Python网络编程——编写一个简单的回显客户端/服务器应用

今天将python中socket模块的基本API学习完后，照着书上的实例编写一个套接字服务器和客户端。采用python3.5版本，在注释中会标明python2和python3的不同之处。

1.代码

(1)服务器端及对应代码解释

 # ！ /usr/bin/env python
 # -*- coding: utf-8 -*-
 # 编写回显服务器

 import socket
 import sys
 import argparse

 # 定义常量
 host = 'localhost'
 data_payload = 2048
 backlog = 5

 def echo_server(port):

     # 创建一个TCP socket
     sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

     # 设置TCP套接字关联选项——重用地址
     sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

     # 建立套接字端口
     server_address = (host, port)
     print("Starting up echo server on %s port %s" % server_address)

     # 将socket绑定到server_address地址
     sock.bind(server_address)

     # 监听客户端
     # backlog指定最多允许多少个客户连接到服务器。它的值至少为1。收到连接请求后，这些请求需要排队，如果队列满，就拒绝请求。
     # 这里设定为5
     sock.listen(backlog)
     # 在调用 Listen 之前，必须首先调用 Bind 方法，否则 Listen 将引发 SocketException。
     while True:
         print("Waiting to receive message from client")

         # 调用accept方法时，socket会时入“waiting”状态。客户请求连接时，方法建立连接并返回服务器。
         # accept方法返回一个含有两个元素的 元组(connection,address)。第一个元素connection
         # 是新的socket对象，服务器必须通过它与客户通信；第二个元素 address是客户的Internet地址。
         client, address = sock.accept()

         # 指定data最大长度为2048字节
         data = client.recv(data_payload)
         if data:
             print("Data: %s" % data)
             client.send(data)
             print("sent %s bytes back to %s" % (data, address))
         # 关闭连接
         client.close()

 if __name__ == '__main__':
     # 创建一个解析对象,其中描述为"Socket Error Examples"
     parser = argparse.ArgumentParser(description='Socket Server Example')
     # 采用add_argument方法
     # name or flags —— 必须的参数，该参数接收选项参数或者是位置参数
     # action：
         # (1)store —— 默认action模式，储存值到指定变量
         # (2)store_const —— 储存值在参数的const部分指定，多用于实现非布尔的命令行flag
         # (3)store_true/store_false —— 布尔开关。可以2个参数对应一个变量
         # (4)append —— 储存值到列表，储存值在参数的const部分指定
         # (5)append_const —— 储存值到列表，储存值在参数的const部分指定
         # (6)version —— 输出版本信息然后退出
     # type —— 把从命名行输入的结果转成设置的类型，通常用来检查值的范围，以及合法性。默认string  
     # required —— 指定某个选项在命名中出现， 默认False, 若为 True, 表示必须输入该参数
     # dest —— 把位置或者选项关联到一个特定的名字
     parser.add_argument('--port', action="store", dest="port", type=int, required=True)
     # 调用parse_args()方法进行解析
     given_args = parser.parse_args()
     port = given_args.port
     echo_server(port)

 def bind(self, address):  # real signature unknown; restored from __doc__
     """
     bind(address)

     Bind the socket to a local address.  For IP sockets, the address is a
     pair (host, port); the host must refer to the local host. For raw packet
     sockets the address is a tuple (ifname, proto [,pkttype [,hatype]])
     """
     pass
 def listen(self, backlog=None):  # real signature unknown; restored from __doc__
     """
     listen([backlog])

     Enable a server to accept connections.  If backlog is specified, it must be
     at least 0 (if it is lower, it is set to 0); it specifies the number of
     unaccepted connections that the system will allow before refusing new
     connections. If not specified, a default reasonable value is chosen.
     """
     pass

服务器端代码

(2)客户端及对应代码解释

 # ！ /usr/bin/env python
 # -*- coding: utf-8 -*-
 # 编写回显客户端

 import socket
 import sys
 import argparse

 host = 'localhost'

 def echo_client(port):
     # 创建TCP socket连接
     sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     # 获取服务器端host和端口号
     server_address = (host, port)
     print("Connecting to %s port %s" % server_address)
     sock.connect(server_address)

     try:
         # 将message内容发送到服务器端
         message = "Test message, This will be echoed"
         print("Sending %s" % message)
         # python2和python3此处不同
         # python2—— sock.sendall(message)
         # sendall()发送完整的TCP数据，成功返回None，失败抛出异常
         sock.sendall(message.encode())

         # 服务器端将发送的数据回传给客户端并打印
         amount_received = 0
         amount_expected = len(message)
         while amount_received < amount_expected:
             data = sock.recv(1024)
             amount_received += len(data)
             print("Received: %s" % data)
     # 处理相对应错误
     except socket.error as e:
         print("socket error: %s" % str(e))
     except Exception as e:
         print("Other exception: %s" % str(e))
     finally:
         print("Closing connection to the server")
         sock.close()

 if __name__ == '__main__':
     parser = argparse.ArgumentParser(description='Socket Server Example')
     parser.add_argument('--port', action="store", dest="port", type=int, required=True)
     given_args = parser.parse_args()
     port = given_args.port
     echo_client(port)

客户端代码

(3)运行结果

 1. 服务器端
 Abel$ python3 1_13a_echo_server.py --port=9900
 Starting up echo server on localhost port 9900
 Waiting to receive message from client

 2.客户端发送数据时，服务器端
 Data: b'Test message, This will be echoed'
 sent b'Test message, This will be echoed' bytes back to ('127.0.0.1', 62389)
 Waiting to receive message from client

 3.客户端
 Abel$ python3 1_13b_echo_client.py --port=9900
 Connecting to localhost port 9900
 Sending Test message, This will be echoed
 Received: b'Test message, This will be echoed'
 Closing connection to the server