类装饰器Nestjs修改类中的每个方法

Question

我想创建一个装饰器，它可以获取类的所有方法并用某些功能包装它们，对于这个例子，只需像这样记录：

export function CustDec<T extends new (...args: any[]) => any>(Target: T) {
  return class extends Target {
    constructor(...args: any[]) {
      super(...args);
      console.log('@--------------------@');
      (Target as any).prototype.alphaMethod = async (args: any[]) => {
        console.log('@-before-@');
        await (Target as any).alphaMethod();
        console.log('@-after-@');
      };
    }
  };
}

问题是当我将此装饰器应用到我的班级时：

import { Controller, Post } from '@nestjs/common';
import { ApiTags } from '@nestjs/swagger';
import { Firewall } from 'src/auth/decorators/firewall.decorator';
import { CustDec } from './feedback.decorator';

@CustDec
@ApiTags('feedback')
@Controller('feedback')
export class FeedbackController {
  constructor() {
    setTimeout(async () => {
      await this.alphaMethod(); // <--- here
    }, 3000);
  }

  @Firewall()
  @Post('')
  async alphaMethod() { // <-- and here
    return 'some promised result';
  }
}

当我尝试在控制器上调用

/feedback

端点时，我收到错误，就好像

Firewall

和

Post

装饰器在我的

CustDec

更改

alphaMethod

后停止工作一样。即使我从 FeedbackController 构造方法内部调用

alphaMethod

，我也会收到另一个错误：

@-before-@
This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason:
TypeError: Target.alphaMethod is not a function
    at FeedbackController.Target.alphaMethod (/home/zagrava/workspace/test-nest/backend/src/feedback/feedback.decorator.ts:8:31)
    at Timeout._onTimeout (/home/zagrava/workspace/test-nest/backend/src/feedback/feedback.controller.ts:12:18)
    at listOnTimeout (node:internal/timers:564:17)
    at processTimers (node:internal/timers:507:7)

如何让我的 CustDec 使用日志记录正确包装类的所有方法？

Answer 1

类装饰器可以像下面这样实现：

function intercept<T extends { new(...args: any[]): {} }>(target: T) {
  const methods = getMethods(target.prototype);
  for (const method of methods) {
    const currentMethod = target.prototype[method]
    target.prototype[method] = async (...args: any[]) => {
      console.log("intercepted", new Date());
      const result = currentMethod(args)
      if (result instanceof Promise) {
        await result
      }
      console.log("executed", new Date());
      return result;
    }
  }
}

这个想法是获取类的所有函数（构造函数本身除外）并将它们包装在自定义函数中。 获取如下类函数的辅助方法对于这种情况很有用：

const getMethods = (obj: any) => Object.getOwnPropertyNames(obj).filter(item => typeof obj[item] === 'function' && item !== "constructor")

游乐场

多个装饰器正在运行

Answer 2

问题很简单，POST和Firewall等装饰器使用反射包创建元数据，因此只需将原始方法的元数据复制粘贴到目标方法即可。

function copyMetadata(
  originalMethod: any,
  targetMethod: any,
) {
  const metadataKeys = Reflect.getOwnMetadataKeys(originalMethod);
  for (const key of metadataKeys) {
    const metadata = Reflect.getMetadata(key, originalMethod);
    Reflect.defineMetadata(key, metadata, targetMethod);
  }
}