sec-websocket-extensions: permessage-deflate not accepted

[RodrigoHamuy]

Which Cloudflare product(s) does this pertain to?

Workers Runtime

What versions & operating system are you using?

Wrangler v4.10.0

Please provide a link to a minimal reproduction

https://edge-chat-demo.cloudflareworkers.com/

Describe the Bug

The docs suggest that Websocket connections are compressed by default ( https://developers.cloudflare.com/workers/configuration/compatibility-flags/#websocket-compression ).

But no matter what we tried, the Cloudflare server side never accepts the permessage-deflate extension.

You can try it directly in any of the live demos from the docs: https://developers.cloudflare.com/durable-objects/demos/

For example the Cloudflare Workers Chat Demo demo: https://edge-chat-demo.cloudflareworkers.com/
Source: https://github.com/cloudflare/workers-chat-demo

Steps to reproduce:

1. With Chrome DevTools open, go to https://edge-chat-demo.cloudflareworkers.com/
2. Fill your name and a chat room to enter.
3. Go to Chrome DevTools > Network > WS > and look for the websocket connection.

Expected: sec-websocket-extensions: permessage-deflate should be in the response header.
Currently: It is not.

[vicb]

@RodrigoHamuy could you please attach a minimal repro with only code needed to trigger the issue - please add a link to a GH repository with the source code.
Thanks

[kentonv]

Note that your compatibility date must be set to at least 2023-08-15 to get websocket compression. The edge-chat-demo is much older than that and hasn't been updated.

[kentonv]

Compat flag: https://developers.cloudflare.com/workers/configuration/compatibility-flags/#websocket-compression

[MellowYarker]

Note that your compatibility date must be set to at least 2023-08-15 to get websocket compression. The edge-chat-demo is much older than that and hasn't been updated.

@RodrigoHamuy if you deploy the current version of https://github.com/cloudflare/workers-chat-demo, websocket compression will work by default. I've confirmed this here https://2025-chat-demo.milanmiladinovic.workers.dev/ (sec-websocket-extensions: permessage-deflate; client_max_window_bits=15 in the response). As Kenton said, the current deployment of the edge chat demo is old.

[redsquare]

@kentonv Sorry to trouble you - do you know if this should work with agents+durable objects?