/*
 * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
 * Please refer to the LICENSE.txt for licensing details.
 */

package ch.ethz.ssh2;

import java.io.CharArrayWriter;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketTimeoutException;
import java.security.KeyPair;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;

import ch.ethz.ssh2.auth.AgentProxy;
import ch.ethz.ssh2.auth.AuthenticationManager;
import ch.ethz.ssh2.channel.ChannelManager;
import ch.ethz.ssh2.compression.CompressionFactory;
import ch.ethz.ssh2.crypto.CryptoWishList;
import ch.ethz.ssh2.crypto.cipher.BlockCipherFactory;
import ch.ethz.ssh2.crypto.digest.MAC;
import ch.ethz.ssh2.packets.PacketIgnore;
import ch.ethz.ssh2.transport.ClientTransportManager;
import ch.ethz.ssh2.transport.HTTPProxyClientTransportManager;
import ch.ethz.ssh2.transport.KexManager;
import ch.ethz.ssh2.util.TimeoutService;
import ch.ethz.ssh2.util.TimeoutService.TimeoutToken;

/**
 * A <code>Connection</code> is used to establish an encrypted TCP/IP
 * connection to a SSH-2 server.
 * <p/>
 * Typically, one
 * <ol>
 * <li>creates a {@link #Connection(String) Connection} object.</li>
 * <li>calls the {@link #connect() connect()} method.</li>
 * <li>calls some of the authentication methods (e.g., {@link #authenticateWithPublicKey(String, File, String) authenticateWithPublicKey()}).</li>
 * <li>calls one or several times the {@link #openSession() openSession()} method.</li>
 * <li>finally, one must close the connection and release resources with the {@link #close() close()} method.</li>
 * </ol>
 *
 * @author Christian Plattner
 * @version $Id: Connection.java 160 2014-05-01 14:30:26Z dkocher@sudo.ch $
 */

public class Connection {
    /**
     * The identifier presented to the SSH-2 server. This is the same
     * as the "softwareversion" defined in RFC 4253.
     * <p/>
     * <b>NOTE: As per the RFC, the "softwareversion" string MUST consist of printable
     * US-ASCII characters, with the exception of whitespace characters and the minus sign (-).</b>
     */
    private String softwareversion
        = String.format("Ganymed_%s", Version.getSpecification());

    /* Will be used to generate all random data needed for the current connection.
     * Note: SecureRandom.nextBytes() is thread safe.
     */

    private SecureRandom generator;

    /**
     * Unless you know what you are doing, you will never need this.
     *
     * @return The list of supported cipher algorithms by this implementation.
     */

    public static synchronized String[] getAvailableCiphers() {
        return BlockCipherFactory.getDefaultCipherList();
    }

    /**
     * Unless you know what you are doing, you will never need this.
     *
     * @return The list of supported MAC algorthims by this implementation.
     */

    public static synchronized String[] getAvailableMACs() {
        return MAC.getMacList();
    }

    /**
     * Unless you know what you are doing, you will never need this.
     *
     * @return The list of supported server host key algorthims by this implementation.
     */

    public static synchronized String[] getAvailableServerHostKeyAlgorithms() {
        return KexManager.getDefaultServerHostkeyAlgorithmList();
    }

    private AuthenticationManager am;

    private boolean authenticated;
    private ChannelManager cm;

    private CryptoWishList cryptoWishList
        = new CryptoWishList();

    private DHGexParameters dhgexpara
        = new DHGexParameters();

    private final String hostname;

    private final int port;

    private ClientTransportManager tm;

    private boolean tcpNoDelay = false;

    private HTTPProxyData proxy;

    private List<ConnectionMonitor> connectionMonitors
        = new ArrayList<ConnectionMonitor>();

    /**
     * Prepares a fresh <code>Connection</code> object which can then be used
     * to establish a connection to the specified SSH-2 server.
     * <p/>
     * Same as {@link #Connection(String, int) Connection(hostname, 22)}.
     *
     * @param hostname the hostname of the SSH-2 server.
     */
    public Connection(String hostname) {
        this(hostname, 22);
    }

    /**
     * Prepares a fresh <code>Connection</code> object which can then be used
     * to establish a connection to the specified SSH-2 server.
     *
     * @param hostname the host where we later want to connect to.
     * @param port     port on the server, normally 22.
     */
    public Connection(String hostname, int port) {
        this.hostname = hostname;
        this.port = port;
    }

    /**
     * Prepares a fresh <code>Connection</code> object which can then be used
     * to establish a connection to the specified SSH-2 server.
     *
     * @param hostname        the host where we later want to connect to.
     * @param port            port on the server, normally 22.
     * @param softwareversion Allows you to set a custom "softwareversion" string as defined in RFC 4253.
     *                        <b>NOTE: As per the RFC, the "softwareversion" string MUST consist of printable
     *                        US-ASCII characters, with the exception of whitespace characters and the minus sign (-).</b>
     */
    public Connection(String hostname, int port, String softwareversion) {
        this.hostname = hostname;
        this.port = port;
        this.softwareversion = softwareversion;
    }

    public Connection(String hostname, int port, final HTTPProxyData proxy) {
        this.hostname = hostname;
        this.port = port;
        this.proxy = proxy;
    }

    public Connection(String hostname, int port, String softwareversion, final HTTPProxyData proxy) {
        this.hostname = hostname;
        this.port = port;
        this.softwareversion = softwareversion;
        this.proxy = proxy;
    }

