Lib/urllib/request.py

"""An extensible library for opening URLs using a variety of protocols

The simplest way to use this module is to call the urlopen function,
which accepts a string containing a URL or a Request object (described
below).  It opens the URL and returns the results as file-like
object; the returned object has some extra methods described below.

The OpenerDirector manages a collection of Handler objects that do
all the actual work.  Each Handler implements a particular protocol or
option.  The OpenerDirector is a composite object that invokes the
Handlers needed to open the requested URL.  For example, the
HTTPHandler performs HTTP GET and POST requests and deals with
non-error returns.  The HTTPRedirectHandler automatically deals with
HTTP 301, 302, 303 and 307 redirect errors, and the HTTPDigestAuthHandler
deals with digest authentication.

urlopen(url, data=None) -- Basic usage is the same as original
urllib.  pass the url and optionally data to post to an HTTP URL, and
get a file-like object back.  One difference is that you can also pass
a Request instance instead of URL.  Raises a URLError (subclass of
IOError); for HTTP errors, raises an HTTPError, which can also be
treated as a valid response.

build_opener -- Function that creates a new OpenerDirector instance.
Will install the default handlers.  Accepts one or more Handlers as
arguments, either instances or Handler classes that it will
instantiate.  If one of the argument is a subclass of the default
handler, the argument will be installed instead of the default.

install_opener -- Installs a new opener as the default opener.

objects of interest:

OpenerDirector -- Sets up the User Agent as the Python-urllib client and manages
the Handler classes, while dealing with requests and responses.

Request -- An object that encapsulates the state of a request.  The
state can be as simple as the URL.  It can also include extra HTTP
headers, e.g. a User-Agent.

BaseHandler --

internals:
BaseHandler and parent
_call_chain conventions

Example usage:

import urllib.request

# set up authentication info
authinfo = urllib.request.HTTPBasicAuthHandler()
authinfo.add_password(realm='PDQ Application',
                      uri='https://mahler:8092/site-updates.py',
                      user='klem',
                      passwd='geheim$parole')

proxy_support = urllib.request.ProxyHandler({"http" : "http://ahad-haam:3128"})

# build a new opener that adds authentication and caching FTP handlers
opener = urllib.request.build_opener(proxy_support, authinfo,
                                     urllib.request.CacheFTPHandler)

# install it
urllib.request.install_opener(opener)

f = urllib.request.urlopen('http://www.python.org/')
"""

# XXX issues:
# If an authentication error handler that tries to perform
# authentication for some reason but fails, how should the error be
# signalled?  The client needs to know the HTTP error code.  But if
# the handler knows that the problem was, e.g., that it didn't know
# that hash algo that requested in the challenge, it would be good to
# pass that information along to the client, too.
# ftp errors aren't handled cleanly
# check digest against correct (i.e. non-apache) implementation

# Possible extensions:
# complex proxies  XXX not sure what exactly was meant by this
# abstract factory for opener

import base64
import bisect
import email
import hashlib
import http.client
import io
import os
import posixpath
import random
import re
import socket
import sys
import time

from urllib.error import URLError, HTTPError, ContentTooShortError
from urllib.parse import (
    urlparse, urlsplit, urljoin, unwrap, quote, unquote,
    splittype, splithost, splitport, splituser, splitpasswd,
    splitattr, splitquery, splitvalue, to_bytes, urlunparse)
from urllib.response import addinfourl, addclosehook

# check for SSL
try:
    import ssl
except:
    _have_ssl = False
else:
    _have_ssl = True

# used in User-Agent header sent
__version__ = sys.version[:3]

_opener = None
def urlopen(url, data=None, timeout=socket._GLOBAL_DEFAULT_TIMEOUT):
    global _opener
    if _opener is None:
        _opener = build_opener()
    return _opener.open(url, data, timeout)

def install_opener(opener):
    global _opener
    _opener = opener

# TODO(jhylton): Make this work with the same global opener.
_urlopener = None
def urlretrieve(url, filename=None, reporthook=None, data=None):
    global _urlopener
    if not _urlopener:
        _urlopener = FancyURLopener()
    return _urlopener.retrieve(url, filename, reporthook, data)

def urlcleanup():
    if _urlopener:
        _urlopener.cleanup()
    global _opener
    if _opener:
        _opener = None

# copied from cookielib.py
_cut_port_re = re.compile(r":\d+$", re.ASCII)
def request_host(request):
    """Return request-host, as defined by RFC 2965.

    Variation from RFC: returned value is lowercased, for convenient
    comparison.

    """
    url = request.full_url
    host = urlparse(url)[1]
    if host == "":
        host = request.get_header("Host", "")

    # remove port, if present
    host = _cut_port_re.sub("", host, 1)
    return host.lower()

class Request:

    def __init__(self, url, data=None, headers={},
                 origin_req_host=None, unverifiable=False):
        # unwrap('<URL:type://host/path>') --> 'type://host/path'
        self.full_url = unwrap(url)
        self.data = data
        self.headers = {}
        self._tunnel_host = None
        for key, value in headers.items():
            self.add_header(key, value)
        self.unredirected_hdrs = {}
        if origin_req_host is None:
            origin_req_host = request_host(self)
        self.origin_req_host = origin_req_host
        self.unverifiable = unverifiable
        self._parse()

    def _parse(self):
        self.type, rest = splittype(self.full_url)
        if self.type is None:
            raise ValueError("unknown url type: %s" % self.full_url)
        self.host, self.selector = splithost(rest)
        if self.host:
            self.host = unquote(self.host)

    def get_method(self):
        if self.data is not None:
            return "POST"
        else:
            return "GET"

    # Begin deprecated methods

    def add_data(self, data):
        if self.has_data():
            raise TypeError("Request Obj already contains data: %s" %
                            self.data)
        self.data = data

    def has_data(self):
        return self.data is not None

    def get_data(self):
        return self.data

    def get_full_url(self):
        return self.full_url

    def get_type(self):
        return self.type

    def get_host(self):
        return self.host

    def get_selector(self):
        return self.selector

    def is_unverifiable(self):
        return self.unverifiable

    def get_origin_req_host(self):
        return self.origin_req_host

    # End deprecated methods

    def set_proxy(self, host, type):
        if self.type == 'https' and not self._tunnel_host:
            self._tunnel_host = self.host
        else:
            self.type= type
            self.selector = self.full_url
        self.host = host

    def has_proxy(self):
        return self.selector == self.full_url

    def add_header(self, key, val):
        # useful for something like authentication
        self.headers[key.capitalize()] = val

    def add_unredirected_header(self, key, val):
        # will not be added to a redirected request
        self.unredirected_hdrs[key.capitalize()] = val

    def has_header(self, header_name):
        return (header_name in self.headers or
                header_name in self.unredirected_hdrs)

    def get_header(self, header_name, default=None):
        return self.headers.get(
            header_name,
            self.unredirected_hdrs.get(header_name, default))

    def header_items(self):
        hdrs = self.unredirected_hdrs.copy()
        hdrs.update(self.headers)
        return list(hdrs.items())

class OpenerDirector:
    def __init__(self):
        client_version = "Python-urllib/%s" % __version__
        self.addheaders = [('User-agent', client_version)]
        # manage the individual handlers
        self.handlers = []
        self.handle_open = {}
        self.handle_error = {}
        self.process_response = {}
        self.process_request = {}

    def add_handler(self, handler):
        if not hasattr(handler, "add_parent"):
            raise TypeError("expected BaseHandler instance, got %r" %
                            type(handler))

        added = False
        for meth in dir(handler):
            if meth in ["redirect_request", "do_open", "proxy_open"]:
                # oops, coincidental match
                continue

            i = meth.find("_")
            protocol = meth[:i]
            condition = meth[i+1:]

            if condition.startswith("error"):
                j = condition.find("_") + i + 1
                kind = meth[j+1:]
                try:
                    kind = int(kind)
                except ValueError:
                    pass
                lookup = self.handle_error.get(protocol, {})
                self.handle_error[protocol] = lookup
            elif condition == "open":
                kind = protocol
                lookup = self.handle_open
            elif condition == "response":
                kind = protocol
                lookup = self.process_response
            elif condition == "request":
                kind = protocol
                lookup = self.process_request
            else:
                continue

            handlers = lookup.setdefault(kind, [])
            if handlers:
                bisect.insort(handlers, handler)
            else:
                handlers.append(handler)
            added = True

        if added:
            # the handlers must work in an specific order, the order
            # is specified in a Handler attribute
            bisect.insort(self.handlers, handler)
            handler.add_parent(self)

    def close(self):
        # Only exists for backwards compatibility.
        pass

    def _call_chain(self, chain, kind, meth_name, *args):
        # Handlers raise an exception if no one else should try to handle
        # the request, or return None if they can't but another handler
        # could.  Otherwise, they return the response.
        handlers = chain.get(kind, ())
        for handler in handlers:
            func = getattr(handler, meth_name)
            result = func(*args)
            if result is not None:
                return result

    def open(self, fullurl, data=None, timeout=socket._GLOBAL_DEFAULT_TIMEOUT):
        # accept a URL or a Request object
        if isinstance(fullurl, str):
            req = Request(fullurl, data)
        else:
            req = fullurl
            if data is not None:
                req.data = data

        req.timeout = timeout
        protocol = req.type

        # pre-process request
        meth_name = protocol+"_request"
        for processor in self.process_request.get(protocol, []):
            meth = getattr(processor, meth_name)
            req = meth(req)

        response = self._open(req, data)

