freeipa/ipalib/rpc.py

# Authors:
#   Jason Gerard DeRose <jderose@redhat.com>
#   Rob Crittenden <rcritten@redhat.com>
#
# Copyright (C) 2008  Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
RPC client and shared RPC client/server functionality.

This module adds some additional functionality on top of the ``xmlrpc.client``
module in the Python standard library (``xmlrpclib`` in Python 2).
For documentation on the ``xmlrpclib`` module, see:

    http://docs.python.org/2/library/xmlrpclib.html

Also see the `ipaserver.rpcserver` module.
"""

from __future__ import absolute_import

from decimal import Decimal
import datetime
import os
import locale
import base64
import json
import socket
import gzip

import gssapi
from dns import resolver, rdatatype
from dns.exception import DNSException
from ssl import SSLError
import six
from six.moves import urllib

from ipalib.backend import Connectible
from ipalib.constants import LDAP_GENERALIZED_TIME_FORMAT
from ipalib.errors import (public_errors, UnknownError, NetworkError,
    KerberosError, XMLRPCMarshallError, JSONError)
from ipalib import errors, capabilities
from ipalib.request import context, Connection
from ipapython.ipa_log_manager import root_logger
from ipapython import ipautil
from ipapython import kernel_keyring
from ipapython.cookie import Cookie
from ipapython.dnsutil import DNSName
from ipalib.text import _
from ipalib.util import create_https_connection
from ipalib.krb_utils import KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN, KRB5KRB_AP_ERR_TKT_EXPIRED, \
                             KRB5_FCC_PERM, KRB5_FCC_NOFILE, KRB5_CC_FORMAT, \
                             KRB5_REALM_CANT_RESOLVE, KRB5_CC_NOTFOUND, get_principal
from ipapython.dn import DN
from ipapython.kerberos import Principal
from ipalib.capabilities import VERSION_WITHOUT_CAPABILITIES
from ipalib import api

# The XMLRPC client is in  "six.moves.xmlrpc_client", but pylint
# cannot handle that
try:
    from xmlrpclib import (Binary, Fault, DateTime, dumps, loads, ServerProxy,
            Transport, ProtocolError, MININT, MAXINT)
except ImportError:
    # pylint: disable=import-error
    from xmlrpc.client import (Binary, Fault, DateTime, dumps, loads, ServerProxy,
            Transport, ProtocolError, MININT, MAXINT)


if six.PY3:
    unicode = str

COOKIE_NAME = 'ipa_session'
KEYRING_COOKIE_NAME = '%s_cookie:%%s' % COOKIE_NAME

errors_by_code = dict((e.errno, e) for e in public_errors)


def client_session_keyring_keyname(principal):
    '''
    Return the key name used for storing the client session data for
    the given principal.
    '''

    return KEYRING_COOKIE_NAME % principal

def update_persistent_client_session_data(principal, data):
    '''
    Given a principal create or update the session data for that
    principal in the persistent secure storage.

    Raises ValueError if unable to perform the action for any reason.
    '''

    try:
        keyname = client_session_keyring_keyname(principal)
    except Exception as e:
        raise ValueError(str(e))

    # kernel_keyring only raises ValueError (why??)
    kernel_keyring.update_key(keyname, data)

def read_persistent_client_session_data(principal):
    '''
    Given a principal return the stored session data for that
    principal from the persistent secure storage.

    Raises ValueError if unable to perform the action for any reason.
    '''

    try:
        keyname = client_session_keyring_keyname(principal)
    except Exception as e:
        raise ValueError(str(e))

    # kernel_keyring only raises ValueError (why??)
    return kernel_keyring.read_key(keyname)

def delete_persistent_client_session_data(principal):
    '''
    Given a principal remove the session data for that
    principal from the persistent secure storage.

    Raises ValueError if unable to perform the action for any reason.
    '''

    try:
        keyname = client_session_keyring_keyname(principal)
    except Exception as e:
        raise ValueError(str(e))

    # kernel_keyring only raises ValueError (why??)
    kernel_keyring.del_key(keyname)

def xml_wrap(value, version):
    """
    Wrap all ``str`` in ``xmlrpc.client.Binary``.

    Because ``xmlrpc.client.dumps()`` will itself convert all ``unicode`` instances
    into UTF-8 encoded ``str`` instances, we don't do it here.

    So in total, when encoding data for an XML-RPC packet, the following
    transformations occur:

        * All ``str`` instances are treated as binary data and are wrapped in
          an ``xmlrpc.client.Binary()`` instance.

        * Only ``unicode`` instances are treated as character data. They get
          converted to UTF-8 encoded ``str`` instances (although as mentioned,
          not by this function).

