Improve getObj example to catch no-existing ObjectId and default to listing existing ObjectIds when none is provided

ChangeLog.md

@@ -1,5 +1,13 @@
 # Revision history for Hufflepdf
 
+## 0.2.0.1  -- 2019-11-27
+
+* Fix bug discovered while running Hufflepdf on a PDF output from pdftk : magic keywords like `obj`, `stream` or `xref` can have spaces after them before the EOL
+
+## 0.2.0.0  -- 2019-10-14
+
+* Implement PDF's multilayer update mechanism
+
 ## 0.1.1.1  -- 2019-05-31
 
 * Fix a bug preventing files with the «trailer» keyword on the same line as the dictionary that follows it to be parsed

Hufflepdf.cabal

@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                Hufflepdf
-version:             0.1.1.1
+version:             0.2.0.1
 synopsis:            A PDF parser
 -- description:         
 license:             BSD3
@@ -20,6 +20,7 @@ library
                      , PDF.EOL
                      , PDF.Object
                      , PDF.Output
+                     , PDF.Update
   other-modules:       Data.ByteString.Char8.Util
                      , PDF.Body
                      , PDF.Parser
@@ -32,3 +33,21 @@ library
   hs-source-dirs:      src
   ghc-options:         -Wall
   default-language:    Haskell2010
+
+executable             equivalent
+  main-is:             examples/equivalent.hs
+  build-depends:       base
+                     , bytestring
+                     , Hufflepdf
+  ghc-options:         -Wall
+  default-language:    Haskell2010
+
+executable             getObj
+  main-is:             examples/getObj.hs
+  build-depends:       base
+                     , bytestring
+                     , containers
+                     , Hufflepdf
+                     , zlib
+  ghc-options:         -Wall
+  default-language:    Haskell2010

examples/equivalent.hs

@@ -0,0 +1,13 @@
+import qualified Data.ByteString.Char8 as BS (readFile)
+import qualified Data.ByteString.Lazy.Char8 as Lazy (writeFile)
+import PDF (parseDocument, render)
+import System.Environment (getArgs)
+import System.IO (hPutStrLn, stderr)
+
+main :: IO ()
+main = do
+  [inputFile, outputFile] <- getArgs
+  result <- parseDocument <$> BS.readFile inputFile
+  case result of
+    Left parseError -> hPutStrLn stderr parseError
+    Right doc -> Lazy.writeFile outputFile $ render doc

examples/getObj.hs

@@ -0,0 +1,53 @@
+{-# LANGUAGE NamedFieldPuns #-}
+
+import Codec.Compression.Zlib (decompress)
+import Data.ByteString.Lazy.Char8 (ByteString)
+import qualified Data.ByteString.Char8 as BS (readFile)
+import qualified Data.ByteString.Lazy.Char8 as Lazy (fromStrict, putStr, toStrict)
+import Data.Map ((!?))
+import qualified Data.Map as Map (keys, lookup)
+import PDF (Document(..), parseDocument)
+import qualified PDF.EOL as EOL (Style)
+import PDF.Object (Content(..), DirectObject(..), Object(..), Name(..))
+import PDF.Output (ObjectId(..))
+import qualified PDF.Output as Output (render)
+import PDF.Update (unify)
+import System.Environment (getArgs, getProgName)
+import System.Exit (die)
+import Text.Printf (printf)
+
+display :: EOL.Style -> Object -> ByteString
+display eolStyle d@(Direct _) = Output.render eolStyle d
+display eolStyle s@(Stream {header, streamContent}) = Output.render eolStyle $
+  case Map.lookup (Name "Filter") header of
+    Just (NameObject (Name "FlateDecode")) -> Stream {
+          header
+        , streamContent = Lazy.toStrict . decompress $ Lazy.fromStrict streamContent
+      }
+    _ -> s
+
+extractObject :: ObjectId -> Document -> Either String ByteString
+extractObject objectId (Document {eolStyle, updates}) =
+  case objects content !? objectId of
+    Nothing -> Left $ "No object has ID " ++ show (getObjectId objectId)
+    Just o -> Right $ display eolStyle o
+  where
+    content = unify updates
+
+listObjectIds :: Document -> Either String [String]
+listObjectIds =
+  Right . prependTitle . toString . Map.keys . objects . unify . updates
+  where
+    toString = fmap (show . getObjectId)
+    prependTitle = ("ObjectIds defined in this PDF:":)
+
+main :: IO ()
+main = do
+  (inputFile, getData) <- parse =<< getArgs
+  input <- BS.readFile inputFile
+  either die id $ (parseDocument input >>= getData)
+  where
+    parse [inputFile] = return (inputFile, fmap (mapM_ putStrLn) . listObjectIds)
+    parse [inputFile, objectId] = return
+      (inputFile, fmap Lazy.putStr . extractObject (ObjectId (read objectId)))
+    parse _ = die . printf "Syntax: %s inputFile [OBJECT_ID]\n" =<< getProgName

