feat(queries): Report amount of remaining items in query

client/src/query.rs

@@ -159,27 +159,27 @@ impl QueryExecutor for Client {
     fn start_query(
         &self,
         query: QueryWithParams,
-    ) -> Result<(QueryOutputBatchBox, Option<Self::Cursor>), Self::Error> {
+    ) -> Result<(QueryOutputBatchBox, u64, Option<Self::Cursor>), Self::Error> {
         let request_head = self.get_query_request_head();
 
         let request = QueryRequest::Start(query);
 
         let response = request_head.assemble(request).build()?.send()?;
         let response = decode_iterable_query_response(&response)?;
 
-        let (batch, cursor) = response.into_parts();
+        let (batch, remaining_items, cursor) = response.into_parts();
 
         let cursor = cursor.map(|cursor| QueryCursor {
             request_head,
             cursor,
         });
 
-        Ok((batch, cursor))
+        Ok((batch, remaining_items, cursor))
     }
 
     fn continue_query(
         cursor: Self::Cursor,
-    ) -> Result<(QueryOutputBatchBox, Option<Self::Cursor>), Self::Error> {
+    ) -> Result<(QueryOutputBatchBox, u64, Option<Self::Cursor>), Self::Error> {
         let QueryCursor {
             request_head,
             cursor,
@@ -190,14 +190,14 @@ impl QueryExecutor for Client {
         let response = request_head.assemble(request).build()?.send()?;
         let response = decode_iterable_query_response(&response)?;
 
-        let (batch, cursor) = response.into_parts();
+        let (batch, remaining_items, cursor) = response.into_parts();
 
         let cursor = cursor.map(|cursor| QueryCursor {
             request_head,
             cursor,
         });
 
-        Ok((batch, cursor))
+        Ok((batch, remaining_items, cursor))
     }
 }
 

client/tests/integration/pagination.rs

@@ -24,6 +24,33 @@ fn limits_should_work() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn reported_length_should_be_accurate() -> Result<()> {
+    let (_rt, _peer, client) = <PeerBuilder>::new().with_port(11_170).start_with_runtime();
+    wait_for_genesis_committed(&vec![client.clone()], 0);
+
+    register_assets(&client)?;
+
+    let mut iter = client
+        .query(asset::all_definitions())
+        .with_pagination(Pagination {
+            limit: Some(nonzero!(7_u64)),
+            offset: 1,
+        })
+        .with_fetch_size(FetchSize::new(Some(nonzero!(3_u64))))
+        .execute()?;
+
+    assert_eq!(iter.len(), 7);
+
+    for _ in 0..4 {
+        iter.next().unwrap().unwrap();
+    }
+
+    assert_eq!(iter.len(), 3);
+
+    Ok(())
+}
+
 #[test]
 fn fetch_size_should_work() -> Result<()> {
     // use the lower-level API to inspect the batch size
@@ -49,9 +76,10 @@ fn fetch_size_should_work() -> Result<()> {
             FetchSize::new(Some(nonzero!(3_u64))),
         ),
     );
-    let (first_batch, _continue_cursor) = client.start_query(query)?;
+    let (first_batch, remaining_items, _continue_cursor) = client.start_query(query)?;
 
     assert_eq!(first_batch.len(), 3);
+    assert_eq!(remaining_items, 4);
 
     Ok(())
 }

client_cli/src/main.rs

@@ -1176,11 +1176,11 @@ mod json {
                             // we can't really do type-erased iterable queries in a nice way right now...
                             use iroha::data_model::query::builder::QueryExecutor;
 
-                            let (mut first_batch, mut continue_cursor) =
+                            let (mut first_batch, _remaining_items, mut continue_cursor) =
                                 client.start_query(query)?;
 
                             while let Some(cursor) = continue_cursor {
-                                let (next_batch, next_continue_cursor) =
+                                let (next_batch, _remaining_items, next_continue_cursor) =
                                     <Client as QueryExecutor>::continue_query(cursor)?;
 
                                 first_batch.extend(next_batch);

core/src/query/cursor.rs

@@ -12,6 +12,7 @@ trait BatchedTrait {
         &mut self,
         cursor: u64,
     ) -> Result<(QueryOutputBatchBox, Option<NonZeroU64>), UnknownCursor>;
+    fn remaining(&self) -> u64;
 }
 
 struct BatchedInner<I> {
@@ -22,7 +23,7 @@ struct BatchedInner<I> {
 
 impl<I> BatchedTrait for BatchedInner<I>
 where
-    I: Iterator,
+    I: ExactSizeIterator,
     QueryOutputBatchBox: From<Vec<I::Item>>,
 {
     fn next_batch(
@@ -76,6 +77,10 @@ where
                 .map(|cursor| NonZeroU64::new(cursor).expect("Cursor is never 0")),
         ))
     }
+
+    fn remaining(&self) -> u64 {
+        self.iter.len() as u64
+    }
 }
 
