Move from fail to SMTPException everywhere in the module

src/Network/HaskellNet/SMTP.hs

@@ -72,6 +72,7 @@ module Network.HaskellNet.SMTP
     , connectStream
     , closeSMTP
     , gracefullyCloseSMTP
+    , SMTPException(..)
     ) where
 
 import Network.HaskellNet.BSStream
@@ -174,13 +175,16 @@ connectSMTP :: String     -- ^ name of the server
             -> IO SMTPConnection
 connectSMTP = flip connectSMTPPort 25
 
--- | create SMTPConnection from already connected Stream
-connectStream :: BSStream -> IO SMTPConnection
+-- | Create SMTPConnection from already connected Stream
+--
+-- Throws @CantConnect :: SMTPException@ in case if got illegal
+-- greeting.
+connectStream :: HasCallStack => BSStream -> IO SMTPConnection
 connectStream st =
     do (code1, _) <- parseResponse st
-       unless (code1 == 220) $
-              do bsClose st
-                 fail "cannot connect to the server"
+       unless (code1 == 220) $ do
+         bsClose st
+         throwIO $ UnexpectedGreeting code1
        senderHost <- T.pack <$> getHostName
        msg <- tryCommand (SMTPC st []) (EHLO senderHost) 3 [250]
        return (SMTPC st (tail $ BS.lines msg))

src/Network/HaskellNet/SMTP/Internal.hs

@@ -158,6 +158,8 @@ data SMTPException
   | AuthNegotiationFailed ReplyCode BS.ByteString
     -- | Can't send email because no recipients were specified.
   | NoRecipients Mail
+    -- | Received an unexpected greeting from the server.
+  | UnexpectedGreeting ReplyCode
   deriving (Show)
   deriving (Typeable)
 
@@ -178,6 +180,8 @@ instance Exception SMTPException where
     "Authentication failed. code: " ++ show code ++ ", msg: " ++ BS.unpack msg
   displayException (NoRecipients _mail) =
     "No recipients were specified"
+  displayException (UnexpectedGreeting code) =
+    "Expected greeting from the server, but got: " <> show code
 
 
 -- | Safe wrapper for running a client command over the SMTP
@@ -341,7 +345,6 @@ sendMailData sender receivers dat conn = do
    sendAndCheck (DATA dat)
    return ()
   where
-    -- Try the command once and @fail@ if the response isn't 250.
     sendAndCheck cmd = tryCommand conn cmd 1 [250, 251]
 
 -- | Just a crlf constant.