/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.net;

import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Proxy;
import java.net.Socket;
import java.net.SocketException;
import java.nio.charset.Charset;

import javax.net.ServerSocketFactory;
import javax.net.SocketFactory;

/**
 * The SocketClient provides the basic operations that are required of client objects accessing sockets. It is meant to be subclassed to avoid having to rewrite
 * the same code over and over again to open a socket, close a socket, set timeouts, etc. Of special note is the {@link #setSocketFactory setSocketFactory }
 * method, which allows you to control the type of Socket the SocketClient creates for initiating network connections. This is especially useful for adding SSL
 * or proxy support as well as better support for applets. For example, you could create a {@link javax.net.SocketFactory} that requests browser security
 * capabilities before creating a socket. All classes derived from SocketClient should use the {@link #_socketFactory_ _socketFactory_ } member variable to
 * create Socket and ServerSocket instances rather than instantiating them by directly invoking a constructor. By honoring this contract you guarantee that a
 * user will always be able to provide his own Socket implementations by substituting his own SocketFactory.
 *
 * @see SocketFactory
 */
public abstract class SocketClient {
    /**
     * The end of line character sequence used by most IETF protocols. That is a carriage return followed by a newline: "\r\n"
     */
    public static final String NETASCII_EOL = "\r\n";

    /** The default SocketFactory shared by all SocketClient instances. */
    private static final SocketFactory DEFAULT_SOCKET_FACTORY = SocketFactory.getDefault();

    /** The default {@link ServerSocketFactory} */
    private static final ServerSocketFactory DEFAULT_SERVER_SOCKET_FACTORY = ServerSocketFactory.getDefault();

    /** The socket's connect timeout (0 = infinite timeout) */
    private static final int DEFAULT_CONNECT_TIMEOUT = 60000;

    /**
     * A ProtocolCommandSupport object used to manage the registering of ProtocolCommandListeners and the firing of ProtocolCommandEvents.
     */
    private ProtocolCommandSupport commandSupport;

    /** The timeout to use after opening a socket. */
    protected int _timeout_;

    /** The socket used for the connection. */
    protected Socket _socket_;

    /** The hostname used for the connection (null = no hostname supplied). */
    protected String _hostname_;

    /** The remote socket address used for the connection. */
    protected InetSocketAddress remoteInetSocketAddress;

    /** The default port the client should connect to. */
    protected int _defaultPort_;

    /** The socket's InputStream. */
    protected InputStream _input_;

    /** The socket's OutputStream. */
    protected OutputStream _output_;

    /** The socket's SocketFactory. */
    protected SocketFactory _socketFactory_;

    /** The socket's ServerSocket Factory. */
    protected ServerSocketFactory _serverSocketFactory_;

    protected int connectTimeout = DEFAULT_CONNECT_TIMEOUT;

    /** Hint for SO_RCVBUF size */
    private int receiveBufferSize = -1;

    /** Hint for SO_SNDBUF size */
    private int sendBufferSize = -1;

    /** The proxy to use when connecting. */
    private Proxy connProxy;

    /**
     * Charset to use for byte IO.
     */
    private Charset charset = Charset.defaultCharset();

    /**
     * Default constructor for SocketClient. Initializes _socket_ to null, _timeout_ to 0, _defaultPort to 0, _isConnected_ to false, charset to
     * {@code Charset.defaultCharset()} and _socketFactory_ to a shared instance of {@link org.apache.commons.net.DefaultSocketFactory}.
     */
    public SocketClient() {
        _socket_ = null;
        _hostname_ = null;
        _input_ = null;
        _output_ = null;
        _timeout_ = 0;
        _defaultPort_ = 0;
        _socketFactory_ = DEFAULT_SOCKET_FACTORY;
        _serverSocketFactory_ = DEFAULT_SERVER_SOCKET_FACTORY;
    }

