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Filename : netutil.py
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#!/usr/bin/env python
#
# Copyright 2011 Facebook
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

"""Miscellaneous network utility code."""
# pylint: skip-file

from __future__ import absolute_import, division, print_function

import errno
import os
import sys
import socket
import stat

from salt.ext.tornado.concurrent import dummy_executor, run_on_executor
from salt.ext.tornado.ioloop import IOLoop
from salt.ext.tornado.platform.auto import set_close_exec
from salt.ext.tornado.util import PY3, Configurable, errno_from_exception

try:
    import ssl
except ImportError:
    # ssl is not available on Google App Engine
    ssl = None

try:
    import certifi
except ImportError:
    # certifi is optional as long as we have ssl.create_default_context.
    if ssl is None or hasattr(ssl, 'create_default_context'):
        certifi = None
    else:
        raise

if PY3:
    xrange = range

if hasattr(ssl, 'match_hostname') and hasattr(ssl, 'CertificateError'):  # python 3.2+
    ssl_match_hostname = ssl.match_hostname
    SSLCertificateError = ssl.CertificateError
elif ssl is None:
    ssl_match_hostname = SSLCertificateError = None  # type: ignore
else:
    #import backports.ssl_match_hostname
    #ssl_match_hostname = backports.ssl_match_hostname.match_hostname
    #SSLCertificateError = backports.ssl_match_hostname.CertificateError  # type: ignore
    #"""The match_hostname() function from Python 3.7.0, essential when using SSL."""

    import sys
    import socket as _socket

    try:
        # Divergence: Python-3.7+'s _ssl has this exception type but older Pythons do not
        from _ssl import SSLCertVerificationError
        CertificateError = SSLCertVerificationError
    except:
        class CertificateError(ValueError):
            pass

    SSLCertificateError = CertificateError

    #__version__ = '3.7.0.1'


    # Divergence: Added to deal with ipaddess as bytes on python2
    def _to_text(obj):
        if isinstance(obj, str) and sys.version_info < (3,):
            obj = unicode(obj, encoding='ascii', errors='strict')
        elif sys.version_info >= (3,) and isinstance(obj, bytes):
            obj = str(obj, encoding='ascii', errors='strict')
        return obj


    def _to_bytes(obj):
        if isinstance(obj, str) and sys.version_info >= (3,):
            obj = bytes(obj, encoding='ascii', errors='strict')
        elif sys.version_info < (3,) and isinstance(obj, unicode):
            obj = obj.encode('ascii', 'strict')
        return obj


    def _dnsname_match(dn, hostname):
        """Matching according to RFC 6125, section 6.4.3

        - Hostnames are compared lower case.
        - For IDNA, both dn and hostname must be encoded as IDN A-label (ACE).
        - Partial wildcards like 'www*.example.org', multiple wildcards, sole
          wildcard or wildcards in labels other then the left-most label are not
          supported and a CertificateError is raised.
        - A wildcard must match at least one character.
        """
        if not dn:
            return False

        wildcards = dn.count('*')
        # speed up common case w/o wildcards
        if not wildcards:
            return dn.lower() == hostname.lower()

        if wildcards > 1:
            # Divergence .format() to percent formatting for Python < 2.6
            raise CertificateError(
                "too many wildcards in certificate DNS name: %s" % repr(dn))

        dn_leftmost, sep, dn_remainder = dn.partition('.')

        if '*' in dn_remainder:
            # Only match wildcard in leftmost segment.
            # Divergence .format() to percent formatting for Python < 2.6
            raise CertificateError(
                "wildcard can only be present in the leftmost label: "
                "%s." % repr(dn))

        if not sep:
            # no right side
            # Divergence .format() to percent formatting for Python < 2.6
            raise CertificateError(
                "sole wildcard without additional labels are not support: "
                "%s." % repr(dn))

        if dn_leftmost != '*':
            # no partial wildcard matching
            # Divergence .format() to percent formatting for Python < 2.6
            raise CertificateError(
                "partial wildcards in leftmost label are not supported: "
                "%s." % repr(dn))

        hostname_leftmost, sep, hostname_remainder = hostname.partition('.')
        if not hostname_leftmost or not sep:
            # wildcard must match at least one char
            return False
        return dn_remainder.lower() == hostname_remainder.lower()


    def _inet_paton(ipname):
        """Try to convert an IP address to packed binary form

