How to break while loop when a new message arrives?

Question

I have used Python socket in ESP as a server and Laptop as a client. I customized the socket codes from this site. When I send the loop as the client input, I enter a loop on the server. I don't know how the while loop is broken when I send a word other than loop, For example "Hello".

server.py:

import socket

host = ''
port = 5560

def setupServer():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    print("Socket created.")
    try:
        s.bind((host, port))
    except socket.error as msg:
        print(msg)
    print("Socket bind comlete.")
    return s

def setupConnection():
    s.listen(1)
    conn, address = s.accept()
    print("Connected to: " + address[0] + ":" + str(address[1]))
    return conn

def Hello_():
    print('Hello')

def Loop_():
    while True:
        print('yes')
        
def dataTransfer(conn):
    while True:
        data = conn.recv(1024) 
        data = data.decode('utf-8')
        dataMessage = data.split(' ', 1)
        command = dataMessage[0]

        if command == 'loop':
            Loop_()
        if command == 'Hello':
            Hello_()         
        else:
            print("X")

    conn.close()

s = setupServer()

while True:
    try:
        conn = setupConnection()
        dataTransfer(conn)
    except:
        break

client.py

import socket

host = '192.168.56.1'
port = 5560

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host, port))

while True:
    command = input("Enter your command: ")
    s.send(str.encode(command))
    
s.close()

I know your time is valuable and I appreciate your attention for spending time for help me.

How do you mean "broken"? Once the server has printed the response to the "Hello" command (that is, has printed "Hello"), it simply waits for the next command. Only when you enter "loop" as command, the server gets into an infinite loop, blocking all communications with clients. — 9769953
– 9769953, Commented Apr 8, 2021 at 14:49
@00 I want the Loop_() method to return when more message is received on the socket. — mehdi alizade
– mehdi alizade, Commented Apr 8, 2021 at 15:13

quamrana · Accepted Answer · 2021-04-08 15:50:19Z

2

If you want the Loop_() method to return when more data is received on the socket, you can modify the method so that it calls select() to poll the socket to see if more data has arrived, as shown below. (Note that I've added a conn argument to the Loop_() method so I can pass in the socket to check it)

import select

[...]

def Loop_(conn):
    while True:
        print('yes')
        inReady, outReady, exReady = select.select([conn], [], [], 0.0)
        if (conn in inReady):
           print('more data has arrived at the TCP socket, returning from Loop_()')
           break

def dataTransfer(conn):
    while True:
        data = conn.recv(1024)
        data = data.decode('utf-8')
        dataMessage = data.split(' ', 1)
        command = dataMessage[0]

        if command == 'loop':
            Loop_(conn)
        if command == 'Hello':
            Hello_()
        else:
            print("X")

    conn.close()

edited Apr 8, 2021 at 15:50

quamrana

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answered Apr 8, 2021 at 15:00

Jeremy Friesner

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3 Comments

mehdi alizade Over a year ago

Thanks, I needed exactly that, but now when I send the loop, it prints yes and exits the program.

Jeremy Friesner Over a year ago

Don’t forget to add the ‘import select’ line to the top of the script

Jeremy Friesner Over a year ago

Note that the except: break clause at the end of your script is swallowing up any error messages so that you can't see them when something goes wrong. You probably want to at least print out the exception when you catch it, so you can see what happened.

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