In certain error/failure circumstances ftpClient.listFiles(param) returns an
empty list instead of null or an exception
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Key: NET-427
URL: https://issues.apache.org/jira/browse/NET-427
Project: Commons Net
Issue Type: Bug
Components: FTP
Affects Versions: 3.0.1
Environment: SunOS 5.10 Generic_144489-06
Reporter: Mario Zannone
Priority: Minor
According to the API docs ftpClient.listFiles(String) should return
null or an exception on error conditions or failure:
The convention for all the FTP command methods in FTPClient is
such that they either return a boolean value or some other value.
The boolean methods return true on a successful completion reply
from the FTP server and false on a reply resulting in an error
condition or failure. The methods returning a value other than
boolean return a value containing the higher level data produced
by the FTP command, or null if a reply resulted in an error
condition or failure.
(
http://commons.apache.org/net/apidocs/org/apache/commons/net/ftp/FTPClient.html
)
However in certain error/failure circumstances listFiles(param)
returns an empty list instead of null.
Note that an empty list is a correct response when param does not
match any file.
We were able to bypass the problem checking the ftp reply with
getReplyCode(). However, this listFiles behaviour is unexpected
and should at least be documented.
The error is not systematic and not easy to diagnose or replicate.
We were able to reproduce it using cron to run the attached
program every minute on a slow and unreliable connection;
in 24h the error did show only a couple of times.
Attachments: test program and excerpt from the test log.
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