        Supports IPv4 addresses on all platforms and IPv6 on platforms with IPv6
        support.
        """
        # inet_aton() also accepts strings like '1'
        # Divergence: We make sure we have native string type for all python versions
        try:
            b_ipname = _to_bytes(ipname)
        except UnicodeError:
            raise ValueError("%s must be an all-ascii string." % repr(ipname))

        # Set ipname in native string format
        if sys.version_info < (3,):
            n_ipname = b_ipname
        else:
            n_ipname = ipname

        if n_ipname.count('.') == 3:
            try:
                return _socket.inet_aton(n_ipname)
            # Divergence: OSError on late python3.  socket.error earlier.
            # Null bytes generate ValueError on python3(we want to raise
            # ValueError anyway), TypeError # earlier
            except (OSError, _socket.error, TypeError):
                pass

        try:
            return _socket.inet_pton(_socket.AF_INET6, n_ipname)
        # Divergence: OSError on late python3.  socket.error earlier.
        # Null bytes generate ValueError on python3(we want to raise
        # ValueError anyway), TypeError # earlier
        except (OSError, _socket.error, TypeError):
            # Divergence .format() to percent formatting for Python < 2.6
            raise ValueError("%s is neither an IPv4 nor an IP6 "
                             "address." % repr(ipname))
        except AttributeError:
            # AF_INET6 not available
            pass

        # Divergence .format() to percent formatting for Python < 2.6
        raise ValueError("%s is not an IPv4 address." % repr(ipname))


    def _ipaddress_match(ipname, host_ip):
        """Exact matching of IP addresses.

        RFC 6125 explicitly doesn't define an algorithm for this
        (section 1.7.2 - "Out of Scope").
        """
        # OpenSSL may add a trailing newline to a subjectAltName's IP address
        ip = _inet_paton(ipname.rstrip())
        return ip == host_ip


    def match_hostname(cert, hostname):
        """Verify that *cert* (in decoded format as returned by
        SSLSocket.getpeercert()) matches the *hostname*.  RFC 2818 and RFC 6125
        rules are followed.

        The function matches IP addresses rather than dNSNames if hostname is a
        valid ipaddress string. IPv4 addresses are supported on all platforms.
        IPv6 addresses are supported on platforms with IPv6 support (AF_INET6
        and inet_pton).

        CertificateError is raised on failure. On success, the function
        returns nothing.
        """
        if not cert:
            raise ValueError("empty or no certificate, match_hostname needs a "
                             "SSL socket or SSL context with either "
                             "CERT_OPTIONAL or CERT_REQUIRED")
        try:
            # Divergence: Deal with hostname as bytes
            host_ip = _inet_paton(_to_text(hostname))
        except ValueError:
            # Not an IP address (common case)
            host_ip = None
        except UnicodeError:
            # Divergence: Deal with hostname as byte strings.
            # IP addresses should be all ascii, so we consider it not
            # an IP address if this fails
            host_ip = None
        dnsnames = []
        san = cert.get('subjectAltName', ())
        for key, value in san:
            if key == 'DNS':
                if host_ip is None and _dnsname_match(value, hostname):
                    return
                dnsnames.append(value)
            elif key == 'IP Address':
                if host_ip is not None and _ipaddress_match(value, host_ip):
                    return
                dnsnames.append(value)
        if not dnsnames:
            # The subject is only checked when there is no dNSName entry
            # in subjectAltName
            for sub in cert.get('subject', ()):
                for key, value in sub:
                    # XXX according to RFC 2818, the most specific Common Name
                    # must be used.
                    if key == 'commonName':
                        if _dnsname_match(value, hostname):
                            return
                        dnsnames.append(value)
        if len(dnsnames) > 1:
            raise CertificateError("hostname %r "
                "doesn't match either of %s"
                % (hostname, ', '.join(map(repr, dnsnames))))
        elif len(dnsnames) == 1:
            raise CertificateError("hostname %r "
                "doesn't match %r"
                % (hostname, dnsnames[0]))
        else:
            raise CertificateError("no appropriate commonName or "
                "subjectAltName fields were found")