    // helper method to allow code to be shared with connect(String,...) methods
    private void _connect(final InetSocketAddress remoteInetSocketAddress, final InetAddress localAddr, final int localPort) throws IOException {
        this.remoteInetSocketAddress = remoteInetSocketAddress;
        _socket_ = _socketFactory_.createSocket();
        if (receiveBufferSize != -1) {
            _socket_.setReceiveBufferSize(receiveBufferSize);
        }
        if (sendBufferSize != -1) {
            _socket_.setSendBufferSize(sendBufferSize);
        }
        if (localAddr != null) {
            _socket_.bind(new InetSocketAddress(localAddr, localPort));
        }
        _socket_.connect(remoteInetSocketAddress, connectTimeout);
        _connectAction_();
    }

    /**
     * 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. The last action performed by every connect() method after opening a socket is to
     * call this method.
     * <p>
     * This method sets the timeout on the just opened socket to the default timeout set by {@link #setDefaultTimeout setDefaultTimeout() }, sets _input_ and
     * _output_ to the socket's InputStream and OutputStream respectively, and sets _isConnected_ to true.
     * <p>
     * Subclasses overriding this method should start by calling <code> super._connectAction_() </code> first to ensure the initialization of the aforementioned
     * protected variables.
     *
     * @throws IOException (SocketException) if a problem occurs with the socket
     */
    protected void _connectAction_() throws IOException {
        applySocketAttributes();
        _input_ = _socket_.getInputStream();
        _output_ = _socket_.getOutputStream();
    }

    /**
     * Adds a ProtocolCommandListener.
     *
     * @param listener The ProtocolCommandListener to add.
     * @since 3.0
     */
    public void addProtocolCommandListener(final ProtocolCommandListener listener) {
        getCommandSupport().addProtocolCommandListener(listener);
    }

    /**
     * Applies socket attributes.
     *
     * @throws SocketException if there is an error in the underlying protocol, such as a TCP error.
     * @since 3.8.0
     */
    protected void applySocketAttributes() throws SocketException {
        _socket_.setSoTimeout(_timeout_);
    }

    private void closeQuietly(final Closeable close) {
        if (close != null) {
            try {
                close.close();
            } catch (final IOException e) {
                // Ignored
            }
        }
    }

    private void closeQuietly(final Socket socket) {
        if (socket != null) {
            try {
                socket.close();
            } catch (final IOException e) {
                // Ignored
            }
        }
    }

    /**
     * Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port. Before returning,
     * {@link #_connectAction_ _connectAction_() } is called to perform connection initialization actions.
     *
     * @param host The remote host.
     * @throws SocketException If the socket timeout could not be set.
     * @throws IOException     If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from
     *                         it.
     */
    public void connect(final InetAddress host) throws SocketException, IOException {
        _hostname_ = null;
        connect(host, _defaultPort_);
    }

    /**
     * Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port. Before returning,
     * {@link #_connectAction_ _connectAction_() } is called to perform connection initialization actions.
     *
     * @param host The remote host.
     * @param port The port to connect to on the remote host.
     * @throws SocketException If the socket timeout could not be set.
     * @throws IOException     If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from
     *                         it.
     */
    public void connect(final InetAddress host, final int port) throws SocketException, IOException {
        _hostname_ = null;
        _connect(new InetSocketAddress(host, port), null, -1);
    }

    /**
     * Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port. Before returning,
     * {@link #_connectAction_ _connectAction_() } is called to perform connection initialization actions.
     *
     * @param host      The remote host.
     * @param port      The port to connect to on the remote host.
     * @param localAddr The local address to use.
     * @param localPort The local port to use.
     * @throws SocketException If the socket timeout could not be set.
     * @throws IOException     If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from
     *                         it.
     */
    public void connect(final InetAddress host, final int port, final InetAddress localAddr, final int localPort) throws SocketException, IOException {
        _hostname_ = null;
        _connect(new InetSocketAddress(host, port), localAddr, localPort);
    }

