text: # -*- test-case-name: twisted.web.test.test_webclient,twisted.web.test.test_agent -*-
  # Copyright (c) Twisted Matrix Laboratories.
  # See LICENSE for details.
  
  """
  HTTP client.
  """
  
  
  import os
  import collections
  import warnings
  
  from urllib.parse import urljoin, urldefrag
  from urllib.parse import urlunparse as _urlunparse
  
  import zlib
  from functools import wraps
  
  from zope.interface import implementer
  
  from twisted.python.compat import nativeString, networkString
  from twisted.python.deprecate import deprecatedModuleAttribute, deprecated
  from twisted.python.failure import Failure
  from incremental import Version
  
  from twisted.web.iweb import IPolicyForHTTPS, IAgentEndpointFactory
  from twisted.python.deprecate import getDeprecationWarningString
  from twisted.web import http
  from twisted.internet import defer, protocol, task
  from twisted.internet.abstract import isIPv6Address
  from twisted.internet.interfaces import IProtocol, IOpenSSLContextFactory
  from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS
  from twisted.python.util import InsensitiveDict
  from twisted.python.components import proxyForInterface
  from twisted.web import error
  from twisted.web.iweb import UNKNOWN_LENGTH, IAgent, IBodyProducer, IResponse
  from twisted.web.http_headers import Headers
  from twisted.logger import Logger
  
  from twisted.web._newclient import _ensureValidURI, _ensureValidMethod
  
  
  def urlunparse(parts):
      result = _urlunparse(tuple([p.decode("charmap") for p in parts]))
      return result.encode("charmap")
  
  
  class PartialDownloadError(error.Error):
      """
      Page was only partially downloaded, we got disconnected in middle.
  
      @ivar response: All of the response body which was downloaded.
      """
  
  
  class HTTPPageGetter(http.HTTPClient):
      """
      Gets a resource via HTTP, then quits.
  
      Typically used with L{HTTPClientFactory}.  Note that this class does not, by
      itself, do anything with the response.  If you want to download a resource
      into a file, use L{HTTPPageDownloader} instead.
  
      @ivar _completelyDone: A boolean indicating whether any further requests are
          necessary after this one completes in order to provide a result to
          C{self.factory.deferred}.  If it is C{False}, then a redirect is going
          to be followed.  Otherwise, this protocol's connection is the last one
          before firing the result Deferred.  This is used to make sure the result
          Deferred is only fired after the connection is cleaned up.
      """
  
      quietLoss = 0
      followRedirect = True
      failed = 0
  
      _completelyDone = True
  
      _specialHeaders = set(
          (b"host", b"user-agent", b"cookie", b"content-length"),
      )
  
      def connectionMade(self):
          method = _ensureValidMethod(getattr(self.factory, "method", b"GET"))
          self.sendCommand(method, _ensureValidURI(self.factory.path))
          if self.factory.scheme == b"http" and self.factory.port != 80:
              host = b"%b:%d" % (self.factory.host, self.factory.port)
          elif self.factory.scheme == b"https" and self.factory.port != 443:
              host = b"%b:%d" % (self.factory.host, self.factory.port)
          else:
              host = self.factory.host
          self.sendHeader(b"Host", self.factory.headers.get(b"host", host))
          self.sendHeader(b"User-Agent", self.factory.agent)
          data = getattr(self.factory, "postdata", None)
          if data is not None:
              self.sendHeader(b"Content-Length", b"%d" % (len(data),))
  
          cookieData = []
          for (key, value) in self.factory.headers.items():
              if key.lower() not in self._specialHeaders:
                  # we calculated it on our own
                  self.sendHeader(key, value)
              if key.lower() == b"cookie":
                  cookieData.append(value)
          for cookie, cookval in self.factory.cookies.items():
              cookieData.append(cookie + b"=" + cookval)
          if cookieData:
              self.sendHeader(b"Cookie", b"; ".join(cookieData))
          self.endHeaders()
          self.headers = {}
  
          if data is not None:
              self.transport.write(data)
  
      def handleHeader(self, key, value):
          """
          Called every time a header is received. Stores the header information
          as key-value pairs in the C{headers} attribute.
  
          @type key: C{str}
          @param key: An HTTP header field name.
  
          @type value: C{str}
          @param value: An HTTP header field value.
          """
          key = key.lower()
          l = self.headers.setdefault(key, [])
          l.append(value)
  
      def handleStatus(self, version, status, message):
          """
          Handle the HTTP status line.
  
          @param version: The HTTP version.
          @type version: L{bytes}
          @param status: The HTTP status code, an integer represented as a
              bytestring.
          @type status: L{bytes}
          @param message: The HTTP status message.
          @type message: L{bytes}
          """
          self.version, self.status, self.message = version, status, message
          self.factory.gotStatus(version, status, message)
  
      def handleEndHeaders(self):
          self.factory.gotHeaders(self.headers)
          m = getattr(
              self, "handleStatus_" + nativeString(self.status), self.handleStatusDefault
          )
          m()
  
      def handleStatus_200(self):
          pass
  
      handleStatus_201 = lambda self: self.handleStatus_200()
      handleStatus_202 = lambda self: self.handleStatus_200()
  
      def handleStatusDefault(self):
          self.failed = 1
  
      def handleStatus_301(self):
          l = self.headers.get(b"location")
          if not l:
              self.handleStatusDefault()
              return
          url = l[0]
          if self.followRedirect:
              self.factory._redirectCount += 1
              if self.factory._redirectCount >= self.factory.redirectLimit:
                  err = error.InfiniteRedirection(
                      self.status, b"Infinite redirection detected", location=url
                  )
                  self.factory.noPage(Failure(err))
                  self.quietLoss = True
                  self.transport.loseConnection()
                  return
  
              self._completelyDone = False
              self.factory.setURL(url)
  
              from twisted.internet import reactor
  
              if self.factory.scheme == b"https":
                  from twisted.internet import ssl
  
                  contextFactory = ssl.ClientContextFactory()
                  reactor.connectSSL(
                      nativeString(self.factory.host),
                      self.factory.port,
                      self.factory,
                      contextFactory,
                  )
              else:
                  reactor.connectTCP(
                      nativeString(self.factory.host), self.factory.port, self.factory
                  )
          else:
              self.handleStatusDefault()
              self.factory.noPage(
                  Failure(error.PageRedirect(self.status, self.message, location=url))
              )
          self.quietLoss = True
          self.transport.loseConnection()
  
      def handleStatus_302(self):
          if self.afterFoundGet:
              self.handleStatus_303()
          else:
              self.handleStatus_301()
  
      def handleStatus_303(self):
          self.factory.method = b"GET"
          self.handleStatus_301()
  
      def connectionLost(self, reason):
          """
          When the connection used to issue the HTTP request is closed, notify the
          factory if we have not already, so it can produce a result.
          """
          if not self.quietLoss:
              http.HTTPClient.connectionLost(self, reason)
              self.factory.noPage(reason)
          if self._completelyDone:
              # Only if we think we're completely done do we tell the factory that
              # we're "disconnected".  This way when we're following redirects,
              # only the last protocol used will fire the _disconnectedDeferred.
              self.factory._disconnectedDeferred.callback(None)
  
      def handleResponse(self, response):
          if self.quietLoss:
              return
          if self.failed:
              self.factory.noPage(
                  Failure(error.Error(self.status, self.message, response))
              )
          if self.factory.method == b"HEAD":
              # Callback with empty string, since there is never a response
              # body for HEAD requests.
              self.factory.page(b"")
          elif self.length != None and self.length != 0:
              self.factory.noPage(
                  Failure(PartialDownloadError(self.status, self.message, response))
              )
          else:
              self.factory.page(response)
          # server might be stupid and not close connection. admittedly
          # the fact we do only one request per connection is also
          # stupid...
          self.transport.loseConnection()
  
      def timeout(self):
          self.quietLoss = True
          self.transport.abortConnection()
          self.factory.noPage(
              defer.TimeoutError(
                  "Getting %s took longer than %s seconds."
                  % (self.factory.url, self.factory.timeout)
              )
          )
  
  
  class HTTPPageDownloader(HTTPPageGetter):
  
      transmittingPage = 0
  
      def handleStatus_200(self, partialContent=0):
          HTTPPageGetter.handleStatus_200(self)
          self.transmittingPage = 1
          self.factory.pageStart(partialContent)
  
      def handleStatus_206(self):
          self.handleStatus_200(partialContent=1)
  
      def handleResponsePart(self, data):
          if self.transmittingPage:
              self.factory.pagePart(data)
  
      def handleResponseEnd(self):
          if self.length:
              self.transmittingPage = 0
              self.factory.noPage(Failure(PartialDownloadError(self.status)))
          if self.transmittingPage:
              self.factory.pageEnd()
              self.transmittingPage = 0
          if self.failed:
              self.factory.noPage(Failure(error.Error(self.status, self.message, None)))
              self.transport.loseConnection()
  
  
  class HTTPClientFactory(protocol.ClientFactory):
      """Download a given URL.
  