    ssl_match_hostname = match_hostname


if hasattr(ssl, 'SSLContext'):
    if hasattr(ssl, 'create_default_context'):
        # Python 2.7.9+, 3.4+
        # Note that the naming of ssl.Purpose is confusing; the purpose
        # of a context is to authentiate the opposite side of the connection.
        # On Windows, ssl.create_default_context() calls load_default_certs(),
        # which reads the OS root store as a single blob; a single malformed
        # cert there aborts the whole load with ASN1 NOT_ENOUGH_DATA under
        # OpenSSL 3.5.x (shipped by relenv >= 0.22.13). See cpython#104135.
        # Point at certifi to bypass the OS store.
        #
        # Needed on Python 3.10 and 3.11: cpython merged the iterate-and-skip
        # variant of _load_windows_store_certs into Lib/ssl.py for the 3.12
        # branch but never backported it to 3.10 (security-only) or 3.11
        # (still in bug-fix mode but the backport never landed). 3008.x and
        # later use Python 3.14 whose stdlib already has the upstream fix
        # and does not need this branch. DO NOT forward-merge this
        # special-case to a branch whose onedir Python is >= 3.12 - collapse
        # it back to the unconditional ssl.create_default_context() form.
        #
        # DURABLE CLEANUP: this disappears once relenv carries the
        # cpython#104135 patch in its cpython build. See salt/__init__.py
        # for the cleanup pointer.
        #
        # Companion work-arounds (delete together with this block):
        #   - salt/__init__.py: _load_windows_store_certs monkey-patch
        #   - cicd/windows-ssl-104135-patch.py + the Patch-Lib/ssl.py steps
        #     in .github/workflows/{build-deps-ci,test,test-packages}-
        #     action.yml's Windows jobs.
        if sys.platform == 'win32' and certifi is not None:
            _client_ssl_defaults = ssl.create_default_context(
                ssl.Purpose.SERVER_AUTH, cafile=certifi.where())
            _server_ssl_defaults = ssl.create_default_context(
                ssl.Purpose.CLIENT_AUTH, cafile=certifi.where())
        else:
            _client_ssl_defaults = ssl.create_default_context(
                ssl.Purpose.SERVER_AUTH)
            _server_ssl_defaults = ssl.create_default_context(
                ssl.Purpose.CLIENT_AUTH)
    else:
        # Python 3.2-3.3
        _client_ssl_defaults = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
        _client_ssl_defaults.verify_mode = ssl.CERT_REQUIRED
        _client_ssl_defaults.load_verify_locations(certifi.where())
        _server_ssl_defaults = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
        if hasattr(ssl, 'OP_NO_COMPRESSION'):
            # Disable TLS compression to avoid CRIME and related attacks.
            # This constant wasn't added until python 3.3.
            _client_ssl_defaults.options |= ssl.OP_NO_COMPRESSION
            _server_ssl_defaults.options |= ssl.OP_NO_COMPRESSION

elif ssl:
    # Python 2.6-2.7.8
    _client_ssl_defaults = dict(cert_reqs=ssl.CERT_REQUIRED,
                                ca_certs=certifi.where())
    _server_ssl_defaults = {}
else:
    # Google App Engine
    _client_ssl_defaults = dict(cert_reqs=None,
                                ca_certs=None)
    _server_ssl_defaults = {}

# ThreadedResolver runs getaddrinfo on a thread. If the hostname is unicode,
# getaddrinfo attempts to import encodings.idna. If this is done at
# module-import time, the import lock is already held by the main thread,
# leading to deadlock. Avoid it by caching the idna encoder on the main
# thread now.
u'foo'.encode('idna')

# For undiagnosed reasons, 'latin1' codec may also need to be preloaded.
u'foo'.encode('latin1')

# These errnos indicate that a non-blocking operation must be retried
# at a later time.  On most platforms they're the same value, but on
# some they differ.
_ERRNO_WOULDBLOCK = (errno.EWOULDBLOCK, errno.EAGAIN)

if hasattr(errno, "WSAEWOULDBLOCK"):
    _ERRNO_WOULDBLOCK += (errno.WSAEWOULDBLOCK,)  # type: ignore

# Default backlog used when calling sock.listen()
_DEFAULT_BACKLOG = 128


def bind_sockets(port, address=None, family=socket.AF_UNSPEC,
                 backlog=_DEFAULT_BACKLOG, flags=None, reuse_port=False):
    """Creates listening sockets bound to the given port and address.

    Returns a list of socket objects (multiple sockets are returned if
    the given address maps to multiple IP addresses, which is most common
    for mixed IPv4 and IPv6 use).

    Address may be either an IP address or hostname.  If it's a hostname,
    the server will listen on all IP addresses associated with the
    name.  Address may be an empty string or None to listen on all
    available interfaces.  Family may be set to either `socket.AF_INET`
    or `socket.AF_INET6` to restrict to IPv4 or IPv6 addresses, otherwise
    both will be used if available.

    The ``backlog`` argument has the same meaning as for
    `socket.listen() <socket.socket.listen>`.

    ``flags`` is a bitmask of AI_* flags to `~socket.getaddrinfo`, like
    ``socket.AI_PASSIVE | socket.AI_NUMERICHOST``.

    ``reuse_port`` option sets ``SO_REUSEPORT`` option for every socket
    in the list. If your platform doesn't support this option ValueError will
    be raised.
    """
    if reuse_port and not hasattr(socket, "SO_REUSEPORT"):
        raise ValueError("the platform doesn't support SO_REUSEPORT")

    sockets = []
    if address == "":
        address = None
    if not socket.has_ipv6 and family == socket.AF_UNSPEC:
        # Python can be compiled with --disable-ipv6, which causes
        # operations on AF_INET6 sockets to fail, but does not
        # automatically exclude those results from getaddrinfo
        # results.
        # http://bugs.python.org/issue16208
        family = socket.AF_INET
    if flags is None:
        flags = socket.AI_PASSIVE
    bound_port = None
    for res in set(socket.getaddrinfo(address, port, family, socket.SOCK_STREAM,
                                      0, flags)):
        af, socktype, proto, canonname, sockaddr = res
        if (sys.platform == 'darwin' and address == 'localhost' and
                af == socket.AF_INET6 and sockaddr[3] != 0):
            # Mac OS X includes a link-local address fe80::1%lo0 in the
            # getaddrinfo results for 'localhost'.  However, the firewall
            # doesn't understand that this is a local address and will
            # prompt for access (often repeatedly, due to an apparent
            # bug in its ability to remember granting access to an
            # application). Skip these addresses.
            continue
        try:
            sock = socket.socket(af, socktype, proto)
        except socket.error as e:
            if errno_from_exception(e) == errno.EAFNOSUPPORT:
                continue
            raise
        set_close_exec(sock.fileno())
        if os.name != 'nt':
            sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        if reuse_port:
            sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
        if af == socket.AF_INET6:
            # On linux, ipv6 sockets accept ipv4 too by default,
            # but this makes it impossible to bind to both
            # 0.0.0.0 in ipv4 and :: in ipv6.  On other systems,
            # separate sockets *must* be used to listen for both ipv4
            # and ipv6.  For consistency, always disable ipv4 on our
            # ipv6 sockets and use a separate ipv4 socket when needed.
            #
            # Python 2.x on windows doesn't have IPPROTO_IPV6.
            if hasattr(socket, "IPPROTO_IPV6"):
                sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 1)

        # automatic port allocation with port=None
        # should bind on the same port on IPv4 and IPv6
        host, requested_port = sockaddr[:2]
        if requested_port == 0 and bound_port is not None:
            sockaddr = tuple([host, bound_port] + list(sockaddr[2:]))

        sock.setblocking(0)
        sock.bind(sockaddr)
        bound_port = sock.getsockname()[1]
        sock.listen(backlog)
        sockets.append(sock)
    return sockets


if hasattr(socket, 'AF_UNIX'):
    def bind_unix_socket(file, mode=0o600, backlog=_DEFAULT_BACKLOG):
        """Creates a listening unix socket.

