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

(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)

 (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