputFilename( "output.txt" );
 		while ( downloader.readMetaData() )
-			downloader.readBinary();
+			downloader.receiveBinary();
 	}
 }
diff --git a/src/main/java/org/openslx/filetransfer/Downloader.java b/src/main/java/org/openslx/filetransfer/Downloader.java
index c860f5e..da882b9 100644
--- a/src/main/java/org/openslx/filetransfer/Downloader.java
+++ b/src/main/java/org/openslx/filetransfer/Downloader.java
@@ -1,74 +1,46 @@
 package org.openslx.filetransfer;
 
-import java.io.DataInputStream;
-import java.io.DataOutputStream;
 import java.io.File;
 import java.io.IOException;
 import java.io.RandomAccessFile;
 import java.net.SocketTimeoutException;
-import java.nio.charset.StandardCharsets;
 
 import javax.net.ssl.SSLContext;
 import javax.net.ssl.SSLSocket;
-import javax.net.ssl.SSLSocketFactory;
 
 import org.apache.log4j.Logger;
 
-public class Downloader
+public class Downloader extends Transfer
 {
 	// Some instance variables.
-	private SSLSocketFactory sslSocketFactory;
-	private SSLSocket satelliteSocket;
-	private DataOutputStream dataToServer;
-	private DataInputStream dataFromServer;
-	private String TOKEN = null;
-	private String RANGE = null;
 	private String outputFilename = null;
-	private String ERROR = null;
 
-	private static Logger log = Logger.getLogger( Downloader.class );
+	private static final Logger log = Logger.getLogger( Downloader.class );
 
 	/***********************************************************************/
 	/**
-	 * Constructor for satellite downloader.
-	 * Tries to connect to specific ip and port and sending type of action.
+	 * Actively initiate a connection to a remote peer for downloading.
 	 * 
-	 * @param ip
-	 * @param port
+	 * @param host Host name or address to connect to
+	 * @param port Port to connect to
+	 * @throws IOException
 	 */
-	public Downloader( String ip, int port, SSLContext context )
+	public Downloader( String host, int port, SSLContext context ) throws IOException
 	{
-		try {
-			// create socket.
-			sslSocketFactory = context.getSocketFactory();
-
-			satelliteSocket = (SSLSocket)sslSocketFactory.createSocket( ip, port );
-			satelliteSocket.setSoTimeout( 2000 ); // set socket timeout.
-
-			dataToServer = new DataOutputStream( satelliteSocket.getOutputStream() );
-			dataToServer.writeByte( 'D' );
-			dataFromServer = new DataInputStream( satelliteSocket.getInputStream() );
-		} catch ( Exception e ) {
-			e.printStackTrace();
-		}
+		super( host, port, context, log );
+		dataToServer.writeByte( 'D' );
 	}
 
 	/***********************************************************************/
 	/**
-	 * Constructor for master downloader.
-	 * Given parameter is the socket over which the transfer is going.
+	 * Constructor used by Listener to create an incoming download connection.
 	 * 
-	 * @param socket
+	 * @param socket established connection to peer which requested an upload.
+	 * @throws IOException 
 	 */
-	public Downloader( SSLSocket socket )
+	protected Downloader( SSLSocket socket ) throws IOException
 	{
-		try {
-			satelliteSocket = socket;
-			dataToServer = new DataOutputStream( satelliteSocket.getOutputStream() );
-			dataFromServer = new DataInputStream( satelliteSocket.getInputStream() );
-		} catch ( IOException e ) {
-			e.printStackTrace();
-		}
+		super( socket, log );
 	}
 
 	/***********************************************************************/
@@ -95,211 +67,16 @@ public class Downloader
 