    /**
     * After a successful connect, one has to authenticate oneself. This method
     * is based on DSA (it uses DSA to sign a challenge sent by the server).
     * <p/>
     * If the authentication phase is complete, <code>true</code> will be
     * returned. If the server does not accept the request (or if further
     * authentication steps are needed), <code>false</code> is returned and
     * one can retry either by using this or any other authentication method
     * (use the <code>getRemainingAuthMethods</code> method to get a list of
     * the remaining possible methods).
     *
     * @param user     A <code>String</code> holding the username.
     * @param pem      A <code>String</code> containing the DSA private key of the
     *                 user in OpenSSH key format (PEM, you can't miss the
     *                 "-----BEGIN DSA PRIVATE KEY-----" tag). The string may contain
     *                 linefeeds.
     * @param password If the PEM string is 3DES encrypted ("DES-EDE3-CBC"), then you
     *                 must specify the password. Otherwise, this argument will be
     *                 ignored and can be set to <code>null</code>.
     * @return whether the connection is now authenticated.
     * @throws IOException
     * @deprecated You should use one of the {@link #authenticateWithPublicKey(String, File, String) authenticateWithPublicKey()}
     * methods, this method is just a wrapper for it and will
     * disappear in future builds.
     */
    @Deprecated

    public synchronized boolean authenticateWithDSA(String user, String pem, String password) throws IOException {
        if (tm == null) {
            throw new IllegalStateException("Connection is not established!");
        }

        if (authenticated) {
            throw new IllegalStateException("Connection is already authenticated!");
        }

        if (am == null) {
            am = new AuthenticationManager(tm);
        }

        if (cm == null) {
            cm = new ChannelManager(tm);
        }

        if (user == null) {
            throw new IllegalArgumentException("user argument is null");
        }

        if (pem == null) {
            throw new IllegalArgumentException("pem argument is null");
        }

        authenticated = am.authenticatePublicKey(user, pem.toCharArray(), password, getOrCreateSecureRND());
        return authenticated;
    }

    /**
     * A wrapper that calls {@link #authenticateWithKeyboardInteractive(String, String[], InteractiveCallback)
     * authenticateWithKeyboardInteractivewith} a <code>null</code> submethod list.
     *
     * @param user A <code>String</code> holding the username.
     * @param cb   An <code>InteractiveCallback</code> which will be used to
     *             determine the responses to the questions asked by the server.
     * @return whether the connection is now authenticated.
     * @throws IOException
     */

    public synchronized boolean authenticateWithKeyboardInteractive(String user, InteractiveCallback cb)
    throws IOException {
        return authenticateWithKeyboardInteractive(user, null, cb);
    }

    /**
     * After a successful connect, one has to authenticate oneself. This method
     * is based on "keyboard-interactive", specified in
     * draft-ietf-secsh-auth-kbdinteract-XX. Basically, you have to define a
     * callback object which will be feeded with challenges generated by the
     * server. Answers are then sent back to the server. It is possible that the
     * callback will be called several times during the invocation of this
     * method (e.g., if the server replies to the callback's answer(s) with
     * another challenge...)
     * <p/>
     * If the authentication phase is complete, <code>true</code> will be
     * returned. If the server does not accept the request (or if further
     * authentication steps are needed), <code>false</code> is returned and
     * one can retry either by using this or any other authentication method
     * (use the <code>getRemainingAuthMethods</code> method to get a list of
     * the remaining possible methods).
     * <p/>
     * Note: some SSH servers advertise "keyboard-interactive", however, any
     * interactive request will be denied (without having sent any challenge to
     * the client).
     *
     * @param user       A <code>String</code> holding the username.
     * @param submethods An array of submethod names, see
     *                   draft-ietf-secsh-auth-kbdinteract-XX. May be <code>null</code>
     *                   to indicate an empty list.
     * @param cb         An <code>InteractiveCallback</code> which will be used to
     *                   determine the responses to the questions asked by the server.
     * @return whether the connection is now authenticated.
     * @throws IOException
     */

    public synchronized boolean authenticateWithKeyboardInteractive(String user, String[] submethods,
            InteractiveCallback cb) throws IOException {
        if (cb == null) {
            throw new IllegalArgumentException("Callback may not ne NULL!");
        }

        if (tm == null) {
            throw new IllegalStateException("Connection is not established!");
        }

        if (authenticated) {
            throw new IllegalStateException("Connection is already authenticated!");
        }

        if (am == null) {
            am = new AuthenticationManager(tm);
        }

        if (cm == null) {
            cm = new ChannelManager(tm);
        }

        if (user == null) {
            throw new IllegalArgumentException("user argument is null");
        }

        authenticated = am.authenticateInteractive(user, submethods, cb);
        return authenticated;
    }

    public synchronized boolean authenticateWithAgent(String user, AgentProxy proxy) throws IOException {
        if (tm == null) {
            throw new IllegalStateException("Connection is not established!");
        }

        if (authenticated) {
            throw new IllegalStateException("Connection is already authenticated!");
        }

        if (am == null) {
            am = new AuthenticationManager(tm);
        }

        if (cm == null) {
            cm = new ChannelManager(tm);
        }

        if (user == null) {
            throw new IllegalArgumentException("user argument is null");
        }

        authenticated = am.authenticatePublicKey(user, proxy);
        return authenticated;
    }

    /**
     * After a successful connect, one has to authenticate oneself. This method
     * sends username and password to the server.
     * <p/>
     * If the authentication phase is complete, <code>true</code> will be
     * returned. If the server does not accept the request (or if further
     * authentication steps are needed), <code>false</code> is returned and
     * one can retry either by using this or any other authentication method
     * (use the <code>getRemainingAuthMethods</code> method to get a list of
     * the remaining possible methods).
     * <p/>
     * Note: if this method fails, then please double-check that it is actually
     * offered by the server (use {@link #getRemainingAuthMethods(String) getRemainingAuthMethods()}.
     * <p/>
     * Often, password authentication is disabled, but users are not aware of it.
     * Many servers only offer "publickey" and "keyboard-interactive". However,
     * even though "keyboard-interactive" *feels* like password authentication
     * (e.g., when using the putty or openssh clients) it is *not* the same mechanism.
     *
     * @param user
     * @param password
     * @return if the connection is now authenticated.
     * @throws IOException
     */

    public synchronized boolean authenticateWithPassword(String user, String password) throws IOException {
        if (tm == null) {
            throw new IllegalStateException("Connection is not established!");
        }

        if (authenticated) {
            throw new IllegalStateException("Connection is already authenticated!");
        }

        if (am == null) {
            am = new AuthenticationManager(tm);
        }

        if (cm == null) {
            cm = new ChannelManager(tm);
        }

        if (user == null) {
            throw new IllegalArgumentException("user argument is null");
        }

        if (password == null) {
            throw new IllegalArgumentException("password argument is null");
        }

        authenticated = am.authenticatePassword(user, password);
        return authenticated;
    }

