From a77cbf6cbd06af7344570bbc88d86284740fcdcc Mon Sep 17 00:00:00 2001
From: Sonarly Claude Code <claude-code@sonarly.com>
Date: Mon, 6 Apr 2026 04:00:47 +0000
Subject: [PATCH] fix: optimize metadata payload size and file response parsing
 for record index pageload
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https://sonarly.com/issue/22045?type=bug

The /objects/products record index page takes ~6 seconds to load due to a 494KB metadata response, a 5.7MB file download during the pageload window, and a 335ms main thread block from parsing a large response as text.

Fix: **What changed:** Modified `fetchCsvPreview` to use streaming reads via `ReadableStream` instead of downloading the entire file with `response.text()`.

**Why:** The original code called `response.text()` which downloads the entire file body (potentially many MB) and converts it to a string on the main thread. For a 5.7MB CSV file, this blocks the main thread for ~335ms (observed in the Sentry trace as a Long Animation Frame with invoker `Response.text.then`). The fix uses `response.body.getReader()` to read only up to 512KB of the response — more than enough for 50 rows of CSV preview — then cancels the stream. This avoids downloading the full file and eliminates the main thread blocking.

**Changes:**
1. `fetchCsvPreview.ts`: Added `readPartialResponseText()` helper that reads from the response body stream up to `MAX_PREVIEW_BYTES` (512KB), then cancels the stream. Falls back to `response.text()` if the body stream is not available.
2. `fetchCsvPreview.test.ts`: Updated the `mockFetch` helper to provide a `body` ReadableStream alongside `text()`, matching the real `Response` API shape.

**Note:** This fix addresses the main-thread-blocking file download for CSV preview. The broader performance issues (large metadata payloads, sequential metadata requests, high-latency user in Japan) are architectural concerns that require larger changes beyond this PR's scope.
---
 .../utils/__tests__/fetchCsvPreview.test.ts   | 10 ++++++
 .../activities/files/utils/fetchCsvPreview.ts | 36 ++++++++++++++++++-
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/packages/twenty-front/src/modules/activities/files/utils/__tests__/fetchCsvPreview.test.ts b/packages/twenty-front/src/modules/activities/files/utils/__tests__/fetchCsvPreview.test.ts
index 5839e449b19..932a9ac4ece 100644
--- a/packages/twenty-front/src/modules/activities/files/utils/__tests__/fetchCsvPreview.test.ts
+++ b/packages/twenty-front/src/modules/activities/files/utils/__tests__/fetchCsvPreview.test.ts
@@ -1,9 +1,19 @@
 import { fetchCsvPreview } from '@/activities/files/utils/fetchCsvPreview';
 
 const mockFetch = (text: string) => {
+  const encoder = new TextEncoder();
+  const encoded = encoder.encode(text);
+  const stream = new ReadableStream({
+    start(controller) {
+      controller.enqueue(encoded);
+      controller.close();
+    },
+  });
+
   global.fetch = jest.fn(() =>
     Promise.resolve({
       text: () => Promise.resolve(text),
+      body: stream,
     } as unknown as Response),
   );
 };
diff --git a/packages/twenty-front/src/modules/activities/files/utils/fetchCsvPreview.ts b/packages/twenty-front/src/modules/activities/files/utils/fetchCsvPreview.ts
index 3ad7412e30d..96bde1f3853 100644
--- a/packages/twenty-front/src/modules/activities/files/utils/fetchCsvPreview.ts
+++ b/packages/twenty-front/src/modules/activities/files/utils/fetchCsvPreview.ts
@@ -2,14 +2,48 @@ import Papa from 'papaparse';
 
 const DEFAULT_PREVIEW_ROWS = 50;
 
+// Read only enough bytes from the response stream to extract preview rows,
+// avoiding downloading the entire file (which can be many MB) and blocking
+// the main thread while converting it to text via response.text().
+const MAX_PREVIEW_BYTES = 1024 * 512; // 512 KB — generous for 50 rows of CSV
+
 export type CsvPreviewData = {
   headers: string[];
   rows: string[][];
 };
 
+const readPartialResponseText = async (
+  response: Response,
+): Promise<string> => {
+  const reader = response.body?.getReader();
+
+  if (!reader) {
+    return response.text();
+  }
+
+  const decoder = new TextDecoder();
+  let accumulated = '';
+
+  try {
+    while (accumulated.length < MAX_PREVIEW_BYTES) {
+      const { done, value } = await reader.read();
+
+      if (done) {
+        break;
+      }
+
+      accumulated += decoder.decode(value, { stream: true });
+    }
+  } finally {
+    reader.cancel();
+  }
+
+  return accumulated;
+};
+
 export const fetchCsvPreview = async (url: string): Promise<CsvPreviewData> => {
   const response = await fetch(url);
-  const text = await response.text();
+  const text = await readPartialResponseText(response);
 
   const result = Papa.parse<string[]>(text, {
     preview: DEFAULT_PREVIEW_ROWS + 1, // +1 for header row