/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 examples.ftp;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.SocketException;
import java.net.UnknownHostException;
import org.apache.commons.net.tftp.TFTP;
import org.apache.commons.net.tftp.TFTPClient;

/***
 * This is an example of a simple Java tftp client.
 * Notice how all of the code is really just argument processing and
 * error handling.
 * <p>
 * Usage: tftp [options] hostname localfile remotefile
 * hostname   - The name of the remote host
 * localfile  - The name of the local file to send or the name to use for
 *              the received file
 * remotefile - The name of the remote file to receive or the name for
 *              the remote server to use to name the local file being sent.
 * options: (The default is to assume -r -b)
 *        -s Send a local file
 *        -r Receive a remote file
 *        -a Use ASCII transfer mode
 *        -b Use binary transfer mode
 * <p>
 ***/
public final class TFTPExample
{
    static final String USAGE =
        "Usage: tftp [options] hostname localfile remotefile\n\n" +
        "hostname   - The name of the remote host\n" +
        "localfile  - The name of the local file to send or the name to use for\n" +
        "\tthe received file\n" +
        "remotefile - The name of the remote file to receive or the name for\n" +
        "\tthe remote server to use to name the local file being sent.\n\n" +
        "options: (The default is to assume -r -b)\n" +
        "\t-s Send a local file\n" +
        "\t-r Receive a remote file\n" +
        "\t-a Use ASCII transfer mode\n" +
        "\t-b Use binary transfer mode\n";

    public final static void main(String[] args)
    {
        boolean receiveFile = true, closed;
        int transferMode = TFTP.BINARY_MODE, argc;
        String arg, hostname, localFilename, remoteFilename;
        TFTPClient tftp;

        // Parse options
        for (argc = 0; argc < args.length; argc++)
        {
            arg = args[argc];
            if (arg.startsWith("-"))
            {
                if (arg.equals("-r")) {
                    receiveFile = true;
                } else if (arg.equals("-s")) {
                    receiveFile = false;
                } else if (arg.equals("-a")) {
                    transferMode = TFTP.ASCII_MODE;
                } else if (arg.equals("-b")) {
                    transferMode = TFTP.BINARY_MODE;
                } else {
                    System.err.println("Error: unrecognized option.");
                    System.err.print(USAGE);
                    System.exit(1);
                }
            } else {
                break;
            }
        }

        // Make sure there are enough arguments
        if (args.length - argc != 3)
        {
            System.err.println("Error: invalid number of arguments.");
            System.err.print(USAGE);
            System.exit(1);
        }

        // Get host and file arguments
        hostname = args[argc];
        localFilename = args[argc + 1];
        remoteFilename = args[argc + 2];

        // Create our TFTP instance to handle the file transfer.
        tftp = new TFTPClient();

        // We want to timeout if a response takes longer than 60 seconds
        tftp.setDefaultTimeout(60000);

        // Open local socket
        try
        {
            tftp.open();
        }
        catch (SocketException e)
        {
            System.err.println("Error: could not open local UDP socket.");
            System.err.println(e.getMessage());
            System.exit(1);
        }

        // We haven't closed the local file yet.
        closed = false;

        // If we're receiving a file, receive, otherwise send.
        if (receiveFile)
        {
            FileOutputStream output = null;
            File file;

            file = new File(localFilename);

            // If file exists, don't overwrite it.
            if (file.exists())
            {
                System.err.println("Error: " + localFilename + " already exists.");
                System.exit(1);
            }

            // Try to open local file for writing
            try
            {
                output = new FileOutputStream(file);
            }
            catch (IOException e)
            {
                tftp.close();
                System.err.println("Error: could not open local file for writing.");
                System.err.println(e.getMessage());
                System.exit(1);
            }

