# Source code for tornado.netutil

    #
    # 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."""

    import asyncio
    import concurrent.futures
    import errno
    import os
    import sys
    import socket
    import ssl
    import stat

    from tornado.concurrent import dummy_executor, run_on_executor
    from tornado.ioloop import IOLoop
    from tornado.util import Configurable, errno_from_exception

    from typing import List, Callable, Any, Type, Dict, Union, Tuple, Awaitable, Optional

    # Note that the naming of ssl.Purpose is confusing; the purpose
    # of a context is to authenticate the opposite side of the connection.
    _client_ssl_defaults = ssl.create_default_context(ssl.Purpose.SERVER_AUTH)
    _server_ssl_defaults = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
    if hasattr(ssl, "OP_NO_COMPRESSION"):
        # See netutil.ssl_options_to_context
        _client_ssl_defaults.options |= ssl.OP_NO_COMPRESSION
        _server_ssl_defaults.options |= ssl.OP_NO_COMPRESSION

    # 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.
    "foo".encode("idna")

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

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

    def bind_sockets(
        port: int,
        address: Optional[str] = None,
        family: socket.AddressFamily = socket.AF_UNSPEC,
        backlog: int = _DEFAULT_BACKLOG,
        flags: Optional[int] = None,
        reuse_port: bool = False,
    ) -> List[socket.socket]:
        """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
        unique_addresses = set()  # type: set
        for res in sorted(
            socket.getaddrinfo(address, port, family, socket.SOCK_STREAM, 0, flags),
            key=lambda x: x[0],
        ):
            if res in unique_addresses:
                continue

            unique_addresses.add(res)

            af, socktype, proto, canonname, sockaddr = res
            if (
                sys.platform == "darwin"
                and address == "localhost"
                and af == socket.AF_INET6
                and sockaddr[3] != 0  # type: ignore
            ):
                # 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
            if os.name != "nt":
                try:
                    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
                except socket.error as e:
                    if errno_from_exception(e) != errno.ENOPROTOOPT:
                        # Hurd doesn't support SO_REUSEADDR.
                        raise
            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(False)
            try:
                sock.bind(sockaddr)
            except OSError as e:
                if (
                    errno_from_exception(e) == errno.EADDRNOTAVAIL
                    and address == "localhost"
                    and sockaddr[0] == "::1"
                ):
                    # On some systems (most notably docker with default
                    # configurations), ipv6 is partially disabled:
                    # socket.has_ipv6 is true, we can create AF_INET6
                    # sockets, and getaddrinfo("localhost", ...,
                    # AF_PASSIVE) resolves to ::1, but we get an error
                    # when binding.
                    #
                    # Swallow the error, but only for this specific case.
                    # If EADDRNOTAVAIL occurs in other situations, it
                    # might be a real problem like a typo in a
                    # configuration.
                    sock.close()
                    continue
                else:
                    raise
            bound_port = sock.getsockname()[1]
            sock.listen(backlog)
            sockets.append(sock)
        return sockets

    if hasattr(socket, "AF_UNIX"):

        def bind_unix_socket(
            file: str, mode: int = 0o600, backlog: int = _DEFAULT_BACKLOG
        ) -> socket.socket:
            """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)
            try:
                sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
            except socket.error as e:
                if errno_from_exception(e) != errno.ENOPROTOOPT:
                    # Hurd doesn't support SO_REUSEADDR
                    raise
            sock.setblocking(False)
            try:
                st = os.stat(file)
            except FileNotFoundError:
                pass
            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: socket.socket, callback: Callable[[socket.socket, Any], None]
    ) -> Callable[[], 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.

        A callable is returned which, when called, will remove the `.IOLoop`
        event handler and stop processing further incoming connections.

        .. versionchanged:: 5.0
           The ``io_loop`` argument (deprecated since version 4.1) has been removed.