    /**
     * Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port. Before returning,
     * {@link #_connectAction_ _connectAction_() } is called to perform connection initialization actions.
     *
     * @param hostname The name of the remote host.
     * @throws SocketException               If the socket timeout could not be set.
     * @throws IOException                   If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is
     *                                       derived from it.
     * @throws java.net.UnknownHostException If the hostname cannot be resolved.
     */
    public void connect(final String hostname) throws SocketException, IOException {
        connect(hostname, _defaultPort_);
    }

    /**
     * Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port. Before returning,
     * {@link #_connectAction_ _connectAction_() } is called to perform connection initialization actions.
     *
     * @param hostname The name of the remote host.
     * @param port     The port to connect to on the remote host.
     * @throws SocketException               If the socket timeout could not be set.
     * @throws IOException                   If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is
     *                                       derived from it.
     * @throws java.net.UnknownHostException If the hostname cannot be resolved.
     */
    public void connect(final String hostname, final int port) throws SocketException, IOException {
        connect(hostname, port, null, -1);
    }

    /**
     * Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port. Before returning,
     * {@link #_connectAction_ _connectAction_() } is called to perform connection initialization actions.
     *
     * @param hostname  The name of the remote host.
     * @param port      The port to connect to on the remote host.
     * @param localAddr The local address to use.
     * @param localPort The local port to use.
     * @throws SocketException               If the socket timeout could not be set.
     * @throws IOException                   If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is
     *                                       derived from it.
     * @throws java.net.UnknownHostException If the hostname cannot be resolved.
     */
    public void connect(final String hostname, final int port, final InetAddress localAddr, final int localPort) throws SocketException, IOException {
        _hostname_ = hostname;
        _connect(new InetSocketAddress(hostname, port), localAddr, localPort);
    }

    /**
     * Create the CommandSupport instance if required
     */
    protected void createCommandSupport() {
        commandSupport = new ProtocolCommandSupport(this);
    }

    /**
     * Disconnects the socket connection. You should call this method after you've finished using the class instance and also before you call {@link #connect
     * connect() } again. _isConnected_ is set to false, _socket_ is set to null, _input_ is set to null, and _output_ is set to null.
     *
     * @throws IOException If there is an error closing the socket.
     */
    public void disconnect() throws IOException {
        closeQuietly(_socket_);
        closeQuietly(_input_);
        closeQuietly(_output_);
        _socket_ = null;
        _hostname_ = null;
        _input_ = null;
        _output_ = null;
    }

    /**
     * If there are any listeners, send them the command details.
     *
     * @param command the command name
     * @param message the complete message, including command name
     * @since 3.0
     */
    protected void fireCommandSent(final String command, final String message) {
        if (getCommandSupport().getListenerCount() > 0) {
            getCommandSupport().fireCommandSent(command, message);
        }
    }

    /**
     * If there are any listeners, send them the reply details.
     *
     * @param replyCode the code extracted from the reply
     * @param reply     the full reply text
     * @since 3.0
     */
    protected void fireReplyReceived(final int replyCode, final String reply) {
        if (getCommandSupport().getListenerCount() > 0) {
            getCommandSupport().fireReplyReceived(replyCode, reply);
        }
    }

    /**
     * Gets the charset.
     *
     * @return the charset.
     * @since 3.3
     */
    public Charset getCharset() {
        return charset;
    }

    /**
     * Gets the charset name.
     *
     * @return the charset.
     * @since 3.3
     * @deprecated Since the code now requires Java 1.6 as a minimum
     */
    @Deprecated
    public String getCharsetName() {
        return charset.name();
    }

    /**
     * Subclasses can override this if they need to provide their own instance field for backwards compatibility.
     *
     * @return the CommandSupport instance, may be {@code null}
     * @since 3.0
     */
    protected ProtocolCommandSupport getCommandSupport() {
        return commandSupport;
    }

    /**
     * Get the underlying socket connection timeout.
     *
     * @return timeout (in ms)
     * @since 2.0
     */
    public int getConnectTimeout() {
        return connectTimeout;
    }

    /**
     * Returns the current value of the default port (stored in {@link #_defaultPort_ _defaultPort_ }).
     *
     * @return The current value of the default port.
     */
    public int getDefaultPort() {
        return _defaultPort_;
    }

