floating point exception in mail/headers when msglist is empty...

[Matthew Whitworth]

The headers command in the 'mail' program generates a floating point
exception when the specified msglist returns no messages:

--

address@hidden:~$ gdb --quiet /usr/local/bin/mail
(gdb) set args --file --nosum
(gdb) run
Starting program: /usr/local/stow/mailutils/bin/mail --file --nosum
[New Thread 1024 (LWP 1666)]
mail (mailutils) 0.0.9d, Copyright (C) 2001 Free Software Foundation, Inc.
mail is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
Send bug reports to <address@hidden>.
? headers :u

Program received signal SIGFPE, Arithmetic exception.
[Switching to Thread 1024 (LWP 1666)]
0x0804c54a in mail_headers (argc=2, argv=0x80909f0) at headers.c:44
44        lines = (lines / num) - 2;
(gdb) bt
#0  0x0804c54a in mail_headers (argc=2, argv=0x80909f0) at
headers.c:44
#1  0x08051615 in util_do_command (c=0x808e9b0 "h :u") at util.c:131
#2  0x0804d7aa in mail_mainloop (input=0x804cbf4 <mail_cmdline>, 
    closure=0x805a51c, do_history=1) at mail.c:502
#3  0x0804d6a0 in main (argc=2, argv=0x805a828) at mail.c:465

--

As demonstrated, the exception seems to be generated by a
divide-by-zero in headers.c:44.  I have patched the file headers.c on
my own system to fix this, but my patch reflects the behavior of the
headers command according to the Single UNIX Specification
(http://www.opengroup.org/onlinepubs/007908799/xcu/mailx.html), in
which headers takes a single message argument rather than a msglist
and displays a screenfull of headers from that point on.  (Actually,
mine cheats and uses the first message in the msglist, but whatever.)

--

Index: headers.c
===================================================================
RCS file: /cvsroot/mailutils/mailutils/mail/headers.c,v
retrieving revision 1.11
diff -r1.11 headers.c
28a29,35
> /*
>  * NOTE: for the time being, we just find the first message in the
>  *       msglist and then print the next (lines - 2) headers unless
>  *       that would go past the end of the mailbox, in which case we
>  *       start at (total - (lines - 2))...
>  */
> 
44,46c51,60
<   lines = (lines / num) - 2;
<   if (lines < 0)
<     lines = util_screen_lines ();
---
>   if (num == 0)
>     {
>       fprintf(ofile, "No applicable messages.\n");
>       return 1;
>     }
> 
>   if (lines > 2)
>     lines -= 2;
> 
>   cursor = list->msg_part[0];
50,52c64
<       low = list->msg_part[0] - (lines / 2);
<       if (low < 1)
<       low = 1;
---
>       low = list->msg_part[0];
53a66
> 

--

It appears that you are trying to extend the functionality of the
headers command, but I could not find any documentation to explain
how.  I am interested in contributing to the development of the
mailutils/mail program (and/or contributing to the documentation), but
do not want to submit any more patches until I am sure how you intend
to modify the program's behavior.  If such documentation exists,
please nudge me in the general direction.

Thank you,

Matthew