 	/***********************************************************************/
 	/**
-	 * Method for sending token for identification from satellite to master.
-	 * 
-	 * @param t
-	 */
-	public Boolean sendToken( String token )
-	{
-		try {
-			TOKEN = token;
-			String sendToken = "TOKEN=" + TOKEN;
-			byte[] data = sendToken.getBytes( StandardCharsets.UTF_8 );
-			dataToServer.writeByte( data.length );
-			dataToServer.write( data );
-		} catch ( SocketTimeoutException ste ) {
-			ste.printStackTrace();
-			log.info( "Socket timeout occured ... close connection." );
-			this.close();
-		} catch ( IOException e ) {
-			e.printStackTrace();
-			readMetaData();
-			if ( ERROR != null ) {
-				if ( ERROR == "timeout" ) {
-					log.info( "Socket timeout occured ... close connection." );
-					this.close();
-				}
-			}
-			log.info( "Sending TOKEN in Downloader failed..." );
-			return false;
-		}
-		return true;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method to send range of the file, which should be uploaded.
-	 * Helpful for knowing how much was already uploaded if
-	 * connection aborts.
-	 * 
-	 * @param a
-	 * @param b
-	 */
-	public Boolean sendRange( int a, int b )
-	{
-		try {
-			RANGE = a + ":" + b;
-			String sendRange = "RANGE=" + RANGE;
-			byte[] data = sendRange.getBytes( StandardCharsets.UTF_8 );
-			dataToServer.writeByte( data.length );
-			dataToServer.write( data );
-		} catch ( SocketTimeoutException ste ) {
-			ste.printStackTrace();
-			log.info( "Socket timeout occured ... close connection." );
-			this.close();
-		} catch ( IOException e ) {
-			e.printStackTrace();
-			readMetaData();
-			if ( ERROR != null ) {
-				if ( ERROR == "timeout" ) {
-					log.info( "Socket timeout occured ... close connection." );
-					this.close();
-				}
-			}
-			log.info( "Sending RANGE in Uploader failed..." );
-			return false;
-		}
-		return true;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for reading incoming token for identification.
+	 * Method to request a byte range within the file to download. This
+	 * method is called by the party that initiated the connection.
 	 * 
+	 * @param startOffset offset in file where to start the transfer (inclusive)
+	 * @param endOffset end offset where to end the transfer (exclusive)
+	 * @return success or failure
 	 */
-	public String getToken()
+	public boolean requestRange( int startOffset, int endOffset )
 	{
-		return TOKEN;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for reading range of file, which is downloaded.
-	 * Helpful for knowing how much is already downloaded if connection aborts.
-	 */
-	public String getRange()
-	{
-		return RANGE;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Getter for beginning of RANGE.
-	 * 
-	 * @return
-	 */
-	public int getStartOfRange()
-	{
-		if ( RANGE != null ) {
-			String[] splitted = RANGE.split( ":" );
-			return Integer.parseInt( splitted[0] );
-		}
-		return -1;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Getter for end of RANGE.
-	 * 
-	 * @return
-	 */
-	public int getEndOfRange()
-	{
-		if ( RANGE != null ) {
-			String[] splitted = RANGE.split( ":" );
-			return Integer.parseInt( splitted[1] );
-		}
-		return -1;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for returning difference of current Range.
-	 * 
-	 * @return
-	 */
-	public int getDiffOfRange()
-	{
-		int diff = Math.abs( getEndOfRange() - getStartOfRange() );
-		return diff;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for reading MetaData, like TOKEN and FileRange.
-	 * Split incoming bytes after first '=' and store value to specific
-	 * variable.
-	 * 
-	 */
-	public Boolean readMetaData()
-	{
-		try {
-			while ( true ) {
-				byte[] incoming = new byte[ 255 ]; // TODO: problematische Größe.
-
-				// First get length.
-				int retLengthByte;
-				retLengthByte = dataFromServer.read( incoming, 0, 1 );
-				if (retLengthByte != 1) {
-					this.close();
-					return false;
-				}
-				
-				int length = incoming[0] & 0xFF;
-				log.info( "length (downloader): " + length );
-
-				if ( length == 0 )
-					break;
-
-				/**
-				 * Read the next available bytes and split by '=' for
-				 * getting TOKEN or RANGE.
-				 */
-				int hasRead = 0;
-				while ( hasRead < length ) {
-					int ret = dataFromServer.read( incoming, hasRead, length - hasRead );
-					if ( ret == -1 ) {
-						log.info( "Error occured while reading Metadata." );
-						return false;
-					}
-					hasRead += ret;
-				}
-
-				String data = new String( incoming, 0, length, "UTF-8" );
-				// System.out.println(data);
-
-				String[] splitted = data.split( "=" );
-				// System.out.println("splitted[0]: " + splitted[0]);
-				// System.out.println("splitted[1]: " + splitted[1]);
-				if ( splitted[0] != null && splitted[0].equals( "TOKEN" ) ) {
-					if ( splitted[1] != null )
-						TOKEN = splitted[1];
-					log.info( "TOKEN: " + TOKEN );
-				}
-				else if ( splitted[0].equals( "RANGE" ) ) {
-					if ( splitted[1] != null )
-						RANGE = splitted[1];
-					log.info( "RANGE: '" + RANGE + "'" );
-				}
-				else if ( splitted[0].equals( "ERROR" ) ) {
-					if ( splitted[1] != null )
-						ERROR = splitted[1];
-					log.info( "ERROR: " + ERROR );
-					return false;
-				}
-			}
-		} catch ( SocketTimeoutException ste ) {
-			ste.printStackTrace();
-			sendErrorCode( "timeout" );
-			log.info( "Socket Timeout occured in Downloader." );
-			this.close();
-			return false;
-		} catch ( Exception e ) {
-			e.printStackTrace();
-			this.close();
-			return false;
-		}
-		return true;
+		return super.sendRange( startOffset, endOffset );
 	}
 
