RedirectResponse is sent with invalid content-type when route has non-html default format

[Seldaek]

Symfony version(s) affected

5.x.x, probably even earlier

Description

When a route has a default format set to smth else than html, and a redirect happens, the response format gets set on the redirect response incorrectly (because RedirectResponse always has html as content)

This isn't a huge problem in practice as the browser typically does not render this intermediate page's content, but it is nonetheless incorrect.

How to reproduce

#[Route('/test', name: 'test', defaults: ['_format' => 'json'])]
public function testAction()
{
        return $this->redirect('/test2');
}

Load /test, check the response headers of the 302:

HTTP/1.1 302 Found
Content-Type: application/json
Location: /test2
[...]

If the _format=>json is removed from the Route, then it uses the correct default:

Content-Type: text/html; charset=UTF-8

Possible Solution

Perhaps the _format response listener should not mess with RedirectResponse instances?

Additional Context

No response

[smnandre]

Wonder if the content-type should be kept here.. Same debate took place in fetch repo some time ago : whatwg/fetch#609

[Seldaek]

There is a response body so IMO there should be a content type set with it.

[smnandre]

This seems to be due to the Response::prepare() method.

So maybe the RedirectResponse should set its content-type to text/html everytime it sets the response body ?

[Seldaek]

Yes that sounds like a reasonable fix.