Text.Pandoc.MIME: add exported function getCharset.

[API change]

src/Text/Pandoc/MIME.hs

@@ -10,8 +10,13 @@
 
 Mime type lookup.
 -}
-module Text.Pandoc.MIME ( MimeType, getMimeType, getMimeTypeDef,
-                          extensionFromMimeType, mediaCategory ) where
+module Text.Pandoc.MIME (
+  MimeType,
+  getMimeType,
+  getMimeTypeDef,
+  getCharset,
+  extensionFromMimeType,
+  mediaCategory ) where
 import Data.List (isPrefixOf, isSuffixOf)
 import qualified Data.Map as M
 import qualified Data.Text as T
@@ -54,6 +59,14 @@ reverseMimeTypes = M.fromList $ map swap mimeTypesList
 mimeTypes :: M.Map T.Text MimeType
 mimeTypes = M.fromList mimeTypesList
 
+-- | Get the charset from a mime type, if one is present.
+getCharset :: MimeType -> Maybe T.Text
+getCharset mt =
+  let (_,y) = T.breakOn "charset=" mt
+   in if T.null y
+         then Nothing
+         else Just $ T.toUpper $ T.takeWhile (/= ';') $ T.drop 8 y
+
 -- | Collection of common mime types.
 -- Except for first entry, list borrowed from
 -- <https://github.com/Happstack/happstack-server/blob/master/src/Happstack/Server/FileServe/BuildingBlocks.hs happstack-server>