I am learning socket programming and python. I need to create a client that sends a command to a server (list or get ). The server then validates the command. My client program can display "list" or "get" , but it doesn't show the error message when I enter other things.
Also, it only works one time; when I enter a different command after receiving a reply from the server, it gives me the following error:
Traceback (most recent call last):
File "fclient.py", line 49, in
client_socket.send(command)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/socket.py", line 170, in _dummy
raise error(EBADF, 'Bad file descriptor')
I'm totally lost. What is the best way to get a command line input in the client program and send it to the server and ask the server to validate the command line parameter? Can someone take a look and point me to the right direction? Your help is greatly appreciated.
Client.py
import socket #for sockets
import sys #for exit
command = ' '
socksize = 1024
#return a socket descriptor which can be used in other socket related functions
#properties: address family: AF_INET (IP v4)
#properties: type: SOCK_STREAM (connection oriented TCP protocol)
try:
#create an AF_INET, STREAM socket (TCP)
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
except socket.error, msg: #error handling
print 'Failed to create socket. Error code: ' + str(msg[0]) + ', Error message: ' + msg[1]
sys.exit();
print 'Socket Created'
#Get the IP address of the remote host/url
#connect to IP on a certain 'port' using the connect
#host = 'flip3.engr.oregonstate.edu'
#port = 30021
#host = 'www.google.com'
#port = 80
host = '' #symbolic name meaning the local host
port = 8888 #arbitrary non-privileged port
try:
remote_ip = socket.gethostbyname(host)
except socket.gaierror:
#could not resolve
print 'Hostname could not be resolved. Existing'
sys.exit()
print 'IP address of ' + host + ' is ' + remote_ip
#Connect to remote server
client_socket.connect((remote_ip, port))
print 'Socket Connected to ' + host + ' on ip ' + remote_ip
#Send some data to remote server
while True:
print 'Enter a command: list or get <filename>'
command = raw_input()
if command.strip() == 'quit':
break
client_socket.send(command)
data = client_socket.recv(socksize)
print data
#Close the socket
client_socket.close()
Server.py
import socket
import sys
from thread import *
#HOST = 'flip3.engr.oregonstate.edu' #symbolic name meaning all available interfaces
#PORT = 30021
HOST = ''
PORT = 8888
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created'
try:
server_socket.bind((HOST, PORT)) #bind to a address(and port)
except socket.error, msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit()
print 'Socket bind complete'
#put the socket in listening mode
server_socket.listen(10) #maximum 10 connections
print 'TCP Server Waiting for client on port 30021'
#wait to accept a connection - blocking call
client, addr = server_socket.accept()
#display client information
print 'Connected with ' + addr[0] + ':' + str(addr[1])
#keep talking with the client
while 1:
#Receiving from client
data = client.recv(1024)
if (data == 'list' or data == 'get'):
reply = 'receive: ' + data
client.send(reply)
break;
else:
reply = 'wrong command'
client.send(reply)
client.close()
The first problem is that you close your client socket inside your loop, closing it after receiving the reply to the first command. Move closing the socket out of the loop instead and introduce an exit condition to exit the loop:
#Connect to remote server
client_socket.connect((remote_ip, port))
print 'Socket Connected to ' + host + ' on ip ' + remote_ip
#Send some data to remote server
while True:
print 'Enter a command: list or get <filename>'
command = raw_input()
if command.strip() == 'quit':
break
client_socket.send(command)
data = client_socket.recv(socksize)
print data
# Close the socket
client_socket.close()
You're doing something similar on the server side: You try to reopen the listening socket every iteration. Move this part out of the loop as well:
#wait to accept a connection - blocking call
client, addr = server_socket.accept()
#display client information
print 'Connected with ' + addr[0] + ':' + str(addr[1])
The reason your command parsing doesn't work is because of this statement:
if (data == 'list' or 'get'):
What you meant to write here is
if (data == 'list' or data == 'get'):
The first expression will evaluate like this:
Is data == 'list'?
If yes, that sub-expression evaluates to True and is therefore what a or b will return.
If not, the second operand to or is chosen, which is the string 'get'.
The result of that or expression will now be implicitely cast to boolean by the if statement:
Case 1: True is already True
Case 2: A non-empty string cast to boolean evaluates to True as well
So your if statement will always evaluate to True, that's why your command parsing didn't work.
To write
if (data == 'list' or data == 'get'):
in a nicer form, I would suggest to use
if (data.strip() in ('list' 'get')):
Lastly, you should wrap your socket code in a try..finally to make sure the sockets are always closed even if exceptions like a KeyboardInterrupt happen:
try:
#keep talking with the client
while 1:
#Receiving from client
data = client.recv(1024)
if (data.strip() in ('list' 'get')):
reply = 'receive: ' + data
client.send(reply)
else:
reply = 'wrong command'
client.send(reply)
except KeyboardInterrupt:
print "Exiting gracefully."
finally:
server_socket.close()
(The finally clause gets executed under all circumstances - whether handled or undhandled exceptions happened, or not)
One problem is that you close client_socket in your while loop. After that, client_socket.send() will not work anymore. There are at least two ways to fix this:
Move client_socket.connect() into your while loop also.