    /**
     * After a successful connect, one has to authenticate oneself.
     * This method can be used to explicitly use the special "none"
     * authentication method (where only a username has to be specified).
     * <p/>
     * Note 1: The "none" method may always be tried by clients, however as by
     * the specs, the server will not explicitly announce it. In other words,
     * the "none" token will never show up in the list returned by
     * {@link #getRemainingAuthMethods(String)}.
     * <p/>
     * Note 2: no matter which one of the authenticateWithXXX() methods
     * you call, the library will always issue exactly one initial "none"
     * authentication request to retrieve the initially allowed list of
     * authentication methods by the server. Please read RFC 4252 for the
     * details.
     * <p/>
     * If the authentication phase is complete, <code>true</code> will be
     * returned. If further authentication steps are needed, <code>false</code>
     * is returned and one can retry by any other authentication method
     * (use the <code>getRemainingAuthMethods</code> method to get a list of
     * the remaining possible methods).
     *
     * @param user
     * @return if the connection is now authenticated.
     * @throws IOException
     */

    public synchronized boolean authenticateWithNone(String user) throws IOException {
        if (tm == null) {
            throw new IllegalStateException("Connection is not established!");
        }

        if (authenticated) {
            throw new IllegalStateException("Connection is already authenticated!");
        }

        if (am == null) {
            am = new AuthenticationManager(tm);
        }

        if (cm == null) {
            cm = new ChannelManager(tm);
        }

        if (user == null) {
            throw new IllegalArgumentException("user argument is null");
        }

        /* Trigger the sending of the PacketUserauthRequestNone packet */
        /* (if not already done)                                       */
        authenticated = am.authenticateNone(user);
        return authenticated;
    }

    /**
     * After a successful connect, one has to authenticate oneself.
     * The authentication method "publickey" works by signing a challenge
     * sent by the server. The signature is either DSA or RSA based - it
     * just depends on the type of private key you specify, either a DSA
     * or RSA private key in PEM format. And yes, this is may seem to be a
     * little confusing, the method is called "publickey" in the SSH-2 protocol
     * specification, however since we need to generate a signature, you
     * actually have to supply a private key =).
     * <p/>
     * The private key contained in the PEM file may also be encrypted ("Proc-Type: 4,ENCRYPTED").
     * The library supports DES-CBC and DES-EDE3-CBC encryption, as well
     * as the more exotic PEM encrpytions AES-128-CBC, AES-192-CBC and AES-256-CBC.
     * <p/>
     * If the authentication phase is complete, <code>true</code> will be
     * returned. If the server does not accept the request (or if further
     * authentication steps are needed), <code>false</code> is returned and
     * one can retry either by using this or any other authentication method
     * (use the <code>getRemainingAuthMethods</code> method to get a list of
     * the remaining possible methods).
     * <p/>
     * NOTE PUTTY USERS: Event though your key file may start with "-----BEGIN..."
     * it is not in the expected format. You have to convert it to the OpenSSH
     * key format by using the "puttygen" tool (can be downloaded from the Putty
     * website). Simply load your key and then use the "Conversions/Export OpenSSH key"
     * functionality to get a proper PEM file.
     *
     * @param user          A <code>String</code> holding the username.
     * @param pemPrivateKey A <code>char[]</code> containing a DSA or RSA private key of the
     *                      user in OpenSSH key format (PEM, you can't miss the
     *                      "-----BEGIN DSA PRIVATE KEY-----" or "-----BEGIN RSA PRIVATE KEY-----"
     *                      tag). The char array may contain linebreaks/linefeeds.
     * @param password      If the PEM structure is encrypted ("Proc-Type: 4,ENCRYPTED") then
     *                      you must specify a password. Otherwise, this argument will be ignored
     *                      and can be set to <code>null</code>.
     * @return whether the connection is now authenticated.
     * @throws IOException
     */

    public synchronized boolean authenticateWithPublicKey(String user, char[] pemPrivateKey, String password)
    throws IOException {
        if (tm == null) {
            throw new IllegalStateException("Connection is not established!");
        }

        if (authenticated) {
            throw new IllegalStateException("Connection is already authenticated!");
        }

        if (am == null) {
            am = new AuthenticationManager(tm);
        }

        if (cm == null) {
            cm = new ChannelManager(tm);
        }

        if (user == null) {
            throw new IllegalArgumentException("user argument is null");
        }

        if (pemPrivateKey == null) {
            throw new IllegalArgumentException("pemPrivateKey argument is null");
        }

        authenticated = am.authenticatePublicKey(user, pemPrivateKey, password, getOrCreateSecureRND());
        return authenticated;
    }

    /**
     * After a successful connect, one has to authenticate oneself. The
     * authentication method "publickey" works by signing a challenge sent by
     * the server. The signature is either DSA or RSA based - it just depends on
     * the type of private key you specify, either a DSA or RSA private key in
     * PEM format. And yes, this is may seem to be a little confusing, the
     * method is called "publickey" in the SSH-2 protocol specification, however
     * since we need to generate a signature, you actually have to supply a
     * private key =).
     * <p>
     * If the authentication phase is complete, <code>true</code> will be
     * returned. If the server does not accept the request (or if further
     * authentication steps are needed), <code>false</code> is returned and
     * one can retry either by using this or any other authentication method
     * (use the <code>getRemainingAuthMethods</code> method to get a list of
     * the remaining possible methods).
     *
     * @param user
     *            A <code>String</code> holding the username.
     * @param pair
     *            A <code>RSAPrivateKey</code> or <code>DSAPrivateKey</code>
     *            containing a DSA or RSA private key of
     *            the user in Trilead object format.
     *
     * @return whether the connection is now authenticated.
     * @throws IOException
     */

    public synchronized boolean authenticateWithPublicKey(String user, KeyPair pair)
    throws IOException {
        if (tm == null)
            throw new IllegalStateException("Connection is not established!");

        if (authenticated)
            throw new IllegalStateException("Connection is already authenticated!");

        if (am == null)
            am = new AuthenticationManager(tm);

        if (cm == null)
            cm = new ChannelManager(tm);

        if (user == null)
            throw new IllegalArgumentException("user argument is null");

        if (pair == null)
            throw new IllegalArgumentException("Key pair argument is null");

        authenticated = am.authenticatePublicKey(user, pair, getOrCreateSecureRND());
        return authenticated;
    }

