Learning Python Network Programming

Programming with Sockets

As we are capturing packets on a non-standard port, Wireshark doesn't decode
it in the Data section (as shown in the middle pane of the preceding screenshot).
However, you can see the decoded text on the bottom pane where the server's
timestamp is shown on the right side.

Working with UDP sockets

Unlike TCP, UDP doesn't check for errors in the exchanged datagram. We can create
UDP client/servers similar to the TCP client/servers. The only difference is you have
to specify SOCK_DGRAM instead of SOCK_STREAM when you create the socket object.

Let us create a UDP server. Use the following code to create the UDP server:

from socket import socket, AF_INET, SOCK_DGRAM

maxsize = 4096

sock = socket(AF_INET,SOCK_DGRAM)

sock.bind(('',12345))

while True:

data, addr = sock.recvfrom(maxsize)

resp = "UDP server sending data"

sock.sendto(resp,addr)

Now, you can create a UDP client to send some data to the UDP server, as shown in
the following code:

from socket import socket, AF_INET, SOCK_DGRAM

MAX_SIZE = 4096

PORT = 12345

if __name__ == '__main__':

sock = socket(AF_INET,SOCK_DGRAM)

msg = "Hello UDP server"

sock.sendto(msg.encode(),('', PORT))

data, addr = sock.recvfrom(MAX_SIZE)

print("Server says:")

print(repr(data))

In the preceding code snippet, the UDP client sends a single line of text Hello UDP
server and receives the response from the server. The following screenshot shows
the request sent from the client to the server: