Implement TCP fragmentation for HTTP Persistent (keep-alive) sessions.

New option `-k` splits HTTP request into two segments, and either
send only the first one (Windows would retransmit the other one
based on ACK number in ACK reply) or both (with `-n` enabled).

This fixes behaviour on some DPI which trace persistent sessions
but do not reassemble packages.

README.md

@@ -18,6 +18,8 @@ Usage: goodbyedpi.exe [OPTION...]
  -s          remove space between host header and its value
  -m          mix Host header case (test.com -> tEsT.cOm)
  -f [value]  set HTTP fragmentation to value
+ -k [value]  enable HTTP persistent (keep-alive) fragmentation and set it to value
+ -n          do not wait for first segment ACK when -k is enabled
  -e [value]  set HTTPS fragmentation to value
  -a          additional space between Method and Request-URI (enables -s, may break sites)
  -w          try to find and parse HTTP traffic on all processed ports (not only on port 80)
@@ -28,15 +30,15 @@ Usage: goodbyedpi.exe [OPTION...]
  --blacklist [txtfile]  perform HTTP tricks only to host names and subdomains from
                         supplied text file. This option can be supplied multiple times.
 
- -1          -p -r -s -f 2 -e 2 (most compatible mode, default)
+ -1          -p -r -s -f 2 -k 2 -n -e 2 (most compatible mode, default)
- -2          -p -r -s -f 2 -e 40 (better speed yet still compatible)
+ -2          -p -r -s -f 2 -k 2 -n -e 40 (better speed for HTTPS yet still compatible)
- -3          -p -r -s -e 40 (even better speed)
+ -3          -p -r -s -e 40 (better speed for HTTP and HTTPS)
  -4          -p -r -s (best speed)
 ```
 
-Try to run `goodbyedpi.exe -1 -a -m --dns-addr 77.88.8.8 --dns-port 1253` first. This is the most hardcore mode which will show if this program is suitable for your ISP and DPI vendor. If you can open blocked websites with these options, it means your ISP has DPI which can be circumvented. This is the slowest and prone to break websites mode, but suitable for most DPI.
+To check if your ISP's DPI could be circumvented, run `3_all_dnsredir_hardcore.cmd` first. This is the most hardcore mode which will show if this program is suitable for your ISP and DPI vendor at all. If you can open blocked websites with this mode, it means your ISP has DPI which can be circumvented. This is the slowest and prone to break websites mode, but suitable for most DPI.
 
-Try `-1` to see if it works too.
+Try `goodbyedpi -1` to see if it works too.
 
 Then try `goodbyedpi.exe -2`. It should be faster for HTTPS sites. Mode `-3` speed ups HTTP websites.
 
@@ -53,6 +55,7 @@ Most Passive DPI send HTTP 302 Redirect if you try to access blocked website ove
 Active DPI is more tricky to fool. Currently the software uses 4 methods to circumvent Active DPI:
 
 * TCP-level fragmentation for first data packet
+* TCP-level fragmentation for persistent (keep-alive) HTTP sessions
 * Replacing `Host` header with `hoSt`
 * Removing space between header name and value in `Host` header
 * Adding additional space between HTTP Method (GET, POST etc) and URI

goodbyedpi.c

@@ -39,6 +39,22 @@
                    "(ip.SrcAddr < 169.254.0.0 or ip.SrcAddr > 169.254.255.255)" \
                    ")"
 
+#define SET_HTTP_FRAGMENT_SIZE_OPTION(fragment_size) do { \
+    if (!http_fragment_size) { \
+        http_fragment_size = fragment_size; \
+        if (http_fragment_size <= 0 || http_fragment_size > 65535) { \
+            printf(fragment_size_message); \
+            exit(EXIT_FAILURE); \
+        } \
+    } \
+    else if (http_fragment_size != fragment_size) { \
+        printf( \
+            "WARNING: HTTP fragment size is already set to %d, not changing.\n", \
+            http_fragment_size \
+        ); \
+    } \
+} while (0)
+
 static HANDLE filters[MAX_FILTERS];
 static int filter_num = 0;
 static const char *http10_redirect_302 = "HTTP/1.0 302 ";
@@ -207,19 +223,23 @@ static void change_window_size(const char *pkt, int size) {
 }
 
 /* HTTP method end without trailing space */
-static PVOID find_http_method_end(const char *pkt, int offset) {
+static PVOID find_http_method_end(const char *pkt, int http_frag, int *is_fragmented) {
     unsigned int i;
     for (i = 0; i<(sizeof(http_methods) / sizeof(*http_methods)); i++) {
         if (memcmp(pkt, http_methods[i], strlen(http_methods[i])) == 0) {
+            if (is_fragmented)
+                *is_fragmented = 0;
             return (char*)pkt + strlen(http_methods[i]) - 1;
         }
         /* Try to find HTTP method in a second part of fragmented packet */
-        if ((offset == 1 || offset == 2) &&
+        if ((http_frag == 1 || http_frag == 2) &&
-            memcmp(pkt, http_methods[i] + offset,
+            memcmp(pkt, http_methods[i] + http_frag,
-                   strlen(http_methods[i]) - offset) == 0
+                   strlen(http_methods[i]) - http_frag) == 0
            )
         {
-            return (char*)pkt + strlen(http_methods[i]) - offset - 1;
+            if (is_fragmented)
+                *is_fragmented = 1;
+            return (char*)pkt + strlen(http_methods[i]) - http_frag - 1;
         }
     }
     return NULL;
@@ -242,6 +262,8 @@ int main(int argc, char *argv[]) {
     conntrack_info_t dns_conn_info;
 
     int do_passivedpi = 0, do_fragment_http = 0,
