+{-# LANGUAGE TypeFamilies #-}
+
-- | General XML stuff.
--
module Xml (
+ DtdName(..),
+ FromXml(..),
parse_opts,
- pickle_unpickle )
+ pickle_unpickle,
+ unpickleable )
where
+import Control.Exception ( SomeException(..), catch )
import Text.XML.HXT.Core (
(>>>),
(/>),
+ PU,
SysConfigList,
XmlPickler(..),
hasName,
- no,
readDocument,
runX,
- withPreserveComment,
withRemoveWS,
- withSubstDTDEntities,
- withValidate,
xpickleVal,
xunpickleVal,
yes )
+
+-- | A typeclass for XML types that can be converted into an associated
+-- database type. The story behind this is long, but basically, we need
+-- to different types for each XML thingie we're going to import: a
+-- database type and an XML type. Both Groundhog and HXT are very
+-- particular about the types that they can use, and there's no way
+-- to reuse e.g. a type that HXT can pickle in Groundhog. So this
+-- typeclass gives us a way to get the database type from the XML
+-- type that we have to define for HXT.
+--
+class FromXml a where
+ -- | Each instance a must declare its associated database type (Db a)
+ type Db a :: *
+
+ -- | And provide a function for getting a (Db a) out of an "a".
+ from_xml :: a -> Db a
+
+
+-- | Represents the DTD filename ("SYSTEM") part of the DOCTYPE
+-- definition.
+newtype DtdName = DtdName String
+
-- | A list of options passed to 'readDocument' when we parse an XML
--- document. We don't validate because the DTDs from TSN are
--- wrong. As a result, we don't want to keep useless DTDs
--- areound. Thus we disable 'withSubstDTDEntities' which, when
--- combined with "withValidate no", prevents HXT from trying to read
--- the DTD at all.
+-- document. All cosmetic whitespace should be removed, otherwise we
+-- have to parse it in each pickler.
--
parse_opts :: SysConfigList
-parse_opts =
- [ withPreserveComment no,
- withRemoveWS yes,
- withSubstDTDEntities no,
- withValidate no ]
+parse_opts = [ withRemoveWS yes ]
-- | Given a root element name and a file path, return both the
-- to 'xpickle' would be ambiguous. By returning some @a@s, we allow
-- the caller to annotate its type.
--
+-- Note that this will happily pickle nothing to nothing and then
+-- unpickle it back to more nothing. So the fact that the
+-- before/after results from this function agree does not mean that
+-- the document was successfully unpickled!
+--
pickle_unpickle :: XmlPickler a
=> String
-> FilePath
pickle_unpickle root_element filepath = do
-- We need to check only the root message element since
-- readDocument produces a bunch of other junk.
- expected <- runX $ arr_getobj
+ expected <- runX arr_getobj
actual <- runX $ arr_getobj
>>>
xpickleVal xpickle
hasName root_element
>>>
xunpickleVal xpickle
+
+
+
+-- | Is the given XML file unpickleable? Unpickling will be attempted
+-- using the @unpickler@ argument. If we unilaterally used the
+-- generic 'xpickle' function for our unpickler, a type ambiguity
+-- would result. By taking the unpickler as an argument, we allow
+-- the caller to indirectly specify a concrete type.
+--
+unpickleable :: XmlPickler a => FilePath -> PU a -> IO Bool
+unpickleable filepath unpickler = do
+ xmldoc <- try_unpickle `catch` (\(SomeException _) -> return [])
+ return $ (not . null) xmldoc
+ where
+ try_unpickle = runX $ readDocument parse_opts filepath
+ >>>
+ xunpickleVal unpickler