socket_fd_leak

# Demo of wrong handling of tcp connection

# if we shutdown the write end without closing the connection, the fd will
# still be there, while the network connection is gone. It will lead to an
# open fd leak. Basically it appears in lsof, not in netstat.

# lsof output:
# python  12594 vagrant    8u  sock    0,7      0t0   74285 can't identify protocol
# ...

import socket
import os
import sys
import time

PORT = 9918
NUM = 1

sd = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sd.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sd.bind(('0.0.0.0', PORT))
sd.listen(5)

for i in range(NUM):
    if os.fork() == 0:
        sd.close()
        cd = socket.socket(socket.AF_INET,
                           socket.SOCK_STREAM)
        cd.connect(('127.0.0.1', PORT))
        sys.exit()


print "Server process pid=%i" % (os.getpid(),)
sockets = []

for i in range(NUM):
    (cd, address) = sd.accept()
    # cd.setblocking(0) # don't change anything
    sockets.append(cd)

os.system("lsof -p %i" % (os.getpid(),))

print 'rw'
for cd in sockets:
    # cd.shutdown(socket.SHUT_WR)   # can't identify protocol
    cd.send('fxxxxx') # can't identify protocol
    r = cd.recv(32)
    print len(r)

for i in range(2):
    time.sleep(1)
    os.system("lsof -p %i" % (os.getpid(),))

# print 'close'
# for cd in sockets:
    # cd.close()

for i in range(2):
    time.sleep(1)
    os.system("lsof -p %i" % (os.getpid(),))