            // Try to receive remote file via TFTP
            try
            {
                tftp.receiveFile(remoteFilename, transferMode, output, hostname);
            }
            catch (UnknownHostException e)
            {
                System.err.println("Error: could not resolve hostname.");
                System.err.println(e.getMessage());
                System.exit(1);
            }
            catch (IOException e)
            {
                System.err.println(
                    "Error: I/O exception occurred while receiving file.");
                System.err.println(e.getMessage());
                System.exit(1);
            }
            finally
            {
                // Close local socket and output file
                tftp.close();
                try
                {
                    if (output != null) {
                        output.close();
                    }
                    closed = true;
                }
                catch (IOException e)
                {
                    closed = false;
                    System.err.println("Error: error closing file.");
                    System.err.println(e.getMessage());
                }
            }

            if (!closed) {
                System.exit(1);
            }

        } else {
            // We're sending a file
            FileInputStream input = null;

            // Try to open local file for reading
            try
            {
                input = new FileInputStream(localFilename);
            }
            catch (IOException e)
            {
                tftp.close();
                System.err.println("Error: could not open local file for reading.");
                System.err.println(e.getMessage());
                System.exit(1);
            }

            // Try to send local file via TFTP
            try
            {
                tftp.sendFile(remoteFilename, transferMode, input, hostname);
            }
            catch (UnknownHostException e)
            {
                System.err.println("Error: could not resolve hostname.");
                System.err.println(e.getMessage());
                System.exit(1);
            }
            catch (IOException e)
            {
                System.err.println(
                    "Error: I/O exception occurred while sending file.");
                System.err.println(e.getMessage());
                System.exit(1);
            }
            finally
            {
                // Close local socket and input file
                tftp.close();
                try
                {
                    if (input != null) {
                        input.close();
                    }
                    closed = true;
                }
                catch (IOException e)
                {
                    closed = false;
                    System.err.println("Error: error closing file.");
                    System.err.println(e.getMessage());
                }
            }

            if (!closed) {
                System.exit(1);
            }

        }

    }

}

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.commons.net.tftp;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintStream;
import java.net.SocketTimeoutException;
import java.util.HashSet;
import java.util.Iterator;

import org.apache.commons.net.io.FromNetASCIIOutputStream;
import org.apache.commons.net.io.ToNetASCIIInputStream;

/**
 * A fully multi-threaded tftp server. Can handle multiple clients at the same time. Implements RFC
 * 1350 and wrapping block numbers for large file support.
 *
 * To launch, just create an instance of the class. An IOException will be thrown if the server
 * fails to start for reasons such as port in use, port denied, etc.
 *
 * To stop, use the shutdown method.
 *
 * To check to see if the server is still running (or if it stopped because of an error), call the
 * isRunning() method.
 *
 * By default, events are not logged to stdout/stderr. This can be changed with the
 * setLog and setLogError methods.
 *
 * <p>
 * Example usage is below:
 *
 * <code>
 * public static void main(String[] args) throws Exception
 *  {
 *      if (args.length != 1)
 *      {
 *          System.out
 *                  .println("You must provide 1 argument - the base path for the server to serve from.");
 *          System.exit(1);
 *      }
 *
 *      TFTPServer ts = new TFTPServer(new File(args[0]), new File(args[0]), GET_AND_PUT);
 *      ts.setSocketTimeout(2000);
 *
 *      System.out.println("TFTP Server running.  Press enter to stop.");
 *      new InputStreamReader(System.in).read();
 *
 *      ts.shutdown();
 *      System.out.println("Server shut down.");
 *      System.exit(0);
 *  }
 *
 * </code>
 *
 *
 * @author <A HREF="mailto:daniel.armbrust.list@gmail.com">Dan Armbrust</A>
 * @since 2.0
 */

public class TFTPServer implements Runnable
{
    private static final int DEFAULT_TFTP_PORT = 69;
    public static enum ServerMode { GET_ONLY, PUT_ONLY, GET_AND_PUT; }

    private HashSet<TFTPTransfer> transfers_ = new HashSet<TFTPTransfer>();
    private volatile boolean shutdownServer = false;
    private TFTP serverTftp_;
    private File serverReadDirectory_;
    private File serverWriteDirectory_;
    private int port_;
    private Exception serverException = null;
    private ServerMode mode_;

    /* /dev/null output stream (default) */
    private static final PrintStream nullStream = new PrintStream(
            new OutputStream() {
                @Override
                public void write(int b){}
                @Override
                public void write(byte[] b) throws IOException {}
                }
            );

