FTP Timeout on NLST when directory is empty

EDIT: Learned that Webmethods actually uses NLST, not LIST, if that matters

Our business uses the WebMethods integration server to handle most of our outbound communications, and its FTP functionality leaves something to be desired. We are having a problem that may be specific to WebMethods, but if anyone can point me in a direction of what kinds of things might cause this I'd appreciate it.

When polling two of our partners' FTP servers, we connect without issue but, when doing a NLST on a directory that is empty (no files and no subdirectories) it's timing out. The actual error is:

com.wm.net.ftpCException: [ISC.0064.9010] java.net.SocketTimeoutException: Accept timed out

It's being thrown during the invocation of the pub.client.ftp:ls service. I've logged in with a number of FTP clients without a problem to the same sites. I've used whatever the default FTP client is in windows, FileZilla and lftp. All without issue. The servers themselves aren't the same FTP server software from what I can tell. One is Microsoft FTP, the other I'm uncertain on but is definitely not Microsoft.

Any idea what could cause an FTP client to timeout when waiting for a NLST response on an empty directory? The visible responses from the FTP server appear to be the same, but is there a difference in how NLST responds for an empty directory that I'm unaware of?

This problem is consistent on these two servers. Everything functions fine on directories with files or subdirectories within it, but not when empty.

Any thoughts or directions would be appreciated.

Thanks!

Eric Sipple

Solution

I tried this in WebMethods IS Version 6.5 Updates WmPRT_6-5-1_SP1, IS_6-5_SP3.

It worked perfectly first time.

I turned on debugging on the FTP server (Debian's default ftpd). WebMethods' NLST honours the active/passive parameter passed to it.

There's nothing special about the NLST command, nor its correct behaviour with an empty directory -- if LIST works, then so should RETR, STOR and NLST. If NLST works with a non-empty directory, it should work with an empty one.

So my guess is that either:

Your version of WM has a bug mine doesn't
Your FTP server has a bug mine doesn't
There's a wacky protocol-aware firewall in your system that doesn't like FTP data sockets with no data in them.

Firewall vendors are a bit wayward when it comes to FTP... When testing with other clients, make sure it's from the same machine on which WebMethods Integration Server is running.

Just for the record, here's what should happen for an active NLST

client opens a listening socket, and sends a PORT command with that socket's details
client sends NLST command
server connects to client's listening socket (this is the data socket)
server transmits listing over data socket (in this case, zero bytes)
server closes data socket

... and in passive mode

client sends PASV command
server opens a listening socket, and replies with PASV response containing its details
client connects to listening socket (this is the data socket)
client sends NLST command
server transmits listing over data socket (zero bytes again)
server closes data socket