    /**
     * A convenience wrapper function which reads in a private key (PEM format, either DSA or RSA)
     * and then calls <code>authenticateWithPublicKey(String, char[], String)</code>.
     * <p/>
     * NOTE PUTTY USERS: Event though your key file may start with "-----BEGIN..."
     * it is not in the expected format. You have to convert it to the OpenSSH
     * key format by using the "puttygen" tool (can be downloaded from the Putty
     * website). Simply load your key and then use the "Conversions/Export OpenSSH key"
     * functionality to get a proper PEM file.
     *
     * @param user     A <code>String</code> holding the username.
     * @param pemFile  A <code>File</code> object pointing to a file containing a DSA or RSA
     *                 private key of the user in OpenSSH key format (PEM, you can't miss the
     *                 "-----BEGIN DSA PRIVATE KEY-----" or "-----BEGIN RSA PRIVATE KEY-----"
     *                 tag).
     * @param password If the PEM file is encrypted then you must specify the password.
     *                 Otherwise, this argument will be ignored and can be set to <code>null</code>.
     * @return whether the connection is now authenticated.
     * @throws IOException
     */

    public synchronized boolean authenticateWithPublicKey(String user, File pemFile, String password)
    throws IOException {
        if (pemFile == null) {
            throw new IllegalArgumentException("pemFile argument is null");
        }

        char[] buff = new char[256];
        CharArrayWriter cw = new CharArrayWriter();
        FileReader fr = new FileReader(pemFile);

        while (true) {
            int len = fr.read(buff);

            if (len < 0) {
                break;
            }

            cw.write(buff, 0, len);
        }

        fr.close();
        return authenticateWithPublicKey(user, cw.toCharArray(), password);
    }

    /**
     * Add a {@link ConnectionMonitor} to this connection. Can be invoked at any time,
     * but it is best to add connection monitors before invoking
     * <code>connect()</code> to avoid glitches (e.g., you add a connection monitor after
     * a successful connect(), but the connection has died in the mean time. Then,
     * your connection monitor won't be notified.)
     * <p/>
     * You can add as many monitors as you like. If a monitor has already been added, then
     * this method does nothing.
     *
     * @param cmon An object implementing the {@link ConnectionMonitor} interface.
     * @see ConnectionMonitor
     */

    public synchronized void addConnectionMonitor(ConnectionMonitor cmon) {
        if (!connectionMonitors.contains(cmon)) {
            connectionMonitors.add(cmon);

            if (tm != null) {
                tm.setConnectionMonitors(connectionMonitors);
            }
        }
    }

    /**
     * Remove a {@link ConnectionMonitor} from this connection.
     *
     * @param cmon
     * @return whether the monitor could be removed
     */

    public synchronized boolean removeConnectionMonitor(ConnectionMonitor cmon) {
        boolean existed = connectionMonitors.remove(cmon);

        if (tm != null) {
            tm.setConnectionMonitors(connectionMonitors);
        }

        return existed;
    }

    /**
     * Controls whether compression is used on the link or not.
     * <p>
     * Note: This can only be called before connect()
     * @param enabled whether to enable compression
     * @throws IOException
     */

    public synchronized void setCompression(boolean enabled) throws IOException {
        if (tm != null)
            throw new IOException("Connection to " + hostname + " is already in connected state!");

        if (enabled) enableCompression();
        else         disableCompression();
    }

    /**
     * Close the connection to the SSH-2 server. All assigned sessions will be
     * closed, too. Can be called at any time. Don't forget to call this once
     * you don't need a connection anymore - otherwise the receiver thread may
     * run forever.
     */

    public synchronized void close() {
        if (cm != null) {
            cm.closeAllChannels();
        }

        if (tm != null) {
            tm.close();
            tm = null;
        }

        am = null;
        cm = null;
        authenticated = false;
    }

    public synchronized void close(IOException t) {
        if (cm != null) {
            cm.closeAllChannels();
        }

        if (tm != null) {
            tm.close(t);
            tm = null;
        }

        am = null;
        cm = null;
        authenticated = false;
    }

    /**
     * Same as {@link #connect(ServerHostKeyVerifier, int, int) connect(null, 0, 0)}.
     *
     * @return see comments for the {@link #connect(ServerHostKeyVerifier, int, int) connect(ServerHostKeyVerifier, int, int)} method.
     * @throws IOException
     */

    public synchronized ConnectionInfo connect() throws IOException {
        return connect(null, 0, 0);
    }

    /**
     * Same as {@link #connect(ServerHostKeyVerifier, int, int) connect(verifier, 0, 0)}.
     *
     * @return see comments for the {@link #connect(ServerHostKeyVerifier, int, int) connect(ServerHostKeyVerifier, int, int)} method.
     * @throws IOException
     */

    public synchronized ConnectionInfo connect(ServerHostKeyVerifier verifier) throws IOException {
        return connect(verifier, 0, 0);
    }

