Very basic port scanner

portscanner.c

#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/socket.h>
#include <unistd.h>

#define MAXPORTNUM 65535

int main(int argc, char **argv) {
  if (argc < 2) {
    puts("No address was given.");
    return 1;
  }

  int sock = socket(AF_INET, SOCK_STREAM, 0);
  if (sock < 0) {
    perror("Could not open socket");
    return 2;
  }

  for (int port = 0; port <= MAXPORTNUM; port++) {
    struct sockaddr_in address = (struct sockaddr_in){
        .sin_family = AF_INET,
        .sin_addr = inet_addr(argv[1]),
        .sin_port = port,
    };

    int conn = connect(sock, (struct sockaddr *)&address, sizeof(address));
    if (conn < 0) {
      printf("Closed port: %d\n", port);
    } else {
      printf("Open port: %d\n", port);
    }
    close(conn);
  }

  close(sock);
  return 0;
}

portscanner.py

import socket
from sys import argv

MAXPORTNUM = 65535


def main(addr):
    sock = socket.socket()
    open_ports = []
    for port in range(MAXPORTNUM + 1):
        try:
            sock.connect((addr, port))
        except:
            print(f"Closed port: {port}")
        else:
            open_ports.append(port)
            print(f"Open port: {port}")
        sock.close()

    if len(open_ports) == 0:
        print("\nAll ports are closed")
    else:
        print("The following ports are opened")
        for port in open_ports:
            print(port)


if __name__ == "__main__":
    main(argv[1])