/*
 * GoodbyeDPI — Passive DPI blocker and Active DPI circumvention utility.
 */

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <winsock2.h>
#include "windivert.h"

#define die() do { printf("Something went wrong!\n" \
    "Make sure you're running this program with administrator privileges\n"); \
    sleep(10); exit(EXIT_FAILURE); } while (0)

#define MAX_FILTERS 4
#define MAX_PACKET_SIZE 1516
#define IPV4_HDR_LEN 20
#define TCP_HDR_LEN 20
#define IPV4_TOTALLEN_OFFSET 2
#define TCP_WINDOWSIZE_OFFSET 14
    
static HANDLE filters[MAX_FILTERS];
static int filter_num = 0;
static const char *http10_redirect_302 = "HTTP/1.0 302 ";
static const char *http11_redirect_302 = "HTTP/1.1 302 ";
static const char *http_host_find = "\r\nHost: ";
static const char *http_host_replace = "\r\nhoSt: ";
static const char *http_useragent_find = "\r\nUser-Agent: ";
static const char *location_http = "\r\nLocation: http://";
static const char *connection_close = "\r\nConnection: close";
static const char *http_methods[] = {
    "GET ",
    "HEAD ",
    "POST ",
    "PUT ",
    "DELETE ",
    "CONNECT ",
    "OPTIONS ",
    "TRACE ",
    "PATCH ",
    "PROPFIND ",
    "PROPPATCH ",
    "MKCOL ",
    "COPY ",
    "MOVE ",
    "LOCK ",
    "UNLOCK ",
};

static char* dumb_memmem(const char* haystack, int hlen, const char* needle, int nlen) {
    // naive implementation
    if (nlen > hlen) return 0;
    int i;
    for (i=0; i<hlen-nlen+1; i++) {
        if (memcmp(haystack+i,needle,nlen)==0) {
            return (char*)(haystack+i);
        }
    }
    return NULL;
}

static HANDLE init(char *filter, UINT64 flags) {
    LPTSTR errormessage = NULL;
    filter = WinDivertOpen(filter, WINDIVERT_LAYER_NETWORK, 0, flags);
    if (filter != INVALID_HANDLE_VALUE)
        return filter;
    FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
                  FORMAT_MESSAGE_IGNORE_INSERTS,
                  NULL, GetLastError(), MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
                  (LPTSTR)&errormessage, 0, NULL);
    printf("%s", errormessage);
    return NULL;
}

static int deinit(HANDLE handle) {
    if (handle) {
        WinDivertClose(handle);
        return 1;
    }
    return 0;
}

static void deinit_all() {
    for (int i = 0; i < filter_num; i++) {
        deinit(filters[i]);
    }
}

static void sigint_handler(int sig) {
    deinit_all();
    exit(EXIT_SUCCESS);
}

static int is_passivedpi_redirect(const char *pktdata, int pktlen) {
    /* First check if this is HTTP 302 redirect */
    if (memcmp(pktdata, http11_redirect_302, strlen(http11_redirect_302)) == 0 ||
        memcmp(pktdata, http10_redirect_302, strlen(http10_redirect_302)) == 0)
    {
        /* Then check if this is a redirect to new http site with Connection: close */
        if (dumb_memmem(pktdata, pktlen, location_http, strlen(location_http)) &&
            dumb_memmem(pktdata, pktlen, connection_close, strlen(connection_close))) {
            return 1;
        }
    }
    return 0;
}

/* Finds Host header with \r\n before it */
static PVOID find_host_header(const char *pktdata, int pktlen) {
    return dumb_memmem(pktdata, pktlen,
                http_host_find, strlen(http_host_find));
}

/* Finds User-Agent header with \r\n before it */
static PVOID find_useragent_header(const char *pktdata, int pktlen) {
    return dumb_memmem(pktdata, pktlen,
                http_useragent_find, strlen(http_useragent_find));
}

static void change_window_size(const char *pkt, int size) {
    *(uint16_t*)(pkt + IPV4_HDR_LEN + TCP_WINDOWSIZE_OFFSET) = htons(size);
}

/* HTTP method end without trailing space */
static PVOID find_http_method_end(const char *pkt) {
    int i;
    for (i = 0; i<(sizeof(http_methods) / sizeof(*http_methods)); i++) {
        if (memcmp(pkt, http_methods[i], strlen(http_methods[i])) == 0) {
            return (char*)pkt+strlen(http_methods[i]) - 1;
        }
    }
    return NULL;
}

int main(int argc, char *argv[]) {
    static const char fragment_size_message[] =
                "Fragment size should be in range [0 - 65535]\n";
    int i, should_reinject = 0;
    int opt;
    HANDLE w_filter = NULL;
    WINDIVERT_ADDRESS addr;
    char packet[MAX_PACKET_SIZE];
    PVOID packet_data;
    UINT packetLen;
    UINT packet_dataLen;
    PWINDIVERT_IPHDR ppIpHdr;
    PWINDIVERT_TCPHDR ppTcpHdr;

