[Metrics] Add vLLM streaming support for metrics

[JeffLuoo]

Address #178

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[ahg-g]

/ok-to-test

[JeffLuoo]

It seems the change needs to rebase on top of #372.

[JeffLuoo]

cc: @liu-cong @ahg-g

[kfswain]

/lgtm
/approve

[kfswain]

/hold

[kfswain]

/remove-approve
/remove-lgtm

Sorry to be a stickler, I think we should hold on this. We are shooting for an RC tomorrow and I think we can refactor how we handle streaming here. Following PRs should help.

[kfswain]

We seem to throw these stream chunks away after this loop, what if your data is split between 2 chunks? you have no guarantee that will/wont happen

[JeffLuoo]

I don't quite get what you mean. Isn't streaming intended to break down messages into different chunks? E.g.

HTTP/1.1 200 OK
date: Wed, 05 Mar 2025 22:02:33 GMT
server: uvicorn
content-type: text/event-stream; charset=utf-8
x-went-into-resp-headers: true
transfer-encoding: chunked

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":"\n","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":" Write","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":" a","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":" summary","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":" of","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":" the","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":" plot","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":".","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":"\n","logprobs":null,"finish_reason":null,"stop_reason":null}],"usage":null}

data: {"id":"cmpl-33e790a5-7f21-42a9-8d71-6531a679f4a5","object":"text_completion","created":1741212154,"model":"tweet-summary-1","choices":[{"index":0,"text":"Write","logprobs":null,"finish_reason":"length","stop_reason":null}],"usage":null}

data: [DONE]

and the for loop of Process will iterate over all chunks until the streaming is completed.

[kfswain]

I don't think this check is needed, consider removing

[JeffLuoo]

This is to prevent logs being emitted too often. If the envoy proxy is set to STREAMED, each response chunk will print a line of log. So a response with 1000 chunks will have 1000 lines of such information with Info level.

[kfswain]

Here also

[JeffLuoo]

See comment above, this is to prevent noisy logs.

[ahg-g]

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahg-g, JeffLuoo

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[ahg-g]

/hold cancel