// Simple TCP knock client - sends single SYN packets without retries
// Compile: cl /W4 /O2 knock_client.c /ws2_32.lib

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <stdlib.h>

#pragma comment(lib, "ws2_32.lib")

void knock_port(const char* ip, int port) {
    SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (s == INVALID_SOCKET) {
        printf("socket failed: %d\n", WSAGetLastError());
        return;
    }

    // Set socket to close immediately after connect attempt
    BOOL dontlinger = FALSE;
    setsockopt(s, SOL_SOCKET, SO_DONTLINGER, (char*)&dontlinger, sizeof(dontlinger));

    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);
    
    // Connect will send SYN, and we close immediately after
    int result = connect(s, (struct sockaddr*)&addr, sizeof(addr));
    
    // Give it a moment to send the packet
    Sleep(100);
    
    // Close immediately without retrying
    closesocket(s);
    
    if (result == SOCKET_ERROR) {
        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;
    }

    WSADATA wsa;
    if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0) {
        printf("WSAStartup failed\n");
        return 1;
    }

    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) {
            // Wait between knocks
            Sleep(500);
        }
    }

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

    WSACleanup();
    return 0;
}