 	/***********************************************************************/
@@ -307,21 +84,20 @@ public class Downloader
 	 * Method for reading Binary. Reading the current Range of incoming binary.
 	 * 
 	 */
-	public Boolean readBinary()
+	public boolean receiveBinary()
 	{
 		RandomAccessFile file = null;
 		try {
-			int length = getDiffOfRange();
-			byte[] incoming = new byte[ 4000 ]; 
+			int chunkLength = getDiffOfRange();
+			byte[] incoming = new byte[ 64000 ];
 			int hasRead = 0;
 			file = new RandomAccessFile( new File( outputFilename ), "rw" );
 			file.seek( getStartOfRange() );
-			while ( hasRead < length ) {
-				int ret = dataFromServer.read( incoming, 0, Math.min( length - hasRead, incoming.length ) );
+			while ( hasRead < chunkLength ) {
+				int ret = dataFromServer.read( incoming, 0, Math.min( chunkLength - hasRead, incoming.length ) );
 				// log.info("hasRead: " + hasRead + " length: " + length + " ret: " + ret); 
 				if ( ret == -1 ) {
-					log.info( "Error occured in Downloader.readBinary(),"
-							+ " while reading binary." );
+					log.info( "Error occured while receiving payload." );
 					return false;
 				}
 				hasRead += ret;
@@ -333,6 +109,7 @@ public class Downloader
 			sendErrorCode( "timeout" );
 			log.info( "Socket timeout occured ... close connection." );
 			this.close();
+			return false;
 		} catch ( Exception e ) {
 			e.printStackTrace();
 			log.info( "Reading RANGE " + getStartOfRange() + ":" + getEndOfRange()
@@ -347,49 +124,8 @@ public class Downloader
 					e.printStackTrace();
 				}
 			}
+			RANGE = null; // Reset range for next iteration
 		}
 		return true;
 	}
-
-	/***********************************************************************/
-	/**
-	 * Method for sending error Code to server. For example in case of wrong
-	 * token, send code for wrong token.
-	 * 
-	 */
-	public Boolean sendErrorCode( String errString )
-	{
-		try {
-			String sendError = "ERROR=" + errString;
-			byte[] data = sendError.getBytes( StandardCharsets.UTF_8 );
-			dataToServer.writeByte( data.length );
-			dataToServer.write( data );
-		} catch ( IOException e ) {
-			e.printStackTrace();
-			this.close();
-			return false;
-		}
-		return true;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for closing connection, if download has finished.
-	 * 
-	 */
-	public void close()
-	{
-		try {
-			if ( satelliteSocket != null ) {
-				this.satelliteSocket.close();
-				satelliteSocket = null;
-			}
-			if ( dataFromServer != null )
-				dataFromServer.close();
-			if ( dataToServer != null )
-				dataToServer.close();
-		} catch ( IOException e ) {
-			e.printStackTrace();
-		}
-	}
 }
diff --git a/src/main/java/org/openslx/filetransfer/Listener.java b/src/main/java/org/openslx/filetransfer/Listener.java
index 778804d..04f82f5 100644
--- a/src/main/java/org/openslx/filetransfer/Listener.java
+++ b/src/main/java/org/openslx/filetransfer/Listener.java
@@ -1,5 +1,7 @@
 package org.openslx.filetransfer;
 
+import java.io.IOException;
+
 import javax.net.ssl.SSLContext;
 import javax.net.ssl.SSLServerSocket;
 import javax.net.ssl.SSLServerSocketFactory;
@@ -42,10 +44,10 @@ public class Listener extends Thread
 	 */
 	private void listen()
 	{
+		SSLServerSocket welcomeSocket = null;
 		try {
 			SSLServerSocketFactory sslServerSocketFactory = context.getServerSocketFactory();
-			SSLServerSocket welcomeSocket =
-					(SSLServerSocket)sslServerSocketFactory.createServerSocket( this.port );
+			welcomeSocket = (SSLServerSocket)sslServerSocketFactory.createServerSocket( this.port );
 
 			while ( !isInterrupted() ) {
 				SSLSocket connectionSocket = (SSLSocket)welcomeSocket.accept();
@@ -54,27 +56,33 @@ public class Listener extends Thread
 				byte[] b = new byte[ 1 ];
 				int length = connectionSocket.getInputStream().read( b );
 
