portscan.c

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

int port_scan(char *addr)
{
	int sockfd;
	int err;
	uint16_t portno;
	struct addrinfo hints;
	struct addrinfo *addr_info;
	struct addrinfo *temp;
	
	/* Allow IPv4 or IPv6, stream socket with any protocol */
	memset(&hints, 0, sizeof(struct addrinfo));
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_flags = 0;
	hints.ai_protocol = 0;
	
	printf("Ports open for %s:\n", addr);
	
	/* Iterate through each port */
	for (portno = 0; portno < UINT16_MAX; portno++)
	{
		size_t length = snprintf(NULL, 0, "%d", portno);
		char* portno_str = malloc(length + 1);
		
		snprintf(portno_str, length + 1, "%d", portno);
		
		err = getaddrinfo(addr, portno_str, &hints, &addr_info);
		if (err)
		{
			fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(err));
			return err;
		}
		
		for (temp = addr_info; temp != NULL; temp = temp->ai_next)
		{
			sockfd = socket(temp->ai_family,
				temp->ai_socktype,
				temp->ai_protocol);
			if (sockfd < 0)
			{
				fprintf(stderr, "Error opening a socket.\n");
				continue;
			}
			
			err = connect(sockfd, temp->ai_addr, temp->ai_addrlen);
			if (err)
			{
				close(sockfd);
				continue;
			}
			
			printf("%s\n", portno_str);
			
			close(sockfd);
		}
		
		freeaddrinfo(addr_info);
		free(portno_str);
	}
	
	return 0;
}