The relationship between the python Socket programming -python API and Linux Socket API

python socket programming

Server

#!/usr/bin/env python
# coding=utf-8
from socket import  *

HOST = ''
PORT = 2345
BUFSIZE = 1024
ADDR = (HOST,PORT)

#创建AF_INET地址族，TCP的套接字
with socket(AF_INET,SOCK_STREAM) as tcpSerSock:
    #绑定ip和端口
    tcpSerSock.bind(ADDR)
    #监听端口，是否有请求
    tcpSerSock.listen(5)

    while True:
        print("waiting for connect!!")
        #accept() 是阻塞的
        tcpClientSock,addr = tcpSerSock.accept()
        print("the client: ",addr,"is connecting")

        with tcpClientSock:
            #使用一个while循环，持续和客户端通信，直到客户端断开连接或者崩溃
            while True:
                data = tcpClientSock.recv(BUFSIZE)
                #判断客户端是否断开连接
                if not data:
                    break;
                print("client: ",data.decode("utf-8"))
                 #相应客户端请求
                msg = input("server: ")
                tcpClientSock.sendall(msg.encode("utf-8"))
            #客户端退出
            print("client ",addr,"exit!")

Client

#!/usr/bin/env python
# coding=utf-8

from socket import *

HOST = "192.168.8.188"
# HOST = "127.0.0.1"
PORT = 2345
ADDR = (HOST,PORT)

with socket(AF_INET,SOCK_STREAM) as tcpCliSock:
   tcpCliSock.connect(ADDR)
   with tcpCliSock:
       while True:
           msg = input("client:")
           tcpCliSock.sendall(msg.encode('utf-8'))
           data=tcpCliSock.recv(1024)
           if not data:
               break
           print("server: ",data.decode("utf-8"))
       print("server crash")

Start the server process and the client process

python server.py

python client.py

Communication results were as follows:

netstat

netstat view the status of its socket information
as you can see the results of the client process and server process to establish a connection via tcp

isof

COMMAND, PID (process id) and USER (user id), the following output parameters isof -i command can view the open socket connection is connected to the print information of the client, by man lsof, see details

tcpdump

tcpdump packet capture, because there is a port number is 2345, so a tcpdump parameter can be set on the port number, the detailed parameter can be self Baidu

tcpdump capture port number can be seen, above communication procedure is in line with FIG.

Contrast python socket API and linux socket API

Use strace command traces comparison found, python's API is the API of the Linux package.
strace python ./client.py

Python	Linux
socket (AF_INET, SOCK_STREAM)	socket (PF_INET, SOCK_STREAM, IPPRPTO_IP) = 3
bind((host,port))	bind(3,{sa_family=AF_INET,sin_port=htons(2345),sin_addr("0.0.0.0")},16)=0
accept()	accept(3,{sa_family=AF_INET,sin_port=htons(2345),sin_addr("192.168.8.xx)},[16]))=4
recv(BUFERSIZE)	recvfrom(4,buf_address,lenth,0,NULL,NULL)
sendall(msg.encode("utf-8))	sendto(4,msg,sizeof(msg),0,NULL,0)
connect((host,port))	connect(3,{sa_family=AF_INET,sin_port=htons(2345),sin_addr("192.168.8.xx)},[16]))=4

表格中的3 ，4表示文件描述符，熟悉linux系统的朋友对文件描述符想必不会陌生，但可以注意到服务器进程产生了两个文件描述符，先是一个3，对应socket创建，而后accept之后，又产生了一个文件描述符4，对应客户端；而客户端始终只有一个3，对应当前连接，可以看到二者的文件描述符是无必然相等关系的。