video-workflow/server/routes/llm.js

function registerLlmRoutes(app, options) {
  const llmBaseUrl = options.llmBaseUrl;
  const llmApiKey = options.llmApiKey;

  // 非流式调用已迁移至云函数 proxyHub（cloud-functions/08-proxyHub.js）。
  // 但流式 SSE 调用必须走本地 Express（云函数不支持流式输出），由前端 fetch 直连。
  app.post('/api/llm/chat/stream', async (req, res) => {
    try {
      const { model, messages, temperature, max_tokens, ...rest } = req.body || {};
      if (!Array.isArray(messages) || messages.length === 0) {
        return res.status(400).json({ error: '缺少 messages 参数' });
      }

      const payload = {
        model: model || 'gpt-4o',
        messages,
        temperature: temperature ?? 0.7,
        max_tokens: max_tokens || 4096,
        ...rest,
        stream: true,
      };

      const url = `${llmBaseUrl}/v1/chat/completions`;
      console.log(`🤖 [Stream] LLM Chat 请求: model=${payload.model}, messages=${messages.length}条`);

      const upstream = await fetch(url, {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
          'Authorization': `Bearer ${llmApiKey}`,
        },
        body: JSON.stringify(payload),
      });

      if (!upstream.ok) {
        const errText = await upstream.text();
        console.error('🤖 [Stream] 上游错误:', upstream.status, errText);
        return res.status(upstream.status).json({ error: errText || `upstream ${upstream.status}` });
      }

      res.setHeader('Content-Type', 'text/event-stream; charset=utf-8');
      res.setHeader('Cache-Control', 'no-cache, no-transform');
      res.setHeader('Connection', 'keep-alive');
      res.setHeader('X-Accel-Buffering', 'no');
      res.flushHeaders?.();

      const reader = upstream.body.getReader();
      const onAbort = () => {
        try { reader.cancel(); } catch {}
      };
      req.on('close', onAbort);

      try {
        while (true) {
          const { value, done } = await reader.read();
          if (done) break;
          if (value) res.write(Buffer.from(value));
        }
      } finally {
        req.off('close', onAbort);
        res.end();
      }
    } catch (err) {
      console.error('🤖 [Stream] 异常:', err.message);
      if (!res.headersSent) {
        res.status(500).json({ error: `LLM 流式请求失败: ${err.message}` });
      } else {
        try { res.end(); } catch {}
      }
    }
  });
}

module.exports = { registerLlmRoutes };