Loading UTF8 content is not possible with HTML reader class

[T00by1]

This is:

- [x] a bug report
- [ ] a feature request
- [ ] **not** a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

UTF8 HTML content loaded into the spreadsheet.

What is the current behavior?

Failure to load because the validation of tags cannot be completed.
startsWithTag needs to check for BOM when looking for first character in document.

What are the steps to reproduce?

Use Simple example 46. Open template file and add BOM. Retry example.

Which versions of PhpSpreadsheet and PHP are affected?

"phpoffice/phpspreadsheet": "1.6.0"
"php": ">=7.1.20"

Suggested simple solution in startsWithTag :
Make function not static and add

if($this->inputEncoding == 'UTF-8') {
    if(substr($data, 0, 3) === chr(0xEF) . chr(0xBB) . chr(0xBF)) {
      $data = substr($data, 3);
     }
}

[MarkBaker]

HTML markup shouldn't be identified as UTF-8 by a BOM, but by <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> in the header block of the markup.

There is actually a block of code in the HTML Reader that is intended for exactly that:

foreach ($attributeArray as $attributeName => $attributeValue) {
    switch ($attributeName) {
        case 'content':
            //    TODO
            //    Extract character set, so we can convert to UTF-8 if required
            break;
    }
}

though as you can see it's flagged as TODO

However, while this will be implemented in due course, testing for a BOM will not be, as that isn't valid for html markup

[T00by1]

I would respectfully like to disagree.
https://www.w3.org/TR/html5/syntax.html states that HTML documents can have an optional BOM at the start.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
If this is still an issue for you, please try to help by debugging it further and sharing your results.
Thank you for your contributions.

[oleibman]

Fixed by PR #4019.