Introduction to socket

1. How to communicate between processes on different computers

The first problem to be solved is how to uniquely identify a process, otherwise communication can not be started!

On a computer, a process can be uniquely identified by a process number (PID), but this is not feasible in the network.

In fact, the TCP/IP protocol family has helped us solve this problem. The "ip address" of the network layer can uniquely identify the host in the network, while the "protocol + port" of the transport layer can uniquely identify the application process (process) of the host.

In this way, the ip address, protocol and port can be used to identify the process of the network, and the process communication in the network can use this mark to interact with other processes.

2. What is socket?

Socket (socket for short) is a way of interprocess communication. One of the main differences between socket and other interprocess communication is:

It can realize inter-process communication between different hosts. Most of the various services on our network are based on Socket to complete communication.

For example, we browse web pages, QQ chat, email and so on every day.

3. Create socket

Using socket module function socket in Python can accomplish:

import socket
socket.socket(AddressFamily, Type)

Explain:

Create a UDP socket (udp socket)
import socket

# Create sockets for udp
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# Here is the function of using sockets (omitted)...

# Close sockets when not in use
s.close()

udp network program-sending and receiving data

Communication Template

Creating a network program process based on udp is very simple. The specific steps are as follows:

1. Create client socket
2. Send/receive data
3. Close
   

send data

#coding=utf-8

from socket import *

# 1. Create udp sockets
udp_socket = socket(AF_INET, SOCK_DGRAM)

# 2. Prepare the address of the recipient
# '192.168.1.103'denotes the destination ip address
# 8080 represents destination port
dest_addr = ('192.168.1.103', 8080)  # Note that tuples, ip strings, and ports are numbers

# 3. Getting data from keyboard
send_data = input("Please enter the data to be sent:")

# 4. Send data to a specified program on a specified computer
udp_socket.sendto(send_data.encode('utf-8'), dest_addr)

# 5. Close sockets
udp_socket.close()

receive data

#coding=utf-8

from socket import *

# 1. Create udp sockets
udp_socket = socket(AF_INET, SOCK_DGRAM)

# 2. Prepare the address of the recipient
dest_addr = ('192.168.236.129', 8080)

# 3. Getting data from keyboard
send_data = input("Please enter the data to be sent:")

# 4. Send data to a designated computer
udp_socket.sendto(send_data.encode('utf-8'), dest_addr)

# 5. Waiting to receive data sent by the other party
recv_data = udp_socket.recvfrom(1024)  # 1024 represents the maximum number of bytes received this time

# 6. Display the data sent by the other party
# Received data recv_data is a tuple
# The first element is the data sent by the other party.
# The second element is the ip and port of the other party.
print(recv_data[0].decode('gbk'))
print(recv_data[1])

# 7. Close sockets
udp_socket.close()

Coding Conversion

STR - > bytes: encode coding
Bytes - > str: decode decoding

>>> text = 'I am the text'
>>> text
'I am the text'
>>> print(text)
//I am the text
>>> bytesText = text.encode()
>>> bytesText
b'\xe6\x88\x91\xe6\x98\xaf\xe6\x96\x87\xe6\x9c\xac'
>>> print(bytesText)
b'\xe6\x88\x91\xe6\x98\xaf\xe6\x96\x87\xe6\x9c\xac'
>>> type(text)
<class 'str'>
>>> type(bytesText)
<class 'bytes'>
>>> textDecode = bytesText.decode()
>>> textDecode
'I am the text'
>>> print(textDecode)
//I am the text

The decode() and encode() methods can accept parameters, which are declared as follows:

bytes.decode(encoding="utf-8", errors="strict")
str.encode(encoding="utf-8", errors="strict")

Note: The default Chinese encoding in windows is GBK, so the parameters of "gbk" encoding should be passed in when sending data.

udp binding information

Every time a network program is re-run, if it is not determined which port to use, the system will allocate randomly by default.
Keep in mind that this network program uniquely identifies the program on the port during operation, so if the network program on other computers wants to send data to this program, it needs to send this number (port).

Generally speaking, there are many network programs running on a computer. In order not to occupy the same port number with other network programs, udp port number is usually not bound in programming.

But if you need to make a server-side program, you need to bind it.

#coding=utf-8

from socket import *

# 1. Create sockets
udp_socket = socket(AF_INET, SOCK_DGRAM)

# 2. Bind local information. If a network program is not bound, the system will be allocated randomly.
local_addr = ('', 7788) #  ip address and port number, ip generally do not need to write, indicating any ip of this machine
udp_socket.bind(local_addr)

# 3. Waiting to receive data sent by the other party
recv_data = udp_socket.recvfrom(1024) #  1024 represents the maximum number of bytes received this time

# 4. Display received data
print(recv_data[0].decode('gbk'))

# 5. Close sockets
udp_socket.close()

summary

• A udp network program can be unbound. At this time, the operating system will randomly allocate a port. If the program port is re-run, it may change.
• A udp network program can also bind information (ip address, port number). If the binding is successful, the operating system uses this port number to distinguish whether the received network data is the process or not.

udp chatter

import socket


def send_msg(udp_socket):
    """Get keyboard data and send it to each other"""
    # 1. Input data from keyboard
    msg = input("\n Please enter the data to be sent:")
    # 2. Enter the ip address of the other party
    dest_ip = input("\n Please enter each other's ip address:")
    # 3. Enter each other's port
    dest_port = int(input("\n Please enter each other's port:"))
    # 4. Send data
    udp_socket.sendto(msg.encode("utf-8"), (dest_ip, dest_port))


def recv_msg(udp_socket):
    """Receive data and display"""
    # 1. Receiving data
    recv_msg = udp_socket.recvfrom(1024)
    # 2. Decoding
    recv_ip = recv_msg[1]
    recv_msg = recv_msg[0].decode("utf-8")
    # 3. Display the received data
    print(">>>%s:%s" % (str(recv_ip), recv_msg))


def main():
    # 1. Create sockets
    udp_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    # 2. Binding local information
    udp_socket.bind(("", 7890))
    while True:
        # 3. Selection function
        print("="*30)
        print("1:send message")
        print("2:receive messages")
        print("="*30)
        op_num = input("Please enter the serial number of the function to be operated on.:")

        # 4. Call the corresponding function according to the choice
        if op_num == "1":
            send_msg(udp_socket)
        elif op_num == "2":
            recv_msg(udp_socket)
        else:
            print("The input is incorrect. Please re-enter it....")

if __name__ == "__main__":
    main()