Text.XML.Stream.Parse

xml-conduit-1.4.0.4: Pure-Haskell utilities for dealing with XML with the conduit package.

Safe Haskell | None
Language | Haskell98

Text.XML.Stream.Parse

Contents

- Parsing XML files
  - Parser settings
    - Entity decoding
- Event parsing
- Ignoring tags/trees
- Attribute parsing
- Combinators
- Streaming combinators
- Exceptions
- Other types

Description

This module provides both a native Haskell solution for parsing XML documents into a stream of events, and a set of parser combinators for dealing with a stream of events.

As a simple example, if you have the following XML file:

    <?xml version="1.0" encoding="utf-8"?>
    <people>
        <person age="25">Michael</person>
        <person age="2">Eliezer</person>
    </people>

Then this code:

    {-# LANGUAGE OverloadedStrings #-}
    import Control.Monad.Trans.Resource
    import Data.Conduit (($$))
    import Data.Text (Text, unpack)
    import Text.XML.Stream.Parse

    data Person = Person Int Text
        deriving Show

    parsePerson = tagName "person" (requireAttr "age") $ \age -> do
        name <- content
        return $ Person (read $ unpack age) name

    parsePeople = tagNoAttr "people" $ many parsePerson

    main = do
        people <- runResourceT $
                parseFile def "people.xml" $$ force "people required" parsePeople
        print people

will produce:

    [Person {age = 25, name = "Michael"},Person {age = 2, name = "Eliezer"}]

This module also supports streaming results using `yield`. This allows parser results to be processed using conduits while a particular parser (e.g. `many`) is still running. Without using streaming results, you have to wait until the parser finished before you can process the result list. Large XML files might be easier to process by using streaming results. See http://stackoverflow.com/q/21367423/2597135 for a related discussion.

    {-# LANGUAGE OverloadedStrings #-}
    import Control.Monad.Trans.Resource
    import Data.Conduit
    import Data.Text (Text, unpack)
    import Text.XML.Stream.Parse
    import Text.XML (Name)
    import Control.Monad.Trans.Class (lift)
    import Control.Monad (void)
    import qualified Data.Conduit.List as CL

    data Person = Person Int Text deriving Show

    parsePerson = tagName "person" (requireAttr "age") $ \age -> do
        name <- content
        return $ Person (read $ unpack age) name

    parsePeople = void $ tagNoAttr "people" $ manyYield parsePerson

    main = runResourceT $
        parseFile def "people.xml" $$ parsePeople =$ CL.mapM_ (lift . print)

Previous versions of this module contained a number of more sophisticated functions written by Aristid Breitkreuz and Dmitry Olshansky. To keep this package simpler, those functions are being moved to a separate package. This note will be updated with the name of the package(s) when available.

