Websocket+HTTP/2 error with cloudflare load balancing

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
25/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
python
Domain
networking

Research direction

Start by reviewing tornado/simple_httpclient.py around line 658 and reproduce the reported WebSocket request with the curl commands, comparing HTTP/2 and HTTP/1.1 behavior. The report does not define a concrete code change or completion condition, so the expected fix would need to be clarified before implementation.

Written by the indexing model from the issue text.

Description

websocket

I didn't find much online about this, but when connecting through cloudflare to a tornado WebSocket handler I received these headers:

Host: dataframe.vaex.io
X-Real-Ip: 141.101.105.77
X-Forwarded-For: 89.188.19.102, 141.101.105.77
Connection: upgrade
Accept-Encoding: gzip
Cf-Ipcountry: NL
Cf-Ray: 5afa07af2b3cbd82-AMS
X-Forwarded-Proto: https
Cf-Visitor: {"scheme":"https"}
User-Agent: curl/7.68.0
Accept: */*
Origin: http://dataframe.vaex.io
Cf-Request-Id: 03d02321780000bd82a2118200000001
Cf-Connecting-Ip: 89.188.19.102
Cdn-Loop: cloudflare

After which you get the error Connection" must be "Upgrade". The stacktrace in tornado is pretty vague (self.client is None at https://github.com/tornadoweb/tornado/blob/ad6e4acf9eb0df6a07f48fddd5945510bcd4a555/tornado/simple_httpclient.py#L658).

But using curl helped:

$ curl -i -N -H "Connection: Upgrade" -H "Upgrade: websocket" -H "Host: dataframe.vaex.io" -H "Origin: http://dataframe.vaex.io" https://dataframe.vaex.io/websocket

Note the https

https://community.cloudflare.com/t/websocket-pass-through-crashes-worker-script/78482/7 gave me a hint to disable http2:

$ curl -i -N -H "Connection: Upgrade" -H "Upgrade: websocket" -H "Host: dataframe.vaex.io" -H "Origin: http://dataframe.vaex.io" https://dataframe.vaex.io/websocket --http1.1

This worked 🎉

I didn't see an option to choose the HTTP version in tornado, so i disabled https in cloudflare, and I now don't have an issue.

Sorry for the low quality hasty, report. I am in a hurry, but it might be useful for the author(s) or someone with similar issues.

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