nest中获取content-length

本文主要是介绍nest中获取content-length，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

mock项目中nest执行过程：

import { NestFactory } from '@nestjs/core'
import { Module, Req, Injectable, NestMiddleware, NestInterceptor, ExecutionContext, Res, Header, CallHandler, Controller, Get, MiddlewareConsumer, NestModule } from '@nestjs/common'
import { AsyncLocalStorage } from 'async_hooks'
import { Observable, throwError } from 'rxjs'
import { catchError, tap, finalize } from "rxjs/operators"
import { APP_INTERCEPTOR } from '@nestjs/core'
import { Request, Response } from 'express'// 模拟异步操作链数据存储
@Injectable()
class ClsService {als: AsyncLocalStorage<Record<string, unknown>>constructor() {this.als = new AsyncLocalStorage()}get(key: string) {return this.als.getStore()?.[key]}set(key: string, value: unknown) {if (this.als.getStore()) {(this.als.getStore() as Record<string, unknown>)[key] = value}}
}// 模拟中间件
@Injectable()
class ClsMiddleWare implements NestMiddleware {constructor(private ClsService: ClsService) {console.log('Middleware registry')}async use(req: Request, res: Response, next: () => void) {const realIp = req.headers['x-real-ip'] as string || '0.0.0.0'console.log('Middleware executed, IP:', realIp)console.log('Middleware enter', this.ClsService.als.getStore())this.ClsService.als.run({ ip: realIp }, () => {next()setTimeout(() => {console.log('Middleware timeout', this.ClsService.als.getStore())}, 10)console.log('Middleware exit 1', this.ClsService.als.getStore())})console.log('Middleware exit', this.ClsService.als.getStore())}
}// 模拟拦截器
@Injectable()
class LoggingInterceptor implements NestInterceptor {constructor(private ClsService: ClsService) {console.log('Interceptor registry')}intercept(context: ExecutionContext, next: CallHandler): Observable<any> {console.log('Interceptor executed')return next.handle().pipe(tap((result) => {let req = context.switchToHttp().getRequest() as Requestlet res = context.switchToHttp().getResponse()let cl = (res as Response).get("content-length")console.log("sync===", cl, res.get("content-length"), res.headersSent, result)setTimeout(() => {console.log("===async===", cl, res.get("content-length"), res.headersSent, result)}, 0)}),catchError((error) => {// console.log("interceptor", error)return throwError(() => error)}),finalize(() => {// console.log("entry finalize===")}))}
}// 模拟控制器
@Controller('example')
class ExampleController {constructor() { }@Get("")test() {console.log('Controller method executed')return { message: 'this is nest return' }}@Get("express")express(@Req() req: Request,@Res() res: Response) {console.log('Controller method executed')res.send({message: "this is express send"})}@Get("/stream")getExample(@Req() req: Request,@Res() res: Response) {console.log('Controller method executed')let i = 1res.contentType("application/octet-stream")setInterval(() => {res.write(Buffer.from("abcdefg"))if (i++ > 10) {// stream.close()res.end()}}, 1000)}
}// 应用模块
@Module({imports: [],controllers: [ExampleController],providers: [ClsService,{provide: APP_INTERCEPTOR,useClass: LoggingInterceptor,},],
})
export class AppModule implements NestModule {configure(consumer: MiddlewareConsumer) {consumer.apply(ClsMiddleWare).forRoutes('*') // 应用到所有路由}
}// 启动应用
async function bootstrap() {const app = await NestFactory.create(AppModule)await app.listen(3000)
}bootstrap()

此时访问：http://localhost:3000/example

此时控制台输出的内容为：

Middleware executed, IP: 0.0.0.0
Middleware enter undefined
Middleware exit 1 { ip: '0.0.0.0' }
Middleware exit undefined
Interceptor executed
Controller method executed
sync=== undefined undefined false { message: 'this is nest return' }
===async=== undefined 33 true { message: 'this is nest return' }
Middleware timeout { ip: '0.0.0.0' }

这里可以得到4个信息

• 在宏任务0的异步阶段响应头已经发送
• 在未发送时是无法获取content-length的，发送后可获取到
• get(“content-length”)获取的是快照
• 无论在哪个阶段，使用return的方式返回的数据在interceptor中是可以获取的

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接下来访问：http://localhost:3000/example/express

此时控制台输出的内容为：

Middleware executed, IP: 0.0.0.0
Middleware enter undefined
Middleware exit 1 { ip: '0.0.0.0' }
Middleware exit undefined
Interceptor executed
Controller method executed
sync=== 34 34 true undefined
===async=== 34 34 true undefined
Middleware timeout { ip: '0.0.0.0' }

可以看到直接send的情况，同步时已经将响应发送完毕了，此时同步异步都可以拿到headers

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接下来访问：http://localhost:3000/example/stream

此时控制台输出的内容为：

Middleware executed, IP: 0.0.0.0
Middleware enter undefined
Middleware exit 1 { ip: '0.0.0.0' }
Middleware exit undefined
Interceptor executed
Controller method executed
sync=== undefined undefined false undefined
===async=== undefined undefined false undefined
Middleware timeout { ip: '0.0.0.0' }

可以看到直接send的情况，无论是同步还是延时0的宏任务都是拿不到数据的

此时在interceptor中增加：

  res.on("finish", () => {console.log("===response finished", cl, res.get("content-length"), res.headersSent, result)})

此时的控制台输出为：

Middleware executed, IP: 0.0.0.0
Middleware enter undefined
Middleware exit 1 { ip: '0.0.0.0' }
Middleware exit undefined
Interceptor executed
Controller method executed
sync=== undefined undefined false undefined
===async=== undefined undefined false undefined
Middleware timeout { ip: '0.0.0.0' }
===response finished undefined undefined true undefined

可以看到面对数据流的情况，即使是发送完成也无法获取到content-length 这种情况目前可以暂不考虑。

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目前得到的结论是，如果想稳定拿到contentLength，最好是监听finish事件，即

   res.on("finish", () => {console.log("===response finished", res.get("content-length"))})// 可以优化为：res.once("finish", () => {console.log("===response finished", res.get("content-length"))})

鉴于闭包的形式可能引起的内存泄漏的问题，所以最终采用计算result的方式

  let res = context.switchToHttp().getResponse()let contentLength = res.get("content-length")if (!contentLength && result) {try {contentLength = Buffer.from(JSON.stringify(result)).length ?? 0} catch (error) {contentLength ??= 0}}

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