-				log.info( "Length (Listener): " + length );
+				log.debug( "Length (Listener): " + length );
 
 				if ( b[0] == U ) {
-					log.info( "recognized U --> starting Downloader" );
+					log.debug( "recognized U --> starting Downloader" );
 					// --> start Downloader(socket).
 					Downloader d = new Downloader( connectionSocket );
 					incomingEvent.incomingDownloader( d );
 				}
 				else if ( b[0] == D ) {
-					log.info( "recognized D --> starting Uploader" );
+					log.debug( "recognized D --> starting Uploader" );
 					// --> start Uploader(socket).
 					Uploader u = new Uploader( connectionSocket );
 					incomingEvent.incomingUploader( u );
 				}
 				else {
-					log.info( "Got invalid option ... close connection" );
+					log.debug( "Got invalid option ... close connection" );
 					connectionSocket.close();
 				}
 			}
 		} catch ( Exception e ) {
 			e.printStackTrace();	// same as writing to System.err.println(e.toString).
+		} finally {
+			try {
+				welcomeSocket.close();
+			} catch (IOException e) {
+				// Nothing we can do
+			}
 		}
 	}
 
diff --git a/src/main/java/org/openslx/filetransfer/Transfer.java b/src/main/java/org/openslx/filetransfer/Transfer.java
new file mode 100644
index 0000000..34868e3
--- /dev/null
+++ b/src/main/java/org/openslx/filetransfer/Transfer.java
@@ -0,0 +1,327 @@
+package org.openslx.filetransfer;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.net.SocketTimeoutException;
+import java.nio.charset.StandardCharsets;
+
+import javax.net.ssl.SSLContext;
+import javax.net.ssl.SSLSocket;
+import javax.net.ssl.SSLSocketFactory;
+
+import org.apache.log4j.Logger;
+
+public abstract class Transfer
+{
+	protected final SSLSocketFactory sslSocketFactory;
+	protected final SSLSocket satelliteSocket;
+	protected final DataOutputStream dataToServer;
+	protected final DataInputStream dataFromServer;
+	protected String TOKEN = null;
+	protected int[] RANGE = null;
+	protected String ERROR = null;
+
+	protected final Logger log;
+
+	protected Transfer( String ip, int port, SSLContext context, Logger log ) throws IOException
+	{
+		this.log = log;
+		// create socket.
+		sslSocketFactory = context.getSocketFactory();
+
+		satelliteSocket = (SSLSocket)sslSocketFactory.createSocket( ip, port );
+		satelliteSocket.setSoTimeout( 2000 ); // set socket timeout.
+
+		dataToServer = new DataOutputStream( satelliteSocket.getOutputStream() );
+		dataFromServer = new DataInputStream( satelliteSocket.getInputStream() );
+	}
+
+	protected Transfer( SSLSocket socket, Logger log ) throws IOException
+	{
+		this.log = log;
+		satelliteSocket = socket;
+		dataToServer = new DataOutputStream( satelliteSocket.getOutputStream() );
+		dataFromServer = new DataInputStream( satelliteSocket.getInputStream() );
+		sslSocketFactory = null;
+	}
+
+	protected boolean sendRange( int startOffset, int endOffset )
+	{
+		if ( RANGE != null ) {
+			log.warn( "Range already set!" );
+			return false;
+		}
+		try {
+			sendKeyValuePair( "RANGE", startOffset + ":" + endOffset );
+		} catch ( SocketTimeoutException ste ) {
+			ste.printStackTrace();
+			log.info( "Socket timeout occured ... close connection." );
+			this.close();
+		} catch ( IOException e ) {
+			e.printStackTrace();
+			readMetaData();
+			if ( ERROR != null ) {
+				if ( ERROR == "timeout" ) {
+					log.info( "Socket timeout occured ... close connection." );
+					this.close();
+				}
+			}
+			log.info( "Sending RANGE in Uploader failed..." );
+			return false;
+		}
+		return true;
+	}
+
+	/***********************************************************************/
+	/**
+	 * Method for sending token for identification from satellite to master.
+	 * 
+	 * @param token The token to send
+	 */
+	public boolean sendToken( String token )
+	{
+		if ( TOKEN != null ) {
+			log.warn( "Trying to send token while a token is already set! Ignoring..." );
+			return false;
+		}
+		TOKEN = token;
+		try {
+			sendKeyValuePair( "TOKEN", TOKEN );
+		} catch ( SocketTimeoutException ste ) {
+			ste.printStackTrace();
+			log.info( "Socket timeout occured ... close connection." );
+			this.close();
+		} catch ( IOException e ) {
+			e.printStackTrace();
+			readMetaData();
+			if ( ERROR != null ) {
+				if ( ERROR == "timeout" ) {
+					log.info( "Socket timeout occured ... close connection." );
+					this.close();
+				}
+			}
+			log.info( "Sending TOKEN in Downloader failed..." );
+			return false;
+		}
+		return true;
+	}
+
+	/***********************************************************************/
+	/**
+	 * Method for reading incoming token for identification.
+	 * 
+	 */
+	public String getToken()
+	{
+		return TOKEN;
+	}
+
+	private boolean parseRange( String range )
+	{
+		if ( range == null )
+			return true;
+		if ( RANGE != null ) {
+			log.warn( "Warning: RANGE already set when trying to parse from " + range );
+			return false;
+		}
+		String parts[] = range.split( ":", 2 );
+		int ret[] = new int[ 2 ];
+		try {
+			ret[0] = Integer.parseInt( parts[0] );
+			ret[1] = Integer.parseInt( parts[1] );
+		} catch ( Throwable t ) {
