com.p2p.peercds.common.Torrent.java Source code

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/**
 * Copyright (C) 2011-2012 Turn, Inc.
 *
 * Licensed 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 com.p2p.peercds.common;

import static com.p2p.peercds.common.Constants.BUCKET_NAME;
import static com.p2p.peercds.common.Constants.BYTE_ENCODING;
import static com.p2p.peercds.common.Constants.CLOUD_KEY;
import static com.p2p.peercds.common.Constants.PIECE_LENGTH;
import static com.p2p.peercds.common.Constants.SPECIAL_TO_NSP_MAP;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Date;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

import org.apache.commons.codec.binary.Hex;
import org.apache.commons.codec.digest.DigestUtils;
import org.apache.commons.io.FileUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Strings;
import com.p2p.peercds.bcodec.BDecoder;
import com.p2p.peercds.bcodec.BEValue;
import com.p2p.peercds.bcodec.BEncoder;

/**
 * A torrent file tracked by the controller's BitTorrent tracker.
 *
 * <p>
 * This class represents an active torrent on the tracker. The torrent
 * information is kept in-memory, and is created from the byte blob one would
 * usually find in a <tt>.torrent</tt> file.
 * </p>
 *
 * <p>
 * Each torrent also keeps a repository of the peers seeding and leeching this
 * torrent from the tracker.
 * </p>
 *
 * @author mpetazzoni
 * @see <a href="http://wiki.theory.org/BitTorrentSpecification#Metainfo_File_Structure">Torrent meta-info file structure specification</a>
 */

public class Torrent {

    private static final Logger logger = LoggerFactory.getLogger(Torrent.class);

    /**
     *
     * @author dgiffin
     * @author mpetazzoni
     */
    public static class TorrentFile {

        public final File file;
        public final long size;

        public TorrentFile(File file, long size) {
            this.file = file;
            this.size = size;
        }
    }

    protected final byte[] encoded;
    protected final byte[] encoded_info;
    protected final Map<String, BEValue> decoded;
    protected final Map<String, BEValue> decoded_info;
    protected final String cloudKey;

    private final byte[] info_hash;
    private final String hex_info_hash;

    private final List<List<URI>> trackers;
    private final Set<URI> allTrackers;
    private final Date creationDate;
    private final String comment;
    private final String createdBy;
    private final String name;
    private final long size;
    protected final List<TorrentFile> files;

    private final boolean seeder;

    /**
     * Create a new torrent from meta-info binary data.
     *
     * Parses the meta-info data (which should be B-encoded as described in the
     * BitTorrent specification) and create a Torrent object from it.
     *
     * @param torrent The meta-info byte data.
     * @param seeder Whether we'll be seeding for this torrent or not.
     * @throws IOException When the info dictionary can't be read or
     * encoded and hashed back to create the torrent's SHA-1 hash.
     */
    public Torrent(byte[] torrent, boolean seeder) throws IOException {
        this.encoded = torrent;
        this.seeder = seeder;

        this.decoded = BDecoder.bdecode(new ByteArrayInputStream(this.encoded)).getMap();

        this.decoded_info = this.decoded.get("info").getMap();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        BEncoder.bencode(this.decoded_info, baos);
        this.encoded_info = baos.toByteArray();
        this.info_hash = Torrent.hash(this.encoded_info);
        this.hex_info_hash = Torrent.byteArrayToHexString(this.info_hash);

        /**
         * Parses the announce information from the decoded meta-info
         * structure.
         *
         * <p>
         * If the torrent doesn't define an announce-list, use the mandatory
         * announce field value as the single tracker in a single announce
         * tier.  Otherwise, the announce-list must be parsed and the trackers
         * from each tier extracted.
         * </p>
         *
         * @see <a href="http://bittorrent.org/beps/bep_0012.html">BitTorrent BEP#0012 "Multitracker Metadata Extension"</a>
         */
        try {
            this.trackers = new ArrayList<List<URI>>();
            this.allTrackers = new HashSet<URI>();

            if (this.decoded.containsKey("announce-list")) {
                List<BEValue> tiers = this.decoded.get("announce-list").getList();
                for (BEValue tv : tiers) {
                    List<BEValue> trackers = tv.getList();
                    if (trackers.isEmpty()) {
                        continue;
                    }

