Network Programming Fundamentals

1. C/S Architecture

1. Hardware C/S Architecture

　　such as PC-printers

2. Software C/S Architecture

　　such as PC-web server

reference:

　　 https://baike.baidu.com/item/Client%2FServer/1504488?fr=aladdin&fromid=826311&fromtitle=C%2FS

2. OSI seven-layer model

 

　　The seven layers of OSI correspond to various communication protocols in network communication. Understanding the operation process of the seven layers of OSI is the most important part of socket programming. Why do you say this? Look at the picture below:

       

　　As can be seen from the figure, the socket works between the software C/S architecture and the application layer and the transport layer in the OSI seven-layer model

Attached:         

Detailed explanation of the TCP protocol:

　　 https://www.jianshu.com/p/ef892323e68f

3. What kind of shit is a socket?

　　Socket originally refers to a hole or socket. It was originally used as a process communication mechanism for BSD UINX, and is also called a socket. Today's socket is a network programming standard that Windows and Mac operating systems abide by. It is an abstraction layer between the application layer and the transport layer in the OSI seven-layer model. It is used to describe IP addresses and ports. It is a handle of a communication chain. It can be used to realize the communication between different virtual machines or different computers or the communication between different processes in the host. Hosts on the Internet generally run multiple service software and provide several services at the same time. Each service opens a socket and binds it to a port. Different ports correspond to different services.

　　 On the operating system, socket shields the network details of the TCP/IP network transport layer and below, and provides network abstraction for the operating system. Network programs written by developers will use socket abstraction directly or indirectly. Through the socket abstraction, the two major protocols (TCP, UDP) of the transport layer can be directly controlled, and even network layer protocols such as IP and ICMP can be controlled.

       Simply put, a socket is a triplet of IP address + port + protocol that uniquely identifies a communication link, and a communication link on the server side can correspond to multiple clients.

Fourth, the type of socket

1. Filesystem-based socket family

　　Socket family name: AF_UNIX

　　As mentioned earlier, socket was originally used as a process mechanism for UNIX. Everything in UNIX is a file. It is a file-based socket that calls the underlying file system to fetch data. Two socket processes run on the same machine. Communication is done indirectly by accessing the same file system.

 2. Socket family based on network type:

　　Network type socket name: AF_INET

　　IPv4 based sockets, additionally AF_INET6 for IPv6

Five, socket programming

1. Socket workflow

2. Simple implementation of socket based on TCP  

#Server side 
import socket
 
#Instantiate a socket object and specify the network layer protocol, transport layer protocol socket_server 
= socket.socket(socket.AF_INET,socket.SOCK_STREAM) #Bind
 IP , port number 
socket_server.bind(( ' 127.0.0.1 ' ,8080 ) ,)
 #Requests that can be received at the same time 
socket_server.listen(5 )
 #Waiting for connection 
connect,client_address = socket_server.accept() #Set
 the received message, the maximum limit is 1024 
receive_mag = connect.recv(1024 )
 print ( ' Received Client's message: %s ' % receive_mag.decode( ' UTF-8 ' ))
 #send data
connect.send(receive_mag.upper())

#Close the connection 
connect.close()
 

#client import socket _


socket_client = socket.socket(socket.AF_INET,socket.SOCK_STREAM) #Connect
 to the server, specify the IP and port number 
socket_client.connect(( ' 127.0.0.1 ' ,8080 ))
 # Send a message to the server 
socket_client.send( ' Hello ,I am client! ' .encode( ' utf-8 ' ))
data = socket_client.recv(1024 )
 print ( ' Received message from server: %s ' % data.decode( ' utf-8 ' ))

socket_client.close()

3. TCP-based socket connection loop and communication loop

#Server side 
import socket

phone = socket.socket (socket.AF_INET, socket.SOCK_STREAM)
phone.bind(('127.0.0.1',8080))
phone.listen( 5 )
 while True: #Connection loop 
connect,client_address = phone.accept()
 print ( ' Client: ' ,client_address)
 while True: #Communication loop 
try :
msg = connect.recv(1024 )
 print ( ' Client message: ' ,msg)
connect.send(msg+b'from server')
except ConnectionResetError:
break
connect.close()
phone.close()

#client import socket _


phone = socket.socket (socket.AF_INET, socket.SOCK_STREAM)
phone.connect(( ' 127.0.0.1 ' ,8080)) #Dial the phone, the address is the server's ip and port 
while True:
msg = input( ' >>>).strip() 
phone.send(msg.encode( ' utf-8 ' )) #Send a message 
data = phone.recv(1024) #Receive a message 
print (data.decode( ' utf -8 ' ))

phone.close()