        # post-process response
        meth_name = protocol+"_response"
        for processor in self.process_response.get(protocol, []):
            meth = getattr(processor, meth_name)
            response = meth(req, response)

        return response

    def _open(self, req, data=None):
        result = self._call_chain(self.handle_open, 'default',
                                  'default_open', req)
        if result:
            return result

        protocol = req.type
        result = self._call_chain(self.handle_open, protocol, protocol +
                                  '_open', req)
        if result:
            return result

        return self._call_chain(self.handle_open, 'unknown',
                                'unknown_open', req)

    def error(self, proto, *args):
        if proto in ('http', 'https'):
            # XXX http[s] protocols are special-cased
            dict = self.handle_error['http'] # https is not different than http
            proto = args[2]  # YUCK!
            meth_name = 'http_error_%s' % proto
            http_err = 1
            orig_args = args
        else:
            dict = self.handle_error
            meth_name = proto + '_error'
            http_err = 0
        args = (dict, proto, meth_name) + args
        result = self._call_chain(*args)
        if result:
            return result

        if http_err:
            args = (dict, 'default', 'http_error_default') + orig_args
            return self._call_chain(*args)

# XXX probably also want an abstract factory that knows when it makes
# sense to skip a superclass in favor of a subclass and when it might
# make sense to include both

def build_opener(*handlers):
    """Create an opener object from a list of handlers.

    The opener will use several default handlers, including support
    for HTTP, FTP and when applicable HTTPS.

    If any of the handlers passed as arguments are subclasses of the
    default handlers, the default handlers will not be used.
    """
    def isclass(obj):
        return isinstance(obj, type) or hasattr(obj, "__bases__")

    opener = OpenerDirector()
    default_classes = [ProxyHandler, UnknownHandler, HTTPHandler,
                       HTTPDefaultErrorHandler, HTTPRedirectHandler,
                       FTPHandler, FileHandler, HTTPErrorProcessor]
    if hasattr(http.client, "HTTPSConnection"):
        default_classes.append(HTTPSHandler)
    skip = set()
    for klass in default_classes:
        for check in handlers:
            if isclass(check):
                if issubclass(check, klass):
                    skip.add(klass)
            elif isinstance(check, klass):
                skip.add(klass)
    for klass in skip:
        default_classes.remove(klass)

    for klass in default_classes:
        opener.add_handler(klass())

    for h in handlers:
        if isclass(h):
            h = h()
        opener.add_handler(h)
    return opener

class BaseHandler:
    handler_order = 500

    def add_parent(self, parent):
        self.parent = parent

    def close(self):
        # Only exists for backwards compatibility
        pass

    def __lt__(self, other):
        if not hasattr(other, "handler_order"):
            # Try to preserve the old behavior of having custom classes
            # inserted after default ones (works only for custom user
            # classes which are not aware of handler_order).
            return True
        return self.handler_order < other.handler_order


class HTTPErrorProcessor(BaseHandler):
    """Process HTTP error responses."""
    handler_order = 1000  # after all other processing

    def http_response(self, request, response):
        code, msg, hdrs = response.code, response.msg, response.info()

        # According to RFC 2616, "2xx" code indicates that the client's
        # request was successfully received, understood, and accepted.
        if not (200 <= code < 300):
            response = self.parent.error(
                'http', request, response, code, msg, hdrs)

        return response

    https_response = http_response

class HTTPDefaultErrorHandler(BaseHandler):
    def http_error_default(self, req, fp, code, msg, hdrs):
        raise HTTPError(req.full_url, code, msg, hdrs, fp)

class HTTPRedirectHandler(BaseHandler):
    # maximum number of redirections to any single URL
    # this is needed because of the state that cookies introduce
    max_repeats = 4
    # maximum total number of redirections (regardless of URL) before
    # assuming we're in a loop
    max_redirections = 10

    def redirect_request(self, req, fp, code, msg, headers, newurl):
        """Return a Request or None in response to a redirect.

        This is called by the http_error_30x methods when a
        redirection response is received.  If a redirection should
        take place, return a new Request to allow http_error_30x to
        perform the redirect.  Otherwise, raise HTTPError if no-one
        else should try to handle this url.  Return None if you can't
        but another Handler might.
        """
        m = req.get_method()
        if (not (code in (301, 302, 303, 307) and m in ("GET", "HEAD")
            or code in (301, 302, 303) and m == "POST")):
            raise HTTPError(req.full_url, code, msg, headers, fp)

        # Strictly (according to RFC 2616), 301 or 302 in response to
        # a POST MUST NOT cause a redirection without confirmation
        # from the user (of urllib.request, in this case).  In practice,
        # essentially all clients do redirect in this case, so we do
        # the same.
        # be conciliant with URIs containing a space
        newurl = newurl.replace(' ', '%20')
        CONTENT_HEADERS = ("content-length", "content-type")
        newheaders = dict((k, v) for k, v in req.headers.items()
                          if k.lower() not in CONTENT_HEADERS)
        return Request(newurl,
                       headers=newheaders,
                       origin_req_host=req.origin_req_host,
                       unverifiable=True)

    # Implementation note: To avoid the server sending us into an
    # infinite loop, the request object needs to track what URLs we
    # have already seen.  Do this by adding a handler-specific
    # attribute to the Request object.
    def http_error_302(self, req, fp, code, msg, headers):
        # Some servers (incorrectly) return multiple Location headers
        # (so probably same goes for URI).  Use first header.
        if "location" in headers:
            newurl = headers["location"]
        elif "uri" in headers:
            newurl = headers["uri"]
        else:
            return

        # fix a possible malformed URL
        urlparts = urlparse(newurl)
        if not urlparts.path:
            urlparts = list(urlparts)
            urlparts[2] = "/"
        newurl = urlunparse(urlparts)

        newurl = urljoin(req.full_url, newurl)

        # XXX Probably want to forget about the state of the current
        # request, although that might interact poorly with other
        # handlers that also use handler-specific request attributes
        new = self.redirect_request(req, fp, code, msg, headers, newurl)
        if new is None:
            return

        # loop detection
        # .redirect_dict has a key url if url was previously visited.
        if hasattr(req, 'redirect_dict'):
            visited = new.redirect_dict = req.redirect_dict
            if (visited.get(newurl, 0) >= self.max_repeats or
                len(visited) >= self.max_redirections):
                raise HTTPError(req.full_url, code,
                                self.inf_msg + msg, headers, fp)
        else:
            visited = new.redirect_dict = req.redirect_dict = {}
        visited[newurl] = visited.get(newurl, 0) + 1

        # Don't close the fp until we are sure that we won't use it
        # with HTTPError.
        fp.read()
        fp.close()

        return self.parent.open(new, timeout=req.timeout)

    http_error_301 = http_error_303 = http_error_307 = http_error_302

    inf_msg = "The HTTP server returned a redirect error that would " \
              "lead to an infinite loop.\n" \
              "The last 30x error message was:\n"


def _parse_proxy(proxy):
    """Return (scheme, user, password, host/port) given a URL or an authority.

    If a URL is supplied, it must have an authority (host:port) component.
    According to RFC 3986, having an authority component means the URL must
    have two slashes after the scheme:

    >>> _parse_proxy('file:/ftp.example.com/')
    Traceback (most recent call last):
    ValueError: proxy URL with no authority: 'file:/ftp.example.com/'

    The first three items of the returned tuple may be None.

