/*
 * 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
 *
 *      https://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.ftp;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Inet6Address;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Base64;

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.KeyManager;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLException;
import javax.net.ssl.SSLHandshakeException;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;

import org.apache.commons.io.IOUtils;
import org.apache.commons.net.util.SSLContextUtils;
import org.apache.commons.net.util.SSLSocketUtils;
import org.apache.commons.net.util.TrustManagerUtils;

/**
 * FTP over SSL processing. If desired, the JVM property -Djavax.net.debug=all can be used to see wire-level SSL details.
 *
 * Warning: the hostname is not verified against the certificate by default, use {@link #setHostnameVerifier(HostnameVerifier)} or
 * {@link #setEndpointCheckingEnabled(boolean)} (on Java 1.7+) to enable verification. Verification is only performed on client mode connections.
 *
 * @since 2.0
 */
public class FTPSClient extends FTPClient {

// From http://www.iana.org/assignments/port-numbers

//    ftps-data   989/tcp    ftp protocol, data, over TLS/SSL
//    ftps-data   989/udp    ftp protocol, data, over TLS/SSL
//    ftps        990/tcp    ftp protocol, control, over TLS/SSL
//    ftps        990/udp    ftp protocol, control, over TLS/SSL

    /** Default FTPS data port. */
    public static final int DEFAULT_FTPS_DATA_PORT = 989;

    /** Default FTPS port. */
    public static final int DEFAULT_FTPS_PORT = 990;

    /** The value that I can set in PROT command (C = Clear, P = Protected) */
    private static final String[] PROT_COMMAND_VALUE = { "C", "E", "S", "P" };

    /** Default PROT Command */
    private static final String DEFAULT_PROT = "C";

    /** Default secure socket protocol name, i.e. TLS */
    private static final String DEFAULT_PROTOCOL = "TLS";

    /** The AUTH (Authentication/Security Mechanism) command. */
    private static final String CMD_AUTH = "AUTH";

    /** The ADAT (Authentication/Security Data) command. */
    private static final String CMD_ADAT = "ADAT";

    /** The PROT (Data Channel Protection Level) command. */
    private static final String CMD_PROT = "PROT";

    /** The PBSZ (Protection Buffer Size) command. */
    private static final String CMD_PBSZ = "PBSZ";

    /** The MIC (Integrity Protected Command) command. */
    private static final String CMD_MIC = "MIC";

    /** The CONF (Confidentiality Protected Command) command. */
    private static final String CMD_CONF = "CONF";

    /** The ENC (Privacy Protected Command) command. */
    private static final String CMD_ENC = "ENC";

    /** The CCC (Clear Command Channel) command. */
    private static final String CMD_CCC = "CCC";

    /** @deprecated - not used - may be removed in a future release */
    @Deprecated
    public static String KEYSTORE_ALGORITHM;

    /** @deprecated - not used - may be removed in a future release */
    @Deprecated
    public static String TRUSTSTORE_ALGORITHM;

    /** @deprecated - not used - may be removed in a future release */
    @Deprecated
    public static String PROVIDER;

    /** @deprecated - not used - may be removed in a future release */
    @Deprecated
    public static String STORE_TYPE;

    /** The security mode. (True - Implicit Mode / False - Explicit Mode) */
    private final boolean isImplicit;

    /** The secure socket protocol to be used, e.g. SSL/TLS. */
    private final String protocol;

    /** The AUTH Command value */
    private String auth = DEFAULT_PROTOCOL;

    /** The context object. */
    private SSLContext context;

    /** The socket object. */
    private Socket plainSocket;

    /** Controls whether a new SSL session may be established by this socket. Default true. */
    private boolean isCreation = true;

    /** The use client mode flag. */
    private boolean isClientMode = true;

    /** The need client auth flag. */
    private boolean isNeedClientAuth;

    /** The want client auth flag. */
    private boolean isWantClientAuth;

    /** The cipher suites */
    private String[] suites;

    /** The protocol versions */
    private String[] protocols;

    /**
     * The FTPS {@link TrustManager} implementation, default validate only {@link TrustManagerUtils#getValidateServerCertificateTrustManager()}.
     */
    private TrustManager trustManager = TrustManagerUtils.getValidateServerCertificateTrustManager();

    /** The {@link KeyManager}, default null (i.e. use system default). */
    private KeyManager keyManager;

    /** The {@link HostnameVerifier} to use post-TLS, default null (i.e. no verification). */
    private HostnameVerifier hostnameVerifier;

    /** Use Java 1.7+ HTTPS Endpoint Identification Algorithm. */
    private boolean tlsEndpointChecking;

