fuzz: test error conditions

fuzz/fuzz.ml

@@ -9,18 +9,24 @@ let hash =
       const (Pack Digestif.sha512);
     ]
 
-let with_get_into_bytes off (type ctx)
+let with_get_into_bytes off len (type ctx)
     (module Hash : Digestif.S with type ctx = ctx) (ctx : ctx) =
-  let buf = Bytes.create (off + Hash.digest_size) in
-  Hash.get_into_bytes ctx ~off buf ;
+  let buf = Bytes.create len in
+  let () =
+    try Hash.get_into_bytes ctx ~off buf
+    with Invalid_argument e -> (
+      (* Skip if the invalid argument is valid; otherwise fail *)
+      match Bytes.sub buf off Hash.digest_size with
+      | _ -> failf "Hash.get_into_bytes: Invalid_argument %S" e
+      | exception Invalid_argument _ -> bad_test ()) in
   Bytes.sub_string buf off Hash.digest_size
 
 let () =
-  add_test ~name:"get_into_bytes" [ hash; int8; bytes ]
-  @@ fun (Pack hash) off bytes ->
+  add_test ~name:"get_into_bytes" [ hash; int8; range 1024; bytes ]
+  @@ fun (Pack hash) off len bytes ->
   let (module Hash) = Digestif.module_of hash in
   let ctx = Hash.empty in
   let ctx = Hash.feed_string ctx bytes in
-  let a = with_get_into_bytes (abs off) (module Hash) ctx in
+  let a = with_get_into_bytes off len (module Hash) ctx in
   let b = Hash.(to_raw_string (get ctx)) in
   check_eq ~eq:String.equal a b