1 files changed, 34 insertions, 8 deletions
diff --git a/test/test_escape.ml b/test/test_escape.ml
index 1587388..35a9b9d 100644
--- a/test/test_escape.ml
+++ b/test/test_escape.ml
@@ -70,16 +70,41 @@ let test_fold_long_line () =
 let test_fold_never_splits_utf8 () =
   let long = "SUMMARY:" ^ String.concat "" (List.init 40 (fun _ -> "\xc4\x99\xc5\x9b\xc4\x87")) in
   let out = E.fold_ics long in
-  let stripped =
-    String.concat ""
-      (List.filter_map
-         (fun l ->
-           let l = if l <> "" && l.[String.length l - 1] = '\r' then String.sub l 0 (String.length l - 1) else l in
-           if l = "" then None else if l.[0] = ' ' then Some (String.sub l 1 (String.length l - 1)) else Some l)
-         (String.split_on_char '\n' out))
+  let chunks =
+    List.filter_map
+      (fun l ->
+        let l = if l <> "" && l.[String.length l - 1] = '\r' then String.sub l 0 (String.length l - 1) else l in
+        if l = "" then None else if l.[0] = ' ' then Some (String.sub l 1 (String.length l - 1)) else Some l)
+      (String.split_on_char '\n' out)
   in
+  (* The named property: no chunk may START with a UTF-8 continuation byte
+     (0x80-0xBF) -- that would mean the previous fold cut mid-character.
+     Unfolding losslessly (below) cannot detect this on its own: concatenation
+     is insensitive to where the cuts fell, so a fold at ANY position still
+     round-trips. *)
+  List.iter
+    (fun c ->
+      if String.length c > 0 then
+        Alcotest.(check bool) "chunk does not start mid-UTF-8" true (Char.code c.[0] land 0xC0 <> 0x80))
+    chunks;
+  let stripped = String.concat "" chunks in
   check "unfolds to the original" long stripped
 
+(* B1 regression: 100 consecutive UTF-8 continuation bytes (0x80-0xBF) is not
+   producible by valid UTF-8 (whose longest continuation run is 3), but
+   fold_ics must stay TOTAL on arbitrary octet strings. A backoff loop with no
+   hard-cut fallback backs `cut` all the way down to `pos`, yielding a
+   zero-length chunk and recursing on the identical position forever. *)
+let test_fold_pathological_input_terminates () =
+  let pathological = String.make 100 '\x80' in
+  let out = E.fold_ics pathological in
+  let lines = String.split_on_char '\n' out in
+  List.iter
+    (fun l ->
+      let l = if l <> "" && l.[String.length l - 1] = '\r' then String.sub l 0 (String.length l - 1) else l in
+      if String.length l > 75 then Alcotest.failf "line of %d octets exceeds 75" (String.length l))
+    (List.filter (fun l -> l <> "") lines)
+
 let suite =
   ( "Escape",
     [ Alcotest.test_case "latex" `Quick test_latex;
@@ -90,4 +115,5 @@ let suite =
       Alcotest.test_case "flavour names" `Quick test_flavour_names;
       Alcotest.test_case "fold: short unchanged" `Quick test_fold_short_line_unchanged;
       Alcotest.test_case "fold: long line" `Quick test_fold_long_line;
-      Alcotest.test_case "fold: never splits utf8" `Quick test_fold_never_splits_utf8 ] )
+      Alcotest.test_case "fold: never splits utf8" `Quick test_fold_never_splits_utf8;
+      Alcotest.test_case "fold: pathological input terminates" `Quick test_fold_pathological_input_terminates ] )