ImageSize: make imageSize return an Either, not a Maybe.

This will give us better error reporting options.
This is part of a fix for #1834.

src/Text/Pandoc/ImageSize.hs

@@ -70,15 +70,17 @@ imageType img = case B.take 4 img of
                                         -> return Eps
                      _                  -> (hush . Left) "Unknown image type"
 
-imageSize :: ByteString -> Maybe ImageSize
-imageSize img = do
-  t <- imageType img
-  case t of
-       Png  -> pngSize img
-       Gif  -> gifSize img
-       Jpeg -> jpegSize img
-       Eps  -> epsSize img
-       Pdf  -> Nothing  -- TODO
+imageSize :: ByteString -> Either String ImageSize
+imageSize img =
+  case imageType img of
+       Just Png  -> mbToEither "could not determine PNG size" $ pngSize img
+       Just Gif  -> mbToEither "could not determine GIF size" $ gifSize img
+       Just Jpeg -> mbToEither "could not determine JPEG size" $ jpegSize img
+       Just Eps  -> mbToEither "could not determine EPS size" $ epsSize img
+       Just Pdf  -> Left "could not determine PDF size" -- TODO
+       Nothing   -> Left "could not determine image type"
+  where mbToEither msg Nothing  = Left msg
+        mbToEither _   (Just x) = Right x
 
 defaultSize :: (Integer, Integer)
 defaultSize = (72, 72)

src/Text/Pandoc/Writers/Docx.hs

@@ -1120,8 +1120,10 @@ inlineToOpenXML opts (Image alt (src, tit)) = do
           inlinesToOpenXML opts alt
         Right (img, mt) -> do
           ident <- ("rId"++) `fmap` getUniqueId
-          let size = imageSize img
-          let (xpt,ypt) = maybe (120,120) sizeInPoints size
+          (xpt,ypt) <- case imageSize img of
+                             Right size  -> return $ sizeInPoints size
+                             Left msg    -> do liftIO (warn msg)
+                                               return (120,120)
           -- 12700 emu = 1 pt
           let (xemu,yemu) = fitToPage (xpt * 12700, ypt * 12700) (pageWidth * 12700)
           let cNvPicPr = mknode "pic:cNvPicPr" [] $

src/Text/Pandoc/Writers/ODT.hs

@@ -134,8 +134,10 @@ transformPicMath opts entriesRef (Image lab (src,t)) = do
        warn $ "Could not find image `" ++ src ++ "', skipping..."
        return $ Emph lab
      Right (img, mbMimeType) -> do
-       let size = imageSize img
-       let (w,h) = fromMaybe (0,0) $ sizeInPoints `fmap` size
+       (w,h) <- case imageSize img of
+                     Right size -> return $ sizeInPoints size
+                     Left msg   -> do warn msg
+                                      return (0,0)
        let tit' = show w ++ "x" ++ show h
        entries <- readIORef entriesRef
        let extension = fromMaybe (takeExtension $ takeWhile (/='?') src)

src/Text/Pandoc/Writers/RTF.hs

@@ -56,9 +56,9 @@ rtfEmbedImage opts x@(Image _ (src,_)) = do
                              "image/jpeg" -> "\\jpegblip"
                              "image/png"  -> "\\pngblip"
                              _            -> error "Unknown file type"
-         let sizeSpec = case imageSize imgdata of
-                             Nothing -> ""
-                             Just sz -> "\\picw" ++ show xpx ++
+         sizeSpec <- case imageSize imgdata of
+                             Left msg -> warn msg >> return ""
+                             Right sz -> return $ "\\picw" ++ show xpx ++
                                         "\\pich" ++ show ypx ++
                                         "\\picwgoal" ++ show (xpt * 20)
                                         ++ "\\pichgoal" ++ show (ypt * 20)