[net] FTP: NoSuchMethodError thrown when sending command to disconnected FTP server

• Key: NET-102
• Type: Bug
• Status: Closed
• Resolution: Fixed
• Priority: Critical
• Assignee: Unassigned
• Reporter: Anton Spaans
• Affects Version/s: 1.3

Environment

Operating System: Windows 2000
Platform: PC

Description

• This bug only happens when running under JDK1.3.x or lower.
  (when running under JDK1.4.x or higher, this bug does not happen)
• Create and configure an FTP server. Make sure it runs OK.

• Create a program and run it under JDK1.3.x or lower:
  === Test Program ===================================
  ...
  ...
  // Connect to the above FTP server and login
  // Check that everything went fine.
  ...
  while (true)
  {
  try { FTPFile[] files = ftpClient.listFiles("*"); showFiles(files); }
  catch (FTPConnectionClosedException fcce) { // Oops.. the FTP server has been disconnected. System.out.println("Disconnected from FTP Server. Ending prog."); break; // while(true) }
  Thread.sleep(3000);
  }
  ... // close/disconnect and clean-up.
  ...
  ====================================================

• Run the above program. The ftpClient.listFiles(...) works OK.
• At some point, stop the FTP server.

=== Expected result: ===============================
Program ends normally with message "Disconnected from FTP Server. Ending prog."
====================================================

=== Actual result: =================================
Pogram throws java.lang.NoSuchMethodError.
====================================================

=== Stacktrace: ====================================
java.lang.NoSuchMethodError
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:442)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:484)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:533)
at org.apache.commons.net.ftp.FTP.pasv(FTP.java:833)
at org.apache.commons.net.ftp.FTPClient.openDataConnection
(FTPClient.java:493)
at org.apache.commons.net.ftp.FTPClient.initiateListParsing
(FTPClient.java:2356)
at org.apache.commons.net.ftp.FTPClient.initiateListParsing
(FTPClient.java:2330)
at org.apache.commons.net.ftp.FTPClient.listFiles(FTPClient.java:2072)
at org.apache.commons.net.ftp.FTPClient.listFiles(FTPClient.java:2123)
====================================================

=== Probable cause: ================================
The FTP.sendCommand(...) method, on line 442 is as follows:

if (!isConnected() || socket == null || !socket.isConnected())

The 'socket' variable is of type 'java.net.Socket'.
Under JKD1.3, the 'java.net.Socket' class does NOT implement 'isConnected()'.
====================================================

Why this bug is "P1 & critical": If the FTP Server closed the connection (e.g.
due to a time-out), our code catches the FTPConnectionClosedException exception
and tries to reconnect to the server. If this exception is not thrown, but the
NoSuchMethodError is thrown instead, our code fails.

PS: It is hard to find information about which JDK-versions support the
Commons/Net component. This page (http://jakarta.apache.org/commons/net/changes-
report.html#1_3_0), indicates that the component should run correctly at least
under JDK1.3.x.

Comments

[Anton Spaans]

I'm not sure, but it looks like that this bug is related to the fix/patch for
COM-1663 (the patch from "2004-12-30 08:57" never made it into version
1.3.Final...?).

[Rory Winston]

Patch applied.