src/PDF.hs

@@ -19,21 +19,21 @@ import PDF.Object (
     , Structure(..)
     , eofMarker, magicNumber, structure
   )
-import qualified PDF.Output as Output (render, string)
+import qualified PDF.Output as Output (render, line)
-import PDF.Output (Output(..), nextLine)
+import PDF.Output (Output(..))
 import PDF.Parser (Parser, runParser, string, takeAll)
 import Text.Printf (printf)
 
 data Document = Document {
       pdfVersion :: String
     , eolStyle :: EOL.Style
-    , contents :: [Content]
+    , updates :: [Content]
   } deriving Show
 
 instance Output Document where
-  output (Document {pdfVersion, contents}) =
+  output (Document {pdfVersion, updates}) =
-      Output.string (printf "%%PDF-%s" pdfVersion)
+      Output.line (printf "%%PDF-%s" pdfVersion)
-    `nextLine` output contents
+    `mappend` output updates
 
 render :: Document -> Lazy.ByteString
 render document@(Document {eolStyle}) = Output.render eolStyle document
@@ -99,5 +99,5 @@ parseDocument input = do
   (pdfVersion, eolStyle) <- runParser ((,) <$> version <*> EOL.parser) () input
   startXref <- readStartXref eolStyle input
   structuresRead <- readStructures startXref input
-  let contents = populate input <$> structuresRead
+  let updates = populate input <$> structuresRead
-  return $ Document {pdfVersion, eolStyle, contents}
+  return $ Document {pdfVersion, eolStyle, updates}

src/PDF/Body.hs

@@ -14,9 +14,10 @@ import qualified PDF.EOL as EOL (charset, parser)
 import PDF.Object (
       Content(..), DirectObject(..), Flow(..), IndirectObjCoordinates(..)
     , InputStructure(..), Name(..), Number(..), Object(..), Occurrence(..)
-    , Structure(..), XRefEntry(..), XRefSection, XRefSubSection(..)
+    , Structure(..), XRefEntry(..), XRefSection
     , blank, dictionary, directObject, integer, line
   )
+import PDF.Output (ObjectId(..), Offset(..))
 import PDF.Parser (Parser, (<?>), block, char, on, option, runParser, takeAll)
 
 data UserState = UserState {
@@ -30,7 +31,7 @@ type SParser = Parser UserState
 modifyFlow :: (Flow -> Flow) -> SParser ()
 modifyFlow f = modify $ \state -> state {flow = f $ flow state}
 
-addObject :: Int -> Object -> SParser ()
+addObject :: ObjectId -> Object -> SParser ()
 addObject objectId newObject = modifyFlow $ \flow -> flow {
     tmpObjects = Map.insert objectId newObject $ tmpObjects flow
   }
@@ -45,29 +46,20 @@ comment = BS.unpack <$> (option "" afterPercent <* EOL.parser)
   where
     afterPercent = BS.cons <$> char '%' <*> takeAll (not . (`elem` EOL.charset))
 
-lookupOffset :: Int -> XRefSection -> Maybe Int
+lookupOffset :: ObjectId -> SParser Offset
-lookupOffset _ [] = Nothing
+lookupOffset objectId = do
-lookupOffset objectId (xrefSubSection:others) =
-  let XRefSubSection {firstObjectId, entriesNumber, entries} = xrefSubSection in
-  let index = objectId - firstObjectId in
-  if index >= 0 && index < entriesNumber
-  then
-    case Map.lookup index entries of
-      Just (InUse {offset}) -> Just offset
-      _ -> Nothing
-  else lookupOffset objectId others
-
-getOffset :: Int -> SParser Int
-getOffset objectId = do
   table <- gets xreferences
-  case lookupOffset objectId table of
+  case Map.lookup objectId table >>= entryOffset of
     Nothing -> fail $
       "obj " ++ show objectId ++ " is referenced but missing in XRef table"
     Just offset -> return offset
+  where
+    entryOffset (InUse {offset}) = Just offset
+    entryOffset _ = Nothing
 