 /// Unknown cursor error.
@@ -100,7 +105,7 @@ impl QueryBatchedErasedIterator {
     /// Creates a new batched iterator. Boxes the inner iterator to erase its type.
     pub fn new<I>(iter: I, batch_size: NonZeroU64) -> Self
     where
-        I: Iterator + Send + Sync + 'static,
+        I: ExactSizeIterator + Send + Sync + 'static,
         QueryOutputBatchBox: From<Vec<I::Item>>,
     {
         Self {
@@ -128,4 +133,11 @@ impl QueryBatchedErasedIterator {
     ) -> Result<(QueryOutputBatchBox, Option<NonZeroU64>), UnknownCursor> {
         self.inner.next_batch(cursor)
     }
+
+    /// Returns the number of remaining elements in the iterator.
+    ///
+    /// You should not rely on the reported amount being correct for safety, same as [`ExactSizeIterator::len`].
+    pub fn remaining(&self) -> u64 {
+        self.inner.remaining()
+    }
 }

core/src/query/pagination.rs

@@ -45,6 +45,12 @@ impl<I: Iterator> Iterator for Paginated<I> {
     }
 }
 
+impl<I: ExactSizeIterator> ExactSizeIterator for Paginated<I> {
+    fn len(&self) -> usize {
+        self.0.len()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use iroha_data_model::query::parameters::Pagination;

core/src/query/store.rs

@@ -189,18 +189,19 @@ impl LiveQueryStore {
         &self,
         query_id: QueryId,
         cursor: NonZeroU64,
-    ) -> Result<(QueryOutputBatchBox, Option<NonZeroU64>)> {
+    ) -> Result<(QueryOutputBatchBox, u64, Option<NonZeroU64>)> {
         trace!(%query_id, "Advancing existing query");
         let QueryInfo {
             mut live_query,
             authority,
             ..
         } = self.remove(&query_id).ok_or(UnknownCursor)?;
         let (next_batch, next_cursor) = live_query.next_batch(cursor.get())?;
+        let remaining = live_query.remaining();
         if next_cursor.is_some() {
             self.insert(query_id, live_query, authority);
         }
-        Ok((next_batch, next_cursor))
+        Ok((next_batch, remaining, next_cursor))
     }
 
     fn check_capacity(&self, authority: &AccountId) -> Result<()> {
@@ -248,12 +249,20 @@ impl LiveQueryStoreHandle {
         let curr_cursor = 0;
         let (batch, next_cursor) = live_query.next_batch(curr_cursor)?;
 
+        // NOTE: we are checking remaining items _after_ the first batch is taken
+        let remaining_items = live_query.remaining();
+
         // if the cursor is `None` - the query has ended, we can remove it from the store
         if next_cursor.is_some() {
             self.store
                 .insert_new_query(query_id.clone(), live_query, authority.clone())?;
         }
-        Ok(Self::construct_query_response(batch, query_id, next_cursor))
+        Ok(Self::construct_query_response(
+            batch,
+            remaining_items,
+            query_id,
+            next_cursor,
+        ))
     }
 
     /// Retrieve next batch of query output using `cursor`.
@@ -265,9 +274,15 @@ impl LiveQueryStoreHandle {
         &self,
         ForwardCursor { query, cursor }: ForwardCursor,
     ) -> Result<QueryOutput> {
-        let (batch, next_cursor) = self.store.get_query_next_batch(query.clone(), cursor)?;
+        let (batch, remaining, next_cursor) =
+            self.store.get_query_next_batch(query.clone(), cursor)?;
 
-        Ok(Self::construct_query_response(batch, query, next_cursor))
+        Ok(Self::construct_query_response(
+            batch,
+            remaining,
+            query,
+            next_cursor,
+        ))
     }
 
     /// Remove query from the storage if there is any.
@@ -277,11 +292,13 @@ impl LiveQueryStoreHandle {
 
     fn construct_query_response(
         batch: QueryOutputBatchBox,
+        remaining_items: u64,
         query_id: QueryId,
         cursor: Option<NonZeroU64>,
     ) -> QueryOutput {
         QueryOutput::new(
             batch,
+            remaining_items,
             cursor.map(|cursor| ForwardCursor {
                 query: query_id,
                 cursor,
@@ -330,7 +347,7 @@ mod tests {
             )
             .unwrap();
 
-            let (batch, mut current_cursor) = query_store_handle
+            let (batch, _remaining_items, mut current_cursor) = query_store_handle
                 .handle_iter_start(query_output, &ALICE_ID)
                 .unwrap()
                 .into_parts();
@@ -342,7 +359,7 @@ mod tests {
                 let Ok(batched) = query_store_handle.handle_iter_continue(cursor) else {
                     break;
                 };
-                let (batch, cursor) = batched.into_parts();
+                let (batch, _remaining_items, cursor) = batched.into_parts();
                 counter += batch.len();
 
                 current_cursor = cursor;

data_model/src/query/builder.rs

@@ -34,30 +34,31 @@ pub trait QueryExecutor {
         query: SingularQueryBox,
     ) -> Result<SingularQueryOutputBox, Self::Error>;
 