    /**
     * Connect to the SSH-2 server and, as soon as the server has presented its
     * host key, use the {@link ServerHostKeyVerifier#verifyServerHostKey(String,
     * int, String, byte[]) ServerHostKeyVerifier.verifyServerHostKey()}
     * method of the <code>verifier</code> to ask for permission to proceed.
     * If <code>verifier</code> is <code>null</code>, then any host key will be
     * accepted - this is NOT recommended, since it makes man-in-the-middle attackes
     * VERY easy (somebody could put a proxy SSH server between you and the real server).
     * <p/>
     * Note: The verifier will be called before doing any crypto calculations
     * (i.e., diffie-hellman). Therefore, if you don't like the presented host key then
     * no CPU cycles are wasted (and the evil server has less information about us).
     * <p/>
     * However, it is still possible that the server presented a fake host key: the server
     * cheated (typically a sign for a man-in-the-middle attack) and is not able to generate
     * a signature that matches its host key. Don't worry, the library will detect such
     * a scenario later when checking the signature (the signature cannot be checked before
     * having completed the diffie-hellman exchange).
     * <p/>
     * Note 2: The  {@link ServerHostKeyVerifier#verifyServerHostKey(String,
     * int, String, byte[]) ServerHostKeyVerifier.verifyServerHostKey()} method
     * will *NOT* be called from the current thread, the call is being made from a
     * background thread (there is a background dispatcher thread for every
     * established connection).
     * <p/>
     * Note 3: This method will block as long as the key exchange of the underlying connection
     * has not been completed (and you have not specified any timeouts).
     * <p/>
     * Note 4: If you want to re-use a connection object that was successfully connected,
     * then you must call the {@link #close()} method before invoking <code>connect()</code> again.
     *
     * @param verifier       An object that implements the
     *                       {@link ServerHostKeyVerifier} interface. Pass <code>null</code>
     *                       to accept any server host key - NOT recommended.
     * @param connectTimeout Connect the underlying TCP socket to the server with the given timeout
     *                       value (non-negative, in milliseconds). Zero means no timeout.
     * @param kexTimeout     Timeout for complete connection establishment (non-negative,
     *                       in milliseconds). Zero means no timeout. The timeout counts from the
     *                       moment you invoke the connect() method and is cancelled as soon as the
     *                       first key-exchange round has finished. It is possible that
     *                       the timeout event will be fired during the invocation of the
     *                       <code>verifier</code> callback, but it will only have an effect after
     *                       the <code>verifier</code> returns.
     * @return A {@link ConnectionInfo} object containing the details of
     * the established connection.
     * @throws IOException If any problem occurs, e.g., the server's host key is not
     *                     accepted by the <code>verifier</code> or there is problem during
     *                     the initial crypto setup (e.g., the signature sent by the server is wrong).
     *                     <p/>
     *                     In case of a timeout (either connectTimeout or kexTimeout)
     *                     a SocketTimeoutException is thrown.
     *                     <p/>
     *                     An exception may also be thrown if the connection was already successfully
     *                     connected (no matter if the connection broke in the mean time) and you invoke
     *                     <code>connect()</code> again without having called {@link #close()} first.
     *                     <p/>
     *                     If a HTTP proxy is being used and the proxy refuses the connection,
     *                     then a {@link HTTPProxyException} may be thrown, which
     *                     contains the details returned by the proxy. If the proxy is buggy and does
     *                     not return a proper HTTP response, then a normal IOException is thrown instead.
     */

    public synchronized ConnectionInfo connect(ServerHostKeyVerifier verifier, int connectTimeout, int kexTimeout)
    throws IOException {
        final class TimeoutState {
            boolean isCancelled = false;
            boolean timeoutSocketClosed = false;
        }

        if (tm != null) {
            throw new IllegalStateException(String.format("Connection to %s is already in connected state", hostname));
        }

        if (connectTimeout < 0) {
            throw new IllegalArgumentException("connectTimeout must be non-negative!");
        }

        if (kexTimeout < 0) {
            throw new IllegalArgumentException("kexTimeout must be non-negative!");
        }

        final TimeoutState state = new TimeoutState();

        if (null == proxy) {
            tm = new ClientTransportManager(new Socket());
        }
        else {
            tm = new HTTPProxyClientTransportManager(new Socket(), proxy);
        }

        tm.setSoTimeout(connectTimeout);
        tm.setTcpNoDelay(tcpNoDelay);
        tm.setConnectionMonitors(connectionMonitors);

        try {
            TimeoutToken token = null;

            if (kexTimeout > 0) {
                final Runnable timeoutHandler = new Runnable() {
                    public void run() {
                        synchronized (state) {
                            if (state.isCancelled) {
                                return;
                            }

                            state.timeoutSocketClosed = true;
                            tm.close(new SocketTimeoutException("The connect timeout expired"));
                        }
                    }
                };
                long timeoutHorizont = System.currentTimeMillis() + kexTimeout;
                token = TimeoutService.addTimeoutHandler(timeoutHorizont, timeoutHandler);
            }

            tm.connect(hostname, port, softwareversion, cryptoWishList, verifier, dhgexpara, connectTimeout,
                       getOrCreateSecureRND());
            /* Wait until first KEX has finished */
            ConnectionInfo ci = tm.getConnectionInfo(1);

            /* Now try to cancel the timeout, if needed */

            if (token != null) {
                TimeoutService.cancelTimeoutHandler(token);

                /* Were we too late? */

                synchronized (state) {
                    if (state.timeoutSocketClosed) {
                        throw new IOException("This exception will be replaced by the one below =)");
                    }

                    /* Just in case the "cancelTimeoutHandler" invocation came just a little bit
                     * too late but the handler did not enter the semaphore yet - we can
                     * still stop it.
                     */
                    state.isCancelled = true;
                }
            }

            return ci;
        }
        catch (SocketTimeoutException e) {
            throw e;
        }
        catch (HTTPProxyException e) {
            throw e;
        }
        catch (IOException e) {
            // This will also invoke any registered connection monitors
            close(e);

            synchronized (state) {
                /* Show a clean exception, not something like "the socket is closed!?!" */
                if (state.timeoutSocketClosed) {
                    throw new SocketTimeoutException(String.format("The kexTimeout (%d ms) expired.", kexTimeout));
                }
            }

            throw e;
        }
    }

    /**
     * Creates a new {@link LocalPortForwarder}.
     * A <code>LocalPortForwarder</code> forwards TCP/IP connections that arrive at a local
     * port via the secure tunnel to another host (which may or may not be
     * identical to the remote SSH-2 server).
     * <p/>
     * This method must only be called after one has passed successfully the authentication step.
     * There is no limit on the number of concurrent forwardings.
     *
     * @param local_port      the local port the LocalPortForwarder shall bind to.
     * @param host_to_connect target address (IP or hostname)
     * @param port_to_connect target port
     * @return A {@link LocalPortForwarder} object.
     * @throws IOException
     */

    public synchronized LocalPortForwarder createLocalPortForwarder(int local_port, String host_to_connect,
            int port_to_connect) throws IOException {
        this.checkConnection();
        return new LocalPortForwarder(cm, local_port, host_to_connect, port_to_connect);
    }