    /**
     * Returns the default timeout in milliseconds that is used when opening a socket.
     *
     * @return The default timeout in milliseconds that is used when opening a socket.
     */
    public int getDefaultTimeout() {
        return _timeout_;
    }

    /**
     * Returns the current value of the SO_KEEPALIVE flag on the currently opened socket. Delegates to {@link Socket#getKeepAlive()}
     *
     * @return True if SO_KEEPALIVE is enabled.
     * @throws SocketException      if there is a problem with the socket
     * @throws NullPointerException if the socket is not currently open
     * @since 2.2
     */
    public boolean getKeepAlive() throws SocketException {
        return _socket_.getKeepAlive();
    }

    /**
     * Returns the local address to which the client's socket is bound. Delegates to {@link Socket#getLocalAddress()}
     *
     * @return The local address to which the client's socket is bound.
     * @throws NullPointerException if the socket is not currently open
     */
    public InetAddress getLocalAddress() {
        return _socket_.getLocalAddress();
    }

    /**
     * Returns the port number of the open socket on the local host used for the connection. Delegates to {@link Socket#getLocalPort()}
     *
     * @return The port number of the open socket on the local host used for the connection.
     * @throws NullPointerException if the socket is not currently open
     */
    public int getLocalPort() {
        return _socket_.getLocalPort();
    }

    /**
     * Gets the proxy for use with all the connections.
     *
     * @return the current proxy for connections.
     */
    public Proxy getProxy() {
        return connProxy;
    }

    /**
     * Get the current receivedBuffer size
     *
     * @return the size, or -1 if not initialized
     * @since 3.0
     */
    protected int getReceiveBufferSize() {
        return receiveBufferSize;
    }

    /**
     * @return The remote address to which the client is connected. Delegates to {@link Socket#getInetAddress()}
     * @throws NullPointerException if the socket is not currently open
     */
    public InetAddress getRemoteAddress() {
        return _socket_.getInetAddress();
    }

    /**
     * Gets the remote socket address used for the connection.
     *
     * @return the remote socket address used for the connection
     * @since 3.10.0
     */
    protected InetSocketAddress getRemoteInetSocketAddress() {
        return remoteInetSocketAddress;
    }

    /**
     * Returns the port number of the remote host to which the client is connected. Delegates to {@link Socket#getPort()}
     *
     * @return The port number of the remote host to which the client is connected.
     * @throws NullPointerException if the socket is not currently open
     */
    public int getRemotePort() {
        return _socket_.getPort();
    }

    /**
     * Get the current sendBuffer size
     *
     * @return the size, or -1 if not initialized
     * @since 3.0
     */
    protected int getSendBufferSize() {
        return sendBufferSize;
    }

    /**
     * Get the underlying {@link ServerSocketFactory}
     *
     * @return The server socket factory
     * @since 2.2
     */
    public ServerSocketFactory getServerSocketFactory() {
        return _serverSocketFactory_;
    }

    /**
     * Returns the current SO_LINGER timeout of the currently opened socket.
     *
     * @return The current SO_LINGER timeout. If SO_LINGER is disabled returns -1.
     * @throws SocketException      If the operation fails.
     * @throws NullPointerException if the socket is not currently open
     */
    public int getSoLinger() throws SocketException {
        return _socket_.getSoLinger();
    }

    /**
     * Returns the timeout in milliseconds of the currently opened socket.
     *
     * @return The timeout in milliseconds of the currently opened socket.
     * @throws SocketException      If the operation fails.
     * @throws NullPointerException if the socket is not currently open
     */
    public int getSoTimeout() throws SocketException {
        return _socket_.getSoTimeout();
    }

    /**
     * Returns true if Nagle's algorithm is enabled on the currently opened socket.
     *
     * @return True if Nagle's algorithm is enabled on the currently opened socket, false otherwise.
     * @throws SocketException      If the operation fails.
     * @throws NullPointerException if the socket is not currently open
     */
    public boolean getTcpNoDelay() throws SocketException {
        return _socket_.getTcpNoDelay();
    }

