Re: Connection through a telnet-gateway

["Jason M. Felice" <jfelice@xxxxxxxxxxxx>]

Scott Klement wrote:
> 
> On Tue, 11 Jul 2000, Michael Madore wrote:
> 
> > Hi,
> >
> > >
> > > Hmm, I'm not sure about the kind of thing your talking about, but I can
> > > imagine three possibilities:
> > >
> > > 1) A plain old telnet gateway (e.g. not a tn5250 gateway) that requires
> > >    you to type in the name of the remote host at a prompt once you
> > >    sign on.  This would
> >
> > This is what tn-gw is.
> >
> > Mike
> >
> 
> I'm dreaming up a quick hack to telnetstr.c to solve this problem...
> 
> I don't know if this is a good idea, or not... but I thought I'd drop it
> into E-mail while I'm dreaming it... :)
> 
> 1)  Have 2 new options for tn5250rc,  proxy_name, and proxy_prompt
>         (or maybe gateway_xxx instead of proxy_xxx)
> 
> 2)  in telnetstr.c, in the telnet_stream_connect() function, have it
>        check these options, and if they were specified, have it wait
>        for the string given in "proxy_prompt", and when thats found,
>        send the string in "proxy_name".
> 
> 3)  then end the telnet_stream_connect function, and let it do the
        remainder of the work the way that it always does...

Assuming that tn-gw didn't gobble up any telnet option negotiation. 
Actually, come to
think of it, we're pretty passive with the option negotiation and wait
for the server to
query us.

> 
> Perhaps that would solve Andreas' problem, and also add a nice feature
> to tn5250?

It's a weird situation, in other words (I think) a not-normal situation
that should be
handled a different way.  I think the way to handle that is to write a
preload object that
implements the 'connect' function and negotiates with the telnet proxy. 
I've done similar
for other functions.  See the sslwrap package for something similar:
they re-implement the
getpeername() function to return the forwarded address instead of the
forwarding address
for the spawned application.

Something like this would do the trick (not even tested, folks, might be
crashware):

struct sockaddr_in proxy_host = { AF_INET, htons(23),
inet_addr("my.proxy.host") };

int connect (int fd, struct sockaddr *name, int namelen)
{
        static void *dlh = NULL;
        static int (* real_connect) (int, struct sockaddr *, int);
        int rc;
        if (dlh == NULL) {
                dlh = dlopen("/lib/libc.so.6", RTLD_LAZY);
                if (dlh == NULL)
                        return -1;
                real_connect = dlsym (dlh, "connect");
                if (real_connect == NULL)
                        return -1;
        }

        if (name->sa_family == AF_INET && ((struct sockaddr_in*)name)->sin_port
==
                htons(23)) {
                rc = (*real_connect) (fd, &proxy_host, sizeof(proxy_host));
                if (rc == -1)
                        return -1;

                /* Insert code to negotiate with telnet gateway here... */

        } else {
                return (* real_connect) (fd, name, namelen);
        }

        return 0;
}

Then:

export LD_PRELOAD=/path/to/myconnect.so
tn5250 my.as400.com

or just:

LD_PRELOAD=/path/to/myconnect.so

It's a dirty trick and I've used it a few times to add the logic to deal
with strange
proxies and other network situations where the application would
otherwise need to be
hacked.

> 
> -Scott
> 

-Jason M. Felice
(jfelice@cronosys.com)
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