      @type deferred: Deferred
      @ivar deferred: A Deferred that will fire when the content has
            been retrieved. Once this is fired, the ivars `status', `version',
            and `message' will be set.
  
      @type status: bytes
      @ivar status: The status of the response.
  
      @type version: bytes
      @ivar version: The version of the response.
  
      @type message: bytes
      @ivar message: The text message returned with the status.
  
      @type response_headers: dict
      @ivar response_headers: The headers that were specified in the
            response from the server.
  
      @type method: bytes
      @ivar method: The HTTP method to use in the request.  This should be one of
          OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, or CONNECT (case
          matters).  Other values may be specified if the server being contacted
          supports them.
  
      @type redirectLimit: int
      @ivar redirectLimit: The maximum number of HTTP redirects that can occur
            before it is assumed that the redirection is endless.
  
      @type afterFoundGet: C{bool}
      @ivar afterFoundGet: Deviate from the HTTP 1.1 RFC by handling redirects
          the same way as most web browsers; if the request method is POST and a
          302 status is encountered, the redirect is followed with a GET method
  
      @type _redirectCount: int
      @ivar _redirectCount: The current number of HTTP redirects encountered.
  
      @ivar _disconnectedDeferred: A L{Deferred} which only fires after the last
          connection associated with the request (redirects may cause multiple
          connections to be required) has closed.  The result Deferred will only
          fire after this Deferred, so that callers can be assured that there are
          no more event sources in the reactor once they get the result.
      """
  
      protocol = HTTPPageGetter
  
      url = None
      scheme = None
      host = b""
      port = None
      path = None
  
      def __init__(
          self,
          url,
          method=b"GET",
          postdata=None,
          headers=None,
          agent=b"Twisted PageGetter",
          timeout=0,
          cookies=None,
          followRedirect=True,
          redirectLimit=20,
          afterFoundGet=False,
      ):
          self.followRedirect = followRedirect
          self.redirectLimit = redirectLimit
          self._redirectCount = 0
          self.timeout = timeout
          self.agent = agent
          self.afterFoundGet = afterFoundGet
          if cookies is None:
              cookies = {}
          self.cookies = cookies
          if headers is not None:
              self.headers = InsensitiveDict(headers)
          else:
              self.headers = InsensitiveDict()
          if postdata is not None:
              self.headers.setdefault(b"Content-Length", b"%d" % (len(postdata),))
              # just in case a broken http/1.1 decides to keep connection alive
              self.headers.setdefault(b"connection", b"close")
          self.postdata = postdata
          self.method = _ensureValidMethod(method)
  
          self.setURL(url)
  
          self.waiting = 1
          self._disconnectedDeferred = defer.Deferred()
          self.deferred = defer.Deferred()
          # Make sure the first callback on the result Deferred pauses the
          # callback chain until the request connection is closed.
          self.deferred.addBoth(self._waitForDisconnect)
          self.response_headers = None
  
      def _waitForDisconnect(self, passthrough):
          """
          Chain onto the _disconnectedDeferred, preserving C{passthrough}, so that
          the result is only available after the associated connection has been
          closed.
          """
          self._disconnectedDeferred.addCallback(lambda ignored: passthrough)
          return self._disconnectedDeferred
  
      def __repr__(self) -> str:
          return "<%s: %s>" % (self.__class__.__name__, self.url)
  
      def setURL(self, url):
          _ensureValidURI(url.strip())
          self.url = url
          uri = URI.fromBytes(url)
          if uri.scheme and uri.host:
              self.scheme = uri.scheme
              self.host = uri.host
              self.port = uri.port
          self.path = uri.originForm
  
      def buildProtocol(self, addr):
          p = protocol.ClientFactory.buildProtocol(self, addr)
          p.followRedirect = self.followRedirect
          p.afterFoundGet = self.afterFoundGet
          if self.timeout:
              from twisted.internet import reactor
  
              timeoutCall = reactor.callLater(self.timeout, p.timeout)
              self.deferred.addBoth(self._cancelTimeout, timeoutCall)
          return p
  
      def _cancelTimeout(self, result, timeoutCall):
          if timeoutCall.active():
              timeoutCall.cancel()
          return result
  
      def gotHeaders(self, headers):
          """
          Parse the response HTTP headers.
  
          @param headers: The response HTTP headers.
          @type headers: L{dict}
          """
          self.response_headers = headers
          if b"set-cookie" in headers:
              for cookie in headers[b"set-cookie"]:
                  if b"=" in cookie:
                      cookparts = cookie.split(b";")
                      cook = cookparts[0]
                      cook.lstrip()
                      k, v = cook.split(b"=", 1)
                      self.cookies[k.lstrip()] = v.lstrip()
  
      def gotStatus(self, version, status, message):
          """
          Set the status of the request on us.
  
          @param version: The HTTP version.
          @type version: L{bytes}
          @param status: The HTTP status code, an integer represented as a
              bytestring.
          @type status: L{bytes}
          @param message: The HTTP status message.
          @type message: L{bytes}
          """
          self.version, self.status, self.message = version, status, message
  
      def page(self, page):
          if self.waiting:
              self.waiting = 0
              self.deferred.callback(page)
  
      def noPage(self, reason):
          if self.waiting:
              self.waiting = 0
              self.deferred.errback(reason)
  
      def clientConnectionFailed(self, _, reason):
          """
          When a connection attempt fails, the request cannot be issued.  If no
          result has yet been provided to the result Deferred, provide the
          connection failure reason as an error result.
          """
          if self.waiting:
              self.waiting = 0
              # If the connection attempt failed, there is nothing more to
              # disconnect, so just fire that Deferred now.
              self._disconnectedDeferred.callback(None)
              self.deferred.errback(reason)
  
  
  class HTTPDownloader(HTTPClientFactory):
      """
      Download to a file.
      """
  
      protocol = HTTPPageDownloader
      value = None
      _log = Logger()
  
      def __init__(
          self,
          url,
          fileOrName,
          method=b"GET",
          postdata=None,
          headers=None,
          agent=b"Twisted client",
          supportPartial=False,
          timeout=0,
          cookies=None,
          followRedirect=True,
          redirectLimit=20,
          afterFoundGet=False,
      ):
          self.requestedPartial = 0
          if isinstance(fileOrName, str):
              self.fileName = fileOrName
              self.file = None
              if supportPartial and os.path.exists(self.fileName):
                  fileLength = os.path.getsize(self.fileName)
                  if fileLength:
                      self.requestedPartial = fileLength
                      if headers is None:
                          headers = {}
                      headers[b"range"] = b"bytes=%d-" % (fileLength,)
          else:
              self.file = fileOrName
          HTTPClientFactory.__init__(
              self,
              url,
              method=method,
              postdata=postdata,
              headers=headers,
              agent=agent,
              timeout=timeout,
              cookies=cookies,
              followRedirect=followRedirect,
              redirectLimit=redirectLimit,
              afterFoundGet=afterFoundGet,
          )
  
      def gotHeaders(self, headers):
          HTTPClientFactory.gotHeaders(self, headers)
          if self.requestedPartial:
              contentRange = headers.get(b"content-range", None)
              if not contentRange:
                  # server doesn't support partial requests, oh well
                  self.requestedPartial = 0
                  return
              start, end, realLength = http.parseContentRange(contentRange[0])
              if start != self.requestedPartial:
                  # server is acting weirdly
                  self.requestedPartial = 0
  
      def openFile(self, partialContent):
          if partialContent:
              file = open(self.fileName, "rb+")
              file.seek(0, 2)
          else:
              file = open(self.fileName, "wb")
          return file
  
      def pageStart(self, partialContent):
          """Called on page download start.
  
          @param partialContent: tells us if the download is partial download we requested.
          """
          if partialContent and not self.requestedPartial:
              raise ValueError(
                  "we shouldn't get partial content response if we didn't want it!"
              )
          if self.waiting:
              try:
                  if not self.file:
                      self.file = self.openFile(partialContent)
              except IOError:
                  # raise
                  self.deferred.errback(Failure())
  
      def pagePart(self, data):
          if not self.file:
              return
          try:
              self.file.write(data)
          except IOError:
              # raise
              self.file = None
              self.deferred.errback(Failure())
  
      def noPage(self, reason):
          """
          Close the storage file and errback the waiting L{Deferred} with the
          given reason.
          """
          if self.waiting:
              self.waiting = 0
              if self.file:
                  try:
                      self.file.close()
                  except:
                      self._log.failure("Error closing HTTPDownloader file")
              self.deferred.errback(reason)
  
      def pageEnd(self):
          self.waiting = 0
          if not self.file:
              return
          try:
              self.file.close()
          except IOError:
              self.deferred.errback(Failure())
              return
          self.deferred.callback(self.value)
  
  
  class URI:
      """
      A URI object.
  