                    List<URI> tier = new ArrayList<URI>();
                    for (BEValue tracker : trackers) {
                        URI uri = new URI(tracker.getString());

                        // Make sure we're not adding duplicate trackers.
                        if (!this.allTrackers.contains(uri)) {
                            tier.add(uri);
                            this.allTrackers.add(uri);
                        }
                    }

                    // Only add the tier if it's not empty.
                    if (!tier.isEmpty()) {
                        this.trackers.add(tier);
                    }
                }
            } else if (this.decoded.containsKey("announce")) {
                URI tracker = new URI(this.decoded.get("announce").getString());
                this.allTrackers.add(tracker);

                // Build a single-tier announce list.
                List<URI> tier = new ArrayList<URI>();
                tier.add(tracker);
                this.trackers.add(tier);
            }
        } catch (URISyntaxException use) {
            throw new IOException(use);
        }

        this.cloudKey = this.decoded.containsKey(CLOUD_KEY) ? this.decoded.get(CLOUD_KEY).getString() : "";

        this.creationDate = this.decoded.containsKey("creation date")
                ? new Date(this.decoded.get("creation date").getLong() * 1000)
                : null;
        this.comment = this.decoded.containsKey("comment") ? this.decoded.get("comment").getString() : null;
        this.createdBy = this.decoded.containsKey("created by") ? this.decoded.get("created by").getString() : null;
        this.name = this.decoded_info.get("name").getString();

        this.files = new LinkedList<TorrentFile>();

        // Parse multi-file torrent file information structure.
        if (this.decoded_info.containsKey("files")) {
            for (BEValue file : this.decoded_info.get("files").getList()) {
                Map<String, BEValue> fileInfo = file.getMap();
                StringBuilder path = new StringBuilder();
                for (BEValue pathElement : fileInfo.get("path").getList()) {
                    path.append(File.separator).append(pathElement.getString());
                }
                this.files.add(
                        new TorrentFile(new File(this.name, path.toString()), fileInfo.get("length").getLong()));
            }
        } else {
            // For single-file torrents, the name of the torrent is
            // directly the name of the file.
            this.files.add(new TorrentFile(new File(this.name), this.decoded_info.get("length").getLong()));
        }

        // Calculate the total size of this torrent from its files' sizes.
        long size = 0;
        for (TorrentFile file : this.files) {
            size += file.size;
        }
        this.size = size;

        logger.info("{}-file torrent information:", this.isMultifile() ? "Multi" : "Single");
        logger.info("  Torrent name: {}", this.name);
        logger.info("  Announced at:" + (this.trackers.size() == 0 ? " Seems to be trackerless" : ""));
        for (int i = 0; i < this.trackers.size(); i++) {
            List<URI> tier = this.trackers.get(i);
            for (int j = 0; j < tier.size(); j++) {
                logger.info("    {}{}", (j == 0 ? String.format("%2d. ", i + 1) : "    "), tier.get(j));
            }
        }

        if (this.creationDate != null) {
            logger.info("  Created on..: {}", this.creationDate);
        }
        if (!Strings.isNullOrEmpty(cloudKey))
            logger.info("Seems to be a peercds supported torrent. Cloud-key for this torrent is: " + cloudKey);
        else
            logger.info(
                    " As cloud-key is not present, this torrent seems to be created by non-peercds torrent client, all the cloud based optimizations will not be available in this activity ");

        if (this.comment != null) {
            logger.info("  Comment.....: {}", this.comment);
        }
        if (this.createdBy != null) {
            logger.info("  Created by..: {}", this.createdBy);
        }

