stuck in while loop python

Question

I am creating a chat server in python and got quite far as a noob in the language. I am having 1 problem at the moment which I want to solve before I go further, but I cannot seem to find how to get the problem solved.

It is about a while loop that continues..

in the below code is where it goes wrong

while 1:
 try:
 data = self.channel.recv ( 1024 )
 print "Message from client: ", data
 if "exit" in data:
 self.channel.send("You have closed youre connection.\n")
 break
 except KeyboardInterrupt:
 break
 except:
 raise

When this piece of code get executed, on my client I need to enter "exit" to quit the connection. This works as a charm, but when I use CTRL+C to exit the connection, my server prints "Message from client: " a couple of thousand times.

where am I going wrong?

• thegrinner: When you use CTRL+C, is that on the client or server side?
• Florin Stingaciu: It sounds like you're closing the client. Recv probably returns false and thus you're stuck in the while loop.
• bryanvan: I am using CTRL+C on the client side.
• Silas Ray: Think twice about using if 'exit' in data:. If this is a chat server, this means no one can ever send a message containing the word 'exit' unless they manage to make it span across 2 buffer-sized data blocks. if data == 'exit': will probably work more as you'd like.
• bryanvan: @sr2222 I agree. However in the context of my chatserver, it does not seem to work if I replace the if statement with "if data == "exit" ", therefor I replaced the word with "/exit". This works fine now. Thx for the advice.

Answer 1

You're pressing Ctrl-C on the client side. This causes the server's self.channel to get closed.

Since calling recv() on a closed channel immediately returns a blank string, your server code gets stuck in an infinite loop.

To fix this, add the following line to your server code:

data = self.channel.recv ( 1024 )
if not data: break # <<< ADD THIS

Or, as suggested by @sr2222, you can combine both this and your current check into one:

if not data or 'exit' in data: 

This will exit the loop if the channel has been closed.

• Silas Ray: Or just if not data or 'exit' in data:
• bryanvan: Wow damm I indeed missed this... couldnt wrap my head around it, both the answer of NPE and sr2222 are correct. THX
• Silas Ray: Oh, sorry NPE, you are right, it's probably better to have 2 separate checks, since the 'exit' in data check sends data back over the connection, which will not be valid if data is empty.
• NPE: @sr2222: Yes and no. AFAIK, calling send() on a closed channel is a no-op. However, some might question this approach on stylistic grounds.