      @see: U{https://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-21}
      """
  
      def __init__(self, scheme, netloc, host, port, path, params, query, fragment):
          """
          @type scheme: L{bytes}
          @param scheme: URI scheme specifier.
  
          @type netloc: L{bytes}
          @param netloc: Network location component.
  
          @type host: L{bytes}
          @param host: Host name. For IPv6 address literals the brackets are
              stripped.
  
          @type port: L{int}
          @param port: Port number.
  
          @type path: L{bytes}
          @param path: Hierarchical path.
  
          @type params: L{bytes}
          @param params: Parameters for last path segment.
  
          @type query: L{bytes}
          @param query: Query string.
  
          @type fragment: L{bytes}
          @param fragment: Fragment identifier.
          """
          self.scheme = scheme
          self.netloc = netloc
          self.host = host.strip(b"[]")
          self.port = port
          self.path = path
          self.params = params
          self.query = query
          self.fragment = fragment
  
      @classmethod
      def fromBytes(cls, uri, defaultPort=None):
          """
          Parse the given URI into a L{URI}.
  
          @type uri: C{bytes}
          @param uri: URI to parse.
  
          @type defaultPort: C{int} or L{None}
          @param defaultPort: An alternate value to use as the port if the URI
              does not include one.
  
          @rtype: L{URI}
          @return: Parsed URI instance.
          """
          uri = uri.strip()
          scheme, netloc, path, params, query, fragment = http.urlparse(uri)
  
          if defaultPort is None:
              if scheme == b"https":
                  defaultPort = 443
              else:
                  defaultPort = 80
  
          if b":" in netloc:
              host, port = netloc.rsplit(b":", 1)
              try:
                  port = int(port)
              except ValueError:
                  host, port = netloc, defaultPort
          else:
              host, port = netloc, defaultPort
          return cls(scheme, netloc, host, port, path, params, query, fragment)
  
      def toBytes(self):
          """
          Assemble the individual parts of the I{URI} into a fully formed I{URI}.
  
          @rtype: C{bytes}
          @return: A fully formed I{URI}.
          """
          return urlunparse(
              (
                  self.scheme,
                  self.netloc,
                  self.path,
                  self.params,
                  self.query,
                  self.fragment,
              )
          )
  
      @property
      def originForm(self):
          """
          The absolute I{URI} path including I{URI} parameters, query string and
          fragment identifier.
  
          @see: U{https://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-21#section-5.3}
  
          @return: The absolute path in original form.
          @rtype: L{bytes}
          """
          # The HTTP bis draft says the origin form should not include the
          # fragment.
          path = urlunparse((b"", b"", self.path, self.params, self.query, b""))
          if path == b"":
              path = b"/"
          return path
  
  
  def _urljoin(base, url):
      """
      Construct a full ("absolute") URL by combining a "base URL" with another
      URL. Informally, this uses components of the base URL, in particular the
      addressing scheme, the network location and (part of) the path, to provide
      missing components in the relative URL.
  
      Additionally, the fragment identifier is preserved according to the HTTP
      1.1 bis draft.
  
      @type base: C{bytes}
      @param base: Base URL.
  
      @type url: C{bytes}
      @param url: URL to combine with C{base}.
  
      @return: An absolute URL resulting from the combination of C{base} and
          C{url}.
  
      @see: L{urlparse.urljoin}
  
      @see: U{https://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-22#section-7.1.2}
      """
      base, baseFrag = urldefrag(base)
      url, urlFrag = urldefrag(urljoin(base, url))
      return urljoin(url, b"#" + (urlFrag or baseFrag))
  
  
  def _makeGetterFactory(url, factoryFactory, contextFactory=None, *args, **kwargs):
      """
      Create and connect an HTTP page getting factory.
  
      Any additional positional or keyword arguments are used when calling
      C{factoryFactory}.
  
      @param factoryFactory: Factory factory that is called with C{url}, C{args}
          and C{kwargs} to produce the getter
  
      @param contextFactory: Context factory to use when creating a secure
          connection, defaulting to L{None}
  
      @return: The factory created by C{factoryFactory}
      """
      uri = URI.fromBytes(_ensureValidURI(url.strip()))
      factory = factoryFactory(url, *args, **kwargs)
      from twisted.internet import reactor
  
      if uri.scheme == b"https":
          from twisted.internet import ssl
  
          if contextFactory is None:
              contextFactory = ssl.ClientContextFactory()
          reactor.connectSSL(nativeString(uri.host), uri.port, factory, contextFactory)
      else:
          reactor.connectTCP(nativeString(uri.host), uri.port, factory)
      return factory
  
  
  _GETPAGE_REPLACEMENT_TEXT = "https://pypi.org/project/treq/ or twisted.web.client.Agent"
  
  
  def _deprecateGetPageClasses():
      """
      Mark the protocols and factories associated with L{getPage} and
      L{downloadPage} as deprecated.
      """
      for klass in [
          HTTPPageGetter,
          HTTPPageDownloader,
          HTTPClientFactory,
          HTTPDownloader,
      ]:
          deprecatedModuleAttribute(
              Version("Twisted", 16, 7, 0),
              getDeprecationWarningString(
                  klass,
                  Version("Twisted", 16, 7, 0),
                  replacement=_GETPAGE_REPLACEMENT_TEXT,
              ).split("; ")[1],
              klass.__module__,
              klass.__name__,
          )
  
  
  _deprecateGetPageClasses()
  
  
  @deprecated(Version("Twisted", 16, 7, 0), _GETPAGE_REPLACEMENT_TEXT)
  def getPage(url, contextFactory=None, *args, **kwargs):
      """
      Download a web page as a string.
  
      Download a page. Return a deferred, which will callback with a
      page (as a string) or errback with a description of the error.
  
      See L{HTTPClientFactory} to see what extra arguments can be passed.
      """
      return _makeGetterFactory(
          url, HTTPClientFactory, contextFactory=contextFactory, *args, **kwargs
      ).deferred
  
  
  @deprecated(Version("Twisted", 16, 7, 0), _GETPAGE_REPLACEMENT_TEXT)
  def downloadPage(url, file, contextFactory=None, *args, **kwargs):
      """
      Download a web page to a file.
  
      @param file: path to file on filesystem, or file-like object.
  
      See HTTPDownloader to see what extra args can be passed.
      """
      factoryFactory = lambda url, *a, **kw: HTTPDownloader(url, file, *a, **kw)
      return _makeGetterFactory(
          url, factoryFactory, contextFactory=contextFactory, *args, **kwargs
      ).deferred
  
  
  # The code which follows is based on the new HTTP client implementation.  It
  # should be significantly better than anything above, though it is not yet
  # feature equivalent.
  
  from twisted.web.error import SchemeNotSupported
  from twisted.web._newclient import (
      HTTP11ClientProtocol,
      PotentialDataLoss,
      Request,
      RequestGenerationFailed,
      RequestNotSent,
      RequestTransmissionFailed,
      Response,
      ResponseDone,
      ResponseFailed,
      ResponseNeverReceived,
      _WrapperException,
  )
  
  
  try:
      from OpenSSL import SSL
  except ImportError:
      SSL = None
  else:
      from twisted.internet.ssl import (
          CertificateOptions,
          platformTrust,
          optionsForClientTLS,
      )
  
  
  def _requireSSL(decoratee):
      """
      The decorated method requires pyOpenSSL to be present, or it raises
      L{NotImplementedError}.
  
      @param decoratee: A function which requires pyOpenSSL.
      @type decoratee: L{callable}
  
      @return: A function which raises L{NotImplementedError} if pyOpenSSL is not
          installed; otherwise, if it is installed, simply return C{decoratee}.
      @rtype: L{callable}
      """
      if SSL is None:
  
          @wraps(decoratee)
          def raiseNotImplemented(*a, **kw):
              """
              pyOpenSSL is not available.
  
              @param a: The positional arguments for C{decoratee}.
  
              @param kw: The keyword arguments for C{decoratee}.
  
              @raise NotImplementedError: Always.
              """
              raise NotImplementedError("SSL support unavailable")
  
          return raiseNotImplemented
      return decoratee
  
  
  class WebClientContextFactory:
      """
      This class is deprecated.  Please simply use L{Agent} as-is, or if you want
      to customize something, use L{BrowserLikePolicyForHTTPS}.
  
      A L{WebClientContextFactory} is an HTTPS policy which totally ignores the
      hostname and port.  It performs basic certificate verification, however the
      lack of validation of service identity (e.g.  hostname validation) means it
      is still vulnerable to man-in-the-middle attacks.  Don't use it any more.
      """
  
      def _getCertificateOptions(self, hostname, port):
          """
          Return a L{CertificateOptions}.
  