        If a socket with the given name already exists, it will be deleted.
        If any other file with that name exists, an exception will be
        raised.

        Returns a socket object (not a list of socket objects like
        `bind_sockets`)
        """
        sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
        set_close_exec(sock.fileno())
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        sock.setblocking(0)
        try:
            st = os.stat(file)
        except OSError as err:
            if errno_from_exception(err) != errno.ENOENT:
                raise
        else:
            if stat.S_ISSOCK(st.st_mode):
                os.remove(file)
            else:
                raise ValueError("File %s exists and is not a socket", file)
        sock.bind(file)
        os.chmod(file, mode)
        sock.listen(backlog)
        return sock


def add_accept_handler(sock, callback, io_loop=None):
    """Adds an `.IOLoop` event handler to accept new connections on ``sock``.

    When a connection is accepted, ``callback(connection, address)`` will
    be run (``connection`` is a socket object, and ``address`` is the
    address of the other end of the connection).  Note that this signature
    is different from the ``callback(fd, events)`` signature used for
    `.IOLoop` handlers.

    .. versionchanged:: 4.1
       The ``io_loop`` argument is deprecated.
    """
    if io_loop is None:
        io_loop = IOLoop.current()

    def accept_handler(fd, events):
        # More connections may come in while we're handling callbacks;
        # to prevent starvation of other tasks we must limit the number
        # of connections we accept at a time.  Ideally we would accept
        # up to the number of connections that were waiting when we
        # entered this method, but this information is not available
        # (and rearranging this method to call accept() as many times
        # as possible before running any callbacks would have adverse
        # effects on load balancing in multiprocess configurations).
        # Instead, we use the (default) listen backlog as a rough
        # heuristic for the number of connections we can reasonably
        # accept at once.
        for i in xrange(_DEFAULT_BACKLOG):
            try:
                connection, address = sock.accept()
            except socket.error as e:
                # _ERRNO_WOULDBLOCK indicate we have accepted every
                # connection that is available.
                if errno_from_exception(e) in _ERRNO_WOULDBLOCK:
                    return
                # ECONNABORTED indicates that there was a connection
                # but it was closed while still in the accept queue.
                # (observed on FreeBSD).
                if errno_from_exception(e) == errno.ECONNABORTED:
                    continue
                raise
            set_close_exec(connection.fileno())
            callback(connection, address)
    io_loop.add_handler(sock, accept_handler, IOLoop.READ)


def is_valid_ip(ip):
    """Returns true if the given string is a well-formed IP address.

    Supports IPv4 and IPv6.
    """
    if not ip or '\x00' in ip:
        # getaddrinfo resolves empty strings to localhost, and truncates
        # on zero bytes.
        return False
    try:
        res = socket.getaddrinfo(ip, 0, socket.AF_UNSPEC,
                                 socket.SOCK_STREAM,
                                 0, socket.AI_NUMERICHOST)
        return bool(res)
    except socket.gaierror as e:
        if e.args[0] == socket.EAI_NONAME:
            return False
        raise
    return True


class Resolver(Configurable):
    """Configurable asynchronous DNS resolver interface.

