为了实现TCPServer的功能，定义一个类用于继承TCPServer并实现handle_stream方法。HttpServer就是一个很好的例子。
13.1 构造函数
def __init__(self, io_loop=None, ssl_options=None, max_buffer_size=None,
read_chunk_size=None):
self.io_loop = io_loop
self.ssl_options = ssl_options
self._sockets = {} # fd -> socket object
self._pending_sockets = []
self._started = 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'])
实现流程如下：
(1) 设置属性。
(2) 判断是否支持SLL，如果支持，判断证书文件以及秘钥文件是否存在。
13.2 监听 listen
开启指定端口的接收连接。
为了监听多个端口时，这个方法可能会被调用多次。这个方法会立即起作用，不需要调用TCPServer.start方法。但是，还是有必要启动IOLoop。
def listen(self, port, address=""):
"""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)
调用bind_sockets方法来获得sockets集合对象。调用add_sockets方法循环处理每一个sockets对象，主要注册socket建立连接后的处理回调函数。
13.3 添加sockets (add_sockets)
def add_sockets(self, sockets):
"""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.
"""
if self.io_loop is None:
self.io_loop = IOLoop.current() for sock in sockets:
self._sockets[sock.fileno()] = sock
add_accept_handler(sock, self._handle_connection,
io_loop=self.io_loop)
针对每一个socket, 注册socket建立连接后的处理回调函数,回调函数为内部方法_handle_connection。
13.4 关闭服务器(stop)
def stop(self):
"""Stops listening for new connections. Requests currently in progress may still continue after the
server is stopped.
"""
for fd, sock in self._sockets.items():
self.io_loop.remove_handler(fd)
sock.close()
关闭服务器，停止监新的请求连接。在服务器关闭之后，当前正在处理的请求会继续执行。
执行逻辑就是，对服务器中所有的sockets对象，调用两个方法，一个是移除io_loop中的处理回调函数，一个是关闭socket.
13.5 socket的建立连接后的回调函数 _handle_connection
socket处理请求时，这个方法是回调函数，用来处理请求流。如果请求是SSL请求，则初始化SSLIOStream类，如果不是SSL请求，则初始化IOStream类。初始化Stream之后，调用handle_stream方法来处理stream.handler_stream方法一般由TCPServer的子类实现，比如HttpServer就有具体的实现。