        .. versionchanged:: 5.0
           A callable is returned (``None`` was returned before).
        """
        io_loop = IOLoop.current()
        removed = [False]

        def accept_handler(fd: socket.socket, events: int) -> None:
            # 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 range(_DEFAULT_BACKLOG):
                if removed[0]:
                    # The socket was probably closed
                    return
                try:
                    connection, address = sock.accept()
                except BlockingIOError:
                    # EWOULDBLOCK indicates we have accepted every
                    # connection that is available.
                    return
                except ConnectionAbortedError:
                    # ECONNABORTED indicates that there was a connection
                    # but it was closed while still in the accept queue.
                    # (observed on FreeBSD).
                    continue
                callback(connection, address)

        def remove_handler() -> None:
            io_loop.remove_handler(sock)
            removed[0] = True

        io_loop.add_handler(sock, accept_handler, IOLoop.READ)
        return remove_handler

    def is_valid_ip(ip: str) -> bool:
        """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
        except UnicodeError:
            # `socket.getaddrinfo` will raise a UnicodeError from the
            # `idna` decoder if the input is longer than 63 characters,
            # even for socket.AI_NUMERICHOST.  See
            # https://bugs.python.org/issue32958 for discussion
            return False
        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.DefaultLoopResolver`
        * `tornado.netutil.DefaultExecutorResolver` (deprecated)
        * `tornado.netutil.BlockingResolver` (deprecated)
        * `tornado.netutil.ThreadedResolver` (deprecated)
        * `tornado.netutil.OverrideResolver`
        * `tornado.platform.twisted.TwistedResolver` (deprecated)
        * `tornado.platform.caresresolver.CaresResolver` (deprecated)

        .. versionchanged:: 5.0
           The default implementation has changed from `BlockingResolver` to
           `DefaultExecutorResolver`.

        .. versionchanged:: 6.2
           The default implementation has changed from `DefaultExecutorResolver` to
           `DefaultLoopResolver`.
        """

        @classmethod
        def configurable_base(cls) -> Type["Resolver"]:
            return Resolver

        @classmethod
        def configurable_default(cls) -> Type["Resolver"]:
            return DefaultLoopResolver

        def resolve(
            self, host: str, port: int, family: socket.AddressFamily = socket.AF_UNSPEC
        ) -> Awaitable[List[Tuple[int, Any]]]:
            """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`.

            .. versionchanged:: 6.0 The ``callback`` argument was removed.
               Use the returned awaitable object instead.

            """
            raise NotImplementedError()

        def close(self) -> None:
            """Closes the `Resolver`, freeing any resources used.

            .. versionadded:: 3.1

            """
            pass

    def _resolve_addr(
        host: str, port: int, family: socket.AddressFamily = socket.AF_UNSPEC
    ) -> List[Tuple[int, Any]]:
        # 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 fam, socktype, proto, canonname, address in addrinfo:
            results.append((fam, address))
        return results  # type: ignore

    class DefaultExecutorResolver(Resolver):
        """Resolver implementation using `.IOLoop.run_in_executor`.

        .. versionadded:: 5.0

        .. deprecated:: 6.2

           Use `DefaultLoopResolver` instead.
        """

        async def resolve(
            self, host: str, port: int, family: socket.AddressFamily = socket.AF_UNSPEC
        ) -> List[Tuple[int, Any]]:
            result = await IOLoop.current().run_in_executor(
                None, _resolve_addr, host, port, family
            )
            return result

    class DefaultLoopResolver(Resolver):
        """Resolver implementation using `asyncio.loop.getaddrinfo`."""

        async def resolve(
            self, host: str, port: int, family: socket.AddressFamily = socket.AF_UNSPEC
        ) -> List[Tuple[int, Any]]:
            # 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.
            return [
                (fam, address)
                for fam, _, _, _, address in await asyncio.get_running_loop().getaddrinfo(
                    host, port, family=family, type=socket.SOCK_STREAM
                )
            ]

    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:: 5.0
           The ``io_loop`` argument (deprecated since version 4.1) has been removed.

        .. deprecated:: 5.0
           The default `Resolver` now uses `asyncio.loop.getaddrinfo`;
           use that instead of this class.
        """

        def initialize(
            self,
            executor: Optional[concurrent.futures.Executor] = None,
            close_executor: bool = True,
        ) -> None:
            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) -> None:
            if self.close_executor:
                self.executor.shutdown()
            self.executor = None  # type: ignore

        @run_on_executor
        def resolve(
            self, host: str, port: int, family: socket.AddressFamily = socket.AF_UNSPEC
        ) -> List[Tuple[int, Any]]:
            return _resolve_addr(host, port, family)

    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.