-loadNumber :: Int -> SParser Float
+loadNumber :: ObjectId -> SParser Double
 loadNumber objectId = do
-  offset <- getOffset objectId
+  offset <- getOffset <$> lookupOffset objectId
   objectStart <- BS.drop offset <$> gets input
   indirectObjCoordinates `on` (objectStart :: ByteString) >> return ()
   objectValue <- (!objectId) . tmpObjects <$> gets flow
@@ -78,7 +70,7 @@ loadNumber objectId = do
 invalidValue :: Object -> String
 invalidValue v = "Invalid value " ++ show v
 
-getSize :: Maybe DirectObject -> SParser Float
+getSize :: Maybe DirectObject -> SParser Double
 getSize Nothing = fail "Missing '/Length' key on stream"
 getSize (Just (NumberObject (Number size))) = return size
 getSize (Just (Reference (IndirectObjCoordinates {objectId}))) = do
@@ -104,7 +96,7 @@ object = streamObject <|> Direct <$> directObject
 
 indirectObjCoordinates :: SParser IndirectObjCoordinates
 indirectObjCoordinates = do
-  objectId <- integer
+  objectId <- ObjectId <$> integer
   coordinates <- IndirectObjCoordinates objectId <$> integer
   objectValue <- line "obj" *> object <* blank <* line "endobj"
   addObject objectId objectValue
@@ -126,7 +118,7 @@ populate input structure =
         }
   where
     docStructure = inputStructure structure
-    xreferences = xrefSection docStructure
+    xreferences = xRef docStructure
     initialState = UserState {
         input, xreferences, flow = Flow {
             occurrencesStack = [], tmpObjects = Map.empty

src/PDF/Object.hs

@@ -5,6 +5,7 @@ module PDF.Object (
       Content(..)
     , DirectObject(..)
     , Flow(..)
+    , IndexedObjects
     , IndirectObjCoordinates(..)
     , InputStructure(..)
     , Name(..)
@@ -14,7 +15,6 @@ module PDF.Object (
     , Structure(..)
     , XRefEntry(..)
     , XRefSection
-    , XRefSubSection(..)
     , blank
     , dictionary
     , directObject
@@ -31,12 +31,15 @@ import qualified Data.ByteString.Char8 as BS (
     concat, cons, pack, singleton, unpack
   )
 import Data.Map (Map, (!), mapWithKey)
-import qualified Data.Map as Map (elems, fromList, toList)
+import qualified Data.Map as Map (
+    delete, empty, fromList, lookup, minViewWithKey, toList, union
+  )
 import qualified PDF.EOL as EOL (charset, parser)
-import qualified PDF.Output as Output (string)
+import qualified PDF.Output as Output (concat, line, string)
 import PDF.Output (
-      OBuilder, Offset(..), Output(..)
+      OBuilder, ObjectId(..), Offset(..), Output(..), Resource(..)
-    , byteString, getOffsets, join, newLine, nextLine, saveOffset
+    , byteString, getObjectId, getOffset, getOffsets, join, newLine
+    , saveOffset
   )
 import PDF.Parser (
       Parser, (<?>)
@@ -46,7 +49,7 @@ import PDF.Parser (
 import Text.Printf (printf)
 
 line :: String -> Parser u ()
-line l = (string (BS.pack l) *> EOL.parser *> return ()) <?> printf "line «%s»" l
+line l = (string (BS.pack l) *> blank *> return ()) <?> printf "line «%s»" l
 
 magicNumber :: ByteString
 magicNumber = "%PDF-"
@@ -73,6 +76,8 @@ integer = read . BS.unpack <$> decNumber <* blank <?> "decimal integer"
 --          OBJECTS
 -------------------------------------
 
