4.16.1 Some Useful Functions

To illustrate the concept of user-defined functions, this subsection shows the definitions of some of the library functions shipped with mailfromd¹⁴. These functions are contained in modules installed along with the mailfromd binary. To use any of them in your code, require the appropriate module as described in import, e.g. to use the revip function, do require 'revip'.

Functions and their definitions:

1. revip
   

   The function revip, that was used in releases of mailfromd up to 9.0 (see revip) was implemented as follows:

   func revip(string ip) returns string
   do
     return inet_ntoa(ntohl(inet_aton(ip)))
   done
   

   Previously it was implemented using regular expressions. Below we include this variant as well, as an illustration for the use of regular expressions:

   #pragma regex push +extended
   func revip(string ip) returns string
   do
     if ip matches '([0-9]+)\.([0-9]+)\.([0-9]+)\.([0-9]+)'
       return "\4.\3.\2.\1"
     fi
     return ip
   done
   #pragma regex pop
   

2. strip_domain_part
   

   This function returns at most n last components of the domain name domain (see strip_domain_part).

   #pragma regex push +extended
   
   func strip_domain_part(string domain, number n) returns string
   do
     if n > 0 and
       domain matches '.*((\.[^.]+){' . $2 . '})'
       return substring(\1, 1, -1)
     else
       return domain
     fi
   done
   #pragma regex pop
   

3. valid_domain
   

   See valid_domain, for a description of this function. Its definition follows:

   require dns
   
   func valid_domain(string domain) returns number
   do
     return not (resolve(domain) = "0" and not hasmx(domain))
   done
   

4. match_dnsbl
   

   The function match_dnsbl (see match_dnsbl) is defined as follows:

   require dns
   require match_cidr
   #pragma regex push +extended
   
   func match_dnsbl(string address, string zone, string range)
       returns number
   do
     string rbl_ip
     if range = 'ANY'
       set rbl_ip '127.0.0.0/8'
     else
       set rbl_ip range
       if not range matches '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
         return 0
       fi
     fi
   
     if not (address matches '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
             and address != range)
       return 0
     fi
   
     if address matches
           '^([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})$'
       if match_cidr (resolve ("\4.\3.\2.\1", zone), rbl_ip)
         return 1
       else
         return 0
       fi
     fi
     # never reached
   done