    Examples of authority parsing:

    >>> _parse_proxy('proxy.example.com')
    (None, None, None, 'proxy.example.com')
    >>> _parse_proxy('proxy.example.com:3128')
    (None, None, None, 'proxy.example.com:3128')

    The authority component may optionally include userinfo (assumed to be
    username:password):

    >>> _parse_proxy('joe:password@proxy.example.com')
    (None, 'joe', 'password', 'proxy.example.com')
    >>> _parse_proxy('joe:password@proxy.example.com:3128')
    (None, 'joe', 'password', 'proxy.example.com:3128')

    Same examples, but with URLs instead:

    >>> _parse_proxy('http://proxy.example.com/')
    ('http', None, None, 'proxy.example.com')
    >>> _parse_proxy('http://proxy.example.com:3128/')
    ('http', None, None, 'proxy.example.com:3128')
    >>> _parse_proxy('http://joe:password@proxy.example.com/')
    ('http', 'joe', 'password', 'proxy.example.com')
    >>> _parse_proxy('http://joe:password@proxy.example.com:3128')
    ('http', 'joe', 'password', 'proxy.example.com:3128')

    Everything after the authority is ignored:

    >>> _parse_proxy('ftp://joe:password@proxy.example.com/rubbish:3128')
    ('ftp', 'joe', 'password', 'proxy.example.com')

    Test for no trailing '/' case:

    >>> _parse_proxy('http://joe:password@proxy.example.com')
    ('http', 'joe', 'password', 'proxy.example.com')

    """
    scheme, r_scheme = splittype(proxy)
    if not r_scheme.startswith("/"):
        # authority
        scheme = None
        authority = proxy
    else:
        # URL
        if not r_scheme.startswith("//"):
            raise ValueError("proxy URL with no authority: %r" % proxy)
        # We have an authority, so for RFC 3986-compliant URLs (by ss 3.
        # and 3.3.), path is empty or starts with '/'
        end = r_scheme.find("/", 2)
        if end == -1:
            end = None
        authority = r_scheme[2:end]
    userinfo, hostport = splituser(authority)
    if userinfo is not None:
        user, password = splitpasswd(userinfo)
    else:
        user = password = None
    return scheme, user, password, hostport

class ProxyHandler(BaseHandler):
    # Proxies must be in front
    handler_order = 100

    def __init__(self, proxies=None):
        if proxies is None:
            proxies = getproxies()
        assert hasattr(proxies, 'keys'), "proxies must be a mapping"
        self.proxies = proxies
        for type, url in proxies.items():
            setattr(self, '%s_open' % type,
                    lambda r, proxy=url, type=type, meth=self.proxy_open: \
                    meth(r, proxy, type))

    def proxy_open(self, req, proxy, type):
        orig_type = req.type
        proxy_type, user, password, hostport = _parse_proxy(proxy)
        if proxy_type is None:
            proxy_type = orig_type

        if req.host and proxy_bypass(req.host):
            return None

        if user and password:
            user_pass = '%s:%s' % (unquote(user),
                                   unquote(password))
            creds = base64.b64encode(user_pass.encode()).decode("ascii")
            req.add_header('Proxy-authorization', 'Basic ' + creds)
        hostport = unquote(hostport)
        req.set_proxy(hostport, proxy_type)
        if orig_type == proxy_type or orig_type == 'https':
            # let other handlers take care of it
            return None
        else:
            # need to start over, because the other handlers don't
            # grok the proxy's URL type
            # e.g. if we have a constructor arg proxies like so:
            # {'http': 'ftp://proxy.example.com'}, we may end up turning
            # a request for http://acme.example.com/a into one for
            # ftp://proxy.example.com/a
            return self.parent.open(req, timeout=req.timeout)

class HTTPPasswordMgr:

    def __init__(self):
        self.passwd = {}

    def add_password(self, realm, uri, user, passwd):
        # uri could be a single URI or a sequence
        if isinstance(uri, str):
            uri = [uri]
        if not realm in self.passwd:
            self.passwd[realm] = {}
        for default_port in True, False:
            reduced_uri = tuple(
                [self.reduce_uri(u, default_port) for u in uri])
            self.passwd[realm][reduced_uri] = (user, passwd)

    def find_user_password(self, realm, authuri):
        domains = self.passwd.get(realm, {})
        for default_port in True, False:
            reduced_authuri = self.reduce_uri(authuri, default_port)
            for uris, authinfo in domains.items():
                for uri in uris:
                    if self.is_suburi(uri, reduced_authuri):
                        return authinfo
        return None, None

    def reduce_uri(self, uri, default_port=True):
        """Accept authority or URI and extract only the authority and path."""
        # note HTTP URLs do not have a userinfo component
        parts = urlsplit(uri)
        if parts[1]:
            # URI
            scheme = parts[0]
            authority = parts[1]
            path = parts[2] or '/'
        else:
            # host or host:port
            scheme = None
            authority = uri
            path = '/'
        host, port = splitport(authority)
        if default_port and port is None and scheme is not None:
            dport = {"http": 80,
                     "https": 443,
                     }.get(scheme)
            if dport is not None:
                authority = "%s:%d" % (host, dport)
        return authority, path

    def is_suburi(self, base, test):
        """Check if test is below base in a URI tree

        Both args must be URIs in reduced form.
        """
        if base == test:
            return True
        if base[0] != test[0]:
            return False
        common = posixpath.commonprefix((base[1], test[1]))
        if len(common) == len(base[1]):
            return True
        return False


class HTTPPasswordMgrWithDefaultRealm(HTTPPasswordMgr):

    def find_user_password(self, realm, authuri):
        user, password = HTTPPasswordMgr.find_user_password(self, realm,
                                                            authuri)
        if user is not None:
            return user, password
        return HTTPPasswordMgr.find_user_password(self, None, authuri)


class AbstractBasicAuthHandler:

    # XXX this allows for multiple auth-schemes, but will stupidly pick
    # the last one with a realm specified.

    # allow for double- and single-quoted realm values
    # (single quotes are a violation of the RFC, but appear in the wild)
    rx = re.compile('(?:.*,)*[ \t]*([^ \t]+)[ \t]+'
                    'realm=(["\'])(.*?)\\2', re.I)

    # XXX could pre-emptively send auth info already accepted (RFC 2617,
    # end of section 2, and section 1.2 immediately after "credentials"
    # production).

    def __init__(self, password_mgr=None):
        if password_mgr is None:
            password_mgr = HTTPPasswordMgr()
        self.passwd = password_mgr
        self.add_password = self.passwd.add_password

    def http_error_auth_reqed(self, authreq, host, req, headers):
        # host may be an authority (without userinfo) or a URL with an
        # authority
        # XXX could be multiple headers
        authreq = headers.get(authreq, None)
        if authreq:
            mo = AbstractBasicAuthHandler.rx.search(authreq)
            if mo:
                scheme, quote, realm = mo.groups()
                if scheme.lower() == 'basic':
                    return self.retry_http_basic_auth(host, req, realm)

    def retry_http_basic_auth(self, host, req, realm):
        user, pw = self.passwd.find_user_password(realm, host)
        if pw is not None:
            raw = "%s:%s" % (user, pw)
            auth = "Basic " + base64.b64encode(raw.encode()).decode("ascii")
            if req.headers.get(self.auth_header, None) == auth:
                return None
            req.add_unredirected_header(self.auth_header, auth)
            return self.parent.open(req, timeout=req.timeout)
        else:
            return None


class HTTPBasicAuthHandler(AbstractBasicAuthHandler, BaseHandler):

    auth_header = 'Authorization'

    def http_error_401(self, req, fp, code, msg, headers):
        url = req.full_url
        return self.http_error_auth_reqed('www-authenticate',
                                          url, req, headers)


class ProxyBasicAuthHandler(AbstractBasicAuthHandler, BaseHandler):

    auth_header = 'Proxy-authorization'

    def http_error_407(self, req, fp, code, msg, headers):
        # http_error_auth_reqed requires that there is no userinfo component in
        # authority.  Assume there isn't one, since urllib.request does not (and
        # should not, RFC 3986 s. 3.2.1) support requests for URLs containing
        # userinfo.
        authority = req.host
        return self.http_error_auth_reqed('proxy-authenticate',
                                          authority, req, headers)


def randombytes(n):
    """Return n random bytes."""
    return os.urandom(n)

class AbstractDigestAuthHandler:
    # Digest authentication is specified in RFC 2617.

    # XXX The client does not inspect the Authentication-Info header
    # in a successful response.

    # XXX It should be possible to test this implementation against
    # a mock server that just generates a static set of challenges.

    # XXX qop="auth-int" supports is shaky

    def __init__(self, passwd=None):
        if passwd is None:
            passwd = HTTPPasswordMgr()
        self.passwd = passwd
        self.add_password = self.passwd.add_password
        self.retried = 0
        self.nonce_count = 0
        self.last_nonce = None

    def reset_retry_count(self):
        self.retried = 0

    def http_error_auth_reqed(self, auth_header, host, req, headers):
        authreq = headers.get(auth_header, None)
        if self.retried > 5:
            # Don't fail endlessly - if we failed once, we'll probably
            # fail a second time. Hm. Unless the Password Manager is
            # prompting for the information. Crap. This isn't great
            # but it's better than the current 'repeat until recursion
            # depth exceeded' approach <wink>
            raise HTTPError(req.full_url, 401, "digest auth failed",
                            headers, None)
        else:
            self.retried += 1
        if authreq:
            scheme = authreq.split()[0]
            if scheme.lower() == 'digest':
                return self.retry_http_digest_auth(req, authreq)

    def retry_http_digest_auth(self, req, auth):
        token, challenge = auth.split(' ', 1)
        chal = parse_keqv_list(filter(None, parse_http_list(challenge)))
        auth = self.get_authorization(req, chal)
        if auth:
            auth_val = 'Digest %s' % auth
            if req.headers.get(self.auth_header, None) == auth_val:
                return None
            req.add_unredirected_header(self.auth_header, auth_val)
            resp = self.parent.open(req, timeout=req.timeout)
            return resp

    def get_cnonce(self, nonce):
        # The cnonce-value is an opaque
        # quoted string value provided by the client and used by both client
        # and server to avoid chosen plaintext attacks, to provide mutual
        # authentication, and to provide some message integrity protection.
        # This isn't a fabulous effort, but it's probably Good Enough.
        s = "%s:%s:%s:" % (self.nonce_count, nonce, time.ctime())
        b = s.encode("ascii") + randombytes(8)
        dig = hashlib.sha1(b).hexdigest()
        return dig[:16]

    def get_authorization(self, req, chal):
        try:
            realm = chal['realm']
            nonce = chal['nonce']
            qop = chal.get('qop')
            algorithm = chal.get('algorithm', 'MD5')
            # mod_digest doesn't send an opaque, even though it isn't
            # supposed to be optional
            opaque = chal.get('opaque', None)
        except KeyError:
            return None

