module DNS ( MxSetMap, mx_set_map, normalize_string_domain ) 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 ) -- | A map from domain names (represented as 'String's) to sets of -- mail exchanger names (also represented as 'String's). -- type MxSetMap = Map String MxSet -- | A set of mail exchanger names, represented as 'String's. type MxSet = Set String -- | Normalize a domain name string by converting to a 'Domain', -- calling 'normalize', and then converting back. -- -- ==== __Examples__ -- -- >>> normalize_string_domain "ExAMplE.com" -- "example.com." -- normalize_string_domain :: String -> String normalize_string_domain = 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 withResolver default_rs $ \resolver -> do mxs <- lookupMX resolver domain 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 (String, Set String) make_pair domain = do -- Lookup the @domain@'s MX records. mx_list <- lookup_mxs domain -- Now convert the MX records *back* to strings. let string_mx_list = map BS.unpack mx_list -- Convert the list into a set let string_mx_set = Set.fromList string_mx_list -- Finally, construct the pair and return it. return (BS.unpack domain, string_mx_set)