Synopsis

- parseBytes :: MonadThrow m => ParseSettings -> Conduit ByteString m Event
- parseBytesPos :: MonadThrow m => ParseSettings -> Conduit ByteString m EventPos
- parseText' :: MonadThrow m => ParseSettings -> Conduit Text m Event
- parseText :: MonadThrow m => ParseSettings -> Conduit Text m EventPos
- parseTextPos :: MonadThrow m => ParseSettings -> Conduit Text m EventPos
- detectUtf :: MonadThrow m => Conduit ByteString m Text
- parseFile :: MonadResource m => ParseSettings -> FilePath -> Producer m Event
- parseLBS :: MonadThrow m => ParseSettings -> ByteString -> Producer m Event
- data ParseSettings
- def :: Default a => a
- type DecodeEntities = Text -> Content
- psDecodeEntities :: ParseSettings -> DecodeEntities
- psRetainNamespaces :: ParseSettings -> Bool
- decodeXmlEntities :: DecodeEntities
- decodeHtmlEntities :: DecodeEntities
- tag :: MonadThrow m => (Name -> Maybe a) -> (a -> AttrParser b) -> (b -> ConduitM Event o m c) -> ConduitM Event o m (Maybe c)
- tagPredicate :: MonadThrow m => (Name -> Bool) -> AttrParser a -> (a -> ConduitM Event o m b) -> ConduitM Event o m (Maybe b)
- tagName :: MonadThrow m => Name -> AttrParser a -> (a -> ConduitM Event o m b) -> ConduitM Event o m (Maybe b)
- tagNoAttr :: MonadThrow m => Name -> ConduitM Event o m a -> ConduitM Event o m (Maybe a)
- tagIgnoreAttrs :: MonadThrow m => Name -> ConduitM Event o m a -> ConduitM Event o m (Maybe a)
- tagPredicateIgnoreAttrs :: MonadThrow m => (Name -> Bool) -> ConduitM Event o m a -> ConduitM Event o m (Maybe a)
- content :: MonadThrow m => Consumer Event m Text
- contentMaybe :: MonadThrow m => Consumer Event m (Maybe Text)
- ignoreTag :: MonadThrow m => (Name -> Bool) -> ConduitM Event o m (Maybe ())
- ignoreTagName :: MonadThrow m => Name -> ConduitM Event o m (Maybe ())
- ignoreAnyTagName :: MonadThrow m => [Name] -> ConduitM Event o m (Maybe ())
- ignoreAllTags :: MonadThrow m => ConduitM Event o m (Maybe ())
- ignoreTree :: MonadThrow m => (Name -> Bool) -> ConduitM Event o m (Maybe ())
- ignoreTreeName :: MonadThrow m => Name -> ConduitM Event o m (Maybe ())
- ignoreAnyTreeName :: MonadThrow m => [Name] -> ConduitM Event o m (Maybe ())
- ignoreAllTrees :: MonadThrow m => ConduitM Event o m (Maybe ())
- ignoreAllTreesContent :: MonadThrow m => ConduitM Event o m (Maybe ())
- data AttrParser a
- attr :: Name -> AttrParser (Maybe Text)
- requireAttr :: Name -> AttrParser Text
- optionalAttr :: Name -> AttrParser (Maybe Text)
- requireAttrRaw :: String -> ((Name, [Content]) -> Maybe b) -> AttrParser b
- optionalAttrRaw :: ((Name, [Content]) -> Maybe b) -> AttrParser (Maybe b)
- ignoreAttrs :: AttrParser ()
- orE :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m (Maybe a) -> Consumer Event m (Maybe a)
- choose :: Monad m => [ConduitM Event o m (Maybe a)] -> ConduitM Event o m (Maybe a)
- many :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m [a]
- manyIgnore :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m (Maybe ()) -> Consumer Event m [a]
- many' :: MonadThrow m => Consumer Event m (Maybe a) -> Consumer Event m [a]
- force :: MonadThrow m => String -> m (Maybe a) -> m a
- manyYield :: Monad m => ConduitM a b m (Maybe b) -> Conduit a m b
- manyIgnoreYield :: MonadThrow m => ConduitM Event b m (Maybe b) -> Consumer Event m (Maybe ()) -> Conduit Event m b
- manyYield' :: MonadThrow m => ConduitM Event b m (Maybe b) -> Conduit Event m b
- takeAllTreesContent :: MonadThrow m => Conduit Event m Event
- data XmlException
  - = XmlException {
    - xmlErrorMessage :: String
    - xmlBadInput :: Maybe Event
    }
  - | InvalidEndElement Name (Maybe Event)
  - | InvalidEntity String (Maybe Event)
  - | MissingAttribute String
  - | UnparsedAttributes [(Name, [Content])]
- data PositionRange :: *
- type EventPos = (Maybe PositionRange, Event)

# Parsing XML files

parseBytes :: MonadThrow m => ParseSettings -> Conduit ByteString m Event #

Parses a byte stream into `Event`s. This function is implemented fully in Haskell using attoparsec-text for parsing. The produced error messages do not give line/column information, so you may prefer to stick with the parser provided by libxml-enumerator. However, this has the advantage of not relying on any C libraries.