+type IndexedObjects = Map ObjectId Object
+
 --
 -- Boolean
 --
@@ -83,7 +88,7 @@ boolean =
 --
 -- Number
 --
-newtype Number = Number Float deriving Show
+newtype Number = Number Double deriving Show
 
 instance Output Number where
   output (Number f) = Output.string $
@@ -130,7 +135,7 @@ stringObject =
 newtype Name = Name String deriving (Eq, Ord, Show)
 
 instance Output Name where
-  output (Name n) = "/" `mappend` Output.string n
+  output (Name n) = Output.string ('/':n)
 
 name :: Parser u Name
 name = Name . BS.unpack <$> (char '/' *> takeAll regular) <?> "name"
@@ -153,7 +158,7 @@ instance Output Dictionary where
     where
       keyValues = join " " $ outputKeyVal <$> Map.toList dict
       outputKeyVal :: (Name, DirectObject) -> OBuilder
-      outputKeyVal (key, val) = output key `mappend` " " `mappend` output val
+      outputKeyVal (key, val) = Output.concat [output key, " ", output val]
 
 dictionary :: Parser u Dictionary
 dictionary =
@@ -172,12 +177,13 @@ nullObject = string "null" *> return () <?> "null object"
 -- Reference
 --
 data IndirectObjCoordinates = IndirectObjCoordinates {
-      objectId :: Int
+      objectId :: ObjectId
     , versionNumber :: Int
   } deriving Show
 
 reference :: Parser u IndirectObjCoordinates
-reference = IndirectObjCoordinates <$> integer <*> integer <* char 'R' <?> "reference to an object"
+reference = IndirectObjCoordinates
+  <$> (fmap ObjectId integer) <*> integer <* char 'R' <?> "reference to an object"
 
 --
 -- DirectObject
@@ -198,11 +204,11 @@ instance Output DirectObject where
   output (NumberObject n) = output n
   output (StringObject s) = output s
   output (NameObject n) = output n
-  output (Array a) = "[" `mappend` join " " a `mappend` "]"
+  output (Array a) = Output.concat ["[", join " " a, "]"]
   output (Dictionary d) = output d
   output (Null) = "null"
   output (Reference (IndirectObjCoordinates {objectId, versionNumber})) =
-    Output.string (printf "%d %d R" objectId versionNumber)
+    Output.string (printf "%d %d R" (getObjectId objectId) versionNumber)
 
 directObject :: Parser u DirectObject
 directObject =
@@ -229,25 +235,26 @@ data Object =
 
 instance Output Object where
   output (Direct d) = output d
-  output (Stream {header, streamContent}) =
+  output (Stream {header, streamContent}) = Output.concat [
-      output header
+        output header, newLine
-    `nextLine` "stream"
+      , Output.line "stream"
-    `nextLine` byteString streamContent
+      , byteString streamContent
-    `mappend` "endstream"
+      , "endstream"
+    ]
 
 --
 -- Occurrence
 --
 data Occurrence = Comment String | Indirect IndirectObjCoordinates deriving Show
 
-outputOccurrence :: Map Int Object -> Occurrence -> OBuilder
+outputOccurrence :: IndexedObjects -> Occurrence -> OBuilder
-outputOccurrence _ (Comment c) =
+outputOccurrence _ (Comment c) = Output.line c
-  Output.string c `mappend` newLine
 outputOccurrence objects (Indirect (IndirectObjCoordinates {objectId, versionNumber})) =
-    saveOffset (ObjectId objectId)
+  saveOffset (Object objectId) >> Output.concat [
-  >> Output.string (printf "%d %d obj" objectId versionNumber)
+        Output.line (printf "%d %d obj" (getObjectId objectId) versionNumber)
-  `nextLine` output (objects ! objectId)
+      , output (objects ! objectId), newLine
-  `nextLine` "endobj" `mappend` newLine
+      , Output.line "endobj"
+    ]
 
 -------------------------------------
 --          XREF TABLE
@@ -257,18 +264,18 @@ outputOccurrence objects (Indirect (IndirectObjCoordinates {objectId, versionNum
 -- XRefEntry
 --
 data XRefEntry = InUse {
-      offset :: Int
+      offset :: Offset
     , generation :: Int
   } | Free {
-      nextFree :: Int
+      nextFree :: ObjectId
     , generation :: Int
   } deriving Show
 
 instance Output XRefEntry where
   output (InUse {offset, generation}) =
-      Output.string (printf "%010d %05d n " offset generation) `mappend` newLine
+      Output.line (printf "%010d %05d n " (getOffset offset) generation)
   output (Free {nextFree, generation}) =
-      Output.string (printf "%010d %05d f " nextFree generation) `mappend` newLine
+      Output.line (printf "%010d %05d f " (getObjectId nextFree) generation)
 
 entry :: Parser u XRefEntry
 entry = do
@@ -276,31 +283,56 @@ entry = do
   (inUse big small <|> free big small <?> "XRef entry") <* blank
   where
     inUse :: Int -> Int -> Parser u XRefEntry
-    inUse offset generation = char 'n' *> return (InUse {offset, generation})
+    inUse big generation =
+      char 'n' *> return (InUse {offset = Offset big, generation})
     free :: Int -> Int -> Parser u XRefEntry
-    free nextFree generation = char 'f' *> return (Free {nextFree, generation})
+    free big generation =
+      char 'f' *> return (Free {nextFree = ObjectId big, generation})
 