        if (this.isMultifile()) {
            logger.info("  Found {} file(s) in multi-file torrent structure.", this.files.size());
            int i = 0;
            for (TorrentFile file : this.files) {
                logger.debug("    {}. {} ({} byte(s))", new Object[] { String.format("%2d", ++i),
                        file.file.getPath(), String.format("%,d", file.size) });
            }
        }

        logger.info("  Pieces......: {} piece(s) ({} byte(s)/piece)",
                (this.size / this.decoded_info.get("piece length").getInt()) + 1,
                this.decoded_info.get("piece length").getInt());
        logger.info("  Total size..: {} byte(s)", String.format("%,d", this.size));
    }

    /**
     * Get this torrent's name.
     *
     * <p>
     * For a single-file torrent, this is usually the name of the file. For a
     * multi-file torrent, this is usually the name of a top-level directory
     * containing those files.
     * </p>
     */
    public String getName() {
        return this.name;
    }

    /**
     * Get this torrent's comment string.
     */
    public String getComment() {
        return this.comment;
    }

    /**
     * Get this torrent's creator (user, software, whatever...).
     */
    public String getCreatedBy() {
        return this.createdBy;
    }

    /**
     * Get the total size of this torrent.
     */
    public long getSize() {
        return this.size;
    }

    /**
     * Get the file names from this torrent.
     *
     * @return The list of relative filenames of all the files described in
     * this torrent.
     */
    public List<String> getFilenames() {
        List<String> filenames = new LinkedList<String>();
        for (TorrentFile file : this.files) {
            filenames.add(file.file.getPath());
        }
        return filenames;
    }

    /**
     * Tells whether this torrent is multi-file or not.
     */
    protected boolean isMultifile() {
        return this.files.size() > 1;
    }

    /**
     * Return the hash of the B-encoded meta-info structure of this torrent.
     */
    public byte[] getInfoHash() {
        return this.info_hash;
    }

    /**
     * Get this torrent's info hash (as an hexadecimal-coded string).
     */
    public String getHexInfoHash() {
        return this.hex_info_hash;
    }

    /**
     * Return a human-readable representation of this torrent object.
     *
     * <p>
     * The torrent's name is used.
     * </p>
     */
    public String toString() {
        return this.getName();
    }

    /**
     * Return the B-encoded meta-info of this torrent.
     */
    public byte[] getEncoded() {
        return this.encoded;
    }

    /**
     * Return the trackers for this torrent.
     */
    public List<List<URI>> getAnnounceList() {
        return this.trackers;
    }

    /**
     * Returns the number of trackers for this torrent.
     */
    public int getTrackerCount() {
        return this.allTrackers.size();
    }

    /**
     * Tells whether we were an initial seeder for this torrent.
     */
    public boolean isSeeder() {
        return this.seeder;
    }

    /**
     * Save this torrent meta-info structure into a .torrent file.
     *
     * @param output The stream to write to.
     * @throws IOException If an I/O error occurs while writing the file.
     */
    public void save(OutputStream output) throws IOException {
        output.write(this.getEncoded());
        logger.info("Torrent.Save(): Flushing file");
        output.flush();
    }

    public static byte[] hash(byte[] data) {
        return DigestUtils.sha1(data);
    }

    /**
     * Convert a byte string to a string containing an hexadecimal
     * representation of the original data.
     *
     * @param bytes The byte array to convert.
     */
    public static String byteArrayToHexString(byte[] bytes) {
        return new String(Hex.encodeHex(bytes, false));
    }

    /**
     * Return an hexadecimal representation of the bytes contained in the
     * given string, following the default, expected byte encoding.
     *
     * @param input The input string.
     */
    public static String toHexString(String input) {
        try {
            byte[] bytes = input.getBytes(BYTE_ENCODING);
            return Torrent.byteArrayToHexString(bytes);
        } catch (UnsupportedEncodingException uee) {
            return null;
        }
    }

