在这个demo中，主要是使用了Tornado中异步的TCP client和server来实现一个简单的echo效果（即客户端发送的message会从server端返回到client）。代码的github链接点这里。
1 Server端代码分析
1 import logging
2 from tornado.ioloop import IOLoop
3 from tornado import gen
4 from tornado.iostream import StreamClosedError
5 from tornado.tcpserver import TCPServer
6 from tornado.options import options, define
7
8 define("port", default=9888, help="TCP port to listen on")
9 logger = logging.getLogger(__name__)
10
11
12 class EchoServer(TCPServer):
13 @gen.coroutine
14 def handle_stream(self, stream, address):
15 while True:
16 try:
17 data = yield stream.read_until(b"\n")
18 logger.info("Received bytes: %s", data)
19 if not data.endswith(b"\n"):
20 data = data + b"\n"
21 yield stream.write(data)
22 except StreamClosedError:
23 logger.warning("Lost client at host %s", address[0])
24 break
25 except Exception as e:
26 print(e)
27
28
29 if __name__ == "__main__":
30 options.parse_command_line()
31 server = EchoServer()
32 server.listen(options.port)
33 logger.info("Listening on TCP port %d", options.port)
34 IOLoop.current().start()
server.py
涉及到引入的模块及作用：
import logging //用来记录日志from tornado.ioloop import IOLoopfrom tornado import gen //实现异步from tornado.iostream import StreamClosedError //处理iostreamfrom tornado.tcpserver import TCPServer // 非阻塞单线程的TCP server及其相关哦功能from tornado.options import options, define // options参数相关
server端代码并不复杂，首先定义了默认的监听端口，并且生成了一个logger实例。（logging用法点这里。）
define("port", default=9888, help="TCP port to listen on")
logger = logging.getLogger(__name__)
然后创建EchoServer类如下。这个类继承TCPServer(更多参考)。里面重写了handle_stream方法。handle_stream接收了stream和address两个参数，stream是一个iostream的object，address是client端地址。逻辑比较清晰，使用try, except来捕获io错误，如果没有错误的话，会读取stream内容直到遇到换行停止。读取到的data会写回到client端，通过write(data)。
handle_stream方法是用了@gen.coroutine装饰器和yield来实现异步读取\写回iostream。
class EchoServer(TCPServer):
@gen.coroutine
def handle_stream(self, stream, address):
while True:
try:
data = yield stream.read_until(b"\n")
logger.info("Received bytes: %s", data)
if not data.endswith(b"\n"):
data = data + b"\n"
yield stream.write(data)
except StreamClosedError:
logger.warning("Lost client at host %s", address[0])
break
except Exception as e:
print(e)
最后在main部分，生成一个EchoServer实例并监听定义的端口，然后启动事件的ioloop。
options.parse_command_line()
server = EchoServer()
server.listen(options.port)
logger.info("Listening on TCP port %d", options.port)
IOLoop.current().start()
2 Client端代码分析
1 from __future__ import print_function
2 from tornado.ioloop import IOLoop
3 from tornado import gen
4 from tornado.tcpclient import TCPClient
5 from tornado.options import options, define
6
7 define("host", default="localhost", help="TCP server host")
8 define("port", default=9888, help="TCP port to connect to")
9 define("message", default="ping", help="Message to send")
10
11
12 @gen.coroutine
13 def send_message():
14 stream = yield TCPClient().connect(options.host, options.port)
15 yield stream.write((options.message + "\n").encode())
16 print("Sent to server:", options.message)
17 reply = yield stream.read_until(b"\n")
18 print("Response from server:", reply.decode().strip())
19
20
21 if __name__ == "__main__":
22 options.parse_command_line()
23 IOLoop.current().run_sync(send_message)
client.py
client 端首先定义了3个option, host,port,以及message，分别为要连接的服务端的host ip, 端口和要发送的message.
send_message用来向server端发送和接收数据。同样这里使用@gen.coroutine和yield来实现异步。
@gen.coroutine
def send_message():
stream = yield TCPClient().connect(options.host, options.port)
yield stream.write((options.message + "\n").encode())
print("Sent to server:", options.message)
reply = yield stream.read_until(b"\n")
print("Response from server:", reply.decode().strip())
3 运行效果
server端运行后，可以使用运行client.py发送消息，发送完成后连接会端口。也可以使用telnet保持连接，交互式的发送数据给server端。