async_hooks: AsyncLocalStorage losing context

Version

node v17.3.0 / 16.13.0

Platform

linux (likely all)

Subsystem

async_hooks

What steps will reproduce the bug?

Run

'use strict'

const { AsyncLocalStorage } = require('async_hooks')
const { createServer } = require('http')

const storage = new AsyncLocalStorage()

let counter = 0
createServer((req, res) => {
  const id = counter++;
  console.log('In Middleware with id ' + id);
  storage.run({ id }, function () {
    req.resume()
    req.on('end', onEnd(res))
  });
}).listen(3000)

function onEnd (res) {
  return () => {
    const store = storage.getStore()
    console.log('store is', store)
    res.end(JSON.stringify(store))
  }
}

Then:

curl -d '{}' -H 'Content-Type: application/json' localhost:3000

You'd note that the store is empty.

How often does it reproduce? Is there a required condition?

All of them. Unfortunately the documentation is quite misleading and it assumes the above would work / we do not document the edge cases.

The problem originates on the fact that receiving an HTTP body is part of the http request AsyncRecource. Calling .resume() on it does not imply we are attaching the new storage to that AsyncResource. However our documentation states:

Runs a function synchronously within a context and returns its return value. The store is not accessible outside of the callback function. The store is accessible to any asynchronous operations created within the callback.

Unless somebody knows that calling resume() is not creating a new asynchronous operation, they will be expecting the context to be preserved.

As a further confirmation, the following code works:

'use strict'

const { AsyncLocalStorage } = require('async_hooks')
const { createServer } = require('http')

const storage = new AsyncLocalStorage()

let counter = 0
createServer((req, res) => {
  const id = counter++;
  console.log('In Middleware with id ' + id);
  storage.enterWith({ id })
  req.resume()
  req.on('end', onEnd(res))
}).listen(3000)

function onEnd (res) {
  return () => {
    const store = storage.getStore()
    console.log('store is', store)
    res.end(JSON.stringify(store))
  }
}

What is the expected behavior?

We might decide this is a bug that should be fixed or we might decide to stabilize enterWith and document this case.

The problem is that the current documentation is misleading folks into thinking storage.run() is the right API in all cases but it is not as things are.

What do you see instead?

No response

Additional information

No response

从 HTTP 服务器复现中的 AsyncLocalStorage run/enterWith 行为开始，重点关注 req.resume() 和 req.on('end', ...)。将观察到的上下文传播与文档中针对异步操作的保证进行比较。当项目决定是否应更改传播行为，或记录该边界情况及适当的 API 行为时，即视为完成。