Get rid of client_socket.close(), and move server_socket.accept() above the while loop in Server.py.
There are more sophisticated options involving select() or other methods, but one of the two items above should get you by for now.
Related
I'm learning the sockets python module and I'm looking at the following tutorial code:
'''
Simple socket server using threads
'''
import socket
import sys
from thread import *
HOST = '' # Symbolic name meaning all available interfaces
PORT = 8888 # Arbitrary non-privileged port
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created'
#Bind socket to local host and port
try:
s.bind((HOST, PORT))
except socket.error as msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit()
print 'Socket bind complete'
#Start listening on socket
s.listen(10)
print 'Socket now listening'
#Function for handling connections. This will be used to create threads
def clientthread(conn):
#Sending message to connected client
conn.send('Welcome to the server. Type something and hit enter\n') #send only takes string
#infinite loop so that function do not terminate and thread do not end.
while True:
#Receiving from client
data = conn.recv(1024)
reply = 'OK...' + data
if not data:
break
conn.sendall(reply)
#came out of loop
conn.close()
#now keep talking with the client
while 1:
#wait to accept a connection - blocking call
conn, addr = s.accept()
print 'Connected with ' + addr[0] + ':' + str(addr[1])
#start new thread takes 1st argument as a function name to be run, second is the tuple of arguments to the function.
start_new_thread(clientthread ,(conn,))
s.close()
I'm stuck on the final line, s.close(). I don't understand what this does since the code seems to be stuck in an infinite loop right above, which is never broken. Am I missing something or is s.close() totally extraneous in this instance?
Right now, I'm trying to make a socket server in Python that takes input from a client, processes it, does whatever is need to be done, and then sends a message back to the client showing that it's done.
The problem I am having right now is that the system can't recognize a command that is sent by the client. I am currently using an if statement to compare strings. The data received is decoded into UTF-8. I don't see why the if statement can't compare them.
'''
Simple socket server using threads
'''
import socket
import sys
from thread import *
import cmd
HOST = '' # Symbolic name meaning all available interfaces
PORT = 8888 # Arbitrary non-privileged port
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created'
#Bind socket to local host and port
try:
s.bind((HOST, PORT))
except socket.error as msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit()
print 'Socket bind complete'
#Start listening on socket
s.listen(10)
print 'Socket now listening'
#Function for handling connections. This will be used to create threads
def clientthread(conn):
#Sending message to connected client
conn.send('Welcome to the server. Type something and hit enter\n') #send only takes string
#infinite loop so that function do not terminate and thread do not end.
while True:
#Receiving from client
databyte = conn.recv(1024)
reply = 'OK...' + data
data = databyte.decode('utf-8')
if data == 'light'
print 'light'
if not data:
break
conn.sendall(reply)
#came out of loop
conn.close()
#now keep talking with the client
while 1:
#wait to accept a connection - blocking call
conn, addr = s.accept()
print 'Connected with ' + addr[0] + ':' + str(addr[1])
#start new thread takes 1st argument as a function name to be run, second is the tuple of arguments to the function.
start_new_thread(clientthread ,(conn,))
s.close()
Any help would be appreciated! Thank you in advance!
This code can create socket, connect to selected server and port, and print reply. I have a question, how can I listening to the port longer than one moment? E.g. I want listen to selected port for 20 seconds and print all packets which will come at this time. Is it possible with this code?
import socket
import sys
try:
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
except socket.error as msg:
print("Failed to create socket. Error code: " + str(msg[0]) + ' , Error message : ' + msg[1])
sys.exit();
print('Socket Created')
host = #server
port = #port
try:
remote_ip = socket.gethostbyname( host )
except socket.gaierror:
print('Hostname could not be resolved. Exiting')
sys.exit()
print('Ip address of ' + host + ' is ' + remote_ip)
s.connect((remote_ip , port))
print('Socket Connected to ' + host + ' on ip ' + remote_ip)
reply = s.recv(4096)
print(reply)
You could try setting the timeout for the socket should fit your requirement if I understand correctly that you just need to wait one time for 20 seconds.
s.settimeout(20)
reply = s.recv(4096)
Python Socket settimeout()
However you are not guaranteed to get all the data packets delivered at once. So as was mentioned in a comment, you should be looping. The way to do this would be to place the socket in nonblocking mode.
Outside of your loop, you need a buffer_variable that would hold the total results from the recv().
Prior to entering your loop, you would start a timer. Upon entering you loop you would begin calling recv() on the socket while saving the result in a local_variable. Each time you get something new in local_variable you append it to buffer_variable.
When the timer expires, you would then break the loop, and process your data from buffer_variable accordingly.
