[codex] Avoid ranged octet string index overflow

dnp3/src/app/parse/bytes.rs

@@ -140,7 +140,7 @@ impl<'a> Iterator for RangedBytesIterator<'a> {
         }
         let bytes = self.cursor.read_bytes(self.size).ok()?;
         let index = self.index;
-        self.index += 1;
+        self.index = self.index.saturating_add(1);
         self.remaining -= 1;
         Some((bytes, index))
     }

dnp3/src/app/parse/parser.rs

@@ -1152,6 +1152,25 @@ mod test {
         assert_matches!(headers.next(), None);
     }
 
+    #[test]
+    fn parses_group110var1_at_max_index() {
+        let input = [0x6E, 0x01, 0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0xAA];
+        let mut headers =
+            ObjectParser::parse(ParseOptions::default(), FunctionCode::Response, &input)
+                .unwrap()
+                .iter();
+
+        let bytes: Vec<(&[u8], u16)> = assert_matches!(
+            headers.next().unwrap().details,
+            HeaderDetails::TwoByteStartStop(0xFFFF, 0xFFFF, RangedVariation::Group110VarX(0x01, seq)) => {
+                seq.iter().collect()
+            }
+        );
+
+        assert_eq!(bytes, vec![([0xAA].as_slice(), 0xFFFF)]);
+        assert_matches!(headers.next(), None);
+    }
+
     #[test]
     fn parses_group111var1_as_non_read() {
         let input = [