Added preliminary support for PDF creation via wkhtmltopdf.

To use this:

    pandoc -t html5 -o result.pdf

(and add `--mathjax` if you have math.)

3 files changed, 79 insertions, 21 deletions

diff --git a/README b/README
index ebc8f58d4..ea6226d38 100644
--- a/README
+++ b/README
@@ -24,7 +24,7 @@ markup], [Haddock markup], [OPML], [Emacs Org mode], [DocBook],
 [FictionBook2], [Textile], [groff man] pages, [Emacs Org mode],
 [AsciiDoc], [InDesign ICML], and [Slidy], [Slideous], [DZSlides],
 [reveal.js] or [S5] HTML slide shows. It can also produce [PDF] output
-on systems where LaTeX or ConTeXt is installed.
+on systems where LaTeX, ConTeXt, or `wkhtmltopdf` is installed.
 
 Pandoc's enhanced version of Markdown includes syntax for [footnotes],
 [tables], flexible [ordered lists], [definition lists], [fenced code blocks],
@@ -189,12 +189,13 @@ any header file. The [`natbib`], [`biblatex`], [`bibtex`], and [`biber`]
 packages can optionally be used for [citation rendering]. These are
 included with all recent versions of [TeX Live].
 
-Alternatively, pandoc can use ConTeXt to create a PDF.
+Alternatively, pandoc can use ConTeXt or `wkhtmltopdf` to create a PDF.
 To do this, specify an output file with a `.pdf` extension,
-as before, but add `-t context` to the command line.
+as before, but add `-t context` or `-t html5` to the command line.
 
-PDF output can be controlled using [variables for LaTeX]
-or [variables for ConTeXt].
+PDF output can be controlled using [variables for LaTeX] (if
+LaTeX is used), [variables for ConTeXt] (if ConTeXt is used),
+and `--css` (if `wkhtmltopdf` is used).
 
 [`amsfonts`]: https://ctan.org/pkg/amsfonts
 [`amsmath`]: https://ctan.org/pkg/amsmath
diff --git a/pandoc.hs b/pandoc.hs
index cfb9adc1c..a4906382a 100644
--- a/pandoc.hs
+++ b/pandoc.hs
@@ -1168,6 +1168,7 @@ convertWithOpts opts args = do
   let laTeXOutput = "latex" `isPrefixOf` writerName' ||
                     "beamer" `isPrefixOf` writerName'
   let conTeXtOutput = "context" `isPrefixOf` writerName'
+  let html5Output = "html5" `isPrefixOf` writerName'
 
   let laTeXInput = "latex" `isPrefixOf` readerName' ||
                     "beamer" `isPrefixOf` readerName'
@@ -1367,27 +1368,28 @@ convertWithOpts opts args = do
     IOByteStringWriter f -> f writerOptions doc' >>= writeBinary
     PureStringWriter f
       | pdfOutput -> do
-              -- make sure writer is latex or beamer
-              unless (laTeXOutput || conTeXtOutput) $
+              -- make sure writer is latex or beamer or context or html5
+              unless (laTeXOutput || conTeXtOutput || html5Output) $
                 err 47 $ "cannot produce pdf output with " ++ writerName' ++
                          " writer"
 
-              let texprog = if conTeXtOutput
-                              then "context"
-                              else latexEngine
-              -- check for latex program
-              mbLatex <- findExecutable texprog
-              when (isNothing mbLatex) $
-                   err 41 $ texprog ++ " not found. " ++
-                     texprog ++ " is needed for pdf output."
-
-              res <- makePDF texprog f writerOptions doc'
+              let pdfprog = case () of
+                              _ | conTeXtOutput -> "context"
+                              _ | html5Output   -> "wkhtmltopdf"
+                              _                 -> latexEngine
+              -- check for pdf creating program
+              mbPdfProg <- findExecutable pdfprog
+              when (isNothing mbPdfProg) $
+                   err 41 $ pdfprog ++ " not found. " ++
+                     pdfprog ++ " is needed for pdf output."
+
+              res <- makePDF pdfprog f writerOptions doc'
               case res of
                    Right pdf -> writeBinary pdf
                    Left err' -> do
                      B.hPutStr stderr err'
                      B.hPut stderr $ B.pack [10]
-                     err 43 "Error producing PDF from TeX source"
+                     err 43 "Error producing PDF"
       | otherwise -> selfcontain (f writerOptions doc' ++
                                   ['\n' | not standalone'])
                       >>= writerFn outputFile . handleEntities
diff --git a/src/Text/Pandoc/PDF.hs b/src/Text/Pandoc/PDF.hs
index 0e533ede8..72b563044 100644
--- a/src/Text/Pandoc/PDF.hs
+++ b/src/Text/Pandoc/PDF.hs
@@ -38,6 +38,7 @@ import Text.Pandoc.Compat.Monoid ((<>))
 import System.Exit (ExitCode (..))
 import System.FilePath
 import System.IO (stderr, stdout)
+import System.IO.Temp (withTempFile)
 import System.Directory
 import Data.Digest.Pure.SHA (showDigest, sha1)
 import System.Environment
@@ -49,7 +50,7 @@ import qualified Text.Pandoc.UTF8 as UTF8
 import Text.Pandoc.Definition
 import Text.Pandoc.Walk (walkM)
 import Text.Pandoc.Shared (fetchItem', warn, withTempDir, inDirectory)
-import Text.Pandoc.Options (WriterOptions(..))
+import Text.Pandoc.Options (WriterOptions(..), HTMLMathMethod(..))
 import Text.Pandoc.MIME (extensionFromMimeType, getMimeType)
 import Text.Pandoc.Process (pipeProcess)
 import qualified Data.ByteString.Lazy as BL
@@ -63,18 +64,29 @@ changePathSeparators :: FilePath -> FilePath
 changePathSeparators = intercalate "/" . splitDirectories
 #endif
 
