From 0ae79275a980e158c3ac93df79ed33329150b7e0 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Fri, 10 Aug 2018 15:17:49 -0700
Subject: [PATCH] Avoid non-exhaustive pattern match.

---
 src/Text/Pandoc/ImageSize.hs | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/src/Text/Pandoc/ImageSize.hs b/src/Text/Pandoc/ImageSize.hs
index 00ab86eab..43d4877a0 100644
--- a/src/Text/Pandoc/ImageSize.hs
+++ b/src/Text/Pandoc/ImageSize.hs
@@ -410,20 +410,21 @@ jpegSize img =
 
 jfifSize :: ByteString -> Either String ImageSize
 jfifSize rest =
-  let [dpiDensity,dpix1,dpix2,dpiy1,dpiy2] = map fromIntegral
-                                           $ unpack $ B.take 5 $B.drop 9 rest
-      factor = case dpiDensity of
-                    1 -> id
-                    2 -> \x -> x * 254 `div` 10
-                    _ -> const 72
-      dpix = factor (shift dpix1 8 + dpix2)
-      dpiy = factor (shift dpiy1 8 + dpiy2)
-  in case findJfifSize rest of
-       Left msg    -> Left msg
-       Right (w,h) ->Right ImageSize { pxX = w
+  case map fromIntegral $ unpack $ B.take 5 $ B.drop 9 rest of
+    [dpiDensity,dpix1,dpix2,dpiy1,dpiy2] ->
+      let factor = case dpiDensity of
+                        1 -> id
+                        2 -> \x -> x * 254 `div` 10
+                        _ -> const 72
+          dpix = factor (shift dpix1 8 + dpix2)
+          dpiy = factor (shift dpiy1 8 + dpiy2)
+      in case findJfifSize rest of
+         Left msg    -> Left msg
+         Right (w,h) -> Right ImageSize { pxX = w
                                         , pxY = h
                                         , dpiX = dpix
                                         , dpiY = dpiy }
+    _ -> Left "unable to determine JFIF size"
 
 findJfifSize :: ByteString -> Either String (Integer,Integer)
 findJfifSize bs =