Merge pull request 'fix: yield to event loop after each SSE write to flush socket' (#10) from fix/sse-event-loop-flush into main

Reviewed-on: #10

backend/src/routes/import.ts

@@ -32,15 +32,6 @@ function sseWrite(res: import('express').Response, data: Record<string, unknown>
   res.write(`data: ${JSON.stringify(data)}\n\n`);
 }
 
-/**
- * Send a 2 KB comment block to push past any proxy buffering threshold.
- * Nginx and other reverse proxies often buffer the first few KB before
- * starting to stream — this padding forces the initial flush.
- */
-function ssePadding(res: import('express').Response) {
-  res.write(`: ${' '.repeat(2048)}\n\n`);
-}
-
 const router = Router();
 
 router.post(
@@ -71,7 +62,6 @@ router.post(
       res.setHeader('X-Accel-Buffering', 'no');
       res.socket?.setNoDelay(true);
       res.flushHeaders();
-      ssePadding(res);
 
       try {
         const converted = await convertPdfToStatementStreaming(

backend/src/services/pdfToStatement.ts

@@ -150,6 +150,10 @@ const LLM_PROGRESS_MAX = 98;
 const LLM_PROGRESS_RANGE = LLM_PROGRESS_MAX - LLM_PROGRESS_MIN;
 const THROTTLE_MS = 300;
 
+function yieldToEventLoop(): Promise<void> {
+  return new Promise(resolve => setImmediate(resolve));
+}
+
 export async function convertPdfToStatementStreaming(
   buffer: Buffer,
   onProgress: OnProgress,
@@ -163,6 +167,7 @@ export async function convertPdfToStatementStreaming(
   }
 
   onProgress('pdf', 2, 'Извлечение текста из PDF...');
+  await yieldToEventLoop();
 
   let text: string;
   try {
@@ -186,6 +191,7 @@ export async function convertPdfToStatementStreaming(
   }
 
   onProgress('pdf', 8, 'Текст извлечён, отправка в LLM...');
+  await yieldToEventLoop();
 
   const openai = new OpenAI({
     apiKey: config.llmApiKey,
@@ -205,7 +211,6 @@ export async function convertPdfToStatementStreaming(
       stream: true,
     });
 
-    // Estimate expected output size as ~2x the input PDF text length, clamped
     const expectedChars = Math.max(2_000, Math.min(text.length * 2, 30_000));
 
     let accumulated = '';
@@ -227,11 +232,14 @@ export async function convertPdfToStatementStreaming(
           );
           onProgress('llm', llmProgress, 'Конвертация через LLM...');
           lastEmitTime = now;
+          // Let the event loop flush socket writes to the network
+          await yieldToEventLoop();
         }
       }
     }
 
     onProgress('llm', LLM_PROGRESS_MAX, 'LLM завершил, обработка результата...');
+    await yieldToEventLoop();
 
     const content = accumulated.trim();
     if (!content) {

frontend/nginx.conf

@@ -15,6 +15,7 @@ server {
         proxy_connect_timeout 5s;
         proxy_read_timeout 600s;
         proxy_buffering off;
+        gzip off;
         client_max_body_size 15m;
     }