Simple `http` proxy with `socketPath` leads to `EPIPE` error

[mhassan1]

Version

v16.7.0

Platform

Linux e332ae582690 5.10.47-linuxkit #1 SMP Sat Jul 3 21:51:47 UTC 2021 x86_64 Linux

Subsystem

No response

What steps will reproduce the bug?

I have created a simple HTTP proxy that pipes to a socket:

const http = require('http')
http.createServer((req, res) => {
  const proxyReq = http.request({
    host: null,
    port: null,
    socketPath: 'sock.sock',
    path: req.url,
    method: req.method,
    headers: req.headers
  }, (_res) => {
    res.writeHead(_res.statusCode, _res.headers)
    _res.pipe(res, { end: true })
  })
  req.pipe(proxyReq, { end: true })
}).listen(8080)

On v16.7.0, this leads to an EPIPE error after a few hundred requests. On v16.6.2, it does not hit an EPIPE error after many thousands of requests.

A full Docker Linux reproduction is here: https://github.com/mhassan1/node-16-7-0-proxy-epipe

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

It reproduces every time within a few hundred requests.

What is the expected behavior?

No EPIPE.

What do you see instead?

EPIPE after a few hundred requests:

node:events:371
      throw er; // Unhandled 'error' event
      ^

Error: write EPIPE
    at afterWriteDispatched (node:internal/stream_base_commons:164:15)
    at writeGeneric (node:internal/stream_base_commons:155:3)
    at Socket._writeGeneric (node:net:780:11)
    at Socket._write (node:net:792:8)
    at doWrite (node:internal/streams/writable:408:12)
    at clearBuffer (node:internal/streams/writable:569:7)
    at onwrite (node:internal/streams/writable:461:7)
    at afterWriteDispatched (node:internal/stream_base_commons:167:9)
    at writevGeneric (node:internal/stream_base_commons:147:3)
    at Socket._writeGeneric (node:net:778:11)
Emitted 'error' event on ClientRequest instance at:
    at Socket.socketErrorListener (node:_http_client:447:9)
    at Socket.emit (node:events:394:28)
    at emitErrorNT (node:internal/streams/destroy:157:8)
    at emitErrorCloseNT (node:internal/streams/destroy:122:3)
    at processTicksAndRejections (node:internal/process/task_queues:83:21) {
  errno: -32,
  code: 'EPIPE',
  syscall: 'write'
}

Additional information

• This is a simplified reproduction of the same issue I am seeing when using http-proxy-middleware
• This does not reproduce on OS X
• This does not reproduce when proxying to a port
• This reproduces on v14.18.0 but not v14.17.6
• This does not reproduce when the proxy and the backend are listening in the same Node process; they must be listening in different processes

[mhassan1]

I have linked a few issues from other repositories that seem like they are related; for example: hapijs/hapi#4296.

[kanongil]

Looking at the commits going into v14.18.0, I would say that libuv/libuv@ce15b84 is a likely culprit, as a revert of a previously reverted commit.

[mhassan1]

I have been trying to debug this. Some things I've noticed:

1. If I modify the proxy to use end: false (i.e. req.pipe(proxyReq, { end: false })), EPIPE never happens. If I call proxyReq.end() manually 1 second later, EPIPE does not happen.
2. If I look at proxyReq.socket._writableState when EPIPE happens, it looks identical to the case where EPIPE does not happen. I can't tell what about the state of the ClientRequest is causing the EPIPE to be emitted.

[mhassan1]

This should be resolved by #41116.

[saberph]

Hi,

Do you know when it will be pushed to v14 LTS branch? We are affected by this too.

Thank you =)