Why is the receiver in UDP multicast programming not decoding and the same time limited to a number of characters?

Question

I am trying to insert an input in a UDP multicast program in python. The sender is working fine but the receiving side is not decoding well as i am expecting. If i input more than two characters it throws this error:

Traceback (most recent call last):
  File "/home/felix/PycharmProjects/Multicast UDP programming/client1.py", line 27, in <module>
    data, addr = sock.recv(1024)
ValueError: too many values to unpack (expected 2)

but when i insert the two characters as expected it throws this kind of error:

Traceback (most recent call last):
  File "/home/felix/PycharmProjects/Multicast UDP programming/client1.py", line 33, in <module>
    msg = data.decode()
AttributeError: 'int' object has no attribute 'decode'

The code is shown below. Please help me review it.

Sender.py

import socket

group = '224.1.1.1'
port = 15000


# for all packets sent, after two hops on the network the packet will not be re-sent/broadcast
ttl = 2

# Create the socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)

# Make the socket non-blocking
sock.setblocking(True)

# Set the multicast TTL
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl)

# Get input from the user
input_msg = input("Enter your message: ")

# Sends the packet/message
sock.sendto(input_msg.encode(), (group, port))

sock.close()

Receiver.py

import socket
import struct

cast_grp = socket.gethostbyname('224.1.1.1')
cast_port = 15000

# Create a UDP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

# Bind the socket to the multicast group and port
sock.bind(('', cast_port))

# Joins the multicast group
mreq = struct.pack("4sl", socket.inet_aton(cast_grp), socket.INADDR_ANY)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)

# Make the socket non-blocking
sock.setblocking(True)

# Disable loopback for the multicast group
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_LOOP, 0)

while True:
    # creates a datagram packet and sends over the socket
    try:
        data, addr = sock.recv(1024)
    except socket.error:
        # No data available to receive
        continue

    # Decode the received data
    msg = data.decode()

    # Print the received message
    print(f"{addr}:{msg}")
    break

# Close the socket
sock.close()

I was expecting the code to work well since there are no errors or warnings

Answer 1

The recv method is meant to be called on a connected socket, and as such only returns the data, not the address. You should be using recvfrom instead which gives you both.

data, addr = sock.recvfrom(1024)

Sender output:

Enter your message: hello

Receiver output:

('192.168.184.195', 37957):hello