    Also see `xml_unwrap()`.

    :param value: The simple scalar or simple compound value to wrap.
    """
    if type(value) in (list, tuple):
        return tuple(xml_wrap(v, version) for v in value)
    if isinstance(value, dict):
        return dict(
            (k, xml_wrap(v, version)) for (k, v) in value.items()
        )
    if type(value) is bytes:
        return Binary(value)
    if type(value) is Decimal:
        # transfer Decimal as a string
        return unicode(value)
    if isinstance(value, six.integer_types) and (value < MININT or value > MAXINT):
        return unicode(value)
    if isinstance(value, DN):
        return str(value)

    # Encode datetime.datetime objects as xmlrpc.client.DateTime objects
    if isinstance(value, datetime.datetime):
        if capabilities.client_has_capability(version, 'datetime_values'):
            return DateTime(value)
        else:
            return value.strftime(LDAP_GENERALIZED_TIME_FORMAT)

    if isinstance(value, DNSName):
        if capabilities.client_has_capability(version, 'dns_name_values'):
            return {'__dns_name__': unicode(value)}
        else:
            return unicode(value)

    if isinstance(value, Principal):
        return unicode(value)

    assert type(value) in (unicode, float, bool, type(None)) + six.integer_types
    return value


def xml_unwrap(value, encoding='UTF-8'):
    """
    Unwrap all ``xmlrpc.Binary``, decode all ``str`` into ``unicode``.

    When decoding data from an XML-RPC packet, the following transformations
    occur:

        * The binary payloads of all ``xmlrpc.client.Binary`` instances are
          returned as ``str`` instances.

        * All ``str`` instances are treated as UTF-8 encoded Unicode strings.
          They are decoded and the resulting ``unicode`` instance is returned.

    Also see `xml_wrap()`.

    :param value: The value to unwrap.
    :param encoding: The Unicode encoding to use (defaults to ``'UTF-8'``).
    """
    if type(value) in (list, tuple):
        return tuple(xml_unwrap(v, encoding) for v in value)
    if type(value) is dict:
        if '__dns_name__' in value:
            return DNSName(value['__dns_name__'])
        else:
            return dict(
                (k, xml_unwrap(v, encoding)) for (k, v) in value.items()
            )
    if isinstance(value, bytes):
        return value.decode(encoding)
    if isinstance(value, Binary):
        assert type(value.data) is bytes
        return value.data
    if isinstance(value, DateTime):
        # xmlprc DateTime is converted to string of %Y%m%dT%H:%M:%S format
        return datetime.datetime.strptime(str(value), "%Y%m%dT%H:%M:%S")
    assert type(value) in (unicode, int, float, bool, type(None))
    return value


def xml_dumps(params, version, methodname=None, methodresponse=False,
              encoding='UTF-8'):
    """
    Encode an XML-RPC data packet, transparently wraping ``params``.

    This function will wrap ``params`` using `xml_wrap()` and will
    then encode the XML-RPC data packet using ``xmlrpc.client.dumps()`` (from the
    Python standard library).

    For documentation on the ``xmlrpc.client.dumps()`` function, see:

        http://docs.python.org/library/xmlrpc.client.html#convenience-functions

    Also see `xml_loads()`.

    :param params: A ``tuple`` or an ``xmlrpc.client.Fault`` instance.
    :param methodname: The name of the method to call if this is a request.
    :param methodresponse: Set this to ``True`` if this is a response.
    :param encoding: The Unicode encoding to use (defaults to ``'UTF-8'``).
    """
    if type(params) is tuple:
        params = xml_wrap(params, version)
    else:
        assert isinstance(params, Fault)
    return dumps(params,
        methodname=methodname,
        methodresponse=methodresponse,
        encoding=encoding,
        allow_none=True,
    )


class _JSONPrimer(dict):
    """Fast JSON primer and pre-converter

    Prepare a data structure for JSON serialization. In an ideal world, priming
    could be handled by the default hook of json.dumps(). Unfortunately the
    hook treats Python 2 str as text while FreeIPA considers str as bytes.

    The primer uses a couple of tricks to archive maximum performance:

    * O(1) type look instead of O(n) chain of costly isinstance() calls
    * __missing__ and __mro__ with caching to handle subclasses
    * inline code with minor code duplication (func lookup in enc_list/dict)
    * avoid surplus function calls (e.g. func is _identity, obj.__class__
      instead if type(obj))
    * function default arguments to turn global into local lookups
    * avoid re-creation of bound method objects (e.g. result.append)
    * on-demand lookup of client capabilities with cached values

    Depending on the client version number, the primer converts:

    * bytes -> {'__base64__': b64encode}
    * datetime -> {'__datetime__': LDAP_GENERALIZED_TIME}
    * DNSName -> {'__dns_name__': unicode}

    The _ipa_obj_hook() functions unserializes the marked JSON objects to
    bytes, datetime and DNSName.

