configurator / Data / Configurator.hs

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
{-# LANGUAGE BangPatterns, OverloadedStrings, RecordWildCards,
    ScopedTypeVariables #-}

-- |
-- Module:      Data.Configurator
-- Copyright:   (c) 2011 MailRank, Inc.
-- License:     BSD3
-- Maintainer:  Bryan O'Sullivan <bos@mailrank.com>
-- Stability:   experimental
-- Portability: portable
--
-- A simple (yet powerful) library for working with configuration
-- files.

module Data.Configurator
    (
    -- * Configuration file format
    -- $format

    -- ** Binding a name to a value
    -- $binding

    -- *** Value types
    -- $types

    -- *** String interpolation
    -- $interp

    -- ** Grouping directives
    -- $group

    -- ** Importing files
    -- $import

    -- * Loading configuration data
      autoReload
    , autoConfig
    -- * Lookup functions
    , lookup
    , lookupDefault
    -- * Notification of configuration changes
    -- $notify
    , prefix
    , exact
    , subscribe
    -- * Low-level loading functions
    , load
    , reload
    -- * Helper functions
    , display
    , getMap
    ) where

import Control.Applicative ((<$>))
import Control.Concurrent (ThreadId, forkIO, threadDelay)
import Control.Exception (SomeException, catch, evaluate, handle, throwIO, try)
import Control.Monad (foldM, forM, forM_, join, when)
import Data.Configurator.Instances ()
import Data.Configurator.Parser (interp, topLevel)
import Data.Configurator.Types.Internal
import Data.IORef (atomicModifyIORef, newIORef, readIORef)
import Data.Maybe (catMaybes, fromMaybe, isJust)
import Data.Monoid (mconcat)
import Data.Text.Lazy.Builder (fromString, fromText, toLazyText)
import Data.Text.Lazy.Builder.Int (decimal)
import Prelude hiding (catch, lookup)
import System.Environment (getEnv)
import System.IO (hPutStrLn, stderr)
import System.Posix.Types (EpochTime, FileOffset)
import System.PosixCompat.Files (fileSize, getFileStatus, modificationTime)
import qualified Data.Attoparsec.Text as T
import qualified Data.Attoparsec.Text.Lazy as L
import qualified Data.HashMap.Lazy as H
import qualified Data.Text as T
import qualified Data.Text.Lazy as L
import qualified Data.Text.Lazy.IO as L

loadFiles :: [Path] -> IO (H.HashMap Path [Directive])
loadFiles = foldM go H.empty
 where
   go seen path = do
     ds <- loadOne . T.unpack =<< interpolate path H.empty
     let !seen'    = H.insert path ds seen
         notSeen n = not . isJust . H.lookup n $ seen
     foldM go seen' . filter notSeen . importsOf $ ds
  
-- | Create a 'Config' from the contents of the named files. Throws an
-- exception on error, such as if files do not exist or contain errors.
--
-- File names have any environment variables expanded prior to the
-- first time they are opened, so you can specify a file name such as
-- @\"$(HOME)/myapp.cfg\"@.
load :: [FilePath] -> IO Config
load = load' Nothing

load' :: Maybe AutoConfig -> [FilePath] -> IO Config
load' auto paths0 = do
  let paths = map T.pack paths0
  ds <- loadFiles paths
  m <- newIORef =<< flatten paths ds
  s <- newIORef H.empty
  return Config {
                cfgAuto = auto
              , cfgPaths = H.keys ds
              , cfgMap = m
              , cfgSubs = s
              }

-- | Forcibly reload a 'Config'. Throws an exception on error, such as
-- if files no longer exist or contain errors.
reload :: Config -> IO ()
reload cfg@Config{..} = do
  m' <- flatten cfgPaths =<< loadFiles cfgPaths
  m <- atomicModifyIORef cfgMap $ \m -> (m', m)
  notifySubscribers cfg m m' =<< readIORef cfgSubs