    /**
     * Make various checks on the socket to test if it is available for use. Note that the only sure test is to use it, but these checks may help in some cases.
     *
     * @see <a href="https://issues.apache.org/jira/browse/NET-350">NET-350</a>
     * @return {@code true} if the socket appears to be available for use
     * @since 3.0
     */
    @SuppressWarnings("resource")
    public boolean isAvailable() {
        if (isConnected()) {
            try {
                if (_socket_.getInetAddress() == null) {
                    return false;
                }
                if (_socket_.getPort() == 0) {
                    return false;
                }
                if (_socket_.getRemoteSocketAddress() == null) {
                    return false;
                }
                if (_socket_.isClosed()) {
                    return false;
                }
                /*
                 * these aren't exact checks (a Socket can be half-open), but since we usually require two-way data transfer, we check these here too:
                 */
                if (_socket_.isInputShutdown()) {
                    return false;
                }
                if (_socket_.isOutputShutdown()) {
                    return false;
                }
                /* ignore the result, catch exceptions: */
                // No need to close
                _socket_.getInputStream();
                // No need to close
                _socket_.getOutputStream();
            } catch (final IOException ioex) {
                return false;
            }
            return true;
        }
        return false;
    }

    /**
     * Returns true if the client is currently connected to a server.
     *
     * Delegates to {@link Socket#isConnected()}
     *
     * @return True if the client is currently connected to a server, false otherwise.
     */
    public boolean isConnected() {
        if (_socket_ == null) {
            return false;
        }

        return _socket_.isConnected();
    }

    /**
     * Removes a ProtocolCommandListener.
     *
     * @param listener The ProtocolCommandListener to remove.
     * @since 3.0
     */
    public void removeProtocolCommandListener(final ProtocolCommandListener listener) {
        getCommandSupport().removeProtocolCommandListener(listener);
    }

    /**
     * Sets the charset.
     *
     * @param charset the charset.
     * @since 3.3
     */
    public void setCharset(final Charset charset) {
        this.charset = charset;
    }

    /**
     * Sets the connection timeout in milliseconds, which will be passed to the {@link Socket} object's connect() method.
     *
     * @param connectTimeout The connection timeout to use (in ms)
     * @since 2.0
     */
    public void setConnectTimeout(final int connectTimeout) {
        this.connectTimeout = connectTimeout;
    }

    /**
     * Sets the default port the SocketClient should connect to when a port is not specified. The {@link #_defaultPort_ _defaultPort_ } variable stores this
     * value. If never set, the default port is equal to zero.
     *
     * @param port The default port to set.
     */
    public void setDefaultPort(final int port) {
        _defaultPort_ = port;
    }

    /**
     * Set the default timeout in milliseconds to use when opening a socket. This value is only used previous to a call to {@link #connect connect()} and should
     * not be confused with {@link #setSoTimeout setSoTimeout()} which operates on the currently opened socket. _timeout_ contains the new timeout value.
     *
     * @param timeout The timeout in milliseconds to use for the socket connection.
     */
    public void setDefaultTimeout(final int timeout) {
        _timeout_ = timeout;
    }

    /**
     * Sets the SO_KEEPALIVE flag on the currently opened socket.
     *
     * From the Javadocs, the default keepalive time is 2 hours (although this is implementation dependent). It looks as though the Windows WSA sockets
     * implementation allows a specific keepalive value to be set, although this seems not to be the case on other systems.
     *
     * @param keepAlive If true, keepAlive is turned on
     * @throws SocketException      if there is a problem with the socket
     * @throws NullPointerException if the socket is not currently open
     * @since 2.2
     */
    public void setKeepAlive(final boolean keepAlive) throws SocketException {
        _socket_.setKeepAlive(keepAlive);
    }