    :see: _ipa_obj_hook
    """
    __slots__ = ('version', '_cap_datetime', '_cap_dnsname')

    _identity = object()

    def __init__(self, version, _identity=_identity):
        super(_JSONPrimer, self).__init__()
        self.version = version
        self._cap_datetime = None
        self._cap_dnsname = None
        self.update({
            unicode: _identity,
            bool: _identity,
            type(None): _identity,
            float: _identity,
            Decimal: unicode,
            DN: str,
            Principal: unicode,
            DNSName: self._enc_dnsname,
            datetime.datetime: self._enc_datetime,
            bytes: self._enc_bytes,
            list: self._enc_list,
            tuple: self._enc_list,
            dict: self._enc_dict,
        })
        # int, long
        for t in six.integer_types:
            self[t] = _identity

    def __missing__(self, typ):
        # walk MRO to find best match
        for c in typ.__mro__:
            if c in self:
                self[typ] = self[c]
                return self[c]
        # use issubclass to check for registered ABCs
        for c in self:
            if issubclass(typ, c):
                self[typ] = self[c]
                return self[c]
        raise TypeError(typ)

    def convert(self, obj, _identity=_identity):
        # obj.__class__ is twice as fast as type(obj)
        func = self[obj.__class__]
        return obj if func is _identity else func(obj)

    def _enc_datetime(self, val):
        cap = self._cap_datetime
        if cap is None:
            cap = capabilities.client_has_capability(self.version,
                                                     'datetime_values')
            self._cap_datetime = cap
        if cap:
            return {'__datetime__': val.strftime(LDAP_GENERALIZED_TIME_FORMAT)}
        else:
            return val.strftime(LDAP_GENERALIZED_TIME_FORMAT)

    def _enc_dnsname(self, val):
        cap = self._cap_dnsname
        if cap is None:
            cap = capabilities.client_has_capability(self.version,
                                                     'dns_name_values')
            self._cap_dnsname = cap
        if cap:
            return {'__dns_name__': unicode(val)}
        else:
            return unicode(val)

    def _enc_bytes(self, val):
        encoded = base64.b64encode(val)
        if not six.PY2:
            encoded = encoded.decode('ascii')
        return {'__base64__': encoded}

    def _enc_list(self, val, _identity=_identity):
        result = []
        append = result.append
        for v in val:
            func = self[v.__class__]
            append(v if func is _identity else func(v))
        return result

    def _enc_dict(self, val, _identity=_identity, _iteritems=six.iteritems):
        result = {}
        for k, v in _iteritems(val):
            func = self[v.__class__]
            result[k] = v if func is _identity else func(v)
        return result


def json_encode_binary(val, version, pretty_print=False):
    """Serialize a Python object structure to JSON

    :param object val: Python object structure
    :param str version: client version
    :param bool pretty_print: indent and sort JSON (warning: slow!)
    :return: text
    :note: pretty printing triggers a slow path in Python's JSON module. Only
           use pretty_print in debug mode.
    """
    result = _JSONPrimer(version).convert(val)
    if pretty_print:
        return json.dumps(result, indent=4, sort_keys=True)
    else:
        return json.dumps(result)


def _ipa_obj_hook(dct, _iteritems=six.iteritems, _list=list):
    """JSON object hook

    :see: _JSONPrimer
    """
    if '__base64__' in dct:
        return base64.b64decode(dct['__base64__'])
    elif '__datetime__' in dct:
        return datetime.datetime.strptime(dct['__datetime__'],
                                          LDAP_GENERALIZED_TIME_FORMAT)
    elif '__dns_name__' in dct:
        return DNSName(dct['__dns_name__'])
    else:
        # XXX tests assume tuples. Is this really necessary?
        for k, v in _iteritems(dct):
            if v.__class__ is _list:
                dct[k] = tuple(v)
        return dct


def json_decode_binary(val):
    """Convert serialized JSON string back to Python data structure

    :param val: JSON string
    :type val: str, bytes
    :return: Python data structure
    :see: _ipa_obj_hook, _JSONPrimer
    """
    if isinstance(val, bytes):
        val = val.decode('utf-8')

    return json.loads(val, object_hook=_ipa_obj_hook)


def decode_fault(e, encoding='UTF-8'):
    assert isinstance(e, Fault)
    if isinstance(e.faultString, bytes):
        return Fault(e.faultCode, e.faultString.decode(encoding))
    return e


def xml_loads(data, encoding='UTF-8'):
    """
    Decode the XML-RPC packet in ``data``, transparently unwrapping its params.

