Are websocket frames automatically compressed after adding the permessage-deflate response header?

user_2303937 0
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The bottom line:

I don't see websocket messages compressed, even though the permessage-deflate headers exist on both request and response.

Some details:

I have a nodejs server, and I use Primus (with engine.io under). I use the 'compression' feature of Primus, in order to support permessage-delate.

After I turn it on, I start seeing permessage-deflate header on responses.

But I don't see the websocket frames themselves being compressed.

I sniff the traffic using charlesproxy, and again - the frames look the same as they were before I turned the 'compression' feature on.

Illustration:

Here's an example request from the websocket handshake:

Accept-Encoding:gzip, deflate, br
Accept-Language:en-US,en;q=0.8,he;q=0.6,fr;q=0.4
Cache-Control:no-cache
Connection:Upgrade
Cookie:[some cookies]
Host:[our host]
Origin:https://[our host]
Pragma:no-cache
Sec-WebSocket-Extensions:permessage-deflate; client_max_window_bits
Sec-WebSocket-Key:6nMxnGd0E8GrDg2s1B4tHQ==
Sec-WebSocket-Version:13
Upgrade:websocket
User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36

And this is the corresponding response:

Connection:upgrade
Date:Tue, 11 Jul 2017 14:10:18 GMT
Sec-WebSocket-Accept:lLjOXWbLRVIHw2inxrhx0U1ryrM=
Sec-WebSocket-Extensions:permessage-deflate; client_no_context_takeover
Sec-WebSocket-Version:13
Server:nginx
Upgrade:websocket
WebSocket-Server:uWebSockets

These examples are taken from the Chrome dev tools network inspector. I see something similar in the charlesproxy sniffer.

Other reference:

I saw this:

Implementing permessage-deflate in WebSockets

But I couldn't quite find an valid answer there.

So...

What am I missing here? Do I need to implement something more? Do I need to include any library?

Versions:

  • node - 4.2.4
  • primus - 7.0.2
  • chrome: 59.0.3071.115
  • FF: 54.0.1
  • charles: 4.1.4

Many thanks!

compression
2 Answers

The problem is that uws does not compress data even if it is instructed to do so.

See this issue https://github.com/socketio/engine.io/issues/474

It should work if you tell engine.io to use ws instead of uws. You can do that by setting the EIO_WS_ENGINE env variable to ws or using the wsEngine option of engine.io.

I think there is also a size threshold under which messages are not compressed. If I'm not wrong it's 1 KiB.

user_61400080
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