// Simple TCP knock client - Linux version
// Compile: gcc -o knock_client_linux knock_client_linux.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <time.h>

void knock_port(const char *ip, int port) {
    int s = socket(AF_INET, SOCK_STREAM, 0);
    if (s < 0) {
        perror("socket failed");
        return;
    }

    struct sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons((unsigned short)port);
    inet_pton(AF_INET, ip, &addr.sin_addr);

    printf("Knocking on port %d...\n", port);

    int result = connect(s, (struct sockaddr *)&addr, sizeof(addr));

    usleep(100000);

    close(s);

    if (result < 0) {
        printf("  Connection refused (expected - no listener)\n");
    } else {
        printf("  Connected!\n");
    }
}

int main(int argc, char *argv[]) {
    if (argc < 2) {
        printf("Usage: %s <target_ip> [port1 port2 port3 ...]\n", argv[0]);
        printf("Default ports: 7000 8000 9000\n");
        return 1;
    }

    const char *ip = argv[1];

    int ports[10];
    int num_ports;

    if (argc > 2) {
        num_ports = argc - 2;
        for (int i = 0; i < num_ports && i < 10; i++) {
            ports[i] = atoi(argv[i + 2]);
        }
    } else {
        num_ports = 3;
        ports[0] = 7000;
        ports[1] = 8000;
        ports[2] = 9000;
    }

    printf("Knocking on %s: ", ip);
    for (int i = 0; i < num_ports; i++) {
        printf("%d ", ports[i]);
    }
    printf("\n\n");

    for (int i = 0; i < num_ports; i++) {
        knock_port(ip, ports[i]);
        if (i < num_ports - 1) {
            usleep(500000);
        }
    }

    printf("\nKnock sequence complete!\n");
    printf("Now try connecting to port 31337\n");

    return 0;
}