FTP does not work after being 5 minutes inactive

Question

I have an application that makes simulations.In the beginning of each simulation, FTP connection is created and after that some upload/download files operations are done. then simulation starts.After simulation finishes, again some upload file operations is required for back up simulation related folders

We encounter a problem if simulation takes more than 5 minutes.In the mean time, FTP connection is idle.I get following exceptions.

java.net.SocketException: Software caused connection abort: socket write error
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:202)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:272)
at sun.nio.cs.StreamEncoder.implFlush(StreamEncoder.java:276)
at sun.nio.cs.StreamEncoder.flush(StreamEncoder.java:122)
at java.io.OutputStreamWriter.flush(OutputStreamWriter.java:212)
at java.io.BufferedWriter.flush(BufferedWriter.java:236)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:477)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:537)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:586)
at org.apache.commons.net.ftp.FTP.quit(FTP.java:794)
at org.apache.commons.net.ftp.FTPClient.logout(FTPClient.java:788)


Caused by: java.net.SocketException: Software caused connection abort: recv failed
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:129)
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:264)
at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:306)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:158)
at java.io.InputStreamReader.read(InputStreamReader.java:167)
at java.io.BufferedReader.fill(BufferedReader.java:136)
at java.io.BufferedReader.readLine(BufferedReader.java:299)
at java.io.BufferedReader.readLine(BufferedReader.java:362)
at org.apache.commons.net.ftp.FTP.__getReply(FTP.java:295)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:495)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:537)
at org.apache.commons.net.ftp.FTP.mkd(FTP.java:1363)
at org.apache.commons.net.ftp.FTPClient.makeDirectory(FTPClient.java:1971)

I tried following actions just after simulation is completed, I tried to reinitialize FTP , but no success.I see that connection is active in FTP side

1)FTPClient.isConnected() method returns true

2)When I call FTPClient.connect(), it throws exception FTP is already initialized

3)I tried to set timeouts in connect method of FTP.

public boolean connect() throws IllegalStateException, FileTransferException {
    /*
     * Precondition checks
     */
    final FTPClient clientBefore = this.getClient();
    if (clientBefore != null && clientBefore.isConnected()) {
        throw new IllegalStateException("FTP Client is already initialized");
    }
    // Create the client
    final FTPClient client = new FTPClient();
    client.setConnectTimeout(600000);
    client.setDefaultTimeout(600000);
    // FTPClientConfig conf = new FTPClientConfig(FTPClientConfig.SYST_NT);
    // client.configure(conf);
    log.trace("Connecting to FTP Server at " + config.getCanonicalForm());
    try {
        client.connect(config.getHost(), config.getPort());
        client.setSoTimeout(600000);
    } catch (final IOException ioe) {
        throw new FileTransferException("Error in connecting to " + config.getCanonicalForm(),
                ioe);
    }
    log.trace("Connected to FTP Server at: " + config.getCanonicalForm());
    this.setClient(client);
    // Check that the last operation succeeded
    this.checkLastOperation();
    boolean result;
    try {
        // Login
        if (client.login(config.getUserName(), config.getPassword())) {
            result = true;
            // If there's a pwd defined, cd into it.
            final String pwd = this.getPresentWorkingDirectory();
            if (pwd != null) {
                this.cd(pwd);
            }
        } else {
            result = false;
        }
    } catch (final Exception e) {
        throw new FileTransferException("Could not log in", e);
    }
    return result;
}

Now, I am on deadlock.I do not know what is the problem

Answer 1

If you really have to keep the connection alive, run NOOP commands against the server, so that the control connection remains alive.

Either do it manually:

client.sendNoOp();

Or set the client to do it at fixed interval rates:

client.setControlKeepAliveTimeout(300); // set timeout to 5 minutes

But if you can avoid wasting resources, logout and disconect after the initial download phase, do your local processing and connect / login again for uploading afterwards.

Answer 2

Remember in addition to ftp timeout mentioned by others that any firewalls / NAT in the communication path may time out, in typically less than 5 minutes.

Answer 3

Dive into the source code.

When FTPClient make the control connection connect

client.connect(config.getHost(), config.getPort());

it use some code works like this:

Socket socket = SocketFactory.getDefault().createSocket();

to create a socket to connect to the ftp server.

If you can, set keepalive option to socket, using

socket.setKeepAlive(true);

Hierarchy:

├── SocketClient
│   ├── FTP
│   │   └── FTPClient