-module DNS ( lookup_mxs )
+module DNS (
+ MxSetMap,
+ NormalDomain,
+ mx_set_map,
+ normalize_string )
where
+import qualified Data.ByteString.Char8 as BS ( pack, unpack )
+import Data.List ( nub )
+import Data.Map ( Map )
+import qualified Data.Map as Map ( fromList )
+import Data.Set ( Set )
+import qualified Data.Set as Set ( fromList )
import Network.DNS (
Domain,
defaultResolvConf,
lookupMX,
makeResolvSeed,
+ normalize,
withResolver )
--- Slow since we create the resolver every time.
+-- | A type-safe wrapper around a domain name (represented as a
+-- string) that ensures we've created it by calling
+-- 'normalize_string'. This prevents us from making
+-- comparisons on un-normalized 'Domain's or 'String's.
+--
+newtype NormalDomain =
+ NormalDomain String
+ deriving ( Eq, Ord, Show )
+
+
+-- | A set of mail exchanger names, represented as 'String's. The use
+-- of 'NormalDomain' prevents us from constructing a set of names
+-- that aren't normalized first.
+--
+type MxSet = Set NormalDomain
+
+
+-- | A map from domain names (represented as 'String's) to sets of
+-- mail exchanger names (also represented as 'String's). The use of
+-- 'NormalDomain' in the key prevents us from using keys that aren't
+-- normalized; this is important because we'll be using them for
+-- lookups and want e.g. \"foo.com\" and \"FOO.com\" to look up the
+-- same MX records.
+--
+type MxSetMap = Map NormalDomain MxSet
+
+
+-- | Normalize a domain name string by converting to a 'Domain',
+-- calling 'normalize', and then converting back.
+--
+-- ==== __Examples__
+--
+-- >>> normalize_string "ExAMplE.com"
+-- NormalDomain "example.com."
+--
+normalize_string :: String -> NormalDomain
+normalize_string = NormalDomain . BS.unpack . normalize . BS.pack
+
+
+-- | Retrieve all MX records for the given domain. This is somewhat
+-- inefficient, since we create the resolver every time.
+--
lookup_mxs :: Domain -> IO [Domain]
lookup_mxs domain = do
default_rs <- makeResolvSeed defaultResolvConf
return $ case mxs of
Left _ -> []
Right pairs -> map fst pairs
+
+
+-- | Takes a list of domain names represented as 'String's and
+-- constructs a map from domain names to sets of mail exchangers
+-- (for those domain names) also represented as 'String's.
+--
+-- During construction, we have to switch to the DNS internal
+-- representation of a 'Domain' which uses ByteStrings, but before
+-- we return the map to the client, we want everything to be in
+-- terms of standard 'String's for comparison purposes.
+--
+-- The list of domains is normalized and de-duped before lookups are
+-- performed to avoid doing lookups twice for identical domains.
+--
+mx_set_map :: [String] -> IO MxSetMap
+mx_set_map domains = do
+ -- Construct a list of pairs.
+ pairs <- mapM make_pair unique_domains
+
+ -- And make a map from the pairs.
+ return $ Map.fromList pairs
+
+ where
+ -- Convert, normalize, and de-dupe the @domains@.
+ unique_domains :: [Domain]
+ unique_domains = nub $ map (normalize . BS.pack) domains
+
+ -- | Convert a string domain name into a pair containing the
+ -- domain name in the first component and a set of its mail
+ -- exchangers (as strings) in the second component.
+ --
+ make_pair :: Domain -> IO (NormalDomain, Set NormalDomain)
+ make_pair domain = do
+ -- Lookup the @domain@'s MX records.
+ mx_list <- lookup_mxs domain
+
+ -- Now convert the MX records *back* to strings, and then to
+ -- NormalDomains
+ let normal_mx_list = map (normalize_string . BS.unpack) mx_list
+
+ -- Convert the list into a set...
+ let normal_mx_set = Set.fromList normal_mx_list
+
+ -- The lookup key.
+ let normal_domain = normalize_string $ BS.unpack domain
+
+ -- Finally, construct the pair and return it.
+ return (normal_domain, normal_mx_set)