          @param hostname: ignored
  
          @param port: ignored
  
          @return: A new CertificateOptions instance.
          @rtype: L{CertificateOptions}
          """
          return CertificateOptions(method=SSL.SSLv23_METHOD, trustRoot=platformTrust())
  
      @_requireSSL
      def getContext(self, hostname, port):
          """
          Return an L{OpenSSL.SSL.Context}.
  
          @param hostname: ignored
          @param port: ignored
  
          @return: A new SSL context.
          @rtype: L{OpenSSL.SSL.Context}
          """
          return self._getCertificateOptions(hostname, port).getContext()
  
  
  @implementer(IPolicyForHTTPS)
  class BrowserLikePolicyForHTTPS:
      """
      SSL connection creator for web clients.
      """
  
      def __init__(self, trustRoot=None):
          self._trustRoot = trustRoot
  
      @_requireSSL
      def creatorForNetloc(self, hostname, port):
          """
          Create a L{client connection creator
          <twisted.internet.interfaces.IOpenSSLClientConnectionCreator>} for a
          given network location.
  
          @param tls: The TLS protocol to create a connection for.
          @type tls: L{twisted.protocols.tls.TLSMemoryBIOProtocol}
  
          @param hostname: The hostname part of the URI.
          @type hostname: L{bytes}
  
          @param port: The port part of the URI.
          @type port: L{int}
  
          @return: a connection creator with appropriate verification
              restrictions set
          @rtype: L{client connection creator
              <twisted.internet.interfaces.IOpenSSLClientConnectionCreator>}
          """
          return optionsForClientTLS(hostname.decode("ascii"), trustRoot=self._trustRoot)
  
  
  deprecatedModuleAttribute(
      Version("Twisted", 14, 0, 0),
      getDeprecationWarningString(
          WebClientContextFactory,
          Version("Twisted", 14, 0, 0),
          replacement=BrowserLikePolicyForHTTPS,
      ).split("; ")[1],
      WebClientContextFactory.__module__,
      WebClientContextFactory.__name__,
  )
  
  
  @implementer(IPolicyForHTTPS)
  class HostnameCachingHTTPSPolicy:
      """
      IPolicyForHTTPS that wraps a L{IPolicyForHTTPS} and caches the created
      L{IOpenSSLClientConnectionCreator}.
  
      This policy will cache up to C{cacheSize}
      L{client connection creators <twisted.internet.interfaces.
      IOpenSSLClientConnectionCreator>} for reuse in subsequent requests to
      the same hostname.
  
      @ivar _policyForHTTPS: See C{policyforHTTPS} parameter of L{__init__}.
  
      @ivar _cache: A cache associating hostnames to their
          L{client connection creators <twisted.internet.interfaces.
          IOpenSSLClientConnectionCreator>}.
      @type _cache: L{collections.OrderedDict}
  
      @ivar _cacheSize: See C{cacheSize} parameter of L{__init__}.
  
      @since: Twisted 19.2.0
      """
  
      def __init__(self, policyforHTTPS, cacheSize=20):
          """
          @param policyforHTTPS: The IPolicyForHTTPS to wrap.
          @type policyforHTTPS: L{IPolicyForHTTPS}
  
          @param cacheSize: The maximum size of the hostname cache.
          @type cacheSize: L{int}
          """
          self._policyForHTTPS = policyforHTTPS
          self._cache = collections.OrderedDict()
          self._cacheSize = cacheSize
  
      def creatorForNetloc(self, hostname, port):
          """
          Create a L{client connection creator
          <twisted.internet.interfaces.IOpenSSLClientConnectionCreator>} for a
          given network location and cache it for future use.
  
          @param hostname: The hostname part of the URI.
          @type hostname: L{bytes}
  
          @param port: The port part of the URI.
          @type port: L{int}
  
          @return: a connection creator with appropriate verification
              restrictions set
          @rtype: L{client connection creator
              <twisted.internet.interfaces.IOpenSSLClientConnectionCreator>}
          """
          host = hostname.decode("ascii")
          try:
              creator = self._cache.pop(host)
          except KeyError:
              creator = self._policyForHTTPS.creatorForNetloc(hostname, port)
  
          self._cache[host] = creator
          if len(self._cache) > self._cacheSize:
              self._cache.popitem(last=False)
  
          return creator
  
  
  @implementer(IOpenSSLContextFactory)
  class _ContextFactoryWithContext:
      """
      A L{_ContextFactoryWithContext} is like a
      L{twisted.internet.ssl.ContextFactory} with a pre-created context.
  
      @ivar _context: A Context.
      @type _context: L{OpenSSL.SSL.Context}
      """
  
      def __init__(self, context):
          """
          Initialize a L{_ContextFactoryWithContext} with a context.
  
          @param context: An SSL context.
          @type context: L{OpenSSL.SSL.Context}
          """
          self._context = context
  
      def getContext(self):
          """
          Return the context created by
          L{_DeprecatedToCurrentPolicyForHTTPS._webContextFactory}.
  
          @return: A context.
          @rtype context: L{OpenSSL.SSL.Context}
          """
          return self._context
  
  
  @implementer(IPolicyForHTTPS)
  class _DeprecatedToCurrentPolicyForHTTPS:
      """
      Adapt a web context factory to a normal context factory.
  
      @ivar _webContextFactory: An object providing a getContext method with
          C{hostname} and C{port} arguments.
      @type _webContextFactory: L{WebClientContextFactory} (or object with a
          similar C{getContext} method).
      """
  
      def __init__(self, webContextFactory):
          """
          Wrap a web context factory in an L{IPolicyForHTTPS}.
  
          @param webContextFactory: An object providing a getContext method with
              C{hostname} and C{port} arguments.
          @type webContextFactory: L{WebClientContextFactory} (or object with a
              similar C{getContext} method).
          """
          self._webContextFactory = webContextFactory
  
      def creatorForNetloc(self, hostname, port):
          """
          Called the wrapped web context factory's C{getContext} method with a
          hostname and port number and return the resulting context object.
  
          @param hostname: The hostname part of the URI.
          @type hostname: L{bytes}
  
          @param port: The port part of the URI.
          @type port: L{int}
  
          @return: A context factory.
          @rtype: L{IOpenSSLContextFactory}
          """
          context = self._webContextFactory.getContext(hostname, port)
          return _ContextFactoryWithContext(context)
  
  
  @implementer(IBodyProducer)
  class FileBodyProducer:
      """
      L{FileBodyProducer} produces bytes from an input file object incrementally
      and writes them to a consumer.
  
      Since file-like objects cannot be read from in an event-driven manner,
      L{FileBodyProducer} uses a L{Cooperator} instance to schedule reads from
      the file.  This process is also paused and resumed based on notifications
      from the L{IConsumer} provider being written to.
  
      The file is closed after it has been read, or if the producer is stopped
      early.
  
      @ivar _inputFile: Any file-like object, bytes read from which will be
          written to a consumer.
  
      @ivar _cooperate: A method like L{Cooperator.cooperate} which is used to
          schedule all reads.
  
      @ivar _readSize: The number of bytes to read from C{_inputFile} at a time.
      """
  
      def __init__(self, inputFile, cooperator=task, readSize=2 ** 16):
          self._inputFile = inputFile
          self._cooperate = cooperator.cooperate
          self._readSize = readSize
          self.length = self._determineLength(inputFile)
  
      def _determineLength(self, fObj):
          """
          Determine how many bytes can be read out of C{fObj} (assuming it is not
          modified from this point on).  If the determination cannot be made,
          return C{UNKNOWN_LENGTH}.
          """
          try:
              seek = fObj.seek
              tell = fObj.tell
          except AttributeError:
              return UNKNOWN_LENGTH
          originalPosition = tell()
          seek(0, os.SEEK_END)
          end = tell()
          seek(originalPosition, os.SEEK_SET)
          return end - originalPosition
  
      def stopProducing(self):
          """
          Permanently stop writing bytes from the file to the consumer by
          stopping the underlying L{CooperativeTask}.
          """
          self._inputFile.close()
          try:
              self._task.stop()
          except task.TaskFinished:
              pass
  
      def startProducing(self, consumer):
          """
          Start a cooperative task which will read bytes from the input file and
          write them to C{consumer}.  Return a L{Deferred} which fires after all
          bytes have been written.  If this L{Deferred} is cancelled before it is
          fired, stop reading and writing bytes.
  
