+{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TypeFamilies #-}
-- | General XML stuff.
--
module Xml (
+ Child(..),
DtdName(..),
- ToFromXml(..),
+ FromXml(..),
+ FromXmlFk(..),
+ ToDb(..),
parse_opts,
- pickle_unpickle )
+ parse_opts_novalidate,
+ pickle_unpickle,
+ unpickleable,
+ unsafe_read_document,
+ unsafe_read_invalid_document,
+ unsafe_unpickle )
where
-import Database.Groundhog ( AutoKey )
+-- System imports.
+import Control.Exception ( SomeException(..), catch )
+import Database.Groundhog.Core ( PersistEntity(..) )
import Text.XML.HXT.Core (
(>>>),
(/>),
+ PU,
SysConfigList,
- XmlPickler(..),
- hasName,
+ XmlTree,
+ isElem,
no,
readDocument,
runX,
- withPreserveComment,
withRemoveWS,
withSubstDTDEntities,
withValidate,
xpickleVal,
+ xunpickleDocument,
xunpickleVal,
yes )
--- | A typeclass for types which can be converted into an associated
--- XML 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 XML type from the Groundhog
--- type.
+
+-- | Common associated type shared by 'FromXml' and 'FromXmlFk'. This
+-- basically just forces the client to define the \"database
+-- version\" of his type.
+--
+class ToDb a where
+ -- | Each instance @a@ must declare its associated database type @Db a@.
+ type Db a :: *
+
+-- | 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 most XML thingies we're
+-- going to import: a database type and an XML type.
--
--- At first there appears to be an equally-valid approach, getting the
--- Groundhog type from the XML one. But Groundhog won't use type family
--- instances, so here we are.
+-- 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. This typeclass gives us a standard way
+-- to get the database type from the XML type that we have to define
+-- for HXT.
+--
+class (ToDb a) => FromXml a where
+ -- | A function for getting a @Db a@ out of an @a@.
+ from_xml :: a -> Db a
+
+
+-- | A class for XML representations which are children of other
+-- elements. The foal is to associate a child XML element with its
+-- parent element's database type. This is required to construct the
+-- database analogue of @a@ in 'FromXmlFk'.
--
-class ToFromXml a where
- -- | Each instance a must declare its associated XML type (Xml a)
- type Xml a :: *
- type Container a :: *
+class Child a where
+ -- | The type of our parent object, i.e. to the type to whom our
+ -- foreign key will point.
+ type Parent a :: *
- -- | And provide a function for getting an (Xml a) out of an "a."
- to_xml :: a -> Xml a
- -- | And provide a function for getting an "a" out of an (Xml a).
- from_xml :: Xml a -> a
+-- | Some database types cannot be constructed from the XML type
+-- alone; they must be supplied a foreign key to a parent object
+-- first. Members of this class can be converted from an XML
+-- representation to a database representation in this manner.
+--
+class (Child a, ToDb a) => FromXmlFk a where
+ -- | The function that produces a @Db a@ out of a foreign key and an
+ -- @a@. The parameter order makes it easier to map this function
+ -- over a bunch of things.
+ from_xml_fk :: DefaultKey (Parent a) -> a -> Db a
- -- | Often we need to provide a key to use as a foreign key into
- -- some container. If the instance "belongs" to some other object,
- -- then it might need to be passed a key before it can un-XML
- -- itself. For example, the XML version of 'NewsTeam' doesn't
- -- contain a message ID which is part of its database type.
- from_xml_fk :: AutoKey (Container a) -> Xml a -> a
- from_xml_fk _ = from_xml
--- | Represents the DTD filename ("SYSTEM") part of the DOCTYPE
+-- | 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
+-- would have to parse whitespace in each (un)pickler.
--
parse_opts :: SysConfigList
-parse_opts =
- [ withPreserveComment no,
- withRemoveWS yes,
- withSubstDTDEntities no,
- withValidate no ]
+parse_opts = [ withRemoveWS yes,
+ withSubstDTDEntities no ]
+
+-- | Like 'parse_opts' except we don't validate the document against
+-- its DTD. This is useful when we need to parse a document that we
+-- /know/ is invalid so that we can deliver a better error message.
+--
+parse_opts_novalidate :: SysConfigList
+parse_opts_novalidate = (withValidate no) : parse_opts
--- | Given a root element name and a file path, return both the
--- original unpickled root "object" and the one that was constructed
--- by pickled and unpickling the original. This is used in a number
--- of XML tests which pickle/unpickle and then make sure that the
--- output is the same as the input.
+-- | Given an @unpickler@ and a @filepath@, attempt to unpickle the
+-- root element of @filepath@ using @unpickler@ and return both the
+-- original unpickled object and one constructed by pickling and
+-- unpickling that original. This is used in a number of XML tests
+-- which pickle/unpickle and then make sure that the output is the
+-- same as the input.
--
-- We return the object instead of an XmlTree (which would save us
-- an unpickle call) because otherwise the type of @a@ in the call
-- to 'xpickle' would be ambiguous. By returning some @a@s, we allow
-- the caller to annotate its type.
--
-pickle_unpickle :: XmlPickler a
- => String
- -> FilePath
+-- 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 :: PU a -- ^ @unpickler@ returning an @a@
+ -> FilePath -- ^ Path to the document to unpickle.
-> IO ([a], [a])
-pickle_unpickle root_element filepath = do
+pickle_unpickle unpickler 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
+ xpickleVal unpickler
>>>
- xunpickleVal xpickle
+ xunpickleVal unpickler
return (expected, actual)
where
arr_getobj = readDocument parse_opts filepath
/>
- hasName root_element
+ isElem -- Drop the extra junk readDocument pulls in.
>>>
- xunpickleVal xpickle
+ xunpickleVal unpickler
+
+
+
+-- | 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.
+--
+-- Apologies the the name; unpickleable means \"we can unpickle
+-- it\", not \"not pickleable.\"
+--
+unpickleable :: 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
+
+
+-- | Unpickle from a 'FilePath' using the given pickler. Explode if it
+-- doesn't work.
+--
+unsafe_unpickle :: FilePath -> PU a -> IO a
+unsafe_unpickle filepath unpickler =
+ fmap head $ runX $ xunpickleDocument unpickler parse_opts filepath
+
+
+-- | Read an XML document from a 'FilePath' into an XmlTree. Explode if it
+-- doesn't work.
+--
+unsafe_read_document :: FilePath -> IO XmlTree
+unsafe_read_document filepath =
+ fmap head $ runX $ readDocument parse_opts filepath
+
+-- | The same as 'unsafe_read_document', except it allows you to read
+-- documents which don't validate against their DTDs.
+--
+unsafe_read_invalid_document :: FilePath -> IO XmlTree
+unsafe_read_invalid_document filepath =
+ fmap head $ runX $ readDocument parse_opts_novalidate filepath
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