simple port scanner

scanner.c

/* Original author: Vikraman (vh4x0r @ Freenode) <vikraman.choudhury@gmail.com> */

#define _GNU_SOURCE

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

#define MAXPORT 65535

static void die(char *msg) { /* {{{ */
    perror(msg);
    exit(EXIT_FAILURE);
} /* }}} */

static int is_open(struct addrinfo *servinfo, int port) { /* {{{ */
    int sockfd, ret = 0;

    ((struct sockaddr_in *)servinfo->ai_addr)->sin_port = htons(port);

    if ((sockfd = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol)) < 0)
        return ret;

    if ((connect(sockfd, servinfo->ai_addr, servinfo->ai_addrlen)) == 0) {
        ret = 1;
    }

    close (sockfd);
    return ret;
} /* }}} */

static void scan(struct addrinfo *servinfo) { /* {{{ */
    struct addrinfo *p;
    int             port;
    int             nopen = 0;
    int             openports[MAXPORT + 1];

    for (p = servinfo; p; p = p->ai_next) {
        for (port = 1; port <= MAXPORT; port++) {
            if (!openports[port]) {
                if (is_open(p, port)) {
                    nopen++;
                    openports[port] = 1;
                    printf("  port %-5i is open\n", port);
                }
            }
        }
    }

    printf("\n%i ports closed or filtered.\n", MAXPORT - nopen);
} /* }}} */

int main (int argc, char *argv[]) {
    struct addrinfo *servinfo;
    struct addrinfo hints;

    if (argc != 2) {
        fprintf(stderr, "usage: scanner <host>\n");
        exit(EXIT_FAILURE);
    }

    printf("scanning host %s...\n\n", argv[1]);
    memset(&hints, 0, sizeof hints);

    hints.ai_family   = AF_INET;
    hints.ai_socktype = SOCK_STREAM;

    if (getaddrinfo(argv[1], NULL, &hints, &servinfo) != 0)
        die("error getting address info");

    scan(servinfo);
    exit(EXIT_SUCCESS);
}