          @param consumer: Any L{IConsumer} provider
          """
          self._task = self._cooperate(self._writeloop(consumer))
          d = self._task.whenDone()
  
          def maybeStopped(reason):
              if reason.check(defer.CancelledError):
                  self.stopProducing()
              elif reason.check(task.TaskStopped):
                  pass
              else:
                  return reason
              # IBodyProducer.startProducing's Deferred isn't supposed to fire if
              # stopProducing is called.
              return defer.Deferred()
  
          d.addCallbacks(lambda ignored: None, maybeStopped)
          return d
  
      def _writeloop(self, consumer):
          """
          Return an iterator which reads one chunk of bytes from the input file
          and writes them to the consumer for each time it is iterated.
          """
          while True:
              bytes = self._inputFile.read(self._readSize)
              if not bytes:
                  self._inputFile.close()
                  break
              consumer.write(bytes)
              yield None
  
      def pauseProducing(self):
          """
          Temporarily suspend copying bytes from the input file to the consumer
          by pausing the L{CooperativeTask} which drives that activity.
          """
          self._task.pause()
  
      def resumeProducing(self):
          """
          Undo the effects of a previous C{pauseProducing} and resume copying
          bytes to the consumer by resuming the L{CooperativeTask} which drives
          the write activity.
          """
          self._task.resume()
  
  
  class _HTTP11ClientFactory(protocol.Factory):
      """
      A factory for L{HTTP11ClientProtocol}, used by L{HTTPConnectionPool}.
  
      @ivar _quiescentCallback: The quiescent callback to be passed to protocol
          instances, used to return them to the connection pool.
  
      @ivar _metadata: Metadata about the low-level connection details,
          used to make the repr more useful.
  
      @since: 11.1
      """
  
      def __init__(self, quiescentCallback, metadata):
          self._quiescentCallback = quiescentCallback
          self._metadata = metadata
  
      def __repr__(self) -> str:
          return "_HTTP11ClientFactory({}, {})".format(
              self._quiescentCallback, self._metadata
          )
  
      def buildProtocol(self, addr):
          return HTTP11ClientProtocol(self._quiescentCallback)
  
  
  class _RetryingHTTP11ClientProtocol:
      """
      A wrapper for L{HTTP11ClientProtocol} that automatically retries requests.
  
      @ivar _clientProtocol: The underlying L{HTTP11ClientProtocol}.
  
      @ivar _newConnection: A callable that creates a new connection for a
          retry.
      """
  
      def __init__(self, clientProtocol, newConnection):
          self._clientProtocol = clientProtocol
          self._newConnection = newConnection
  
      def _shouldRetry(self, method, exception, bodyProducer):
          """
          Indicate whether request should be retried.
  
          Only returns C{True} if method is idempotent, no response was
          received, the reason for the failed request was not due to
          user-requested cancellation, and no body was sent. The latter
          requirement may be relaxed in the future, and PUT added to approved
          method list.
  
          @param method: The method of the request.
          @type method: L{bytes}
          """
          if method not in (b"GET", b"HEAD", b"OPTIONS", b"DELETE", b"TRACE"):
              return False
          if not isinstance(
              exception,
              (RequestNotSent, RequestTransmissionFailed, ResponseNeverReceived),
          ):
              return False
          if isinstance(exception, _WrapperException):
              for aFailure in exception.reasons:
                  if aFailure.check(defer.CancelledError):
                      return False
          if bodyProducer is not None:
              return False
          return True
  
      def request(self, request):
          """
          Do a request, and retry once (with a new connection) if it fails in
          a retryable manner.
  
          @param request: A L{Request} instance that will be requested using the
              wrapped protocol.
          """
          d = self._clientProtocol.request(request)
  
          def failed(reason):
              if self._shouldRetry(request.method, reason.value, request.bodyProducer):
                  return self._newConnection().addCallback(
                      lambda connection: connection.request(request)
                  )
              else:
                  return reason
  
          d.addErrback(failed)
          return d
  
  
  class HTTPConnectionPool:
      """
      A pool of persistent HTTP connections.
  
      Features:
       - Cached connections will eventually time out.
       - Limits on maximum number of persistent connections.
  
      Connections are stored using keys, which should be chosen such that any
      connections stored under a given key can be used interchangeably.
  
      Failed requests done using previously cached connections will be retried
      once if they use an idempotent method (e.g. GET), in case the HTTP server
      timed them out.
  
      @ivar persistent: Boolean indicating whether connections should be
          persistent. Connections are persistent by default.
  
      @ivar maxPersistentPerHost: The maximum number of cached persistent
          connections for a C{host:port} destination.
      @type maxPersistentPerHost: C{int}
  
      @ivar cachedConnectionTimeout: Number of seconds a cached persistent
          connection will stay open before disconnecting.
  
      @ivar retryAutomatically: C{boolean} indicating whether idempotent
          requests should be retried once if no response was received.
  
      @ivar _factory: The factory used to connect to the proxy.
  
      @ivar _connections: Map (scheme, host, port) to lists of
          L{HTTP11ClientProtocol} instances.
  
      @ivar _timeouts: Map L{HTTP11ClientProtocol} instances to a
          C{IDelayedCall} instance of their timeout.
  
      @since: 12.1
      """
  
      _factory = _HTTP11ClientFactory
      maxPersistentPerHost = 2
      cachedConnectionTimeout = 240
      retryAutomatically = True
      _log = Logger()
  
      def __init__(self, reactor, persistent=True):
          self._reactor = reactor
          self.persistent = persistent
          self._connections = {}
          self._timeouts = {}
  
      def getConnection(self, key, endpoint):
          """
          Supply a connection, newly created or retrieved from the pool, to be
          used for one HTTP request.
  
          The connection will remain out of the pool (not available to be
          returned from future calls to this method) until one HTTP request has
          been completed over it.
  
          Afterwards, if the connection is still open, it will automatically be
          added to the pool.
  
          @param key: A unique key identifying connections that can be used
              interchangeably.
  
          @param endpoint: An endpoint that can be used to open a new connection
              if no cached connection is available.
  
          @return: A C{Deferred} that will fire with a L{HTTP11ClientProtocol}
             (or a wrapper) that can be used to send a single HTTP request.
          """
          # Try to get cached version:
          connections = self._connections.get(key)
          while connections:
              connection = connections.pop(0)
              # Cancel timeout:
              self._timeouts[connection].cancel()
              del self._timeouts[connection]
              if connection.state == "QUIESCENT":
                  if self.retryAutomatically:
                      newConnection = lambda: self._newConnection(key, endpoint)
                      connection = _RetryingHTTP11ClientProtocol(
                          connection, newConnection
                      )
                  return defer.succeed(connection)
  
          return self._newConnection(key, endpoint)
  
      def _newConnection(self, key, endpoint):
          """
          Create a new connection.
  
          This implements the new connection code path for L{getConnection}.
          """
  
          def quiescentCallback(protocol):
              self._putConnection(key, protocol)
  
          factory = self._factory(quiescentCallback, repr(endpoint))
          return endpoint.connect(factory)
  
      def _removeConnection(self, key, connection):
          """
          Remove a connection from the cache and disconnect it.
          """
          connection.transport.loseConnection()
          self._connections[key].remove(connection)
          del self._timeouts[connection]
  
      def _putConnection(self, key, connection):
          """
          Return a persistent connection to the pool. This will be called by
          L{HTTP11ClientProtocol} when the connection becomes quiescent.
          """
          if connection.state != "QUIESCENT":
              # Log with traceback for debugging purposes:
              try:
                  raise RuntimeError(
                      "BUG: Non-quiescent protocol added to connection pool."
                  )
              except:
                  self._log.failure(
                      "BUG: Non-quiescent protocol added to connection pool."
                  )
              return
          connections = self._connections.setdefault(key, [])
          if len(connections) == self.maxPersistentPerHost:
              dropped = connections.pop(0)
              dropped.transport.loseConnection()
              self._timeouts[dropped].cancel()
              del self._timeouts[dropped]
          connections.append(connection)
          cid = self._reactor.callLater(
              self.cachedConnectionTimeout, self._removeConnection, key, connection
          )
          self._timeouts[connection] = cid
  
      def closeCachedConnections(self):
          """
          Close all persistent connections and remove them from the pool.
  
          @return: L{defer.Deferred} that fires when all connections have been
              closed.
          """
          results = []
          for protocols in self._connections.values():
              for p in protocols:
                  results.append(p.abort())
          self._connections = {}
          for dc in self._timeouts.values():
              dc.cancel()
          self._timeouts = {}
          return defer.gatherResults(results).addCallback(lambda ign: None)
  
  
  class _AgentBase:
      """
      Base class offering common facilities for L{Agent}-type classes.
  
      @ivar _reactor: The C{IReactorTime} implementation which will be used by
          the pool, and perhaps by subclasses as well.
  
