Take the dirty code of «getText» and turn it into a relatively clean module exposing pages, that can be retrieved all at once or by page number (numbered human-style, starting from 1)

Hufflepdf.cabal

@@ -21,9 +21,10 @@ library
                      , PDF.EOL
                      , PDF.Object
                      , PDF.Output
+                     , PDF.Pages
+                     , PDF.Parser
                      , PDF.Text
                      , PDF.Update
-                     , PDF.Parser
   other-modules:       Data.ByteString.Char8.Util
                      , PDF.Body
   -- other-extensions:    
@@ -34,6 +35,7 @@ library
                      , mtl
                      , text
                      , utf8-string
+                     , zlib
   hs-source-dirs:      src
   ghc-options:         -Wall
   default-language:    Haskell2010

examples/getText.hs

@@ -1,141 +1,37 @@
-{-# LANGUAGE NamedFieldPuns #-}
+import qualified Data.ByteString.Char8 as BS (putStrLn, readFile)
-{-# LANGUAGE OverloadedStrings #-}
+import qualified Data.Map as Map (toList)
-
-import Codec.Compression.Zlib (decompress)
-import Control.Monad (foldM)
-import Control.Monad.RWS (RWST(..), ask, evalRWST, get, modify)
-import Control.Monad.Writer (tell)
-import Data.ByteString (ByteString)
-import qualified Data.ByteString.Char8 as BS (pack, putStrLn, readFile)
-import qualified Data.ByteString.Lazy as Lazy (fromStrict, toStrict)
-import Data.Map (Map, (!))
-import qualified Data.Map as Map (empty, insert, lookup, toList)
 import PDF (Document(..), parseDocument)
-import PDF.CMap (CMap, CMappers, cMap, emptyCMap)
+import PDF.Object (Content)
-import PDF.Object (
+import PDF.Pages (Page(..), get, getAll)
-      Content(..), Dictionary, DirectObject(..), IndirectObjCoordinates(..)
-    , Object(..), Name(..), Structure(..)
-  ,)
-import PDF.Output (ObjectId(..))
-import PDF.Text (PageContents(..), pageContents)
 import PDF.Update (unify)
 import System.Environment (getArgs)
-import System.IO (hPutStrLn, stderr)
+import System.Exit (die)
-import Text.Printf (printf)
+import System.IO (BufferMode(..), hSetBuffering, stdout)
 
-type CachedCMaps = Map ObjectId CMap
+onDoc :: FilePath -> (Content -> Either String a) -> IO a
-type T a = RWST Content [ByteString] CachedCMaps [] a
+onDoc inputFile f = do
+  content <- fmap (unify . updates) . parseDocument <$> BS.readFile inputFile
+  case content >>= f of
+    Left someError -> die someError
+    Right value -> return value
 
-list :: [a] -> T a
+displayPage :: Page -> IO ()
-list l = RWST (\_ s -> fillContext s <$> l)
+displayPage = mapM_ BS.putStrLn . contents
-  where
-    fillContext s a = (a, s, [])
 
-handleError :: ObjectId -> a -> String -> T a
+wholeDoc :: FilePath -> IO ()
-handleError objectId defaultValue s =
+wholeDoc inputFile = do
-  (tell . replicate 1 $ BS.pack message) >> return defaultValue
+  pages <- onDoc inputFile getAll
-  where
+  mapM_ (displayPage . snd) $ Map.toList pages
-    message = printf "Object #%d : %s" (getObjectId objectId) s
 