    /**
     * Creates a new {@link LocalPortForwarder}.
     * A <code>LocalPortForwarder</code> forwards TCP/IP connections that arrive at a local
     * port via the secure tunnel to another host (which may or may not be
     * identical to the remote SSH-2 server).
     * <p/>
     * This method must only be called after one has passed successfully the authentication step.
     * There is no limit on the number of concurrent forwardings.
     *
     * @param addr            specifies the InetSocketAddress where the local socket shall be bound to.
     * @param host_to_connect target address (IP or hostname)
     * @param port_to_connect target port
     * @return A {@link LocalPortForwarder} object.
     * @throws IOException
     */

    public synchronized LocalPortForwarder createLocalPortForwarder(InetSocketAddress addr, String host_to_connect,
            int port_to_connect) throws IOException {
        this.checkConnection();
        return new LocalPortForwarder(cm, addr, host_to_connect, port_to_connect);
    }

    /**
     * Creates a new {@link LocalStreamForwarder}.
     * A <code>LocalStreamForwarder</code> manages an Input/Outputstream pair
     * that is being forwarded via the secure tunnel into a TCP/IP connection to another host
     * (which may or may not be identical to the remote SSH-2 server).
     *
     * @param host_to_connect
     * @param port_to_connect
     * @return A {@link LocalStreamForwarder} object.
     * @throws IOException
     */

    public synchronized LocalStreamForwarder createLocalStreamForwarder(String host_to_connect, int port_to_connect)
    throws IOException {
        this.checkConnection();
        return new LocalStreamForwarder(cm, host_to_connect, port_to_connect);
    }

    /**
     * Creates a new {@link DynamicPortForwarder}. A
     * <code>DynamicPortForwarder</code> forwards TCP/IP connections that arrive
     * at a local port via the secure tunnel to another host that is chosen via
     * the SOCKS protocol.
     * <p>
     * This method must only be called after one has passed successfully the
     * authentication step. There is no limit on the number of concurrent
     * forwardings.
     *
     * @param local_port
     * @return A {@link DynamicPortForwarder} object.
     * @throws IOException
     */

    public synchronized DynamicPortForwarder createDynamicPortForwarder(int local_port) throws IOException {
        if (tm == null)
            throw new IllegalStateException("Cannot forward ports, you need to establish a connection first.");

        if (!authenticated)
            throw new IllegalStateException("Cannot forward ports, connection is not authenticated.");

        return new DynamicPortForwarder(cm, local_port);
    }

    /**
     * Creates a new {@link DynamicPortForwarder}. A
     * <code>DynamicPortForwarder</code> forwards TCP/IP connections that arrive
     * at a local port via the secure tunnel to another host that is chosen via
     * the SOCKS protocol.
     * <p>
     * This method must only be called after one has passed successfully the
     * authentication step. There is no limit on the number of concurrent
     * forwardings.
     *
     * @param addr
     *            specifies the InetSocketAddress where the local socket shall
     *            be bound to.
     * @return A {@link DynamicPortForwarder} object.
     * @throws IOException
     */

    public synchronized DynamicPortForwarder createDynamicPortForwarder(InetSocketAddress addr) throws IOException {
        if (tm == null)
            throw new IllegalStateException("Cannot forward ports, you need to establish a connection first.");

        if (!authenticated)
            throw new IllegalStateException("Cannot forward ports, connection is not authenticated.");

        return new DynamicPortForwarder(cm, addr);
    }

    /**
     * Create a very basic {@link SCPClient} that can be used to copy
     * files from/to the SSH-2 server.
     * <p/>
     * Works only after one has passed successfully the authentication step.
     * There is no limit on the number of concurrent SCP clients.
     * <p/>
     * Note: This factory method will probably disappear in the future.
     *
     * @return A {@link SCPClient} object.
     * @throws IOException
     */

    public synchronized SCPClient createSCPClient() throws IOException {
        this.checkConnection();
        return new SCPClient(this);
    }

    /**
     * Force an asynchronous key re-exchange (the call does not block). The
     * latest values set for MAC, Cipher and DH group exchange parameters will
     * be used. If a key exchange is currently in progress, then this method has
     * the only effect that the so far specified parameters will be used for the
     * next (server driven) key exchange.
     * <p/>
     * Note: This implementation will never start a key exchange (other than the initial one)
     * unless you or the SSH-2 server ask for it.
     *
     * @throws IOException In case of any failure behind the scenes.
     */

    public synchronized void forceKeyExchange() throws IOException {
        this.checkConnection();
        tm.forceKeyExchange(cryptoWishList, dhgexpara, null, null, null);
    }

    /**
     * Returns the hostname that was passed to the constructor.
     *
     * @return the hostname
     */

    public synchronized String getHostname() {
        return hostname;
    }

    /**
     * Returns the port that was passed to the constructor.
     *
     * @return the TCP port
     */

    public synchronized int getPort() {
        return port;
    }

    /**
     * Returns a {@link ConnectionInfo} object containing the details of
     * the connection. Can be called as soon as the connection has been
     * established (successfully connected).
     *
     * @return A {@link ConnectionInfo} object.
     * @throws IOException In case of any failure behind the scenes.
     */

    public synchronized ConnectionInfo getConnectionInfo() throws IOException {
        this.checkConnection();
        return tm.getConnectionInfo(1);
    }