 --
 -- XRefSubSection
 --
 data XRefSubSection = XRefSubSection {
-      firstObjectId :: Int
+      firstObjectId :: ObjectId
-    , entriesNumber :: Int
+    , entries :: [XRefEntry]
-    , entries :: Map Int XRefEntry
   } deriving Show
 
 instance Output XRefSubSection where
-  output (XRefSubSection {firstObjectId, entriesNumber, entries}) =
+  output (XRefSubSection {firstObjectId, entries}) =
-      Output.string (printf "%d %d" firstObjectId entriesNumber)
+      Output.line (printf "%d %d" (getObjectId firstObjectId) (length entries))
-    `nextLine` output (Map.elems entries)
+    `mappend` output entries
 
-xrefSubSection :: Parser u XRefSubSection
+xRefSubSection :: Parser u XRefSubSection
-xrefSubSection = do
+xRefSubSection = do
-  (firstObjectId, entriesNumber) <- (,) <$> integer <*> integer <?> "XRef subsection"
+  (firstId, entriesNumber) <- (,) <$> integer <*> integer <?> "XRef subsection"
-  entries <- Map.fromList . zip [firstObjectId..] <$> count entriesNumber entry
+  entries <- count entriesNumber entry
-  return $ XRefSubSection {firstObjectId, entriesNumber, entries}
+  return $ XRefSubSection {firstObjectId = ObjectId firstId, entries}
 
-type XRefSection = [XRefSubSection]
+type XRefSection = Map ObjectId XRefEntry
+
+instance Output XRefSection where
+  output = output . sections
+    where
+      sections tmp =
+        case Map.minViewWithKey tmp of
+          Nothing -> []
+          Just ((objectId@(ObjectId value), firstEntry), rest) ->
+            let (subSection, sndRest) = section objectId [firstEntry] (value + 1) rest in
+            subSection : sections sndRest
+      section firstObjectId stack nextValue tmp =
+        let nextId = ObjectId nextValue in
+        case Map.lookup nextId tmp of
+          Nothing -> (XRefSubSection {firstObjectId, entries = reverse stack}, tmp)
+          Just nextEntry ->
+            section firstObjectId (nextEntry:stack) (nextValue + 1) (Map.delete nextId tmp)
+
+
+xRefSection :: Parser u XRefSection
+xRefSection = foldr addSubsection Map.empty <$>
+  (line "xref" *> xRefSubSection `sepBy` many EOL.parser)
+  where
+    addSubsection (XRefSubSection {firstObjectId, entries}) =
+      Map.union . Map.fromList $ zip ([firstObjectId..]) entries
 
 --
 -- Structure
@@ -311,34 +343,28 @@ data InputStructure = InputStructure {
   }
 
 data Structure = Structure {
-      xrefSection :: XRefSection
+      xRef :: XRefSection
     , trailer :: Dictionary
   } deriving Show
 
 structure :: Parser u Structure
 structure =
     Structure
-  <$> (line "xref" *> xrefSubSection `sepBy` EOL.parser)
+  <$> xRefSection
   <*> (string "trailer" *> blank *> dictionary <* EOL.parser)
 
-updateXrefs :: XRefSection -> Map Offset Int -> (XRefSection, Int)
+updateXrefs :: XRefSection -> Map Resource Offset -> (XRefSection, Offset)
-updateXrefs xrefSection offsets = (
+updateXrefs xRef offsets = (mapWithKey updateEntry xRef, offsets ! StartXRef)
-      updateSubSection <$> xrefSection
-    , offsets ! StartXRef
-  )
   where
-    updateSubSection subSection@(XRefSubSection {firstObjectId, entries}) =
+    updateEntry objectId e@(InUse {}) = e {offset = offsets ! (Object objectId)}
-      subSection {entries = mapWithKey (updateEntry firstObjectId) entries}
+    updateEntry _ e = e
-    updateEntry firstObjectId index e@(InUse {}) =
-      e {offset = offsets ! (ObjectId $ firstObjectId + index)}
-    updateEntry _ _ e = e
 
