feat(api-server): add container loadtest observability

server-rs/crates/api-server/src/api_response.rs

@@ -1,4 +1,13 @@
-use axum::Json;
+use std::convert::Infallible;
+
+use axum::{
+    Json,
+    body::Body,
+    http::{HeaderValue, header},
+    response::{IntoResponse, Response},
+};
+use bytes::Bytes;
+use futures_util::stream;
 use serde::Serialize;
 use serde_json::Value;
 #[cfg(test)]
@@ -32,6 +41,30 @@ where
     Json(serde_json::to_value(data).unwrap_or(Value::Null))
 }
 
+pub fn json_success_data_bytes_response(
+    request_context: Option<&RequestContext>,
+    data_json: Bytes,
+) -> Response {
+    if let Some(context) = request_context
+        && context.wants_envelope()
+    {
+        let meta = serde_json::to_vec(&build_api_response_meta(Some(context)))
+            .map(Bytes::from)
+            .unwrap_or_else(|_| Bytes::from_static(b"null"));
+        let chunks = [
+            Bytes::from_static(b"{\"ok\":true,\"data\":"),
+            data_json,
+            Bytes::from_static(b",\"error\":null,\"meta\":"),
+            meta,
+            Bytes::from_static(b"}"),
+        ];
+        let stream = stream::iter(chunks.into_iter().map(Ok::<Bytes, Infallible>));
+        return json_body_response(Body::from_stream(stream));
+    }
+
+    json_bytes_response(data_json)
+}
+
 pub fn json_error_body(
     request_context: Option<&RequestContext>,
     error: &ApiErrorPayload,
@@ -65,6 +98,19 @@ fn build_api_response_meta(request_context: Option<&RequestContext>) -> ApiRespo
     )
 }
 
+fn json_bytes_response(bytes: Bytes) -> Response {
+    json_body_response(Body::from(bytes))
+}
+
+fn json_body_response(body: Body) -> Response {
+    let mut response = body.into_response();
+    response.headers_mut().insert(
+        header::CONTENT_TYPE,
+        HeaderValue::from_static("application/json; charset=utf-8"),
+    );
+    response
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -106,6 +152,31 @@ mod tests {
         assert!(body.get("meta").is_none());
     }
 
+    #[tokio::test]
+    async fn success_response_streams_cached_data_inside_standard_envelope() {
+        use http_body_util::BodyExt;
+
+        let request_context = build_request_context(true);
+        let response = json_success_data_bytes_response(
+            Some(&request_context),
+            Bytes::from_static(br#"{"items":[]}"#),
+        );
+        let body = response
+            .into_body()
+            .collect()
+            .await
+            .expect("response body should collect")
+            .to_bytes();
+        let payload: Value = serde_json::from_slice(&body).expect("body should be json");
+
+        assert_eq!(payload["ok"], Value::Bool(true));
+        assert_eq!(payload["data"]["items"], Value::Array(Vec::new()));
+        assert_eq!(
+            payload["meta"]["requestId"],
+            Value::String("req-test".to_string())
+        );
+    }
+
     #[test]
     fn error_body_returns_legacy_shape_without_envelope_header() {
         let request_context = build_request_context(false);