104 lines
3.8 KiB
Haskell
104 lines
3.8 KiB
Haskell
{-# LANGUAGE NamedFieldPuns #-}
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module PDF (
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Document(..)
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, parseDocument
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, render
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) where
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import Data.ByteString.Char8 (ByteString)
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import qualified Data.ByteString.Char8 as BS (
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drop, findIndex, head, isPrefixOf, last, length, span, unpack
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)
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import Data.ByteString.Char8.Util (previous, subBS)
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import qualified Data.ByteString.Lazy as Lazy (ByteString)
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import qualified Data.Map as Map (lookup)
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import PDF.Body (populate)
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import qualified PDF.EOL as EOL (Style(..), charset, parser)
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import PDF.Object (
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Content(..), DirectObject(..), InputStructure(..), Name(..), Number(..)
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, Structure(..)
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, eofMarker, magicNumber, structure
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)
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import qualified PDF.Output as Output (render, line)
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import PDF.Output (Output(..))
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import PDF.Parser (Parser, evalParser, string, takeAll)
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import Text.Printf (printf)
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data Document = Document {
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pdfVersion :: String
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, eolStyle :: EOL.Style
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, updates :: [Content]
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} deriving Show
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instance Output Document where
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output (Document {pdfVersion, updates}) =
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Output.line (printf "%%PDF-%s" pdfVersion)
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`mappend` output updates
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render :: Document -> Lazy.ByteString
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render document@(Document {eolStyle}) = Output.render eolStyle document
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version :: Parser () String
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version = BS.unpack <$>
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(string magicNumber *> takeAll (not . (`elem` EOL.charset)))
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check :: Bool -> String -> Either String ()
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check test errorMessage = if test then return () else Left errorMessage
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readStartXref :: EOL.Style -> ByteString -> Either String Int
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readStartXref eolStyle input =
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check (eofMarker `BS.isPrefixOf` (BS.drop eofMarkerPosition input))
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"Badly formed document : missing EOF marker at the end"
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>> return (read . BS.unpack $ subBS startXrefPosition startXrefLength input)
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where
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(eolOffset, eolLastByte) = case eolStyle of
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EOL.CRLF -> (2, '\n')
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EOL.CR -> (1, '\r')
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_ -> (1, '\n')
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eofMarkerPosition =
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BS.length input - BS.length eofMarker
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- if BS.last input == BS.last eofMarker then 0 else eolOffset
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startXrefPosition =
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previous eolLastByte (eofMarkerPosition - eolOffset - 1) input + 1
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startXrefLength = eofMarkerPosition - eolOffset - startXrefPosition
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findNextLine :: ByteString -> Int
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findNextLine input =
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let (line, eolPrefixed) = BS.span notInEol input in
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let nextNotInEol = BS.findIndex notInEol eolPrefixed in
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BS.length line + (maybe (BS.length eolPrefixed) id nextNotInEol)
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where
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notInEol = not . (`elem` EOL.charset)
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findNextSection :: Int -> ByteString -> Int
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findNextSection offset input =
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case BS.findIndex (== BS.head eofMarker) input of
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Nothing -> 0
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Just delta ->
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let newInput = BS.drop delta input in
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let newOffset = offset + delta in
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if BS.isPrefixOf eofMarker newInput
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then newOffset + findNextLine newInput
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else findNextSection (newOffset + 1) (BS.drop 1 newInput)
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readStructures :: Int -> ByteString -> Either String [InputStructure]
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readStructures startXref input =
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evalParser structure () (BS.drop startXref input) >>= stopOrFollow
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where
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stopOrFollow s@(Structure {trailer}) =
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case Map.lookup (Name "Prev") trailer of
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Nothing -> Right [InputStructure (findNextLine input) s]
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Just (NumberObject (Number newStartXref)) ->
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let offset = truncate newStartXref in
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let startOffset = findNextSection offset (BS.drop offset input) in
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(InputStructure startOffset s:) <$> (readStructures offset input)
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Just v -> Left $ "Bad value for Prev entry in trailer: " ++ show v
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parseDocument :: ByteString -> Either String Document
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parseDocument input = do
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(pdfVersion, eolStyle) <- evalParser ((,) <$> version <*> EOL.parser) () input
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startXref <- readStartXref eolStyle input
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structuresRead <- readStructures startXref input
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let updates = populate input <$> structuresRead
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return $ Document {pdfVersion, eolStyle, updates}
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