+			log.warn( "Not parsable range: '" + range + "'" );
+			return false;
+		}
+		if ( ret[1] <= ret[0] ) {
+			log.warn( "Invalid range. Start >= end" );
+			return false;
+		}
+		RANGE = ret;
+		return true;
+	}
+
+	/***********************************************************************/
+	/**
+	 * Getter for beginning of RANGE.
+	 * 
+	 * @return
+	 */
+	public int getStartOfRange()
+	{
+		if ( RANGE != null ) {
+			return RANGE[0];
+		}
+		return -1;
+	}
+
+	/***********************************************************************/
+	/**
+	 * Getter for end of RANGE.
+	 * 
+	 * @return
+	 */
+	public int getEndOfRange()
+	{
+		if ( RANGE != null ) {
+			return RANGE[1];
+		}
+		return -1;
+	}
+
+	/***********************************************************************/
+	/**
+	 * Method for returning difference of current Range.
+	 * 
+	 * @return
+	 */
+	public int getDiffOfRange()
+	{
+		int diff = Math.abs( getEndOfRange() - getStartOfRange() );
+		return diff;
+	}
+
+	/***********************************************************************/
+	/**
+	 * Method for reading MetaData, like TOKEN and FileRange.
+	 * Split incoming bytes after first '=' and store value to specific
+	 * variable.
+	 * 
+	 * @return true on success, false if reading failed
+	 */
+	public boolean readMetaData()
+	{
+		try {
+			while ( true ) {
+				byte[] incoming = new byte[ 255 ];
+
+				// First get length.
+				int retLengthByte;
+				retLengthByte = dataFromServer.read( incoming, 0, 1 );
+				if ( retLengthByte != 1 ) {
+					this.close();
+					return false;
+				}
+
+				int length = incoming[0] & 0xFF;
+				log.debug( "length (downloader): " + length );
+
+				if ( length == 0 )
+					break;
+
+				/*
+				 * Read the next available bytes and split by '=' for
+				 * getting TOKEN or RANGE.
+				 */
+				int hasRead = 0;
+				while ( hasRead < length ) {
+					int ret = dataFromServer.read( incoming, hasRead, length - hasRead );
+					if ( ret == -1 ) {
+						log.warn( "Error occured while reading Metadata." );
+						this.close();
+						return false;
+					}
+					hasRead += ret;
+				}
+
+				String data = new String( incoming, 0, length, StandardCharsets.UTF_8 );
+
+				String[] splitted = data.split( "=", 2 );
+				if ( splitted.length != 2 ) {
+					log.warn( "Invalid key value pair received (" + data + ")" );
+					continue;
+				}
+				if ( splitted[0].equals( "TOKEN" ) ) {
+					if ( TOKEN != null ) {
+						log.warn( "Received a token when a token is already set!" );
+						this.close();
+						return false;
+					}
+					TOKEN = splitted[1];
+					log.debug( "TOKEN: " + TOKEN );
+				}
+				else if ( splitted[0].equals( "RANGE" ) ) {
+					if ( !parseRange( splitted[1] ) ) {
+						this.close();
+						return false;
+					}
+					log.debug( "RANGE: '" + splitted[1] + "'" );
+				}
+				else if ( splitted[0].equals( "ERROR" ) ) {
+					ERROR = splitted[1];
+					log.debug( "ERROR: " + ERROR );
+				}
+			}
+		} catch ( SocketTimeoutException ste ) {
+			ste.printStackTrace();
+			sendErrorCode( "timeout" );
+			log.info( "Socket Timeout occured in Downloader." );
+			this.close();
+			return false;
+		} catch ( Exception e ) {
+			e.printStackTrace();
+			this.close();
+			return false;
+		}
+		return true;
+	}
+
+	private void sendKeyValuePair( String key, String value ) throws IOException
+	{
+		byte[] data = ( key + "=" + value ).getBytes( StandardCharsets.UTF_8 );
+		dataToServer.writeByte( data.length );
+		dataToServer.write( data );
+	}
+
+	/***********************************************************************/
+	/**
+	 * Method for sending error Code to server. For example in case of wrong
+	 * token, send code for wrong token.
+	 * 
+	 */
+	public Boolean sendErrorCode( String errString )
+	{
+		try {
+			sendKeyValuePair( "ERROR", errString );
+		} catch ( IOException e ) {
+			e.printStackTrace();
+			this.close();
+			return false;
+		}
+		return true;
+	}
+
+	/***********************************************************************/
+	/**
+	 * Method for closing connection, if download has finished.
+	 * 
+	 */
+	public void close()
+	{
+		try {
+			if ( satelliteSocket != null ) {
+				this.satelliteSocket.close();
+			}
+			if ( dataFromServer != null )
+				dataFromServer.close();
+			if ( dataToServer != null )
+				dataToServer.close();
+		} catch ( IOException e ) {
+			e.printStackTrace();
+		}
+	}
+
+	/**
+	 * Returns whether this transfer/connection is considered valid or usable,
+	 * which means the socket is still properly connected to the remote peer.
+	 * 
+	 * @return true or false
+	 */
+	public boolean isValid()
+	{
+		return satelliteSocket.isConnected() && !satelliteSocket.isClosed()
+				&& !satelliteSocket.isInputShutdown() && !satelliteSocket.isOutputShutdown();
+	}
+
+}
diff --git a/src/main/java/org/openslx/filetransfer/Uploader.java b/src/main/java/org/openslx/filetransfer/Uploader.java
index 60b9dd6..ff74a9a 100644
--- a/src/main/java/org/openslx/filetransfer/Uploader.java
+++ b/src/main/java/org/openslx/filetransfer/Uploader.java
@@ -1,65 +1,33 @@
 package org.openslx.filetransfer;
 
