How can retrive all TCP UDP opened ports? - c

Question

I need to make a custom port scanner that scan only opened TCP and UDP ports. I'm working in standard C with sockets. For the moment i retrieve all ports in a range i set.
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdlib.h>
#include <errno.h>
int scanPort(struct hostent *hostaddr,int port){
char responce[1024];
char *message="checking port";
struct sockaddr_in server_address;
int socket_d;
int rval;
socket_d = socket(PF_INET,SOCK_STREAM,IPPROTO_TCP);
if(socket_d == -1)
{
perror("Socket()\n");
return errno;
}
memset(&server_address,0,sizeof(server_address));
server_address.sin_family=AF_INET;
server_address.sin_port=htons(port);
memcpy(&server_address.sin_addr,hostaddr->h_addr,hostaddr->h_length);
rval = connect(socket_d,(struct sockaddr *) &server_address, sizeof(server_address));
if(rval == -1)
{
close(socket_d);
return 0;
}else{
close(socket_d);
return 1;
}
}
int main(int argc, char **argv)
{
if(argc < 4){
printf("Exemplu: ./portscanner <adresa_ip> <port_pornire> <port_oprire> \n");
return (EINVAL);
}
int startPort;
int endPort;
int port;
struct hostent *host_address;
host_address = gethostbyname( argv[1] );
startPort = atoi(argv[2]);
endPort = atoi(argv[3]);
for(port = startPort;port<=endPort;port++)
{
if(scanPort(host_address,port)==1){
printf("Port %d is open\n",port);
}
}
}
In the example you can see how i tried to resolve this problem. But i don't see a method to check only the TCP and UDP ports. Please help me with this.
Regards,
Badea Sorin!

Answer 1

There is a plenty ways to do it. I recommend you to install nmap and read the manual.
Many scan methods are implemented there and described in the manual.
You can also refer to the source code if you need more details.
Good luck.