        H, KD = self.get_algorithm_impls(algorithm)
        if H is None:
            return None

        user, pw = self.passwd.find_user_password(realm, req.full_url)
        if user is None:
            return None

        # XXX not implemented yet
        if req.data is not None:
            entdig = self.get_entity_digest(req.data, chal)
        else:
            entdig = None

        A1 = "%s:%s:%s" % (user, realm, pw)
        A2 = "%s:%s" % (req.get_method(),
                        # XXX selector: what about proxies and full urls
                        req.selector)
        if qop == 'auth':
            if nonce == self.last_nonce:
                self.nonce_count += 1
            else:
                self.nonce_count = 1
                self.last_nonce = nonce
            ncvalue = '%08x' % self.nonce_count
            cnonce = self.get_cnonce(nonce)
            noncebit = "%s:%s:%s:%s:%s" % (nonce, ncvalue, cnonce, qop, H(A2))
            respdig = KD(H(A1), noncebit)
        elif qop is None:
            respdig = KD(H(A1), "%s:%s" % (nonce, H(A2)))
        else:
            # XXX handle auth-int.
            raise URLError("qop '%s' is not supported." % qop)

        # XXX should the partial digests be encoded too?

        base = 'username="%s", realm="%s", nonce="%s", uri="%s", ' \
               'response="%s"' % (user, realm, nonce, req.selector,
                                  respdig)
        if opaque:
            base += ', opaque="%s"' % opaque
        if entdig:
            base += ', digest="%s"' % entdig
        base += ', algorithm="%s"' % algorithm
        if qop:
            base += ', qop=auth, nc=%s, cnonce="%s"' % (ncvalue, cnonce)
        return base

    def get_algorithm_impls(self, algorithm):
        # lambdas assume digest modules are imported at the top level
        if algorithm == 'MD5':
            H = lambda x: hashlib.md5(x.encode("ascii")).hexdigest()
        elif algorithm == 'SHA':
            H = lambda x: hashlib.sha1(x.encode("ascii")).hexdigest()
        # XXX MD5-sess
        KD = lambda s, d: H("%s:%s" % (s, d))
        return H, KD

    def get_entity_digest(self, data, chal):
        # XXX not implemented yet
        return None


class HTTPDigestAuthHandler(BaseHandler, AbstractDigestAuthHandler):
    """An authentication protocol defined by RFC 2069

    Digest authentication improves on basic authentication because it
    does not transmit passwords in the clear.
    """

    auth_header = 'Authorization'
    handler_order = 490  # before Basic auth

    def http_error_401(self, req, fp, code, msg, headers):
        host = urlparse(req.full_url)[1]
        retry = self.http_error_auth_reqed('www-authenticate',
                                           host, req, headers)
        self.reset_retry_count()
        return retry


class ProxyDigestAuthHandler(BaseHandler, AbstractDigestAuthHandler):

    auth_header = 'Proxy-Authorization'
    handler_order = 490  # before Basic auth

    def http_error_407(self, req, fp, code, msg, headers):
        host = req.host
        retry = self.http_error_auth_reqed('proxy-authenticate',
                                           host, req, headers)
        self.reset_retry_count()
        return retry

class AbstractHTTPHandler(BaseHandler):

    def __init__(self, debuglevel=0):
        self._debuglevel = debuglevel

    def set_http_debuglevel(self, level):
        self._debuglevel = level

    def do_request_(self, request):
        host = request.host
        if not host:
            raise URLError('no host given')

        if request.data is not None:  # POST
            data = request.data
            if not request.has_header('Content-type'):
                request.add_unredirected_header(
                    'Content-type',
                    'application/x-www-form-urlencoded')
            if not request.has_header('Content-length'):
                request.add_unredirected_header(
                    'Content-length', '%d' % len(data))

        sel_host = host
        if request.has_proxy():
            scheme, sel = splittype(request.selector)
            sel_host, sel_path = splithost(sel)
        if not request.has_header('Host'):
            request.add_unredirected_header('Host', sel_host)
        for name, value in self.parent.addheaders:
            name = name.capitalize()
            if not request.has_header(name):
                request.add_unredirected_header(name, value)

        return request

    def do_open(self, http_class, req):
        """Return an HTTPResponse object for the request, using http_class.

        http_class must implement the HTTPConnection API from http.client.
        """
        host = req.host
        if not host:
            raise URLError('no host given')

        h = http_class(host, timeout=req.timeout) # will parse host:port
        headers = dict(req.headers)
        headers.update(req.unredirected_hdrs)

        # TODO(jhylton): Should this be redesigned to handle
        # persistent connections?

        # We want to make an HTTP/1.1 request, but the addinfourl
        # class isn't prepared to deal with a persistent connection.
        # It will try to read all remaining data from the socket,
        # which will block while the server waits for the next request.
        # So make sure the connection gets closed after the (only)
        # request.
        headers["Connection"] = "close"
        headers = dict((name.title(), val) for name, val in headers.items())

        if req._tunnel_host:
            tunnel_headers = {}
            proxy_auth_hdr = "Proxy-Authorization"
            if proxy_auth_hdr in headers:
                tunnel_headers[proxy_auth_hdr] = headers[proxy_auth_hdr]
                # Proxy-Authorization should not be sent to origin
                # server.
                del headers[proxy_auth_hdr]
            h._set_tunnel(req._tunnel_host, headers=tunnel_headers)

        try:
            h.request(req.get_method(), req.selector, req.data, headers)
            r = h.getresponse()  # an HTTPResponse instance
        except socket.error as err:
            raise URLError(err)

        r.url = req.full_url
        # This line replaces the .msg attribute of the HTTPResponse
        # with .headers, because urllib clients expect the response to
        # have the reason in .msg.  It would be good to mark this
        # attribute is deprecated and get then to use info() or
        # .headers.
        r.msg = r.reason
        return r


class HTTPHandler(AbstractHTTPHandler):

    def http_open(self, req):
        return self.do_open(http.client.HTTPConnection, req)

    http_request = AbstractHTTPHandler.do_request_

if hasattr(http.client, 'HTTPSConnection'):
    class HTTPSHandler(AbstractHTTPHandler):

        def https_open(self, req):
            return self.do_open(http.client.HTTPSConnection, req)

        https_request = AbstractHTTPHandler.do_request_

class HTTPCookieProcessor(BaseHandler):
    def __init__(self, cookiejar=None):
        import http.cookiejar
        if cookiejar is None:
            cookiejar = http.cookiejar.CookieJar()
        self.cookiejar = cookiejar

    def http_request(self, request):
        self.cookiejar.add_cookie_header(request)
        return request

    def http_response(self, request, response):
        self.cookiejar.extract_cookies(response, request)
        return response

    https_request = http_request
    https_response = http_response

class UnknownHandler(BaseHandler):
    def unknown_open(self, req):
        type = req.type
        raise URLError('unknown url type: %s' % type)

def parse_keqv_list(l):
    """Parse list of key=value strings where keys are not duplicated."""
    parsed = {}
    for elt in l:
        k, v = elt.split('=', 1)
        if v[0] == '"' and v[-1] == '"':
            v = v[1:-1]
        parsed[k] = v
    return parsed

def parse_http_list(s):
    """Parse lists as described by RFC 2068 Section 2.