    // don't have access to a logger api, so we will log to these streams, which
    // by default are set to a no-op logger
    private PrintStream log_;
    private PrintStream logError_;

    private int maxTimeoutRetries_ = 3;
    private int socketTimeout_;
    private Thread serverThread;


    /**
     * Start a TFTP Server on the default port (69). Gets and Puts occur in the specified
     * directories.
     *
     * The server will start in another thread, allowing this constructor to return immediately.
     *
     * If a get or a put comes in with a relative path that tries to get outside of the
     * serverDirectory, then the get or put will be denied.
     *
     * GET_ONLY mode only allows gets, PUT_ONLY mode only allows puts, and GET_AND_PUT allows both.
     * Modes are defined as int constants in this class.
     *
     * @param serverReadDirectory directory for GET requests
     * @param serverWriteDirectory directory for PUT requests
     * @param mode A value as specified above.
     * @throws IOException if the server directory is invalid or does not exist.
     */
    public TFTPServer(File serverReadDirectory, File serverWriteDirectory, ServerMode mode)
            throws IOException
    {
        this(serverReadDirectory, serverWriteDirectory, DEFAULT_TFTP_PORT, mode, null, null);
    }

    /**
     * Start a TFTP Server on the specified port. Gets and Puts occur in the specified directory.
     *
     * The server will start in another thread, allowing this constructor to return immediately.
     *
     * If a get or a put comes in with a relative path that tries to get outside of the
     * serverDirectory, then the get or put will be denied.
     *
     * GET_ONLY mode only allows gets, PUT_ONLY mode only allows puts, and GET_AND_PUT allows both.
     * Modes are defined as int constants in this class.
     *
     * @param serverReadDirectory directory for GET requests
     * @param serverWriteDirectory directory for PUT requests
     * @param mode A value as specified above.
     * @param log Stream to write log message to. If not provided, uses System.out
     * @param errorLog Stream to write error messages to. If not provided, uses System.err.
     * @throws IOException if the server directory is invalid or does not exist.
     */
    public TFTPServer(File serverReadDirectory, File serverWriteDirectory, int port, ServerMode mode,
            PrintStream log, PrintStream errorLog) throws IOException
    {
        port_ = port;
        mode_ = mode;
        log_ = (log == null ? nullStream: log);
        logError_ = (errorLog == null ? nullStream : errorLog);
        launch(serverReadDirectory, serverWriteDirectory);
    }

    /**
     * Set the max number of retries in response to a timeout. Default 3. Min 0.
     *
     * @param retries
     */
    public void setMaxTimeoutRetries(int retries)
    {
        if (retries < 0)
        {
            throw new RuntimeException("Invalid Value");
        }
        maxTimeoutRetries_ = retries;
    }

    /**
     * Get the current value for maxTimeoutRetries
     */
    public int getMaxTimeoutRetries()
    {
        return maxTimeoutRetries_;
    }

    /**
     * Set the socket timeout in milliseconds used in transfers. Defaults to the value here:
     * http://commons.apache.org/net/apidocs/org/apache/commons/net/tftp/TFTP.html#DEFAULT_TIMEOUT
     * (5000 at the time I write this) Min value of 10.
     */
    public void setSocketTimeout(int timeout)
    {
        if (timeout < 10)
        {
            throw new RuntimeException("Invalid Value");
        }
        socketTimeout_ = timeout;
    }

    /**
     * The current socket timeout used during transfers in milliseconds.
     */
    public int getSocketTimeout()
    {
        return socketTimeout_;
    }

    /*
     * start the server, throw an error if it can't start.
     */
    private void launch(File serverReadDirectory, File serverWriteDirectory) throws IOException
    {
        log_.println("Starting TFTP Server on port " + port_ + ".  Read directory: "
                + serverReadDirectory + " Write directory: " + serverWriteDirectory
                + " Server Mode is " + mode_);

        serverReadDirectory_ = serverReadDirectory.getCanonicalFile();
        if (!serverReadDirectory_.exists() || !serverReadDirectory.isDirectory())
        {
            throw new IOException("The server read directory " + serverReadDirectory_
                    + " does not exist");
        }

        serverWriteDirectory_ = serverWriteDirectory.getCanonicalFile();
        if (!serverWriteDirectory_.exists() || !serverWriteDirectory.isDirectory())
        {
            throw new IOException("The server write directory " + serverWriteDirectory_
                    + " does not exist");
        }

        serverTftp_ = new TFTP();