This is the sample socket at server side (taken from some website):
import socket
import sys
HOST = '' # Symbolic name, meaning all available interfaces
PORT = 10001 # Arbitrary non-privileged port
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
print 'Socket created'
#Bind socket to local host and port
try:
s.bind((HOST, PORT))
except socket.error as msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit()
print 'Socket bind complete'
#Start listening on socket
s.listen(10)
print 'Socket now listening'
#now keep talking with the client
while 1:
#wait to accept a connection - blocking call
conn, addr = s.accept()
print 'Connected with ' + addr[0] + ':' + str(addr[1])
conn.send("Test Messag")
s.close()
This is the code at client side:
import socket
s=socket.socket()
s.connect((ipaddress,port))
s.setblocking(1)
import time
counter = 0
while True:
print counter
chunk = s.recv(11,socket.MSG_WAITALL)
if not chunk:
raise Exception('Socket error')
print chunk
time.sleep(1)
counter += 1
The server side code runs on an amazon ec2 instance (based on the amazon linux ami)
When I terminate the instance I would expect that the recv method on the socket throws an error, but it does not. Whatever I do, it never throws an error. When I run the server side code in an ipython notebook and restart the kernel, the recv method unlocks and keeps returning empty strings (according to When does socket.recv() raise an exception? this should be in the case of a clean shutdown), but no error is thrown.
What could be the cause of this, I really need to have it throw an exception so I can notify the rest of my code that the server went down in order to start a new one.
When I terminate the instance I would expect that the recv method on the socket throws an error ...
When the server terminates it will do a clean shutdown of the socket, so you will get no exception on the client side. To get what you want you would have to implement some kind of shutdown message inside your application. Then you can distinguish a proper shutdown (with an explicit shutdown message) from just a socket close.
You are making only one tcp connection. You have to make multiple request.
import socket
import time
counter = 0
while True:
print counter
s=socket.socket()
try:
s.connect((ipaddress,port))
s.setblocking(1)
chunk = s.recv(11,socket.MSG_WAITALL)
except Exception as e:
print e
break
print chunk
time.sleep(1)
counter += 1
This may have been already answered but did not find anything or dont know what to search for. I have a socket server threaded for multiple clients (code below) and want the server to run code (ie. check the status of something) and then send a message to the clients. How do I go about doing this?
To clarify, I need to learn how to add a asynchronous task to this code so it can do checking and send a message to the clients if it needs to
Example: while there are clients connected I want the server to continually check a log file and if it changes and if so I want it to send a message to the clients
Server.py(working code)
from socket import *
import thread
BUFF = 1024
HOST = '127.0.0.1'# must be input parameter #TODO
PORT = 9999 # must be input parameter #TODO
def response(key):
return 'Server response: ' + key
def handler(clientsock,addr):
while 1:
data = clientsock.recv(BUFF)
if not data: break
print repr(addr) + ' recv:' + repr(data)
clientsock.send(response(data))
print repr(addr) + ' sent:' + repr(response(data))
if "close" == data.rstrip(): break # type 'close' on client console to close connection from the server side
clientsock.close()
print addr, "- closed connection" #log on console
if __name__=='__main__':
ADDR = (HOST, PORT)
serversock = socket(AF_INET, SOCK_STREAM)
serversock.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
serversock.bind(ADDR)
serversock.listen(5)
while 1:
print 'waiting for connection... listening on port', PORT
clientsock, addr = serversock.accept()
print '...connected from:', addr
thread.start_new_thread(handler, (clientsock, addr))
I have added below code server.py and this works for sending a status change message when log file changes.
import socket
import sys
import time
from thread import *
HOST = 'localhost' # Symbolic name meaning all available interfaces
PORT = 9999 # Arbitrary non-privileged port
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created'
#Bind socket to local host and port
try:
s.bind((HOST, PORT))
except socket.error as msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit()
print 'Socket bind complete'
#Start listening on socket
s.listen(10)
print 'Socket now listening'
#Function for handling connections. This will be used to create threads
def clientthread(conn):
#Sending message to connected client
conn.send('Welcome to the server. Type something and hit enter\n') #send only takes string
data = conn.recv(1024)
#infinite loop so that function do not terminate and thread do not end.
while True:
logfile = open("serverlog.txt","r")
#Receiving from client
logfile.seek(0,2)
while True:
line = logfile.readline()
if not line:
time.sleep(0.1) # Sleep briefly
continue
reply = 'File Changed...Your Data' + data
break
conn.sendall(reply)
#came out of loop
conn.close()
#now keep talking with the client
while 1:
#wait to accept a connection - blocking call
conn, addr = s.accept()
print 'Connected with ' + addr[0] + ':' + str(addr[1])
#start new thread takes 1st argument as a function name to be run, second is the tuple of arguments to the function.
start_new_thread(clientthread ,(conn,))
s.close()
To test it run this server.py in one command prompt and keep it open. something like this
> python server.py
Socket created
Socket bind complete
Socket now listening
And run a simple telnet from other cmd prompt to verify the connection
telnet localhost 9999
Replace localhost with IP. Type anything on these telnet connection and you should get response properly.
Also you can check on server.py cmd prompt for the connections made.
And as I mentioned, check this link.