    /**
     * After a successful connect, one has to authenticate oneself. This method
     * can be used to tell which authentication methods are supported by the
     * server at a certain stage of the authentication process (for the given
     * username).
     * <p/>
     * Note 1: the username will only be used if no authentication step was done
     * so far (it will be used to ask the server for a list of possible
     * authentication methods by sending the initial "none" request). Otherwise,
     * this method ignores the user name and returns a cached method list
     * (which is based on the information contained in the last negative server response).
     * <p/>
     * Note 2: the server may return method names that are not supported by this
     * implementation.
     * <p/>
     * After a successful authentication, this method must not be called
     * anymore.
     *
     * @param user A <code>String</code> holding the username.
     * @return a (possibly emtpy) array holding authentication method names.
     * @throws IOException
     */

    public synchronized String[] getRemainingAuthMethods(String user) throws IOException {
        if (user == null) {
            throw new IllegalArgumentException("user argument may not be NULL!");
        }

        if (tm == null) {
            throw new IllegalStateException("Connection is not established!");
        }

        if (authenticated) {
            throw new IllegalStateException("Connection is already authenticated!");
        }

        if (am == null) {
            am = new AuthenticationManager(tm);
        }

        if (cm == null) {
            cm = new ChannelManager(tm);
        }

        final Set<String> remainingMethods = am.getRemainingMethods(user);
        return remainingMethods.toArray(new String[remainingMethods.size()]);
    }

    /**
     * Determines if the authentication phase is complete. Can be called at any
     * time.
     *
     * @return <code>true</code> if no further authentication steps are
     * needed.
     */

    public synchronized boolean isAuthenticationComplete() {
        return authenticated;
    }

    /**
     * Returns true if there was at least one failed authentication request and
     * the last failed authentication request was marked with "partial success"
     * by the server. This is only needed in the rare case of SSH-2 server setups
     * that cannot be satisfied with a single successful authentication request
     * (i.e., multiple authentication steps are needed.)
     * <p/>
     * If you are interested in the details, then have a look at RFC4252.
     *
     * @return if the there was a failed authentication step and the last one
     * was marked as a "partial success".
     */

    public synchronized boolean isAuthenticationPartialSuccess() {
        if (am == null) {
            return false;
        }

        return am.getPartialSuccess();
    }

    /**
     * Checks if a specified authentication method is available. This method is
     * actually just a wrapper for {@link #getRemainingAuthMethods(String)
     * getRemainingAuthMethods()}.
     *
     * @param user   A <code>String</code> holding the username.
     * @param method An authentication method name (e.g., "publickey", "password",
     *               "keyboard-interactive") as specified by the SSH-2 standard.
     * @return if the specified authentication method is currently available.
     * @throws IOException
     */

    public synchronized boolean isAuthMethodAvailable(String user, String method) throws IOException {
        String methods[] = getRemainingAuthMethods(user);

        for (final String m : methods) {
            if (m.compareTo(method) == 0) {
                return true;
            }
        }

        return false;
    }

    private SecureRandom getOrCreateSecureRND() {
        if (generator == null) {
            generator = new SecureRandom();
        }

        return generator;
    }

    /**
     * Open a new {@link Session} on this connection. Works only after one has passed
     * successfully the authentication step. There is no limit on the number of
     * concurrent sessions.
     *
     * @return A {@link Session} object.
     * @throws IOException
     */

    public synchronized Session openSession() throws IOException {
        this.checkConnection();
        return new Session(cm, getOrCreateSecureRND());
    }

    /**
     * Send an SSH_MSG_IGNORE packet. This method will generate a random data attribute
     * (length between 0 (invlusive) and 16 (exclusive) bytes, contents are random bytes).
     * <p/>
     * This method must only be called once the connection is established.
     *
     * @throws IOException
     */

    public synchronized void sendIgnorePacket() throws IOException {
        SecureRandom rnd = getOrCreateSecureRND();
        byte[] data = new byte[rnd.nextInt(16)];
        rnd.nextBytes(data);
        sendIgnorePacket(data);
    }

    /**
     * Send an SSH_MSG_IGNORE packet with the given data attribute.
     * <p/>
     * This method must only be called once the connection is established.
     *
     * @throws IOException
     */

    public synchronized void sendIgnorePacket(byte[] data) throws IOException {
        this.checkConnection();
        PacketIgnore pi = new PacketIgnore(data);
        tm.sendMessage(pi.getPayload());
    }

    /**
     * Controls whether compression is used on the link or not.
     */

    public synchronized void setCompression(String[] algorithms) {
        CompressionFactory.checkCompressorList(algorithms);
        cryptoWishList.c2s_comp_algos = algorithms;
    }

    public synchronized void enableCompression() {
        cryptoWishList.c2s_comp_algos = CompressionFactory.getDefaultCompressorList();
        cryptoWishList.s2c_comp_algos = CompressionFactory.getDefaultCompressorList();
    }

    public synchronized void disableCompression() {
        cryptoWishList.c2s_comp_algos = new String[] {"none"};
        cryptoWishList.s2c_comp_algos = new String[] {"none"};
    }

    /**
     * Unless you know what you are doing, you will never need this.
     */

    public synchronized void setClient2ServerCiphers(final String[] ciphers) {
        if ((ciphers == null) || (ciphers.length == 0)) {
            throw new IllegalArgumentException();
        }

        BlockCipherFactory.checkCipherList(ciphers);
        cryptoWishList.c2s_enc_algos = ciphers;
    }

    /**
     * Unless you know what you are doing, you will never need this.
     */

    public synchronized void setClient2ServerMACs(final String[] macs) {
        MAC.checkMacList(macs);
        cryptoWishList.c2s_mac_algos = macs;
    }

    /**
     * Sets the parameters for the diffie-hellman group exchange. Unless you
     * know what you are doing, you will never need this. Default values are
     * defined in the {@link DHGexParameters} class.
     *
     * @param dgp {@link DHGexParameters}, non null.
     */

    public synchronized void setDHGexParameters(DHGexParameters dgp) {
        if (dgp == null) {
            throw new IllegalArgumentException();
        }

        dhgexpara = dgp;
    }

    /**
     * Unless you know what you are doing, you will never need this.
     */

    public synchronized void setServer2ClientCiphers(final String[] ciphers) {
        BlockCipherFactory.checkCipherList(ciphers);
        cryptoWishList.s2c_enc_algos = ciphers;
    }