      @ivar _pool: The L{HTTPConnectionPool} used to manage HTTP connections.
      """
  
      def __init__(self, reactor, pool):
          if pool is None:
              pool = HTTPConnectionPool(reactor, False)
          self._reactor = reactor
          self._pool = pool
  
      def _computeHostValue(self, scheme, host, port):
          """
          Compute the string to use for the value of the I{Host} header, based on
          the given scheme, host name, and port number.
          """
          if isIPv6Address(nativeString(host)):
              host = b"[" + host + b"]"
          if (scheme, port) in ((b"http", 80), (b"https", 443)):
              return host
          return b"%b:%d" % (host, port)
  
      def _requestWithEndpoint(
          self, key, endpoint, method, parsedURI, headers, bodyProducer, requestPath
      ):
          """
          Issue a new request, given the endpoint and the path sent as part of
          the request.
          """
          if not isinstance(method, bytes):
              raise TypeError(
                  "method={!r} is {}, but must be bytes".format(method, type(method))
              )
  
          method = _ensureValidMethod(method)
  
          # Create minimal headers, if necessary:
          if headers is None:
              headers = Headers()
          if not headers.hasHeader(b"host"):
              headers = headers.copy()
              headers.addRawHeader(
                  b"host",
                  self._computeHostValue(
                      parsedURI.scheme, parsedURI.host, parsedURI.port
                  ),
              )
  
          d = self._pool.getConnection(key, endpoint)
  
          def cbConnected(proto):
              return proto.request(
                  Request._construct(
                      method,
                      requestPath,
                      headers,
                      bodyProducer,
                      persistent=self._pool.persistent,
                      parsedURI=parsedURI,
                  )
              )
  
          d.addCallback(cbConnected)
          return d
  
  
  @implementer(IAgentEndpointFactory)
  class _StandardEndpointFactory:
      """
      Standard HTTP endpoint destinations - TCP for HTTP, TCP+TLS for HTTPS.
  
      @ivar _policyForHTTPS: A web context factory which will be used to create
          SSL context objects for any SSL connections the agent needs to make.
  
      @ivar _connectTimeout: If not L{None}, the timeout passed to
          L{HostnameEndpoint} for specifying the connection timeout.
  
      @ivar _bindAddress: If not L{None}, the address passed to
          L{HostnameEndpoint} for specifying the local address to bind to.
      """
  
      def __init__(self, reactor, contextFactory, connectTimeout, bindAddress):
          """
          @param reactor: A provider to use to create endpoints.
          @type reactor: see L{HostnameEndpoint.__init__} for acceptable reactor
              types.
  
          @param contextFactory: A factory for TLS contexts, to control the
              verification parameters of OpenSSL.
          @type contextFactory: L{IPolicyForHTTPS}.
  
          @param connectTimeout: The amount of time that this L{Agent} will wait
              for the peer to accept a connection.
          @type connectTimeout: L{float} or L{None}
  
          @param bindAddress: The local address for client sockets to bind to.
          @type bindAddress: L{bytes} or L{None}
          """
          self._reactor = reactor
          self._policyForHTTPS = contextFactory
          self._connectTimeout = connectTimeout
          self._bindAddress = bindAddress
  
      def endpointForURI(self, uri):
          """
          Connect directly over TCP for C{b'http'} scheme, and TLS for
          C{b'https'}.
  
          @param uri: L{URI} to connect to.
  
          @return: Endpoint to connect to.
          @rtype: L{IStreamClientEndpoint}
          """
          kwargs = {}
          if self._connectTimeout is not None:
              kwargs["timeout"] = self._connectTimeout
          kwargs["bindAddress"] = self._bindAddress
  
          try:
              host = nativeString(uri.host)
          except UnicodeDecodeError:
              raise ValueError(
                  (
                      "The host of the provided URI ({uri.host!r}) "
                      "contains non-ASCII octets, it should be ASCII "
                      "decodable."
                  ).format(uri=uri)
              )
  
          endpoint = HostnameEndpoint(self._reactor, host, uri.port, **kwargs)
          if uri.scheme == b"http":
              return endpoint
          elif uri.scheme == b"https":
              connectionCreator = self._policyForHTTPS.creatorForNetloc(
                  uri.host, uri.port
              )
              return wrapClientTLS(connectionCreator, endpoint)
          else:
              raise SchemeNotSupported("Unsupported scheme: %r" % (uri.scheme,))
  
  
  @implementer(IAgent)
  class Agent(_AgentBase):
      """
      L{Agent} is a very basic HTTP client.  It supports I{HTTP} and I{HTTPS}
      scheme URIs.
  
      @ivar _pool: An L{HTTPConnectionPool} instance.
  
      @ivar _endpointFactory: The L{IAgentEndpointFactory} which will
          be used to create endpoints for outgoing connections.
  
      @since: 9.0
      """
  
      def __init__(
          self,
          reactor,
          contextFactory=BrowserLikePolicyForHTTPS(),
          connectTimeout=None,
          bindAddress=None,
          pool=None,
      ):
          """
          Create an L{Agent}.
  
          @param reactor: A reactor for this L{Agent} to place outgoing
              connections.
          @type reactor: see L{HostnameEndpoint.__init__} for acceptable reactor
              types.
  
          @param contextFactory: A factory for TLS contexts, to control the
              verification parameters of OpenSSL.  The default is to use a
              L{BrowserLikePolicyForHTTPS}, so unless you have special
              requirements you can leave this as-is.
          @type contextFactory: L{IPolicyForHTTPS}.
  
          @param connectTimeout: The amount of time that this L{Agent} will wait
              for the peer to accept a connection.
          @type connectTimeout: L{float}
  
          @param bindAddress: The local address for client sockets to bind to.
          @type bindAddress: L{bytes}
  
          @param pool: An L{HTTPConnectionPool} instance, or L{None}, in which
              case a non-persistent L{HTTPConnectionPool} instance will be
              created.
          @type pool: L{HTTPConnectionPool}
          """
          if not IPolicyForHTTPS.providedBy(contextFactory):
              warnings.warn(
                  repr(contextFactory)
                  + " was passed as the HTTPS policy for an Agent, but it does "
                  "not provide IPolicyForHTTPS.  Since Twisted 14.0, you must "
                  "pass a provider of IPolicyForHTTPS.",
                  stacklevel=2,
                  category=DeprecationWarning,
              )
              contextFactory = _DeprecatedToCurrentPolicyForHTTPS(contextFactory)
          endpointFactory = _StandardEndpointFactory(
              reactor, contextFactory, connectTimeout, bindAddress
          )
          self._init(reactor, endpointFactory, pool)
  
      @classmethod
      def usingEndpointFactory(cls, reactor, endpointFactory, pool=None):
          """
          Create a new L{Agent} that will use the endpoint factory to figure
          out how to connect to the server.
  
          @param reactor: A reactor for this L{Agent} to place outgoing
              connections.
          @type reactor: see L{HostnameEndpoint.__init__} for acceptable reactor
              types.
  
          @param endpointFactory: Used to construct endpoints which the
              HTTP client will connect with.
          @type endpointFactory: an L{IAgentEndpointFactory} provider.
  
          @param pool: An L{HTTPConnectionPool} instance, or L{None}, in which
              case a non-persistent L{HTTPConnectionPool} instance will be
              created.
          @type pool: L{HTTPConnectionPool}
  
          @return: A new L{Agent}.
          """
          agent = cls.__new__(cls)
          agent._init(reactor, endpointFactory, pool)
          return agent
  
      def _init(self, reactor, endpointFactory, pool):
          """
          Initialize a new L{Agent}.
  
          @param reactor: A reactor for this L{Agent} to place outgoing
              connections.
          @type reactor: see L{HostnameEndpoint.__init__} for acceptable reactor
              types.
  
          @param endpointFactory: Used to construct endpoints which the
              HTTP client will connect with.
          @type endpointFactory: an L{IAgentEndpointFactory} provider.
  
          @param pool: An L{HTTPConnectionPool} instance, or L{None}, in which
              case a non-persistent L{HTTPConnectionPool} instance will be
              created.
          @type pool: L{HTTPConnectionPool}
  
          @return: A new L{Agent}.
          """
          _AgentBase.__init__(self, reactor, pool)
          self._endpointFactory = endpointFactory
  
      def _getEndpoint(self, uri):
          """
          Get an endpoint for the given URI, using C{self._endpointFactory}.
  
          @param uri: The URI of the request.
          @type uri: L{URI}
  
          @return: An endpoint which can be used to connect to given address.
          """
          return self._endpointFactory.endpointForURI(uri)
  
      def request(self, method, uri, headers=None, bodyProducer=None):
          """
          Issue a request to the server indicated by the given C{uri}.
  
          An existing connection from the connection pool may be used or a new
          one may be created.
  
          I{HTTP} and I{HTTPS} schemes are supported in C{uri}.
  
          @see: L{twisted.web.iweb.IAgent.request}
          """
          uri = _ensureValidURI(uri.strip())
          parsedURI = URI.fromBytes(uri)
          try:
              endpoint = self._getEndpoint(parsedURI)
          except SchemeNotSupported:
              return defer.fail(Failure())
          key = (parsedURI.scheme, parsedURI.host, parsedURI.port)
          return self._requestWithEndpoint(
              key,
              endpoint,
              method,
              parsedURI,
              headers,
              bodyProducer,
              parsedURI.originForm,
          )
  
  
  @implementer(IAgent)
  class ProxyAgent(_AgentBase):
      """
      An HTTP agent able to cross HTTP proxies.
  
