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htmlparser unclosed script tag causes data loss #86155

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htmlparser unclosed script tag causes data loss#86155
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ezio-melotti
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3.13only security fixes3.14bugs and security fixes3.15bugs and security fixesstdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

Description

@waylan
waylan
mannequin
opened on Oct 10, 2020
BPO 41989
Nosy @terryjreedy, @ezio-melotti, @waylan
PRs
  • gh-86155: Fix htmlparser "unclosed script tag causes data loss" #22658
    		•
    Files
  • test_html.py: A simple test
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = 'https://github.com/ezio-melotti'
closed_at = None
created_at = <Date 2020-10-10.01:08:29.514>
labels = ['type-bug', 'library', '3.10']
title = 'htmlparser unclosed script tag causes data loss'
updated_at = <Date 2020-10-16.20:42:44.634>
user = 'https://github.com/waylan'

    bugs.python.org fields:

    activity = <Date 2020-10-16.20:42:44.634>
actor = 'terry.reedy'
assignee = 'ezio.melotti'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-10-10.01:08:29.514>
creator = 'waylan'
dependencies = []
files = ['49505']
hgrepos = []
issue_num = 41989
keywords = ['patch']
message_count = 2.0
messages = ['378359', '378748']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'ezio.melotti', 'waylan']
pr_nums = ['22658']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41989'
versions = ['Python 3.10']

    Linked PRs

    Activity

    1. waylan commented on Oct 10, 2020

      @waylan
      waylanmannequin
      on Oct 10, 2020
      MannequinAuthor

      When the close method of the HtmlParser is called, any cached text data is generally flushed and passed to a data event; except when in data_mode. Specifically, if an unclosed script or style tag has been encountered, a call to close does not flush the data.

      A simple test which demonstrates the issue is attached.

      I see that in Lib/html/parser.py#L244-L249 there are two nested if statements which both check for not self.cdata_elem. Obviously, if we got past the first one, that situation will never exist for the nested one. Somehow this block of code needs a branch for when self.cdata_elem is True.

      I should note that the input is invalid HTML. However, the existing behavior results in data loss. Within any other unclosed tag (other than script or style) any data is still flushed and passed to a data event. I would expect the same behavior here. Although, the data escaping behavior should perhaps be applied as it is with data within properly closed tags.

    2. waylan
      added
      3.7 (EOL)end of life
      3.8 (EOL)end of life
      3.9 (EOL)end of life
      3.10 (EOL)end of life
      stdlibStandard Library Python modules in the Lib/ directory
      type-bugAn unexpected behavior, bug, or error
      on Oct 10, 2020
    3. ezio-melotti
      assigned
      ezio-melotti
      on Oct 12, 2020

    4. 18 remaining items

    5. serhiy-storchaka
      closed this as completedon May 10, 2025
    6. github-project-automation
      moved this from Todo to Done in html.parser issueson May 10, 2025
    7. serhiy-storchaka
      added 2 commits that reference this issue on May 10, 2025

      [3.13] gh-86155: Fix data loss after unclosed script or style tag in …

      e76ff56

      [3.14] gh-86155: Fix data loss after unclosed script or style tag in …

      e7e105f
    8. serhiy-storchaka
      added a commit that references this issue on Jul 4, 2025

      [3.12] pythongh-135661: Fix parsing start and end tags in HTMLParser …

      7b480a6
    9. ambv
      added a commit that references this issue on Jul 4, 2025

      [3.12] gh-135661: Fix parsing start and end tags in HTMLParser accord…

      c555f88
    10. miss-islington
      added 3 commits that reference this issue on Jul 4, 2025

      [3.12] pythongh-135661: Fix parsing start and end tags in HTMLParser …

      74e667c

      [3.12] pythongh-135661: Fix parsing start and end tags in HTMLParser …

      6331eaf

      [3.12] pythongh-135661: Fix parsing start and end tags in HTMLParser …

      6725dad
    11. ambv
      added 3 commits that reference this issue on Jul 12, 2025

      [3.11] gh-135661: Fix parsing start and end tags in HTMLParser accord…

      228509e

      [3.10] gh-135661: Fix parsing start and end tags in HTMLParser accord…

      151e0f0

      [3.9] gh-135661: Fix parsing start and end tags in HTMLParser accordi…

      6c97200
    12. Pranjal095
      added a commit that references this issue on Jul 12, 2025

      pythongh-86155: Fix data loss after unclosed script or style tag in H…

      9b813ed
    13. gentoo-bot
      added a commit that references this issue on Jul 30, 2025

      [3.9] pythongh-135661: Fix parsing start and end tags in HTMLParser a…

      34970e0
    14. taegyunkim
      added a commit that references this issue on Aug 4, 2025

      pythongh-86155: Fix data loss after unclosed script or style tag in H…

      6e4707e
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