Setting connect timeout for FtpClient

Question

When using ftpClient.connect with an existing host who has no ftp service active, timeout occurs only after 5 minutes, which is much too long.

I tried setting diverse timeouts (setDefaultTimeout, setDataTimeout) which did not change anything.

FtpClient inherits from SocketClient which has a setConnectTimeout method, but when I use this I get a java.lang.NoSuchMethodError: org/apache/commons/net/ftp/FTPClient.setConnectTimeout when running it. This seems to be because of some J2SW 1.2 compatibility, as described in Commons-net FAQ:

Q: How can I set a connection timeout? http://wiki.apache.org/commons/Net/FrequentlyAskedQuestions

They suggest to implement an own SocketFactory creating objects from an extended Socket class using a specific timeout. However, when trying to use ftpClient.setSocketFactory I also get a java.lang.NoSuchMethodError.

Any help how I can reduce the connect timeout?

Answer 1

    FTPClient ftp = new FTPClient();

    ftp.setDefaultTimeout();
    ftp.setDataTimeout();
    ftp.setConnectTimeout();
    ftp.setSoTimeout();
    ftp.setControlKeepAliveTimeout();
    ftp.setControlKeepAliveReplyTimeout();

From Apache docs:

   /**
     * 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 an the currently opened socket.  _timeout_ contains
     * the new timeout value.
     * <p>
     * @param timeout  The timeout in milliseconds to use for the socket
     *                 connection.
     */
    void setDefaultTimeout(int timeout);


    /**
     * Sets the timeout in milliseconds to use when reading from the
     * data connection.  This timeout will be set immediately after
     * opening the data connection, provided that the value is &ge; 0.
     * <p>
     * <b>Note:</b> the timeout will also be applied when calling accept()
     * whilst establishing an active local data connection.
     * @param  timeout The default timeout in milliseconds that is used when
     *        opening a data connection socket. The value 0 means an infinite timeout.
     */
    void setDataTimeout(int timeout)
    /**
     * Sets the connection timeout in milliseconds, which will be passed to the {@link java.net.Socket} object's
     * connect() method.
     * @param connectTimeout The connection timeout to use (in ms)
     * @since 2.0
     */
    void setConnectTimeout(int connectTimeout);
    /**
     * 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.
     * @exception SocketException If the operation fails.
     * @throws NullPointerException if the socket is not currently open
     */
    void setSoTimeout(int timeout) throws SocketException;
    /**
     * Set the time to wait between sending control connection keepalive messages
     * when processing file upload or download.
     *
     * @param controlIdle the wait (in secs) between keepalive messages. Zero (or less) disables.
     * @since 3.0
     * @see #setControlKeepAliveReplyTimeout(int)
     */
    void setControlKeepAliveTimeout(long controlIdle);

    /**
     * Set how long to wait for control keep-alive message replies.
     *
     * @param timeout number of milliseconds to wait (defaults to 1000)
     * @since 3.0
     * @see #setControlKeepAliveTimeout(long)
     */
    void setControlKeepAliveReplyTimeout(int timeout)

Answer 2

It must be in the way your calling the setConnectTimeout, because it does exist. setConnectTimeout is not a static call, you must call it after you allocate the FTPClient object and do the set prior to the connect.

FTPClient ftp = new FTPClient();
ftp.setConnectTimeout(5000); // 5000 Milliseconds (5 Seconds)
... 
ftp.connect(server, port); 

Answer 3

Though there is possible solution for that older version of Commons Net library, I suggest to figure out why wrong version of Commons Net is used. To do this you may include following code to the place where FTPClient is used in your webapp:

FTPClient ftpClient = ...;
if(ftpClient.getClass().getClassLoader() instanceof java.net.URLClassLoader) {
    URL[] urls = ((java.net.URLClassLoader) ftpClient.getClass().getClassLoader()).getURLs();
    // log these urls somewhere and check - these are urls from where your FTPClient may be loaded from
}

In case if FTPClient is loaded not by java.net.URLClassLoader then it may get more complicated to check the classpath, though it should not be a problem.

Hope this helps...

Answer 4

Just to add some clarification for these values (after manually testing a lot of combinations, and just to mention that this is related to spring DefaultFtpSessionFactory using underneath apache FTPClient - so applies in the end to that one):

import org.springframework.integration.ftp.session.DefaultFtpSessionFactory;

DefaultFtpSessionFactory factory = new DefaultFtpSessionFactory();

/**
 * Controls 2 values:
 * 1. protected abstract void connect(SocketAddress address, int timeout) throws IOException;
 * --> controls timeout when opening socket connection. this one is by default 0 in java-code,
 * but since OS is controlling this it has some default value - for me in win.
 * it was ~20 seconds. If set to lower value it will be respected. If set >20 in my case,
 * it always treats it as if 20 was set
 * 2. _socket_.setSoTimeout(connectTimeout);
 * --> controls timeout after socket is open (so if FTP server is not responding after
 * socket is successfully connected). Default is unlimited so good to set to some sane value
 * otherwise if no response from FTP Server, connection will hang. Overwrites setDefaultTimeout
 * if already set - but only for this connection time (not after FTP server responds first time
 * with some data).
 */
factory.setConnectTimeout((int) Duration.ofMinutes(1).toMillis());

/**
 * Controls timeout after socket is open (so if FTP server is not responding after socket is
 * successfully connected).(IF NOT ALREADY SET IN setConnectTimeout),
 * but also controls timeout when reading data from socket after the connection has been made.
 * So if FTP client sends "LIST /" command, and there is no answer from FTP server, without
 * setting this it will hang (since default is 0). Set to some sane value
 * (since server can actually be busy with creating listing of folders for longer time etc.).
 */
factory.setDefaultTimeout((int) Duration.ofMinutes(1).toMillis());

/**
 * Controls how long to wait if there is a socket inactivity during FILE-related operations.
 * E.g. if we start to download some file from FTP server, this timeout is respected.
 * This is by default set to 0 (that is infinite wait). If set to 10 seconds, and there is at
 * least some activity in communication (eg. every 9 seconds something is received) then there
 * will be no timeout. Only if there is some delay/inactivity for longer than 10 seconds then
 * there will be socketRead0 timeout exception. Should be set, since this is not affected by
 * setConnectTimeout or setDefaultTimeout.
 */
factory.setDataTimeout((int) Duration.ofMinutes(1).toMillis());