    /**
     * Determine how many threads to use for the piece hashing.
     *
     * <p>
     * If the environment variable TTORRENT_HASHING_THREADS is set to an
     * integer value greater than 0, its value will be used. Otherwise, it
     * defaults to the number of processors detected by the Java Runtime.
     * </p>
     *
     * @return How many threads to use for concurrent piece hashing.
     */
    protected static int getHashingThreadsCount() {
        String threads = System.getenv("TTORRENT_HASHING_THREADS");

        if (threads != null) {
            try {
                int count = Integer.parseInt(threads);
                if (count > 0) {
                    return count;
                }
            } catch (NumberFormatException nfe) {
                // Pass
            }
        }

        return Runtime.getRuntime().availableProcessors();
    }

    /** Torrent loading ---------------------------------------------------- */

    /**
     * Load a torrent from the given torrent file.
     *
     * <p>
     * This method assumes we are not a seeder and that local data needs to be
     * validated.
     * </p>
     *
     * @param torrent The abstract {@link File} object representing the
     * <tt>.torrent</tt> file to load.
     * @throws IOException When the torrent file cannot be read.
     */
    public static Torrent load(File torrent) throws IOException {
        return Torrent.load(torrent, false);
    }

    /**
     * Load a torrent from the given torrent file.
     *
     * @param torrent The abstract {@link File} object representing the
     * <tt>.torrent</tt> file to load.
     * @param seeder Whether we are a seeder for this torrent or not (disables
     * local data validation).
     * @throws IOException When the torrent file cannot be read.
     */
    public static Torrent load(File torrent, boolean seeder) throws IOException {
        byte[] data = FileUtils.readFileToByteArray(torrent);
        return new Torrent(data, seeder);
    }

    /** Torrent creation --------------------------------------------------- */

    /**
     * Create a {@link Torrent} object for a file.
     *
     * <p>
     * Hash the given file to create the {@link Torrent} object representing
     * the Torrent metainfo about this file, needed for announcing and/or
     * sharing said file.
     * </p>
     *
     * @param source The file to use in the torrent.
     * @param announce The announce URI that will be used for this torrent.
     * @param createdBy The creator's name, or any string identifying the
     * torrent's creator.
     */
    public static Torrent create(File source, URI announce, String createdBy)
            throws InterruptedException, IOException {
        return Torrent.create(source, null, announce, null, createdBy);
    }

    /**
     * Create a {@link Torrent} object for a set of files.
     *
     * <p>
     * Hash the given files to create the multi-file {@link Torrent} object
     * representing the Torrent meta-info about them, needed for announcing
     * and/or sharing these files. Since we created the torrent, we're
     * considering we'll be a full initial seeder for it.
     * </p>
     *
     * @param parent The parent directory or location of the torrent files,
     * also used as the torrent's name.
     * @param files The files to add into this torrent.
     * @param announce The announce URI that will be used for this torrent.
     * @param createdBy The creator's name, or any string identifying the
     * torrent's creator.
     */
    public static Torrent create(File parent, List<File> files, URI announce, String createdBy)
            throws InterruptedException, IOException {
        return Torrent.create(parent, files, announce, null, createdBy);
    }

    /**
     * Create a {@link Torrent} object for a file.
     *
     * <p>
     * Hash the given file to create the {@link Torrent} object representing
     * the Torrent metainfo about this file, needed for announcing and/or
     * sharing said file.
     * </p>
     *
     * @param source The file to use in the torrent.
     * @param announceList The announce URIs organized as tiers that will 
     * be used for this torrent
     * @param createdBy The creator's name, or any string identifying the
     * torrent's creator.
     */
    public static Torrent create(File source, List<List<URI>> announceList, String createdBy)
            throws InterruptedException, IOException {
        return Torrent.create(source, null, null, announceList, createdBy);
    }

