fix DoubleEndedIterator impl for Name

crates/proto/src/rr/domain/name.rs

@@ -110,8 +110,7 @@ impl Name {
         LabelIter {
             name: self,
             index: 0,
-            started: false,
-            finished: false,
+            len: self.label_ends.len(),
         }
     }
 
@@ -930,27 +929,23 @@ impl LabelEnc for LabelEncUtf8 {
 pub struct LabelIter<'a> {
     name: &'a Name,
     index: usize,
-    started: bool,
-    finished: bool,
+    len: usize,
 }
 
 impl<'a> Iterator for LabelIter<'a> {
     type Item = &'a [u8];
 
     fn next(&mut self) -> Option<Self::Item> {
-        if self.finished {
+        if self.index >= self.len {
             return None;
         }
-        self.started = true;
+
         let end = *self.name.label_ends.get(self.index)?;
         let start = match self.index {
             0 => 0,
             _ => self.name.label_ends[self.index - 1],
         };
         self.index += 1;
-        if self.index == self.name.label_ends.len() {
-            self.finished = true;
-        }
         Some(&self.name.label_data[start as usize..end as usize])
     }
 
@@ -964,23 +959,18 @@ impl<'a> ExactSizeIterator for LabelIter<'a> {}
 
 impl<'a> DoubleEndedIterator for LabelIter<'a> {
     fn next_back(&mut self) -> Option<Self::Item> {
-        if self.finished {
+        if self.len <= self.index {
             return None;
         }
-        if !self.started {
-            self.index = self.name.label_ends.len().checked_sub(1)?;
-        }
-        self.started = true;
-        let end = *self.name.label_ends.get(self.index)?;
-        let start = match self.index {
+
+        self.len -= 1;
+
+        let end = *self.name.label_ends.get(self.len)?;
+        let start = match self.len {
             0 => 0,
-            _ => self.name.label_ends[self.index - 1],
+            _ => self.name.label_ends[self.len - 1],
         };
-        if self.index == 0 {
-            self.finished = true;
-        } else {
-            self.index -= 1;
-        }
+
         Some(&self.name.label_data[start as usize..end as usize])
     }
 }
@@ -1909,4 +1899,16 @@ mod tests {
             _ => panic!("expected too long message"),
         }
     }
+
+    #[test]
+    fn test_double_ended_iterator() {
+        let name = Name::from_ascii("www.example.com").unwrap();
+        let mut iter = name.iter();
+
+        assert_eq!(iter.next().unwrap(), b"www");
+        assert_eq!(iter.next_back().unwrap(), b"com");
+        assert_eq!(iter.next().unwrap(), b"example");
+        assert!(iter.next_back().is_none());
+        assert!(iter.next().is_none());
+    }
 }