-import java.io.DataInputStream;
-import java.io.DataOutputStream;
 import java.io.File;
 import java.io.IOException;
 import java.io.RandomAccessFile;
 import java.net.SocketTimeoutException;
-import java.net.UnknownHostException;
-import java.nio.charset.StandardCharsets;
-import java.security.KeyManagementException;
-import java.security.KeyStoreException;
-import java.security.NoSuchAlgorithmException;
-import java.security.cert.CertificateException;
 
 import javax.net.ssl.SSLContext;
 import javax.net.ssl.SSLSocket;
-import javax.net.ssl.SSLSocketFactory;
 
 import org.apache.log4j.Logger;
 
-public class Uploader
+public class Uploader extends Transfer
 {
-	// Some member variables.
-	private SSLSocketFactory sslSocketFactory;
-	private SSLSocket satelliteSocket;
-	private DataOutputStream dataToServer;
-	private DataInputStream dataFromServer;
-	private String TOKEN = null;
-	private String RANGE = null;
-	private String ERROR = null;
 
-	private static Logger log = Logger.getLogger( Uploader.class );
+	private static final Logger log = Logger.getLogger( Uploader.class );
 
 	/***********************************************************************/
 	/**
-	 * Constructor for satellite uploader.
-	 * Tries to connect to specific ip and port and sending type of action.
+	 * Actively establish upload connection to given peer.
 	 * 
-	 * @param ip
-	 * @param port
+	 * @param host Host name or address to connect to
+	 * @param port Port to connect to
+	 * @param context ssl context for establishing a secure connection
 	 * @throws IOException
-	 * @throws KeyStoreException
-	 * @throws CertificateException
-	 * @throws NoSuchAlgorithmException
-	 * @throws KeyManagementException
-	 * @throws UnknownHostException
 	 */
-	public Uploader( String ip, int port, SSLContext context )
+	public Uploader( String host, int port, SSLContext context ) throws IOException
 	{
-		try {
-			sslSocketFactory = context.getSocketFactory();
-
-			satelliteSocket = (SSLSocket)sslSocketFactory.createSocket( ip, port );
-			satelliteSocket.setSoTimeout( 2000 ); // set socket timeout.
-
-			dataToServer = new DataOutputStream( satelliteSocket.getOutputStream() );
-			dataToServer.writeByte( 'U' );
-			dataFromServer = new DataInputStream( satelliteSocket.getInputStream() );
-		} catch ( Exception e ) {
-			e.printStackTrace();
-		}
+		super( host, port, context, log );
+		dataToServer.writeByte( 'U' );
 	}
 
