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Re: [Bug-wget] New option "--no-list-a"

From: Steven M. Schweda
Subject: Re: [Bug-wget] New option "--no-list-a"
Date: Sat, 31 Aug 2013 10:24:10 -0500 (CDT)

> some systems (at least info-zip.org) have problems with the ftp
> command "LIST -a".

   If you use an interactive FTP client with that system, you might
notice some interesting things about that FTP server.  For example:

220 server.tmk.com MultiNet FTP Server Process V5.3(17) at [...]

That is, it's part of a third-party (Process Software) IP software
package for a VMS system.  Also:

230- The default listing format is Unix-style. For VMS-style, say "cd []".

There's some code in Wget to deal with the way this particular FTP
server can switch listing formats (between UNIX-ls-like and

   In my (limited) experience, generally, "LIST -a", though
non-standard, is interpreted as desired by FTP servers on UNIX(-like)
systems, but it can be expected to cause problems with other FTP
servers, including some which try to emulate a UNIX(-like) FTP server. 
Which is why there's VMS-specific code to avoid it for FTP servers
which identify themselves as "VMS".  Apparently, this MultiNet FTP
server is configured to provide a file listing in a UNIX-like format (at
least initially), but that does not mean that it emulates all features
of a typical UNIX(-like) FTP server.

   I'd guess that the (vast?) majority of FTP servers which look like
UNIX(-like) FTP servers would deal with "LIST -a" as expected, but some
will not.  I was content to deal with the problem on obviously VMS FTP
servers, but this MultiNet FTP server is one which can try to look
UNIX-like, but which does not do "LIST -a" as expected.  I doubt that a
good, general solution exists.  Asking the user to specify "--no-list-a"
seems far from ideal.

> - if LIST -a returns an empty listing, Wget should fallback to LIST

Looking for an empty listing from "LIST -a" will work in some (most?)
cases, and it's simple, but what happens if there's a file named "-a" on
the server?  It might actually be smarter to look at SYST output, and
maintain a list of UNIX(-like) servers where "LIST -a" is known to fail. 
It might be ugly, but it might also be more reliable than other ways.
For the first one on the list, I'd nominate this one:

FTP> quote "SYST"
215 UNIX MultiNet Unix Emulation V5.3(93)

Recognizing "MultiNet" should be good enough.

   Of course, the fundamental problem here is the way "ls" on a
UNIX(-like) system (and, hence, a typical FTP LIST) can't be trusted to
provide a complete directory listing.  But there's no chance of getting
all those FTP servers fixed, either.


   Steven M. Schweda               address@hidden
   382 South Warwick Street        (+1) 651-699-9818
   Saint Paul  MN  55105-2547

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