This relies on `detectUtf` to determine character encoding, and `parseText'` to do the actual parsing.

parseBytesPos :: MonadThrow m => ParseSettings -> Conduit ByteString m EventPos #

parseText' :: MonadThrow m => ParseSettings -> Conduit Text m Event #

Parses a character stream into `Event`s. This function is implemented fully in Haskell using attoparsec-text for parsing. The produced error messages do not give line/column information, so you may prefer to stick with the parser provided by libxml-enumerator. However, this has the advantage of not relying on any C libraries.

Since 1.2.4

parseText :: MonadThrow m => ParseSettings -> Conduit Text m EventPos #

Deprecated: Please use `parseText'` or `parseTextPos`.

parseTextPos :: MonadThrow m => ParseSettings -> Conduit Text m EventPos #

Same as `parseText'`, but includes the position of each event.

Since 1.2.4

detectUtf :: MonadThrow m => Conduit ByteString m Text #

Automatically determine which UTF variant is being used. This function first checks for BOMs, removing them as necessary, and then check for the equivalent of <?xml for each of UTF-8, UTF-16LEBE, and UTF-32LEBE. It defaults to assuming UTF-8.

parseFile :: MonadResource m => ParseSettings -> FilePath -> Producer m Event #

A helper function which reads a file from disk using `enumFile`, detects character encoding using `detectUtf`, parses the XML using `parseBytes`, and then hands off control to your supplied parser.

parseLBS :: MonadThrow m => ParseSettings -> ByteString -> Producer m Event #

Parse an event stream from a lazy `ByteString`.

## Parser settings

data ParseSettings #

Instances

Default ParseSettings # |
Methods def :: ParseSettings #

def :: Default a => a #

The default value for this type.

type DecodeEntities = Text -> Content #

psDecodeEntities :: ParseSettings -> DecodeEntities #

psRetainNamespaces :: ParseSettings -> Bool #

Whether the original xmlns attributes should be retained in the parsed values. For more information on motivation, see:

https://github.com/snoyberg/xml/issues/38

Default: False

Since 1.2.1

### Entity decoding

decodeXmlEntities :: DecodeEntities #

Default implementation of `DecodeEntities`: handles numeric entities and the five standard character entities (lt, gt, amp, quot, apos).

decodeHtmlEntities :: DecodeEntities #

HTML4-compliant entity decoder. Handles numerics, the five standard character entities, and the additional 248 entities defined by HTML 4 and XHTML 1.

Note that HTML 5 introduces a drastically larger number of entities, and this code does not recognize most of them.

# Event parsing

tag #

Arguments

:: MonadThrow m |
=> (Name -> Maybe a) | Check if this is a correct tag name and return a value that can be used to get an `AttrParser`. If this returns `Nothing`, the function will also return `Nothing`
-> (a -> AttrParser b) | Given the value returned by the name checker, this function will be used to get an `AttrParser` appropriate for the specific tag.
-> (b -> ConduitM Event o m c) | Handler function to handle the attributes and children of a tag, given the value return from the `AttrParser`
-> ConduitM Event o m (Maybe c) |

Deprecated: The signature of this function will change in next release.

The most generic way to parse a tag. It takes a predicate for checking if this is the correct tag name, an `AttrParser` for handling attributes, and then a parser for dealing with content.

`Events` are consumed if and only if the predicate holds.

This function automatically absorbs its balancing closing tag, and will throw an exception if not all of the attributes or child elements are consumed. If you want to allow extra attributes, see `ignoreAttrs`.

This function automatically ignores comments, instructions and whitespace.

tagPredicate #

Arguments

:: MonadThrow m |
=> (Name -> Bool) | Name predicate that returns `True` if the name matches the parser
-> AttrParser a | The attribute parser to be used for tags matching the predicate
-> (a -> ConduitM Event o m b) | Handler function to handle the attributes and children of a tag, given the value return from the `AttrParser`
-> ConduitM Event o m (Maybe b) |

Deprecated: This function will be removed in next release.