        .. deprecated:: 5.0
           The default `Resolver` now uses `.IOLoop.run_in_executor`; use that instead
           of this class.
        """

        def initialize(self) -> None:  # type: ignore
            super().initialize()

    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.

        .. deprecated:: 5.0
           The default `Resolver` now uses `.IOLoop.run_in_executor`; use that instead
           of this class.
        """

        _threadpool = None  # type: ignore
        _threadpool_pid = None  # type: int

        def initialize(self, num_threads: int = 10) -> None:  # type: ignore
            threadpool = ThreadedResolver._create_threadpool(num_threads)
            super().initialize(executor=threadpool, close_executor=False)

        @classmethod
        def _create_threadpool(
            cls, num_threads: int
        ) -> concurrent.futures.ThreadPoolExecutor:
            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:
                cls._threadpool = concurrent.futures.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 be in three formats::

            {
                # Hostname to host or ip
                "example.com": "127.0.1.1",

                # Host+port to host+port
                ("login.example.com", 443): ("localhost", 1443),

                # Host+port+address family to host+port
                ("login.example.com", 443, socket.AF_INET6): ("::1", 1443),
            }

        .. versionchanged:: 5.0
           Added support for host-port-family triplets.
        """

        def initialize(self, resolver: Resolver, mapping: dict) -> None:
            self.resolver = resolver
            self.mapping = mapping

        def close(self) -> None:
            self.resolver.close()

        def resolve(
            self, host: str, port: int, family: socket.AddressFamily = socket.AF_UNSPEC
        ) -> Awaitable[List[Tuple[int, Any]]]:
            if (host, port, family) in self.mapping:
                host, port = self.mapping[(host, port, family)]
            elif (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, family)

    # 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: Union[Dict[str, Any], ssl.SSLContext],
        server_side: Optional[bool] = None,
    ) -> ssl.SSLContext:
        """Try to convert an ``ssl_options`` dictionary to an
        `~ssl.SSLContext` object.

        The ``ssl_options`` dictionary contains keywords to be passed to
        ``ssl.SSLContext.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.

        .. versionchanged:: 6.2

           Added server_side argument. Omitting this argument will
           result in a DeprecationWarning on Python 3.10.

        """
        if isinstance(ssl_options, ssl.SSLContext):
            return ssl_options
        assert isinstance(ssl_options, dict)
        assert all(k in _SSL_CONTEXT_KEYWORDS for k in ssl_options), ssl_options
        # TODO: Now that we have the server_side argument, can we switch to
        # create_default_context or would that change behavior?
        default_version = ssl.PROTOCOL_TLS
        if server_side:
            default_version = ssl.PROTOCOL_TLS_SERVER
        elif server_side is not None:
            default_version = ssl.PROTOCOL_TLS_CLIENT
        context = ssl.SSLContext(ssl_options.get("ssl_version", default_version))
        if "certfile" in ssl_options:
            context.load_cert_chain(
                ssl_options["certfile"], ssl_options.get("keyfile", None)
            )
        if "cert_reqs" in ssl_options:
            if ssl_options["cert_reqs"] == ssl.CERT_NONE:
                # This may have been set automatically by PROTOCOL_TLS_CLIENT but is
                # incompatible with CERT_NONE so we must manually clear it.
                context.check_hostname = False
            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 depends on openssl version 1.0.
            # TODO: Do we need to do this ourselves or can we trust
            # the defaults?
            context.options |= ssl.OP_NO_COMPRESSION
        return context

    def ssl_wrap_socket(
        socket: socket.socket,
        ssl_options: Union[Dict[str, Any], ssl.SSLContext],
        server_hostname: Optional[str] = None,
        server_side: Optional[bool] = None,
        **kwargs: Any
    ) -> ssl.SSLSocket:
        """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 `ssl.SSLContext.wrap_socket`.

        .. versionchanged:: 6.2

           Added server_side argument. Omitting this argument will
           result in a DeprecationWarning on Python 3.10.
        """
        context = ssl_options_to_context(ssl_options, server_side=server_side)
        if server_side is None:
            server_side = False
        assert ssl.HAS_SNI
        # TODO: add a unittest for hostname validation (python added server-side SNI support in 3.4)
        # In the meantime it can be manually tested with
        # python3 -m tornado.httpclient https://sni.velox.ch
        return context.wrap_socket(
            socket, server_hostname=server_hostname, server_side=server_side, **kwargs
        )