SelfContained.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE LambdaCase        #-}
{-# LANGUAGE TupleSections     #-}
{- |
   Module      : Text.Pandoc.SelfContained
   Copyright   : Copyright (C) 2011-2023 John MacFarlane
   License     : GNU GPL, version 2 or above

   Maintainer  : John MacFarlane <jgm@berkeley.edu>
   Stability   : alpha
   Portability : portable

Functions for converting an HTML file into one that can be viewed
offline, by incorporating linked images, CSS, and scripts into
the HTML using data URIs.
-}
module Text.Pandoc.SelfContained ( makeDataURI, makeSelfContained ) where
import Codec.Compression.GZip as Gzip
import Control.Applicative ((<|>))
import Control.Monad.Trans (lift)
import Data.ByteString (ByteString)
import Data.ByteString.Base64 (encodeBase64)
import qualified Data.ByteString.Char8 as B
import qualified Data.ByteString.Lazy as L
import qualified Data.Text as T
import Data.Char (isAlphaNum, isAscii)
import Network.URI (escapeURIString)
import System.FilePath (takeDirectory, takeExtension, (</>))
import Text.HTML.TagSoup
import Text.Pandoc.Class.PandocMonad (PandocMonad (..), fetchItem,
                                      getInputFiles, report, setInputFiles)
import Text.Pandoc.Logging
import Text.Pandoc.Error (PandocError(..))
import Text.Pandoc.MIME (MimeType)
import Text.Pandoc.Shared (renderTags', trim, tshow)
import Text.Pandoc.URI (isURI)
import Text.Pandoc.UTF8 (toString, toText, fromText)
import Text.Pandoc.Parsing (ParsecT, runParserT)
import qualified Text.Pandoc.Parsing as P
import Control.Monad.Except (throwError, catchError)

isOk :: Char -> Bool
isOk c = isAscii c && isAlphaNum c

makeDataURI :: (MimeType, ByteString) -> T.Text
makeDataURI (mime, raw) =
  if textual
     then "data:" <> mime' <> "," <> T.pack (escapeURIString isOk (toString raw))
     else "data:" <> mime' <> ";base64," <> encodeBase64 raw
  where textual = "text/" `T.isPrefixOf` mime
        mime' = if textual && T.any (== ';') mime
                   then mime <> ";charset=utf-8"
                   else mime  -- mime type already has charset

isSourceAttribute :: T.Text -> (T.Text, T.Text) -> Bool
isSourceAttribute tagname (x,_) =
  x == "src" ||
  x == "data-src" ||
  (x == "href" && tagname == "link") ||
  x == "poster" ||
  x == "data-background-image"

