Can't receive multiple messages on server using TCP socket (Python)

Question

I am new to sockets and don't really know how to receive multiple messages from the same client. I only receive the first message and not the rest.

Server code:

import socket

IP = "127.0.0.1"
PORT = 65432

server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.bind((IP, PORT))

server.listen()

while True:
    communication_socket, address = server.accept()
    msg = communication_socket.recv(1024).decode("utf-8")
    print(msg)

Client code:

import socket
import time

HOST = "127.0.0.1"
PORT = 65432

socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socket.connect((HOST, PORT))

socket.send("success".encode("utf-8"))
time.sleep(2)
socket.send("?".encode("utf-8"))
socket.close()

Steffen Ullrich · Accepted Answer · 2021-12-04 18:34:30Z

2

communication_socket, address = server.accept()
msg = communication_socket.recv(1024).decode("utf-8")

The current code accepts the new connection and then does a single recv. That's why it gets only the first data. What you need are multiple recv here after the accept.

... multiple messages from the same client

TCP has no concept of messages. It is only a byte stream. There is no guaranteed 1:1 relation between send and recv, even if it might look like this in many situations. Thus message semantics must be an explicit part of the application protocol, like delimiting messages with new lines, having only fixed size messages or similar.

answered Dec 4, 2021 at 18:34

Steffen Ullrich

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4 Comments

JorisFort Over a year ago

How does one do this?

JorisFort Over a year ago

I want to have a server which receives unlimited messages

Steffen Ullrich Over a year ago

@JorisFort: "How does one do this?" - I'm not sure what part of "you need ... multiple recv ... after the accept" is unclear.

JorisFort Over a year ago

I have already fixed it thanks for your reply :)

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