      @ivar _proxyEndpoint: The endpoint used to connect to the proxy.
  
      @since: 11.1
      """
  
      def __init__(self, endpoint, reactor=None, pool=None):
          if reactor is None:
              from twisted.internet import reactor
          _AgentBase.__init__(self, reactor, pool)
          self._proxyEndpoint = endpoint
  
      def request(self, method, uri, headers=None, bodyProducer=None):
          """
          Issue a new request via the configured proxy.
          """
          uri = _ensureValidURI(uri.strip())
  
          # Cache *all* connections under the same key, since we are only
          # connecting to a single destination, the proxy:
          key = ("http-proxy", self._proxyEndpoint)
  
          # To support proxying HTTPS via CONNECT, we will use key
          # ("http-proxy-CONNECT", scheme, host, port), and an endpoint that
          # wraps _proxyEndpoint with an additional callback to do the CONNECT.
          return self._requestWithEndpoint(
              key,
              self._proxyEndpoint,
              method,
              URI.fromBytes(uri),
              headers,
              bodyProducer,
              uri,
          )
  
  
  class _FakeUrllib2Request:
      """
      A fake C{urllib2.Request} object for C{cookielib} to work with.
  
      @see: U{http://docs.python.org/library/urllib2.html#request-objects}
  
      @type uri: native L{str}
      @ivar uri: Request URI.
  
      @type headers: L{twisted.web.http_headers.Headers}
      @ivar headers: Request headers.
  
      @type type: native L{str}
      @ivar type: The scheme of the URI.
  
      @type host: native L{str}
      @ivar host: The host[:port] of the URI.
  
      @since: 11.1
      """
  
      def __init__(self, uri):
          """
          Create a fake Urllib2 request.
  
          @param uri: Request URI.
          @type uri: L{bytes}
          """
          self.uri = nativeString(uri)
          self.headers = Headers()
  
          _uri = URI.fromBytes(uri)
          self.type = nativeString(_uri.scheme)
          self.host = nativeString(_uri.host)
  
          if (_uri.scheme, _uri.port) not in ((b"http", 80), (b"https", 443)):
              # If it's not a schema on the regular port, add the port.
              self.host += ":" + str(_uri.port)
  
          self.origin_req_host = nativeString(_uri.host)
          self.unverifiable = lambda _: False
  
      def has_header(self, header):
          return self.headers.hasHeader(networkString(header))
  
      def add_unredirected_header(self, name, value):
          self.headers.addRawHeader(networkString(name), networkString(value))
  
      def get_full_url(self):
          return self.uri
  
      def get_header(self, name, default=None):
          headers = self.headers.getRawHeaders(networkString(name), default)
          if headers is not None:
              headers = [nativeString(x) for x in headers]
              return headers[0]
          return None
  
      def get_host(self):
          return self.host
  
      def get_type(self):
          return self.type
  
      def is_unverifiable(self):
          # In theory this shouldn't be hardcoded.
          return False
  
  
  class _FakeUrllib2Response:
      """
      A fake C{urllib2.Response} object for C{cookielib} to work with.
  
      @type response: C{twisted.web.iweb.IResponse}
      @ivar response: Underlying Twisted Web response.
  
      @since: 11.1
      """
  
      def __init__(self, response):
          self.response = response
  
      def info(self):
          class _Meta:
              def getheaders(zelf, name):
                  # PY2
                  headers = self.response.headers.getRawHeaders(name, [])
                  return headers
  
              def get_all(zelf, name, default):
                  # PY3
                  headers = self.response.headers.getRawHeaders(
                      networkString(name), default
                  )
                  h = [nativeString(x) for x in headers]
                  return h
  
          return _Meta()
  
  
  @implementer(IAgent)
  class CookieAgent:
      """
      L{CookieAgent} extends the basic L{Agent} to add RFC-compliant
      handling of HTTP cookies.  Cookies are written to and extracted
      from a C{cookielib.CookieJar} instance.
  
      The same cookie jar instance will be used for any requests through this
      agent, mutating it whenever a I{Set-Cookie} header appears in a response.
  
      @type _agent: L{twisted.web.client.Agent}
      @ivar _agent: Underlying Twisted Web agent to issue requests through.
  
      @type cookieJar: C{cookielib.CookieJar}
      @ivar cookieJar: Initialized cookie jar to read cookies from and store
          cookies to.
  
      @since: 11.1
      """
  
      def __init__(self, agent, cookieJar):
          self._agent = agent
          self.cookieJar = cookieJar
  
      def request(self, method, uri, headers=None, bodyProducer=None):
          """
          Issue a new request to the wrapped L{Agent}.
  
          Send a I{Cookie} header if a cookie for C{uri} is stored in
          L{CookieAgent.cookieJar}. Cookies are automatically extracted and
          stored from requests.
  
          If a C{'cookie'} header appears in C{headers} it will override the
          automatic cookie header obtained from the cookie jar.
  
          @see: L{Agent.request}
          """
          if headers is None:
              headers = Headers()
          lastRequest = _FakeUrllib2Request(uri)
          # Setting a cookie header explicitly will disable automatic request
          # cookies.
          if not headers.hasHeader(b"cookie"):
              self.cookieJar.add_cookie_header(lastRequest)
              cookieHeader = lastRequest.get_header("Cookie", None)
              if cookieHeader is not None:
                  headers = headers.copy()
                  headers.addRawHeader(b"cookie", networkString(cookieHeader))
  
          d = self._agent.request(method, uri, headers, bodyProducer)
          d.addCallback(self._extractCookies, lastRequest)
          return d
  
      def _extractCookies(self, response, request):
          """
          Extract response cookies and store them in the cookie jar.
  
          @type response: L{twisted.web.iweb.IResponse}
          @param response: Twisted Web response.
  
          @param request: A urllib2 compatible request object.
          """
          resp = _FakeUrllib2Response(response)
          self.cookieJar.extract_cookies(resp, request)
          return response
  
  
  class GzipDecoder(proxyForInterface(IResponse)):  # type: ignore[misc]
      """
      A wrapper for a L{Response} instance which handles gzip'ed body.
  
      @ivar original: The original L{Response} object.
  
      @since: 11.1
      """
  
      def __init__(self, response):
          self.original = response
          self.length = UNKNOWN_LENGTH
  
      def deliverBody(self, protocol):
          """
          Override C{deliverBody} to wrap the given C{protocol} with
          L{_GzipProtocol}.
          """
          self.original.deliverBody(_GzipProtocol(protocol, self.original))
  
  
  class _GzipProtocol(proxyForInterface(IProtocol)):  # type: ignore[misc]
      """
      A L{Protocol} implementation which wraps another one, transparently
      decompressing received data.
  
      @ivar _zlibDecompress: A zlib decompress object used to decompress the data
          stream.
  
      @ivar _response: A reference to the original response, in case of errors.
  
      @since: 11.1
      """
  
      def __init__(self, protocol, response):
          self.original = protocol
          self._response = response
          self._zlibDecompress = zlib.decompressobj(16 + zlib.MAX_WBITS)
  
      def dataReceived(self, data):
          """
          Decompress C{data} with the zlib decompressor, forwarding the raw data
          to the original protocol.
          """
          try:
              rawData = self._zlibDecompress.decompress(data)
          except zlib.error:
              raise ResponseFailed([Failure()], self._response)
          if rawData:
              self.original.dataReceived(rawData)
  
      def connectionLost(self, reason):
          """
          Forward the connection lost event, flushing remaining data from the
          decompressor if any.
          """
          try:
              rawData = self._zlibDecompress.flush()
          except zlib.error:
              raise ResponseFailed([reason, Failure()], self._response)
          if rawData:
              self.original.dataReceived(rawData)
          self.original.connectionLost(reason)
  
  
  @implementer(IAgent)
  class ContentDecoderAgent:
      """
      An L{Agent} wrapper to handle encoded content.
  
      It takes care of declaring the support for content in the
      I{Accept-Encoding} header and automatically decompresses the received data
      if the I{Content-Encoding} header indicates a supported encoding.
  
      For example::
  
          agent = ContentDecoderAgent(Agent(reactor),
                                      [(b'gzip', GzipDecoder)])
  
      @param agent: The agent to wrap
      @type agent: L{IAgent}
  
      @param decoders: A sequence of (name, decoder) objects. The name
          declares which encoding the decoder supports. The decoder must accept
          an L{IResponse} and return an L{IResponse} when called. The order
          determines how the decoders are advertised to the server. Names must
          be unique.not be duplicated.
      @type decoders: sequence of (L{bytes}, L{callable}) tuples
  
      @since: 11.1
  
      @see: L{GzipDecoder}
      """
  
      def __init__(self, agent, decoders):
          self._agent = agent
          self._decoders = dict(decoders)
          self._supported = b",".join([decoder[0] for decoder in decoders])
  
      def request(self, method, uri, headers=None, bodyProducer=None):
          """
          Send a client request which declares supporting compressed content.
  