    In particular, parse comma-separated lists where the elements of
    the list may include quoted-strings.  A quoted-string could
    contain a comma.  A non-quoted string could have quotes in the
    middle.  Neither commas nor quotes count if they are escaped.
    Only double-quotes count, not single-quotes.
    """
    res = []
    part = ''

    escape = quote = False
    for cur in s:
        if escape:
            part += cur
            escape = False
            continue
        if quote:
            if cur == '\\':
                escape = True
                continue
            elif cur == '"':
                quote = False
            part += cur
            continue

        if cur == ',':
            res.append(part)
            part = ''
            continue

        if cur == '"':
            quote = True

        part += cur

    # append last part
    if part:
        res.append(part)

    return [part.strip() for part in res]

class FileHandler(BaseHandler):
    # Use local file or FTP depending on form of URL
    def file_open(self, req):
        url = req.selector
        if url[:2] == '//' and url[2:3] != '/':
            req.type = 'ftp'
            return self.parent.open(req)
        else:
            return self.open_local_file(req)

    # names for the localhost
    names = None
    def get_names(self):
        if FileHandler.names is None:
            try:
                FileHandler.names = tuple(
                    socket.gethostbyname_ex('localhost')[2] +
                    socket.gethostbyname_ex(socket.gethostname())[2])
            except socket.gaierror:
                FileHandler.names = (socket.gethostbyname('localhost'),)
        return FileHandler.names

    # not entirely sure what the rules are here
    def open_local_file(self, req):
        import email.utils
        import mimetypes
        host = req.host
        file = req.selector
        localfile = url2pathname(file)
        try:
            stats = os.stat(localfile)
            size = stats.st_size
            modified = email.utils.formatdate(stats.st_mtime, usegmt=True)
            mtype = mimetypes.guess_type(file)[0]
            headers = email.message_from_string(
                'Content-type: %s\nContent-length: %d\nLast-modified: %s\n' %
                (mtype or 'text/plain', size, modified))
            if host:
                host, port = splitport(host)
            if not host or \
                (not port and _safe_gethostbyname(host) in self.get_names()):
                return addinfourl(open(localfile, 'rb'), headers, 'file:'+file)
        except OSError as msg:
            # users shouldn't expect OSErrors coming from urlopen()
            raise URLError(msg)
        raise URLError('file not on local host')

def _safe_gethostbyname(host):
    try:
        return socket.gethostbyname(host)
    except socket.gaierror:
        return None

class FTPHandler(BaseHandler):
    def ftp_open(self, req):
        import ftplib
        import mimetypes
        host = req.host
        if not host:
            raise URLError('ftp error: no host given')
        host, port = splitport(host)
        if port is None:
            port = ftplib.FTP_PORT
        else:
            port = int(port)

        # username/password handling
        user, host = splituser(host)
        if user:
            user, passwd = splitpasswd(user)
        else:
            passwd = None
        host = unquote(host)
        user = unquote(user or '')
        passwd = unquote(passwd or '')

        try:
            host = socket.gethostbyname(host)
        except socket.error as msg:
            raise URLError(msg)
        path, attrs = splitattr(req.selector)
        dirs = path.split('/')
        dirs = list(map(unquote, dirs))
        dirs, file = dirs[:-1], dirs[-1]
        if dirs and not dirs[0]:
            dirs = dirs[1:]
        try:
            fw = self.connect_ftp(user, passwd, host, port, dirs, req.timeout)
            type = file and 'I' or 'D'
            for attr in attrs:
                attr, value = splitvalue(attr)
                if attr.lower() == 'type' and \
                   value in ('a', 'A', 'i', 'I', 'd', 'D'):
                    type = value.upper()
            fp, retrlen = fw.retrfile(file, type)
            headers = ""
            mtype = mimetypes.guess_type(req.full_url)[0]
            if mtype:
                headers += "Content-type: %s\n" % mtype
            if retrlen is not None and retrlen >= 0:
                headers += "Content-length: %d\n" % retrlen
            headers = email.message_from_string(headers)
            return addinfourl(fp, headers, req.full_url)
        except ftplib.all_errors as msg:
            exc = URLError('ftp error: %s' % msg)
            raise exc.with_traceback(sys.exc_info()[2])

    def connect_ftp(self, user, passwd, host, port, dirs, timeout):
        fw = ftpwrapper(user, passwd, host, port, dirs, timeout)
        return fw

class CacheFTPHandler(FTPHandler):
    # XXX would be nice to have pluggable cache strategies
    # XXX this stuff is definitely not thread safe
    def __init__(self):
        self.cache = {}
        self.timeout = {}
        self.soonest = 0
        self.delay = 60
        self.max_conns = 16

    def setTimeout(self, t):
        self.delay = t

    def setMaxConns(self, m):
        self.max_conns = m

    def connect_ftp(self, user, passwd, host, port, dirs, timeout):
        key = user, host, port, '/'.join(dirs), timeout
        if key in self.cache:
            self.timeout[key] = time.time() + self.delay
        else:
            self.cache[key] = ftpwrapper(user, passwd, host, port,
                                         dirs, timeout)
            self.timeout[key] = time.time() + self.delay
        self.check_cache()
        return self.cache[key]

    def check_cache(self):
        # first check for old ones
        t = time.time()
        if self.soonest <= t:
            for k, v in list(self.timeout.items()):
                if v < t:
                    self.cache[k].close()
                    del self.cache[k]
                    del self.timeout[k]
        self.soonest = min(list(self.timeout.values()))

        # then check the size
        if len(self.cache) == self.max_conns:
            for k, v in list(self.timeout.items()):
                if v == self.soonest:
                    del self.cache[k]
                    del self.timeout[k]
                    break
            self.soonest = min(list(self.timeout.values()))

# Code move from the old urllib module

MAXFTPCACHE = 10        # Trim the ftp cache beyond this size

# Helper for non-unix systems
if os.name == 'mac':
    from macurl2path import url2pathname, pathname2url
elif os.name == 'nt':
    from nturl2path import url2pathname, pathname2url
else:
    def url2pathname(pathname):
        """OS-specific conversion from a relative URL of the 'file' scheme
        to a file system path; not recommended for general use."""
        return unquote(pathname)

    def pathname2url(pathname):
        """OS-specific conversion from a file system path to a relative URL
        of the 'file' scheme; not recommended for general use."""
        return quote(pathname)

# This really consists of two pieces:
# (1) a class which handles opening of all sorts of URLs
#     (plus assorted utilities etc.)
# (2) a set of functions for parsing URLs
# XXX Should these be separated out into different modules?


ftpcache = {}
class URLopener:
    """Class to open URLs.
    This is a class rather than just a subroutine because we may need
    more than one set of global protocol-specific options.
    Note -- this is a base class for those who don't want the
    automatic handling of errors type 302 (relocated) and 401
    (authorization needed)."""

    __tempfiles = None

    version = "Python-urllib/%s" % __version__

    # Constructor
    def __init__(self, proxies=None, **x509):
        if proxies is None:
            proxies = getproxies()
        assert hasattr(proxies, 'keys'), "proxies must be a mapping"
        self.proxies = proxies
        self.key_file = x509.get('key_file')
        self.cert_file = x509.get('cert_file')
        self.addheaders = [('User-Agent', self.version)]
        self.__tempfiles = []
        self.__unlink = os.unlink # See cleanup()
        self.tempcache = None
        # Undocumented feature: if you assign {} to tempcache,
        # it is used to cache files retrieved with
        # self.retrieve().  This is not enabled by default
        # since it does not work for changing documents (and I
        # haven't got the logic to check expiration headers
        # yet).
        self.ftpcache = ftpcache
        # Undocumented feature: you can use a different
        # ftp cache by assigning to the .ftpcache member;
        # in case you want logically independent URL openers
        # XXX This is not threadsafe.  Bah.

    def __del__(self):
        self.close()

    def close(self):
        self.cleanup()

    def cleanup(self):
        # This code sometimes runs when the rest of this module
        # has already been deleted, so it can't use any globals
        # or import anything.
        if self.__tempfiles:
            for file in self.__tempfiles:
                try:
                    self.__unlink(file)
                except OSError:
                    pass
            del self.__tempfiles[:]
        if self.tempcache:
            self.tempcache.clear()

    def addheader(self, *args):
        """Add a header to be used by the HTTP interface only
        e.g. u.addheader('Accept', 'sound/basic')"""
        self.addheaders.append(args)

    # External interface
    def open(self, fullurl, data=None):
        """Use URLopener().open(file) instead of open(file, 'r')."""
        fullurl = unwrap(to_bytes(fullurl))
        fullurl = quote(fullurl, safe="%/:=&?~#+!$,;'@()*[]|")
        if self.tempcache and fullurl in self.tempcache:
            filename, headers = self.tempcache[fullurl]
            fp = open(filename, 'rb')
            return addinfourl(fp, headers, fullurl)
        urltype, url = splittype(fullurl)
        if not urltype:
            urltype = 'file'
        if urltype in self.proxies:
            proxy = self.proxies[urltype]
            urltype, proxyhost = splittype(proxy)
            host, selector = splithost(proxyhost)
            url = (host, fullurl) # Signal special case to open_*()
        else:
            proxy = None
        name = 'open_' + urltype
        self.type = urltype
        name = name.replace('-', '_')
        if not hasattr(self, name):
            if proxy:
                return self.open_unknown_proxy(proxy, fullurl, data)
            else:
                return self.open_unknown(fullurl, data)
        try:
            if data is None:
                return getattr(self, name)(url)
            else:
                return getattr(self, name)(url, data)
        except socket.error as msg:
            raise IOError('socket error', msg).with_traceback(sys.exc_info()[2])

    def open_unknown(self, fullurl, data=None):
        """Overridable interface to open unknown URL type."""
        type, url = splittype(fullurl)
        raise IOError('url error', 'unknown url type', type)

    def open_unknown_proxy(self, proxy, fullurl, data=None):
        """Overridable interface to open unknown URL type."""
        type, url = splittype(fullurl)
        raise IOError('url error', 'invalid proxy for %s' % type, proxy)