 	/***********************************************************************/
@@ -69,217 +37,23 @@ public class Uploader
 	 * 
 	 * @throws IOException
 	 */
-	public Uploader( SSLSocket socket )
-	{
-		try {
-			satelliteSocket = socket;
-			dataToServer = new DataOutputStream( satelliteSocket.getOutputStream() );
-			dataFromServer = new DataInputStream( satelliteSocket.getInputStream() );
-		} catch ( IOException e ) {
-			e.printStackTrace();
-		}
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for sending token from satellite to master.
-	 * Needfull for getting to know what should happens over connection.
-	 * 
-	 * @param t
-	 */
-	public Boolean sendToken( String token )
-	{
-		try {
-			TOKEN = token;
-			String sendToken = "TOKEN=" + TOKEN;
-			byte[] data = sendToken.getBytes( StandardCharsets.UTF_8 );
-			dataToServer.writeByte( data.length );
-			dataToServer.write( data );
-		} catch ( SocketTimeoutException ste ) {
-			ste.printStackTrace();
-			log.info( "Socket timeout occured ... close connection." );
-			this.close();
-			return false;
-		} catch ( IOException e ) {
-			e.printStackTrace();
-			readMetaData();
-			if ( ERROR != null ) {
-				if ( ERROR == "timeout" ) {
-					log.info( "Socket timeout occured ... close connection." );
-					this.close();
-				}
-			}
-			log.info( "Sending TOKEN in Uploader failed..." );
-			return false;
-		}
-		return true;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Getter for TOKEN.
-	 */
-	public String getToken()
+	public Uploader( SSLSocket socket ) throws IOException
 	{
-		return TOKEN;
+		super( socket, log );
 	}
 
 	/***********************************************************************/
 	/**
-	 * Method to send range of the file, which should be uploaded.
-	 * Helpful for knowing how much was already uploaded if
-	 * connection aborts.
-	 * 
-	 * @param a
-	 * @param b
-	 */
-	public Boolean sendRange( int a, int b )
-	{
-		try {
-			RANGE = a + ":" + b;
-			String sendRange = "RANGE=" + RANGE;
-			byte[] data = sendRange.getBytes( StandardCharsets.UTF_8 );
-			dataToServer.writeByte( data.length );
-			dataToServer.write( data );
-			dataToServer.writeByte( 0 );
-		} catch ( SocketTimeoutException ste ) {
-			ste.printStackTrace();
-			log.info( "Socket timeout occured ... close connection." );
-			this.close();
-		} catch ( IOException e ) {
-			e.printStackTrace();
-			readMetaData();
-			if ( ERROR != null ) {
-				if ( ERROR == "timeout" ) {
-					log.info( "Socket timeout occured ... close connection." );
-					this.close();
-				}
-			}
-			log.info( "Sending RANGE in Uploader failed..." );
-			return false;
-		}
-		return true;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Getter for RANGE.
+	 * Used by the peer that initiated the connection to tell the remote
+	 * peer which part of the file is being uploaded
 	 * 
+	 * @param startOffset start offset in bytes in the file (inclusive)
+	 * @param endOffset end offset in file (exclusive)
 	 * @return
 	 */
-	public String getRange()
+	public boolean prepareSendRange( int startOffset, int endOffset )
 	{
-		return RANGE;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Getter for beginning of RANGE.
-	 * 
-	 * @return
-	 */
-	public int getStartOfRange()
-	{
-		if ( RANGE != null ) {
-			String[] splitted = RANGE.split( ":" );
-			return Integer.parseInt( splitted[0] );
-		}
-		return -1;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Getter for end of RANGE.
-	 * 
-	 * @return
-	 */
-	public int getEndOfRange()
-	{
-		if ( RANGE != null ) {
-			String[] splitted = RANGE.split( ":" );
-			return Integer.parseInt( splitted[1] );
-		}
-		return -1;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for returning difference of current Range.
-	 * 
-	 * @return
-	 */
-	public int getDiffOfRange()
-	{
-		if ( getStartOfRange() == -1 || getEndOfRange() == -1 ) {
-			return -1;
-		}
-		int diff = Math.abs( getEndOfRange() - getStartOfRange() );
-		return diff;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for reading MetaData, like TOKEN and FileRange.
-	 * Split incoming bytes after first '=' and store value to specific
-	 * variable.
-	 * 
-	 */
-	public Boolean readMetaData()
-	{
-		try {
-			while ( true ) {
-				byte[] incoming = new byte[ 255 ];
-
-				// First get length.
-				dataFromServer.read( incoming, 0, 1 );
-				int length = incoming[0] & 0xFF;
-
-				if ( length == 0 ) // Stop if 0 was read.
-					break;
-
-				/**
-				 * Read the next available bytes and split by '=' for
-				 * getting TOKEN or RANGE.
-				 */
-				int hasRead = 0;
-				while ( hasRead < length ) {
-					int ret = dataFromServer.read( incoming, hasRead, length - hasRead );
-					if ( ret == -1 ) {
-						log.info( "Error in reading Metadata occured!" );
-						return false;
-					}
-					hasRead += ret;
-				}
-				String data = new String( incoming, "UTF-8" );
-
-				String[] splitted = data.split( "=" );
-				if ( splitted[0] != null && splitted[0].equals( "TOKEN" ) ) {
-					if ( splitted[1] != null )
-						TOKEN = splitted[1];
-					log.info( "TOKEN: " + TOKEN );
-				}
-				else if ( splitted[0].equals( "RANGE" ) ) {
-					if ( splitted[1] != null )
-						RANGE = splitted[1];
-					log.info( "RANGE: " + RANGE );
-				}
-				else if ( splitted[0].equals( "ERROR" ) ) {
-					if ( splitted[1] != null )
-						ERROR = splitted[1];
-					log.info( "ERROR: " + ERROR );
-					return false;
-				}
-			}
-		} catch ( SocketTimeoutException ste ) {
-			ste.printStackTrace();
-			sendErrorCode( "timeout" );
-			log.info( "Socket timeout occured ... close connection" );
-			this.close();
-		} catch ( Exception e ) {
-			e.printStackTrace();
-			return false;
-		}
-		return true;
+		return super.sendRange( startOffset, endOffset );
 	}
 
