Your implementation has a race condition in it. If two threads run at the same
time and get the same port from “find_free_port” one of your nc calls will fail.
Also why are you not using the subprocess module?
> On 26 Jul 2018, at 4:11 pm, Andrew Stuart <andrew.stu...@supercoders.com.au>
> wrote:
>
> Thanks to Tim and Rory and Ben Finney who all chipped in with ideas.
>
> Just to follow through, here’s the solution I put together in the end. It
> spawns a netcat process in response to a POST request (Python 3.6). I managed
> to avoid implementing a queueing system and lots of file juggling. It’s just
> plain TCP sockets, not websockets.
>
> Send this to get a new netcat process spawned on a port:
> curl -X POST -H "Content-Type: text/plain" --data ‘example data'
> localhost:8000
>
>
> from http.server import HTTPServer, BaseHTTPRequestHandler
> import socket
> import os
> import io
>
> host = '0.0.0.0'
> port = 8000
>
> def find_free_port():
> with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
> s.bind(('', 0))
> return s.getsockname()[1]
>
> def spawn_netcat(port):
> command = "/bin/nc"
> params = f"nc -l {port}"
> spawnDaemon(command, params.split())
>
> def spawnDaemon(path_to_executable, params):
>
> # Do first fork
> pid = os.fork()
> if (pid != 0):
> os.waitid(os.P_PID, pid, os.WEXITED)
> return
>
> # Decouple from parent environment
> os.chdir("/opt")
> os.setsid()
> os.umask(0)
>
> # Do second fork
> pid = os.fork()
> if (pid != 0):
> os._exit(0)
>
> # exec this process into netcat.....
> os.execv(path_to_executable, params)
>
> class Server(BaseHTTPRequestHandler):
>
> def do_POST(self):
> netcat_listen_port = find_free_port()
> spawn_netcat(netcat_listen_port)
> self.send_response(200)
> self.send_header("Content-type", "text/plain")
> self.end_headers()
> response = io.BytesIO()
> response.write(str(netcat_listen_port).encode())
> self.wfile.write(response.getvalue())
>
> if __name__ == "__main__":
> httpd = HTTPServer((host, port), Server)
> httpd.serve_forever()
>
>
>
>
>
>
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