Python client disconnect if server closes connection

Question

I have server and client code in python in which client sends a request message to server and wait for the response. I have the server code to close the connection when the client doesn't send a proper request. When the server closes the request, the client still is listening forever for the response.

Below is the code

server.py

s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
s.bind((host, port))
s.listen(1)
while True:
 c, addr = s.accept()
 # Receive request
 data = c.recv(1024)
 if data != 'something'
 c.close()
 else
 c.sendall("message"+"End")
 c.close()
s.close()

Client.py

End='End'
def recv_end(the_socket):
 # Snippet from http://code.activestate.com/recipes/408859-socketrecv-three-ways-to-turn-it-into-recvall/
 total_data=[];data=''
 while True:
 data=the_socket.recv(8192)
 if End in data:
 total_data.append(data[:data.find(End)])
 break
 total_data.append(data)
 if len(total_data)>1:
 #check if end_of_data was split
 last_pair=total_data[-2]+total_data[-1]
 if End in last_pair:
 total_data[-2]=last_pair[:last_pair.find(End)]
 total_data.pop()
 break
 return ''.join(total_data)
s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
s.connect((host, port))
s.send("some_request")
data = s.recv_end(1024)
print "<---- " + str(data)
s.close()

I'm new to python and wondering if there is a way for the client to know that the server closed the connection and terminate.

I understand that the client would disconnect if I use normal s.recv(1024). But in my case, I need to send large data to the client so I have used a different function I found from http://code.activestate.com/recipes/408859-socketrecv-three-ways-to-turn-it-into-recvall/.

Is it like the server sends a empty string reply during the close of a connection and in my case, it would send a empty string without the end limiter and hence the client is listening forever ?

• Joaquin Sargiotto: Does your client hangs in the s.recv(1024) call? Or it returns with an empty response?
• Serge Ballesta: I tried your code (after fixing missing : in server) and I cannot reproduce : client displays empty string and exists, and if I modify it to send something, it displays <---- message and exits.
• aBadAssCowboy: @SergeBallesta please check with the edit I made. I'm using a different function to receive with a end limiter because I need to transfer large data.

Answer 1

When you have a loop with recv or anything that reads from a socket or a pipe, you should stop reading as soon as you get a buffer with len 0 :

while True:
 data=the_socket.recv(8192)
 if len(data) == 0: break
 ...

• aBadAssCowboy: So, on close, the server sends a empty response? And that is the only way the client will know that the connection is closed?
• Serge Ballesta: Not exactly. But when a socket is closed on the peer, the read on the other side is aborted and returns 0 bytes. It's the same logic as an eof when reading from a true file.
• Beefy_Swain: Someday the docs will reflect this..