php (or python) listen to unix domain stream socket

Question

I need to create a script that listens to a unix socket and forward the incoming stream to a bot. The scripts are unable to connect. The issues seems to be related to the order of things.

Proof of case

I have created a socket and I am able to write to it. In session 1, I create a listener connection

nc -lU /tmp/tg.sck

In session 2, I write to the socket.

 while true; do echo "hello"; sleep 2; done | nc -U /tmp/tg.sck

The above only works if I do it in that order. ==> Writing before you have a listener results in an error.

Using scripts (does not work)

When I replace the listing process with a PHP (or Python) script, the connection is refused because the socket is not opened.

$ python test.py 
Connecting...
socket.error: [Errno 111] Connection refused

or

$ php test.php 
Warning:  fsockopen(): unable to connect to unix:///tmp/tg.sck:-1 (Connection refused)

Changing the order of things

If I start a working listener using the command nc -lU /tmp/tg.sck then the script does not die, but the writer process does.

Listener scripts

import socket
import sys

server_address = '/tmp/tg.sck'  # Analogous to TCP (address, port) pair
sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
sock.connect(server_address)
sock.recv(512)

and the php script

$fp = fsockopen('unix:///tmp/tg.sck', -1, $errno, $errstr, 30);
if (!$fp) {
  echo "$errstr ($errno)<br />\n";
} else {
  while (!feof($fp)) {
    echo fgets($fp, 4096);
  }
  fclose($fp);
}

Steffen Ullrich · Accepted Answer · 2018-02-03 14:04:36Z

2

When I replace the listing process
...
sock.connect(server_address)

This does not listen but it connects.
To listen use bind,listen and accept the same way as you would do with other listing sockets (TCP, UDP):

server_address = '/tmp/tg.sck'  # Analogous to TCP (address, port) pair
os.unlink(server_address)
sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
sock.bind(server_address)
sock.listen(2)
c,_ = sock.accept()
print c.recv(512)

answered Feb 3, 2018 at 14:04

Steffen Ullrich

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2 Comments

crafter Over a year ago

Great solution @steffen. Can you explain the line c,_ = .... (I am a python newbie, and not seen this before).

Steffen Ullrich Over a year ago

@crafter: c,_ = ... just means to get the two arguments returned by accept but ignore the second one since it is not needed in the code. See also stackoverflow.com/questions/26251861/…

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