-- | Defaults for automatic 'Config' reloading when using
-- 'autoReload'.  The 'interval' is one second, while the 'onError'
-- action ignores its argument and does nothing.
autoConfig :: AutoConfig
autoConfig = AutoConfig {
               interval = 1
             , onError = const $ return ()
             }

-- | Load a 'Config' from the given 'FilePath's, and start a reload
-- thread.
--
-- At intervals, a thread checks for modifications to both the
-- original files and any files they refer to in @import@ directives,
-- and reloads the 'Config' if any files have been modified.
--
-- If the initial attempt to load the configuration files fails, an
-- exception is thrown.  If the initial load succeeds, but a
-- subsequent attempt fails, the 'onError' handler is invoked.
--
-- File names have any environment variables expanded prior to the
-- first time they are opened, so you can specify a file name such as
-- @\"$(HOME)/myapp.cfg\"@.
autoReload :: AutoConfig
           -- ^ Directions for when to reload and how to handle
           -- errors.
           -> [FilePath]
           -- ^ Configuration files to load.
           -> IO (Config, ThreadId)
autoReload AutoConfig{..} _
    | interval < 1 = error "autoReload: negative interval"
autoReload _ []    = error "autoReload: no paths to load"
autoReload auto@AutoConfig{..} paths = do
  cfg <- load' (Just auto) paths
  let loop meta = do
        threadDelay (max interval 1 * 1000000)
        meta' <- getMeta paths
        if meta' == meta
          then loop meta
          else (reload cfg `catch` onError) >> loop meta'
  tid <- forkIO $ loop =<< getMeta paths
  return (cfg, tid)
  
-- | Save both a file's size and its last modification date, so we
-- have a better chance of detecting a modification on a crappy
-- filesystem with timestamp resolution of 1 second or worse.
type Meta = (FileOffset, EpochTime)

getMeta :: [FilePath] -> IO [Maybe Meta]
getMeta paths = forM paths $ \path ->
   handle (\(_::SomeException) -> return Nothing) . fmap Just $ do
     st <- getFileStatus path
     return (fileSize st, modificationTime st)

-- | Look up a name in the given 'Config'.  If a binding exists, and
-- the value can be 'convert'ed to the desired type, return the
-- converted value, otherwise 'Nothing'.
lookup :: Configured a => Config -> Name -> IO (Maybe a)
lookup Config{..} name =
    (join . fmap convert . H.lookup name) <$> readIORef cfgMap

-- | Look up a name in the given 'Config'.  If a binding exists, and
-- the value can be converted to the desired type, return it,
-- otherwise return the default value.
lookupDefault :: Configured a =>
                 a
              -- ^ Default value to return if 'lookup' or 'convert'
              -- fails.
              -> Config -> Name -> IO a
lookupDefault def cfg name = fromMaybe def <$> lookup cfg name

-- | Perform a simple dump of a 'Config' to @stdout@.
display :: Config -> IO ()
display Config{..} = print =<< readIORef cfgMap

-- | Fetch the 'H.HashMap' that maps names to values.
getMap :: Config -> IO (H.HashMap Name Value)
getMap = readIORef . cfgMap

flatten :: [Path] -> H.HashMap Path [Directive] -> IO (H.HashMap Name Value)
flatten roots files = foldM (directive "") H.empty .
                      concat . catMaybes . map (`H.lookup` files) $ roots
 where
  directive pfx m (Bind name (String value)) = do
      v <- interpolate value m
      return $! H.insert (T.append pfx name) (String v) m
  directive pfx m (Bind name value) =
      return $! H.insert (T.append pfx name) value m
  directive pfx m (Group name xs) = foldM (directive pfx') m xs
      where pfx' = T.concat [pfx, name, "."]
  directive pfx m (Import path) =
      case H.lookup path files of
        Just ds -> foldM (directive pfx) m ds
        _       -> return m

