[serve] Record WebSocket disconnect proxy metrics

[RitwijParmar]

Why are these changes needed?

Fixes #64077.

When an ASGI sender closes a WebSocket mid stream, GenericProxy.proxy_request can be finalized at yield message before it sees the final ResponseStatus. The ongoing request gauge is decremented, but request counters, error counters, latency metrics, and access logs are skipped.

This moves proxy request accounting into the wrapper finally block, so a finalized WebSocket stream is still counted once. If no status reached the wrapper, it records WebSocket code 1006.

The HTTP proxy also now lets GeneratorExit propagate instead of routing it through the normal exception response path. That avoids yielding while the async generator is being closed.

Related issue number

#64077

Checks

• python3 -m ruff check python/ray/serve/_private/proxy.py python/ray/serve/tests/unit/test_proxy.py
• python3 -m ruff format --check python/ray/serve/_private/proxy.py python/ray/serve/tests/unit/test_proxy.py
• python3 -m compileall -q python/ray/serve/_private/proxy.py python/ray/serve/tests/unit/test_proxy.py
• git diff --check

I tried the focused pytest for the new test, but this local checkout cannot import ray._raylet because the compiled Ray extension is not built here.

[gemini-code-assist]

Code Review

This pull request ensures that proxy metrics and access logs are recorded correctly when a client disconnects, particularly for WebSocket connections (which are assigned a status code of "1006"). It also handles GeneratorExit explicitly to prevent it from being treated as an unexpected server error. The review feedback highlights a critical issue where raising GeneratorExit leaves status as None for non-websocket requests, potentially causing an AttributeError when status.code is accessed later. A suggestion is provided to defensively set status to a "499" status code (client closed request) when catching GeneratorExit.

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[gemini-code-assist]

By adding except GeneratorExit: raise to prevent GeneratorExit from being caught as an unexpected 500 error, status remains None if the generator is closed before the response starts (e.g., when an HTTP client disconnects early).

In the finally block of send_request_to_replica, if status is None and the request type is not "websocket", it falls through to the else block:

else:
    status_code = status.code

This will raise an unhandled AttributeError: 'NoneType' object has no attribute 'code', masking the original GeneratorExit and potentially causing resource leaks or broken cleanup.

To fix this, we should defensively set status to an appropriate status code (such as "499" for client closed request) when catching GeneratorExit before re-raising it.

Suggested change

	except GeneratorExit:
	raise
	except GeneratorExit:
	if status is None:
	status = ResponseStatus(code="499", is_error=True)
	raise

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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