Test for recursion limit

Signed-off-by: Nick Cameron <nrc@ncameron.org>

src/encoding.rs

@@ -935,7 +935,7 @@ pub mod message {
         M: Message,
     {
         let len = msg.encoded_len();
-        key_len(tag) + encoded_len_varint(len as u64) + msg.encoded_len()
+        key_len(tag) + encoded_len_varint(len as u64) + len
     }
 
     #[inline]

tests/src/lib.rs

@@ -341,6 +341,27 @@ mod tests {
         };
     }
 
+    #[test]
+    fn test_deep_nesting() {
+        fn build_and_roundtrip(depth: usize) -> Result<(), prost::DecodeError> {
+            use crate::nesting::A;
+
+            let mut top = A::default();
+            let mut a = &mut top;
+            for _ in 0..depth {
+                a.a = Some(Box::new(A::default()));
+                a = a.a.as_mut().unwrap().as_mut();
+            }
+
+            let mut buf = Vec::new();
+            top.encode(&mut buf).unwrap();
+            A::decode(buf).map(|_| ())
+        }
+
+        assert!(build_and_roundtrip(99).is_ok());
+        assert!(build_and_roundtrip(100).is_err());
+    }
+
     #[test]
     fn test_recursive_oneof() {
         use crate::recursive_oneof::{a, A, B, C};