convertTags :: PandocMonad m => [Tag T.Text] -> m [Tag T.Text]
convertTags [] = return []
convertTags (t@TagOpen{}:ts)
  | fromAttrib "data-external" t == "1" = (t:) <$> convertTags ts
convertTags (t@(TagOpen "style" _):ts) =
  case span isTagText ts of
    (xs,rest) -> do
      xs' <- mapM (\case
                    TagText s -> TagText . toText <$> cssURLs "" (fromText s)
                    tag -> return tag) xs
      ((t:xs') ++) <$> convertTags rest
convertTags (t@(TagOpen "script" as):tc@(TagClose "script"):ts) =
  case fromAttrib "src" t of
       ""  -> (t:) <$> convertTags ts
       src -> do
           let typeAttr = fromAttrib "type" t
           res <- getData typeAttr src
           rest <- convertTags ts
           case res of
                AlreadyDataURI dataUri -> return $ TagOpen "script"
                     (("src",dataUri) : [(x,y) | (x,y) <- as, x /= "src"]) :
                     TagClose "script" : rest
                Fetched (mime, bs)
                  | ("text/javascript" `T.isPrefixOf` mime ||
                     "application/javascript" `T.isPrefixOf` mime ||
                     "application/x-javascript" `T.isPrefixOf` mime) &&
                     not ("</script" `B.isInfixOf` bs) ->
                     return $
                       TagOpen "script" [("type", typeAttr)|not (T.null typeAttr)]
                       : TagText (toText bs)
                       : TagClose "script"
                       : rest
                  | otherwise ->
                       return  $ TagOpen "script"
                         (("src",makeDataURI (mime, bs)) :
                          [(x,y) | (x,y) <- as, x /= "src"]) :
                        TagClose "script" : rest
                CouldNotFetch _ -> return $ t:tc:rest
convertTags (t@(TagOpen "link" as):ts) =
  case fromAttrib "href" t of
       ""  -> (t:) <$> convertTags ts
       src -> do
           res <- getData (fromAttrib "type" t) src
           case res of
                AlreadyDataURI dataUri -> do
                  rest <- convertTags ts
                  return $ TagOpen "link"
                     (("href",dataUri) : [(x,y) | (x,y) <- as, x /= "href"]) :
                     rest
                Fetched (mime, bs)
                  | "text/css" `T.isPrefixOf` mime
                    && T.null (fromAttrib "media" t)
                    && not ("</" `B.isInfixOf` bs) -> do
                      rest <- convertTags $
                                 dropWhile (==TagClose "link") ts
                      return $
                       TagOpen "style" [("type", "text/css")] -- see #5725
                       : TagText (toText bs)
                       : TagClose "style"
                       : rest
                  | otherwise -> do
                      rest <- convertTags ts
                      return $ TagOpen "link"
                       (("href",makeDataURI (mime, bs)) :
                         [(x,y) | (x,y) <- as, x /= "href"]) : rest
                CouldNotFetch _ -> do
                      rest <- convertTags ts
                      return $ t:rest
convertTags (t@(TagOpen tagname as):ts)
  | any (isSourceAttribute tagname) as
     = do
       as' <- mapM processAttribute as
       rest <- convertTags ts
       return $ TagOpen tagname as' : rest
  where processAttribute (x,y) =
           if isSourceAttribute tagname (x,y)
              then do
                res <- getData (fromAttrib "type" t) y
                case res of
                  AlreadyDataURI enc -> return (x, enc)
                  Fetched (mt,bs) -> return (x, makeDataURI (mt,bs))
                  CouldNotFetch _ -> return (x, y)
              else return (x,y)

convertTags (t:ts) = (t:) <$> convertTags ts

cssURLs :: PandocMonad m
        => FilePath -> ByteString -> m ByteString
cssURLs d orig = do
  res <- runParserT (parseCSSUrls d) () "css" orig
  case res of
       Left e    -> do
         report $ CouldNotParseCSS $ T.pack $ show e
         return orig
       Right bs  -> return bs

parseCSSUrls :: PandocMonad m
             => FilePath -> ParsecT ByteString () m ByteString
parseCSSUrls d = B.concat <$> P.many
  (pCSSWhite <|> pCSSComment <|> pCSSImport d <|> pCSSUrl d <|> pCSSOther)

pCSSImport :: PandocMonad m
           => FilePath -> ParsecT ByteString () m ByteString
pCSSImport d = P.try $ do
  P.string "@import"
  P.spaces
  res <- (pQuoted <|> pUrl) >>= handleCSSUrl d
  P.spaces
  P.char ';'
  P.spaces
  case res of
       Left b       -> return $ B.pack "@import " <> b
       Right (_, b) -> return b

-- Note: some whitespace in CSS is significant, so we can't collapse it!
pCSSWhite :: PandocMonad m => ParsecT ByteString () m ByteString
pCSSWhite = B.singleton <$> P.space <* P.spaces

pCSSComment :: PandocMonad m => ParsecT ByteString () m ByteString
pCSSComment = P.try $ do
  P.string "/*"
  P.manyTill P.anyChar (P.try (P.string "*/"))
  return B.empty

pCSSOther :: PandocMonad m => ParsecT ByteString () m ByteString
pCSSOther =
  (B.pack <$> P.many1 (P.noneOf "u/ \n\r\t")) <|>
  (B.singleton <$> P.char 'u') <|>
  (B.singleton <$> P.char '/')