 	/***********************************************************************/
@@ -288,26 +62,28 @@ public class Uploader
 	 * 
 	 * @param filename
 	 */
-	public Boolean sendFile( String filename )
+	public boolean sendFile( String filename )
 	{
 		RandomAccessFile file = null;
 		try {
 			file = new RandomAccessFile( new File( filename ), "r" );
 
 			if ( getStartOfRange() == -1 ) {
+				this.close();
 				return false;
 			}
 			file.seek( getStartOfRange() );
 
-			byte[] data = new byte[ 4000 ];
+			byte[] data = new byte[ 64000 ];
 			int hasRead = 0;
 			int length = getDiffOfRange();
-//			System.out.println( "diff of Range: " + length );
+			//			System.out.println( "diff of Range: " + length );
 			while ( hasRead < length ) {
 				int ret = file.read( data, 0, Math.min( length - hasRead, data.length ) );
 				if ( ret == -1 ) {
-					log.info( "Error occured in Uploader.sendFile(),"
+					log.warn( "Error occured in Uploader.sendFile(),"
 							+ " while reading from File to send." );
+					this.close();
 					return false;
 				}
 				hasRead += ret;
@@ -316,7 +92,7 @@ public class Uploader
 		} catch ( SocketTimeoutException ste ) {
 			ste.printStackTrace();
 			sendErrorCode( "timeout" );
-			log.info( "Socket timeout occured ... close connection." );
+			log.warn( "Socket timeout occured ... close connection." );
 			this.close();
 			return false;
 		} catch ( IOException ioe ) {
@@ -324,64 +100,27 @@ public class Uploader
 			readMetaData();
 			if ( ERROR != null ) {
 				if ( ERROR == "timeout" ) {
-					log.info( "Socket timeout occured ... close connection." );
+					log.warn( "Socket timeout occured ... close connection." );
 					this.close();
 				}
 			}
-			log.info( "Sending RANGE " + getStartOfRange() + ":" + getEndOfRange() + " of File "
+			log.warn( "Sending RANGE " + getStartOfRange() + ":" + getEndOfRange() + " of File "
 					+ filename + " failed..." );
+			this.close();
 			return false;
 		} catch ( Exception e ) {
 			e.printStackTrace();
+			this.close();
 			return false;
 		} finally {
-			try {
-				file.close();
-			} catch ( IOException e ) {
+			if ( file != null ) {
+				try {
+					file.close();
+				} catch ( IOException e ) {
+				}
 			}
 		}
 		return true;
 	}
 
-	/***********************************************************************/
-	/**
-	 * Method for sending error Code to server. For example in case of wrong
-	 * token, send code for wrong token.
-	 * 
-	 */
-	public Boolean sendErrorCode( String errString )
-	{
-		try {
-			String sendError = "ERROR=" + errString;
-			byte[] data = sendError.getBytes( StandardCharsets.UTF_8 );
-			dataToServer.writeByte( data.length );
-			dataToServer.write( data );
-		} catch ( IOException e ) {
-			e.printStackTrace();
-			this.close();
-			return false;
-		}
-		return true;
-	}
-
-	/***********************************************************************/
-	/**
-	 * Method for closing connection, if upload has finished.
-	 * 
-	 */
-	public void close()
-	{
-		try {
-			if ( satelliteSocket != null ) {
-				this.satelliteSocket.close();
-				satelliteSocket = null;
-			}
-			if ( dataFromServer != null )
-				dataFromServer.close();
-			if ( dataToServer != null )
-				dataToServer.close();
-		} catch ( IOException e ) {
-			e.printStackTrace();
-		}
-	}
 }