append(): check for not_modified

src/lib.rs

@@ -153,7 +153,21 @@ impl<B: StoreBackend> Store<B> {
     }
 
     fn append(&mut self, key: &str, value: &[u8]) -> Result<(), Error<B::Error>> {
-        let free_offset = self.get_bytes_used()?;
+        let free_offset = {
+            let mut iter = Iter::new(self.backend.data().as_ref());
+            let mut not_modified = false;
+            while let Some(result) = iter.next() {
+                let (record_key, record_value) = result?;
+                if key.as_bytes() == record_key {
+                    not_modified = value == record_value;
+                }
+            }
+            if not_modified {
+                return Ok(())
+            }
+            iter.offset
+        };
+
         unsafe { self.append_at(free_offset, key.as_bytes(), value)? };
         Ok(())
     }

src/test.rs

@@ -130,6 +130,20 @@ fn write_many() {
     assert_eq!(store.read("bar").unwrap().unwrap(), b"SPAM");
 }
 
+#[test]
+#[cfg(feature = "postcard-values")]
+fn write_value_many() {
+    let mut store = make_store();
+    store.write_value("quux", (false, 3u8, -42i16)).unwrap();
+    for i in 0..1000u32 {
+        store.write_value("bar", i).unwrap();
+        assert_eq!(store.read_value("bar"), Ok(Some(i)));
+        store.write_value("foo", i % 2 == 0).unwrap();
+        assert_eq!(store.read_value("foo"), Ok(Some(i % 2 == 0)));
+    }
+    assert_eq!(store.read_value("quux"), Ok(Some((false, 3u8, -42i16))));
+}
+
 #[test]
 fn no_flash() {
     let mut store = Store::new(no_flash::NoFlash);