text: """
      sphinx.builders.linkcheck
      ~~~~~~~~~~~~~~~~~~~~~~~~~
  
      The CheckExternalLinksBuilder class.
  
      :copyright: Copyright 2007-2020 by the Sphinx team, see AUTHORS.
      :license: BSD, see LICENSE for details.
  """
  
  import json
  import queue
  import re
  import socket
  import threading
  import time
  from datetime import datetime, timezone
  from email.utils import parsedate_to_datetime
  from html.parser import HTMLParser
  from os import path
  from typing import Any, Dict, List, NamedTuple, Optional, Set, Tuple
  from urllib.parse import unquote, urlparse
  
  from docutils import nodes
  from docutils.nodes import Element, Node
  from requests import Response
  from requests.exceptions import HTTPError, TooManyRedirects
  
  from sphinx.application import Sphinx
  from sphinx.builders import Builder
  from sphinx.locale import __
  from sphinx.util import encode_uri, logging, requests
  from sphinx.util.console import darkgray, darkgreen, purple, red, turquoise  # type: ignore
  from sphinx.util.nodes import get_node_line
  
  logger = logging.getLogger(__name__)
  
  uri_re = re.compile('([a-z]+:)?//')  # matches to foo:// and // (a protocol relative URL)
  
  RateLimit = NamedTuple('RateLimit', (('delay', float), ('next_check', float)))
  
  DEFAULT_REQUEST_HEADERS = {
      'Accept': 'text/html,application/xhtml+xml;q=0.9,*/*;q=0.8',
  }
  CHECK_IMMEDIATELY = 0
  QUEUE_POLL_SECS = 1
  DEFAULT_DELAY = 60.0
  
  
  def node_line_or_0(node: Element) -> int:
      """
      PriorityQueue items must be comparable. The line number is part of the
      tuple used by the PriorityQueue, keep an homogeneous type for comparison.
      """
      return get_node_line(node) or 0
  
  
  class AnchorCheckParser(HTMLParser):
      """Specialized HTML parser that looks for a specific anchor."""
  
      def __init__(self, search_anchor: str) -> None:
          super().__init__()
  
          self.search_anchor = search_anchor
          self.found = False
  
      def handle_starttag(self, tag: Any, attrs: Any) -> None:
          for key, value in attrs:
              if key in ('id', 'name') and value == self.search_anchor:
                  self.found = True
                  break
  
  
  def check_anchor(response: requests.requests.Response, anchor: str) -> bool:
      """Reads HTML data from a response object `response` searching for `anchor`.
      Returns True if anchor was found, False otherwise.
      """
      parser = AnchorCheckParser(anchor)
      # Read file in chunks. If we find a matching anchor, we break
      # the loop early in hopes not to have to download the whole thing.
      for chunk in response.iter_content(chunk_size=4096, decode_unicode=True):
          if isinstance(chunk, bytes):    # requests failed to decode
              chunk = chunk.decode()      # manually try to decode it
  
          parser.feed(chunk)
          if parser.found:
              break
      parser.close()
      return parser.found
  
  
  class CheckExternalLinksBuilder(Builder):
      """
      Checks for broken external links.
      """
      name = 'linkcheck'
      epilog = __('Look for any errors in the above output or in '
                  '%(outdir)s/output.txt')
  
      def init(self) -> None:
          self.to_ignore = [re.compile(x) for x in self.app.config.linkcheck_ignore]
          self.anchors_ignore = [re.compile(x)
                                 for x in self.app.config.linkcheck_anchors_ignore]
          self.auth = [(re.compile(pattern), auth_info) for pattern, auth_info
                       in self.app.config.linkcheck_auth]
          self.good = set()       # type: Set[str]
          self.broken = {}        # type: Dict[str, str]
          self.redirected = {}    # type: Dict[str, Tuple[str, int]]
          # set a timeout for non-responding servers
          socket.setdefaulttimeout(5.0)
          # create output file
          open(path.join(self.outdir, 'output.txt'), 'w').close()
          # create JSON output file
          open(path.join(self.outdir, 'output.json'), 'w').close()
  
