Genkit 中间件：给 AI 应用加一层"可编程拦截网"

import { genkit, z } from 'genkit';
import { googleAI, gemini15Flash } from '@genkit-ai/googleai';

const ai = genkit({
  plugins: [googleAI()],
  model: gemini15Flash,
});

// 定义中间件：记录每次模型调用的耗时和输入 token 数
const timingMiddleware = ai.middleware({
  // 拦截模型调用
  onModelCall: async (ctx, next) => {
    const start = Date.now();
    console.log(`[middleware] 模型调用开始, prompt 长度: ${ctx.prompt.length}`);

    // 调用 next() 让模型真正执行
    const result = await next(ctx);

    const elapsed = Date.now() - start;
    console.log(`[middleware] 模型调用完成, 耗时 ${elapsed}ms, 输出长度: ${result.text.length}`);

    // 可以修改结果后再返回
    return result;
  },
});

// 把中间件挂载到 flow 上
const chatFlow = ai.defineFlow(
  {
    name: 'chat',
    inputSchema: z.string(),
    outputSchema: z.string(),
    middleware: [timingMiddleware], // 关键：注册中间件
  },
  async (input) => {
    const { text } = await ai.generate({ prompt: input });
    return text;
  }
);

// 本地运行测试
async function main() {
  const response = await chatFlow('用三句话解释什么是向量数据库');
  console.log('最终输出:', response);
}

main();

npm install genkit @genkit-ai/googleai
export GOOGLE_API_KEY="your-api-key-here"
npx genkit start  # 启动本地开发 UI，或在代码中直接调用 main()

const safetyMiddleware = ai.middleware({
  onModelCall: async (ctx, next) => {
    const result = await next(ctx);

    // 对模型输出做敏感信息扫描
    const sensitivePatterns = [/密码是\s*\S+/gi, /API[_-]?key\s*[:=]\s*\S+/gi];
    let filteredText = result.text;
    for (const pattern of sensitivePatterns) {
      filteredText = filteredText.replace(pattern, '[已过滤]');
    }

    // 返回过滤后的结果，下游完全不知道原始输出包含敏感内容
    return { ...result, text: filteredText };
  },
});

const toolGuardMiddleware = ai.middleware({
  onToolExecution: async (ctx, next) => {
    // ctx 包含工具名称和输入参数
    const blockedTools = ['dropDatabase', 'deleteAllUsers'];
    if (blockedTools.includes(ctx.toolName)) {
      throw new Error(`工具 ${ctx.toolName} 已被安全策略禁止调用`);
    }

    // 对参数做基本校验
    if (ctx.toolName === 'queryDatabase' && ctx.args.sql?.includes('DROP')) {
      throw new Error('SQL 参数包含危险操作，已拦截');
    }

    console.log(`[tool-guard] 允许执行工具: ${ctx.toolName}`);
    return await next(ctx);
  },
});

const loopLimitMiddleware = ai.middleware({
  onGenerationLoop: async (ctx, next) => {
    // ctx 中可以获取当前迭代步数
    const MAX_STEPS = 20;

    if (ctx.stepCount >= MAX_STEPS) {
      console.warn(`[loop-limit] Agent 已迭代 ${ctx.stepCount} 步，强制终止`);
      return { text: '任务执行超时，已自动终止。请简化需求或检查工具返回。', stop: true };
    }

    return await next(ctx);
  },
});

const secureChatFlow = ai.defineFlow(
  {
    name: 'secureChat',
    inputSchema: z.string(),
    outputSchema: z.string(),
    middleware: [loopLimitMiddleware, toolGuardMiddleware, safetyMiddleware, timingMiddleware],
  },
  async (input) => {
    const { text } = await ai.generate({
      prompt: input,
      tools: [queryDatabaseTool, searchTool], // Agent 可调用工具
      maxTurns: 30, // 生成循环最大轮次（中间件可以进一步收紧）
    });
    return text;
  }
);