Next-i18next: Cannot set headers after they are sent to the client - ^ 4.3.0

[clement-faure]

Describe the bug

Error on server middleware (server.use(nextI18NextMiddleware(nextI18next))) when res.writeHead({ Location: "/" }) from _app.tsx happen in version 4.3.0 (next-i18next) but works fine in 4.2.0 (next-i18next)

Occurs in next-i18next version

next-i18next - 4.3.0
yarn - 1.22.4

Steps to reproduce

Basic setup and add res.writeHead(302, { Location: "/" }); in _app.jsx

Screenshot

Expected behaviour

Should work normally like in version 4.3.0 (next-i18next)

OS (please complete the following information)

• Device: MBP 2019 16
• Browser: Chrome 81.0.4044.138

[isaachinman]

Please provide a reproducible repo.

[adrai]

Maybe related: https://github.com/i18next/i18next-http-middleware/pull/4#issuecomment-627270885

[clement-faure]

I'm sorry, i just noticed i gave you the wrong version. The issue was happening on version "next-i18next": "^4.3.0".

With 4.4.2, all works fine i just have a message "no possibility found to set header"

[kachkaev]

_no possibility found to set header_ is quite annoying, especially given that it is printed unconditionally, both in dev and prod 🤔 @cfaure004, did you manage to find the workaround or the root cause?

[adrai]

@kachkaev This is a different issue...

There seems to be a different way for setting the header...

PRs are welcome

[adrai]

Ahh you mean the second time... when the header is already sent...?
Will probably change the logic to return in that case

[adrai]

@kachkaev should be better with [email protected]

[kachkaev]

Many thanks for releasing the new version @adrai! I can confirm that I no longer see log statements with [email protected] and [email protected] 🎉

It might be still worth investigating the situation further. If I understand correctly, we just silenced the unsuccessful header setting attempt. Perhaps, the logic should change so that it did not happen at all?

[adrai]

This must be somewhere in next-i18next or in userland... 🤷‍♂️
any help is welcome

[isaachinman]

We'll need @cfaure004 to provide a reproducible example.

[clement-faure]

About what ? The message "no possibility found to set header" ?

This initial issue is not happening on latest version.

[clement-faure]

I think we can close this issue.

[adrai]

Can you create an example with the old version which reproduces the error?
This would be very helpful to investigate the root cause.

[clement-faure]

Ok no problem, i'll do that

[adrai]

👍 make sure you use i18next-http-middleware <= 1.0.6

[clement-faure]

On my side, i've always used middleware included in next-i18next package

const nextI18NextMiddleware = require('next-i18next/middleware').default

[clement-faure]

I've been able to reproduced the message "no possibility found to set header" but not to reproduce the initial error

https://github.com/cfaure004/next-i18next-issues-716

[clement-faure]

Finally i've been able to reproduce the initial issue using [email protected], all is in my repo 👍

[isaachinman]

On my side, i've always used middleware included in next-i18next package

Yes, that's what you _should_ be doing. We need a repro of that, not using i18next-http-middleware/cjs directly.

[adrai]

thx @cfaure004 I found somethig... it's caused by the redirect... here: https://github.com/cfaure004/next-i18next-issues-716/blob/master/pages/_app.jsx#L48
which seems correct (I'm not a nextjs expert)...

I also found in i18next-http-middleware that certain header values can be set twice (because of the languageChanged event), so I tried to optimize this with [email protected]

[clement-faure]

On my side, i've always used middleware included in next-i18next package

Yes, that's what you _should_ be doing. We need a repro of that, not using i18next-http-middleware/cjs directly.

@isaachinman I have not been able to reproduce the issue using previous versions of next-i18next library, i think it was an outdated dependency. I just created this exemple to help @adrai to identify where does the issue was coming from.

Great @adrai !