Hello,

Attached is  a patch that implement  the generate() operator as  part of
dhcp-eval. generate()  is similar  to execute() in  that it  executes an
external  program.  However,  unlike  execute(), generate()  is  a  data
expression: it  reads up to 1024  bytes from the standard  output of the
resulting child process  and makes them available as a  C string. It can
therefore  be  combined with  substring(),  concat()  and other  similar
operators for maximum flexibility.
Similarly to  execute(), generate() can be  disabled through ./configure
--disable-generate.

generate() typically enables users to generate complex DHCP options that
would  otherwise  require the  implementation  of  many more  operators.
For  instance,  we  recently  stumbled  upon  an  ISP  which  expects  a
particular value  for options 90  or 11 (authentication). This  value is
computed using a proprietary, ISP-specific algorithm (it involves random
salts,  MD5 hashing  and  a  password... far  from  rocket science,  but
definitely  ISP-specific) and  should  be renewed  systematically or  at
least frequently.
Moreover, this algorithm is likely  to change often enough to discourage
its implementation in C  within dhclient/dhcpd. generate() enables users
to  delegate tricky  value generations  to external  programs which  can
be  implemented  using more  high-level  languages  and can  be  updated
frequently.

Note: the attached  patch modifies configure.ac and config  h.in but the
configure script itself needs to be regenerated.

Let  me know  whether this  feature is  welcome within  isc-dhcp and  if
anything ought to be improved in the attached patch.

Thanks in advance.
-- 
Xavier G.