socket recv not returning

Question

I can't understand why socket recv doesn't return. I have a client application that send string to a server. The client is executed in a terminal. This is the code

client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print "Enter client sender"
try:
 client.connect((target, port))
 if len(buffer):
 client.send(buffer)
 while True:
 print "Enter loop"
 recv_len = 1
 response = ""
 while recv_len:
 print "Enter loop 2"
 data = client.recv(4096)
 print "Afer recv"
 recv_len = len(data)
 print recv_len
 response += data
 if recv_len < 4096:
 break
 print response,
 buffer = raw_input("")
 buffer += "\n"
 client.send(buffer)
except:
 print "[*] Exception Exiting"
 client.close()

But the "After recv" label is never reached. Why? Can you help me? What is wrong?

Answer 1

Your code is generally correct, although bufferis a built-in type and you should avoid using it as a variable name (but it will still work if you do).

On a blocking socket (the default state), recv will block until there is some data available for reading. Make sure the other endpoint is sending (and flushing to the socket) a response.

You might find tcpdump or Wireshark useful to see the packets actually being transmitted. Also, I suggest you use nc or a similar generic TCP socket tool to debug this. E.g., nc -4 -l localhost PORT (-4 because your AF_INET implies IPv4).