Lua: support custom bytestring readers.

6 files changed, 111 insertions, 25 deletions

diff --git a/doc/custom-readers.md b/doc/custom-readers.md
index add2317a2..601d879dd 100644
--- a/doc/custom-readers.md
+++ b/doc/custom-readers.md
@@ -76,6 +76,23 @@ ensuring backwards compatibility.
 [patterns]: http://lua-users.org/wiki/PatternsTutorial
 [lpeg]: http://www.inf.puc-rio.br/~roberto/lpeg/
 
+# Bytestring readers
+
+Pandoc expects text input to be UTF-8 encoded. However, formats
+like docx, odt, epub, etc. are not text but binary formats. To
+read them, pandoc supports `ByteStringReader` functions. These
+functions work just like the `Reader` function that process text
+input, but instead of a list of sources, `ByteStringReader`
+functions are passed a bytestring, i.e., a string that contains
+the binary input.
+
+``` lua
+-- read input as epub
+function ByteStringReader (input)
+  return pandoc.read(input, 'epub')
+end
+```
+
 # Example: plain text reader
 
 This is a simple example using [lpeg] to parse the input
diff --git a/pandoc-lua-engine/pandoc-lua-engine.cabal b/pandoc-lua-engine/pandoc-lua-engine.cabal
index b8f3abbd1..a122b935c 100644
--- a/pandoc-lua-engine/pandoc-lua-engine.cabal
+++ b/pandoc-lua-engine/pandoc-lua-engine.cabal
@@ -21,6 +21,7 @@ description:         This package provides a pandoc scripting engine based on
 extra-source-files:  README.md
                    , test/bytestring.bin
                    , test/bytestring.lua
+                   , test/bytestring-reader.lua
                    , test/lua/*.lua
                    , test/lua/module/*.lua
                    , test/lua/module/partial.test
@@ -131,4 +132,5 @@ test-suite test-pandoc-lua-engine
                      , text                  >= 1.1.1   && < 2.1
   other-modules:       Tests.Lua
                      , Tests.Lua.Module
+                     , Tests.Lua.Reader
                      , Tests.Lua.Writer
diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Reader.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Reader.hs
index 44781c9fb..6aeda526f 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Reader.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Reader.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE LambdaCase          #-}
 {-# LANGUAGE OverloadedStrings   #-}
+{-# LANGUAGE TypeApplications    #-}
 {- |
    Module      : Text.Pandoc.Lua.Reader
    Copyright   : Copyright (C) 2021-2022 John MacFarlane
@@ -17,8 +18,9 @@ import Control.Monad ((<=<), when)
 import Control.Monad.IO.Class (MonadIO)
 import Data.Maybe (fromMaybe)
 import HsLua as Lua hiding (Operation (Div))
-import HsLua.Core.Run (newGCManagedState, withGCManagedState)
+import HsLua.Core.Run (GCManagedState, newGCManagedState, withGCManagedState)
 import Text.Pandoc.Class (PandocMonad, findFileWithDataFallback, report)
+import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Logging
 import Text.Pandoc.Lua.Global (Global (..), setGlobals)
 import Text.Pandoc.Lua.Init (runLuaWith)
@@ -42,14 +44,23 @@ readCustom luaFile = do
     -- to handle this more gracefully):
     when (stat /= Lua.OK)
       Lua.throwErrorAsException
-    pure (reader luaState)
+    getCustomReader luaState
 