    /**
     * Constructor for FTPSClient, calls {@link #FTPSClient(String, boolean)}.
     *
     * Sets protocol to {@link #DEFAULT_PROTOCOL} - i.e. TLS - and security mode to explicit (isImplicit = false)
     */
    public FTPSClient() {
        this(DEFAULT_PROTOCOL, false);
    }

    /**
     * Constructor for FTPSClient, using {@link #DEFAULT_PROTOCOL} - i.e. TLS Calls {@link #FTPSClient(String, boolean)}
     *
     * @param isImplicit The security mode (Implicit/Explicit).
     */
    public FTPSClient(final boolean isImplicit) {
        this(DEFAULT_PROTOCOL, isImplicit);
    }

    /**
     * Constructor for FTPSClient, using {@link #DEFAULT_PROTOCOL} - i.e. TLS The default TrustManager is set from
     * {@link TrustManagerUtils#getValidateServerCertificateTrustManager()}
     *
     * @param isImplicit The security mode(Implicit/Explicit).
     * @param context    A pre-configured SSL Context
     */
    public FTPSClient(final boolean isImplicit, final SSLContext context) {
        this(DEFAULT_PROTOCOL, isImplicit);
        this.context = context;
    }

    /**
     * Constructor for FTPSClient, using {@link #DEFAULT_PROTOCOL} - i.e. TLS and isImplicit {@code false} Calls {@link #FTPSClient(boolean, SSLContext)}
     *
     * @param context A pre-configured SSL Context
     */
    public FTPSClient(final SSLContext context) {
        this(false, context);
    }

    /**
     * Constructor for FTPSClient, using explicit mode, calls {@link #FTPSClient(String, boolean)}.
     *
     * @param protocol the protocol to use
     */
    public FTPSClient(final String protocol) {
        this(protocol, false);
    }

    /**
     * Constructor for FTPSClient allowing specification of protocol and security mode. If isImplicit is true, the port is set to {@link #DEFAULT_FTPS_PORT}
     * i.e. 990. The default TrustManager is set from {@link TrustManagerUtils#getValidateServerCertificateTrustManager()}
     *
     * @param protocol   the protocol
     * @param isImplicit The security mode(Implicit/Explicit).
     */
    public FTPSClient(final String protocol, final boolean isImplicit) {
        this.protocol = protocol;
        this.isImplicit = isImplicit;
        if (isImplicit) {
            setDefaultPort(DEFAULT_FTPS_PORT);
        }
    }

    /**
     * Because there are so many connect() methods, the _connectAction_() method is provided as a means of performing some action immediately after establishing
     * a connection, rather than reimplementing all the connect() methods.
     *
     * @throws IOException If there is any problem with establishing the connection.
     * @see org.apache.commons.net.SocketClient#_connectAction_()
     */
    @Override
    protected void _connectAction_() throws IOException {
        // Implicit mode.
        if (isImplicit) {
            applySocketAttributes();
            sslNegotiation();
        }
        super._connectAction_();
        // Explicit mode.
        if (!isImplicit) {
            execAUTH();
            sslNegotiation();
        }
    }

    /**
     * Returns a socket of the data connection. Wrapped as an {@link SSLSocket}, which carries out handshake processing.
     *
     * @param command The int representation of the FTP command to send.
     * @param arg     The arguments to the FTP command. If this parameter is set to null, then the command is sent with no arguments.
     * @return corresponding to the established data connection. Null is returned if an FTP protocol error is reported at any point during the establishment and
     *         initialization of the connection.
     * @throws IOException If there is any problem with the connection.
     * @see FTPClient#_openDataConnection_(int, String)
     * @deprecated (3.3) Use {@link FTPClient#_openDataConnection_(FTPCmd, String)} instead
     */
    @Override
    // Strictly speaking this is not needed, but it works round a Clirr bug
    // So rather than invoke the parent code, we do it here
    @Deprecated
    protected Socket _openDataConnection_(final int command, final String arg) throws IOException {
        return _openDataConnection_(FTPCommand.getCommand(command), arg);
    }

    /**
     * Returns a socket of the data connection. Wrapped as an {@link SSLSocket}, which carries out handshake processing.
     *
     * @param command The textual representation of the FTP command to send.
     * @param arg     The arguments to the FTP command. If this parameter is set to null, then the command is sent with no arguments.
     * @return corresponding to the established data connection. Null is returned if an FTP protocol error is reported at any point during the establishment and
     *         initialization of the connection.
     * @throws IOException If there is any problem with the connection.
     * @see FTPClient#_openDataConnection_(int, String)
     * @since 3.2
     */
    @Override
    protected Socket _openDataConnection_(final String command, final String arg) throws IOException {
        final Socket socket = openDataSecureConnection(command, arg);
        _prepareDataSocket_(socket);
        if (socket instanceof SSLSocket) {
            final SSLSocket sslSocket = (SSLSocket) socket;

            sslSocket.setUseClientMode(isClientMode);
            sslSocket.setEnableSessionCreation(isCreation);