    int do_passivedpi = 0, do_fragment_http = 0,
        do_fragment_https = 0, do_host = 0,
        do_host_removespace = 0, do_additional_space = 0;
    int http_fragment_size = 2;
    int https_fragment_size = 2;
    char *data_addr, *data_addr_rn, *host_addr, *useragent_addr, *method_addr;
    int data_len, host_len;

    printf("GoodbyeDPI: Passive DPI blocker and Active DPI circumvention utility\n");

    if (argc == 1) {
        /* enable mode -1 by default */
        do_passivedpi = do_host = do_host_removespace \
            = do_fragment_http = do_fragment_https = 1;
    }

    while ((opt = getopt(argc, argv, "1234prsaf:e:")) != -1) {
        switch (opt) {
            case '1':
                do_passivedpi = do_host = do_host_removespace \
                = do_fragment_http = do_fragment_https = 1;
                break;
            case '2':
                do_passivedpi = do_host = do_host_removespace \
                = do_fragment_http = do_fragment_https = 1;
                https_fragment_size = 40;
                break;
            case '3':
                do_passivedpi = do_host = do_host_removespace \
                = do_fragment_https = 1;
                https_fragment_size = 40;
            case '4':
                do_passivedpi = do_host = do_host_removespace = 1;
                break;
            case 'p':
                do_passivedpi = 1;
                break;
            case 'r':
                do_host = 1;
                break;
            case 's':
                do_host_removespace = 1;
                break;
            case 'a':
                do_additional_space = 1;
                do_host_removespace = 1;
                break;
            case 'f':
                do_fragment_http = 1;
                http_fragment_size = atoi(optarg);
                if (http_fragment_size <= 0 || http_fragment_size > 65535) {
                    printf(fragment_size_message);
                    exit(EXIT_FAILURE);
                }
                break;
            case 'e':
                do_fragment_https = 1;
                https_fragment_size = atoi(optarg);
                if (https_fragment_size <= 0 || https_fragment_size > 65535) {
                    printf(fragment_size_message);
                    exit(EXIT_FAILURE);
                }
                break;
            default:
                printf("Usage: goodbyedpi.exe [OPTION...]\n"
                " -p          block passive DPI\n"
                " -r          replace Host with hoSt\n"
                " -s          remove space between host header and its value\n"
                " -a          additional space between Method and Request-URI (enables -s, may break sites)\n"
                " -f [value]  set HTTP fragmentation to value\n"
                " -e [value]  set HTTPS fragmentation to value\n"
                "\n"
                " -1          -p -r -s -f 2 -e 2 (most compatible mode, default)\n"
                " -2          -p -r -s -f 2 -e 40 (better speed yet still compatible)\n"
                " -3          -p -r -s -e 40 (even better speed)\n"
                " -4          -p -r -s (best speed)\n");
                exit(EXIT_FAILURE);
        }
    }

    printf("Block passive: %d, Fragment HTTP: %d, Fragment HTTPS: %d, "
           "hoSt: %d, Host no space: %d, Additional space: %d\n",
           do_passivedpi, (do_fragment_http ? http_fragment_size : 0),
           (do_fragment_https ? https_fragment_size : 0),
           do_host, do_host_removespace, do_additional_space);

    printf("\nOpening filter\n");
    filter_num = 0;

    if (do_passivedpi) {
        /* Filter for inbound RST packets with ID = 0 or 1 */
        filters[filter_num] = init("inbound and (ip.Id == 0x0001 or ip.Id == 0x0000) and "
                        "(tcp.SrcPort == 443 or tcp.SrcPort == 80) and tcp.Rst",
                        WINDIVERT_FLAG_DROP);
        filter_num++;
    }

    /* 
     * Filter for inbound HTTP redirection packets and
     * active DPI circumvention
     */
    filters[filter_num] = init("(inbound and (ip.Id == 0x0001 or ip.Id == 0x0000) and tcp.SrcPort == 80 and tcp.Ack) "
                      "or (inbound and (tcp.SrcPort == 80 or tcp.SrcPort == 443) and tcp.Ack and tcp.Syn) "
                      "or (outbound and (tcp.DstPort == 80 or tcp.DstPort == 443) and tcp.Ack)",
                      0);

    w_filter = filters[filter_num];
    filter_num++;

    for (i = 0; i < filter_num; i++) {
        if (filters[i] == NULL)
            die();
    }

    printf("Filter activated!\n");
    signal(SIGINT, sigint_handler);

    while (1) {
        if (WinDivertRecv(w_filter, packet, sizeof(packet), &addr, &packetLen)) {
            //printf("Got %s packet, len=%d!\n", addr.Direction ? "inbound" : "outbound",
            //       packetLen);
            should_reinject = 1;

            if (WinDivertHelperParsePacket(packet, packetLen, &ppIpHdr,
                NULL, NULL, NULL, &ppTcpHdr, NULL, &packet_data, &packet_dataLen)) {
                //printf("Got parsed packet, len=%d!\n", packet_dataLen);
                /* Got a packet WITH DATA */