pCSSUrl :: PandocMonad m
        => FilePath -> ParsecT ByteString () m ByteString
pCSSUrl d = P.try $ do
  res <- pUrl >>= handleCSSUrl d
  case res of
       Left b -> return b
       Right (mt,b) -> do
         let enc = makeDataURI (mt, b)
         return $ fromText $ "url(" <> enc <> ")"

pQuoted :: PandocMonad m
        => ParsecT ByteString () m (T.Text, ByteString)
pQuoted = P.try $ do
  quote <- P.oneOf "\"'"
  url <- T.pack <$> P.manyTill P.anyChar (P.char quote)
  let fallback = fromText $ T.singleton quote <> trim url <> T.singleton quote
  return (url, fallback)

pUrl :: PandocMonad m
     => ParsecT ByteString () m (T.Text, ByteString)
pUrl = P.try $ do
  P.string "url("
  P.spaces
  quote <- P.option Nothing (Just <$> P.oneOf "\"'")
  url <- T.pack <$> P.manyTill P.anyChar (maybe (P.lookAhead (P.char ')')) P.char quote)
  P.spaces
  P.char ')'
  let fallback = fromText ("url(" <> maybe "" T.singleton quote <> trim url <>
                            maybe "" T.singleton quote <> ")")
  return (url, fallback)

handleCSSUrl :: PandocMonad m
             => FilePath -> (T.Text, ByteString)
             -> ParsecT ByteString () m
                  (Either ByteString (MimeType, ByteString))
handleCSSUrl d (url, fallback) =
  case escapeURIString (/='|') (T.unpack $ trim url) of
      '#':_ -> return $ Left fallback
      'd':'a':'t':'a':':':_ -> return $ Left fallback
      u ->  do let url' = if isURI (T.pack u) then T.pack u else T.pack (d </> u)
               res <- lift $ getData "" url'
               case res of
                    AlreadyDataURI uri -> return $ Left (fromText $ "url(" <> uri <> ")")
                    Fetched (mt', raw) -> do
                      -- note that the downloaded CSS may
                      -- itself contain url(...).
                      (mt, b) <- if "text/css" `T.isPrefixOf` mt'
                                    -- see #5725: in HTML5, content type
                                    -- isn't allowed on style type attribute
                                    then ("text/css",) <$> cssURLs d raw
                                    else return (mt', raw)
                      return $ Right (mt, b)
                    CouldNotFetch _ -> return $ Left fallback

data GetDataResult =
    AlreadyDataURI T.Text
  | CouldNotFetch PandocError
  | Fetched (MimeType, ByteString)
  deriving (Show)

getData :: PandocMonad m
        => MimeType -> T.Text
        -> m GetDataResult
getData mimetype src
  | "data:" `T.isPrefixOf` src = return $ AlreadyDataURI src -- already data: uri
  | otherwise = catchError fetcher handler
 where
   fetcher = do
      let ext = T.toLower $ T.pack $ takeExtension $ T.unpack src
      (raw, respMime) <- fetchItem src
      let raw' = if ext `elem` [".gz", ".svgz"]
                 then B.concat $ L.toChunks $ Gzip.decompress $ L.fromChunks [raw]
                 else raw
      let mime = case (mimetype, respMime) of
                  ("",Nothing) -> "application/octet-stream"
                  (x, Nothing) -> x
                  (_, Just x ) -> x
      result <- if "text/css" `T.isPrefixOf` mime
                then do
                  oldInputs <- getInputFiles
                  setInputFiles [T.unpack src]
                  res <- cssURLs (takeDirectory $ T.unpack src) raw'
                  setInputFiles oldInputs
                  return res
               else return raw'
      return $ Fetched (mime, result)
   handler e = case e of
                 PandocResourceNotFound r -> do
                   report $ CouldNotFetchResource r ""
                   return $ CouldNotFetch e
                 PandocHttpError u er -> do
                   report $ CouldNotFetchResource u (tshow er)
                   return $ CouldNotFetch e
                 _ -> throwError e




-- | Convert HTML into self-contained HTML, incorporating images,
-- scripts, and CSS using data: URIs.
makeSelfContained :: PandocMonad m => T.Text -> m T.Text
makeSelfContained inp = do
  let tags = parseTags inp
  out' <- convertTags tags
  return $ renderTags' out'