    /**
     * Create a {@link Torrent} object for a set of files.
     *
     * <p>
     * Hash the given files to create the multi-file {@link Torrent} object
     * representing the Torrent meta-info about them, needed for announcing
     * and/or sharing these files. Since we created the torrent, we're
     * considering we'll be a full initial seeder for it.
     * </p>
     *
     * @param source The parent directory or location of the torrent files,
     * also used as the torrent's name.
     * @param files The files to add into this torrent.
     * @param announceList The announce URIs organized as tiers that will 
     * be used for this torrent
     * @param createdBy The creator's name, or any string identifying the
     * torrent's creator.
     */
    public static Torrent create(File source, List<File> files, List<List<URI>> announceList, String createdBy)
            throws InterruptedException, IOException {
        return Torrent.create(source, files, null, announceList, createdBy);
    }

    /**
     * Helper method to create a {@link Torrent} object for a set of files.
     *
     * <p>
     * Hash the given files to create the multi-file {@link Torrent} object
     * representing the Torrent meta-info about them, needed for announcing
     * and/or sharing these files. Since we created the torrent, we're
     * considering we'll be a full initial seeder for it.
     * </p>
     *
     * @param parent The parent directory or location of the torrent files,
     * also used as the torrent's name.
     * @param files The files to add into this torrent.
     * @param announce The announce URI that will be used for this torrent.
     * @param announceList The announce URIs organized as tiers that will 
     * be used for this torrent
     * @param createdBy The creator's name, or any string identifying the
     * torrent's creator.
     */
    private static Torrent create(File parent, List<File> files, URI announce, List<List<URI>> announceList,
            String createdBy) throws InterruptedException, IOException {
        MessageDigest md = DigestUtils.getSha1Digest();
        if (files == null || files.isEmpty()) {
            logger.info("Creating single-file torrent for {}...", parent.getName());
        } else {
            logger.info("Creating {}-file torrent {}...", files.size(), parent.getName());
        }

        Map<String, BEValue> torrent = new HashMap<String, BEValue>();

        if (announce != null) {
            torrent.put("announce", new BEValue(announce.toString()));
        }
        if (announceList != null) {
            List<BEValue> tiers = new LinkedList<BEValue>();
            for (List<URI> trackers : announceList) {
                List<BEValue> tierInfo = new LinkedList<BEValue>();
                for (URI trackerURI : trackers) {
                    tierInfo.add(new BEValue(trackerURI.toString()));
                }
                tiers.add(new BEValue(tierInfo));
            }
            torrent.put("announce-list", new BEValue(tiers));
        }

        torrent.put("creation date", new BEValue(new Date().getTime() / 1000));
        torrent.put("created by", new BEValue(createdBy));

        Map<String, BEValue> info = new HashMap<String, BEValue>();
        info.put("name", new BEValue(parent.getName()));
        info.put("piece length", new BEValue(PIECE_LENGTH));
        long size = 0;
        int numFiles = 0;
        if (files == null || files.isEmpty()) {
            info.put("length", new BEValue(parent.length()));
            size = parent.length();
            numFiles++;
            info.put("pieces", new BEValue(Torrent.hashFile(parent), BYTE_ENCODING));
        } else {
            List<BEValue> fileInfo = new LinkedList<BEValue>();
            List<File> updatedFilesList = new ArrayList<File>();
            updateFileInfo(files, parent, parent, fileInfo, updatedFilesList);
            logger.info("Number of files in this multi-file torrent: " + updatedFilesList.size());
            for (File file : updatedFilesList)
                size = size + file.length();
            logger.info("Number of bytes in this multi-file torrent: " + size);
            numFiles = updatedFilesList.size();
            info.put("files", new BEValue(fileInfo));
            BEValue piecesValue = new BEValue(Torrent.hashFiles(updatedFilesList), BYTE_ENCODING);
            info.put("pieces", piecesValue);
        }

