msys.dnsLookup
Name
msys.dnsLookup — Perform a DNS lookup
Synopsis
msys.dnsLookup(name, recordtype, options);
name: string recordtype: string (optional) options: table (optional)
Description
If recordtype is not specified, it defaults to A. Otherwise, recordtype is a string from the following list:
-
ALookup the IPv4 address -
AAAALookup the IPv6 address -
TXTLookup a TXT record -
MXLookup an MX record -
PTRLookup a PTR record -
NSLookup an NS record
Warning
If recordtype is passed an invalid value, then an exception is thrown. In this case, the inbound session will return a 421 error.
options is a table with the following keys:
-
prioritycan be either true or false. If unspecified, false is assumed. -
serveroptional alternate DNS server to query instead of the system default resolver.
On success, the return value is a table containing the results.
For records with a preference value, if priority is set to true, the values returned are themselves tables with the first element being the preference value and the second element the string value. Otherwise, the values returned are just the string values. Regardless of the value of the priority setting, the returned records are ordered based on their preference, with the "best" record first. For other records, the values are simply string values that are ordered as they appear in the DNS response. For a failed lookup, two values are returned:
-
nilto indicate error -
errmsgthe error message
The idiom for performing a DNS lookup is:
local results, errmsg, result; results, errmsg = msys.dnsLookup('messagesystems.com', 'A'); if results == nil then print("ERROR: " .. errmsg); return; end if results ~= nil then for k,v in ipairs(results) do print("key: " .. k .. "and value: " .. v) end end
Note
Results of msys.dnsLookup() invocations in your policy scripts can also be queried from the system console by using dns_cache stats.
Because this function is in the msys namespace, an explicit require('msys') is not necessary.