# Source code for tornado.tcpserver

    #
    # 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.

    """A non-blocking, single-threaded TCP server."""

    import errno
    import os
    import socket
    import ssl

    from tornado import gen
    from tornado.log import app_log
    from tornado.ioloop import IOLoop
    from tornado.iostream import IOStream, SSLIOStream
    from tornado.netutil import bind_sockets, add_accept_handler, ssl_wrap_socket
    from tornado import process
    from tornado.util import errno_from_exception

    import typing
    from typing import Union, Dict, Any, Iterable, Optional, Awaitable

    if typing.TYPE_CHECKING:
        from typing import Callable, List  # noqa: F401

    class TCPServer(object):
        r"""A non-blocking, single-threaded TCP server.

        To use `TCPServer`, define a subclass which overrides the `handle_stream`
        method. For example, a simple echo server could be defined like this::

          from tornado.tcpserver import TCPServer
          from tornado.iostream import StreamClosedError
          from tornado import gen

          class EchoServer(TCPServer):
              async def handle_stream(self, stream, address):
                  while True:
                      try:
                          data = await stream.read_until(b"\n")
                          await stream.write(data)
                      except StreamClosedError:
                          break

        To make this server serve SSL traffic, send the ``ssl_options`` keyword
        argument with an `ssl.SSLContext` object. For compatibility with older
        versions of Python ``ssl_options`` may also be a dictionary of keyword
        arguments for the `ssl.wrap_socket` method.::

           ssl_ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
           ssl_ctx.load_cert_chain(os.path.join(data_dir, "mydomain.crt"),
                                   os.path.join(data_dir, "mydomain.key"))
           TCPServer(ssl_options=ssl_ctx)

        `TCPServer` initialization follows one of three patterns:

        1. `listen`: simple single-process::

                server = TCPServer()
                server.listen(8888)
                IOLoop.current().start()

        2. `bind`/`start`: simple multi-process::

                server = TCPServer()
                server.bind(8888)
                server.start(0)  # Forks multiple sub-processes
                IOLoop.current().start()

           When using this interface, an `.IOLoop` must *not* be passed
           to the `TCPServer` constructor.  `start` will always start
           the server on the default singleton `.IOLoop`.

        3. `add_sockets`: advanced multi-process::

                sockets = bind_sockets(8888)
                tornado.process.fork_processes(0)
                server = TCPServer()
                server.add_sockets(sockets)
                IOLoop.current().start()

           The `add_sockets` interface is more complicated, but it can be
           used with `tornado.process.fork_processes` to give you more
           flexibility in when the fork happens.  `add_sockets` can
           also be used in single-process servers if you want to create
           your listening sockets in some way other than
           `~tornado.netutil.bind_sockets`.

        .. versionadded:: 3.1
           The ``max_buffer_size`` argument.

        .. versionchanged:: 5.0
           The ``io_loop`` argument has been removed.
        """

        def __init__(
            self,
            ssl_options: Optional[Union[Dict[str, Any], ssl.SSLContext]] = None,
            max_buffer_size: Optional[int] = None,
            read_chunk_size: Optional[int] = None,
        ) -> None:
            self.ssl_options = ssl_options
            self._sockets = {}  # type: Dict[int, socket.socket]
            self._handlers = {}  # type: Dict[int, Callable[[], None]]
            self._pending_sockets = []  # type: List[socket.socket]
            self._started = False
            self._stopped = False
            self.max_buffer_size = max_buffer_size
            self.read_chunk_size = read_chunk_size

            # Verify the SSL options. Otherwise we don't get errors until clients
            # connect. This doesn't verify that the keys are legitimate, but
            # the SSL module doesn't do that until there is a connected socket
            # which seems like too much work
            if self.ssl_options is not None and isinstance(self.ssl_options, dict):
                # Only certfile is required: it can contain both keys
                if "certfile" not in self.ssl_options:
                    raise KeyError('missing key "certfile" in ssl_options')

                if not os.path.exists(self.ssl_options["certfile"]):
                    raise ValueError(
                        'certfile "%s" does not exist' % self.ssl_options["certfile"]
                    )
                if "keyfile" in self.ssl_options and not os.path.exists(
                    self.ssl_options["keyfile"]
                ):
                    raise ValueError(
                        'keyfile "%s" does not exist' % self.ssl_options["keyfile"]
                    )

        def listen(self, port: int, address: str = "") -> None:
            """Starts accepting connections on the given port.

            This method may be called more than once to listen on multiple ports.
            `listen` takes effect immediately; it is not necessary to call
            `TCPServer.start` afterwards.  It is, however, necessary to start
            the `.IOLoop`.
            """
            sockets = bind_sockets(port, address=address)
            self.add_sockets(sockets)

        def add_sockets(self, sockets: Iterable[socket.socket]) -> None:
            """Makes this server start accepting connections on the given sockets.