  where
-  reader st = TextReader $ \opts srcs -> liftIO . withGCManagedState st $ do
+  readerField = "PANDOC Reader function"
+  inLua st = liftIO . withGCManagedState @PandocError st
+  byteStringReader :: MonadIO m => GCManagedState -> Reader m
+  byteStringReader st = ByteStringReader $ \ropts input -> inLua st $ do
+    getfield registryindex readerField
+    push input
+    push ropts
+    callTrace 2 1
+    forcePeek $ peekPandoc top
+  textReader st = TextReader $ \ropts srcs -> inLua st $ do
     let input = toSources srcs
-    getglobal "Reader"
+    getfield registryindex readerField
     push input
-    push opts
+    push ropts
     pcallTrace 2 1 >>= \case
       OK -> forcePeek $ peekPandoc top
       ErrRun -> do
@@ -59,25 +70,38 @@ readCustom luaFile = do
           Failure {} ->
             -- not a string error object. Bail!
             throwErrorAsException
-          Success errmsg -> do
+          Success errmsg ->
             if "string expected, got pandoc Sources" `T.isInfixOf` errmsg
-              then do
-                pop 1
-                _ <- unPandocLua $ do
-                  report $ Deprecated "old Reader function signature" $
-                    T.unlines
-                    [ "Reader functions should accept a sources list; "
-                    , "functions expecting `string` input are deprecated. "
-                    , "Use `tostring` to convert the first argument to a "
-                    , "string."
-                    ]
-                getglobal "Reader"
-                push $ sourcesToText input  -- push sources as string
-                push opts
-                callTrace 2 1
-                forcePeek $ peekPandoc top
-              else
-                -- nothing we can do here
-                throwErrorAsException
+            then do
+              pop 1
+              _ <- unPandocLua $ do
+                report $ Deprecated "old Reader function signature" $
+                  T.unlines
+                  [ "Reader functions should accept a sources list; "
+                  , "functions expecting `string` input are deprecated. "
+                  , "Use `tostring` to convert the first argument to a "
+                  , "string."
+                  ]
+              getglobal "Reader"
+              push $ sourcesToText input  -- push sources as string
+              push ropts
+              callTrace 2 1
+              forcePeek $ peekPandoc top
+            else
+              -- nothing we can do here
+              throwErrorAsException
       _ ->  -- not a runtime error, we won't be able to recover from that
-        throwErrorAsException
+              throwErrorAsException
+  getCustomReader st = do
+    getglobal "Reader" >>= \case
+      TypeNil -> do
+        pop 1
+        getglobal "ByteStringReader" >>= \case
+          TypeNil -> failLua $ "No reader function found: either 'Reader' or "
+                     <> "'ByteStringReader' must be defined."
+          _ -> do
+            setfield registryindex readerField
+            pure (byteStringReader st)
+      _ -> do
+        setfield registryindex readerField
+        pure (textReader st)
diff --git a/pandoc-lua-engine/test/Tests/Lua/Reader.hs b/pandoc-lua-engine/test/Tests/Lua/Reader.hs
new file mode 100644
index 000000000..16474bd91
--- /dev/null
+++ b/pandoc-lua-engine/test/Tests/Lua/Reader.hs
@@ -0,0 +1,34 @@
+{-# LANGUAGE LambdaCase        #-}
+{- |
+Module      : Tests.Lua.Reader
+Copyright   : © 2022 Albert Krewinkel
+License     : GPL-2.0-or-later
+Maintainer  : Albert Krewinkel <[email protected]>
+
+Tests for custom Lua readers.
+-}
+module Tests.Lua.Reader (tests) where
+
+import Data.Char (chr)
+import Data.Default (Default (def))
+import Text.Pandoc.Class (runIOorExplode)
+import Text.Pandoc.Lua (readCustom)
+import Text.Pandoc.Readers (Reader (ByteStringReader, TextReader))
+import Test.Tasty (TestTree)
+import Test.Tasty.HUnit ((@?=), testCase)
+
+import qualified Data.ByteString.Lazy as BL
+import qualified Data.Text as T
+import qualified Text.Pandoc.Builder as B
+
+tests :: [TestTree]
+tests =
+  [ testCase "read binary to code block" $ do
+    input <- BL.readFile "bytestring.bin"
+    doc <- runIOorExplode $
+      readCustom "bytestring-reader.lua" >>= \case
+        ByteStringReader f -> f def input
+        TextReader {}      -> error "Expected a bytestring reader"
+    let bytes = mconcat $ map (B.str . T.singleton . chr) [0..255]
+    doc @?= B.doc (B.plain bytes)
+  ]
diff --git a/pandoc-lua-engine/test/bytestring-reader.lua b/pandoc-lua-engine/test/bytestring-reader.lua
new file mode 100644
index 000000000..7908479ec
--- /dev/null
+++ b/pandoc-lua-engine/test/bytestring-reader.lua
@@ -0,0 +1,7 @@
+function ByteStringReader (input, opts)
+  local chars = pandoc.List{}
+  for i = 1, #input do
+    chars:insert(utf8.char(input:byte(i,i)))
+  end
+  return pandoc.Pandoc(pandoc.Plain(pandoc.Str(table.concat(chars))))
+end
diff --git a/pandoc-lua-engine/test/test-pandoc-lua-engine.hs b/pandoc-lua-engine/test/test-pandoc-lua-engine.hs
index 035d92812..21febddb5 100644
--- a/pandoc-lua-engine/test/test-pandoc-lua-engine.hs
+++ b/pandoc-lua-engine/test/test-pandoc-lua-engine.hs
@@ -2,6 +2,7 @@ module Main (main) where
 import Test.Tasty (TestTree, defaultMain, testGroup)
 import qualified Tests.Lua
 import qualified Tests.Lua.Module
+import qualified Tests.Lua.Reader
 import qualified Tests.Lua.Writer
 import System.Directory (withCurrentDirectory)
 
@@ -13,4 +14,5 @@ tests = testGroup "pandoc Lua engine"
   [ testGroup "Lua filters" Tests.Lua.tests
   , testGroup "Lua modules" Tests.Lua.Module.tests
   , testGroup "Custom writers" Tests.Lua.Writer.tests
+  , testGroup "Custom readers" Tests.Lua.Reader.tests
   ]