        // This is the value used in response to each client.
        socketTimeout_ = serverTftp_.getDefaultTimeout();

        // we want the server thread to listen forever.
        serverTftp_.setDefaultTimeout(0);

        serverTftp_.open(port_);

        serverThread = new Thread(this);
        serverThread.setDaemon(true);
        serverThread.start();
    }

    @Override
    protected void finalize() throws Throwable
    {
        shutdown();
    }

    /**
     * check if the server thread is still running.
     *
     * @return true if running, false if stopped.
     * @throws Exception throws the exception that stopped the server if the server is stopped from
     *             an exception.
     */
    public boolean isRunning() throws Exception
    {
        if (shutdownServer && serverException != null)
        {
            throw serverException;
        }
        return !shutdownServer;
    }

    public void run()
    {
        try
        {
            while (!shutdownServer)
            {
                TFTPPacket tftpPacket;

                tftpPacket = serverTftp_.receive();

                TFTPTransfer tt = new TFTPTransfer(tftpPacket);
                synchronized(transfers_)
                {
                    transfers_.add(tt);
                }

                Thread thread = new Thread(tt);
                thread.setDaemon(true);
                thread.start();
            }
        }
        catch (Exception e)
        {
            if (!shutdownServer)
            {
                serverException = e;
                logError_.println("Unexpected Error in TFTP Server - Server shut down! + " + e);
            }
        }
        finally
        {
            shutdownServer = true; // set this to true, so the launching thread can check to see if it started.
            if (serverTftp_ != null && serverTftp_.isOpen())
            {
                serverTftp_.close();
            }
        }
    }

    /**
     * Stop the tftp server (and any currently running transfers) and release all opened network
     * resources.
     */
    public void shutdown()
    {
        shutdownServer = true;

        synchronized(transfers_)
        {
            Iterator<TFTPTransfer> it = transfers_.iterator();
            while (it.hasNext())
            {
                it.next().shutdown();
            }
        }

        try
        {
            serverTftp_.close();
        }
        catch (RuntimeException e)
        {
            // noop
        }

        try {
            serverThread.join();
        } catch (InterruptedException e) {
            // we've done the best we could, return
        }
    }

    /*
     * An instance of an ongoing transfer.
     */
    private class TFTPTransfer implements Runnable
    {
        private TFTPPacket tftpPacket_;

        private boolean shutdownTransfer = false;

        TFTP transferTftp_ = null;

        public TFTPTransfer(TFTPPacket tftpPacket)
        {
            tftpPacket_ = tftpPacket;
        }

        public void shutdown()
        {
            shutdownTransfer = true;
            try
            {
                transferTftp_.close();
            }
            catch (RuntimeException e)
            {
                // noop
            }
        }

        public void run()
        {
            try
            {
                transferTftp_ = new TFTP();

                transferTftp_.beginBufferedOps();
                transferTftp_.setDefaultTimeout(socketTimeout_);

                transferTftp_.open();

                if (tftpPacket_ instanceof TFTPReadRequestPacket)
                {
                    handleRead(((TFTPReadRequestPacket) tftpPacket_));
                }
                else if (tftpPacket_ instanceof TFTPWriteRequestPacket)
                {
                    handleWrite((TFTPWriteRequestPacket) tftpPacket_);
                }
                else
                {
                    log_.println("Unsupported TFTP request (" + tftpPacket_ + ") - ignored.");
                }
            }
            catch (Exception e)
            {
                if (!shutdownTransfer)
                {
                    logError_
                            .println("Unexpected Error in during TFTP file transfer.  Transfer aborted. "
                                    + e);
                }
            }
            finally
            {
                try
                {
                    if (transferTftp_ != null && transferTftp_.isOpen())
                    {
                        transferTftp_.endBufferedOps();
                        transferTftp_.close();
                    }
                }
                catch (Exception e)
                {
                    // noop
                }
                synchronized(transfers_)
                {
                    transfers_.remove(this);
                }
            }
        }