          # create queues and worker threads
          self.rate_limits = {}  # type: Dict[str, RateLimit]
          self.wqueue = queue.PriorityQueue()  # type: queue.PriorityQueue
          self.rqueue = queue.Queue()  # type: queue.Queue
          self.workers = []  # type: List[threading.Thread]
          for i in range(self.app.config.linkcheck_workers):
              thread = threading.Thread(target=self.check_thread, daemon=True)
              thread.start()
              self.workers.append(thread)
  
      def check_thread(self) -> None:
          kwargs = {}
          if self.app.config.linkcheck_timeout:
              kwargs['timeout'] = self.app.config.linkcheck_timeout
  
          def get_request_headers() -> Dict:
              url = urlparse(uri)
              candidates = ["%s://%s" % (url.scheme, url.netloc),
                            "%s://%s/" % (url.scheme, url.netloc),
                            uri,
                            "*"]
  
              for u in candidates:
                  if u in self.config.linkcheck_request_headers:
                      headers = dict(DEFAULT_REQUEST_HEADERS)
                      headers.update(self.config.linkcheck_request_headers[u])
                      return headers
  
              return {}
  
          def check_uri() -> Tuple[str, str, int]:
              # split off anchor
              if '#' in uri:
                  req_url, anchor = uri.split('#', 1)
                  for rex in self.anchors_ignore:
                      if rex.match(anchor):
                          anchor = None
                          break
              else:
                  req_url = uri
                  anchor = None
  
              # handle non-ASCII URIs
              try:
                  req_url.encode('ascii')
              except UnicodeError:
                  req_url = encode_uri(req_url)
  
              # Get auth info, if any
              for pattern, auth_info in self.auth:
                  if pattern.match(uri):
                      break
              else:
                  auth_info = None
  
              # update request headers for the URL
              kwargs['headers'] = get_request_headers()
  
              try:
                  if anchor and self.app.config.linkcheck_anchors:
                      # Read the whole document and see if #anchor exists
                      response = requests.get(req_url, stream=True, config=self.app.config,
                                              auth=auth_info, **kwargs)
                      response.raise_for_status()
                      found = check_anchor(response, unquote(anchor))
  
                      if not found:
                          raise Exception(__("Anchor '%s' not found") % anchor)
                  else:
                      try:
                          # try a HEAD request first, which should be easier on
                          # the server and the network
                          response = requests.head(req_url, allow_redirects=True,
                                                   config=self.app.config, auth=auth_info,
                                                   **kwargs)
                          response.raise_for_status()
                      except (HTTPError, TooManyRedirects) as err:
                          if isinstance(err, HTTPError) and err.response.status_code == 429:
                              raise
                          # retry with GET request if that fails, some servers
                          # don't like HEAD requests.
                          response = requests.get(req_url, stream=True,
                                                  config=self.app.config,
                                                  auth=auth_info, **kwargs)
                          response.raise_for_status()
              except HTTPError as err:
                  if err.response.status_code == 401:
                      # We'll take "Unauthorized" as working.
                      return 'working', ' - unauthorized', 0
                  elif err.response.status_code == 429:
                      next_check = self.limit_rate(err.response)
                      if next_check is not None:
                          self.wqueue.put((next_check, uri, docname, lineno), False)
                          return 'rate-limited', '', 0
                      return 'broken', str(err), 0
                  elif err.response.status_code == 503:
                      # We'll take "Service Unavailable" as ignored.
                      return 'ignored', str(err), 0
                  else:
                      return 'broken', str(err), 0
              except Exception as err:
                  return 'broken', str(err), 0
              else:
                  netloc = urlparse(req_url).netloc
                  try:
                      del self.rate_limits[netloc]
                  except KeyError:
                      pass
              if response.url.rstrip('/') == req_url.rstrip('/'):
                  return 'working', '', 0
              else:
                  new_url = response.url
                  if anchor:
                      new_url += '#' + anchor
                  # history contains any redirects, get last
                  if response.history:
                      code = response.history[-1].status_code
                      return 'redirected', new_url, code
                  else:
                      return 'redirected', new_url, 0
  