    By default, a blocking implementation is used (which simply calls
    `socket.getaddrinfo`).  An alternative implementation can be
    chosen with the `Resolver.configure <.Configurable.configure>`
    class method::

        Resolver.configure('tornado.netutil.ThreadedResolver')

    The implementations of this interface included with Tornado are

    * `tornado.netutil.BlockingResolver`
    * `tornado.netutil.ThreadedResolver`
    * `tornado.netutil.OverrideResolver`
    * `tornado.platform.twisted.TwistedResolver`
    * `tornado.platform.caresresolver.CaresResolver`
    """
    @classmethod
    def configurable_base(cls):
        return Resolver

    @classmethod
    def configurable_default(cls):
        return BlockingResolver

    def resolve(self, host, port, family=socket.AF_UNSPEC, callback=None):
        """Resolves an address.

        The ``host`` argument is a string which may be a hostname or a
        literal IP address.

        Returns a `.Future` whose result is a list of (family,
        address) pairs, where address is a tuple suitable to pass to
        `socket.connect <socket.socket.connect>` (i.e. a ``(host,
        port)`` pair for IPv4; additional fields may be present for
        IPv6). If a ``callback`` is passed, it will be run with the
        result as an argument when it is complete.

        :raises IOError: if the address cannot be resolved.

        .. versionchanged:: 4.4
           Standardized all implementations to raise `IOError`.
        """
        raise NotImplementedError()

    def close(self):
        """Closes the `Resolver`, freeing any resources used.

        .. versionadded:: 3.1

        """
        pass


class ExecutorResolver(Resolver):
    """Resolver implementation using a `concurrent.futures.Executor`.

    Use this instead of `ThreadedResolver` when you require additional
    control over the executor being used.

    The executor will be shut down when the resolver is closed unless
    ``close_resolver=False``; use this if you want to reuse the same
    executor elsewhere.

    .. versionchanged:: 4.1
       The ``io_loop`` argument is deprecated.
    """
    def initialize(self, io_loop=None, executor=None, close_executor=True):
        self.io_loop = io_loop or IOLoop.current()
        if executor is not None:
            self.executor = executor
            self.close_executor = close_executor
        else:
            self.executor = dummy_executor
            self.close_executor = False

    def close(self):
        if self.close_executor:
            self.executor.shutdown()
        self.executor = None

    @run_on_executor
    def resolve(self, host, port, family=socket.AF_UNSPEC):
        # On Solaris, getaddrinfo fails if the given port is not found
        # in /etc/services and no socket type is given, so we must pass
        # one here.  The socket type used here doesn't seem to actually
        # matter (we discard the one we get back in the results),
        # so the addresses we return should still be usable with SOCK_DGRAM.
        addrinfo = socket.getaddrinfo(host, port, family, socket.SOCK_STREAM)
        results = []
        for family, socktype, proto, canonname, address in addrinfo:
            results.append((family, address))
        return results


class BlockingResolver(ExecutorResolver):
    """Default `Resolver` implementation, using `socket.getaddrinfo`.

    The `.IOLoop` will be blocked during the resolution, although the
    callback will not be run until the next `.IOLoop` iteration.
    """
    def initialize(self, io_loop=None):
        super(BlockingResolver, self).initialize(io_loop=io_loop)


class ThreadedResolver(ExecutorResolver):
    """Multithreaded non-blocking `Resolver` implementation.

    Requires the `concurrent.futures` package to be installed
    (available in the standard library since Python 3.2,
    installable with ``pip install futures`` in older versions).

    The thread pool size can be configured with::

        Resolver.configure('tornado.netutil.ThreadedResolver',
                           num_threads=10)

    .. versionchanged:: 3.1
       All ``ThreadedResolvers`` share a single thread pool, whose
       size is set by the first one to be created.
    """
    _threadpool = None  # type: ignore
    _threadpool_pid = None  # type: int

    def initialize(self, io_loop=None, num_threads=10):
        threadpool = ThreadedResolver._create_threadpool(num_threads)
        super(ThreadedResolver, self).initialize(
            io_loop=io_loop, executor=threadpool, close_executor=False)

    @classmethod
    def _create_threadpool(cls, num_threads):
        pid = os.getpid()
        if cls._threadpool_pid != pid:
            # Threads cannot survive after a fork, so if our pid isn't what it
            # was when we created the pool then delete it.
            cls._threadpool = None
        if cls._threadpool is None:
            from concurrent.futures import ThreadPoolExecutor
            cls._threadpool = ThreadPoolExecutor(num_threads)
            cls._threadpool_pid = pid
        return cls._threadpool


class OverrideResolver(Resolver):
    """Wraps a resolver with a mapping of overrides.