            The ``sockets`` parameter is a list of socket objects such as
            those returned by `~tornado.netutil.bind_sockets`.
            `add_sockets` is typically used in combination with that
            method and `tornado.process.fork_processes` to provide greater
            control over the initialization of a multi-process server.
            """
            for sock in sockets:
                self._sockets[sock.fileno()] = sock
                self._handlers[sock.fileno()] = add_accept_handler(
                    sock, self._handle_connection
                )

        def add_socket(self, socket: socket.socket) -> None:
            """Singular version of `add_sockets`.  Takes a single socket object."""
            self.add_sockets([socket])

        def bind(
            self,
            port: int,
            address: Optional[str] = None,
            family: socket.AddressFamily = socket.AF_UNSPEC,
            backlog: int = 128,
            reuse_port: bool = False,
        ) -> None:
            """Binds this server to the given port on the given address.

            To start the server, call `start`. If you want to run this server
            in a single process, you can call `listen` as a shortcut to the
            sequence of `bind` and `start` calls.

            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>`. The ``reuse_port`` argument
            has the same meaning as for `.bind_sockets`.

            This method may be called multiple times prior to `start` to listen
            on multiple ports or interfaces.

            .. versionchanged:: 4.4
               Added the ``reuse_port`` argument.
            """
            sockets = bind_sockets(
                port, address=address, family=family, backlog=backlog, reuse_port=reuse_port
            )
            if self._started:
                self.add_sockets(sockets)
            else:
                self._pending_sockets.extend(sockets)

        def start(
            self, num_processes: Optional[int] = 1, max_restarts: Optional[int] = None
        ) -> None:
            """Starts this server in the `.IOLoop`.

            By default, we run the server in this process and do not fork any
            additional child process.

            If num_processes is ``None`` or <= 0, we detect the number of cores
            available on this machine and fork that number of child
            processes. If num_processes is given and > 1, we fork that
            specific number of sub-processes.

            Since we use processes and not threads, there is no shared memory
            between any server code.

            Note that multiple processes are not compatible with the autoreload
            module (or the ``autoreload=True`` option to `tornado.web.Application`
            which defaults to True when ``debug=True``).
            When using multiple processes, no IOLoops can be created or
            referenced until after the call to ``TCPServer.start(n)``.

            Values of ``num_processes`` other than 1 are not supported on Windows.

            The ``max_restarts`` argument is passed to `.fork_processes`.

            .. versionchanged:: 6.0

               Added ``max_restarts`` argument.
            """
            assert not self._started
            self._started = True
            if num_processes != 1:
                process.fork_processes(num_processes, max_restarts)
            sockets = self._pending_sockets
            self._pending_sockets = []
            self.add_sockets(sockets)

        def stop(self) -> None:
            """Stops listening for new connections.

            Requests currently in progress may still continue after the
            server is stopped.
            """
            if self._stopped:
                return
            self._stopped = True
            for fd, sock in self._sockets.items():
                assert sock.fileno() == fd
                # Unregister socket from IOLoop
                self._handlers.pop(fd)()
                sock.close()

        def handle_stream(
            self, stream: IOStream, address: tuple
        ) -> Optional[Awaitable[None]]:
            """Override to handle a new `.IOStream` from an incoming connection.

            This method may be a coroutine; if so any exceptions it raises
            asynchronously will be logged. Accepting of incoming connections
            will not be blocked by this coroutine.

            If this `TCPServer` is configured for SSL, ``handle_stream``
            may be called before the SSL handshake has completed. Use
            `.SSLIOStream.wait_for_handshake` if you need to verify the client's
            certificate or use NPN/ALPN.

            .. versionchanged:: 4.2
               Added the option for this method to be a coroutine.
            """
            raise NotImplementedError()

        def _handle_connection(self, connection: socket.socket, address: Any) -> None:
            if self.ssl_options is not None:
                assert ssl, "Python 2.6+ and OpenSSL required for SSL"
                try:
                    connection = ssl_wrap_socket(
                        connection,
                        self.ssl_options,
                        server_side=True,
                        do_handshake_on_connect=False,
                    )
                except ssl.SSLError as err:
                    if err.args[0] == ssl.SSL_ERROR_EOF:
                        return connection.close()
                    else:
                        raise
                except socket.error as err:
                    # If the connection is closed immediately after it is created
                    # (as in a port scan), we can get one of several errors.
                    # wrap_socket makes an internal call to getpeername,
                    # which may return either EINVAL (Mac OS X) or ENOTCONN
                    # (Linux).  If it returns ENOTCONN, this error is
                    # silently swallowed by the ssl module, so we need to
                    # catch another error later on (AttributeError in
                    # SSLIOStream._do_ssl_handshake).
                    # To test this behavior, try nmap with the -sT flag.
                    # https://github.com/tornadoweb/tornado/pull/750
                    if errno_from_exception(err) in (errno.ECONNABORTED, errno.EINVAL):
                        return connection.close()
                    else:
                        raise
            try:
                if self.ssl_options is not None:
                    stream = SSLIOStream(
                        connection,
                        max_buffer_size=self.max_buffer_size,
                        read_chunk_size=self.read_chunk_size,
                    )  # type: IOStream
                else:
                    stream = IOStream(
                        connection,
                        max_buffer_size=self.max_buffer_size,
                        read_chunk_size=self.read_chunk_size,
                    )

                future = self.handle_stream(stream, address)
                if future is not None:
                    IOLoop.current().add_future(
                        gen.convert_yielded(future), lambda f: f.result()
                    )
            except Exception:
                app_log.error("Error in connection callback", exc_info=True)