[Benchmark] fix request loss if "ping" is returned

[sywangyi]

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[gemini-code-assist]

Summary of Changes

Hello @sywangyi, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue in the benchmark code where streamed responses might be incorrectly parsed or dropped if they contain 'ping' messages, which are sometimes sent by servers to keep the connection alive. The change adds a check to filter out these specific messages, ensuring that only actual data chunks are processed, thereby preventing potential request loss or parsing errors during benchmarking.

Highlights

• Bug Fix: Implemented logic to prevent request loss in streamed responses when 'ping' messages (starting with ':') are received, specifically within the OpenAI chat completions benchmark function.
• Streamed Response Handling: Modified the parsing of streamed data chunks to explicitly check for and skip chunks that appear to be 'ping' messages rather than actual data.

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[sywangyi]

use VLLM multimodality benchmark to test tgi backend，find request loss issue because “：” is returned and json load fail

[gemini-code-assist]

Code Review

This pull request aims to fix request loss caused by unhandled "ping" messages in Server-Sent Events (SSE) streams. The change correctly identifies and skips these ping messages (lines starting with a colon) before attempting to parse the chunk as JSON. This should prevent errors and ensure smoother data processing.

My review includes a couple of suggestions to enhance code clarity and maintainability. Additionally, the pull request description is currently a template; please update it with details about the purpose, testing, and results of this change for better context and future reference. No specific style guide was provided, so the feedback adheres to general Python best practices.

[aarnphm]

Can you update https://github.com/vllm-project/vllm/blob/main/vllm/benchmarks/endpoint_request_func.py instead?

We ought to retire some benchmarks script in this folder eventually.

[sywangyi]

@aarnphm done for the change,could you revisit the pr？