        TreeMap<String, BEValue> sortInfoMap = new TreeMap<String, BEValue>();
        sortInfoMap.putAll(info);
        info = new HashMap<String, BEValue>();
        info.putAll(sortInfoMap);
        sortInfoMap = null;

        torrent.put("info", new BEValue(info));

        md.update(torrent.get("info").getMap().get("pieces").getBytes());
        byte[] digest = md.digest();
        byte[] transformedDigest = new byte[digest.length];
        int i = 0;
        for (byte bt : digest) {
            short s = (short) (bt & 0xFF);
            if (s >= 127) {
                s = (short) (s - 127);
                if (s < 32)
                    s = (short) (s + 32);
            } else if (s < 32)
                s = (short) (s + 32);
            transformedDigest[i++] = (byte) s;
        }
        for (byte b : transformedDigest)
            logger.debug(new Byte(b).toString());
        logger.info("digest str " + new String(digest));
        logger.info("transformed digest str " + new String(transformedDigest));
        logger.info("Replacing special characters in the cloud key with regular characters");
        String cloudKeyForFile = new String(transformedDigest, "UTF-8");
        for (String nsChar : SPECIAL_TO_NSP_MAP.keySet()) {
            if (cloudKeyForFile.contains(nsChar))
                cloudKeyForFile = cloudKeyForFile.replaceAll(java.util.regex.Pattern.quote(nsChar),
                        SPECIAL_TO_NSP_MAP.get(nsChar));
        }

        logger.info("Sanitized cloud Key: " + cloudKeyForFile);
        CloudUploadProgressListener listener = new CloudUploadProgressListener(size, numFiles);
        boolean success = false;
        try {
            success = CloudHelper.uploadTorrent(BUCKET_NAME, cloudKeyForFile.trim(), parent, listener);
        } catch (S3FetchException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        if (!success)
            logger.info("File won't be uploaded to cloud as file is present in swarm and uploaded to cloud");
        else
            logger.info("New file has been introduced in the swarm and has been uploaded to the cloud");

        torrent.put(CLOUD_KEY, new BEValue(cloudKeyForFile));

        TreeMap<String, BEValue> sortTorrentMap = new TreeMap<String, BEValue>();
        sortTorrentMap.putAll(torrent);
        torrent = new HashMap<String, BEValue>();
        torrent.putAll(sortTorrentMap);
        sortTorrentMap = null;

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        BEncoder.bencode(new BEValue(torrent), baos);
        return new Torrent(baos.toByteArray(), true);
    }

    private static void updateFileInfo(List<File> filesList, File parent, File actualParent, List<BEValue> fileInfo,
            List<File> files) throws UnsupportedEncodingException {

        for (File file : filesList) {
            if (!file.isDirectory()) {
                Map<String, BEValue> fileMap = new HashMap<String, BEValue>();
                fileMap.put("length", new BEValue(file.length()));

                LinkedList<BEValue> filePath = new LinkedList<BEValue>();
                File actual = file;
                while (file != null) {
                    if (file.equals(actualParent)) {
                        break;
                    }

                    filePath.addFirst(new BEValue(file.getName()));
                    file = file.getParentFile();
                }

                fileMap.put("path", new BEValue(filePath));
                fileInfo.add(new BEValue(fileMap));
                logger.info("adding file: " + actual.getName() + " to the files list");
                files.add(actual);
            } else {
                logger.info("Making recursive call");
                updateFileInfo(Arrays.asList(file.listFiles(Constants.hiddenFilesFilter)), file, actualParent,
                        fileInfo, files);
            }
        }
    }

    /**
     * A {@link Callable} to hash a data chunk.
     *
     * @author mpetazzoni
     */
    private static class CallableChunkHasher implements Callable<String> {

        private final MessageDigest md;
        private final ByteBuffer data;