    /**
     * Unless you know what you are doing, you will never need this.
     */

    public synchronized void setServer2ClientMACs(final String[] macs) {
        MAC.checkMacList(macs);
        cryptoWishList.s2c_mac_algos = macs;
    }

    /**
     * Define the set of allowed server host key algorithms to be used for
     * the following key exchange operations.
     * <p/>
     * Unless you know what you are doing, you will never need this.
     *
     * @param algos An array of allowed server host key algorithms.
     *              SSH-2 defines <code>ssh-dss</code> and <code>ssh-rsa</code>.
     *              The entries of the array must be ordered after preference, i.e.,
     *              the entry at index 0 is the most preferred one. You must specify
     *              at least one entry.
     */

    public synchronized void setServerHostKeyAlgorithms(final String[] algos) {
        KexManager.checkServerHostkeyAlgorithmsList(algos);
        cryptoWishList.serverHostKeyAlgorithms = algos;
    }

    /**
     * Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm) on the underlying socket.
     * <p/>
     * Can be called at any time. If the connection has not yet been established
     * then the passed value will be stored and set after the socket has been set up.
     * The default value that will be used is <code>false</code>.
     *
     * @param enable the argument passed to the <code>Socket.setTCPNoDelay()</code> method.
     * @throws IOException
     */

    public synchronized void setTCPNoDelay(boolean enable) throws IOException {
        tcpNoDelay = enable;

        if (tm != null) {
            tm.setTcpNoDelay(enable);
        }
    }

    /**
     * Used to tell the library that the connection shall be established through
     * a proxy server. It only makes sense to call this method before calling
     * the {@link #connect() connect()} method.
     * <p>
     * At the moment, only HTTP proxies are supported.
     * <p>
     * Note: This method can be called any number of times. The
     * {@link #connect() connect()} method will use the value set in the last
     * preceding invocation of this method.
     *
     * @see HTTPProxyData
     *
     * @param proxy
     *            Connection information about the proxy. If <code>null</code>,
     *            then no proxy will be used (non surprisingly, this is also the
     *            default).
     */

    public synchronized void setProxyData(HTTPProxyData proxy) {
        this.proxy = proxy;
    }

    /**
     * Request a remote port forwarding.
     * If successful, then forwarded connections will be redirected to the given target address.
     * You can cancle a requested remote port forwarding by calling
     * {@link #cancelRemotePortForwarding(int) cancelRemotePortForwarding()}.
     * <p/>
     * A call of this method will block until the peer either agreed or disagreed to your request-
     * <p/>
     * Note 1: this method typically fails if you
     * <ul>
     * <li>pass a port number for which the used remote user has not enough permissions (i.e., port
     * &lt; 1024)</li>
     * <li>or pass a port number that is already in use on the remote server</li>
     * <li>or if remote port forwarding is disabled on the server.</li>
     * </ul>
     * <p/>
     * Note 2: (from the openssh man page): By default, the listening socket on the server will be
     * bound to the loopback interface only. This may be overriden by specifying a bind address.
     * Specifying a remote bind address will only succeed if the server's <b>GatewayPorts</b> option
     * is enabled (see sshd_config(5)).
     *
     * @param bindAddress   address to bind to on the server:
     *                      <ul>
     *                      <li>"" means that connections are to be accepted on all protocol families
     *                      supported by the SSH implementation</li>
     *                      <li>"0.0.0.0" means to listen on all IPv4 addresses</li>
     *                      <li>"::" means to listen on all IPv6 addresses</li>
     *                      <li>"localhost" means to listen on all protocol families supported by the SSH
     *                      implementation on loopback addresses only, [RFC3330] and RFC3513]</li>
     *                      <li>"127.0.0.1" and "::1" indicate listening on the loopback interfaces for
     *                      IPv4 and IPv6 respectively</li>
     *                      </ul>
     * @param bindPort      port number to bind on the server (must be &gt; 0)
     * @param targetAddress the target address (IP or hostname)
     * @param targetPort    the target port
     * @throws IOException
     */

    public synchronized void requestRemotePortForwarding(String bindAddress, int bindPort, String targetAddress,
            int targetPort) throws IOException {
        this.checkConnection();

        if ((bindAddress == null) || (targetAddress == null) || (bindPort <= 0) || (targetPort <= 0)) {
            throw new IllegalArgumentException();
        }

        cm.requestGlobalForward(bindAddress, bindPort, targetAddress, targetPort);
    }

    /**
     * Cancel an earlier requested remote port forwarding.
     * Currently active forwardings will not be affected (e.g., disrupted).
     * Note that further connection forwarding requests may be received until
     * this method has returned.
     *
     * @param bindPort the allocated port number on the server
     * @throws IOException if the remote side refuses the cancel request or another low
     *                     level error occurs (e.g., the underlying connection is closed)
     */

    public synchronized void cancelRemotePortForwarding(int bindPort) throws IOException {
        this.checkConnection();
        cm.requestCancelGlobalForward(bindPort);
    }

    /**
     * Provide your own instance of SecureRandom. Can be used, e.g., if you
     * want to seed the used SecureRandom generator manually.
     * <p/>
     * The SecureRandom instance is used during key exchanges, public key authentication,
     * x11 cookie generation and the like.
     *
     * @param rnd a SecureRandom instance
     */

    public synchronized void setSecureRandom(SecureRandom rnd) {
        if (rnd == null) {
            throw new IllegalArgumentException();
        }

        this.generator = rnd;
    }

    private void checkConnection() throws IllegalStateException {
        if (tm == null) {
            throw new IllegalStateException("You need to establish a connection first.");
        }

        if (!authenticated) {
            throw new IllegalStateException("The connection is not authenticated.");
        }
    }
}