 --
 -- Flow
 --
 data Flow = Flow {
       occurrencesStack :: [Occurrence]
-    , tmpObjects :: Map Int Object
+    , tmpObjects :: IndexedObjects
   } deriving Show
 
 --
@@ -346,25 +372,26 @@ data Flow = Flow {
 --
 data Content = Content {
       occurrences :: [Occurrence]
-    , objects :: Map Int Object
+    , objects :: IndexedObjects
     , docStructure :: Structure
   } deriving Show
 
-outputBody :: ([Occurrence], Map Int Object) -> OBuilder
+outputBody :: ([Occurrence], IndexedObjects) -> OBuilder
 outputBody (occurrences, objects) =
   output (outputOccurrence objects <$> occurrences) <* saveOffset StartXRef
 
 instance Output Content where
   output (Content {occurrences, objects, docStructure}) =
-    fmap (updateXrefs xrefSection) <$> getOffsets (outputBody (occurrences, objects))
+    fmap (updateXrefs xRef) <$> getOffsets (outputBody (occurrences, objects))
-    >>= \(body, (xref, startXRef)) ->
+    >>= \(body, (xref, startXRef)) -> Output.concat [
-        body
+          body
-      `mappend` "xref"
+        , Output.line "xref"
-      `nextLine` output xref
+        , output xref
-      `mappend` "trailer"
+        , Output.line "trailer"
-      `nextLine` output trailer
+        , output trailer, newLine
-      `nextLine` "startxref"
+        , Output.line "startxref"
-      `nextLine` (Output.string (printf "%d" startXRef))
+        , Output.line (printf "%d" (getOffset startXRef))
-      `nextLine` byteString eofMarker
+        , byteString eofMarker
+      ]
     where
-      Structure {xrefSection, trailer} = docStructure
+      Structure {xRef, trailer} = docStructure

src/PDF/Output.hs

@@ -2,17 +2,21 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 module PDF.Output (
       OBuilder
+    , ObjectId(..)
     , OContext(..)
     , Offset(..)
     , Output(..)
+    , Resource(..)
     , byteString
     , char
+    , concat
     , getOffsets
     , join
+    , line
     , newLine
-    , nextLine
     , saveOffset
     , string
     , render
@@ -28,10 +32,14 @@ import qualified Data.Map as Map (singleton)
 import Data.String (IsString(..))
 import Control.Monad.RWS (RWS, runRWS, ask, get, listen, modify, tell)
 import qualified PDF.EOL as EOL (Style(..))
+import Prelude hiding (concat)
 
-data Offset = StartXRef | ObjectId Int deriving (Eq, Ord)
+newtype ObjectId = ObjectId {getObjectId :: Int} deriving (Enum, Eq, Ord, Show)
+newtype Offset = Offset {getOffset :: Int} deriving (Show)
 
-newtype OContext a = OContext (RWS EOL.Style (Map Offset Int) Int a)
+data Resource = StartXRef | Object ObjectId deriving (Eq, Ord)
+
+newtype OContext a = OContext (RWS EOL.Style (Map Resource Offset) Offset a)
 type OBuilder = OContext Builder
 
 instance Functor OContext where
@@ -44,20 +52,23 @@ instance Applicative OContext where
 instance Monad OContext where
   (>>=) (OContext a) f = OContext (a >>= (\x -> let OContext y = f x in y))
 
-saveOffset :: Offset -> OContext ()
+saveOffset :: Resource -> OContext ()
-saveOffset offset = OContext $
+saveOffset resource = OContext $
-  get >>= tell . Map.singleton offset
+  get >>= tell . Map.singleton resource
 
 lift :: (a -> Builder) -> a -> OBuilder
 lift f a = return (f a)
 
-getOffsets :: OBuilder -> OContext (OBuilder, Map Offset Int)
+getOffsets :: OBuilder -> OContext (OBuilder, Map Resource Offset)
 getOffsets (OContext builder) =
   OContext (listen builder >>= \(a, w) -> return (return a, w))
 
 append :: OBuilder -> OBuilder -> OBuilder
 append (OContext a) (OContext b) = OContext (mappend <$> a <*> b)
 