    # External interface
    def retrieve(self, url, filename=None, reporthook=None, data=None):
        """retrieve(url) returns (filename, headers) for a local object
        or (tempfilename, headers) for a remote object."""
        url = unwrap(to_bytes(url))
        if self.tempcache and url in self.tempcache:
            return self.tempcache[url]
        type, url1 = splittype(url)
        if filename is None and (not type or type == 'file'):
            try:
                fp = self.open_local_file(url1)
                hdrs = fp.info()
                del fp
                return url2pathname(splithost(url1)[1]), hdrs
            except IOError as msg:
                pass
        fp = self.open(url, data)
        try:
            headers = fp.info()
            if filename:
                tfp = open(filename, 'wb')
            else:
                import tempfile
                garbage, path = splittype(url)
                garbage, path = splithost(path or "")
                path, garbage = splitquery(path or "")
                path, garbage = splitattr(path or "")
                suffix = os.path.splitext(path)[1]
                (fd, filename) = tempfile.mkstemp(suffix)
                self.__tempfiles.append(filename)
                tfp = os.fdopen(fd, 'wb')
            try:
                result = filename, headers
                if self.tempcache is not None:
                    self.tempcache[url] = result
                bs = 1024*8
                size = -1
                read = 0
                blocknum = 0
                if reporthook:
                    if "content-length" in headers:
                        size = int(headers["Content-Length"])
                    reporthook(blocknum, bs, size)
                while 1:
                    block = fp.read(bs)
                    if not block:
                        break
                    read += len(block)
                    tfp.write(block)
                    blocknum += 1
                    if reporthook:
                        reporthook(blocknum, bs, size)
            finally:
                tfp.close()
        finally:
            fp.close()
        del fp
        del tfp

        # raise exception if actual size does not match content-length header
        if size >= 0 and read < size:
            raise ContentTooShortError(
                "retrieval incomplete: got only %i out of %i bytes"
                % (read, size), result)

        return result

    # Each method named open_<type> knows how to open that type of URL

    def _open_generic_http(self, connection_factory, url, data):
        """Make an HTTP connection using connection_class.

        This is an internal method that should be called from
        open_http() or open_https().

        Arguments:
        - connection_factory should take a host name and return an
          HTTPConnection instance.
        - url is the url to retrieval or a host, relative-path pair.
        - data is payload for a POST request or None.
        """

        user_passwd = None
        proxy_passwd= None
        if isinstance(url, str):
            host, selector = splithost(url)
            if host:
                user_passwd, host = splituser(host)
                host = unquote(host)
            realhost = host
        else:
            host, selector = url
            # check whether the proxy contains authorization information
            proxy_passwd, host = splituser(host)
            # now we proceed with the url we want to obtain
            urltype, rest = splittype(selector)
            url = rest
            user_passwd = None
            if urltype.lower() != 'http':
                realhost = None
            else:
                realhost, rest = splithost(rest)
                if realhost:
                    user_passwd, realhost = splituser(realhost)
                if user_passwd:
                    selector = "%s://%s%s" % (urltype, realhost, rest)
                if proxy_bypass(realhost):
                    host = realhost

            #print "proxy via http:", host, selector
        if not host: raise IOError('http error', 'no host given')

        if proxy_passwd:
            import base64
            proxy_auth = base64.b64encode(proxy_passwd).strip()
        else:
            proxy_auth = None

        if user_passwd:
            import base64
            auth = base64.b64encode(user_passwd).strip()
        else:
            auth = None
        http_conn = connection_factory(host)
        headers = {}
        if proxy_auth:
            headers["Proxy-Authorization"] = "Basic %s" % proxy_auth
        if auth:
            headers["Authorization"] =  "Basic %s" % auth
        if realhost:
            headers["Host"] = realhost
        for header, value in self.addheaders:
            headers[header] = value

        if data is not None:
            headers["Content-Type"] = "application/x-www-form-urlencoded"
            http_conn.request("POST", selector, data, headers)
        else:
            http_conn.request("GET", selector, headers=headers)

        try:
            response = http_conn.getresponse()
        except http.client.BadStatusLine:
            # something went wrong with the HTTP status line
            raise URLError("http protocol error: bad status line")

        # According to RFC 2616, "2xx" code indicates that the client's
        # request was successfully received, understood, and accepted.
        if 200 <= response.status < 300:
            return addinfourl(response, response.msg, "http:" + url,
                              response.status)
        else:
            return self.http_error(
                url, response.fp,
                response.status, response.reason, response.msg, data)

    def open_http(self, url, data=None):
        """Use HTTP protocol."""
        return self._open_generic_http(http.client.HTTPConnection, url, data)

    def http_error(self, url, fp, errcode, errmsg, headers, data=None):
        """Handle http errors.

        Derived class can override this, or provide specific handlers
        named http_error_DDD where DDD is the 3-digit error code."""
        # First check if there's a specific handler for this error
        name = 'http_error_%d' % errcode
        if hasattr(self, name):
            method = getattr(self, name)
            if data is None:
                result = method(url, fp, errcode, errmsg, headers)
            else:
                result = method(url, fp, errcode, errmsg, headers, data)
            if result: return result
        return self.http_error_default(url, fp, errcode, errmsg, headers)

    def http_error_default(self, url, fp, errcode, errmsg, headers):
        """Default error handler: close the connection and raise IOError."""
        void = fp.read()
        fp.close()
        raise HTTPError(url, errcode, errmsg, headers, None)

    if _have_ssl:
        def _https_connection(self, host):
            return http.client.HTTPSConnection(host,
                                           key_file=self.key_file,
                                           cert_file=self.cert_file)

        def open_https(self, url, data=None):
            """Use HTTPS protocol."""
            return self._open_generic_http(self._https_connection, url, data)

    def open_file(self, url):
        """Use local file or FTP depending on form of URL."""
        if not isinstance(url, str):
            raise URLError('file error', 'proxy support for file protocol currently not implemented')
        if url[:2] == '//' and url[2:3] != '/' and url[2:12].lower() != 'localhost/':
            return self.open_ftp(url)
        else:
            return self.open_local_file(url)

    def open_local_file(self, url):
        """Use local file."""
        import mimetypes, email.utils
        from io import StringIO
        host, file = splithost(url)
        localname = url2pathname(file)
        try:
            stats = os.stat(localname)
        except OSError as e:
            raise URLError(e.errno, e.strerror, e.filename)
        size = stats.st_size
        modified = email.utils.formatdate(stats.st_mtime, usegmt=True)
        mtype = mimetypes.guess_type(url)[0]
        headers = email.message_from_string(
            'Content-Type: %s\nContent-Length: %d\nLast-modified: %s\n' %
            (mtype or 'text/plain', size, modified))
        if not host:
            urlfile = file
            if file[:1] == '/':
                urlfile = 'file://' + file
            return addinfourl(open(localname, 'rb'), headers, urlfile)
        host, port = splitport(host)
        if (not port
           and socket.gethostbyname(host) in (localhost() + thishost())):
            urlfile = file
            if file[:1] == '/':
                urlfile = 'file://' + file
            return addinfourl(open(localname, 'rb'), headers, urlfile)
        raise URLError('local file error', 'not on local host')

    def open_ftp(self, url):
        """Use FTP protocol."""
        if not isinstance(url, str):
            raise URLError('ftp error', 'proxy support for ftp protocol currently not implemented')
        import mimetypes
        from io import StringIO
        host, path = splithost(url)
        if not host: raise URLError('ftp error', 'no host given')
        host, port = splitport(host)
        user, host = splituser(host)
        if user: user, passwd = splitpasswd(user)
        else: passwd = None
        host = unquote(host)
        user = unquote(user or '')
        passwd = unquote(passwd or '')
        host = socket.gethostbyname(host)
        if not port:
            import ftplib
            port = ftplib.FTP_PORT
        else:
            port = int(port)
        path, attrs = splitattr(path)
        path = unquote(path)
        dirs = path.split('/')
        dirs, file = dirs[:-1], dirs[-1]
        if dirs and not dirs[0]: dirs = dirs[1:]
        if dirs and not dirs[0]: dirs[0] = '/'
        key = user, host, port, '/'.join(dirs)
        # XXX thread unsafe!
        if len(self.ftpcache) > MAXFTPCACHE:
            # Prune the cache, rather arbitrarily
            for k in self.ftpcache.keys():
                if k != key:
                    v = self.ftpcache[k]
                    del self.ftpcache[k]
                    v.close()
        try:
            if not key in self.ftpcache:
                self.ftpcache[key] = \
                    ftpwrapper(user, passwd, host, port, dirs)
            if not file: type = 'D'
            else: type = 'I'
            for attr in attrs:
                attr, value = splitvalue(attr)
                if attr.lower() == 'type' and \
                   value in ('a', 'A', 'i', 'I', 'd', 'D'):
                    type = value.upper()
            (fp, retrlen) = self.ftpcache[key].retrfile(file, type)
            mtype = mimetypes.guess_type("ftp:" + url)[0]
            headers = ""
            if mtype:
                headers += "Content-Type: %s\n" % mtype
            if retrlen is not None and retrlen >= 0:
                headers += "Content-Length: %d\n" % retrlen
            headers = email.message_from_string(headers)
            return addinfourl(fp, headers, "ftp:" + url)
        except ftperrors() as msg:
            raise URLError('ftp error', msg).with_traceback(sys.exc_info()[2])