            // server mode
            if (!isClientMode) {
                sslSocket.setNeedClientAuth(isNeedClientAuth);
                sslSocket.setWantClientAuth(isWantClientAuth);
            }
            if (suites != null) {
                sslSocket.setEnabledCipherSuites(suites);
            }
            if (protocols != null) {
                sslSocket.setEnabledProtocols(protocols);
            }
            sslSocket.startHandshake();
        }

        return socket;
    }

    /**
     * Performs any custom initialization for a newly created SSLSocket (before the SSL handshake happens). Called by {@link #_openDataConnection_(int, String)}
     * immediately after creating the socket. The default implementation is a no-op
     *
     * @param socket the socket to set up
     * @throws IOException on error
     * @since 3.1
     */
    protected void _prepareDataSocket_(final Socket socket) throws IOException {
    }

    /**
     * Check the value that can be set in PROT Command value.
     *
     * @param prot Data Channel Protection Level.
     * @return True - A set point is right / False - A set point is not right
     */
    private boolean checkPROTValue(final String prot) {
        for (final String element : PROT_COMMAND_VALUE) {
            if (element.equals(prot)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Closes sockets.
     *
     * @param socket    main socket for proxy if enabled.
     * @param sslSocket SSL socket.
     * @throws IOException closing sockets is not successful.
     */
    private void closeSockets(final Socket socket, final Socket sslSocket) throws IOException {
        IOUtils.close(socket, sslSocket);
    }

    /**
     * Create SSL socket from plain socket.
     *
     * @param socket
     * @return SSL Socket
     * @throws IOException
     */
    private SSLSocket createSSLSocket(final Socket socket) throws IOException {
        if (socket != null) {
            final SSLSocketFactory f = context.getSocketFactory();
            return (SSLSocket) f.createSocket(socket, _hostname_, socket.getPort(), false);
        }
        return null;
    }

    /**
     * Closes the connection to the FTP server and restores connection parameters to the default values.
     * <p>
     * Calls {@code setSocketFactory(null)} and {@code setServerSocketFactory(null)} to reset the factories that may have been changed during the session, e.g.
     * by {@link #execPROT(String)}
     *
     * @throws IOException If an error occurs while disconnecting.
     * @since 3.0
     */
    @Override
    public void disconnect() throws IOException {
        super.disconnect();
        IOUtils.close(plainSocket);
        setSocketFactory(null);
        setServerSocketFactory(null);
    }

    /**
     * Sends the ADAT command with the specified authentication data.
     *
     * @param data The data to send with the command.
     * @return server reply.
     * @throws IOException If an I/O error occurs while sending the command.
     * @since 3.0
     */
    public int execADAT(final byte[] data) throws IOException {
        if (data != null) {
            return sendCommand(CMD_ADAT, Base64.getEncoder().encodeToString(data));
        }
        return sendCommand(CMD_ADAT);
    }

    /**
     * Sends the AUTH command.
     *
     * @throws SSLException If the server reply code equals neither "234" nor "334".
     * @throws IOException  If an I/O error occurs while either sending the command.
     */
    protected void execAUTH() throws SSLException, IOException {
        final int replyCode = sendCommand(CMD_AUTH, auth);
        if (FTPReply.SECURITY_MECHANISM_IS_OK == replyCode) {
            // replyCode = 334
            // I carry out an ADAT command.
        } else if (FTPReply.SECURITY_DATA_EXCHANGE_COMPLETE != replyCode) {
            throw new SSLException(getReplyString());
        }
    }

    /**
     * Sends the AUTH command with the specified mechanism.
     *
     * @param mechanism The mechanism name to send with the command.
     * @return server reply.
     * @throws IOException If an I/O error occurs while sending the command.
     * @since 3.0
     */
    public int execAUTH(final String mechanism) throws IOException {
        return sendCommand(CMD_AUTH, mechanism);
    }

    /**
     * Sends the CCC command to the server. The CCC (Clear Command Channel) command causes the underlying {@link SSLSocket} instance to be assigned to a plain
     * {@link Socket} instances
     *
     * @return server reply.
     * @throws IOException If an I/O error occurs while sending the command.
     * @since 3.0
     */
    public int execCCC() throws IOException {

// This will be performed by sendCommand(String, String)
//        if (FTPReply.isPositiveCompletion(repCode)) {
//            _socket_.close();
//            _socket_ = plainSocket;
//            _controlInput_ = new BufferedReader(
//                new InputStreamReader(
//                    _socket_.getInputStream(), getControlEncoding()));
//            _controlOutput_ = new BufferedWriter(
//                new OutputStreamWriter(
//                    _socket_.getOutputStream(), getControlEncoding()));
//        }
        return sendCommand(CMD_CCC);
    }

