Using hono-node with the cors middleware causes a memory leak

[krzkz94]

What version of Hono are you using?

4.8.12

What runtime/platform is your app running on? (with version if possible)

Node

What steps can reproduce the bug?

Clone this repo
https://github.com/krzkz94/hono-context-memory-leak

Follow the outlined steps
(install, run app, run autocannon)

Notice heap size increasing

npx tsx src/index.ts
Server is running on http://localhost:3000
{ before: '9.09', after: '9.09' }
{ before: '9.11', after: '9.11' }
{ before: '51.49', after: '51.50' }
{ before: '67.14', after: '67.14' }
{ before: '111.91', after: '111.91' }
{ before: '155.77', after: '155.77' }
{ before: '126.81', after: '126.81' }
{ before: '162.79', after: '162.79' }
{ before: '207.94', after: '207.94' }
{ before: '254.23', after: '254.23' }
{ before: '302.14', after: '302.14' }
{ before: '342.52', after: '342.52' }
{ before: '380.52', after: '380.52' }
{ before: '248.96', after: '248.96' }
{ before: '288.23', after: '288.23' }
{ before: '339.07', after: '339.07' }
{ before: '382.03', after: '382.03' }
{ before: '424.34', after: '424.34' }
{ before: '458.85', after: '458.85' }
{ before: '511.55', after: '511.55' }
{ before: '552.79', after: '552.79' }
{ before: '596.38', after: '596.38' }
{ before: '590.64', after: '590.64' }

Node22

What is the expected behavior?

Heap size stays consistent with minimal increases, for example, below, it's the result without the cors middleware.

tsx watch src/index.ts

Server is running on http://localhost:3000
{ before: '17.41', after: '17.41' }
{ before: '11.33', after: '11.33' }
{ before: '10.58', after: '10.58' }
{ before: '23.65', after: '23.65' }
{ before: '14.78', after: '14.78' }
{ before: '17.13', after: '17.13' }
{ before: '16.21', after: '16.21' }
{ before: '16.23', after: '16.23' }
{ before: '13.44', after: '13.45' }
{ before: '14.90', after: '14.90' }
{ before: '21.29', after: '21.29' }
{ before: '18.71', after: '18.71' }
{ before: '14.91', after: '14.91' }
{ before: '13.46', after: '13.46' }

What do you see instead?

Heap size increases and stays high even after the test ends

{ before: '8.94', after: '8.94' }
{ before: '8.96', after: '8.96' }
{ before: '30.07', after: '30.07' }
{ before: '77.18', after: '77.18' }
{ before: '87.71', after: '87.71' }
{ before: '131.37', after: '131.37' }
{ before: '164.34', after: '164.34' }
{ before: '206.36', after: '206.36' }
{ before: '157.07', after: '157.07' }
{ before: '189.13', after: '189.13' }
{ before: '232.51', after: '232.51' }
{ before: '280.68', after: '280.68' }
{ before: '328.30', after: '328.30' }
{ before: '366.00', after: '366.00' }
{ before: '410.61', after: '410.61' }
{ before: '461.95', after: '461.95' }
{ before: '491.38', after: '491.38' }
{ before: '314.48', after: '314.48' }
{ before: '363.24', after: '363.24' }
{ before: '412.60', after: '412.60' }
{ before: '451.58', after: '451.58' }
{ before: '492.87', after: '492.87' }
{ before: '509.95', after: '509.95' } <- end of test
{ before: '509.95', after: '509.95' }
{ before: '509.96', after: '509.96' }
{ before: '509.96', after: '509.96' }
{ before: '509.97', after: '509.97' }
{ before: '509.97', after: '509.97' }
{ before: '509.97', after: '509.98' }
{ before: '509.98', after: '509.98' }
{ before: '509.99', after: '509.99' }
{ before: '509.99', after: '509.99' }
{ before: '509.99', after: '510.00' }

Additional information

It seems a bug with node-server and how things are handled when accessing the headers, running this with Bun's native HTTP server, doesn't cause issues. (bun --expose-gc src/index.ts) - also, removing the serve() wrapper around the object and just exporting default.

Basically accessing c.req.header('origin') (or any header for the matter), builds memory pressure, and under constant load, keeps increasing the memory requirement without ever giving it a chance to be cleaned up until either (a) the load stops or (b) the application runs out of memory

[omarkhatibco]

I'm facing the same issue, my server is crashing every 10 mins.

[yusukebe]

@omarkhatibco

I'll work on investigating it. One question, are you running your app on Node.js? or other runtime?

[omarkhatibco]

Hey @yusukebe ,

It's a simple node.js server with 1 endpoint.

you can see in the image the memory leak, it starts to happens yesterday when I merged my PR which includes latest version of Hono v4.8.12

The workaround what to disable cors plugin and just use normal headers in the response.

[yusukebe]

@omarkhatibco

it starts to happens yesterday when I merged my PR which includes latest version of Hono v4.8.12

Does this mean the previous version you used did not cause a memory leak? Let me know the previous version.

[krzkz94]

@yusukebe I upgraded from 4.7.9 as I experienced the issue there and it did not go away with 4.8.12 - mind you, I had some other issues in my app with memory management and managed to fix all of them except this one so I don't want to lead you the wrong way by saying that it was there already in 4.7.9

[yusukebe]

@krzkz94 Okay, thanks!

[yusukebe]

@krzkz94

What version of @hono/node-server do you use?

[omarkhatibco]

Hey @yusukebe

I just noticed that the issue start to appear on 25th on July, I couldn't test which one, but I think that last one I had no problem with was 4.8.5 and @hono/node-server was on 1.17.0

you can see the image below

[krzkz94]

@yusukebe Should've mentioned it, my bad

"@hono/node-server": "1.18.1",
"hono": "4.8.12"

[yusukebe]

@omarkhatibco @krzkz94 Thanks!

[yusukebe]

This is a bug in @hono/node-server. You can reproduce it with the following code without hono. Should be fixed. I'll transfer this issue to the honojs/node-server repository.

import { serve } from '@hono/node-server'

setInterval(() => {
  const before = process.memoryUsage().heapUsed / 1024 / 1024
  global.gc?.()
  const after = process.memoryUsage().heapUsed / 1024 / 1024
  console.log({ before: before.toFixed(2), after: after.toFixed(2) })
}, 1_000)

serve(
  {
    fetch: (req) => {
      req.headers.get('foo') // <===
      return new Response('foo')
    },
    port: 3000
  },
  (info) => {
    console.log(`Server is running on http://localhost:${info.port}`)
  }
)

[yusukebe]

Hi @usualoma

Sorry for again and again.

This memory leak is caused by introducing a lightweight request in the Node.js Adapter. As proof, the problem does not occur with version 1.2.3 before 1.3.0 that includes the lightweight request feature.

Here is the minimal repro: https://github.com/yusukebe/hono-nodejs-adapter-memory-leak

Can you investigate it?