    This function will decode the XML-RPC packet in ``data`` using
    ``xmlrpc.client.loads()`` (from the Python standard library).  If ``data``
    contains a fault, ``xmlrpc.client.loads()`` will itself raise an
    ``xmlrpc.client.Fault`` exception.

    Assuming an exception is not raised, this function will then unwrap the
    params in ``data`` using `xml_unwrap()`.  Finally, a
    ``(params, methodname)`` tuple is returned containing the unwrapped params
    and the name of the method being called.  If the packet contains no method
    name, ``methodname`` will be ``None``.

    For documentation on the ``xmlrpc.client.loads()`` function, see:

        http://docs.python.org/2/library/xmlrpclib.html#convenience-functions

    Also see `xml_dumps()`.

    :param data: The XML-RPC packet to decode.
    """
    try:
        (params, method) = loads(data)
        return (xml_unwrap(params), method)
    except Fault as e:
        raise decode_fault(e)


class DummyParser(object):
    def __init__(self):
        self.data = []

    def feed(self, data):
        self.data.append(data)

    def close(self):
        return b''.join(self.data)


class MultiProtocolTransport(Transport):
    """Transport that handles both XML-RPC and JSON"""
    def __init__(self, *args, **kwargs):
        Transport.__init__(self)
        self.protocol = kwargs.get('protocol', None)

    def getparser(self):
        if self.protocol == 'json':
            parser = DummyParser()
            return parser, parser
        else:
            return Transport.getparser(self)

    def send_content(self, connection, request_body):
        if self.protocol == 'json':
            connection.putheader("Content-Type", "application/json")
        else:
            connection.putheader("Content-Type", "text/xml")

        # gzip compression would be set up here, but we have it turned off
        # (encode_threshold is None)

        connection.putheader("Content-Length", str(len(request_body)))
        connection.endheaders(request_body)


class LanguageAwareTransport(MultiProtocolTransport):
    """Transport sending Accept-Language header"""
    def get_host_info(self, host):
        host, extra_headers, x509 = MultiProtocolTransport.get_host_info(
            self, host)

        try:
            lang = locale.setlocale(locale.LC_ALL, '').split('.')[0].lower()
        except locale.Error:
            # fallback to default locale
            lang = 'en_us'

        if not isinstance(extra_headers, list):
            extra_headers = []

        extra_headers.append(
            ('Accept-Language', lang.replace('_', '-'))
        )
        extra_headers.append(
            ('Referer', 'https://%s/ipa/xml' % str(host))
        )

        return (host, extra_headers, x509)


class SSLTransport(LanguageAwareTransport):
    """Handles an HTTPS transaction to an XML-RPC server."""
    def make_connection(self, host):
        host, self._extra_headers, _x509 = self.get_host_info(host)

        if self._connection and host == self._connection[0]:
            return self._connection[1]

        conn = create_https_connection(
            host, 443,
            api.env.tls_ca_cert,
            tls_version_min=api.env.tls_version_min,
            tls_version_max=api.env.tls_version_max)

        conn.connect()

        self._connection = host, conn
        return self._connection[1]


class KerbTransport(SSLTransport):
    """
    Handles Kerberos Negotiation authentication to an XML-RPC server.
    """
    flags = [gssapi.RequirementFlag.mutual_authentication,
             gssapi.RequirementFlag.out_of_sequence_detection]

    def __init__(self, *args, **kwargs):
        SSLTransport.__init__(self, *args, **kwargs)
        self._sec_context = None
        self.service = kwargs.pop("service", "HTTP")
        self.ccache = kwargs.pop("ccache", None)

    def _handle_exception(self, e, service=None):
        minor = e.min_code
        if minor == KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN:
            raise errors.ServiceError(service=service)
        elif minor == KRB5_FCC_NOFILE:
            raise errors.NoCCacheError()
        elif minor == KRB5KRB_AP_ERR_TKT_EXPIRED:
            raise errors.TicketExpired()
        elif minor == KRB5_FCC_PERM:
            raise errors.BadCCachePerms()
        elif minor == KRB5_CC_FORMAT:
            raise errors.BadCCacheFormat()
        elif minor == KRB5_REALM_CANT_RESOLVE:
            raise errors.CannotResolveKDC()
        elif minor == KRB5_CC_NOTFOUND:
            raise errors.CCacheError()
        else:
            raise errors.KerberosError(message=unicode(e))

    def get_host_info(self, host):
        """
        Two things can happen here. If we have a session we will add
        a cookie for that. If not we will set an Authorization header.
        """
        (host, extra_headers, x509) = SSLTransport.get_host_info(self, host)

        if not isinstance(extra_headers, list):
            extra_headers = []

        session_cookie = getattr(context, 'session_cookie', None)
        if session_cookie:
            extra_headers.append(('Cookie', session_cookie))
            return (host, extra_headers, x509)