-extractText :: Object -> T ()
+singlePage :: FilePath -> Int -> IO ()
-extractText object = do
+singlePage inputFile pageNumber =
-  pageDict <- dict object
+  onDoc inputFile (`get` pageNumber) >>= displayPage
-  cMappers <- loadCMappers =<< getFont pageDict
-  contentsId <- target =<< key "Contents" pageDict
-  contents <- stream =<< getObject contentsId
-  either (handleError contentsId ()) (tell . chunks) (pageContents cMappers contents)
-
-stream :: Object -> T ByteString
-stream (Stream {header, streamContent}) = return $
-  case Map.lookup (Name "Filter") header of
-    Just (NameObject (Name "FlateDecode")) ->
-      Lazy.toStrict . decompress . Lazy.fromStrict $ streamContent
-    _ -> streamContent
-stream _ = list []
-
-getFont :: Dictionary -> T Dictionary
-getFont pageDict =
-  key "Resources" pageDict
-  >>= dict . Direct
-  >>= key "Font"
-  >>= follow
-  >>= dict
-
-cache :: (ObjectId -> T CMap) -> ObjectId -> T CMap
-cache loader objectId = do
-  loaded <- get
-  case Map.lookup objectId loaded of
-    Just value -> return value
-    Nothing -> do
-      value <- loader objectId
-      modify (Map.insert objectId value) >> return value
-
-loadFont :: ObjectId -> T CMap
-loadFont objectId =
-  getObject objectId
-  >>= dict
-  >>= key "ToUnicode"
-  >>= follow
-  >>= stream
-  >>= either (handleError objectId emptyCMap) return . cMap
-
-loadCMappers :: Dictionary -> T CMappers
-loadCMappers = foldM loadCMapper Map.empty . Map.toList
-  where
-    loadCMapper :: CMappers -> (Name, DirectObject) -> T CMappers
-    loadCMapper output (name, Reference (IndirectObjCoordinates {objectId})) = do
-      flip (Map.insert name) output <$> cache loadFont objectId
-    loadCMapper output _ = return output
-
-getObject :: ObjectId -> T Object
-getObject objectId = do
-  content <- ask
-  return (objects content ! objectId)
-
-key :: String -> Dictionary -> T DirectObject
-key keyName dictionary =
-  case Map.lookup (Name keyName) dictionary of
-    Just obj -> return obj
-    _ -> list []
-
-target :: DirectObject -> T ObjectId
-target (Reference (IndirectObjCoordinates {objectId})) = return objectId
-target _ = list []
-
-follow :: DirectObject -> T Object
-follow directObject = target directObject >>= getObject
-
-dict :: Object -> T Dictionary
-dict (Direct (Dictionary dictionary)) = return dictionary
-dict _ = list []
-
-pagesList :: T ObjectId
-pagesList = do
-  root <- dict =<< follow =<< key "Root" . trailer . docStructure =<< ask
-  pages <- dict =<< follow =<< key "Pages" root
-  case Map.lookup (Name "Kids") pages of
-    Just (Array kids) -> list $ filterObjectIds kids
-    _ -> list []
-
-filterObjectIds :: [DirectObject] -> [ObjectId]
-filterObjectIds objects = do
-  object <- objects
-  case object of
-    Reference (IndirectObjCoordinates {objectId}) -> [objectId]
-    _ -> []
-
-listTextObjects :: Document -> [ByteString]
-listTextObjects (Document {updates}) =
-  snd =<< evalRWST rwsMain (unify updates) Map.empty
-  where
-    rwsMain =
-      pagesList >>= getObject >>= extractText
-  
 
 main :: IO ()
 main = do
-  [inputFile] <- getArgs
+  hSetBuffering stdout LineBuffering
-  result <- parseDocument <$> BS.readFile inputFile
+  args <- getArgs
-  case result of
+  case args of
-    Left parseError -> hPutStrLn stderr $ show parseError
+    [inputFile] -> wholeDoc inputFile
-    Right doc -> mapM_ BS.putStrLn $ listTextObjects doc
+    [inputFile, pageNumber] -> singlePage inputFile (read pageNumber)
+    _ -> die "Syntax: getText INPUT_FILE [PAGE_NUMBER]"

