UDP learn by Python3
Find max packet size
# coding: utf-8
import socket
def find_max_udp_packet_size():
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
max_sz = 0
l, r = 0, 65535 - 8 - 20
while l <= r:
mid = int((l + r) / 2)
ok = True
try:
sock.sendto(b'A' * mid, ('localhost', 9))
except socket.error:
ok = False
if ok:
max_sz = mid
l = mid + 1
else:
r = mid - 1
return max_sz
def main():
max_sz = find_max_udp_packet_size()
print('max_sz = %s' % max_sz)
if __name__ == '__main__':
main()
I used the code above to find the max size of a UDP packet size by default configuration.
The result on my computer is:
$ uname -v
Darwin Kernel Version 19.2.0: Sat Nov 9 03:47:04 PST 2019; root:xnu-6153.61.1~20/RELEASE_X86_64
$ python3 --version
Python 3.6.4
$ python3 udp_packet_size.py
max_sz = 9216
More test
Use the code below to test.
# coding: utf-8
import socket
from IPython import embed
def main():
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
embed()
sock.close()
if __name__ == '__main__':
main()
In [1]: sock.bind(('localhost', 10001))
In [2]: receiver = ('localhost', 10002)
In [3]: sock.sendto(b'01234567', receiver)
Out[3]: 8
In [4]: sock.sendto(b'01234567', receiver)
Out[4]: 8
In [5]: sock.sendto(b'01234567', receiver)
Out[5]: 8
In [6]: sock.sendto(b'01234567', receiver)
Out[6]: 8
In [1]: sock.bind(('localhost', 10002))
In [2]: receiver = ('localhost', 10001)
In [3]: print(sock.recvfrom(1024))
(b'01234567', ('127.0.0.1', 10001))
In [4]: print(sock.recvfrom(4))
(b'0123', ('127.0.0.1', 10001))
In [5]: print(sock.recvfrom(4))
(b'0123', ('127.0.0.1', 10001))
In [6]: print(sock.recvfrom(4))
(b'0123', ('127.0.0.1', 10001))
In [7]: print(sock.recvfrom(4))
We can see that if the bufsize
is smaller the length of the packet received, will only read bufsize
bytes of the received data, and the rest of that packet will not be returned in subsequent reads.