A simplified version of `tag` which matches against boolean predicates.

tagName #

Arguments

:: MonadThrow m |
=> Name | The tag name this parser matches to (includes namespaces)
-> AttrParser a | The attribute parser to be used for tags matching the predicate
-> (a -> ConduitM Event o m b) | Handler function to handle the attributes and children of a tag, given the value return from the `AttrParser`
-> ConduitM Event o m (Maybe b) |

Deprecated: This function will be removed in next release.

A simplified version of `tag` which matches for specific tag names instead of taking a predicate function. This is often sufficient, and when combined with OverloadedStrings and the IsString instance of `Name`, can prove to be very concise. . Note that `Name` is namespace sensitive. When using the `IsString` instance of name, use > "{http:/ab}c" :: Name to match the tag `c` in the XML namespace `http://a/b`

tagNoAttr #

Arguments

:: MonadThrow m |
=> Name | The name this parser matches to
-> ConduitM Event o m a | Handler function to handle the children of the matched tag
-> ConduitM Event o m (Maybe a) |

Deprecated: The signature of this function will change in next release.

A further simplified tag parser, which requires that no attributes exist.

tagIgnoreAttrs #

Arguments

:: MonadThrow m |
=> Name | The name this parser matches to
-> ConduitM Event o m a | Handler function to handle the children of the matched tag
-> ConduitM Event o m (Maybe a) |

Deprecated: The signature of this function will change in next release.

A further simplified tag parser, which ignores all attributes, if any exist

tagPredicateIgnoreAttrs #

Arguments

:: MonadThrow m |
=> (Name -> Bool) | The name predicate this parser matches to
-> ConduitM Event o m a | Handler function to handle the children of the matched tag
-> ConduitM Event o m (Maybe a) |

Deprecated: This function will be removed in next release.

A further simplified tag parser, which ignores all attributes, if any exist

content :: MonadThrow m => Consumer Event m Text #

Grabs the next piece of content. If none if available, returns `empty`. This is simply a wrapper around `contentMaybe`.

contentMaybe :: MonadThrow m => Consumer Event m (Maybe Text) #

Grabs the next piece of content if available. This function skips over any comments and instructions and concatenates all content until the next start or end tag.

# Ignoring tags/trees

ignoreTag #

Arguments

:: MonadThrow m |
=> (Name -> Bool) | The predicate name to match to
-> ConduitM Event o m (Maybe ()) |

Deprecated: The signature of this function will change in next release.

Ignore an empty tag and all of its attributes by predicate. This does not ignore the tag recursively (i.e. it assumes there are no child elements). This functions returns `Just` if the tag matched.

ignoreTagName #

Arguments

:: MonadThrow m |
=> Name | The name to match to
-> ConduitM Event o m (Maybe ()) |

Deprecated: This function will be removed in next release.

Like `ignoreTag`, but matches an exact name

ignoreAnyTagName #

Arguments

:: MonadThrow m |
=> [Name] | The name to match to
-> ConduitM Event o m (Maybe ()) |

Deprecated: This function will be removed in next release.

Like `ignoreTagName`, but matches any name from a list of names.

ignoreAllTags :: MonadThrow m => ConduitM Event o m (Maybe ()) #

Deprecated: This function will be removed in next release.

Like `ignoreTag`, but matches all tag name.

    ignoreAllTags = ignoreTag (const True)

ignoreTree #

Arguments

:: MonadThrow m |
=> (Name -> Bool) | The predicate name to match to
-> ConduitM Event o m (Maybe ()) |

Deprecated: The signature of this function will change in next release.

Ignore an empty tag, its attributes and its children subtree recursively. Both content and text events are ignored. This functions returns `Just` if the tag matched.

ignoreTreeName :: MonadThrow m => Name -> ConduitM Event o m (Maybe ()) #

Deprecated: This function will be removed in next release.

Like `ignoreTagName`, but also ignores non-empty tabs

ignoreAnyTreeName #

Arguments

:: MonadThrow m |
=> [Name] | The name to match to
-> ConduitM Event o m (Maybe ()) |

Deprecated: This function will be removed in next release.

Like `ignoreTagName`, but matches any name from a list of names.

ignoreAllTrees :: MonadThrow m => ConduitM Event o m (Maybe ()) #

Deprecated: This function will be removed in next release.

Like `ignoreAllTags`, but ignores entire subtrees.

    ignoreAllTrees = ignoreTree (const True)

ignoreAllTreesContent :: MonadThrow m => ConduitM Event o m (Maybe ()) #

Deprecated: This function will be renamed into `ignoreAnyTreeContent` in next release.

Like `ignoreAllTrees`, but also ignores all content events

# Attribute parsing

data AttrParser a #

A monad for parsing attributes. By default, it requires you to deal with all attributes present on an element, and will throw an exception if there are unhandled attributes. Use the `requireAttr`, `attr` et al functions for handling an attribute, and `ignoreAttrs` if you would like to skip the rest of the attributes on an element.

`Alternative` instance behaves like `First` monoid: it chooses first parser which doesn't fail.

Instances

Monad AttrParser # |
Methods (>>=) :: AttrParser a -> (a -> AttrParser b) -> AttrParser b # (>>) :: AttrParser a -> AttrParser b -> AttrParser b # return :: a -> AttrParser a # fail :: String -> AttrParser a #
Functor AttrParser # |
Methods fmap :: (a -> b) -> AttrParser a -> AttrParser b # (<$) :: a -> AttrParser b -> AttrParser a #
Applicative AttrParser # |
Methods pure :: a -> AttrParser a # (<*>) :: AttrParser (a -> b) -> AttrParser a -> AttrParser b # (*>) :: AttrParser a -> AttrParser b -> AttrParser b # (<*) :: AttrParser a -> AttrParser b -> AttrParser a #
Alternative AttrParser # |
Methods empty :: AttrParser a # (<|>) :: AttrParser a -> AttrParser a -> AttrParser a # some :: AttrParser a -> AttrParser [a] # many :: AttrParser a -> AttrParser [a] #
MonadThrow AttrParser # |
Methods throwM :: Exception e => e -> AttrParser a #

attr :: Name -> AttrParser (Maybe Text) #

Return the value for an attribute if present.

requireAttr :: Name -> AttrParser Text #

Shortcut composition of `force` and `attr`.

optionalAttr :: Name -> AttrParser (Maybe Text) #

Deprecated: Please use `attr`.

requireAttrRaw :: String -> ((Name, [Content]) -> Maybe b) -> AttrParser b #

optionalAttrRaw :: ((Name, [Content]) -> Maybe b) -> AttrParser (Maybe b) #

ignoreAttrs :: AttrParser () #

Skip the remaining attributes on an element. Since this will clear the list of attributes, you must call this after any calls to `requireAttr`, `optionalAttr`, etc.

# Combinators

orE #

Arguments

:: Monad m |
=> Consumer Event m (Maybe a) | The first (preferred) parser
-> Consumer Event m (Maybe a) | The second parser, only executed if the first parser fails
-> Consumer Event m (Maybe a) |

Get the value of the first parser which returns `Just`. If no parsers succeed (i.e., return `Just`), this function returns `Nothing`.

    orE a b = choose [a, b]

choose #

Arguments

:: Monad m |
=> [ConduitM Event o m (Maybe a)] | List of parsers that will be tried in order.
-> ConduitM Event o m (Maybe a) | Result of the first parser to succeed, or `Nothing` if no parser succeeded

Get the value of the first parser which returns `Just`. If no parsers succeed (i.e., return `Just`), this function returns `Nothing`.

many :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m [a] #

Keep parsing elements as long as the parser returns `Just`.