        /*
         * Handle a tftp read request.
         */
        private void handleRead(TFTPReadRequestPacket trrp) throws IOException, TFTPPacketException
        {
            InputStream is = null;
            try
            {
                if (mode_ == ServerMode.PUT_ONLY)
                {
                    transferTftp_.bufferedSend(new TFTPErrorPacket(trrp.getAddress(), trrp
                            .getPort(), TFTPErrorPacket.ILLEGAL_OPERATION,
                            "Read not allowed by server."));
                    return;
                }

                try
                {
                    is = new BufferedInputStream(new FileInputStream(buildSafeFile(
                            serverReadDirectory_, trrp.getFilename(), false)));
                }
                catch (FileNotFoundException e)
                {
                    transferTftp_.bufferedSend(new TFTPErrorPacket(trrp.getAddress(), trrp
                            .getPort(), TFTPErrorPacket.FILE_NOT_FOUND, e.getMessage()));
                    return;
                }
                catch (Exception e)
                {
                    transferTftp_.bufferedSend(new TFTPErrorPacket(trrp.getAddress(), trrp
                            .getPort(), TFTPErrorPacket.UNDEFINED, e.getMessage()));
                    return;
                }

                if (trrp.getMode() == TFTP.NETASCII_MODE)
                {
                    is = new ToNetASCIIInputStream(is);
                }

                byte[] temp = new byte[TFTPDataPacket.MAX_DATA_LENGTH];

                TFTPPacket answer;

                int block = 1;
                boolean sendNext = true;

                int readLength = TFTPDataPacket.MAX_DATA_LENGTH;

                TFTPDataPacket lastSentData = null;

                // We are reading a file, so when we read less than the
                // requested bytes, we know that we are at the end of the file.
                while (readLength == TFTPDataPacket.MAX_DATA_LENGTH && !shutdownTransfer)
                {
                    if (sendNext)
                    {
                        readLength = is.read(temp);
                        if (readLength == -1)
                        {
                            readLength = 0;
                        }

                        lastSentData = new TFTPDataPacket(trrp.getAddress(), trrp.getPort(), block,
                                temp, 0, readLength);
                        transferTftp_.bufferedSend(lastSentData);
                    }

                    answer = null;

                    int timeoutCount = 0;

                    while (!shutdownTransfer
                            && (answer == null || !answer.getAddress().equals(trrp.getAddress()) || answer
                                    .getPort() != trrp.getPort()))
                    {
                        // listen for an answer.
                        if (answer != null)
                        {
                            // The answer that we got didn't come from the
                            // expected source, fire back an error, and continue
                            // listening.
                            log_.println("TFTP Server ignoring message from unexpected source.");
                            transferTftp_.bufferedSend(new TFTPErrorPacket(answer.getAddress(),
                                    answer.getPort(), TFTPErrorPacket.UNKNOWN_TID,
                                    "Unexpected Host or Port"));
                        }
                        try
                        {
                            answer = transferTftp_.bufferedReceive();
                        }
                        catch (SocketTimeoutException e)
                        {
                            if (timeoutCount >= maxTimeoutRetries_)
                            {
                                throw e;
                            }
                            // didn't get an ack for this data. need to resend
                            // it.
                            timeoutCount++;
                            transferTftp_.bufferedSend(lastSentData);
                            continue;
                        }
                    }

                    if (answer == null || !(answer instanceof TFTPAckPacket))
                    {
                        if (!shutdownTransfer)
                        {
                            logError_
                                    .println("Unexpected response from tftp client during transfer ("
                                            + answer + ").  Transfer aborted.");
                        }
                        break;
                    }
                    else
                    {
                        // once we get here, we know we have an answer packet
                        // from the correct host.
                        TFTPAckPacket ack = (TFTPAckPacket) answer;
                        if (ack.getBlockNumber() != block)
                        {
                            /*
                             * The origional tftp spec would have called on us to resend the
                             * previous data here, however, that causes the SAS Syndrome.
                             * http://www.faqs.org/rfcs/rfc1123.html section 4.2.3.1 The modified
                             * spec says that we ignore a duplicate ack. If the packet was really
                             * lost, we will time out on receive, and resend the previous data at
                             * that point.
                             */
                            sendNext = false;
                        }
                        else
                        {
                            // send the next block
                            block++;
                            if (block > 65535)
                            {
                                // wrap the block number
                                block = 0;
                            }
                            sendNext = true;
                        }
                    }
                }
            }
            finally
            {
                try
                {
                    if (is != null)
                    {
                        is.close();
                    }
                }
                catch (IOException e)
                {
                    // noop
                }
            }
        }

