perf(servers): avoid rebuilding JSON records payload

Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com>

src/servers/src/http/result/json_result.rs

@@ -105,11 +105,11 @@ impl IntoResponse for JsonResponse {
                     })
                     .collect();
 
-                json!({
-                    "data": data,
-                    "execution_time_ms": execution_time,
-                })
-                .to_string()
+                let data = Value::Array(data.into_iter().map(Value::Object).collect());
+                let mut payload = Map::new();
+                payload.insert("data".to_string(), data);
+                payload.insert("execution_time_ms".to_string(), Value::from(execution_time));
+                Value::Object(payload).to_string()
             }
         };
 
@@ -133,3 +133,122 @@ impl IntoResponse for JsonResponse {
             .into_response()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use axum::body::to_bytes;
+    use axum::http::{StatusCode, header};
+    use serde_json::{Map, Value, json};
+
+    use super::*;
+    use crate::http::{ColumnSchema, HttpRecordsOutput, OutputSchema};
+
+    fn records(column_names: &[&str], rows: Vec<Vec<Value>>) -> HttpRecordsOutput {
+        let total_rows = rows.len();
+        HttpRecordsOutput {
+            schema: OutputSchema::new(
+                column_names
+                    .iter()
+                    .map(|name| ColumnSchema::new((*name).to_string(), "Json".to_string()))
+                    .collect(),
+            ),
+            rows,
+            total_rows,
+            metrics: Default::default(),
+        }
+    }
+
+    fn old_records_payload(records: &HttpRecordsOutput, execution_time: u64) -> String {
+        let schema = records.schema();
+        let data: Vec<Map<String, Value>> = records
+            .rows()
+            .iter()
+            .map(|row| {
+                schema
+                    .column_schemas
+                    .iter()
+                    .enumerate()
+                    .map(|(i, col)| (col.name.clone(), row[i].clone()))
+                    .collect()
+            })
+            .collect();
+
+        json!({
+            "data": data,
+            "execution_time_ms": execution_time,
+        })
+        .to_string()
+    }
+
+    #[tokio::test]
+    async fn test_records_response_matches_old_json_representation() {
+        let records = records(
+            &["z", "a", "z", "nested", "escaped", "nullable"],
+            vec![
+                vec![
+                    json!(1),
+                    json!("first"),
+                    json!(2),
+                    json!({"outer": {"items": [null, "value"]}}),
+                    json!("line\nwith \"quotes\" and \\slashes"),
+                    Value::Null,
+                ],
+                vec![
+                    json!(3),
+                    json!("second"),
+                    json!(4),
+                    json!({"array": [true, {"key": "value"}]}),
+                    json!("\tescaped"),
+                    Value::Null,
+                ],
+            ],
+        );
+        let execution_time = 42;
+        let expected = old_records_payload(&records, execution_time);
+
+        let response = JsonResponse {
+            output: vec![GreptimeQueryOutput::Records(records)],
+            execution_time_ms: execution_time,
+        }
+        .into_response();
+
+        assert_eq!(StatusCode::OK, response.status());
+        let body = to_bytes(response.into_body(), usize::MAX).await.unwrap();
+        assert_eq!(expected.as_bytes(), body.as_ref());
+    }
+
+    #[tokio::test]
+    async fn test_empty_records_response_matches_old_json_representation_and_headers() {
+        let records = records(&[], vec![]);
+        let execution_time = 42;
+        let expected = old_records_payload(&records, execution_time);
+
+        let response = JsonResponse {
+            output: vec![GreptimeQueryOutput::Records(records)],
+            execution_time_ms: execution_time,
+        }
+        .into_response();
+
+        assert_eq!(StatusCode::OK, response.status());
+        assert_eq!(
+            mime::APPLICATION_JSON.as_ref(),
+            response.headers().get(header::CONTENT_TYPE).unwrap()
+        );
+        assert_eq!(
+            ResponseFormat::Json.as_str(),
+            response.headers().get(&GREPTIME_DB_HEADER_FORMAT).unwrap()
+        );
+        assert_eq!(
+            execution_time.to_string(),
+            response
+                .headers()
+                .get(&GREPTIME_DB_HEADER_EXECUTION_TIME)
+                .unwrap()
+                .to_str()
+                .unwrap()
+        );
+
+        let body = to_bytes(response.into_body(), usize::MAX).await.unwrap();
+        assert_eq!(expected.as_bytes(), body.as_ref());
+    }
+}