+concat :: [OBuilder] -> OBuilder
+concat = foldl mappend mempty
+
 #if MIN_VERSION_base(4,11,0)
 instance Semigroup OBuilder where
   (<>) = append
@@ -83,7 +94,7 @@ instance Output Bool where
   output True = string "true"
 
 instance Output a => Output [a] where
-  output = foldl mappend mempty . fmap output
+  output = concat . fmap output
 
 join :: Output a => String -> [a] -> OBuilder
 join _ [] = mempty
@@ -91,27 +102,30 @@ join _ [a] = output a
 join separator (a:as) =
   output a `mappend` string separator `mappend` (join separator as)
 
-newLine :: OBuilder
+offset :: (Int -> Int) -> OContext ()
-newLine = OContext $ buildEOL =<< ask
+offset f = OContext $ modify $ \(Offset o) -> Offset (f o)
-  where
-    buildEOL EOL.CR = return (char8 '\r') <* modify (+1)
-    buildEOL EOL.LF = return (char8 '\n') <* modify (+1)
-    buildEOL EOL.CRLF = return (string8 "\r\n") <* modify (+2)
 
-nextLine :: OBuilder -> OBuilder -> OBuilder
+newLine :: OBuilder
-nextLine a b = a `mappend` newLine `mappend` b
+newLine = buildEOL =<< OContext ask
+  where
+    buildEOL EOL.CR = return (char8 '\r') <* offset (+1)
+    buildEOL EOL.LF = return (char8 '\n') <* offset (+1)
+    buildEOL EOL.CRLF = return (string8 "\r\n") <* offset (+2)
 
 char :: Char -> OBuilder
-char c = lift char8 c <* OContext (modify (+1))
+char c = lift char8 c <* offset (+1)
 
 string :: String -> OBuilder
-string s = lift string8 s <* OContext (modify (+ toEnum (length s)))
+string s = lift string8 s <* offset (+ toEnum (length s))
+
+line :: String -> OBuilder
+line l = string l `mappend` newLine
 
 byteString :: ByteString -> OBuilder
-byteString bs = lift B.byteString bs <* OContext (modify (+ BS.length bs))
+byteString bs = lift B.byteString bs <* offset (+ BS.length bs)
 
 render :: Output a => EOL.Style -> a -> Lazy.ByteString
 render eolStyle a =
   let OContext builder = output a in
-  let (outputByteString, _, _) = runRWS builder eolStyle 0 in
+  let (outputByteString, _, _) = runRWS builder eolStyle (Offset 0) in
   toLazyByteString outputByteString

src/PDF/Update.hs

@@ -0,0 +1,47 @@
+{-# LANGUAGE NamedFieldPuns #-}
+module PDF.Update (
+    unify
+  ) where
+
+import Data.Map (member)
+import qualified Data.Map as Map (empty, union)
+import PDF.Object (
+      Content(..), IndexedObjects, IndirectObjCoordinates(..), Occurrence(..)
+    , Structure(..)
+  )
+
+emptyContent :: Content
+emptyContent = Content {
+      docStructure = Structure {xRef = Map.empty, trailer = Map.empty}
+    , objects = Map.empty
+    , occurrences = []
+  }
+
+unify :: [Content] -> Content
+unify = foldl complete emptyContent
+  where
+    complete tmpContent older =
+      let mergedObjects = Map.union (objects tmpContent) (objects older) in
+      Content {
+          docStructure =
+            unifyDocStructure (docStructure tmpContent) (docStructure older)
+        , objects = mergedObjects
+        , occurrences = 
+            unifyOccurrences mergedObjects (occurrences tmpContent) (occurrences older)
+      }
+
+unifyDocStructure :: Structure -> Structure -> Structure
+unifyDocStructure update original = Structure {
+      xRef = Map.union (xRef update) (xRef original)
+    , trailer = Map.union (trailer update) (trailer original)
+  }
+
+unifyOccurrences :: IndexedObjects -> [Occurrence] -> [Occurrence] -> [Occurrence]
+unifyOccurrences objects update = foldr addOlder update
+  where
+    addOlder occurrence@(Comment _) existing = occurrence : existing
+    addOlder occurrence@(Indirect indirect) existing =
+      if objectId indirect `member` objects
+      then occurrence : existing
+      else existing
+