Open ports scanner

main.c

#include <stdio.h>
#include <sys/socket.h>
#include <errno.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <time.h>

#define BLUE  "\x1b[34m"
#define RED   "\x1b[31m"
#define GREEN "\x1b[32m"
#define RESET "\x1b[0m"

void display_results(int open_count, int total, double scan_time)
{
    printf(BLUE "\nScan completed in %.2f seconds\n" RESET, scan_time);
    printf("Result: " GREEN "%d open" RESET " and " RED "%d closed" RESET " ports found\n", open_count, total - open_count);
}

int resolve_hostname(const char* hostname, struct sockaddr_in* sa)
{
    struct hostent *host;

    memset(sa, 0, sizeof(*sa));
    sa->sin_family = AF_INET;

    // is ip address or domain?
    if (isdigit(hostname[0]))
    {
        sa->sin_addr.s_addr = inet_addr(hostname);
        return 1;
    } else if ((host = gethostbyname(hostname)) != 0)
    {
        memcpy(&sa->sin_addr, host->h_addr, host->h_length);
        return 1;
    }

    herror(hostname);
    return 0;
}

void scan_port_range(const char* hostname, int start_port, int end_port)
{
    struct sockaddr_in sa;
    int sock, err, i;
    int open_count = 0;
    clock_t begin_time, end_time;
    double scan_time;
    struct timeval timeout;
    
    begin_time = clock();

    if (!resolve_hostname(hostname, &sa))
    {
        fprintf(stderr, RED "Err: cannot resolve hostname %s\n" RESET, hostname);
        exit(2);
    }

    printf(BLUE "\nStarting scan on %s port %d-%d\n\n" RESET, hostname, start_port, end_port);

    timeout.tv_sec = 0;
    timeout.tv_usec = 100000;

    for (i = start_port; i <= end_port; i++)
    {
        printf("Scanning port %i", i);
        fflush(stdout);

        sa.sin_port = htons(i);
        sock = socket(AF_INET, SOCK_STREAM, 0);

        if (sock < 0)
        {
            perror("Socket creation failed");
            exit(1);
        }

        setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, (const char*)&timeout, sizeof timeout);
        setsockopt(sock, SOL_SOCKET, SO_SNDTIMEO, (const char*)&timeout, sizeof timeout);

        err = connect(sock, (struct sockaddr*)&sa, sizeof sa);

        if (err < 0)
        {
            printf("\r            \r");
        } else
        {
            printf("\r" GREEN "Port %i is open" RESET "\n", i);
            open_count++;
        }
        close(sock);
    }

    end_time = clock();
    scan_time = (double)(end_time - begin_time) / CLOCKS_PER_SEC;

    display_results(open_count, end_port - start_port + 1, scan_time);
}

int main(int argc, char **argv) 
{
    char hostname[100];
    int start, end;

    printf(BLUE "=== Simple port scanner ===\n" RESET);
    printf("Enter hostname or IP: ");
    fgets(hostname, sizeof(hostname), stdin);
    hostname[strcspn(hostname, "\n")] = 0;
    
    printf("Enter start port number: ");
    scanf("%d", &start);

    printf("Enter end port number: ");
    scanf("%d", &end);

    scan_port_range(hostname, start, end);

    return 0;
}