harbl-cli/src/OptionalConfiguration.hs

   1 {-# LANGUAGE DeriveDataTypeable #-}
   2 {-# LANGUAGE FlexibleInstances #-}
   3
   4 -- | An OptionalConfiguration is just like a 'Configuration', except
   5 --   all of its fields are optional. The user can set options in two
   6 --   places: the command-line, and a configuration file. Obviously if
   7 --   a parameter is set in one place, it doesn't need to be set in the
   8 --   other. Thus, the latter needs to be optional.
   9 --
  10 module OptionalConfiguration (
  11   OptionalConfiguration(..),
  12   merge_maybe,
  13   merge_monoid,
  14   from_rc )
  15 where
  16
  17 -- System imports.
  18 import qualified Data.Configurator as DC (
  19   Worth(Optional),
  20   load,
  21   lookup )
  22 import Data.Data ( Data )
  23 import Data.Maybe ( fromMaybe )
  24 import Data.Monoid ( Monoid(..) )
  25 import Data.Text ( pack )
  26 import Data.Typeable ( Typeable )
  27 import Paths_harbl ( getSysconfDir )
  28 import System.Console.CmdArgs.Default ( Default(..) )
  29 import System.Directory ( getHomeDirectory )
  30 import System.FilePath ( (</>) )
  31 import System.IO.Error ( catchIOError )
  32 import System.IO ( hPrint, stderr )
  33
  34 -- Harbl library imports.
  35 import Network.DNS.RBL.Weight ( Weight )
  36
  37 -- Local imports.
  38 import Hosts ( Hosts(..) )
  39 import Lists ( Lists(..) )
  40
  41
  42 -- | The same as 'Configuration', except everything is optional. It's
  43 --   easy to merge two of these by simply dropping the 'Nothing's in
  44 --   favor of the 'Just's. The 'xml_files' are left un-maybed so that
  45 --   cmdargs can parse more than one of them.
  46 --
  47 data OptionalConfiguration =
  48   OptionalConfiguration {
  49     hosts :: Hosts,
  50     lists :: Lists,
  51     threshold :: Maybe Weight }
  52     deriving (Show, Data, Typeable)
  53
  54
  55 -- | Choose a nonempty monoid from our two arguments, preferring the
  56 --   second. So if the second monoid is non-'mempty', we'll return
  57 --   that. Otherwise the first.
  58 --
  59 --   ==== _Examples_
  60 --
  61 --   The second list is preferred if both are nonempty:
  62 --
  63 --   >>> merge_monoid [1,2] [3,4]
  64 --   [3,4]
  65 --
  66 --   However, if the second list is empty, the first is returned:
  67 --
  68 --   >>> merge_monoid [1,2] []
  69 --   [1,2]
  70 --
  71 --   And if both are empty, we return the first (i.e. empty) list:
  72 --
  73 --   >>> merge_monoid [] []
  74 --   []
  75 --
  76 merge_monoid :: (Eq a, Monoid a) => a -> a -> a
  77 merge_monoid l1 l2 = if l2 == mempty then l1 else l2
  78
  79
  80 -- | Like 'merge_monoid', except for optional things. We take two
  81 --   (potentially 'Nothing') values, and then try to choose a
  82 --   non-'Nothing' one, preferring the second argument.
  83 --
  84 --   ==== _Examples_
  85 --
  86 --   The second is preferred if it is non-'Nothing':
  87 --
  88 --   >>> merge_maybes (Just 3) (Just 4)
  89 --   Just 4
  90 --
  91 --   >>> merge_maybes Nothing (Just 4)
  92 --   Just 4
  93 --
  94 --   However, if the second argument is 'Nothing', the first is
  95 --   returned:
  96 --
  97 --   >>> merge_maybes (Just 1) Nothing
  98 --   Just 1
  99 --
 100 --   If both are 'Nothing', we return 'Nothing':
 101 --
 102 --   >>> merge_maybes Nothing Nothing
 103 --   Nothing
 104 --
 105 merge_maybes :: (Maybe a) -> (Maybe a) -> (Maybe a)
 106 merge_maybes _ y@(Just _) = y
 107 merge_maybes x@(Just _) Nothing = x
 108 merge_maybes Nothing Nothing = Nothing
 109
 110
 111 -- | Return the (thing contained in the) second argument if it is
 112 --   non-'Nothing'. Otherwise return the first argument.
 113 --
 114 --   ==== _Examples_
 115 --
 116 --   The second is preferred if it is non-'Nothing':
 117 --
 118 --   >>> merge_maybe 3 (Just 4)
 119 --   4
 120 --
 121 --   However, if the second argument is 'Nothing', the first is
 122 --   returned:
 123 --
 124 --   >>> merge_maybe 1 Nothing
 125 --   1
 126 --
 127 merge_maybe :: a -> Maybe a -> a
 128 merge_maybe x Nothing = x
 129 merge_maybe _ (Just y) = y
 130
 131
 132 -- | The Monoid instance for these lets us \"combine\" two
 133 --   OptionalConfigurations. The \"combine\" operation that we'd like to
 134 --   perform is, essentially, to mash them together. So if we have two
 135 --   OptionalConfigurations, each half full, we could combine them
 136 --   into one big one.
 137 --
 138 --   This is used to merge command-line and config-file settings.
 139 --
 140 instance Monoid OptionalConfiguration where
 141   -- | An empty OptionalConfiguration.
 142   mempty = OptionalConfiguration mempty mempty Nothing
 143
 144   -- | Combine @cfg1@ and @cfg2@, giving precedence to @cfg2@.
 145   cfg1 `mappend` cfg2 = OptionalConfiguration hs ls t
 146     where
 147       hs = merge_monoid (hosts cfg1) (hosts cfg2)
 148       ls = merge_monoid (lists cfg1) (lists cfg2)
 149       t  = merge_maybes (threshold cfg1) (threshold cfg2)
 150
 151
 152 -- | Obtain an OptionalConfiguration from harblrc in either the global
 153 --   configuration directory or the user's home directory. The one in
 154 --   $HOME is prefixed by a dot so that it is hidden.
 155 --
 156 --   We make an attempt at cross-platform compatibility; we will try
 157 --   to find the correct directory even on Windows. But if the calls
 158 --   to getHomeDirectory/getSysconfDir fail for whatever reason, we
 159 --   fall back to using the Unix-specific /etc and $HOME.
 160 --
 161 from_rc :: IO OptionalConfiguration
 162 from_rc = do
 163   etc  <- catchIOError getSysconfDir (\e -> do
 164                                         hPrint stderr e
 165                                         return "/etc")
 166   home <- catchIOError getHomeDirectory (\e -> do
 167                                            hPrint stderr e
 168                                            return "$(HOME)")
 169   let global_config_path = etc </> "harblrc"
 170   let user_config_path = home </> ".harblrc"
 171   cfg <- DC.load [ DC.Optional global_config_path,
 172                    DC.Optional user_config_path ]
 173   cfg_lists <- DC.lookup cfg (pack "lists")
 174   cfg_hosts <- DC.lookup cfg (pack "hosts")
 175   cfg_threshold <- DC.lookup cfg (pack "threshold")
 176   return $ OptionalConfiguration
 177              (fromMaybe def cfg_hosts)
 178              (fromMaybe def cfg_lists)
 179              cfg_threshold