interpolate :: T.Text -> H.HashMap Name Value -> IO T.Text
interpolate s env
    | "$" `T.isInfixOf` s =
      case T.parseOnly interp s of
        Left err   -> throwIO $ ParseError "" err
        Right xs -> (L.toStrict . toLazyText . mconcat) <$> mapM interpret xs
    | otherwise = return s
 where
  interpret (Literal x)   = return (fromText x)
  interpret (Interpolate name) =
      case H.lookup name env of
        Just (String x) -> return (fromText x)
        Just (Number n) -> return (decimal n)
        Just _          -> error "type error"
        _ -> do
          e <- try . getEnv . T.unpack $ name
          case e of
            Left (_::SomeException) ->
                throwIO . ParseError "" $ "no such variable " ++ show name
            Right x -> return (fromString x)

importsOf :: [Directive] -> [Path]
importsOf (Import path : xs) = path : importsOf xs
importsOf (Group _ ys : xs)  = importsOf ys ++ importsOf xs
importsOf (_ : xs)           = importsOf xs
importsOf _                  = []

loadOne :: FilePath -> IO [Directive]
loadOne path = do
  s <- L.readFile path
  p <- evaluate (L.eitherResult $ L.parse topLevel s)
       `catch` \(e::ConfigError) ->
       throwIO $ case e of
                   ParseError _ err -> ParseError path err
  case p of
    Left err -> throwIO (ParseError path err)
    Right ds -> return ds

-- | Subscribe for notifications.  The given action will be invoked
-- when any change occurs to a configuration property matching the
-- supplied pattern.
subscribe :: Config -> Pattern -> ChangeHandler -> IO ()
subscribe Config{..} pat act = do
  m' <- atomicModifyIORef cfgSubs $ \m ->
        let m' = H.insertWith (++) pat [act] m in (m', m')
  evaluate m' >> return ()

notifySubscribers :: Config -> H.HashMap Name Value -> H.HashMap Name Value
                  -> H.HashMap Pattern [ChangeHandler] -> IO ()
notifySubscribers Config{..} m m' subs = H.foldrWithKey go (return ()) subs
 where
  changedOrGone = H.foldrWithKey check [] m
      where check n v nvs = case H.lookup n m' of
                              Just v' | v /= v'   -> (n,Just v'):nvs
                                      | otherwise -> nvs
                              _                   -> (n,Nothing):nvs
  new = H.foldrWithKey check [] m'
      where check n v nvs = case H.lookup n m of
                              Nothing -> (n,v):nvs
                              _       -> nvs
  notify p n v a = a n v `catch` maybe report onError cfgAuto
    where report e = hPutStrLn stderr $
                     "*** a ChangeHandler threw an exception for " ++
                     show (p,n) ++ ": " ++ show e
  go p@(Exact n) acts next = (const next =<<) $ do
    let v' = H.lookup n m'
    when (H.lookup n m /= v') . mapM_ (notify p n v') $ acts
  go p@(Prefix n) acts next = (const next =<<) $ do
    let matching = filter (T.isPrefixOf n . fst)
    forM_ (matching new) $ \(n',v) -> mapM_ (notify p n' (Just v)) acts
    forM_ (matching changedOrGone) $ \(n',v) -> mapM_ (notify p n' v) acts

-- $format
--
-- A configuration file consists of a series of directives and
-- comments, encoded in UTF-8.  A comment begins with a \"@#@\"
-- character, and continues to the end of a line.
--
-- Files and directives are processed from first to last, top to
-- bottom.