    def open_data(self, url, data=None):
        """Use "data" URL."""
        if not isinstance(url, str):
            raise URLError('data error', 'proxy support for data protocol currently not implemented')
        # ignore POSTed data
        #
        # syntax of data URLs:
        # dataurl   := "data:" [ mediatype ] [ ";base64" ] "," data
        # mediatype := [ type "/" subtype ] *( ";" parameter )
        # data      := *urlchar
        # parameter := attribute "=" value
        try:
            [type, data] = url.split(',', 1)
        except ValueError:
            raise IOError('data error', 'bad data URL')
        if not type:
            type = 'text/plain;charset=US-ASCII'
        semi = type.rfind(';')
        if semi >= 0 and '=' not in type[semi:]:
            encoding = type[semi+1:]
            type = type[:semi]
        else:
            encoding = ''
        msg = []
        msg.append('Date: %s'%time.strftime('%a, %d %b %Y %T GMT',
                                            time.gmtime(time.time())))
        msg.append('Content-type: %s' % type)
        if encoding == 'base64':
            import base64
            # XXX is this encoding/decoding ok?
            data = base64.decodebytes(data.encode('ascii')).decode('latin1')
        else:
            data = unquote(data)
        msg.append('Content-Length: %d' % len(data))
        msg.append('')
        msg.append(data)
        msg = '\n'.join(msg)
        headers = email.message_from_string(msg)
        f = io.StringIO(msg)
        #f.fileno = None     # needed for addinfourl
        return addinfourl(f, headers, url)


class FancyURLopener(URLopener):
    """Derived class with handlers for errors we can handle (perhaps)."""

    def __init__(self, *args, **kwargs):
        URLopener.__init__(self, *args, **kwargs)
        self.auth_cache = {}
        self.tries = 0
        self.maxtries = 10

    def http_error_default(self, url, fp, errcode, errmsg, headers):
        """Default error handling -- don't raise an exception."""
        return addinfourl(fp, headers, "http:" + url, errcode)

    def http_error_302(self, url, fp, errcode, errmsg, headers, data=None):
        """Error 302 -- relocated (temporarily)."""
        self.tries += 1
        if self.maxtries and self.tries >= self.maxtries:
            if hasattr(self, "http_error_500"):
                meth = self.http_error_500
            else:
                meth = self.http_error_default
            self.tries = 0
            return meth(url, fp, 500,
                        "Internal Server Error: Redirect Recursion", headers)
        result = self.redirect_internal(url, fp, errcode, errmsg, headers,
                                        data)
        self.tries = 0
        return result

    def redirect_internal(self, url, fp, errcode, errmsg, headers, data):
        if 'location' in headers:
            newurl = headers['location']
        elif 'uri' in headers:
            newurl = headers['uri']
        else:
            return
        void = fp.read()
        fp.close()
        # In case the server sent a relative URL, join with original:
        newurl = urljoin(self.type + ":" + url, newurl)
        return self.open(newurl)

    def http_error_301(self, url, fp, errcode, errmsg, headers, data=None):
        """Error 301 -- also relocated (permanently)."""
        return self.http_error_302(url, fp, errcode, errmsg, headers, data)

    def http_error_303(self, url, fp, errcode, errmsg, headers, data=None):
        """Error 303 -- also relocated (essentially identical to 302)."""
        return self.http_error_302(url, fp, errcode, errmsg, headers, data)

    def http_error_307(self, url, fp, errcode, errmsg, headers, data=None):
        """Error 307 -- relocated, but turn POST into error."""
        if data is None:
            return self.http_error_302(url, fp, errcode, errmsg, headers, data)
        else:
            return self.http_error_default(url, fp, errcode, errmsg, headers)

    def http_error_401(self, url, fp, errcode, errmsg, headers, data=None):
        """Error 401 -- authentication required.
        This function supports Basic authentication only."""
        if not 'www-authenticate' in headers:
            URLopener.http_error_default(self, url, fp,
                                         errcode, errmsg, headers)
        stuff = headers['www-authenticate']
        import re
        match = re.match('[ \t]*([^ \t]+)[ \t]+realm="([^"]*)"', stuff)
        if not match:
            URLopener.http_error_default(self, url, fp,
                                         errcode, errmsg, headers)
        scheme, realm = match.groups()
        if scheme.lower() != 'basic':
            URLopener.http_error_default(self, url, fp,
                                         errcode, errmsg, headers)
        name = 'retry_' + self.type + '_basic_auth'
        if data is None:
            return getattr(self,name)(url, realm)
        else:
            return getattr(self,name)(url, realm, data)

    def http_error_407(self, url, fp, errcode, errmsg, headers, data=None):
        """Error 407 -- proxy authentication required.
        This function supports Basic authentication only."""
        if not 'proxy-authenticate' in headers:
            URLopener.http_error_default(self, url, fp,
                                         errcode, errmsg, headers)
        stuff = headers['proxy-authenticate']
        import re
        match = re.match('[ \t]*([^ \t]+)[ \t]+realm="([^"]*)"', stuff)
        if not match:
            URLopener.http_error_default(self, url, fp,
                                         errcode, errmsg, headers)
        scheme, realm = match.groups()
        if scheme.lower() != 'basic':
            URLopener.http_error_default(self, url, fp,
                                         errcode, errmsg, headers)
        name = 'retry_proxy_' + self.type + '_basic_auth'
        if data is None:
            return getattr(self,name)(url, realm)
        else:
            return getattr(self,name)(url, realm, data)

    def retry_proxy_http_basic_auth(self, url, realm, data=None):
        host, selector = splithost(url)
        newurl = 'http://' + host + selector
        proxy = self.proxies['http']
        urltype, proxyhost = splittype(proxy)
        proxyhost, proxyselector = splithost(proxyhost)
        i = proxyhost.find('@') + 1
        proxyhost = proxyhost[i:]
        user, passwd = self.get_user_passwd(proxyhost, realm, i)
        if not (user or passwd): return None
        proxyhost = "%s:%s@%s" % (quote(user, safe=''),
                                  quote(passwd, safe=''), proxyhost)
        self.proxies['http'] = 'http://' + proxyhost + proxyselector
        if data is None:
            return self.open(newurl)
        else:
            return self.open(newurl, data)

    def retry_proxy_https_basic_auth(self, url, realm, data=None):
        host, selector = splithost(url)
        newurl = 'https://' + host + selector
        proxy = self.proxies['https']
        urltype, proxyhost = splittype(proxy)
        proxyhost, proxyselector = splithost(proxyhost)
        i = proxyhost.find('@') + 1
        proxyhost = proxyhost[i:]
        user, passwd = self.get_user_passwd(proxyhost, realm, i)
        if not (user or passwd): return None
        proxyhost = "%s:%s@%s" % (quote(user, safe=''),
                                  quote(passwd, safe=''), proxyhost)
        self.proxies['https'] = 'https://' + proxyhost + proxyselector
        if data is None:
            return self.open(newurl)
        else:
            return self.open(newurl, data)

    def retry_http_basic_auth(self, url, realm, data=None):
        host, selector = splithost(url)
        i = host.find('@') + 1
        host = host[i:]
        user, passwd = self.get_user_passwd(host, realm, i)
        if not (user or passwd): return None
        host = "%s:%s@%s" % (quote(user, safe=''),
                             quote(passwd, safe=''), host)
        newurl = 'http://' + host + selector
        if data is None:
            return self.open(newurl)
        else:
            return self.open(newurl, data)

    def retry_https_basic_auth(self, url, realm, data=None):
        host, selector = splithost(url)
        i = host.find('@') + 1
        host = host[i:]
        user, passwd = self.get_user_passwd(host, realm, i)
        if not (user or passwd): return None
        host = "%s:%s@%s" % (quote(user, safe=''),
                             quote(passwd, safe=''), host)
        newurl = 'https://' + host + selector
        if data is None:
            return self.open(newurl)
        else:
            return self.open(newurl, data)

    def get_user_passwd(self, host, realm, clear_cache = 0):
        key = realm + '@' + host.lower()
        if key in self.auth_cache:
            if clear_cache:
                del self.auth_cache[key]
            else:
                return self.auth_cache[key]
        user, passwd = self.prompt_user_passwd(host, realm)
        if user or passwd: self.auth_cache[key] = (user, passwd)
        return user, passwd

    def prompt_user_passwd(self, host, realm):
        """Override this in a GUI environment!"""
        import getpass
        try:
            user = input("Enter username for %s at %s: " % (realm, host))
            passwd = getpass.getpass("Enter password for %s in %s at %s: " %
                (user, realm, host))
            return user, passwd
        except KeyboardInterrupt:
            print()
            return None, None