        # Set the remote host principal
        service = self.service + "@" + host.split(':')[0]

        try:
            creds = None
            if self.ccache:
                creds = gssapi.Credentials(usage='initiate',
                                           store={'ccache': self.ccache})
            name = gssapi.Name(service, gssapi.NameType.hostbased_service)
            self._sec_context = gssapi.SecurityContext(creds=creds, name=name,
                                                       flags=self.flags)
            response = self._sec_context.step()
        except gssapi.exceptions.GSSError as e:
            self._handle_exception(e, service=service)

        self._set_auth_header(extra_headers, response)

        return (host, extra_headers, x509)

    def _set_auth_header(self, extra_headers, token):
        for (h, v) in extra_headers:
            if h == 'Authorization':
                extra_headers.remove((h, v))
                break

        if token:
            extra_headers.append(
                ('Authorization', 'negotiate %s' % base64.b64encode(token).decode('ascii'))
            )

    def _auth_complete(self, response):
        if self._sec_context:
            header = response.getheader('www-authenticate', '')
            token = None
            for field in header.split(','):
                k, _dummy, v = field.strip().partition(' ')
                if k.lower() == 'negotiate':
                    try:
                        token = base64.b64decode(v.encode('ascii'))
                        break
                    # b64decode raises TypeError on invalid input
                    except (TypeError, UnicodeError):
                        pass
            if not token:
                raise KerberosError(
                    message=u"No valid Negotiate header in server response")
            token = self._sec_context.step(token=token)
            if self._sec_context.complete:
                self._sec_context = None
                return True
            self._set_auth_header(self._extra_headers, token)
            return False
        return True

    def single_request(self, host, handler, request_body, verbose=0):
        # Based on Python 2.7's xmllib.Transport.single_request
        try:
            h = SSLTransport.make_connection(self, host)

            if verbose:
                h.set_debuglevel(1)

            while True:
                if six.PY2:
                    # pylint: disable=no-value-for-parameter
                    self.send_request(h, handler, request_body)
                    # pylint: enable=no-value-for-parameter
                    self.send_host(h, host)
                    self.send_user_agent(h)
                    self.send_content(h, request_body)
                    response = h.getresponse(buffering=True)
                else:
                    self.__send_request(h, host, handler, request_body, verbose)
                    response = h.getresponse()

                if response.status != 200:
                    if (response.getheader("content-length", 0)):
                        response.read()

                    if response.status == 401:
                        if not self._auth_complete(response):
                            continue

                    raise ProtocolError(
                        host + handler,
                        response.status, response.reason,
                        response.msg)

                self.verbose = verbose
                if not self._auth_complete(response):
                    continue
                return self.parse_response(response)
        except gssapi.exceptions.GSSError as e:
            self._handle_exception(e)
        finally:
            self.close()

    if six.PY3:
        def __send_request(self, connection, host, handler, request_body, debug):
            # Based on xmlrpc.client.Transport.send_request
            headers = self._extra_headers[:]
            if debug:
                connection.set_debuglevel(1)
            if self.accept_gzip_encoding and gzip:
                connection.putrequest("POST", handler, skip_accept_encoding=True)
                connection.putheader("Accept-Encoding", "gzip")
                headers.append(("Accept-Encoding", "gzip"))
            else:
                connection.putrequest("POST", handler)
            headers.append(("User-Agent", self.user_agent))
            self.send_headers(connection, headers)  # pylint: disable=E1101
            self.send_content(connection, request_body)
            return connection

    def store_session_cookie(self, cookie_header):
        '''
        Given the contents of a Set-Cookie header scan the header and
        extract each cookie contained within until the session cookie
        is located. Examine the session cookie if the domain and path
        are specified, if not update the cookie with those values from
        the request URL. Then write the session cookie into the key
        store for the principal. If the cookie header is None or the
        session cookie is not present in the header no action is
        taken.

        Context Dependencies:

        The per thread context is expected to contain:
            principal
                The current pricipal the HTTP request was issued for.
            request_url
                The URL of the HTTP request.

