What if the user is running some other software which already makes use of
that port?
T.
> -----Original Message-----
> From: owner-apps-at-eso.org [mailto:owner-apps-at-eso.org] On
> Behalf Of Mike Fitzpatrick
> Sent: 17 February 2007 05:15
> To: Patrick Dowler
> Cc: apps-at-ivoa.net
> Subject: Re: Applications Messaging Standard
>
> On 2/16/07, Patrick Dowler <patrick.dowler-at-nrc-cnrc.gc.ca> wrote:
>
> > On a multi-user machine, the initial hand-shake could
> exchange the user-name
> > to make sure client and hub are running under the same user
> (spoofable, but
> > we aren't trying to make this overly secure, just simple for users).
> >
> > If there is a collision on the port in a multi-user
> environment, just
> > increment the port number and try again. So clients and
> hubs start by
> > connecting to port N and checking the user; if they connect
> and find the same
> > user is running the hub, the client proceeds and the (2nd)
> hub terminates
> > quietly (or not). If the new hub doesn't find anything, it
> tries to take the
> > port (starts listening). If the client or hub finds a hub
> but user doesn't
> > match, they try again on port N+1. If the client doesn't
> find a hub, it
> > probably has to check higher port numbers (in case that
> users hub was not the
> > first to start and hence is on port N+something). For
> sanity and quick
> > failure, one would want relatively short socket connection
> timeouts and to
> > limit the number of times one would increment the port
> number and try again.
>
> Admittedly it will be a rare case, but I think I see a hole in this
> scheme: Assume
> two users start msg-enabled apps at about the same time, so
> the first users
> get the well-know port (say 2000) and the second user gets
> (N+1, 2001). If
> the first user shuts down then port 2000 is now free, if the
> second user then
> starts another msg-enabled app in their session it will try to connect
> to port 2000
> and/or possibly start a second hub since the port is free and it has
> no reason to
> look for N+1.
>
> How about a scheme where the address is some agreed base value (call
> it 2000) but apps/hubs use the userid as an offset? This guarantees a
> unique
> port for each user, can be overridden by an env var to start
> a separate session,
> and avoids "port scanning" since a user will only every try a single
> port number.
> I dont know if Windows has a concept of 'userid' but they
> could just fallback to
> the base address anyway. Assuming the userid is the same
> across a LAN all
> we need is a host name to connect to "our" hub on a remote
> machine since
> we'll already know what the port will be.
>
> -Mike
>
http://www.Taglocity.com Tags: IVOA, apps Received on 2007-02-17Z09:31:05