    /**
     * Sends the CONF command with the specified data.
     *
     * @param data The data to send with the command.
     * @return server reply.
     * @throws IOException If an I/O error occurs while sending the command.
     * @since 3.0
     */
    public int execCONF(final byte[] data) throws IOException {
        if (data != null) {
            return sendCommand(CMD_CONF, Base64.getEncoder().encodeToString(data));
        }
        return sendCommand(CMD_CONF, ""); // perhaps "=" or just sendCommand(String)?
    }

    /**
     * Sends the ENC command with the specified data.
     *
     * @param data The data to send with the command.
     * @return server reply.
     * @throws IOException If an I/O error occurs while sending the command.
     * @since 3.0
     */
    public int execENC(final byte[] data) throws IOException {
        if (data != null) {
            return sendCommand(CMD_ENC, Base64.getEncoder().encodeToString(data));
        }
        return sendCommand(CMD_ENC, ""); // perhaps "=" or just sendCommand(String)?
    }

    /**
     * Sends the MIC command with the specified data.
     *
     * @param data The data to send with the command.
     * @return server reply.
     * @throws IOException If an I/O error occurs while sending the command.
     * @since 3.0
     */
    public int execMIC(final byte[] data) throws IOException {
        if (data != null) {
            return sendCommand(CMD_MIC, Base64.getEncoder().encodeToString(data));
        }
        return sendCommand(CMD_MIC, ""); // perhaps "=" or just sendCommand(String)?
    }

    /**
     * PBSZ command. pbsz value: 0 to (2^32)-1 decimal integer.
     *
     * @param pbsz Protection Buffer Size.
     * @throws SSLException If the server reply code does not equal "200".
     * @throws IOException  If an I/O error occurs while sending the command.
     * @see #parsePBSZ(long)
     */
    public void execPBSZ(final long pbsz) throws SSLException, IOException {
        if (pbsz < 0 || 4294967295L < pbsz) { // 32-bit unsigned number
            throw new IllegalArgumentException();
        }
        final int status = sendCommand(CMD_PBSZ, String.valueOf(pbsz));
        if (FTPReply.COMMAND_OK != status) {
            throw new SSLException(getReplyString());
        }
    }

    /**
     * PROT command.
     * <ul>
     * <li>C - Clear</li>
     * <li>S - Safe(SSL protocol only)</li>
     * <li>E - Confidential(SSL protocol only)</li>
     * <li>P - Private</li>
     * </ul>
     * <strong>N.B.</strong> the method calls {@link #setSocketFactory(javax.net.SocketFactory)} and
     * {@link #setServerSocketFactory(javax.net.ServerSocketFactory)}
     *
     * @param prot Data Channel Protection Level, if {@code null}, use {@link #DEFAULT_PROT}.
     * @throws SSLException If the server reply code does not equal {@code 200}.
     * @throws IOException  If an I/O error occurs while sending the command.
     */
    public void execPROT(String prot) throws SSLException, IOException {
        if (prot == null) {
            prot = DEFAULT_PROT;
        }
        if (!checkPROTValue(prot)) {
            throw new IllegalArgumentException();
        }
        if (FTPReply.COMMAND_OK != sendCommand(CMD_PROT, prot)) {
            throw new SSLException(getReplyString());
        }
        if (DEFAULT_PROT.equals(prot)) {
            setSocketFactory(null);
            setServerSocketFactory(null);
        } else {
            setSocketFactory(new FTPSSocketFactory(context));
            setServerSocketFactory(new FTPSServerSocketFactory(context));
            initSslContext();
        }
    }

    /**
     * Extract the data from a reply with a prefix, e.g. PBSZ=1234 => 1234
     *
     * @param prefix the prefix to find
     * @param reply  where to find the prefix
     * @return the remainder of the string after the prefix, or null if the prefix was not present.
     */
    private String extractPrefixedData(final String prefix, final String reply) {
        final int idx = reply.indexOf(prefix);
        if (idx == -1) {
            return null;
        }
        // Cannot use trim before substring as leading space would affect the offset.
        return reply.substring(idx + prefix.length()).trim();
    }

    /**
     * Gets AUTH command use value.
     *
     * @return AUTH command use value.
     */
    public String getAuthValue() {
        return auth;
    }

    /**
     * Gets the names of the cipher suites which could be enabled for use on this connection. When the underlying {@link Socket} is not an {@link SSLSocket}
     * instance, returns null.
     *
     * @return An array of cipher suite names, or {@code null}
     */
    public String[] getEnabledCipherSuites() {
        if (_socket_ instanceof SSLSocket) {
            return ((SSLSocket) _socket_).getEnabledCipherSuites();
        }
        return null;
    }