        /*
         * handle a tftp write request.
         */
        private void handleWrite(TFTPWriteRequestPacket twrp) throws IOException,
                TFTPPacketException
        {
            OutputStream bos = null;
            try
            {
                if (mode_ == ServerMode.GET_ONLY)
                {
                    transferTftp_.bufferedSend(new TFTPErrorPacket(twrp.getAddress(), twrp
                            .getPort(), TFTPErrorPacket.ILLEGAL_OPERATION,
                            "Write not allowed by server."));
                    return;
                }

                int lastBlock = 0;
                String fileName = twrp.getFilename();

                try
                {
                    File temp = buildSafeFile(serverWriteDirectory_, fileName, true);
                    if (temp.exists())
                    {
                        transferTftp_.bufferedSend(new TFTPErrorPacket(twrp.getAddress(), twrp
                                .getPort(), TFTPErrorPacket.FILE_EXISTS, "File already exists"));
                        return;
                    }
                    bos = new BufferedOutputStream(new FileOutputStream(temp));

                    if (twrp.getMode() == TFTP.NETASCII_MODE)
                    {
                        bos = new FromNetASCIIOutputStream(bos);
                    }
                }
                catch (Exception e)
                {
                    transferTftp_.bufferedSend(new TFTPErrorPacket(twrp.getAddress(), twrp
                            .getPort(), TFTPErrorPacket.UNDEFINED, e.getMessage()));
                    return;
                }

                TFTPAckPacket lastSentAck = new TFTPAckPacket(twrp.getAddress(), twrp.getPort(), 0);
                transferTftp_.bufferedSend(lastSentAck);

                while (true)
                {
                    // get the response - ensure it is from the right place.
                    TFTPPacket dataPacket = null;

                    int timeoutCount = 0;

                    while (!shutdownTransfer
                            && (dataPacket == null
                                    || !dataPacket.getAddress().equals(twrp.getAddress()) || dataPacket
                                    .getPort() != twrp.getPort()))
                    {
                        // listen for an answer.
                        if (dataPacket != null)
                        {
                            // The data that we got didn't come from the
                            // expected source, fire back an error, and continue
                            // listening.
                            log_.println("TFTP Server ignoring message from unexpected source.");
                            transferTftp_.bufferedSend(new TFTPErrorPacket(dataPacket.getAddress(),
                                    dataPacket.getPort(), TFTPErrorPacket.UNKNOWN_TID,
                                    "Unexpected Host or Port"));
                        }

                        try
                        {
                            dataPacket = transferTftp_.bufferedReceive();
                        }
                        catch (SocketTimeoutException e)
                        {
                            if (timeoutCount >= maxTimeoutRetries_)
                            {
                                throw e;
                            }
                            // It didn't get our ack. Resend it.
                            transferTftp_.bufferedSend(lastSentAck);
                            timeoutCount++;
                            continue;
                        }
                    }

                    if (dataPacket != null && dataPacket instanceof TFTPWriteRequestPacket)
                    {
                        // it must have missed our initial ack. Send another.
                        lastSentAck = new TFTPAckPacket(twrp.getAddress(), twrp.getPort(), 0);
                        transferTftp_.bufferedSend(lastSentAck);
                    }
                    else if (dataPacket == null || !(dataPacket instanceof TFTPDataPacket))
                    {
                        if (!shutdownTransfer)
                        {
                            logError_
                                    .println("Unexpected response from tftp client during transfer ("
                                            + dataPacket + ").  Transfer aborted.");
                        }
                        break;
                    }
                    else
                    {
                        int block = ((TFTPDataPacket) dataPacket).getBlockNumber();
                        byte[] data = ((TFTPDataPacket) dataPacket).getData();
                        int dataLength = ((TFTPDataPacket) dataPacket).getDataLength();
                        int dataOffset = ((TFTPDataPacket) dataPacket).getDataOffset();