+        do_fragment_http_persistent = 0,
+        do_fragment_http_persistent_nowait = 0,
         do_fragment_https = 0, do_host = 0,
         do_host_removespace = 0, do_additional_space = 0,
         do_http_allports = 0,
@@ -253,6 +275,7 @@ int main(int argc, char *argv[]) {
     uint16_t dns_port = htons(53);
     char *host_addr, *useragent_addr, *method_addr;
     int host_len, useragent_len;
+    int http_req_fragmented;
 
     char *hdr_name_addr = NULL, *hdr_value_addr = NULL;
     int hdr_value_len;
@@ -270,15 +293,19 @@ int main(int argc, char *argv[]) {
             = do_fragment_http = do_fragment_https = 1;
     }
 
-    while ((opt = getopt_long(argc, argv, "1234prsaf:e:mw", long_options, NULL)) != -1) {
+    while ((opt = getopt_long(argc, argv, "1234prsaf:e:mwk:n", long_options, NULL)) != -1) {
         switch (opt) {
             case '1':
                 do_passivedpi = do_host = do_host_removespace \
-                = do_fragment_http = do_fragment_https = 1;
+                = do_fragment_http = do_fragment_https \
+                = do_fragment_http_persistent \
+                = do_fragment_http_persistent_nowait = 1;
                 break;
             case '2':
                 do_passivedpi = do_host = do_host_removespace \
-                = do_fragment_http = do_fragment_https = 1;
+                = do_fragment_http = do_fragment_https \
+                = do_fragment_http_persistent \
+                = do_fragment_http_persistent_nowait = 1;
                 https_fragment_size = 40;
                 break;
             case '3':
@@ -307,11 +334,14 @@ int main(int argc, char *argv[]) {
                 break;
             case 'f':
                 do_fragment_http = 1;
-                http_fragment_size = atoi(optarg);
+                SET_HTTP_FRAGMENT_SIZE_OPTION(atoi(optarg));
-                if (http_fragment_size <= 0 || http_fragment_size > 65535) {
+                break;
-                    printf(fragment_size_message);
+            case 'k':
-                    exit(EXIT_FAILURE);
+                do_fragment_http_persistent = 1;
-                }
+                SET_HTTP_FRAGMENT_SIZE_OPTION(atoi(optarg));
+                break;
+            case 'n':
+                do_fragment_http_persistent_nowait = 1;
                 break;
             case 'e':
                 do_fragment_https = 1;
@@ -382,6 +412,8 @@ int main(int argc, char *argv[]) {
                 " -a          additional space between Method and Request-URI (enables -s, may break sites)\n"
                 " -m          mix Host header case (test.com -> tEsT.cOm)\n"
                 " -f [value]  set HTTP fragmentation to value\n"
+                " -k [value]  enable HTTP persistent (keep-alive) fragmentation and set it to value\n"
+                " -n          do not wait for first segment ACK when -k is enabled\n"
                 " -e [value]  set HTTPS fragmentation to value\n"
                 " -w          try to find and parse HTTP traffic on all processed ports (not only on port 80)\n"
                 " --port      [value]    additional TCP port to perform fragmentation on (and HTTP tricks with -w)\n"
@@ -391,21 +423,23 @@ int main(int argc, char *argv[]) {
                 " --blacklist [txtfile]  perform HTTP tricks only to host names and subdomains from\n"
                 "                        supplied text file. This option can be supplied multiple times.\n"
                 "\n"
-                " -1          -p -r -s -f 2 -e 2 (most compatible mode, default)\n"
+                " -1          -p -r -s -f 2 -k 2 -n -e 2 (most compatible mode, default)\n"
-                " -2          -p -r -s -f 2 -e 40 (better speed yet still compatible)\n"
+                " -2          -p -r -s -f 2 -k 2 -n -e 40 (better speed for HTTPS yet still compatible)\n"
-                " -3          -p -r -s -e 40 (even better speed)\n"
+                " -3          -p -r -s -e 40 (better speed for HTTP and HTTPS)\n"
                 " -4          -p -r -s (best speed)\n");
                 exit(EXIT_FAILURE);
         }
     }
 
-    printf("Block passive: %d, Fragment HTTP: %d, Fragment HTTPS: %d, "
+    printf("Block passive: %d, Fragment HTTP: %d, Fragment persistent HTTP: %d, "
+           "Fragment HTTPS: %d, "
            "hoSt: %d, Host no space: %d, Additional space: %d, Mix Host: %d, "
-           "HTTP AllPorts: %d, DNS redirect: %d\n",
+           "HTTP AllPorts: %d, HTTP Persistent Nowait: %d, DNS redirect: %d\n",
            do_passivedpi, (do_fragment_http ? http_fragment_size : 0),
+           (do_fragment_http_persistent ? http_fragment_size : 0),
            (do_fragment_https ? https_fragment_size : 0),
            do_host, do_host_removespace, do_additional_space, do_host_mixedcase,
-           do_http_allports, do_dns_redirect
+           do_http_allports, do_fragment_http_persistent_nowait, do_dns_redirect
           );
 
     if (do_fragment_http && http_fragment_size > 2) {
@@ -472,18 +506,68 @@ int main(int argc, char *argv[]) {
                         packet_dataLen > 16 &&
                         (do_http_allports ? 1 : (ppTcpHdr->DstPort == htons(80))) &&
                         find_http_method_end(packet_data,
-                                             (do_fragment_http ? http_fragment_size : 0)) &&
