[Exim] SMTP "port" string expansion patch

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Autor: Adam Thornton
Datum:  
To: exim-users
Betreff: [Exim] SMTP "port" string expansion patch
I found that it would be very useful to have the "port" option to smtp
take an expanded string rather than a literal string; I'll explain the
situation for which I needed it after the patch.

Anyhow, the required patch is a small one, to smtp_out.c. It shouldn't
break anything for anyone who doesn't need this, and it should add a
minimal amount of overhead, since expand_string returns very quickly if
there are no "$" characters in the string.

I submit this in the hope that a) it may be useful to someone else, and
b) that it may get accepted into the mainstream tree, in case it *is*
useful to other people.

Adam

**********CUT HERE****************

--- smtp_out.c.orig    2003-10-29 14:57:34.000000000 -0600
+++ smtp_out.c    2003-10-29 17:38:19.000000000 -0600
@@ -89,7 +89,7 @@
 produces the number in network byte order.


 Arguments:
-  pstring     string representation of the port
+  istring     string representation of the port (may be expanded)
   addr        the mail address being handled (for setting errors)
   port        stick the port in here
   msg         for adding to error message
@@ -99,8 +99,21 @@
 */


 BOOL
-smtp_get_port(uschar *pstring, address_item *addr, int *port, uschar
*msg)
+smtp_get_port(uschar *istring, address_item *addr, int *port, uschar
*msg)
 {
+  uschar *pstring;
+
+ pstring=expand_string(istring);
+ if (pstring == NULL)
+   {
+     if (expand_string_forcedfail) return TRUE;
+     addr->transport_return = PANIC;
+     addr->message = string_sprintf("failed to expand \"port\" "
+                    "option for %s: %s", msg, expand_string_message);
+     return FALSE;
+   }
+
+
 if (isdigit(*pstring))
   {
   uschar *end;


**********CUT HERE****************

So, why did I need an expandable port?

Well, I'm working on a product that uses exim in a Linux/390-under-VM
context. Basically, I'm replacing VM's built-in SMTP handler with a new
virtual machine that runs Exim under the covers.

This needs to be a drop-in replacement, which means that mail has to
appear to the outside world to both go to and come from the VM IP stack.

VM does not provide port-forwarding or NAT capabilities in its stack.
Hence I needed a port forwarder. Doing inbound port 25 to the Linux
Exim-running guest was easy. Outbound, from that guest to an arbitrary
host, was a little more problematic. What I ended up with was a VM
service that listens on a control port and maps requested host/port
combos to a local port (on VM's stack), and then returns the local port
number (don't worry--the forwarder will only take commands from
localhost or from the IP address assigned to the Linux guest, which is
usually connected on a virtual point-to-point link, which only exists in
the S/390 or zSeries box's memory). The idea, then, is that I use Exim
to connect to my VM TCP/IP stack, only for the port number, I use '${run
{blah....} }' to get the dynamically assigned port. Then I deliver that
mail to the port, which is, in turn, forwarded to the actual host's SMTP
port, but which appears to that host to have come directly from VM.

Adam