Question

I’m new to using Python and sockets in general (only started yesterday) so I’ve been having a lot of issues trying to set up a TCP client and server. The issue I’m having is that I want to send a key from the server to the client. I know that the server grabs the key correctly as it prints out the correct key, however it has a 0 appended to it in a new line and when the key is sent to the client the only thing that is displayed is ” b’0′ “.

I’ve made very little progress due to my lack of experience and after searching for hours I still haven’t found a solution to my problem.

Here is the server code:

import os
from socket import * #import the socket library


HOST = '' #We are the host
PORT = 29876
ADDR = (HOST, PORT)
BUFFSIZE = 4096
message = 'Hello, World!'


serv =  socket( AF_INET,SOCK_STREAM)
serv.bind(ADDR,) 
serv.listen(5) 
print ('listening...')


conn,addr = serv.accept()
print (conn,addr)
print ('...connected')


key = os.system("cat ~/.ssh/id_rsa.pub")
conn.send(str(key))
print (key)


conn.close()

Here is the client code

from socket import *
import os

HOST = 'xxx.xxx.xxx.xxx'
PORT = 29876 
ADDR = (HOST,PORT)
BUFFSIZE = 4096
message = "Hello, World!"

cli = socket( AF_INET, SOCK_STREAM)
cli.connect(ADDR,)

data = cli.recv(BUFFSIZE)
print (data)

cli.close()

As you can tell from my code I’m using Python 3.3
Any help with this issue is greatly appreciated.

Answer 1

os.system() does not return the process’s output, but the return value (ie. integer 0).

If you only want to read a file, do it manually:

with open(os.path.expanduser("~/.ssh/id_rsa.pub")) as f:
    key = f.read()
    conn.sendall(key)

If you need process output, read the documentation for the subprocess module.