Merge pull request 'fix: disable gzip and pad SSE events to prevent proxy buffering' (#9) from fix/sse-gzip-buffering into main

Reviewed-on: #9

backend/src/routes/import.ts

@@ -28,17 +28,14 @@ function isJsonFile(file: { mimetype: string; originalname: string }): boolean {
   );
 }
 
-function sseWrite(res: import('express').Response, data: Record<string, unknown>) {
+const SSE_PAD_TARGET = 4096;
-  res.write(`data: ${JSON.stringify(data)}\n\n`);
-}
 
-/**
+function sseWrite(res: import('express').Response, data: Record<string, unknown>) {
- * Send a 2 KB comment block to push past any proxy buffering threshold.
+  const payload = `data: ${JSON.stringify(data)}\n\n`;
- * Nginx and other reverse proxies often buffer the first few KB before
+  const pad = Math.max(0, SSE_PAD_TARGET - payload.length);
- * starting to stream — this padding forces the initial flush.
+  // SSE comment lines (": ...") are ignored by the browser but push
- */
+  // data past proxy buffer thresholds so each event is delivered immediately.
-function ssePadding(res: import('express').Response) {
+  res.write(pad > 0 ? `: ${' '.repeat(pad)}\n${payload}` : payload);
-  res.write(`: ${' '.repeat(2048)}\n\n`);
 }
 
 const router = Router();
@@ -71,7 +68,6 @@ router.post(
       res.setHeader('X-Accel-Buffering', 'no');
       res.socket?.setNoDelay(true);
       res.flushHeaders();
-      ssePadding(res);
 
       try {
         const converted = await convertPdfToStatementStreaming(

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;
     }