tags: python net

Another simple example of sockets. The `server.py` runs a server on port 1026.
Opening a TCP socket to this port and reading it returns the hostname of the server.
The `massclient.py` uses threads for each machine on a /24 subnet, and it gets
the subnet using the `connect 8.8.8.8` trick to avoid getting the answer of localhost.
(Interestingly [ChatGPT]() kept giving me code that returned the IP for localhost.)

## client.py
```py
import socket
from icecream import ic
import sys
import re

args = sys.argv[1:]

def make_local(n):
  s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
  s.connect(("8.8.8.8", 80))
  x = s.getsockname()[0]
  s.close()
  xs = x.split(".")
  xs[-1] = str(n)
  return ".".join(xs)

def do_arg(arg):
  if m := re.match(r"(\d+\.){3}\d+$",arg):
    ip = arg
  elif arg.isnumeric():
    ip = make_local(arg)
  else:
    ip = arg
  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  try:
    s.connect((ip,1026))
    data = s.recv(1024)
    print(ip,data.decode())
  except ConnectionRefusedError:
    print(ip,"#Connection Refused")
  except TimeoutError:
    print(ip,"#Timeout")
  except Exception as e:
    ic(e)

for arg in args:
  do_arg(arg)
```

## massclient.py
```py
import socket
from icecream import ic
import sys
import re
import threading

args = sys.argv[1:]

def make_local(n):
  s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
  s.connect(("8.8.8.8", 80))
  x = s.getsockname()[0]
  s.close()
  xs = x.split(".")
  xs[-1] = str(n)
  return ".".join(xs)

def do_arg(arg):
  if m := re.match(r"(\d+\.){3}\d+$",arg):
    ip = arg
  elif arg.isnumeric() or type(arg) is int:
    ip = make_local(arg)
  else:
    ip = arg
  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  s.settimeout(0.5)
  try:
    s.connect((ip,1026))
    data = s.recv(1024)
    return data.decode()
  except TimeoutError:
    return None
  except ConnectionRefusedError:
    return None
  except Exception as e:
    ic(e)
    return None

def get_name_task(idx):
  ip = make_local(idx)
  result = do_arg(ip)
  if result is not None:
    found[ip] = result

found = {}
threads = []
for i in range(2,254):
  thread = threading.Thread(target=get_name_task,args=(i,))
  threads.append(thread)
  thread.start()

for thread in threads:
  thread.join()

for ip, name in found.items():
  print(ip,name)
```

## server.py
```py
import socket
import threading

def hostname():
  return socket.gethostname()

def handle_client(client_socket):
  client_socket.send(hostname().encode())
  client_socket.close()

def main():
  host = "0.0.0.0"
  port = 1026
  try:
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server_socket.bind((host,port))
    server_socket.listen()

    while True:
      client_socket, client_address = server_socket.accept()
      client_thread = threading.Thread(target=handle_client, args=(client_socket,))
      client_thread.start()
  except Exception as e:
    ic(2)
  finally:
    server_socket.close()

if __name__ == main():
  main()

```