Simple TCP port scanner for beginners

[billy786]

This is a simple port scanner created by me when i was learning socket programming in C. I thought it might be usefull to someone and decide to post it hope you enjoy it.

The code is using tcp connect with an if statement to determine whether the port is opened or closes within a for loop which is for the port range.

/* A TCP port scanner created by billy
www.softhardware.co.uk*/

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdlib.h>
#include <errno.h>


/* Main programs starts*/
int main(int argc, char **argv)
{
   int   sd;         //socket descriptor
   int    port;         //port number
   int   start;         //start port
   int    end;         //end port
   int    rval;         //socket descriptor for connect   
   char    responce[1024];      //to receive data
   char   *message="shell";       //data to send
   struct hostent *hostaddr;   //To be used for IPaddress
   struct sockaddr_in servaddr;   //socket structure
   
   if (argc < 4 )
   {
      printf("------Created By www.h4ck-y0u.org-----------\n");
      printf("--------------------------------------------------\n");
      printf("Usage: ./tscan <IPaddress> <Start Port> <End Port>\n");
      printf("--------------------------------------------------\n");
      return (EINVAL);
   }
   start = atoi(argv[2]);
   end   = atoi(argv[3]);
   for (port=start; port<=end; port++)
   {

         //portno is ascii to int second argument      

   sd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP); //created the tcp socket
   if (sd == -1)
   {
     perror("Socket()\n");
     return (errno);
   }   

   memset( &servaddr, 0, sizeof(servaddr));

   servaddr.sin_family = AF_INET;
   servaddr.sin_port = htons(port); //set the portno
   
   hostaddr = gethostbyname( argv[1] ); //get the ip 1st argument
   
   memcpy(&servaddr.sin_addr, hostaddr->h_addr, hostaddr->h_length);
      
   //below connects to the specified ip in hostaddr
   
 

   rval = connect(sd, (struct sockaddr *) &servaddr, sizeof(servaddr));
   if (rval == -1)
   {
   printf("Port %d is closed\n", port);
   close(sd);
   }
   else
   printf("Port %d is open\n",port);
   
   close(sd);         //socket descriptor
   }
   
}

[torleif]

Nice and simple, also I see another fan of the unix like #include <sys/types.h>. I only learnt about this recently and was using a complicated cross platform library

[Xav]

You should post this in the Tutorials section. Very nice. +rep given.