1 files changed, 20 insertions, 5 deletions
diff --git a/main.roc b/main.roc
index 94139c4..033ff1d 100644
--- a/main.roc
+++ b/main.roc
@@ -6,14 +6,29 @@ app "roctorrent"
 
 bDecodeStr: List U8 -> Result (List U8) [Malformatted]
 bDecodeStr = \i ->
-  List.splitFirst i ':'
-  |> Result.mapErr \_err -> Malformatted
-  |> Result.map \{before, } -> before
+  when (List.splitFirst i ':') is
+    Ok {before, after} -> 
+      when (Str.fromUtf8 before) is 
+      Ok ls -> 
+        when (Str.toU32 ls) is
+        Ok l -> 
+          if Num.toU32 (List.len after) == l then 
+            Ok after
+          else 
+            Err Malformatted
+        Err _err -> Err Malformatted
+      Err _err -> Err Malformatted
+    Err _err -> Err Malformatted
 
 expect 
-  res = bDecodeStr (Str.toUtf8 "foo")
-  res == Err Malformatted
+  res = bDecodeStr (Str.toUtf8 "3:foo")
+  res == Ok (Str.toUtf8 "foo")
 
+expect 
+  errCases = ["foo", "1:foo", "4:foo", ":", "foo:", "1:", "::"]
+  List.all errCases \t -> 
+    res = bDecodeStr (Str.toUtf8 t)
+    res == Err Malformatted
 
 main = 
   Stdout.line "Hello, World"