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# 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
# 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:
data = await stream.read_until(b"\n")
await stream.write(data)
except StreamClosedError:
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` initialization follows one of three patterns:
1. `listen`: simple single-process::
server = TCPServer()
2. `bind`/`start`: simple multi-process::
server = TCPServer()
server.start(0) # Forks multiple sub-processes
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)
server = TCPServer()
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
.. versionadded:: 3.1
The ``max_buffer_size`` argument.
.. versionchanged:: 5.0
The ``io_loop`` argument has been removed.
def __init__(
ssl_options: Union[Dict[str, Any], ssl.SSLContext] = None,
max_buffer_size: int = None,
read_chunk_size: 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(
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)
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."""
def bind(
port: int,
address: 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:
def start(self, num_processes: Optional[int] = 1) -> 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)``.
assert not self._started
self._started = True
if num_processes != 1:
sockets = self._pending_sockets
self._pending_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:
self._stopped = True
for fd, sock in self._sockets.items():
assert sock.fileno() == fd
# Unregister socket from IOLoop
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"
connection = ssl_wrap_socket(
except ssl.SSLError as err:
if err.args[0] == ssl.SSL_ERROR_EOF:
return connection.close()
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.
if errno_from_exception(err) in (errno.ECONNABORTED, errno.EINVAL):
return connection.close()
if self.ssl_options is not None:
stream = SSLIOStream(
) # type: IOStream
stream = IOStream(
future = self.handle_stream(stream, address)
if future is not None:
gen.convert_yielded(future), lambda f: f.result()
except Exception:
app_log.error("Error in connection callback", exc_info=True)