src/PDF/Pages.hs

@@ -0,0 +1,171 @@
+{-# LANGUAGE NamedFieldPuns #-}
+module PDF.Pages (
+      Page(..)
+    , get
+    , getAll
+  ) where
+
+import Codec.Compression.Zlib (decompress)
+import Control.Monad (foldM)
+import Control.Monad.RWS (RWST(..), ask, evalRWST, mapRWST, modify)
+import qualified Control.Monad.RWS as RWS (get)
+import Data.ByteString (ByteString)
+import qualified Data.ByteString.Lazy as Lazy (fromStrict, toStrict)
+import Data.Map (Map, (!))
+import qualified Data.Map as Map (empty, fromList, insert, lookup, toList)
+import PDF.CMap (CMap, CMappers, cMap)
+import PDF.Object (
+      Content(..), Dictionary, DirectObject(..), IndirectObjCoordinates(..)
+    , Object(..), Name(..), Structure(..)
+  ,)
+import PDF.Output (ObjectId(..))
+import PDF.Text (pageContents)
+import Prelude hiding (fail)
+import Text.Printf (printf)
+
+type CachedCMaps = Map ObjectId CMap
+type T = RWST Content () CachedCMaps (Either String)
+data Page = Page {
+      contents :: [ByteString]
+    , source :: ObjectId
+  }
+
+infixl 1 \\=
+(\\=) :: T a -> (a -> Either String b) -> T b
+x \\= f = mapRWST ((\(a, s, w) -> (\b -> (b, s, w)) <$> f a) =<<) x
+
+infixl 1 //=
+(//=) :: Either String a -> (a -> T b) -> T b
+(//=) (Left e) _ = RWST (\_ _ -> Left e)
+(//=) (Right a) f = f a
+
+lift :: Either String a -> T a
+lift x = x //= return
+
+expected :: Show a => String -> a -> Either String b
+expected name = Left . printf "Not a %s: %s" name . show
+
+stream :: Object -> Either String ByteString
+stream (Stream {header, streamContent}) = Right $
+  case Map.lookup (Name "Filter") header of
+    Just (NameObject (Name "FlateDecode")) ->
+      Lazy.toStrict . decompress . Lazy.fromStrict $ streamContent
+    _ -> streamContent
+stream obj = expected "stream" obj
+
+getResource :: DirectObject -> T Dictionary
+getResource (Dictionary dictionary) = return dictionary
+getResource (Reference (IndirectObjCoordinates {objectId})) =
+  getObject objectId \\= dict
+getResource directObject =
+  lift $ expected "resource (dictionary or reference)" directObject
+
+getFont :: Dictionary -> T Dictionary
+getFont pageDict =
+  key "Resources" pageDict
+  //= getResource
+  \\= key "Font"
+  >>= follow
+  \\= dict
+
+cache :: (ObjectId -> T CMap) -> ObjectId -> T CMap
+cache loader objectId =
+  (maybe load return . Map.lookup objectId) =<< RWS.get
+  where
+    load = do
+      value <- loader objectId
+      modify $ Map.insert objectId value
+      return value
+
+loadFont :: ObjectId -> T CMap
+loadFont objectId =
+  (getObject objectId
+  \\= dict
+  \\= key "ToUnicode"
+  >>= follow)
+  \\= stream
+  \\= cMap
+
+loadCMappers :: Dictionary -> T CMappers
+loadCMappers = foldM loadCMapper Map.empty . Map.toList
+  where
+    loadCMapper :: CMappers -> (Name, DirectObject) -> T CMappers
+    loadCMapper output (name, Reference (IndirectObjCoordinates {objectId})) =
+      flip (Map.insert name) output <$> cache loadFont objectId
+      --maybe output (flip (Map.insert name) output) <$> cache loadFont objectId
+    loadCMapper output _ = return output
+
+getObject :: ObjectId -> T Object
+getObject objectId = do
+  content <- ask
+  return (objects content ! objectId)
+
+key :: String -> Dictionary -> Either String DirectObject
+key keyName dictionary =
+  maybe (Left errorMessage) Right (Map.lookup (Name keyName) dictionary)
+  where
+    errorMessage =
+      printf "Key %s not found in dictionary %s" keyName (show dictionary)
+
+target :: DirectObject -> Either String ObjectId
+target (Reference (IndirectObjCoordinates {objectId})) = Right objectId
+target directObject = expected "reference" directObject
+
+many :: DirectObject -> [DirectObject]
+many (Array l) =  l
+many directObject = [directObject]
+
+follow :: DirectObject -> T Object
+follow directObject = target directObject //= getObject
+
+dict :: Object -> Either String Dictionary
+dict (Direct (Dictionary dictionary)) = Right dictionary
+dict obj = expected "dictionary" obj
+
+dictObject :: String -> Dictionary -> T Dictionary
+dictObject keyName dictionary = key keyName dictionary //= follow \\= dict
+
+pagesList :: T [ObjectId]
+pagesList = do
+  root <- dictObject "Root" . trailer . docStructure =<< ask
+  pages <- dictObject "Pages" root
+  case Map.lookup (Name "Kids") pages of
+    Just (Array kids) -> return $ getReferences kids
+    _ -> return []
+
+getReferences :: [DirectObject] -> [ObjectId]
+getReferences objects = do
+  object <- objects
+  case object of
+    Reference (IndirectObjCoordinates {objectId}) -> [objectId]
+    _ -> []
+
+extractText :: Object -> T [ByteString]
+extractText object = do
+  pageDict <- lift $ dict object
+  cMappers <- loadCMappers =<< getFont pageDict
+  let objects = ((many <$> (key "Contents" pageDict)) :: Either String [DirectObject])
+  concat <$> (objects //= (mapM $ loadContent cMappers))
+  where
+    loadContent :: CMappers -> DirectObject -> T [ByteString]
+    loadContent cMappers directObject =
+      follow directObject \\= stream \\= pageContents cMappers
+
+loadPage :: ObjectId -> T Page
+loadPage source =
+  (\contents -> Page {contents, source}) <$> (extractText =<< getObject source)
+
+getAll :: Content -> Either String (Map Int Page)
+getAll content = fst <$> evalRWST getPages content Map.empty
+  where
+    numbered = Map.fromList . zip [1..]
+    getPages = numbered <$> (mapM loadPage =<< pagesList)
+
+get :: Content -> Int -> Either String Page
+get content pageNumber
+  | pageNumber < 1 = Left "Pages start at 1"
+  | otherwise = fst <$> evalRWST getPage content Map.empty
+  where
+    firstPage [] = lift $ Left "Page is out of bounds"
+    firstPage (p:_) = loadPage p
+    getPage = drop (pageNumber - 1) <$> pagesList >>= firstPage