    /**
     * Gets the names of the protocol versions which are currently enabled for use on this connection. When the underlying {@link Socket} is not an
     * {@link SSLSocket} instance, returns null.
     *
     * @return An array of protocols, or {@code null}
     */
    public String[] getEnabledProtocols() {
        if (_socket_ instanceof SSLSocket) {
            return ((SSLSocket) _socket_).getEnabledProtocols();
        }
        return null;
    }

    /**
     * Gets true if new SSL sessions may be established by this socket. When the underlying {@link Socket} instance is not SSL-enabled (i.e. an instance of
     * {@link SSLSocket} with {@link SSLSocket}{@link #getEnableSessionCreation()}) enabled, this returns False.
     *
     * @return true - Indicates that sessions may be created; this is the default. false - indicates that an existing session must be resumed.
     */
    public boolean getEnableSessionCreation() {
        if (_socket_ instanceof SSLSocket) {
            return ((SSLSocket) _socket_).getEnableSessionCreation();
        }
        return false;
    }

    /**
     * Gets the currently configured {@link HostnameVerifier}. The verifier is only used on client mode connections.
     *
     * @return A HostnameVerifier instance.
     * @since 3.4
     */
    public HostnameVerifier getHostnameVerifier() {
        return hostnameVerifier;
    }

    /**
     * Gets the {@link KeyManager} instance.
     *
     * @return The {@link KeyManager} instance
     */
    private KeyManager getKeyManager() {
        return keyManager;
    }

    /**
     * Gets true if the socket will require client authentication. When the underlying {@link Socket} is not an {@link SSLSocket} instance, returns false.
     *
     * @return true - If the server mode socket should request that the client authenticate itself.
     */
    public boolean getNeedClientAuth() {
        if (_socket_ instanceof SSLSocket) {
            return ((SSLSocket) _socket_).getNeedClientAuth();
        }
        return false;
    }

    /**
     * Gets the secure socket protocol to be used, e.g. SSL/TLS.
     *
     * @return the protocol
     * @since 3.11.0
     */
    protected String getProtocol() {
        return protocol;
    }

    /**
     * Gets the protocol versions. The {@link #getEnabledProtocols()} method gets the value from the socket while
     * this method gets its value from this instance's config.
     *
     * @return a clone of the protocols, may be null
     * @since 3.11.0
     */
    protected String[] getProtocols() {
        return protocols == null ? null : protocols.clone();
    }

    /**
     * Gets the cipher suites. The {@link #getEnabledCipherSuites()} method gets the value from the socket while
     * this method gets its value from this instance's config.
     *
     * @return a clone of the suites, may be null
     * @since 3.11.0
     */
    protected String[] getSuites() {
        return suites == null ? null : suites.clone();
    }

    /**
     * Gets the currently configured {@link TrustManager}.
     *
     * @return A TrustManager instance.
     */
    public TrustManager getTrustManager() {
        return trustManager;
    }

    /**
     * Gets whether the socket is set to use client mode in its first handshake. When the underlying {@link Socket} is not an {@link SSLSocket} instance,
     * returns false.
     *
     * @return true - If the socket should start its first handshake in "client" mode.
     */
    public boolean getUseClientMode() {
        if (_socket_ instanceof SSLSocket) {
            return ((SSLSocket) _socket_).getUseClientMode();
        }
        return false;
    }

    /**
     * Gets whether the socket will request client authentication. When the underlying {@link Socket} is not an {@link SSLSocket} instance, returns false.
     *
     * @return true - If the server mode socket should request that the client authenticate itself.
     */
    public boolean getWantClientAuth() {
        if (_socket_ instanceof SSLSocket) {
            return ((SSLSocket) _socket_).getWantClientAuth();
        }
        return false;
    }

    /**
     * Performs a lazy init of the SSL context
     *
     * @throws IOException
     */
    private void initSslContext() throws IOException {
        if (context == null) {
            context = SSLContextUtils.createSSLContext(protocol, getKeyManager(), getTrustManager());
        }
    }

    /**
     * Tests the use client mode flag. The {@link #getUseClientMode()} method gets the value from the socket while
     * this method gets its value from this instance's config.
     *
     * @return True If the socket should start its first handshake in "client" mode.
     * @since 3.11.0
     */
    protected boolean isClientMode() {
        return isClientMode;
    }

    /**
     * Tests whether a new SSL session may be established by this socket. Default true
     *
     * @return True if session may be established
     * @since 3.11.0
     */
    protected boolean isCreation() {
        return isCreation;
    }

    /**
     * Tests whether or not endpoint identification using the HTTPS algorithm on Java 1.7+ is enabled. The default behavior is for this to be disabled.
     *
     * This check is only performed on client mode connections.
     *
     * @return True if enabled, false if not.
     * @since 3.4
     */
    public boolean isEndpointCheckingEnabled() {
        return tlsEndpointChecking;
    }

    /**
     * Tests the security mode. (True - Implicit Mode / False - Explicit Mode).
     *
     * @return True if enabled, false if not.
     * @since 3.11.0
     */
    protected boolean isImplicit() {
        return isImplicit;
    }

    /**
     * Tests the need client auth flag. The {@link #getNeedClientAuth()} method gets the value from the socket while
     * this method gets its value from this instance's config.
     *
     * @return True if enabled, false if not.
     * @since 3.11.0
     */
    protected boolean isNeedClientAuth() {
        return isNeedClientAuth;
    }

    /**
     * Tests the want client auth flag. The {@link #getWantClientAuth()} method gets the value from the socket while
     * this method gets its value from this instance's config.
     *
     * @return True if enabled, false if not.
     * @since 3.11.0
     */
    protected boolean isWantClientAuth() {
        return isWantClientAuth;
    }

    /**
     * Establishes a data connection with the FTP server, returning a Socket for the connection if successful. If a restart offset has been set with
     * {@link #setRestartOffset(long)}, a REST command is issued to the server with the offset as an argument before establishing the data connection. Active
     * mode connections also cause a local PORT command to be issued.
     *
     * @param command The text representation of the FTP command to send.
     * @param arg     The arguments to the FTP command. If this parameter is set to null, then the command is sent with no argument.
     * @return A Socket corresponding to the established data connection. Null is returned if an FTP protocol error is reported at any point during the
     *         establishment and initialization of the connection.
     * @throws IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
     * @since 3.1
     */
    private Socket openDataSecureConnection(final String command, final String arg) throws IOException {
        if (getDataConnectionMode() != ACTIVE_LOCAL_DATA_CONNECTION_MODE && getDataConnectionMode() != PASSIVE_LOCAL_DATA_CONNECTION_MODE) {
            return null;
        }

        final boolean isInet6Address = getRemoteAddress() instanceof Inet6Address;

        final Socket socket;
        Socket sslSocket = null;
        final int soTimeoutMillis = DurationUtils.toMillisInt(getDataTimeout());
        if (getDataConnectionMode() == ACTIVE_LOCAL_DATA_CONNECTION_MODE) {
            // if no activePortRange was set (correctly) -> getActivePort() = 0
            // -> new ServerSocket(0) -> bind to any free local port
            try (ServerSocket server = _serverSocketFactory_.createServerSocket(getActivePort(), 1, getHostAddress())) {
                // Try EPRT only if remote server is over IPv6, if not use PORT,
                // because EPRT has no advantage over PORT on IPv4.
                // It could even have the disadvantage,
                // that EPRT will make the data connection fail, because
                // today's intelligent NAT Firewalls are able to
                // substitute IP addresses in the PORT command,
                // but might not be able to recognize the EPRT command.
                if (isInet6Address) {
                    if (!FTPReply.isPositiveCompletion(eprt(getReportHostAddress(), server.getLocalPort()))) {
                        return null;
                    }
                } else if (!FTPReply.isPositiveCompletion(port(getReportHostAddress(), server.getLocalPort()))) {
                    return null;
                }

                if (getRestartOffset() > 0 && !restart(getRestartOffset())) {
                    return null;
                }

                if (!FTPReply.isPositivePreliminary(sendCommand(command, arg))) {
                    return null;
                }

                // For now, let's just use the data timeout value for waiting for
                // the data connection. It may be desirable to let this be a
                // separately configurable value. In any case, we really want
                // to allow preventing the accept from blocking indefinitely.
                if (soTimeoutMillis >= 0) {
                    server.setSoTimeout(soTimeoutMillis);
                }
                socket = server.accept();

                // Ensure the timeout is set before any commands are issued on the new socket
                if (soTimeoutMillis >= 0) {
                    socket.setSoTimeout(soTimeoutMillis);
                }
                if (getReceiveDataSocketBufferSize() > 0) {
                    socket.setReceiveBufferSize(getReceiveDataSocketBufferSize());
                }
                if (getSendDataSocketBufferSize() > 0) {
                    socket.setSendBufferSize(getSendDataSocketBufferSize());
                }
            }
        } else { // We must be in PASSIVE_LOCAL_DATA_CONNECTION_MODE

