WARNING, NEW BEHAVIOUR: The patch is using descriptor 4 instead of 
STDERR now!

Adds the possibility for a qmail-queue-replacement to offer custom
error (=bounce) messages.

You have to write the error message to filedescriptor 4 and exit 82, 
in order to use the custom message. Format of the message:

Dthis is a custom fatal error message
Zthis is a custom temporary failure message

Thanks to Richard Lyons <frob-qmail webcentral.com.au> for spotting a 
wrong errstr declaration.

Thanks to Jeremy Hinton for noting that I forget to include the patch to
qmail.h

This patch has been made by Flavio Curti <fcu-software at no-way.org> and is
provided AS IS. Do with it as you wish, I'm not responsible for anything that
breaks because of this patch.

EXAMPLES

Perl:
open(FD,">&4");
print FD "Ztemporary failure message";
close(FD);
exit(82);

Shell:
echo -n "Zpermanent failure after data" >&4
exit 82;

C (non-djb-style):
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>

char    err[] = "Zpermanently refusing";

int main() {
        write(4,err,(strlen(err)+1));
        exit(82);
}

--- qmail.c	1998-06-15 12:53:16.000000000 +0200
+++ ../../qmail-1.03/qmail.c	2004-10-13 22:35:37.000000000 +0200
@@ -14,20 +14,30 @@
 {
   int pim[2];
   int pie[2];
+  int pierr[2];
 
   if (pipe(pim) == -1) return -1;
   if (pipe(pie) == -1) { close(pim[0]); close(pim[1]); return -1; }
+  if (pipe(pierr) == -1) { 
+    close(pim[0]); close(pim[1]); 
+    close(pie[0]); close(pie[1]); 
+    close(pierr[0]); close(pierr[1]); 
+    return -1; 
+  }
  
   switch(qq->pid = vfork()) {
     case -1:
+      close(pierr[0]); close(pierr[1]);
       close(pim[0]); close(pim[1]);
       close(pie[0]); close(pie[1]);
       return -1;
     case 0:
       close(pim[1]);
       close(pie[1]);
+      close(pierr[0]); /* we want to receive data */
       if (fd_move(0,pim[0]) == -1) _exit(120);
       if (fd_move(1,pie[0]) == -1) _exit(120);
+      if (fd_move(4,pierr[1]) == -1) _exit(120);
       if (chdir(auto_qmail) == -1) _exit(61);
       execv(*binqqargs,binqqargs);
       _exit(120);
@@ -35,6 +45,7 @@
 
   qq->fdm = pim[1]; close(pim[0]);
   qq->fde = pie[1]; close(pie[0]);
+  qq->fderr = pierr[0]; close(pierr[1]);
   substdio_fdbuf(&qq->ss,write,qq->fdm,qq->buf,sizeof(qq->buf));
   qq->flagerr = 0;
   return 0;
@@ -82,10 +93,22 @@
 {
   int wstat;
   int exitcode;
+  int match;
+  char ch;
+  static char errstr[256];
+  int len = 0;
 
   qmail_put(qq,"",1);
   if (!qq->flagerr) if (substdio_flush(&qq->ss) == -1) qq->flagerr = 1;
   close(qq->fde);
+  substdio_fdbuf(&qq->ss,read,qq->fderr,qq->buf,sizeof(qq->buf));
+  while( substdio_bget(&qq->ss,&ch,1) && len < 255){
+    errstr[len]=ch;
+    len++;
+  }
+  if (len > 0) errstr[len]='\0'; /* add str-term */
+
+  close(qq->fderr);
 
   if (wait_pid(&wstat,qq->pid) != qq->pid)
     return "Zqq waitpid surprise (#4.3.0)";
@@ -118,8 +141,11 @@
     case 81: return "Zqq internal bug (#4.3.0)";
     case 120: return "Zunable to exec qq (#4.3.0)";
     default:
+      if (exitcode == 82 && len > 2){
+        return errstr;
+      }
       if ((exitcode >= 11) && (exitcode <= 40))
-	return "Dqq permanent problem (#5.3.0)";
+        return "Dqq permanent problem (#5.3.0)";
       return "Zqq temporary problem (#4.3.0)";
   }
 }
--- qmail.h	1998-06-15 12:53:16.000000000 +0200
+++ ../../qmail-1.03/qmail.h	2004-05-26 14:48:23.000000000 +0200
@@ -8,6 +8,7 @@
   unsigned long pid;
   int fdm;
   int fde;
+  int fderr;
   substdio ss;
   char buf[1024];
 } ;