                /* Handle INBOUND packet with data and find HTTP REDIRECT in there */
                if (addr.Direction == WINDIVERT_DIRECTION_INBOUND && packet_dataLen > 16) {
                    /* If INBOUND packet with DATA (tcp.Ack) */

                    /* Drop packets from filter with HTTP 30x Redirect */
                    if (do_passivedpi && is_passivedpi_redirect(packet_data, packet_dataLen)) {
                        //printf("Dropping HTTP Redirect packet!\n");
                        should_reinject = 0;
                    }
                }
                /* Handle OUTBOUND packet, search for Host header */
                else if (addr.Direction == WINDIVERT_DIRECTION_OUTBOUND && 
                        packet_dataLen > 16 && ppTcpHdr->DstPort == htons(80) &&
                        find_http_method_end(packet_data) &&
                        (do_host || do_host_removespace)) {

                    data_addr = find_host_header(packet_data, packet_dataLen);
                    if (data_addr) {

                        if (do_host) {
                            /* Replace "Host: " with "hoSt: " */
                            memcpy(data_addr, http_host_replace, strlen(http_host_replace));
                            //printf("Replaced Host header!\n");
                        }

                        if (do_additional_space && do_host_removespace) {
                            /* End of "Host:" without trailing space */
                            host_addr = data_addr + strlen(http_host_find) - 1;
                            method_addr = find_http_method_end(packet_data);

                            if (method_addr) {
                                memmove(method_addr + 1, method_addr, (PVOID)host_addr - (PVOID)method_addr);
                            }
                        }
                        else if (do_host_removespace) {
                            host_addr = data_addr + strlen(http_host_find);

                            data_addr_rn = dumb_memmem(host_addr,
                                                       packet_dataLen - ((PVOID)host_addr - packet_data),
                                                       "\r\n", 2);
                            if (data_addr_rn) {
                                /* We move Host header value by one byte to the left and then
                                 * "insert" stolen space to the end of User-Agent value because
                                 * some web servers are not tolerant to additional space in the
                                 * end of Host header.
                                 *
                                 * Nothing is done if User-Agent header is missing.
                                 */
                                host_len = data_addr_rn - host_addr;
                                useragent_addr = find_useragent_header(packet_data, packet_dataLen);
                                if (host_len <= 253 && useragent_addr && useragent_addr > host_addr) {
                                    /* Performing action only if User-Agent header goes after Host */

                                    useragent_addr += strlen(http_useragent_find);
                                    /* useragent_addr is in the beginning of User-Agent value */

                                    data_len = packet_dataLen - ((PVOID)useragent_addr - packet_data);
                                    data_addr_rn = dumb_memmem(useragent_addr,
                                                               data_len, "\r\n", 2);
                                    /* data_addr_rn is in the end of User-Agent value */

                                    if (data_addr_rn) {
                                        data_len = (PVOID)data_addr_rn - (PVOID)host_addr;

                                        /* Move one byte to the left from "Host:"
                                         * to the end of User-Agen
                                         */
                                        memmove(host_addr - 1, host_addr, data_len);
                                        /* Put space in the end of User-Agent header */
                                        *(char*)(data_addr_rn - 1) = ' ';
                                        //printf("Replaced Host header!\n");
                                    }
                                }
                            }
                        }

                        WinDivertHelperCalcChecksums(packet, packetLen, 0);
                    }
                }
            }
            /* Else if we got TCP packet without data */
            else if (WinDivertHelperParsePacket(packet, packetLen, &ppIpHdr,
                NULL, NULL, NULL, &ppTcpHdr, NULL, NULL, NULL)) {
                /* If we got SYN+ACK packet */
                if (addr.Direction == WINDIVERT_DIRECTION_INBOUND && 
                    ppTcpHdr->Syn == 1) {
                    //printf("Changing Window Size!\n");
                    if (do_fragment_http && ppTcpHdr->SrcPort == htons(80)) {
                        change_window_size(packet, http_fragment_size);
                        WinDivertHelperCalcChecksums(packet, packetLen, 0);
                    }
                    else if (do_fragment_https && ppTcpHdr->SrcPort != htons(80)) {
                        change_window_size(packet, https_fragment_size);
                        WinDivertHelperCalcChecksums(packet, packetLen, 0);
                    }
                }
            }

            if (should_reinject) {
                //printf("Re-injecting!\n");
                WinDivertSend(w_filter, packet, packetLen, &addr, NULL);
            }
        }
        else {
            // error, ignore
            printf("Error receiving packet!\n");
            break;
        }
    }
}