pager: add timeouts to SingleConnectionPagerWorker

The SingleConnectionPagerWorker now supports request timeouts
when fetching pages. This is for consistency with the main
PagerWorker implementation.

Note that for now, no metadata queries specify timeouts, so
the default per-Session execution profile's timeout will be used.
Nothing prevents us from specifying custom timeouts for metadata
queries in the future, thanks to this commit.

Author: wprzytula

scylla/src/client/pager.rs

@@ -8,6 +8,7 @@ use std::ops::ControlFlow;
 use std::pin::Pin;
 use std::sync::Arc;
 use std::task::{Context, Poll};
+use std::time::Duration;
 
 use futures::Stream;
 use scylla_cql::Consistency;
@@ -618,6 +619,7 @@ where
 struct SingleConnectionPagerWorker<Fetcher> {
     sender: ProvingSender<Result<ReceivedPage, NextPageError>>,
     fetcher: Fetcher,
+    timeout: Option<Duration>,
 }
 
 impl<Fetcher, FetchFut> SingleConnectionPagerWorker<Fetcher>
@@ -627,8 +629,8 @@ where
 {
     async fn work(mut self) -> PageSendAttemptedProof {
         match self.do_work().await {
-            Ok(proof) => proof,
-            Err(err) => {
+            Ok(Ok(proof)) => proof,
+            Ok(Err(err)) => {
                 let (proof, _) = self
                     .sender
                     .send(Err(NextPageError::RequestFailure(
@@ -637,15 +639,46 @@ where
                     .await;
                 proof
             }
+            Err(RequestTimeoutError(timeout)) => {
+                let (proof, _) = self
+                    .sender
+                    .send(Err(NextPageError::RequestFailure(
+                        RequestError::RequestTimeout(timeout),
+                    )))
+                    .await;
+                proof
+            }
         }
     }
 
-    async fn do_work(&mut self) -> Result<PageSendAttemptedProof, RequestAttemptError> {
+    async fn do_work(
+        &mut self,
+    ) -> Result<Result<PageSendAttemptedProof, RequestAttemptError>, RequestTimeoutError> {
         let mut paging_state = PagingState::start();
         loop {
-            let response = (self.fetcher)(paging_state)
-                .await
-                .and_then(QueryResponse::into_non_error_query_response)?;
+            let runner = async {
+                (self.fetcher)(paging_state)
+                    .await
+                    .and_then(QueryResponse::into_non_error_query_response)
+            };
+            let response_res = match self.timeout {
+                Some(timeout) => {
+                    match tokio::time::timeout(timeout, runner).await {
+                        Ok(res) => res,
+                        Err(_) /* tokio::time::error::Elapsed */ => {
+                            return Err(RequestTimeoutError(timeout));
+                        }
+                    }
+                }
+
+                None => runner.await,
+            };
+            let response = match response_res {
+                Ok(resp) => resp,
+                Err(err) => {
+                    return Ok(Err(err));
+                }
+            };
 
             match response.response {
                 NonErrorResponseWithDeserializedMetadata::Result(
@@ -662,7 +695,7 @@ where
 
                     if send_result.is_err() {
                         // channel was closed, QueryPager was dropped - should shutdown
-                        return Ok(proof);
+                        return Ok(Ok(proof));
                     }
 
                     match paging_state_response.into_paging_control_flow() {
@@ -671,7 +704,7 @@ where
                         }
                         ControlFlow::Break(()) => {
                             // Reached the last query, shutdown
-                            return Ok(proof);
+                            return Ok(Ok(proof));
                         }
                     }
                 }
@@ -681,12 +714,12 @@ where
 
                     // We must attempt to send something because the iterator expects it.
                     let (proof, _) = self.sender.send_empty_page(response.tracing_id, None).await;
-                    return Ok(proof);
+                    return Ok(Ok(proof));
                 }
                 _ => {
-                    return Err(RequestAttemptError::UnexpectedResponse(
+                    return Ok(Err(RequestAttemptError::UnexpectedResponse(
                         response.response.to_response_kind(),
-                    ));
+                    )));
                 }
             }
         }
@@ -1054,6 +1087,12 @@ If you are using this API, you are probably doing something wrong."
         let (sender, receiver) = mpsc::channel::<Result<ReceivedPage, NextPageError>>(1);
 
         let page_size = query.get_validated_page_size();
+        let timeout = query.get_request_timeout().or_else(|| {
+            query
+                .get_execution_profile_handle()?
+                .access()
+                .request_timeout
+        });
 
         let worker_task = async move {
             let worker = SingleConnectionPagerWorker {
@@ -1067,6 +1106,7 @@ If you are using this API, you are probably doing something wrong."
                         paging_state,
                     )
                 },
+                timeout,
             };
             worker.work().await
         };
@@ -1084,6 +1124,12 @@ If you are using this API, you are probably doing something wrong."
         let (sender, receiver) = mpsc::channel::<Result<ReceivedPage, NextPageError>>(1);
 
         let page_size = prepared.get_validated_page_size();
+        let timeout = prepared.get_request_timeout().or_else(|| {
+            prepared
+                .get_execution_profile_handle()?
+                .access()
+                .request_timeout
+        });
 
         let worker_task = async move {
             let worker = SingleConnectionPagerWorker {
@@ -1098,6 +1144,7 @@ If you are using this API, you are probably doing something wrong."
                         paging_state,
                     )
                 },
+                timeout,
             };
             worker.work().await
         };