[Python] Why does my server socket not receive data?

I have some problems with socket programming. I started learning this topic and created a small echo server/client application from the tutorial, after that I created a multithreaded version of it for multiple clients. It works fine with the following code:

Server:

from Rest_Endpoint.thread import ConnectionThread

HOST = ''
PORT = 6000

def start_server():
server: socket = socket.socket(family=socket.AF_INET, type=socket.SOCK_STREAM)
server.bind((HOST,PORT))
server.listen(10)
print('listen to port', PORT)
server.setblocking(False)

while True:
try:
conn, addr = server.accept() # Will throw BlockingIOError if no connections
print('Connected by:', addr)
thread_spawn(conn, addr)
except BlockingIOError:
# No incoming connection; continue the loop
continue
except Exception as e:
print(f'Unexpected error: {e}')
break

def thread_spawn(conn, addr):
print('spawn new connection thread')
ConnectionThread(conn=conn, addr=addr).run()

def main():
start_server()


if __name__ == '__main__':
main()


Spawned thread:

import threading

class ConnectionThread(threading.Thread):
def __init__(self,conn,addr, **kwargs) -> None:
self.conn = conn
self.addr = addr
super().__init__()

def handle_data(self):
print('Connected by', self.addr)
while True:
print(f' waiting for message {self.__repr__()}')
data = self.conn.recv(1024)

if data:
print('prints data: ')
print(data)
self.conn.sendall(data)

def run(self) -> None:
self.handle_data()


Client:

# Echo client program
import socket

HOST = '' # The remote host
PORT = 6000 # The same port as used by the server
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
try:
# Connect to the server
s.connect((HOST, PORT))
print(f'Connected to server at {HOST}:{PORT}')

while True:
# message = input()
# bmessage = (message + '\n').encode('utf-8')
s.sendall(b'test')
# print(bmessage)'

except ConnectionRefusedError:
print(f"Could not connect to server at {HOST}:{PORT}. Ensure the server is running.")
except Exception as e:
print(f"An error occurred: {e}")


When I start the client program, I get this:

Connected by ('127.0.0.1', 51804)
waiting for message <ConnectionThread(Thread-1, initial)>
prints data:
b'testtesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttest'


I understand, that tcp is a stream and because of the while True Loop I do get this result of multiple test in a row.

But when I try to switch the client code to:

while True:
message = input()
bmessage = (message).encode('utf-8')
s.sendall(b'test')
print(bmessage)


I don't receive any message at the server side and I do not understand why. It connects, but I do not get any data.

Maybe someone can help me with an explanation.

This client code does not work:

# Echo client program
import socket

HOST = '' # The remote host
PORT = 6000 # The same port as used by the server
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
try:
# Connect to the server
s.connect((HOST, PORT))
print(f'Connected to server at {HOST}:{PORT}')

while True:
message = input()
bmessage = (message).encode('utf-8')
s.sendall(b'test')
print(bmessage)

except ConnectionRefusedError:
print(f"Could not connect to server at {HOST}:{PORT}. Ensure the server is running.")
except Exception as e:
print(f"An error occurred: {e}")

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