Memory leak in http-proxy dependency when client closes connection prematurely

Checks

• I understand project setup issues should be asked on StackOverflow or in GitHub Discussions.
• I updated to latest http-proxy-middleware.

Describe the bug (be clear and concise)

This is an issue of http-proxy, but I decided to report it here as well because:

• http-proxy-middleware is affected by this issue
• last http-proxy version was released in 2020, so I don’t expect them to fix it soon
• this issue could be fixed on http-proxy-middleware side

Here is a complete description of this issue: https://github.com/http-party/node-http-proxy/issues/1586

Step-by-step reproduction instructions

Here is a minimal example to reproduce the above-mentioned memory leak:

const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');

const server = express()
	.use(createProxyMiddleware({ target: 'http://127.0.0.1:5000' }))
	.listen(7000);

server.once('listening', () => {
	console.log('server is listenning');
});

I used http-server to create an upstream server:

npx http-server . -p 5000

Memory leak appears when client sends a http request, but then closes connection prematurely after receiving HTTP headers without waiting for HTTP body.

I used cURL to simulate this behavior:

curl http://localhost:7000/15142e1388c685f57c58e0babbede1f1.jpg

Memory leak could be reproduces with cURL when requesting any binary file from a TTY terminal, since cURL doesn’t support printing binary data to terminals and just closes the connection.

Expected behavior (be clear and concise)

Memory should not leak

How is http-proxy-middleware used in your project?

↪ npm ls http-proxy-middleware
culture-ru-gateway@1.0.6-alpha.0 /home/leonid/Documents/culture/gateway
└── http-proxy-middleware@2.0.6

What http-proxy-middleware configuration are you using?

{
	retry: {
		factor: 2,
		randomize: true,
		retries: 30,
		minTimeout: 10,
		maxTimeout: 500
	},
	xfwd: true,
	logLevel: 'warn'
}

What OS/version and node/version are you seeing the problem?

System:
    OS: Linux 5.13 Ubuntu 20.04.4 LTS (Focal Fossa)
    CPU: (8) x64 Intel(R) Core(TM) i7-10510U CPU @ 1.80GHz
    Memory: 5.11 GB / 15.34 GB
    Container: Yes
    Shell: 5.0.17 - /bin/bash
  Binaries:
    Node: 16.15.0 - ~/.nvm/versions/node/v16.15.0/bin/node
    npm: 8.5.5 - ~/.nvm/versions/node/v16.15.0/bin/npm
  Managers:
    Apt: 2.0.8 - /usr/bin/apt
    Cargo: 1.49.0 - ~/.cargo/bin/cargo
    pip3: 20.0.2 - /usr/bin/pip3
    RubyGems: 3.1.2 - /usr/bin/gem
  Utilities:
    CMake: 3.16.3 - /usr/bin/cmake
    Make: 4.2.1 - /usr/bin/make
    GCC: 9.4.0 - /usr/bin/gcc
    Git: 2.25.1 - /usr/bin/git
    Ninja: 1.10.0 - /usr/bin/ninja
    FFmpeg: 4.2.4 - /usr/bin/ffmpeg
  Servers:
    Nginx: 1.18.0 - /usr/sbin/nginx
  Virtualization:
    Docker: 20.10.12 - /usr/bin/docker
  IDEs:
    Nano: 4.8 - /usr/bin/nano
    Sublime Text: 4126 - /usr/bin/subl
    VSCode: 1.67.1 - /usr/bin/code
  Languages:
    Bash: 5.0.17 - /usr/bin/bash
    Perl: 5.30.0 - /usr/bin/perl
    Python3: 3.8.10 - /usr/bin/python3
    Ruby: 2.7.0 - /usr/bin/ruby
    Rust: 1.49.0 - /home/leonid/.cargo/bin/rustc
  Databases:
    MongoDB: 4.4.14 - /usr/bin/mongo
  Browsers:
    Chrome: 101.0.4951.64

Additional context (optional)

Here is a code I used to fix http-proxy memory leak in my project:

proxy.on('proxyRes', (proxyRes, req, res) => {
	const cleanup = (err) => {
		// cleanup event listeners to allow clean garbage collection
		proxyRes.removeListener('error', cleanup);
		proxyRes.removeListener('close', cleanup);
		res.removeListener('error', cleanup);
		res.removeListener('close', cleanup);

		// destroy all source streams to propagate the caught event backward
		req.destroy(err);
		proxyRes.destroy(err);
	};

	proxyRes.once('error', cleanup);
	proxyRes.once('close', cleanup);
	res.once('error', cleanup);
	res.once('close', cleanup);
});

The actual code could be simpler since:

• it should be enough to listen only for 'close' events since they are always emitted after 'error' events (unless emitClose is false)
• it’s probably not necessary to call removeListener manually, because those listeners should not prevent streams from being garbage collected (but who knows, I certainly don’t want to test it)

[lbeschastny]

I just added a hotfix branch to my reproduction example repository to demonstrate that it fixes the memory leak in question

[lbeschastny]

Here is another fix for this memory leak: http-party/node-http-proxy#1559.

It was published to npm as http-proxy-node16.