-    /// Starts an iterable query and returns the first batch of results.
+    /// Starts an iterable query and returns the first batch of results, the remaining number of results and a cursor to continue the query.
     ///
     /// # Errors
     ///
     /// Returns an error if the query execution fails.
     fn start_query(
         &self,
         query: QueryWithParams,
-    ) -> Result<(QueryOutputBatchBox, Option<Self::Cursor>), Self::Error>;
+    ) -> Result<(QueryOutputBatchBox, u64, Option<Self::Cursor>), Self::Error>;
 
-    /// Continues an iterable query from the given cursor and returns the next batch of results.
+    /// Continues an iterable query from the given cursor and returns the next batch of results, the remaining number of results and a cursor to continue the query.
     ///
     /// # Errors
     ///
     /// Returns an error if the query execution fails.
     fn continue_query(
         cursor: Self::Cursor,
-    ) -> Result<(QueryOutputBatchBox, Option<Self::Cursor>), Self::Error>;
+    ) -> Result<(QueryOutputBatchBox, u64, Option<Self::Cursor>), Self::Error>;
 }
 
 /// An iterator over results of an iterable query.
 #[derive(Debug)]
 pub struct QueryIterator<E: QueryExecutor, T> {
     current_batch_iter: vec::IntoIter<T>,
+    remaining_items: u64,
     continue_cursor: Option<E::Cursor>,
 }
 
@@ -73,12 +74,14 @@ where
     /// Returns an error if the type of the batch does not match the expected type `T`.
     pub fn new(
         first_batch: QueryOutputBatchBox,
+        remaining_items: u64,
         continue_cursor: Option<E::Cursor>,
     ) -> Result<Self, <Vec<T> as TryFrom<QueryOutputBatchBox>>::Error> {
         let batch: Vec<T> = first_batch.try_into()?;
 
         Ok(Self {
             current_batch_iter: batch.into_iter(),
+            remaining_items,
             continue_cursor,
         })
     }
@@ -102,7 +105,7 @@ where
         let cursor = self.continue_cursor.take()?;
 
         // get a next batch from iroha
-        let (batch, cursor) = match E::continue_query(cursor) {
+        let (batch, remaining_items, cursor) = match E::continue_query(cursor) {
             Ok(r) => r,
             Err(e) => return Some(Err(e)),
         };
@@ -115,11 +118,23 @@ where
             .expect("BUG: iroha returned unexpected type in iterable query");
 
         self.current_batch_iter = batch.into_iter();
+        self.remaining_items = remaining_items;
 
         self.next()
     }
 }
 
+impl<E, T> ExactSizeIterator for QueryIterator<E, T>
+where
+    E: QueryExecutor,
+    Vec<T>: TryFrom<QueryOutputBatchBox>,
+    <Vec<T> as TryFrom<QueryOutputBatchBox>>::Error: core::fmt::Debug,
+{
+    fn len(&self) -> usize {
+        self.current_batch_iter.len() + self.remaining_items as usize
+    }
+}
+
 /// An error that can occur when constraining the number of results of an iterable query to one.
 #[derive(
     Debug,
@@ -256,9 +271,10 @@ where
             },
         };
 
-        let (first_batch, continue_cursor) = self.query_executor.start_query(query)?;
+        let (first_batch, remaining_items, continue_cursor) =
+            self.query_executor.start_query(query)?;
 
-        let iterator = QueryIterator::<E, Q::Item>::new(first_batch, continue_cursor)
+        let iterator = QueryIterator::<E, Q::Item>::new(first_batch, remaining_items, continue_cursor)
             .expect(
                 "INTERNAL BUG: iroha returned unexpected type in iterable query. Is there a schema mismatch?",
             );

data_model/src/query/mod.rs

@@ -166,6 +166,8 @@ mod model {
     pub struct QueryOutput {
         /// A single batch of results
         pub batch: QueryOutputBatchBox,
+        /// The number of items in the query remaining to be fetched after this batch
+        pub remaining_items: u64,
         /// If not `None`, contains a cursor that can be used to fetch the next batch of results. Otherwise the current batch is the last one.
         pub continue_cursor: Option<ForwardCursor>,
     }
@@ -308,16 +310,21 @@ impl SingularQuery for SingularQueryBox {
 
 impl QueryOutput {
     /// Create a new [`QueryOutput`] from the iroha response parts.
-    pub fn new(batch: QueryOutputBatchBox, continue_cursor: Option<ForwardCursor>) -> Self {
+    pub fn new(
+        batch: QueryOutputBatchBox,
+        remaining_items: u64,
+        continue_cursor: Option<ForwardCursor>,
+    ) -> Self {
         Self {
             batch,
+            remaining_items,
             continue_cursor,
         }
     }
 
     /// Split this [`QueryOutput`] into its constituent parts.
-    pub fn into_parts(self) -> (QueryOutputBatchBox, Option<ForwardCursor>) {
-        (self.batch, self.continue_cursor)
+    pub fn into_parts(self) -> (QueryOutputBatchBox, u64, Option<ForwardCursor>) {
+        (self.batch, self.remaining_items, self.continue_cursor)
     }
 }