[Zope-dev] ZServer and ftp port-1 data channel

[Kent Polk]

On 26 Sep 2000 12:50:00 -0500, Shane Hathaway wrote:
>Here's what Sam Rushing told me regarding this issue.
>
>Shane Hathaway writes:
> > I hear that you have found a way to get Medusa to use the correct
>port
> > in active mode FTP.  This could be a great benefit to the Zope
> > community.  Anything you have (diffs, modified files, or any kind of
> > info) on the subject would be very much appreciated.
>
(Sam writes:)
 [...]

>See the 'bind_local_minus_one' variable of the ftp_channel class.
>This should be checked into the medusa cvs, but I'll attach a copy as
>well.
>
>    /* According to one expert, the very nature of the FTP protocol,
>     * and it's multiple data-connections creates problems with
>     * "rapid-fire" connections (transfering lots of files) causing
>     * an eventual "Address already in use" error.  As a result, this
>     * nasty kludge retries ten times (once per second) if the
>     * port being bound to is INPORT_ANY)
>     */

This does not occur just during 'rapid-fire connections'. AFAI can
tell, it *always* fails to bind to port 20 in this case. So I don't
think this is the problem.

Back to my question - Why would a port 20 bind() lock up the medusa
process when absolutely no other transaction is transpiring on the
server? Under what condidtions woudla bind() simply stop? - not
fail, just fail to return from the bind() call?

>In other words, it's just bound to fail.  A forking server can afford
>this sort of persistence, but in medusa I think it'd be overkill; I'd
>have to set up event timers, an object to maintain the retry state,
>etc.... [this alone it might add 50% to the size of ftp_server.py]
>---
>
>I'd have to agree with Sam, it's just not worth the effort.

So you are saying ZServer just isn't ever going to support Active
ftp clients in the correct port-1 manner?  If so, you might want
to put a LARGE BANNER disclaimer about this matter as this makes
ZServer unusable from most ftp clients that try to access it from
behind standard a firewall.  (And yes, on checking, it appears that
the only OSes we could locate that come with a passive ftp client
by default are the BSD's).