fix: send SSE heartbeat to prevent WebChat disconnect during compression#7003
fix: send SSE heartbeat to prevent WebChat disconnect during compression#7003he-yufeng wants to merge 1 commit intoAstrBotDevs:masterfrom
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When context compression triggers with slow reasoning models (e.g. deepseek-reasoner), the backend can go 30+ seconds without pushing any SSE data. The client-side EventSource / browser then assumes the connection is dead and disconnects, causing the WebUI to hang indefinitely since it never receives the eventual response. Fix: yield an SSE comment (`: heartbeat`) on every empty poll cycle. Comment lines are defined in the SSE spec as keep-alive signals -- the EventSource API ignores them but the HTTP connection stays open. Fixes AstrBotDevs#6938
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Summary of ChangesHello, 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! 此拉取请求旨在解决 WebChat 客户端在后端执行长时间操作（如上下文压缩）时，因 SSE 连接超时而断开的问题。通过在无数据传输期间发送 SSE 心跳信号，确保客户端连接持续活跃，从而避免 WebUI 假死并提升用户在与推理模型交互时的体验稳定性。 Highlights
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Code Review
This pull request implements a Server-Sent Events (SSE) heartbeat mechanism to prevent client timeouts during potentially long-running backend operations, such as context compression. This is achieved by returning a sentinel value when asyncio.wait_for times out in _poll_webchat_stream_result and subsequently sending an SSE heartbeat comment (: heartbeat\n\n) in the stream function when this sentinel is detected. The review suggests improving readability and maintainability by extracting the ": heartbeat\n\n" string into a module-level constant.
| # doesn't time out during slow backend ops like | ||
| # context compression with reasoning models (#6938). | ||
| if not client_disconnected: | ||
| yield ": heartbeat\n\n" |
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为了提高代码的可读性和可维护性，建议将 SSE 心跳消息 ": heartbeat\n\n" 提取为一个模块级别的常量。这样可以避免在代码中出现魔法字符串，并且如果将来需要修改心跳消息，只需在一个地方进行更改。
例如，可以在文件顶部定义：
SSE_HEARTBEAT = ": heartbeat\n\n"然后在 stream 函数中使用它。
| yield ": heartbeat\n\n" | |
| yield SSE_HEARTBEAT |
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问题
使用推理模型（如 deepseek-reasoner）时，如果对话历史较长触发了上下文压缩，压缩过程可能需要 30+ 秒。在这段时间内 SSE stream 没有推送任何数据，客户端 EventSource 判定连接超时并主动断开，导致 WebUI 假死（一直转圈）。
后端最终完成压缩并生成回复后，由于前端已断开连接，消息无法推送，用户只能刷新页面。
修复
在
_poll_webchat_stream_result返回空结果（queue 无新数据）时，yield 一个 SSE comment（: heartbeat\n\n）。根据 SSE 规范，以
:开头的行是 comment/keep-alive 信号——客户端 EventSource API 会忽略 comment 内容，但 HTTP 连接保持活跃。这样即使压缩耗时很长，连接也不会断开。改动只有 1 个文件 8 行，零副作用。
Fixes #6938
Summary by Sourcery
Bug Fixes: