[wip] Shutdown Websocket Connections Gracefully in the queue-proxy

[dprotaso]

• have the websocket server test image send a close message when shutting down gracefully
• include an e2e test that asserts websockets connections are gracefully handled
• include a special handler to track hijacked connections and create a drain method

[knative-prow]

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[codecov]

Codecov Report

❌ Patch coverage is 53.57143% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.13%. Comparing base (4004491) to head (8edef60).

Files with missing lines	Patch %	Lines
pkg/queue/sharedmain/main.go	0.00%	7 Missing ⚠️
pkg/queue/sharedmain/handlers.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16362      +/-   ##
==========================================
- Coverage   80.17%   80.13%   -0.04%     
==========================================
  Files         216      217       +1     
  Lines       13440    13461      +21     
==========================================
+ Hits        10775    10787      +12     
- Misses       2300     2309       +9     
  Partials      365      365              

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[dprotaso]

One observation I have is that the activator will drop hijacked connections similar to the queue proxy.

Hijacking happens implicitly with the httputil.ReverseProxy - https://cs.opensource.google/go/go/+/refs/tags/go1.25.6:src/net/http/httputil/reverseproxy.go;l=504

The solution in the queue-proxy is straight forward because we know K8s will send a TERM signal to the user container - thus we can expect apps to return a close frame when that happens. Those are the changes I made to our websocket server. This isn't necessary but just maybe it's a good practice

With the activator though - there's no way to signal downstream to end the connection. We maybe could send a close frame on the connection but it makes the activator protocol aware and I don't think we can write a message on an upstream connection like this (it could be interleaved with another).

Given this - I don't think the activator issue should prevent this change from merging - but just the solution there isn't straighforward.

[dprotaso]

/retest

hmm

websocket_test.go:162: Successfully wrote: "Hello, websocket"
websocket_test.go:190: error running test failed to read message: read tcp 10.250.69.110:60956->34.138.223.27:80: read: connection reset by peer