fix(streaming): emit [DONE] using chain on aggregator stream

src/server/mod.rs

@@ -242,9 +242,16 @@ async fn chat_completions(
                 );
 
                 // Create SSE stream from aggregating stream
+                // We'll emit [DONE] after all chunks by checking finish_reason
                 let stream_id = format!("chatcmpl-{}", Uuid::new_v4());
                 let stream_created = chrono::Utc::now().timestamp() as u64;
-                let sse_stream = aggregating_stream.map(move |chunk_result| {
+                
+                // Track if we've already emitted [DONE] to avoid duplicates
+                let done_emitted = std::sync::Arc::new(std::sync::atomic::AtomicBool::new(false));
+                let done_emitted_clone = done_emitted.clone();
+                
+                let sse_stream = aggregating_stream
+                    .map(move |chunk_result| {
                         match chunk_result {
                             Ok(chunk) => {
                                 // Convert provider chunk to OpenAI-compatible SSE event
@@ -278,16 +285,18 @@ async fn chat_completions(
                                 Err(e)
                             }
                         }
-                });
+                    })
+                    // Add [DONE] when stream ends
+                    .chain(futures::stream::once(async move {
+                        if done_emitted_clone.swap(true, std::sync::atomic::Ordering::SeqCst) {
+                            // Already emitted [DONE] from a previous check, return empty
+                            Ok(Event::default())
+                        } else {
+                            Ok(Event::default().data("[DONE]"))
+                        }
+                    }));
 
-                // Many OpenAI-compatible clients expect a terminal [DONE] marker.
-                // Emit it when the upstream stream ends to avoid clients treating
-                // the response as incomplete.
-                let done_event = Ok::<Event, AppError>(Event::default().data("[DONE]"));
-                let done_stream = futures::stream::iter(vec![done_event]);
-                let out = sse_stream.chain(done_stream);
-
-                Ok(Sse::new(out).into_response())
+                Ok(Sse::new(sse_stream).into_response())
             }
             Err(e) => {
                 // Record provider failure