fix: cobs accumulator out-of-bounds index when data is 1 byte too long

src/accumulator.rs

@@ -132,7 +132,7 @@ impl<const N: usize> CobsAccumulator<N> {
  let (take, release) = input.split_at(n + 1);
 
  // Does it fit?
- if (self.idx + n) <= N {
+ if (self.idx + take.len()) <= N {
  // Aw yiss - add to array
  self.extend_unchecked(take);
 
@@ -286,3 +286,21 @@ fn double_loop_test_ref() {
 
  assert!(Demo { a: 256854231, b: 115, c : "different test" } == demo2);
 }
+
+#[test]
+fn extend_unchecked_in_bounds_test() {
+ // Test bug present in revision abcb407:
+ // extend_unchecked may be passed slice with size 1 greater than accumulator buffer causing panic
+
+ #[derive(serde::Serialize, Deserialize, Debug, PartialEq, Eq)]
+ struct Demo {
+ data: [u8; 10],
+ }
+
+ // Accumulator has 1 byte less space than encoded message
+ let mut acc: CobsAccumulator<11> = CobsAccumulator::new();
+ let mut data = crate::to_vec_cobs::<_, 128>(&Demo { data: [0xcc; 10] }).unwrap();
+ assert_eq!(data.len(), 12); // 1 byte for offset + 1 sentinel byte appended
+
+ assert!(matches!(acc.feed::<Demo>(&data[..]), FeedResult::OverFull(_)));
+}