        '''

        if cookie_header is None:
            return

        principal = getattr(context, 'principal', None)
        request_url = getattr(context, 'request_url', None)
        root_logger.debug("received Set-Cookie (%s)'%s'", type(cookie_header),
                          cookie_header)

        if not isinstance(cookie_header, list):
            cookie_header = [cookie_header]

        # Search for the session cookie
        session_cookie = None
        try:
            for cookie in cookie_header:
                session_cookie = \
                    Cookie.get_named_cookie_from_string(cookie, COOKIE_NAME,
                                                        request_url)
                if session_cookie is not None:
                    break
        except Exception as e:
            root_logger.error("unable to parse cookie header '%s': %s", cookie_header, e)
            return

        if session_cookie is None:
            return

        cookie_string = str(session_cookie)
        root_logger.debug("storing cookie '%s' for principal %s", cookie_string, principal)
        try:
            update_persistent_client_session_data(principal, cookie_string)
        except Exception as e:
            # Not fatal, we just can't use the session cookie we were sent.
            pass

    def parse_response(self, response):
        if six.PY2:
            header = response.msg.getheaders('Set-Cookie')
        else:
            header = response.msg.get_all('Set-Cookie')
        self.store_session_cookie(header)
        return SSLTransport.parse_response(self, response)


class DelegatedKerbTransport(KerbTransport):
    """
    Handles Kerberos Negotiation authentication and TGT delegation to an
    XML-RPC server.
    """
    flags = [gssapi.RequirementFlag.delegate_to_peer,
             gssapi.RequirementFlag.mutual_authentication,
             gssapi.RequirementFlag.out_of_sequence_detection]


class RPCClient(Connectible):
    """
    Forwarding backend plugin for XML-RPC client.

    Also see the `ipaserver.rpcserver.xmlserver` plugin.
    """

    # Values to set on subclasses:
    session_path = None
    server_proxy_class = ServerProxy
    protocol = None
    env_rpc_uri_key = None

    def get_url_list(self, rpc_uri):
        """
        Create a list of urls consisting of the available IPA servers.
        """
        # the configured URL defines what we use for the discovered servers
        (_scheme, _netloc, path, _params, _query, _fragment
            ) = urllib.parse.urlparse(rpc_uri)
        servers = []
        name = '_ldap._tcp.%s.' % self.env.domain

        try:
            answers = resolver.query(name, rdatatype.SRV)
        except DNSException:
            answers = []

        for answer in answers:
            server = str(answer.target).rstrip(".")
            servers.append('https://%s%s' % (ipautil.format_netloc(server), path))

        servers = list(set(servers))
        # the list/set conversion won't preserve order so stick in the
        # local config file version here.
        cfg_server = rpc_uri
        if cfg_server in servers:
            # make sure the configured master server is there just once and
            # it is the first one
            servers.remove(cfg_server)
            servers.insert(0, cfg_server)
        else:
            servers.insert(0, cfg_server)

        return servers

    def get_session_cookie_from_persistent_storage(self, principal):
        '''
        Retrieves the session cookie for the given principal from the
        persistent secure storage. Returns None if not found or unable
        to retrieve the session cookie for any reason, otherwise
        returns a Cookie object containing the session cookie.
        '''

        # Get the session data, it should contain a cookie string
        # (possibly with more than one cookie).
        try:
            cookie_string = read_persistent_client_session_data(principal)
        except Exception:
            return None

        # Search for the session cookie within the cookie string
        try:
            session_cookie = Cookie.get_named_cookie_from_string(cookie_string, COOKIE_NAME)
        except Exception:
            return None

        return session_cookie

    def apply_session_cookie(self, url):
        '''
        Attempt to load a session cookie for the current principal
        from the persistent secure storage. If the cookie is
        successfully loaded adjust the input url's to point to the
        session path and insert the session cookie into the per thread
        context for later insertion into the HTTP request. If the
        cookie is not successfully loaded then the original url is
        returned and the per thread context is not modified.

        Context Dependencies:

        The per thread context is expected to contain:
            principal
                The current pricipal the HTTP request was issued for.

        The per thread context will be updated with:
            session_cookie
                A cookie string to be inserted into the Cookie header
                of the HTPP request.