          def check(docname: str) -> Tuple[str, str, int]:
              # check for various conditions without bothering the network
              if len(uri) == 0 or uri.startswith(('#', 'mailto:', 'tel:')):
                  return 'unchecked', '', 0
              elif not uri.startswith(('http:', 'https:')):
                  if uri_re.match(uri):
                      # non supported URI schemes (ex. ftp)
                      return 'unchecked', '', 0
                  else:
                      srcdir = path.dirname(self.env.doc2path(docname))
                      if path.exists(path.join(srcdir, uri)):
                          return 'working', '', 0
                      else:
                          for rex in self.to_ignore:
                              if rex.match(uri):
                                  return 'ignored', '', 0
                          else:
                              self.broken[uri] = ''
                              return 'broken', '', 0
              elif uri in self.good:
                  return 'working', 'old', 0
              elif uri in self.broken:
                  return 'broken', self.broken[uri], 0
              elif uri in self.redirected:
                  return 'redirected', self.redirected[uri][0], self.redirected[uri][1]
              for rex in self.to_ignore:
                  if rex.match(uri):
                      return 'ignored', '', 0
  
              # need to actually check the URI
              for _ in range(self.app.config.linkcheck_retries):
                  status, info, code = check_uri()
                  if status != "broken":
                      break
  
              if status == "working":
                  self.good.add(uri)
              elif status == "broken":
                  self.broken[uri] = info
              elif status == "redirected":
                  self.redirected[uri] = (info, code)
  
              return (status, info, code)
  
          while True:
              next_check, uri, docname, lineno = self.wqueue.get()
              if uri is None:
                  break
              netloc = urlparse(uri).netloc
              try:
                  # Refresh rate limit.
                  # When there are many links in the queue, workers are all stuck waiting
                  # for responses, but the builder keeps queuing. Links in the queue may
                  # have been queued before rate limits were discovered.
                  next_check = self.rate_limits[netloc].next_check
              except KeyError:
                  pass
              if next_check > time.time():
                  # Sleep before putting message back in the queue to avoid
                  # waking up other threads.
                  time.sleep(QUEUE_POLL_SECS)
                  self.wqueue.put((next_check, uri, docname, lineno), False)
                  self.wqueue.task_done()
                  continue
              status, info, code = check(docname)
              if status == 'rate-limited':
                  logger.info(darkgray('-rate limited-   ') + uri + darkgray(' | sleeping...'))
              else:
                  self.rqueue.put((uri, docname, lineno, status, info, code))
              self.wqueue.task_done()
  
      def limit_rate(self, response: Response) -> Optional[float]:
          next_check = None
          retry_after = response.headers.get("Retry-After")
          if retry_after:
              try:
                  # Integer: time to wait before next attempt.
                  delay = float(retry_after)
              except ValueError:
                  try:
                      # An HTTP-date: time of next attempt.
                      until = parsedate_to_datetime(retry_after)
                  except (TypeError, ValueError):
                      # TypeError: Invalid date format.
                      # ValueError: Invalid date, e.g. Oct 52th.
                      pass
                  else:
                      next_check = datetime.timestamp(until)
                      delay = (until - datetime.now(timezone.utc)).total_seconds()
              else:
                  next_check = time.time() + delay
          netloc = urlparse(response.url).netloc
          if next_check is None:
              max_delay = self.app.config.linkcheck_rate_limit_timeout
              try:
                  rate_limit = self.rate_limits[netloc]
              except KeyError:
                  delay = DEFAULT_DELAY
              else:
                  last_wait_time = rate_limit.delay
                  delay = 2.0 * last_wait_time
                  if delay > max_delay and last_wait_time < max_delay:
                      delay = max_delay
              if delay > max_delay:
                  return None
              next_check = time.time() + delay
          self.rate_limits[netloc] = RateLimit(delay, next_check)
          return next_check
  
      def process_result(self, result: Tuple[str, str, int, str, str, int]) -> None:
          uri, docname, lineno, status, info, code = result
  