                        if (block > lastBlock || (lastBlock == 65535 && block == 0))
                        {
                            // it might resend a data block if it missed our ack
                            // - don't rewrite the block.
                            bos.write(data, dataOffset, dataLength);
                            lastBlock = block;
                        }

                        lastSentAck = new TFTPAckPacket(twrp.getAddress(), twrp.getPort(), block);
                        transferTftp_.bufferedSend(lastSentAck);
                        if (dataLength < TFTPDataPacket.MAX_DATA_LENGTH)
                        {
                            // end of stream signal - The tranfer is complete.
                            bos.close();

                            // But my ack may be lost - so listen to see if I
                            // need to resend the ack.
                            for (int i = 0; i < maxTimeoutRetries_; i++)
                            {
                                try
                                {
                                    dataPacket = transferTftp_.bufferedReceive();
                                }
                                catch (SocketTimeoutException e)
                                {
                                    // this is the expected route - the client
                                    // shouldn't be sending any more packets.
                                    break;
                                }

                                if (dataPacket != null
                                        && (!dataPacket.getAddress().equals(twrp.getAddress()) || dataPacket
                                                .getPort() != twrp.getPort()))
                                {
                                    // make sure it was from the right client...
                                    transferTftp_
                                            .bufferedSend(new TFTPErrorPacket(dataPacket
                                                    .getAddress(), dataPacket.getPort(),
                                                    TFTPErrorPacket.UNKNOWN_TID,
                                                    "Unexpected Host or Port"));
                                }
                                else
                                {
                                    // This means they sent us the last
                                    // datapacket again, must have missed our
                                    // ack. resend it.
                                    transferTftp_.bufferedSend(lastSentAck);
                                }
                            }

                            // all done.
                            break;
                        }
                    }
                }
            }
            finally
            {
                if (bos != null)
                {
                    bos.close();
                }
            }
        }

        /*
         * Utility method to make sure that paths provided by tftp clients do not get outside of the
         * serverRoot directory.
         */
        private File buildSafeFile(File serverDirectory, String fileName, boolean createSubDirs)
                throws IOException
        {
            File temp = new File(serverDirectory, fileName);
            temp = temp.getCanonicalFile();

            if (!isSubdirectoryOf(serverDirectory, temp))
            {
                throw new IOException("Cannot access files outside of tftp server root.");
            }

            // ensure directory exists (if requested)
            if (createSubDirs)
            {
                createDirectory(temp.getParentFile());
            }

            return temp;
        }

        /*
         * recursively create subdirectories
         */
        private void createDirectory(File file) throws IOException
        {
            File parent = file.getParentFile();
            if (parent == null)
            {
                throw new IOException("Unexpected error creating requested directory");
            }
            if (!parent.exists())
            {
                // recurse...
                createDirectory(parent);
            }

            if (parent.isDirectory())
            {
                if (file.isDirectory())
                {
                    return;
                }
                boolean result = file.mkdir();
                if (!result)
                {
                    throw new IOException("Couldn't create requested directory");
                }
            }
            else
            {
                throw new IOException(
                        "Invalid directory path - file in the way of requested folder");
            }
        }

        /*
         * recursively check to see if one directory is a parent of another.
         */
        private boolean isSubdirectoryOf(File parent, File child)
        {
            File childsParent = child.getParentFile();
            if (childsParent == null)
            {
                return false;
            }
            if (childsParent.equals(parent))
            {
                return true;
            }
            else
            {
                return isSubdirectoryOf(parent, childsParent);
            }
        }
    }

    /**
     * Set the stream object to log debug / informational messages. By default, this is a no-op
     *
     * @param log
     */
    public void setLog(PrintStream log)
    {
        this.log_ = log;
    }

    /**
     * Set the stream object to log error messsages. By default, this is a no-op
     *
     * @param logError
     */
    public void setLogError(PrintStream logError)
    {
        this.logError_ = logError;
    }
}