"""
tcp_disconnect.py
Echo network data test program in python. This easily translates to C & Java.
A server program might want to confirm that a tcp client is still connected
before it sends a data. That is, detect if its connected without reading from socket.
This will demonstrate how to detect a TCP client disconnect without reading data.
The method to do this:
1) select on socket as poll (no wait)
2) if no recv data waiting, then client still connected
3) if recv data waiting, the read one char using PEEK flag
4) if PEEK data len=0, then client has disconnected, otherwise its connected.
Note, the peek flag will read data without removing it from tcp queue.
To see it in action: 0) run this program on one computer 1) from another computer,
connect via telnet port 12345, 2) type a line of data 3) wait to see it echo,
4) type another line, 5) disconnect quickly, 6) watch the program will detect the
disconnect and exit.
John Masinter, 17-Dec-2008
"""
import socket
import time
import select
HOST = '' # all local interfaces
PORT = 12345 # port to listen
# listen for new TCP connections
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((HOST, PORT))
s.listen(1)
# accept new conneciton
conn, addr = s.accept()
print 'Connected by', addr
# loop reading/echoing, until client disconnects
try:
conn.send("Send me data, and I will echo it back after a short delay.\n")
while 1:
data = conn.recv(1024) # recv all data queued
if not data: break # client disconnected
time.sleep(3) # simulate time consuming work
# below will detect if client disconnects during sleep
r, w, e = select.select([conn], [], [], 0) # more data waiting?
print "select: r=%s w=%s e=%s" % (r,w,e) # debug output to command line
if r: # yes, data avail to read.
t = conn.recv(1024, socket.MSG_PEEK) # read without remove from queue
print "peek: len=%d, data=%s" % (len(t),t) # debug output
if len(t)==0: # length of data peeked 0?
print "Client disconnected." # client disconnected
break # quit program
conn.send("-->"+data) # echo only if still connected
finally:
conn.close()
0 votes
Regardez ici (pour les pires scénarios) : tldp.org/HOWTO/TCP-Keepalive-HOWTO/overview.html (Vérification des pairs morts)
5 votes
Parce qu'il y a tellement de réponses fausses et trompeuses, voici la bonne réponse : Suivez les spécifications du protocole que vous implémentez au-dessus de TCP. Il doit préciser si cela se fait par des délais d'attente, des échecs d'écriture ou tout autre mécanisme. Si vous concevez un protocole, assurez-vous de concevoir un moyen de détecter la déconnexion du client, si cela est nécessaire.