          filename = self.env.doc2path(docname, None)
          linkstat = dict(filename=filename, lineno=lineno,
                          status=status, code=code, uri=uri,
                          info=info)
          if status == 'unchecked':
              self.write_linkstat(linkstat)
              return
          if status == 'working' and info == 'old':
              self.write_linkstat(linkstat)
              return
          if lineno:
              logger.info('(line %4d) ', lineno, nonl=True)
          if status == 'ignored':
              if info:
                  logger.info(darkgray('-ignored- ') + uri + ': ' + info)
              else:
                  logger.info(darkgray('-ignored- ') + uri)
              self.write_linkstat(linkstat)
          elif status == 'local':
              logger.info(darkgray('-local-   ') + uri)
              self.write_entry('local', docname, filename, lineno, uri)
              self.write_linkstat(linkstat)
          elif status == 'working':
              logger.info(darkgreen('ok        ') + uri + info)
              self.write_linkstat(linkstat)
          elif status == 'broken':
              if self.app.quiet or self.app.warningiserror:
                  logger.warning(__('broken link: %s (%s)'), uri, info,
                                 location=(filename, lineno))
              else:
                  logger.info(red('broken    ') + uri + red(' - ' + info))
              self.write_entry('broken', docname, filename, lineno, uri + ': ' + info)
              self.write_linkstat(linkstat)
          elif status == 'redirected':
              try:
                  text, color = {
                      301: ('permanently', purple),
                      302: ('with Found', purple),
                      303: ('with See Other', purple),
                      307: ('temporarily', turquoise),
                      308: ('permanently', purple),
                  }[code]
              except KeyError:
                  text, color = ('with unknown code', purple)
              linkstat['text'] = text
              logger.info(color('redirect  ') + uri + color(' - ' + text + ' to ' + info))
              self.write_entry('redirected ' + text, docname, filename,
                               lineno, uri + ' to ' + info)
              self.write_linkstat(linkstat)
  
      def get_target_uri(self, docname: str, typ: str = None) -> str:
          return ''
  
      def get_outdated_docs(self) -> Set[str]:
          return self.env.found_docs
  
      def prepare_writing(self, docnames: Set[str]) -> None:
          return
  
      def write_doc(self, docname: str, doctree: Node) -> None:
          logger.info('')
          n = 0
  
          # reference nodes
          for refnode in doctree.traverse(nodes.reference):
              if 'refuri' not in refnode:
                  continue
              uri = refnode['refuri']
              lineno = node_line_or_0(refnode)
              uri_info = (CHECK_IMMEDIATELY, uri, docname, lineno)
              self.wqueue.put(uri_info, False)
              n += 1
  
          # image nodes
          for imgnode in doctree.traverse(nodes.image):
              uri = imgnode['candidates'].get('?')
              if uri and '://' in uri:
                  lineno = node_line_or_0(imgnode)
                  uri_info = (CHECK_IMMEDIATELY, uri, docname, lineno)
                  self.wqueue.put(uri_info, False)
                  n += 1
  
          done = 0
          while done < n:
              self.process_result(self.rqueue.get())
              done += 1
  
          if self.broken:
              self.app.statuscode = 1
  
      def write_entry(self, what: str, docname: str, filename: str, line: int,
                      uri: str) -> None:
          with open(path.join(self.outdir, 'output.txt'), 'a') as output:
              output.write("%s:%s: [%s] %s\n" % (filename, line, what, uri))
  
      def write_linkstat(self, data: dict) -> None:
          with open(path.join(self.outdir, 'output.json'), 'a') as output:
              output.write(json.dumps(data))
              output.write('\n')
  
      def finish(self) -> None:
          self.wqueue.join()
          # Shutdown threads.
          for worker in self.workers:
              self.wqueue.put((CHECK_IMMEDIATELY, None, None, None), False)
  
  
  def setup(app: Sphinx) -> Dict[str, Any]:
      app.add_builder(CheckExternalLinksBuilder)
  
      app.add_config_value('linkcheck_ignore', [], None)
      app.add_config_value('linkcheck_auth', [], None)
      app.add_config_value('linkcheck_request_headers', {}, None)
      app.add_config_value('linkcheck_retries', 1, None)
      app.add_config_value('linkcheck_timeout', None, None, [int])
      app.add_config_value('linkcheck_workers', 5, None)
      app.add_config_value('linkcheck_anchors', True, None)
      # Anchors starting with ! are ignored since they are
      # commonly used for dynamic pages
      app.add_config_value('linkcheck_anchors_ignore', ["^!"], None)
      app.add_config_value('linkcheck_rate_limit_timeout', 300.0, None)
  
      return {
          'version': 'builtin',
          'parallel_read_safe': True,
          'parallel_write_safe': True,
      }
  