    /**
     * Sets the proxy for use with all the connections. The proxy is used for connections established after the call to this method.
     *
     * @param proxy the new proxy for connections.
     * @since 3.2
     */
    public void setProxy(final Proxy proxy) {
        setSocketFactory(new DefaultSocketFactory(proxy));
        connProxy = proxy;
    }

    /**
     * Sets the underlying socket receive buffer size.
     *
     * @param size The size of the buffer in bytes.
     * @throws SocketException never (but subclasses may wish to do so)
     * @since 2.0
     */
    public void setReceiveBufferSize(final int size) throws SocketException {
        receiveBufferSize = size;
    }

    /**
     * Set the underlying socket send buffer size.
     *
     * @param size The size of the buffer in bytes.
     * @throws SocketException never thrown, but subclasses might want to do so
     * @since 2.0
     */
    public void setSendBufferSize(final int size) throws SocketException {
        sendBufferSize = size;
    }

    /**
     * Sets the ServerSocketFactory used by the SocketClient to open ServerSocket connections. If the factory value is null, then a default factory is used
     * (only do this to reset the factory after having previously altered it).
     *
     * @param factory The new ServerSocketFactory the SocketClient should use.
     * @since 2.0
     */
    public void setServerSocketFactory(final ServerSocketFactory factory) {
        if (factory == null) {
            _serverSocketFactory_ = DEFAULT_SERVER_SOCKET_FACTORY;
        } else {
            _serverSocketFactory_ = factory;
        }
    }

    /**
     * Sets the SocketFactory used by the SocketClient to open socket connections. If the factory value is null, then a default factory is used (only do this to
     * reset the factory after having previously altered it). Any proxy setting is discarded.
     *
     * @param factory The new SocketFactory the SocketClient should use.
     */
    public void setSocketFactory(final SocketFactory factory) {
        if (factory == null) {
            _socketFactory_ = DEFAULT_SOCKET_FACTORY;
        } else {
            _socketFactory_ = factory;
        }
    }

    /**
     * Sets the SO_LINGER timeout on the currently opened socket.
     *
     * @param on  True if linger is to be enabled, false if not.
     * @param val The {@code linger} timeout (in hundredths of a second?)
     * @throws SocketException      If the operation fails.
     * @throws NullPointerException if the socket is not currently open
     */
    public void setSoLinger(final boolean on, final int val) throws SocketException {
        _socket_.setSoLinger(on, val);
    }

    /**
     * Set the timeout in milliseconds of a currently open connection. Only call this method after a connection has been opened by {@link #connect connect()}.
     * <p>
     * To set the initial timeout, use {@link #setDefaultTimeout(int)} instead.
     *
     * @param timeout The timeout in milliseconds to use for the currently open socket connection.
     * @throws SocketException      If the operation fails.
     * @throws NullPointerException if the socket is not currently open
     */
    public void setSoTimeout(final int timeout) throws SocketException {
        _socket_.setSoTimeout(timeout);
    }

    /**
     * Enables or disables the Nagle's algorithm (TCP_NODELAY) on the currently opened socket.
     *
     * @param on True if Nagle's algorithm is to be enabled, false if not.
     * @throws SocketException      If the operation fails.
     * @throws NullPointerException if the socket is not currently open
     */
    public void setTcpNoDelay(final boolean on) throws SocketException {
        _socket_.setTcpNoDelay(on);
    }

    /**
     * Verifies that the remote end of the given socket is connected to the same host that the SocketClient is currently connected to. This is useful for
     * doing a quick security check when a client needs to accept a connection from a server, such as an FTP data connection or a BSD R command standard error
     * stream.
     *
     * @param socket the item to check against
     * @return True if the remote hosts are the same, false if not.
     */
    public boolean verifyRemote(final Socket socket) {
        final InetAddress host1;
        final InetAddress host2;

        host1 = socket.getInetAddress();
        host2 = getRemoteAddress();

        return host1.equals(host2);
    }

    /*
     * N.B. Fields cannot be pulled up into a super-class without breaking binary compatibility, so the abstract method is needed to pass the instance to the
     * methods which were moved here.
     */
}