perf: use Content-Length header instead of res.body() for network size#746
Open
Gonzih wants to merge 1 commit intogarrytan:mainfrom
Open
perf: use Content-Length header instead of res.body() for network size#746Gonzih wants to merge 1 commit intogarrytan:mainfrom
Gonzih wants to merge 1 commit intogarrytan:mainfrom
Conversation
…e tracking res.body() buffers the entire HTTP response into a Node Buffer. For large responses (JS bundles, images, API payloads) this is O(response_size) memory pressure per request and blocks the event loop while Playwright reads the full response body just to get a byte count. Fix: read the Content-Length response header first (O(1), zero I/O). Fall back to res.body() only for chunked transfer encoding where Content-Length is legitimately absent. This is particularly noticeable on pages with heavy network traffic — downloading a 2MB JS bundle previously allocated a full 2MB Buffer just to call .length on it. Closes garrytan#711
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
The Problem
In `browser-manager.ts`, the `requestfinished` handler calls `res.body()` to get the response size:
```typescript
const body = await res.body().catch(() => null);
const size = body ? body.length : 0;
```
`res.body()` in Playwright buffers the entire response into a Node `Buffer`. For a 2MB JS bundle, that's a 2MB allocation per network request, just to call `.length` on it. Under load (SPA with 50+ network requests on page load), this is significant memory pressure and event loop blocking.
Issue #711.
Fix
Read `Content-Length` from response headers first — it's O(1) and already cached by Playwright. Only fall back to `res.body()` for chunked transfer encoding where `Content-Length` is genuinely absent.
Most HTTP/1.1 and HTTP/2 responses include `Content-Length`. The fallback covers streaming/chunked responses where the header is missing by design.
sent from mStack