fix: max_wait_time in http handler not work when result set is large … (#16267)

* fix: max_wait_time in http handler not work when result set is large and return fast.

* fix

Author: youngsofun

src/query/service/src/servers/http/v1/query/page_manager.rs

@@ -124,75 +124,71 @@ impl PageManager {
 
     fn append_block(
         &mut self,
-        rows: &mut Vec<Vec<Option<String>>>,
+        res: &mut Vec<Vec<Option<String>>>,
         block: DataBlock,
-        remain_rows: usize,
+        remain_rows: &mut usize,
         remain_size: &mut usize,
     ) -> Result<()> {
         let format_settings = {
             let guard = self.format_settings.read();
             guard.as_ref().unwrap().clone()
         };
-        let mut iter = block_to_strings(&block, &format_settings)?
-            .into_iter()
-            .peekable();
-        let chunk: Vec<_> = iter
-            .by_ref()
-            .take(remain_rows)
-            .take_while(|r| {
-                let size = row_size(r);
-                let ok = *remain_size > size;
-                if ok {
-                    *remain_size -= size;
-                }
-                ok
-            })
-            .collect();
-        rows.extend(chunk);
-        self.row_buffer = iter.by_ref().collect();
+        let rows = block_to_strings(&block, &format_settings)?;
+        let mut i = 0;
+        while *remain_rows > 0 && *remain_size > 0 && i < rows.len() {
+            let size = row_size(&rows[i]);
+            if *remain_size > size {
+                *remain_size -= size;
+                *remain_rows -= 1;
+                i += 1;
+            } else {
+                *remain_size = 0;
+            }
+        }
+        res.extend_from_slice(&rows[..i]);
+        self.row_buffer = rows[i..].iter().cloned().collect();
         Ok(())
     }
 
     #[async_backtrace::framed]
     async fn collect_new_page(&mut self, tp: &Wait) -> Result<(StringBlock, bool)> {
         let mut res: Vec<Vec<Option<String>>> = Vec::with_capacity(self.max_rows_per_page);
-        let mut max_size_per_page = 10 * 1024 * 1024;
-        while res.len() < self.max_rows_per_page {
+        let mut remain_size = 10 * 1024 * 1024;
+        let mut remain_rows = self.max_rows_per_page;
+        while remain_rows > 0 && remain_size > 0 {
             if let Some(row) = self.row_buffer.pop_front() {
                 let size = row_size(&row);
-                if max_size_per_page > size {
+                if remain_size > size {
                     res.push(row);
-                    max_size_per_page -= size;
-                    continue;
+                    remain_size -= size;
+                    remain_rows -= 1;
+                } else {
+                    remain_size = 0;
                 }
-            }
-            break;
-        }
-        loop {
-            assert!(self.max_rows_per_page >= res.len());
-            let remain_rows = self.max_rows_per_page - res.len();
-            if remain_rows == 0 {
+            } else {
                 break;
             }
+        }
+
+        while remain_rows > 0 && remain_size > 0 {
             match tp {
                 Wait::Async => match self.block_receiver.try_recv() {
                     Some(block) => {
-                        self.append_block(&mut res, block, remain_rows, &mut max_size_per_page)?
+                        self.append_block(&mut res, block, &mut remain_rows, &mut remain_size)?
                     }
                     None => break,
                 },
                 Wait::Deadline(t) => {
                     let now = Instant::now();
                     let d = *t - now;
+                    if d.is_zero() {
+                        // timeout() will return Ok if the future completes immediately
+                        break;
+                    }
                     match tokio::time::timeout(d, self.block_receiver.recv()).await {
                         Ok(Some(block)) => {
                             debug!("http query got new block with {} rows", block.num_rows());
-                            self.append_block(
-                                &mut res,
-                                block,
-                                remain_rows,
-                                &mut max_size_per_page,
-                            )?;
+                            self.append_block(&mut res, block, &mut remain_rows, &mut remain_size)?;
                         }
                         Ok(None) => {
                             info!("http query reach end of blocks");