Simplify Indexed DB batching code by starting from an empty-string key

crates/matrix-sdk-indexeddb/src/crypto_store/mod.rs

@@ -1205,44 +1205,30 @@ async fn fetch_from_object_store_batched<R, F>(
 where
     F: Fn(JsValue) -> Result<R>,
 {
-    enum NextBatch {
-        First,          // In the first batch we don't start from a key
-        Later(JsValue), // In later batches we have a starting key
-    }
-
     let mut result = Vec::new();
-    let mut next_batch = NextBatch::First;
     let mut batch_n = 0;
 
+    // The empty string is before all keys in Indexed DB - first batch starts there.
+    let mut latest_key: JsValue = "".into();
+
     loop {
         debug!("Fetching Indexed DB records starting from {}", batch_n * batch_size);
 
         // See https://github.com/Alorel/rust-indexed-db/issues/31 - we
         // would like to use `get_all_with_key_and_limit` if it ever exists
         // but for now we use a cursor and manually limit batch size.
 
-        // Get hold of a cursor for this batch
-        let cursor = match &next_batch {
-            NextBatch::First => object_store.open_cursor(),
-
-            NextBatch::Later(latest_key) => {
-                // We want a cursor starting after the last key we processed
-                let after_latest_key = IdbKeyRange::lower_bound_with_open(latest_key, true);
-
-                // This key should always be valid since it was returned by `cursor.key()`.
-                // (Note: the key doesn't have to exist to be valid, so even if
-                // somehow the entry was deleted, we should not panic here.)
-                let after_latest_key = after_latest_key.expect("Key was not valid!");
-
-                object_store.open_cursor_with_range(&after_latest_key)
-            }
-        }?
-        .await?;
+        // Get hold of a cursor for this batch. (This should not panic in expect()
+        // because we always use "", or the result of cursor.key(), both of
+        // which are valid keys.)
+        let after_latest_key =
+            IdbKeyRange::lower_bound_with_open(&latest_key, true).expect("Key was not valid!");
+        let cursor = object_store.open_cursor_with_range(&after_latest_key)?.await?;
 
         // Fetch batch_size records into result
         let next_key = fetch_batch(cursor, batch_size, &f, &mut result).await?;
         if let Some(next_key) = next_key {
-            next_batch = NextBatch::Later(next_key);
+            latest_key = next_key;
         } else {
             break;
         }