Mailfromd
	General-Purpose Mail Filter	Sergey Poznyakoff

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4.12.2.1 Some Useful Functions

To illustrate the concept of user-defined functions, this subsection shows definitions of some of the library functions shipped with mailfromd. 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 Require and Import, e.g. to use the revip function, do require 'revip'.

Functions and their definitions:

2. revip
   

   The function revip (see revip) is 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

3. 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 return domainpart %domain elif domainpart(%domain) matches '.*((\.[^.]+){' $2 '})' return substring(\1, 1, -1) else return %domain fi done #pragma regex pop

4. 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

5. 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

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