[middleware][cleanup] Remove unused HtmlValidationMiddleware (#3871)

## What changes were proposed in this pull request?

- `HtmlValidationMiddleware` was commented out in `settings.py` 9 years ago and was never used. It makes sense to remove the related dead code.

## How was this patch tested?

- Manually

desktop/core/src/desktop/middleware.py

@@ -491,112 +491,6 @@ def _get_allowed(self, request, response=None):
     return allowed
 
 
-try:
-  import tidylib
-  _has_tidylib = True
-except Exception as ex:
-  # The exception type is not ImportError. It's actually an OSError.
-  logging.warn("Failed to import tidylib (for debugging). Is libtidy installed?")
-  _has_tidylib = False
-
-
-class HtmlValidationMiddleware(MiddlewareMixin):
-  """
-  If configured, validate output html for every response.
-  """
-  def __init__(self, get_response):
-    self.get_response = get_response
-    self._logger = logging.getLogger('HtmlValidationMiddleware')
-
-    if not _has_tidylib:
-      logging.error("HtmlValidationMiddleware not activatived: Failed to import tidylib.")
-      return
-
-    # Things that we don't care about
-    self._to_ignore = (
-      re.compile('- Warning: <.*> proprietary attribute "data-'),
-      re.compile('- Warning: trimming empty'),
-      re.compile('- Info:'),
-    )
-
-    # Find the directory to write tidy html output
-    try:
-      self._outdir = os.path.join(tempfile.gettempdir(), 'hue_html_validation')
-      if not os.path.isdir(self._outdir):
-        os.mkdir(self._outdir, 0o755)
-    except Exception as ex:
-      self._logger.exception('Failed to get temp directory: %s', (ex,))
-      self._outdir = tempfile.mkdtemp(prefix='hue_html_validation-')
-
-    # Options to pass to libtidy. See
-    # http://tidy.sourceforge.net/docs/quickref.html
-    self._options = {
-      'show-warnings': 1,
-      'output-html': 0,
-      'output-xhtml': 1,
-      'char-encoding': 'utf8',
-      'output-encoding': 'utf8',
-      'indent': 1,
-      'wrap': 0,
-    }
-
-  def process_response(self, request, response):
-
-    if not _has_tidylib or not self._is_html(request, response):
-      return response
-
-    html, errors = tidylib.tidy_document(response.content,
-                                         self._options,
-                                         keep_doc=True)
-    if not errors:
-      return response
-
-    # Filter out what we care about
-    err_list = errors.rstrip().split('\n')
-    err_list = self._filter_warnings(err_list)
-    if not err_list:
-      return response
-
-    try:
-      fn = resolve(request.path)[0]
-      fn_name = '%s.%s' % (fn.__module__, fn.__name__)
-    except Exception:
-      LOG.exception('failed to resolve url')
-      fn_name = '<unresolved_url>'
-
-    # Write the two versions of html out for offline debugging
-    filename = os.path.join(self._outdir, fn_name)
-
-    result = "HTML tidy result: %s [%s]:" \
-             "\n\t%s" \
-             "\nPlease see %s.orig %s.tidy\n-------" % \
-             (request.path, fn_name, '\n\t'.join(err_list), filename, filename)
-
-    file(filename + '.orig', 'w').write(i18n.smart_str(response.content))
-    file(filename + '.tidy', 'w').write(i18n.smart_str(html))
-    file(filename + '.info', 'w').write(i18n.smart_str(result))
-
-    self._logger.error(result)
-
-    return response
-
-  def _filter_warnings(self, err_list):
-    """A hacky way to filter out things that we don't care about."""
-    res = []
-    for err in err_list:
-      for ignore in self._to_ignore:
-        if ignore.search(err):
-          break
-      else:
-        res.append(err)
-    return res
-
-  def _is_html(self, request, response):
-    return not is_ajax(request) and \
-        'html' in response['Content-Type'] and \
-        200 <= response.status_code < 300
-
-
 class ProxyMiddleware(MiddlewareMixin):
 
   def __init__(self, get_response):

desktop/core/src/desktop/settings.py

@@ -165,9 +165,6 @@
     'crequest.middleware.CrequestMiddleware',
 ]
 
-# if os.environ.get(ENV_DESKTOP_DEBUG):
-#   MIDDLEWARE.append('desktop.middleware.HtmlValidationMiddleware')
-#   logging.debug("Will try to validate generated HTML.")
 
 ROOT_URLCONF = 'desktop.urls'