-- $binding
--
-- A binding associates a name with a value.
--
-- > my_string = "hi mom! \u2603"
-- > your-int-33 = 33
-- > his_bool = on
-- > HerList = [1, "foo", off]
--
-- A name must begin with a Unicode letter, which is followed by zero
-- or more of a Unicode alphanumeric code point, hyphen \"@-@\", or
-- underscore \"@_@\".
--
-- Bindings are created or overwritten in the order in which they are
-- encountered.  It is legitimate for a name to be bound multiple
-- times, in which case the last value wins.
--
-- > a = 1
-- > a = true
-- > # value of a is now true, not 1

-- $types
--
-- The configuration file format supports the following data types:
--
-- * Booleans, represented as @on@ or @off@, @true@ or @false@.  These
--   are case sensitive, so do not try to use @True@ instead of
--   @true@!
--
-- * Integers, represented in base 10.
--
-- * Unicode strings, represented as text (possibly containing escape
--   sequences) surrounded by double quotes.
--
-- * Heterogeneous lists of values, represented as an opening square
--   bracket \"@[@\", followed by a series of comma-separated values,
--   ending with a closing square bracket \"@]@\".
--
-- The following escape sequences are recognised in a text string:
--
-- * @\\n@ - newline
--
-- * @\\r@ - carriage return
--
-- * @\\t@ - horizontal tab
--
-- * @\\\\@ - backslash
--
-- * @\\\"@ - double quote
--
-- * @\\u@/xxxx/ - Unicode character from the basic multilingual
--   plane, encoded as four hexadecimal digits
--
-- * @\\u@/xxxx/@\\u@/xxxx/ - Unicode character from an astral plane,
--   as two hexadecimal-encoded UTF-16 surrogates

-- $interp
--
-- Strings support interpolation, so that you can dynamically
-- construct a string based on data in your configuration or the OS
-- environment.
--
-- If a string value contains the special sequence \"@$(foo)@\" (for
-- any name @foo@), then the name @foo@ will be looked up in the
-- configuration data and its value substituted.  If that name cannot
-- be found, it will be looked up in the OS environment.
--
-- For security reasons, it is an error for a string interpolation
-- fragment to contain a name that cannot be found in either the
-- current configuration or the environment.
--
-- To represent a single literal \"@$@\" character in a string, double
-- it: \"@$$@\".

-- $group
--
-- It is possible to group a number of directives together under a
-- single prefix:
--
-- > my-group
-- > {
-- >   a = 1
-- >
-- >   # groups support nesting
-- >   nested {
-- >     b = "yay!"
-- >   }
-- > }
--
-- The name of a group is used as a prefix for the items in the
-- group. For instance, the value of \"@a@\" above can be retrieved
-- using 'lookup' by supplying the name \"@my-group.a@\", and \"@b@\"
-- will be named \"@my-group.nested.b@\".

-- $import
--
-- To import the contents of another configuration file, use the
-- @import@ directive.
--
-- > import "$(HOME)/etc/myapp.cfg"
--
-- It is an error for an @import@ directive to name a file that does
-- not exist, cannot be read, or contains errors.
--
-- If an @import@ appears inside a group, the group's naming prefix
-- will be applied to all of the names imported from the given
-- configuration file.
--
-- Supposing we have a file named \"@foo.cfg@\":
--
-- > bar = 1
--
-- And another file that imports it into a group:
--
-- > hi {
-- >   import "foo.cfg"
-- > }
--
-- This will result in a value named \"@hi.bar@\".

-- $notify
--
-- To more efficiently support an application's need to dynamically
-- reconfigure, a subsystem may ask to be notified when a
-- configuration property is changed as a result of a reload, using
-- the 'subscribe' action.
Tip: Filter by directory path e.g. /media app.js to search for public/media/app.js.
Tip: Use camelCasing e.g. ProjME to search for ProjectModifiedEvent.java.
Tip: Filter by extension type e.g. /repo .js to search for all .js files in the /repo directory.
Tip: Separate your search with spaces e.g. /ssh pom.xml to search for src/ssh/pom.xml.
Tip: Use ↑ and ↓ arrow keys to navigate and return to view the file.
Tip: You can also navigate files with Ctrl+j (next) and Ctrl+k (previous) and view the file with Ctrl+o.
Tip: You can also navigate files with Alt+j (next) and Alt+k (previous) and view the file with Alt+o.