        '''

        original_url = url
        principal = getattr(context, 'principal', None)

        session_cookie = self.get_session_cookie_from_persistent_storage(principal)
        if session_cookie is None:
            self.log.debug("failed to find session_cookie in persistent storage for principal '%s'",
                           principal)
            return original_url
        else:
            self.debug("found session_cookie in persistent storage for principal '%s', cookie: '%s'",
                       principal, session_cookie)

        # Decide if we should send the cookie to the server
        try:
            session_cookie.http_return_ok(original_url)
        except Cookie.Expired as e:
            self.debug("deleting session data for principal '%s': %s", principal, e)
            try:
                delete_persistent_client_session_data(principal)
            except Exception as e:
                pass
            return original_url
        except Cookie.URLMismatch as e:
            self.debug("not sending session cookie, URL mismatch: %s", e)
            return original_url
        except Exception as e:
            self.error("not sending session cookie, unknown error: %s", e)
            return original_url

        # O.K. session_cookie is valid to be returned, stash it away where it will will
        # get included in a HTTP Cookie headed sent to the server.
        self.log.debug("setting session_cookie into context '%s'", session_cookie.http_cookie())
        setattr(context, 'session_cookie', session_cookie.http_cookie())

        # Form the session URL by substituting the session path into the original URL
        scheme, netloc, path, params, query, fragment = urllib.parse.urlparse(original_url)
        path = self.session_path
        # urlencode *can* take one argument
        # pylint: disable=too-many-function-args
        session_url = urllib.parse.urlunparse((scheme, netloc, path, params, query, fragment))

        return session_url

    def create_connection(self, ccache=None, verbose=None, fallback=None,
                          delegate=None, ca_certfile=None):
        if verbose is None:
            verbose = self.api.env.verbose
        if fallback is None:
            fallback = self.api.env.fallback
        if delegate is None:
            delegate = self.api.env.delegate
        if ca_certfile is None:
            ca_certfile = self.api.env.tls_ca_cert
        try:
            rpc_uri = self.env[self.env_rpc_uri_key]
            principal = get_principal(ccache_name=ccache)
            stored_principal = getattr(context, 'principal', None)
            if principal != stored_principal:
                try:
                    delattr(context, 'session_cookie')
                except AttributeError:
                    pass
            setattr(context, 'principal', principal)
            # We have a session cookie, try using the session URI to see if it
            # is still valid
            if not delegate:
                rpc_uri = self.apply_session_cookie(rpc_uri)
        except (errors.CCacheError, ValueError):
            # No session key, do full Kerberos auth
            pass
        context.ca_certfile = ca_certfile
        urls = self.get_url_list(rpc_uri)
        serverproxy = None
        for url in urls:
            kw = dict(allow_none=True, encoding='UTF-8')
            kw['verbose'] = verbose
            if url.startswith('https://'):
                if delegate:
                    transport_class = DelegatedKerbTransport
                else:
                    transport_class = KerbTransport
            else:
                transport_class = LanguageAwareTransport
            kw['transport'] = transport_class(protocol=self.protocol,
                                              service='HTTP', ccache=ccache)
            self.log.info('trying %s' % url)
            setattr(context, 'request_url', url)
            serverproxy = self.server_proxy_class(url, **kw)
            if len(urls) == 1:
                # if we have only 1 server and then let the
                # main requester handle any errors. This also means it
                # must handle a 401 but we save a ping.
                return serverproxy
            try:
                command = getattr(serverproxy, 'ping')
                try:
                    command([], {})
                except Fault as e:
                    e = decode_fault(e)
                    if e.faultCode in errors_by_code:
                        error = errors_by_code[e.faultCode]
                        raise error(message=e.faultString)
                    else:
                        raise UnknownError(
                            code=e.faultCode,
                            error=e.faultString,
                            server=url,
                        )
                # We don't care about the response, just that we got one
                break
            except KerberosError as krberr:
                # kerberos error on one server is likely on all
                raise errors.KerberosError(message=unicode(krberr))
            except ProtocolError as e:
                if hasattr(context, 'session_cookie') and e.errcode == 401:
                    # Unauthorized. Remove the session and try again.
                    delattr(context, 'session_cookie')
                    try:
                        delete_persistent_client_session_data(principal)
                    except Exception as e:
                        # This shouldn't happen if we have a session but it isn't fatal.
                        pass
                    return self.create_connection(ccache, verbose, fallback, delegate)
                if not fallback:
                    raise
                serverproxy = None
            except Exception as e:
                if not fallback:
                    raise
                else:
                    self.log.info('Connection to %s failed with %s', url, e)
                serverproxy = None

        if serverproxy is None:
            raise NetworkError(uri=_('any of the configured servers'),
                error=', '.join(urls))
        return serverproxy

    def destroy_connection(self):
        conn = getattr(context, self.id, None)
        if conn is not None:
            conn = conn.conn._ServerProxy__transport
            conn.close()

    def _call_command(self, command, params):
        """Call the command with given params"""
        # For XML, this method will wrap/unwrap binary values
        # For JSON we do that in the proxy
        return command(*params)

    def forward(self, name, *args, **kw):
        """
        Forward call to command named ``name`` over XML-RPC.