    This can be used to make local DNS changes (e.g. for testing)
    without modifying system-wide settings.

    The mapping can contain either host strings or host-port pairs.
    """
    def initialize(self, resolver, mapping):
        self.resolver = resolver
        self.mapping = mapping

    def close(self):
        self.resolver.close()

    def resolve(self, host, port, *args, **kwargs):
        if (host, port) in self.mapping:
            host, port = self.mapping[(host, port)]
        elif host in self.mapping:
            host = self.mapping[host]
        return self.resolver.resolve(host, port, *args, **kwargs)


# These are the keyword arguments to ssl.wrap_socket that must be translated
# to their SSLContext equivalents (the other arguments are still passed
# to SSLContext.wrap_socket).
_SSL_CONTEXT_KEYWORDS = frozenset(['ssl_version', 'certfile', 'keyfile',
                                   'cert_reqs', 'ca_certs', 'ciphers'])


def ssl_options_to_context(ssl_options):
    """Try to convert an ``ssl_options`` dictionary to an
    `~ssl.SSLContext` object.

    The ``ssl_options`` dictionary contains keywords to be passed to
    `ssl.wrap_socket`.  In Python 2.7.9+, `ssl.SSLContext` objects can
    be used instead.  This function converts the dict form to its
    `~ssl.SSLContext` equivalent, and may be used when a component which
    accepts both forms needs to upgrade to the `~ssl.SSLContext` version
    to use features like SNI or NPN.
    """
    if isinstance(ssl_options, dict):
        assert all(k in _SSL_CONTEXT_KEYWORDS for k in ssl_options), ssl_options
    if (not hasattr(ssl, 'SSLContext') or
            isinstance(ssl_options, ssl.SSLContext)):
        return ssl_options
    context = ssl.SSLContext(
        ssl_options.get('ssl_version', ssl.PROTOCOL_SSLv23))
    if 'certfile' in ssl_options:
        context.load_cert_chain(ssl_options['certfile'], ssl_options.get('keyfile', None))
    if 'cert_reqs' in ssl_options:
        context.verify_mode = ssl_options['cert_reqs']
    if 'ca_certs' in ssl_options:
        context.load_verify_locations(ssl_options['ca_certs'])
    if 'ciphers' in ssl_options:
        context.set_ciphers(ssl_options['ciphers'])
    if hasattr(ssl, 'OP_NO_COMPRESSION'):
        # Disable TLS compression to avoid CRIME and related attacks.
        # This constant wasn't added until python 3.3.
        context.options |= ssl.OP_NO_COMPRESSION
    return context


def ssl_wrap_socket(socket, ssl_options, server_hostname=None, **kwargs):
    """Returns an ``ssl.SSLSocket`` wrapping the given socket.

    ``ssl_options`` may be either an `ssl.SSLContext` object or a
    dictionary (as accepted by `ssl_options_to_context`).  Additional
    keyword arguments are passed to ``wrap_socket`` (either the
    `~ssl.SSLContext` method or the `ssl` module function as
    appropriate).
    """
    context = ssl_options_to_context(ssl_options)
    if hasattr(ssl, 'SSLContext') and isinstance(context, ssl.SSLContext):
        if server_hostname is not None and getattr(ssl, 'HAS_SNI'):
            # Python doesn't have server-side SNI support so we can't
            # really unittest this, but it can be manually tested with
            # python3.2 -m tornado.httpclient https://sni.velox.ch
            return context.wrap_socket(socket, server_hostname=server_hostname,
                                       **kwargs)
        else:
            return context.wrap_socket(socket, **kwargs)
    else:
        return ssl.wrap_socket(socket, **dict(context, **kwargs))  # type: ignore