          @see: L{Agent.request}.
          """
          if headers is None:
              headers = Headers()
          else:
              headers = headers.copy()
          headers.addRawHeader(b"accept-encoding", self._supported)
          deferred = self._agent.request(method, uri, headers, bodyProducer)
          return deferred.addCallback(self._handleResponse)
  
      def _handleResponse(self, response):
          """
          Check if the response is encoded, and wrap it to handle decompression.
          """
          contentEncodingHeaders = response.headers.getRawHeaders(b"content-encoding", [])
          contentEncodingHeaders = b",".join(contentEncodingHeaders).split(b",")
          while contentEncodingHeaders:
              name = contentEncodingHeaders.pop().strip()
              decoder = self._decoders.get(name)
              if decoder is not None:
                  response = decoder(response)
              else:
                  # Add it back
                  contentEncodingHeaders.append(name)
                  break
          if contentEncodingHeaders:
              response.headers.setRawHeaders(
                  b"content-encoding", [b",".join(contentEncodingHeaders)]
              )
          else:
              response.headers.removeHeader(b"content-encoding")
          return response
  
  
  @implementer(IAgent)
  class RedirectAgent:
      """
      An L{Agent} wrapper which handles HTTP redirects.
  
      The implementation is rather strict: 301 and 302 behaves like 307, not
      redirecting automatically on methods different from I{GET} and I{HEAD}.
  
      See L{BrowserLikeRedirectAgent} for a redirecting Agent that behaves more
      like a web browser.
  
      @param redirectLimit: The maximum number of times the agent is allowed to
          follow redirects before failing with a L{error.InfiniteRedirection}.
  
      @cvar _redirectResponses: A L{list} of HTTP status codes to be redirected
          for I{GET} and I{HEAD} methods.
  
      @cvar _seeOtherResponses: A L{list} of HTTP status codes to be redirected
          for any method and the method altered to I{GET}.
  
      @since: 11.1
      """
  
      _redirectResponses = [
          http.MOVED_PERMANENTLY,
          http.FOUND,
          http.TEMPORARY_REDIRECT,
          http.PERMANENT_REDIRECT,
      ]
      _seeOtherResponses = [http.SEE_OTHER]
  
      def __init__(self, agent, redirectLimit=20):
          self._agent = agent
          self._redirectLimit = redirectLimit
  
      def request(self, method, uri, headers=None, bodyProducer=None):
          """
          Send a client request following HTTP redirects.
  
          @see: L{Agent.request}.
          """
          deferred = self._agent.request(method, uri, headers, bodyProducer)
          return deferred.addCallback(self._handleResponse, method, uri, headers, 0)
  
      def _resolveLocation(self, requestURI, location):
          """
          Resolve the redirect location against the request I{URI}.
  
          @type requestURI: C{bytes}
          @param requestURI: The request I{URI}.
  
          @type location: C{bytes}
          @param location: The redirect location.
  
          @rtype: C{bytes}
          @return: Final resolved I{URI}.
          """
          return _urljoin(requestURI, location)
  
      def _handleRedirect(self, response, method, uri, headers, redirectCount):
          """
          Handle a redirect response, checking the number of redirects already
          followed, and extracting the location header fields.
          """
          if redirectCount >= self._redirectLimit:
              err = error.InfiniteRedirection(
                  response.code, b"Infinite redirection detected", location=uri
              )
              raise ResponseFailed([Failure(err)], response)
          locationHeaders = response.headers.getRawHeaders(b"location", [])
          if not locationHeaders:
              err = error.RedirectWithNoLocation(
                  response.code, b"No location header field", uri
              )
              raise ResponseFailed([Failure(err)], response)
          location = self._resolveLocation(uri, locationHeaders[0])
          deferred = self._agent.request(method, location, headers)
  
          def _chainResponse(newResponse):
              newResponse.setPreviousResponse(response)
              return newResponse
  
          deferred.addCallback(_chainResponse)
          return deferred.addCallback(
              self._handleResponse, method, uri, headers, redirectCount + 1
          )
  
      def _handleResponse(self, response, method, uri, headers, redirectCount):
          """
          Handle the response, making another request if it indicates a redirect.
          """
          if response.code in self._redirectResponses:
              if method not in (b"GET", b"HEAD"):
                  err = error.PageRedirect(response.code, location=uri)
                  raise ResponseFailed([Failure(err)], response)
              return self._handleRedirect(response, method, uri, headers, redirectCount)
          elif response.code in self._seeOtherResponses:
              return self._handleRedirect(response, b"GET", uri, headers, redirectCount)
          return response
  
  
  class BrowserLikeRedirectAgent(RedirectAgent):
      """
      An L{Agent} wrapper which handles HTTP redirects in the same fashion as web
      browsers.
  
      Unlike L{RedirectAgent}, the implementation is more relaxed: 301 and 302
      behave like 303, redirecting automatically on any method and altering the
      redirect request to a I{GET}.
  
      @see: L{RedirectAgent}
  
      @since: 13.1
      """
  
      _redirectResponses = [http.TEMPORARY_REDIRECT]
      _seeOtherResponses = [
          http.MOVED_PERMANENTLY,
          http.FOUND,
          http.SEE_OTHER,
          http.PERMANENT_REDIRECT,
      ]
  
  
  class _ReadBodyProtocol(protocol.Protocol):
      """
      Protocol that collects data sent to it.
  
      This is a helper for L{IResponse.deliverBody}, which collects the body and
      fires a deferred with it.
  
      @ivar deferred: See L{__init__}.
      @ivar status: See L{__init__}.
      @ivar message: See L{__init__}.
  
      @ivar dataBuffer: list of byte-strings received
      @type dataBuffer: L{list} of L{bytes}
      """
  
      def __init__(self, status, message, deferred):
          """
          @param status: Status of L{IResponse}
          @ivar status: L{int}
  
          @param message: Message of L{IResponse}
          @type message: L{bytes}
  
          @param deferred: deferred to fire when response is complete
          @type deferred: L{Deferred} firing with L{bytes}
          """
          self.deferred = deferred
          self.status = status
          self.message = message
          self.dataBuffer = []
  
      def dataReceived(self, data):
          """
          Accumulate some more bytes from the response.
          """
          self.dataBuffer.append(data)
  
      def connectionLost(self, reason):
          """
          Deliver the accumulated response bytes to the waiting L{Deferred}, if
          the response body has been completely received without error.
          """
          if reason.check(ResponseDone):
              self.deferred.callback(b"".join(self.dataBuffer))
          elif reason.check(PotentialDataLoss):
              self.deferred.errback(
                  PartialDownloadError(
                      self.status, self.message, b"".join(self.dataBuffer)
                  )
              )
          else:
              self.deferred.errback(reason)
  
  
  def readBody(response):
      """
      Get the body of an L{IResponse} and return it as a byte string.
  
      This is a helper function for clients that don't want to incrementally
      receive the body of an HTTP response.
  
      @param response: The HTTP response for which the body will be read.
      @type response: L{IResponse} provider
  
      @return: A L{Deferred} which will fire with the body of the response.
          Cancelling it will close the connection to the server immediately.
      """
  
      def cancel(deferred):
          """
          Cancel a L{readBody} call, close the connection to the HTTP server
          immediately, if it is still open.
  
          @param deferred: The cancelled L{defer.Deferred}.
          """
          abort = getAbort()
          if abort is not None:
              abort()
  
      d = defer.Deferred(cancel)
      protocol = _ReadBodyProtocol(response.code, response.phrase, d)
  
      def getAbort():
          return getattr(protocol.transport, "abortConnection", None)
  
      response.deliverBody(protocol)
  
      if protocol.transport is not None and getAbort() is None:
          warnings.warn(
              "Using readBody with a transport that does not have an "
              "abortConnection method",
              category=DeprecationWarning,
              stacklevel=2,
          )
  
      return d
  
  
  __all__ = [
      "Agent",
      "BrowserLikePolicyForHTTPS",
      "BrowserLikeRedirectAgent",
      "ContentDecoderAgent",
      "CookieAgent",
      "downloadPage",
      "getPage",
      "GzipDecoder",
      "HTTPClientFactory",
      "HTTPConnectionPool",
      "HTTPDownloader",
      "HTTPPageDownloader",
      "HTTPPageGetter",
      "PartialDownloadError",
      "ProxyAgent",
      "readBody",
      "RedirectAgent",
      "RequestGenerationFailed",
      "RequestTransmissionFailed",
      "Response",
      "ResponseDone",
      "ResponseFailed",
      "ResponseNeverReceived",
      "URI",
  ]
  