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gh-135661: Fix parsing start and end tags in HTMLParser #135930

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@serhiy-storchaka serhiy-storchaka commented Jun 25, 2025

  • Whitespaces no longer accepted between </ and the tag name. E.g. </ script> does not end the script section.

  • Vertical tabulation (\v) and non-ASCII whitespaces no longer recognized as whitespaces. The only whitespaces are \t\n\r\f .

  • Null character (U+0000) no longer ends the tag name.

  • End tag can have attributes and slashes after tag name. It no longer ends after the first > in quoted attribute value. E.g. </script/foo=">"/>.

  • Multiple slashes and whitespaces between the last attribute and closing > are now accepted in both start and end tags. E.g. <a foo=bar/ //>.

  • Multiple = between attribute name and value are no longer collapsed. E.g. <a foo==bar> produces attribute "foo" with value "=bar".

  • Whitespaces between the = separator and attribute name or value are no longer ignored. E.g. <a foo =bar> produces two attributes "foo" and "=bar", both with value None; <a foo= bar> produces two attributes: "foo" with value "" and "bar" with value None.

* Whitespaces no longer accepted between `</` and the tag name.
  E.g. `</ script>` does not end the script section.

* Vertical tabulation (`\v`) and non-ASCII whitespaces no longer recognized
  as whitespaces. The only whitespaces are `\t\n\r\f `.

* Null character (U+0000) no longer ends the tag name.

* End tag can have attributes and slashes after tag name. It no longer ends
  after the first `>` in quoted attribute value. E.g. `</script/foo=">"/>`.

* Multiple slashes and whitespaces between the last attribute and closing `>`
  are now accepted in both start and end tags. E.g. `<a foo=bar/ //>`.

* Multiple `=` between attribute name and value are no longer collapsed.
  E.g. `<a foo==bar>` produces attribute "foo" with value "=bar".

* Whitespaces between the `=` separator and attribute name or value are no
  longer ignored. E.g. `<a foo =bar>` produces two attributes "foo" and
  "=bar", both with value None; `<a foo= bar>` produces two attributes:
  "foo" with value "" and "bar" with value None.
@serhiy-storchaka
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I tried to minimize changes and split this PR on several PRs, but they would not be independent, and all these changes are needed to fix the possible XSS.

I am planning further refactoring, but this is only for the main branch.

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