-makePDF :: String              -- ^ pdf creator (pdflatex, lualatex, xelatex)
+makePDF :: String              -- ^ pdf creator (pdflatex, lualatex,
+                               -- xelatex, context, wkhtmltopdf)
         -> (WriterOptions -> Pandoc -> String)  -- ^ writer
         -> WriterOptions       -- ^ options
         -> Pandoc              -- ^ document
         -> IO (Either ByteString ByteString)
+makePDF "wkhtmltopdf" writer opts doc =
+  wkhtml2pdf (writerVerbose opts) args source
+    where args = case writerHTMLMathMethod opts of
+            -- with MathJax, wait til all math is rendered:
+                      MathJax _ -> ["--run-script", "MathJax.Hub.Register.StartupHook('End Typeset', function() { window.status = 'mathjax_loaded' });",
+                                    "--window-status", "mathjax_loaded"]
+                      _ -> []
+          source = writer opts doc
 makePDF program writer opts doc = withTempDir "tex2pdf." $ \tmpdir -> do
   doc' <- handleImages opts tmpdir doc
   let source = writer opts doc'
       args   = writerLaTeXArgs opts
   case program of
      "context" -> context2pdf (writerVerbose opts) tmpdir source
-     _ -> tex2pdf' (writerVerbose opts) args tmpdir program source
+     _ | program `elem` ["pdflatex", "lualatex", "xelatex"]
+         -> tex2pdf' (writerVerbose opts) args tmpdir program source
+     _ -> return $ Left $ UTF8.fromStringLazy $ "Unknown program " ++ program
 
 handleImages :: WriterOptions
              -> FilePath      -- ^ temp dir to store images
@@ -235,6 +247,49 @@ runTeXProgram verbose program args runNumber numRuns tmpDir source = do
                    else return Nothing
          return (exit, out <> err, pdf)
 
+wkhtml2pdf  :: Bool         -- ^ Verbose output
+            -> [String]     -- ^ Args to wkhtmltopdf
+            -> String       -- ^ HTML5 source
+            -> IO (Either ByteString ByteString)
+wkhtml2pdf verbose args source = do
+  file <- withTempFile "." "wkhtml2pdf.html" $ \fp _ -> return fp
+  pdfFile <- withTempFile "." "wkhtml2pdf.pdf" $ \fp _ -> return fp
+  UTF8.writeFile file source
+  let programArgs = args ++ [file, pdfFile]
+  env' <- getEnvironment
+  when verbose $ do
+    putStrLn "[makePDF] Command line:"
+    putStrLn $ "wkhtmltopdf" ++ " " ++ unwords (map show programArgs)
+    putStr "\n"
+    putStrLn "[makePDF] Environment:"
+    mapM_ print env'
+    putStr "\n"
+    putStrLn $ "[makePDF] Contents of " ++ file ++ ":"
+    B.readFile file >>= B.putStr
+    putStr "\n"
+  (exit, out, err) <- pipeProcess (Just env') "wkhtmltopdf"
+                              programArgs BL.empty
+  removeFile file
+  when verbose $ do
+    B.hPutStr stdout out
+    B.hPutStr stderr err
+    putStr "\n"
+  pdfExists <- doesFileExist pdfFile
+  mbPdf <- if pdfExists
+            -- We read PDF as a strict bytestring to make sure that the
+            -- temp directory is removed on Windows.
+            -- See https://github.com/jgm/pandoc/issues/1192.
+            then do
+              res <- (Just . B.fromChunks . (:[])) `fmap` BS.readFile pdfFile
+              removeFile pdfFile
+              return res
+            else return Nothing
+  let log' = out <> err
+  return $ case (exit, mbPdf) of
+             (ExitFailure _, _)      -> Left log'
+             (ExitSuccess, Nothing)  -> Left ""
+             (ExitSuccess, Just pdf) -> Right pdf
+
 context2pdf :: Bool         -- ^ Verbose output
             -> FilePath     -- ^ temp directory for output
             -> String       -- ^ ConTeXt source