# Utility functions

_localhost = None
def localhost():
    """Return the IP address of the magic hostname 'localhost'."""
    global _localhost
    if _localhost is None:
        _localhost = socket.gethostbyname('localhost')
    return _localhost

_thishost = None
def thishost():
    """Return the IP addresses of the current host."""
    global _thishost
    if _thishost is None:
        _thishost = tuple(socket.gethostbyname_ex(socket.gethostname()[2]))
    return _thishost

_ftperrors = None
def ftperrors():
    """Return the set of errors raised by the FTP class."""
    global _ftperrors
    if _ftperrors is None:
        import ftplib
        _ftperrors = ftplib.all_errors
    return _ftperrors

_noheaders = None
def noheaders():
    """Return an empty email Message object."""
    global _noheaders
    if _noheaders is None:
        _noheaders = email.message_from_string("")
    return _noheaders


# Utility classes

class ftpwrapper:
    """Class used by open_ftp() for cache of open FTP connections."""

    def __init__(self, user, passwd, host, port, dirs, timeout=None):
        self.user = user
        self.passwd = passwd
        self.host = host
        self.port = port
        self.dirs = dirs
        self.timeout = timeout
        self.init()

    def init(self):
        import ftplib
        self.busy = 0
        self.ftp = ftplib.FTP()
        self.ftp.connect(self.host, self.port, self.timeout)
        self.ftp.login(self.user, self.passwd)
        for dir in self.dirs:
            self.ftp.cwd(dir)

    def retrfile(self, file, type):
        import ftplib
        self.endtransfer()
        if type in ('d', 'D'): cmd = 'TYPE A'; isdir = 1
        else: cmd = 'TYPE ' + type; isdir = 0
        try:
            self.ftp.voidcmd(cmd)
        except ftplib.all_errors:
            self.init()
            self.ftp.voidcmd(cmd)
        conn = None
        if file and not isdir:
            # Try to retrieve as a file
            try:
                cmd = 'RETR ' + file
                conn = self.ftp.ntransfercmd(cmd)
            except ftplib.error_perm as reason:
                if str(reason)[:3] != '550':
                    raise URLError('ftp error', reason).with_traceback(
                        sys.exc_info()[2])
        if not conn:
            # Set transfer mode to ASCII!
            self.ftp.voidcmd('TYPE A')
            # Try a directory listing. Verify that directory exists.
            if file:
                pwd = self.ftp.pwd()
                try:
                    try:
                        self.ftp.cwd(file)
                    except ftplib.error_perm as reason:
                        raise URLError('ftp error', reason) from reason
                finally:
                    self.ftp.cwd(pwd)
                cmd = 'LIST ' + file
            else:
                cmd = 'LIST'
            conn = self.ftp.ntransfercmd(cmd)
        self.busy = 1
        # Pass back both a suitably decorated object and a retrieval length
        return (addclosehook(conn[0].makefile('rb'), self.endtransfer), conn[1])
    def endtransfer(self):
        if not self.busy:
            return
        self.busy = 0
        try:
            self.ftp.voidresp()
        except ftperrors():
            pass

    def close(self):
        self.endtransfer()
        try:
            self.ftp.close()
        except ftperrors():
            pass

# Proxy handling
def getproxies_environment():
    """Return a dictionary of scheme -> proxy server URL mappings.

    Scan the environment for variables named <scheme>_proxy;
    this seems to be the standard convention.  If you need a
    different way, you can pass a proxies dictionary to the
    [Fancy]URLopener constructor.

    """
    proxies = {}
    for name, value in os.environ.items():
        name = name.lower()
        if value and name[-6:] == '_proxy':
            proxies[name[:-6]] = value
    return proxies

def proxy_bypass_environment(host):
    """Test if proxies should not be used for a particular host.

    Checks the environment for a variable named no_proxy, which should
    be a list of DNS suffixes separated by commas, or '*' for all hosts.
    """
    no_proxy = os.environ.get('no_proxy', '') or os.environ.get('NO_PROXY', '')
    # '*' is special case for always bypass
    if no_proxy == '*':
        return 1
    # strip port off host
    hostonly, port = splitport(host)
    # check if the host ends with any of the DNS suffixes
    for name in no_proxy.split(','):
        if name and (hostonly.endswith(name) or host.endswith(name)):
            return 1
    # otherwise, don't bypass
    return 0


if sys.platform == 'darwin':
    def getproxies_internetconfig():
        """Return a dictionary of scheme -> proxy server URL mappings.

        By convention the mac uses Internet Config to store
        proxies.  An HTTP proxy, for instance, is stored under
        the HttpProxy key.

        """
        try:
            import ic
        except ImportError:
            return {}

        try:
            config = ic.IC()
        except ic.error:
            return {}
        proxies = {}
        # HTTP:
        if 'UseHTTPProxy' in config and config['UseHTTPProxy']:
            try:
                value = config['HTTPProxyHost']
            except ic.error:
                pass
            else:
                proxies['http'] = 'http://%s' % value
        # FTP: XXX To be done.
        # Gopher: XXX To be done.
        return proxies

    def proxy_bypass(host):
        if getproxies_environment():
            return proxy_bypass_environment(host)
        else:
            return 0

    def getproxies():
        return getproxies_environment() or getproxies_internetconfig()

elif os.name == 'nt':
    def getproxies_registry():
        """Return a dictionary of scheme -> proxy server URL mappings.

        Win32 uses the registry to store proxies.

        """
        proxies = {}
        try:
            import winreg
        except ImportError:
            # Std module, so should be around - but you never know!
            return proxies
        try:
            internetSettings = winreg.OpenKey(winreg.HKEY_CURRENT_USER,
                r'Software\Microsoft\Windows\CurrentVersion\Internet Settings')
            proxyEnable = winreg.QueryValueEx(internetSettings,
                                               'ProxyEnable')[0]
            if proxyEnable:
                # Returned as Unicode but problems if not converted to ASCII
                proxyServer = str(winreg.QueryValueEx(internetSettings,
                                                       'ProxyServer')[0])
                if '=' in proxyServer:
                    # Per-protocol settings
                    for p in proxyServer.split(';'):
                        protocol, address = p.split('=', 1)
                        # See if address has a type:// prefix
                        import re
                        if not re.match('^([^/:]+)://', address):
                            address = '%s://%s' % (protocol, address)
                        proxies[protocol] = address
                else:
                    # Use one setting for all protocols
                    if proxyServer[:5] == 'http:':
                        proxies['http'] = proxyServer
                    else:
                        proxies['http'] = 'http://%s' % proxyServer
                        proxies['ftp'] = 'ftp://%s' % proxyServer
            internetSettings.Close()
        except (WindowsError, ValueError, TypeError):
            # Either registry key not found etc, or the value in an
            # unexpected format.
            # proxies already set up to be empty so nothing to do
            pass
        return proxies

    def getproxies():
        """Return a dictionary of scheme -> proxy server URL mappings.

        Returns settings gathered from the environment, if specified,
        or the registry.

        """
        return getproxies_environment() or getproxies_registry()

    def proxy_bypass_registry(host):
        try:
            import winreg
            import re
        except ImportError:
            # Std modules, so should be around - but you never know!
            return 0
        try:
            internetSettings = winreg.OpenKey(winreg.HKEY_CURRENT_USER,
                r'Software\Microsoft\Windows\CurrentVersion\Internet Settings')
            proxyEnable = winreg.QueryValueEx(internetSettings,
                                               'ProxyEnable')[0]
            proxyOverride = str(winreg.QueryValueEx(internetSettings,
                                                     'ProxyOverride')[0])
            # ^^^^ Returned as Unicode but problems if not converted to ASCII
        except WindowsError:
            return 0
        if not proxyEnable or not proxyOverride:
            return 0
        # try to make a host list from name and IP address.
        rawHost, port = splitport(host)
        host = [rawHost]
        try:
            addr = socket.gethostbyname(rawHost)
            if addr != rawHost:
                host.append(addr)
        except socket.error:
            pass
        try:
            fqdn = socket.getfqdn(rawHost)
            if fqdn != rawHost:
                host.append(fqdn)
        except socket.error:
            pass
        # make a check value list from the registry entry: replace the
        # '<local>' string by the localhost entry and the corresponding
        # canonical entry.
        proxyOverride = proxyOverride.split(';')
        # now check if we match one of the registry values.
        for test in proxyOverride:
            if test == '<local>':
                if '.' not in rawHost:
                    return 1
            test = test.replace(".", r"\.")     # mask dots
            test = test.replace("*", r".*")     # change glob sequence
            test = test.replace("?", r".")      # change glob char
            for val in host:
                # print "%s <--> %s" %( test, val )
                if re.match(test, val, re.I):
                    return 1
        return 0

    def proxy_bypass(host):
        """Return a dictionary of scheme -> proxy server URL mappings.

        Returns settings gathered from the environment, if specified,
        or the registry.

        """
        if getproxies_environment():
            return proxy_bypass_environment(host)
        else:
            return proxy_bypass_registry(host)

else:
    # By default use environment variables
    getproxies = getproxies_environment
    proxy_bypass = proxy_bypass_environment