Address comments

Signed-off-by: Yilin Chen <sticnarf@gmail.com>

src/transaction/mod.rs

@@ -34,7 +34,7 @@ enum Mutation {
 }
 
 impl Mutation {
-    fn with_key(self, key: Key) -> kvrpcpb::Mutation {
+    fn into_proto_with_key(self, key: Key) -> kvrpcpb::Mutation {
         let mut pb = kvrpcpb::Mutation {
             key: key.into(),
             ..Default::default()
@@ -141,36 +141,29 @@ impl Transaction {
         &self,
         keys: impl IntoIterator<Item = impl Into<Key>>,
     ) -> Result<impl Iterator<Item = (Key, Option<Value>)>> {
-        let mut keys_from_snapshot = Vec::new();
+        let mut undetermined_keys = Vec::new();
-        let mut results_in_buffer = keys
+        let mut results_in_buffer = Vec::new();
-            .into_iter()
+        for key in keys {
-            .map(|key| {
+            let key = key.into();
-                let key = key.into();
+            let mutation_value = self.get_from_mutations(&key);
-                let mutation_value = self.get_from_mutations(&key);
+            // If the value cannot be determined according to the buffered mutations, we need to
-                if let MutationValue::Undetermined = mutation_value {
+            // query from the snapshot.
-                    keys_from_snapshot.push(key.clone());
+            if let MutationValue::Undetermined = mutation_value {
-                }
+                undetermined_keys.push(key.clone());
-                (key, mutation_value)
-            })
-            .collect::<Vec<_>>()
-            .into_iter();
-        let mut results_from_snapshot = self
-            .snapshot
-            .batch_get(keys_from_snapshot)
-            .await?
-            .peekable();
-        Ok(std::iter::from_fn(move || {
-            let (key, mutation_value) = results_in_buffer.next()?;
-            match mutation_value {
-                MutationValue::Determined(value) => Some((key, value)),
-                MutationValue::Undetermined => match results_from_snapshot.peek() {
-                    Some((key_from_snapshot, _)) if &key == key_from_snapshot => {
-                        results_from_snapshot.next()
-                    }
-                    _ => Some((key, None)),
-                },
             }
-        }))
+            results_in_buffer.push((key, mutation_value));
+        }
+        let mut results_from_snapshot = self.snapshot.batch_get(undetermined_keys).await?;
+        Ok(results_in_buffer
+            .into_iter()
+            .map(move |(key, mutation_value)| match mutation_value {
+                MutationValue::Determined(value) => (key, value),
+                // `results_from_snapshot` should contain all undetermined keys. If not, it's a bug
+                // in `Snapshot::batch_get`.
+                MutationValue::Undetermined => results_from_snapshot
+                    .next()
+                    .expect("not enough results from snapshot"),
+            }))
     }
 
     pub fn scan(&self, _range: impl RangeBounds<Key>) -> Scanner {
@@ -310,7 +303,7 @@ impl Transaction {
         let _rpc_mutations: Vec<_> = self
             .mutations
             .iter()
-            .map(|(k, v)| v.clone().with_key(k.clone()))
+            .map(|(k, v)| v.clone().into_proto_with_key(k.clone()))
             .collect();
         unimplemented!()
     }