src/Main.hs: support NULLMX (RFC7505)

[email-validator.git] / src / Main.hs

diff --git a/src/Main.hs b/src/Main.hs
index 7a57dad3ad9179196dd1465cf16b29e38180106d..74789e70f4e2cedbf0be6584c3b14626046bed52 100644 (file)
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -1,45 +1,39 @@
 {-# LANGUAGE DoAndIfThenElse #-}
 {-# LANGUAGE RecordWildCards #-}
 
-module Main
+module Main (main)
 where
 
 import Control.Concurrent.ParallelIO.Global (
    parallelInterleaved,
    stopGlobalPool )
-import Control.Monad ( unless )
 import qualified Data.ByteString.Char8 as BS (
   hGetContents,
   hPutStrLn,
   lines,
   null,
-  pack,
-  readFile )
+  pack )
 import Network.DNS (
   Domain,
   Resolver,
-  ResolvConf(..),
+  ResolvConf( resolvTimeout ),
   defaultResolvConf,
   makeResolvSeed,
   withResolver )
 import Network.DNS.Lookup ( lookupA, lookupMX )
-import System.Directory ( doesFileExist )
-import System.Exit ( exitWith, ExitCode(..) )
 import System.IO (
-  IOMode( WriteMode ),
-  hClose,
   hFlush,
-  openFile,
   stdin,
   stdout )
 
 
-import CommandLine ( Args(..), get_args )
+import CommandLine (
+  Args( Args, accept_a, rfc5322 ),
+  get_args )
 import EmailAddress(
   Address,
   parts,
   validate_syntax )
-import ExitCodes ( exit_input_file_doesnt_exist )
 
 
 -- | Resolver parameters. We increase the default timeout from 3 to 10
@@ -47,25 +41,58 @@ import ExitCodes ( exit_input_file_doesnt_exist )
 resolv_conf ::  ResolvConf
 resolv_conf = defaultResolvConf { resolvTimeout = 10 * 1000 * 1000 }
 
--- | A list of common domains, there's no need to waste MX lookups
---   on these.
+-- | A list of common domains, there's no need to waste MX lookups on
+--   these. This is a very limited list; I don't want to be in the
+--   business of monitoring a million domains for MX record updates.
 common_domains :: [Domain]
 common_domains = map BS.pack [ "aol.com",
                                "comcast.net",
+                               "cox.net",
                                "gmail.com",
+                               "gmx.de",
+                               "googlemail.com",
+                               "hotmail.com",
+                               "icloud.com",
+                               "live.com",
+                               "me.com",
                                "msn.com",
+                               "outlook.com",
+                               "proton.me",
+                               "protonmail.ch",
+                               "protonmail.com",
                                "yahoo.com",
                                "verizon.net" ]
 
 
--- | Check whether the given domain has a valid MX record.
+-- | Check whether the given domain has a valid MX record. NULLMX
+--   (RFC7505) records consisting of a single period must not be
+--   accepted.
+--
+--   Two points about NULLMX:
+--
+--   * RFC7505 states that a domain MUST NOT have any other MX records
+--   if it has a NULLMX record. We don't enforce this. If you have a
+--   NULLMX record and some other MX record, we will reluctantly
+--   consider the second one valid.
+--
+--   * RFC7505 also states that a NULLMX record must have a priority
+--   of 0. We do not enforce this either. We ignore any records
+--   containing an empty label (i.e. a single dot). Such a record will
+--   not be deliverable anyway, and in light of the first item, means
+--   that we will not \"incorrectly\" reject batshit-crazy domains
+--   that have a NULLMX record (but with a non-zero priority) in
+--   addition to other, valid MX records.
+--
+
 validate_mx :: Resolver -> Domain -> IO Bool
 validate_mx resolver domain
   | domain `elem` common_domains = return True
   | otherwise = do
       result <- lookupMX resolver domain
-      case result of
-        -- A list of one or more elements?
+      let nullmx = BS.pack "." :: Domain
+      let non_null = (\(mx,_) -> mx /= nullmx) :: (Domain,Int) -> Bool
+      let non_null_mxs = fmap (filter non_null) result
+      case non_null_mxs of
         Right (_:_) -> return True
         _           -> return False
 
@@ -108,22 +135,8 @@ main :: IO ()
 main = do
   Args{..} <- get_args
 
-  -- Get the input from either stdin, or the file given on the command
-  -- line.
-  input <- case input_file of
-             Nothing   -> BS.hGetContents stdin
-             Just path -> do
-               is_file <- doesFileExist path
-               unless is_file $
-                 exitWith (ExitFailure exit_input_file_doesnt_exist)
-               BS.readFile path
-
-  -- Do the same for the output handle and stdout.
-  output_handle <- case output_file of
-                     Nothing -> return stdout
-                     Just path -> openFile path WriteMode
-
-  -- Split the input into lines.
+  -- Split stdin into lines, which should result in a list of addresses.
+  input <- BS.hGetContents stdin
   let addresses = BS.lines input
 
   -- And remove the empty ones.
@@ -145,10 +158,7 @@ main = do
 
   -- Output the results.
   let valid_addresses = map fst valid_results
-  _ <- mapM (BS.hPutStrLn output_handle) valid_addresses
+  mapM_ (BS.hPutStrLn stdout) valid_addresses
 
   stopGlobalPool
-
-  -- Clean up. It's safe to try to close stdout.
-  hFlush output_handle
-  hClose output_handle
+  hFlush stdout