        This method will encode and forward an XML-RPC request, and will then
        decode and return the corresponding XML-RPC response.

        :param command: The name of the command being forwarded.
        :param args: Positional arguments to pass to remote command.
        :param kw: Keyword arguments to pass to remote command.
        """
        server = getattr(context, 'request_url', None)
        self.log.info("Forwarding '%s' to %s server '%s'",
                      name, self.protocol, server)
        command = getattr(self.conn, name)
        params = [args, kw]
        try:
            return self._call_command(command, params)
        except Fault as e:
            e = decode_fault(e)
            self.debug('Caught fault %d from server %s: %s', e.faultCode,
                server, e.faultString)
            if e.faultCode in errors_by_code:
                error = errors_by_code[e.faultCode]
                raise error(message=e.faultString)
            raise UnknownError(
                code=e.faultCode,
                error=e.faultString,
                server=server,
            )
        except SSLError as e:
            raise NetworkError(uri=server, error=str(e))
        except ProtocolError as e:
            # By catching a 401 here we can detect the case where we have
            # a single IPA server and the session is invalid. Otherwise
            # we always have to do a ping().
            session_cookie = getattr(context, 'session_cookie', None)
            if session_cookie and e.errcode == 401:
                # Unauthorized. Remove the session and try again.
                delattr(context, 'session_cookie')
                try:
                    principal = getattr(context, 'principal', None)
                    delete_persistent_client_session_data(principal)
                except Exception as e:
                    # This shouldn't happen if we have a session but it isn't fatal.
                    pass

                # Create a new serverproxy with the non-session URI
                serverproxy = self.create_connection(os.environ.get('KRB5CCNAME'), self.env.verbose, self.env.fallback, self.env.delegate)
                setattr(context, self.id, Connection(serverproxy, self.disconnect))
                return self.forward(name, *args, **kw)
            raise NetworkError(uri=server, error=e.errmsg)
        except socket.error as e:
            raise NetworkError(uri=server, error=str(e))
        except (OverflowError, TypeError) as e:
            raise XMLRPCMarshallError(error=str(e))


class xmlclient(RPCClient):
    session_path = '/ipa/session/xml'
    server_proxy_class = ServerProxy
    protocol = 'xml'
    env_rpc_uri_key = 'xmlrpc_uri'

    def _call_command(self, command, params):
        version = params[1].get('version', VERSION_WITHOUT_CAPABILITIES)
        params = xml_wrap(params, version)
        result = command(*params)
        return xml_unwrap(result)


class JSONServerProxy(object):
    def __init__(self, uri, transport, encoding, verbose, allow_none):
        split_uri = urllib.parse.urlsplit(uri)
        if split_uri.scheme not in ("http", "https"):
            raise IOError("unsupported XML-RPC protocol")
        self.__host = split_uri.netloc
        self.__handler = split_uri.path
        self.__transport = transport

        assert encoding == 'UTF-8'
        assert allow_none
        self.__verbose = verbose

        # FIXME: Some of our code requires ServerProxy internals.
        # But, xmlrpc.client.ServerProxy's _ServerProxy__transport can be accessed
        # by calling serverproxy('transport')
        self._ServerProxy__transport = transport

    def __request(self, name, args):
        print_json = self.__verbose >= 2
        payload = {'method': unicode(name), 'params': args, 'id': 0}
        version = args[1].get('version', VERSION_WITHOUT_CAPABILITIES)
        payload = json_encode_binary(
            payload, version, pretty_print=print_json)

        if print_json:
            root_logger.info(
                'Request: %s',
                payload
            )

        response = self.__transport.request(
            self.__host,
            self.__handler,
            payload.encode('utf-8'),
            verbose=self.__verbose >= 3,
        )

        try:
            response = json_decode_binary(response)
        except ValueError as e:
            raise JSONError(error=str(e))

        if print_json:
            root_logger.info(
                'Response: %s',
                json.dumps(response, sort_keys=True, indent=4)
            )
        error = response.get('error')
        if error:
            try:
                error_class = errors_by_code[error['code']]
            except KeyError:
                raise UnknownError(
                    code=error.get('code'),
                    error=error.get('message'),
                    server=self.__host,
                )
            else:
                kw = error.get('data', {})
                kw['message'] = error['message']
                raise error_class(**kw)

        return response['result']

    def __getattr__(self, name):
        def _call(*args):
            return self.__request(name, args)
        return _call


class jsonclient(RPCClient):
    session_path = '/ipa/session/json'
    server_proxy_class = JSONServerProxy
    protocol = 'json'
    env_rpc_uri_key = 'jsonrpc_uri'