        CallableChunkHasher(ByteBuffer buffer) {
            this.md = DigestUtils.getSha1Digest();

            this.data = ByteBuffer.allocate(buffer.remaining());
            buffer.mark();
            this.data.put(buffer);
            this.data.clear();
            buffer.reset();
        }

        @Override
        public String call() throws UnsupportedEncodingException {
            this.md.reset();
            this.md.update(this.data.array());
            return new String(md.digest(), BYTE_ENCODING);
        }
    }

    /**
     * Return the concatenation of the SHA-1 hashes of a file's pieces.
     *
     * <p>
     * Hashes the given file piece by piece using the default Torrent piece
     * length (see {@link #PIECE_LENGTH}) and returns the concatenation of
     * these hashes, as a string.
     * </p>
     *
     * <p>
     * This is used for creating Torrent meta-info structures from a file.
     * </p>
     *
     * @param file The file to hash.
     */
    private static String hashFile(File file) throws InterruptedException, IOException {
        return Torrent.hashFiles(Arrays.asList(new File[] { file }));
    }

    private static String hashFiles(List<File> files) throws InterruptedException, IOException {
        int threads = getHashingThreadsCount();
        ExecutorService executor = Executors.newFixedThreadPool(threads);
        ByteBuffer buffer = ByteBuffer.allocate(PIECE_LENGTH);
        List<Future<String>> results = new LinkedList<Future<String>>();
        StringBuilder hashes = new StringBuilder();

        long length = 0L;
        int pieces = 0;

        long start = System.nanoTime();
        for (File file : files) {
            logger.info("Hashing data from {} with {} threads ({} pieces)...", new Object[] { file.getName(),
                    threads, (int) (Math.ceil((double) file.length() / PIECE_LENGTH)) });

            length += file.length();

            FileInputStream fis = new FileInputStream(file);
            FileChannel channel = fis.getChannel();
            int step = 10;

            try {
                while (channel.read(buffer) > 0) {
                    if (buffer.remaining() == 0) {
                        buffer.clear();
                        results.add(executor.submit(new CallableChunkHasher(buffer)));
                    }

                    if (results.size() >= threads) {
                        pieces += accumulateHashes(hashes, results);
                    }

                    if (channel.position() / (double) channel.size() * 100f > step) {
                        logger.info("  ... {}% complete", step);
                        step += 10;
                    }
                }
            } finally {
                channel.close();
                fis.close();
            }
        }

        // Hash the last bit, if any
        if (buffer.position() > 0) {
            buffer.limit(buffer.position());
            buffer.position(0);
            results.add(executor.submit(new CallableChunkHasher(buffer)));
        }

        pieces += accumulateHashes(hashes, results);

        // Request orderly executor shutdown and wait for hashing tasks to
        // complete.
        executor.shutdown();
        while (!executor.isTerminated()) {
            Thread.sleep(10);
        }
        long elapsed = System.nanoTime() - start;

        int expectedPieces = (int) (Math.ceil((double) length / PIECE_LENGTH));
        logger.info("Hashed {} file(s) ({} bytes) in {} pieces ({} expected) in {}ms.", new Object[] { files.size(),
                length, pieces, expectedPieces, String.format("%.1f", elapsed / 1e6), });

        return hashes.toString();
    }

    /**
     * Accumulate the piece hashes into a given {@link StringBuilder}.
     *
     * @param hashes The {@link StringBuilder} to append hashes to.
     * @param results The list of {@link Future}s that will yield the piece
     *   hashes.
     */
    private static int accumulateHashes(StringBuilder hashes, List<Future<String>> results)
            throws InterruptedException, IOException {
        try {
            int pieces = results.size();
            for (Future<String> chunk : results) {
                hashes.append(chunk.get());
            }
            results.clear();
            return pieces;
        } catch (ExecutionException ee) {
            throw new IOException("Error while hashing the torrent data!", ee);
        }
    }
}