manyIgnore :: Monad m => Consumer Event m (Maybe a) -> Consumer Event m (Maybe ()) -> Consumer Event m [a] #

Keep parsing elements as long as the parser returns `Just` or the ignore parser returns `Just`.

many' :: MonadThrow m => Consumer Event m (Maybe a) -> Consumer Event m [a] #

Like `many`, but any tags and content the consumer doesn't match on are silently ignored.

force #

Arguments

:: MonadThrow m |
=> String | Error message
-> m (Maybe a) | Optional parser to be forced
-> m a |

Force an optional parser into a required parser. All of the `tag` functions, `attr`, `choose` and `many` deal with `Maybe` parsers. Use this when you want to finally force something to happen.

# Streaming combinators

manyYield :: Monad m => ConduitM a b m (Maybe b) -> Conduit a m b #

Like `many`, but uses `yield` so the result list can be streamed to downstream conduits without waiting for `manyYield` to finish

manyIgnoreYield #

Arguments

:: MonadThrow m |
=> ConduitM Event b m (Maybe b) | Consuming parser that generates the result stream
-> Consumer Event m (Maybe ()) | Ignore parser that consumes elements to be ignored
-> Conduit Event m b |

Like `manyIgnore`, but uses `yield` so the result list can be streamed to downstream conduits without waiting for `manyYield` to finish

manyYield' :: MonadThrow m => ConduitM Event b m (Maybe b) -> Conduit Event m b #

Like `many'`, but uses `yield` so the result list can be streamed to downstream conduits without waiting for `manyYield` to finish

takeAllTreesContent :: MonadThrow m => Conduit Event m Event #

Deprecated: This function will be removed in next release.

Like `ignoreAllTreesContent`, but stream the corresponding `Event`s rather than ignoring them. Incomplete elements (without a closing-tag) will trigger an `XmlException`.

    >>> runResourceT $ parseLBS def "text<a></a>" $$ takeAllTreesContent =$= consume
    Just [ EventContent (ContentText "text"), EventBeginElement "a" [], EventEndElement "a"]

    >>> runResourceT $ parseLBS def "</a><b></b>" $$ takeAllTreesContent =$= consume
    Just [ ]

    >>> runResourceT $ parseLBS def "<b><c></c></b></a>text" $$ takeAllTreesContent =$= consume
    Just [ EventBeginElement "b" [], EventBeginElement "c" [], EventEndElement "c", EventEndElement "b" ]

Since 1.4.0

# Exceptions

data XmlException #

Constructors

XmlException |
Fields xmlErrorMessage :: String xmlBadInput :: Maybe Event
InvalidEndElement Name (Maybe Event) |
InvalidEntity String (Maybe Event) |
MissingAttribute String |
UnparsedAttributes [(Name, [Content])] |

Instances

Show XmlException # |
Methods showsPrec :: Int -> XmlException -> ShowS # show :: XmlException -> String # showList :: [XmlException] -> ShowS #
Exception XmlException # |
Methods toException :: XmlException -> SomeException # fromException :: SomeException -> Maybe XmlException # displayException :: XmlException -> String #

# Other types

data PositionRange :: * #

Instances

Eq PositionRange |
Methods (==) :: PositionRange -> PositionRange -> Bool # (/=) :: PositionRange -> PositionRange -> Bool #
Ord PositionRange |
Methods compare :: PositionRange -> PositionRange -> Ordering # (<) :: PositionRange -> PositionRange -> Bool # (<=) :: PositionRange -> PositionRange -> Bool # (>) :: PositionRange -> PositionRange -> Bool # (>=) :: PositionRange -> PositionRange -> Bool # max :: PositionRange -> PositionRange -> PositionRange # min :: PositionRange -> PositionRange -> PositionRange #
Show PositionRange |
Methods showsPrec :: Int -> PositionRange -> ShowS # show :: PositionRange -> String # showList :: [PositionRange] -> ShowS #

type EventPos = (Maybe PositionRange, Event) #