Add pdns_server lua2 backend example.

diff --git a/modules/lua2backend/examples/pdns_server_example.lua b/modules/lua2backend/examples/pdns_server_example.lua
new file mode 100644 (file)
index 0000000..7e8812d
--- /dev/null
+++ b/modules/lua2backend/examples/pdns_server_example.lua
@@ -0,0 +1,117 @@
+-- Powerdns server lua example
+-- $Id: pdns_server_example.lua,v 1643ea3f7d25 2025/09/08 17:47:01 grin $
+--
+-- Simulates a "smart" country lookup DNSBL, handling multiple
+-- countries for matching in the query, also a lot of log spam.
+--
+-- contributed by Peter 'grin' Gervai, 2025
+--
+-- test: dig 4.3.2.1.aa-td-bq.666666.c.example.hu
+--       dig 4.3.2.1.aa-td-qq-bq.666666.c.example.hu
+
+pdnslog( "lua: starting the backend")
+
+local base_labels = { "c", "example", "hu" } -- this is our base zone, word by word
+local base_domain = ""
+for _, val in ipairs(base_labels) do -- generate stringy base domain
+       base_domain = base_domain .. val .. "."
+end
+
+-- required function: the lookup
+function dns_lookup(qtype, qname, domain_id, ctx)
+        pdnslog("Got a request for " .. tostring(qname))
+
+        local peer_ip = ctx.source_address
+        if peer_ip ~= nil and peer_ip ~= "127.0.0.1" then -- state of the art access control
+            pdnslog("Access denied for the ip "..peer_ip)
+            return {}
+        end
+
+        if qtype:getName() ~= "A" and qtype:getName() ~= "ANY" then
+                -- we only serve A/ANY here (only get ANY from pdns_server)
+                pdnslog("We only server A/ANY! not "..qtype:getName())
+                return {}
+        end
+
+        if qname:toString() == base_domain then
+            -- we got a query for the base domain, let's fake a SOA to keep subqueries coming
+               return generate_SOA(qname)
+        end
+
+        if qname:countLabels() ~= 9 then -- we need exactly 9 words
+                pdnslog("We need the Right Length, not "..qname:countLabels())
+                return {}
+        end
+
+        local labels = qname:getRawLabels() -- split words into a table
+        -- skip wildcard queries (both external and internal)
+        if labels[1] == "*" then return {} end
+
+        for i, lbl in ipairs(base_labels) do -- verify fixed word positions
+                if lbl ~= labels[i+6] then
+                        pdnslog("Label pos:" .. i .. " mismatch: "..labels[i+6].." vs "..lbl)
+                        return {}
+                end
+        end
+
+        -- check API key
+        if not verified_api_key(labels[6], peer_ip) then
+                pdnslog("API key mismatch: " .. labels[6] .. " from " .. peer_ip)
+                return {}
+        end
+
+        -- generate a table of countries from the query
+        local countries = {}
+        for c in string.gmatch(labels[5], "[^-]+") do -- split by '-'
+                if not string.find(c, "^%a%a%a?%a?$") then -- 2-4 letters
+                        pdnslog("Illegal country: " ..c)
+                        return {}
+                end
+                countries[string.lower(c)] = true -- a "set"
+        end
+
+        -- get ip from query (the lazy way)
+        local ip_numbers={}
+        for i = 1,4 do table.insert(ip_numbers, labels[5-i]) end
+        local query_ip = table.concat(ip_numbers, ".")
+
+        -- lookup ip
+        local ip_country = string.lower(lookup_ip_country(query_ip))
+        if countries[ip_country] ~= nil then
+                -- match! return A and AAAA, and let pdns_server to pick what it wants
+                -- (which will be ipv4, v6 is useless here)
+                return {
+                       { name=qname, type=newQType("A"), content="127.0.0.1", ttl=86400 },
+                       { name=qname, type=newQType("AAAA"), content="2001:db8::42", ttl=6 },
+                }
+        end
+        return {}
+end
+
+function generate_SOA(qname) -- generate a fake soa, also set domain_id to something (not required, -1 is default)
+       return {{ name=qname, type="SOA", content="local. admin.local. 1 7200 3600 86400 3600", ttl=6, domain_id=3 }}
+end
+
+function verified_api_key(key, ip) -- very secure best industrial practice method (shall use some db backend for example)
+        if key == "666666" then return true end
+        pdnslog("API key wrongy-wrongy!")
+        return false
+end
+
+function lookup_ip_country(ip) -- this would do some lookups, too.
+       return "QQ"
+end
+
+-- this is kind of optional, but used by the next function
+function dns_get_domaininfo(domain)
+       if tostring(domain) == base_domain then return { serial=os.time() } end -- we use all the defaults
+       return nil
+end
+
+-- this is required if you want to serve the domain!
+-- returns all the domains served by this backend.
+function dns_get_all_domains()
+       local domains={}
+       domains[newDN(base_domain)] = dns_get_domaininfo(newDN(base_domain))
+       return domains
+end