+                                             (do_fragment_http ? http_fragment_size : 0),
-                        (do_host || do_host_removespace || do_host_mixedcase))
+                                             &http_req_fragmented) &&
+                        (do_host || do_host_removespace ||
+                        do_host_mixedcase || do_fragment_http_persistent))
                 {
 
                     /* Find Host header */
                     if (find_header_and_get_info(packet_data, packet_dataLen,
                         http_host_find, &hdr_name_addr, &hdr_value_addr, &hdr_value_len) &&
                         hdr_value_len > 0 && hdr_value_len <= HOST_MAXLEN &&
-                        (do_blacklist ? blackwhitelist_check_hostname(hdr_value_addr, hdr_value_len) : 1)) {
+                        (do_blacklist ? blackwhitelist_check_hostname(hdr_value_addr, hdr_value_len) : 1))
+                    {
                         host_addr = hdr_value_addr;
                         host_len = hdr_value_len;
 
+                        /*
+                         * Handle new HTTP request in new
+                         * connection (when Window Size modification disabled)
+                         * or already established connection (keep-alive).
+                         * We split HTTP request into two packets: one of http_fragment_size length
+                         * and another of original_size - http_fragment_size length.
+                         *
+                         * The second packet of a splitted part is not really needed to be sent
+                         * as Windows understand that is hasn't been sent by checking
+                         * ack number of received packet and retransmitting missing part again,
+                         * but it's better to send it anyway since it eliminates one RTT.
+                         */
+                        if (do_fragment_http_persistent && !http_req_fragmented) {
+                            ppIpHdr->Length = htons(
+                                ntohs(ppIpHdr->Length) -
+                                packet_dataLen + http_fragment_size
+                            );
+                            WinDivertHelperCalcChecksums(
+                                packet, packetLen - packet_dataLen + http_fragment_size, 0
+                            );
+                            WinDivertSend(
+                                w_filter, packet,
+                                packetLen - packet_dataLen + http_fragment_size,
+                                &addr, NULL
+                            );
+                            if (do_fragment_http_persistent_nowait) {
+                                ppIpHdr->Length = htons(
+                                    ntohs(ppIpHdr->Length) -
+                                    http_fragment_size + packet_dataLen - http_fragment_size
+                                );
+                                memmove(packet_data,
+                                        packet_data + http_fragment_size,
+                                        packet_dataLen);
+                                packet_dataLen -= http_fragment_size;
+                                packetLen -= http_fragment_size;
+                                hdr_value_addr -= http_fragment_size;
+                                hdr_name_addr -= http_fragment_size;
+                                host_addr = hdr_value_addr;
+
+                                ppTcpHdr->SeqNum = htonl(ntohl(ppTcpHdr->SeqNum) + http_fragment_size);
+                                should_recalc_checksum = 1;
+                            }
+                            else {
+                                continue;
+                            }
+                        }
+
                         if (do_host_mixedcase) {
                             mix_case(host_addr, host_len);
                             should_recalc_checksum = 1;
@@ -501,7 +585,8 @@ int main(int argc, char *argv[]) {
                         if (do_additional_space && do_host_removespace) {
                             /* End of "Host:" without trailing space */
                             method_addr = find_http_method_end(packet_data,
-                                                            (do_fragment_http ? http_fragment_size : 0));
+                                                            (do_fragment_http ? http_fragment_size : 0),
+                                                            NULL);
 
                             if (method_addr) {
                                 memmove(method_addr + 1, method_addr,
@@ -568,6 +653,10 @@ int main(int argc, char *argv[]) {
                 if (addr.Direction == WINDIVERT_DIRECTION_INBOUND &&
                     ppTcpHdr->Syn == 1 && ppTcpHdr->Ack == 1) {
                     //printf("Changing Window Size!\n");
+                    /*
+                     * Window Size is changed even if do_fragment_http_persistent
+                     * is enabled as there could be non-HTTP data on port 80
+                     */
                     if (do_fragment_http && ppTcpHdr->SrcPort == htons(80)) {
                         change_window_size(packet, http_fragment_size);
                         should_recalc_checksum = 1;