            // Try EPSV command first on IPv6 - and IPv4 if enabled.
            // When using IPv4 with NAT it has the advantage
            // to work with more rare configurations.
            // E.g. if FTP server has a static PASV address (external network)
            // and the client is coming from another internal network.
            // In that case the data connection after PASV command would fail,
            // while EPSV would make the client succeed by taking just the port.
            final boolean attemptEPSV = isUseEPSVwithIPv4() || isInet6Address;
            if (attemptEPSV && epsv() == FTPReply.ENTERING_EPSV_MODE) {
                _parseExtendedPassiveModeReply(_replyLines.get(0));
            } else {
                if (isInet6Address) {
                    return null; // Must use EPSV for IPV6
                }
                // If EPSV failed on IPV4, revert to PASV
                if (pasv() != FTPReply.ENTERING_PASSIVE_MODE) {
                    return null;
                }
                _parsePassiveModeReply(_replyLines.get(0));
            }

            if (getProxy() != null) {
                socket = new Socket(getProxy());
            } else {
                socket = _socketFactory_.createSocket();
            }

            if (getReceiveDataSocketBufferSize() > 0) {
                socket.setReceiveBufferSize(getReceiveDataSocketBufferSize());
            }
            if (getSendDataSocketBufferSize() > 0) {
                socket.setSendBufferSize(getSendDataSocketBufferSize());
            }
            if (getPassiveLocalIPAddress() != null) {
                socket.bind(new InetSocketAddress(getPassiveLocalIPAddress(), 0));
            }

            // For now, let's just use the data timeout value for waiting for
            // the data connection. It may be desirable to let this be a
            // separately configurable value. In any case, we really want
            // to allow preventing the accept from blocking indefinitely.
            if (soTimeoutMillis >= 0) {
                socket.setSoTimeout(soTimeoutMillis);
            }

            socket.connect(new InetSocketAddress(getPassiveHost(), getPassivePort()), connectTimeout);

            if (getProxy() != null) {
                sslSocket = context.getSocketFactory().createSocket(socket, getPassiveHost(), getPassivePort(), true);
            }

            if (getRestartOffset() > 0 && !restart(getRestartOffset())) {
                closeSockets(socket, sslSocket);
                return null;
            }

            if (!FTPReply.isPositivePreliminary(sendCommand(command, arg))) {
                closeSockets(socket, sslSocket);
                return null;
            }
        }

        if (isRemoteVerificationEnabled() && !verifyRemote(socket)) {
            // Grab the host before we close the socket to avoid NET-663
            final InetAddress socketHost = socket.getInetAddress();

            closeSockets(socket, sslSocket);

            throw new IOException(
                    "Host attempting data connection " + socketHost.getHostAddress() + " is not same as server " + getRemoteAddress().getHostAddress());
        }

        return getProxy() != null ? sslSocket : socket;
    }

    /**
     * Parses the given ADAT response line and base64-decodes the data.
     *
     * @param reply The ADAT reply to parse.
     * @return the data in the reply, base64-decoded.
     * @since 3.0
     */
    public byte[] parseADATReply(final String reply) {
        if (reply == null) {
            return null;
        }
        return Base64.getDecoder().decode(extractPrefixedData("ADAT=", reply));
    }

    /**
     * PBSZ command. pbsz value: 0 to (2^32)-1 decimal integer. Issues the command and parses the response to return the negotiated value.
     *
     * @param pbsz Protection Buffer Size.
     * @throws SSLException If the server reply code does not equal "200".
     * @throws IOException  If an I/O error occurs while sending the command.
     * @return the negotiated value.
     * @see #execPBSZ(long)
     * @since 3.0
     */
    public long parsePBSZ(final long pbsz) throws SSLException, IOException {
        execPBSZ(pbsz);
        long minvalue = pbsz;
        final String remainder = extractPrefixedData("PBSZ=", getReplyString());
        if (remainder != null) {
            final long replysz = Long.parseLong(remainder);
            if (replysz < minvalue) {
                minvalue = replysz;
            }
        }
        return minvalue;
    }

    // DEPRECATED - for API compatibility only - DO NOT USE

    /**
     * Send an FTP command. A successful CCC (Clear Command Channel) command causes the underlying {@link SSLSocket} instance to be assigned to a plain
     * {@link Socket}
     *
     * @param command The FTP command.
     * @return server reply.
     * @throws IOException  If an I/O error occurs while sending the command.
     * @throws SSLException if a CCC command fails
     * @see org.apache.commons.net.ftp.FTP#sendCommand(String)
     */
    // Would like to remove this method, but that will break any existing clients that are using CCC
    @Override
    public int sendCommand(final String command, final String args) throws IOException {
        final int repCode = super.sendCommand(command, args);
        /* If CCC is issued, restore socket i/o streams to unsecured versions */
        if (CMD_CCC.equals(command)) {
            if (FTPReply.COMMAND_OK != repCode) {
                throw new SSLException(getReplyString());
            }
            _socket_.close();
            _socket_ = plainSocket;
            _controlInput_ = new BufferedReader(new InputStreamReader(_socket_.getInputStream(), getControlEncoding()));
            _controlOutput_ = new BufferedWriter(new OutputStreamWriter(_socket_.getOutputStream(), getControlEncoding()));
        }
        return repCode;
    }

