fix: Ignore non-HTML responses in storePreviousURL

[tearoom6]

Description

In this PR, I added an exclusion condition for storePreviousURL: "Response Content-Type is not text/html".

Background

In our application, some images are composited in the CodeIgnitor controller and returned.

The request URL for such case is saved as _ci_previous_url because it does not meet any of the exclusion conditions of the existing storePreviousURL implementation, and when redirecting back, etc., there is a case where the request is redirected to the URL of the image.

The URL to store as previous_url is usually considered to be an HTML (text/html) case, so I have added that as a condition.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[MGatner]

I was worried this would be too restrictive because there might be some served content of a variant type. A little research suggests that the content type should actually be this restrictive:

text/html: All HTML content should be served with this type.

I would like to see a tests added to confirm & exempt this - it should be fairly easy, copying what we already have.

[kenjis]

This fix seems to be reasonable. The image URL is not a page.

previous_url([$returnObject = false])
Returns the full URL (including segments) of the page the user was previously on.
https://codeigniter4.github.io/CodeIgniter4/helpers/url_helper.html

But this changes the behavior of storePreviousURL() and previous_url(), so
it is better to add at least the changelog.
https://codeigniter4.github.io/CodeIgniter4/changelogs/v4.2.0.html#breaking

[kenjis]

@tearoom6
Thank you for sending this PR.

We expect all contributions to conform to our style guide, be commented (inside the PHP source files), be documented (in the user guide), and unit tested (in the test folder).
https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#contributions

The user guide and unit testing are missing.
See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#unit-testing for unit testing.
Could you add them?

[tearoom6]

@MGatner @kenjis
Thank you for your feedbacks! I have added the unit test case and updated the documentation.
In addition, the original commit was not signed, so I also added signature to the commit. (forced push was needed to do so.)

I would appreciate it if you could review it again.

[kenjis]

In the upgrade note, we write what to do when upgrading.
Since it seems unlikely that any developers were using non-HTML URLs, is there no need to list it?

[tearoom6]

I see, I understood. I have removed it from the upgrade note 👍

[kenjis]

@tearoom6 Thank you for updating.

The PHPStan errors are not related to this PR.

But these errors was fixed in the latest develop.
So if you rebase this branch, all GitHub Action checks would pass.
See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/workflow.md#pushing-your-branch

There is no conflict, so we can merge this PR if you don't rebase.

[kenjis]

LGTM!

[tearoom6]

Thank you for reviewing and the advices!

[MGatner]

Very nice work! Thank you for your contribution.