    /**
     * Sets AUTH command use value. This processing is done before connected processing.
     *
     * @param auth AUTH command use value.
     */
    public void setAuthValue(final String auth) {
        this.auth = auth;
    }

    /**
     * Sets which particular cipher suites are enabled for use on this connection. Called before server negotiation.
     *
     * @param cipherSuites The cipher suites.
     */
    public void setEnabledCipherSuites(final String[] cipherSuites) {
        suites = cipherSuites.clone();
    }

    /**
     * Sets which particular protocol versions are enabled for use on this connection. I perform setting before a server negotiation.
     *
     * @param protocolVersions The protocol versions.
     */
    public void setEnabledProtocols(final String[] protocolVersions) {
        protocols = protocolVersions.clone();
    }

    /**
     * Sets whether a new SSL session may be established by this socket.
     *
     * @param isCreation The established socket flag.
     */
    public void setEnabledSessionCreation(final boolean isCreation) {
        this.isCreation = isCreation;
    }

    /**
     * Sets automatic endpoint identification checking using the HTTPS algorithm is supported on Java 1.7+. The default behavior is for this to be disabled.
     *
     * This check is only performed on client mode connections.
     *
     * @param enable Enable automatic endpoint identification checking using the HTTPS algorithm on Java 1.7+.
     * @since 3.4
     */
    public void setEndpointCheckingEnabled(final boolean enable) {
        tlsEndpointChecking = enable;
    }

    /**
     * Sets to override the default {@link HostnameVerifier} to use. The verifier is only used on client mode connections.
     *
     * @param newHostnameVerifier The HostnameVerifier implementation to set or {@code null} to disable.
     * @since 3.4
     */
    public void setHostnameVerifier(final HostnameVerifier newHostnameVerifier) {
        hostnameVerifier = newHostnameVerifier;
    }

    /**
     * Sets a {@link KeyManager} to use
     *
     * @param keyManager The KeyManager implementation to set.
     * @see org.apache.commons.net.util.KeyManagerUtils
     */
    public void setKeyManager(final KeyManager keyManager) {
        this.keyManager = keyManager;
    }

    /**
     * Sets the socket to require client authentication.
     *
     * @param isNeedClientAuth The need client auth flag.
     */
    public void setNeedClientAuth(final boolean isNeedClientAuth) {
        this.isNeedClientAuth = isNeedClientAuth;
    }

    /**
     * Sets to override the default {@link TrustManager} to use; if set to {@code null}, the default TrustManager from the JVM will be used.
     *
     * @param trustManager The TrustManager implementation to set, may be {@code null}
     * @see org.apache.commons.net.util.TrustManagerUtils
     */
    public void setTrustManager(final TrustManager trustManager) {
        this.trustManager = trustManager;
    }

    /**
     * Sets the socket to use client (or server) mode in its first handshake.
     *
     * @param isClientMode The use client mode flag.
     */
    public void setUseClientMode(final boolean isClientMode) {
        this.isClientMode = isClientMode;
    }

    /**
     * Sets the socket to request client authentication, but only if such a request is appropriate to the cipher suite negotiated.
     *
     * @param isWantClientAuth The want client auth flag.
     */
    public void setWantClientAuth(final boolean isWantClientAuth) {
        this.isWantClientAuth = isWantClientAuth;
    }

    /**
     * SSL/TLS negotiation. Acquires an SSL socket of a control connection and carries out handshake processing.
     *
     * @throws IOException If server negotiation fails
     */
    protected void sslNegotiation() throws IOException {
        plainSocket = _socket_;
        initSslContext();
        final SSLSocket socket = createSSLSocket(_socket_);
        socket.setEnableSessionCreation(isCreation);
        socket.setUseClientMode(isClientMode);

        // client mode
        if (isClientMode) {
            if (tlsEndpointChecking) {
                SSLSocketUtils.enableEndpointNameVerification(socket);
            }
        } else { // server mode
            socket.setNeedClientAuth(isNeedClientAuth);
            socket.setWantClientAuth(isWantClientAuth);
        }

        if (protocols != null) {
            socket.setEnabledProtocols(protocols);
        }
        if (suites != null) {
            socket.setEnabledCipherSuites(suites);
        }
        socket.startHandshake();

        // TODO the following setup appears to duplicate that in the super class methods
        _socket_ = socket;
        _controlInput_ = new BufferedReader(new InputStreamReader(socket.getInputStream(), getControlEncoding()));
        _controlOutput_ = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream(), getControlEncoding()));

        if (isClientMode && hostnameVerifier != null && !hostnameVerifier.verify(_hostname_, socket.getSession())) {
            throw new SSLHandshakeException("Hostname doesn't match certificate");
        }
    }
}