Update Makefile

We can't reliably distinguish HTTP data from other data on port 80 when fragmentation is used.
HTTP method code has a special case which tries to find HTTP method when fragmentation = 1 or 2 is used,
but not for other values.

Makefile

@@ -1,8 +1,14 @@
+CPREFIX = x86_64-w64-mingw32
+WINDIVERTHEADERS = ../../include
+WINDIVERTLIBS = ../binary
+
 TARGET = goodbyedpi.exe
-LIBS = -L ../binary -lWinDivert -lws2_32
+LIBS = -L $(WINDIVERTLIBS) -lWinDivert -lws2_32
-CC = x86_64-w64-mingw32-gcc
+CC = $(CPREFIX)-gcc
-CCWINDRES = x86_64-w64-mingw32-windres
+CCWINDRES = $(CPREFIX)-windres
-CFLAGS = -Wall -I ../../include -L ../binary -O2
+CFLAGS = -Wall -I $(WINDIVERTHEADERS) -L $(WINDIVERTLIBS) \
+         -O2 -pie -fPIE -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2
+LDFLAGS = -pie
 
 .PHONY: default all clean
 

README.md

@@ -3,7 +3,7 @@ GoodbyeDPI — Passive Deep Packet Inspection blocker and Active DPI circumventi
 
 This software designed to bypass Deep Packet Inspection systems found in many Internet Service Providers which block access to certain websites.
 
-It handles DPI connected using optical splitter or port mirroring (**Passive DPI**) which do not block any data but just replying faster then requested destination, and **Active DPI** connected in sequence.
+It handles DPI connected using optical splitter or port mirroring (**Passive DPI**) which do not block any data but just replying faster than requested destination, and **Active DPI** connected in sequence.
 
 **Windows 7, 8, 8.1 and 10** with administrator privileges required.
 
@@ -11,21 +11,82 @@ It handles DPI connected using optical splitter or port mirroring (**Passive DPI
 
 Download [latest version from Releases page](https://github.com/ValdikSS/GoodbyeDPI/releases) and run.
 
+```
+Usage: goodbyedpi.exe [OPTION...]
+ -p          block passive DPI
+ -r          replace Host with hoSt
+ -s          remove space between host header and its value
+ -f [value]  set HTTP fragmentation to value
+ -e [value]  set HTTPS fragmentation to value
+ -a          additional space between Method and Request-URI (enables -s, may break sites)
+
+ -1          -p -r -s -f 2 -e 2 (most compatible mode, default)
+ -2          -p -r -s -f 2 -e 40 (better speed yet still compatible)
+ -3          -p -r -s -e 40 (even better speed)
+ -4          -p -r -s (best speed)
+```
+
+Try to run `goodbyedpi.exe -1 -a` first. If you can open blocked websites 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.
+
+Then try `goodbyedpi.exe -2`. It should be faster for HTTPS sites. Mode `-3` speed ups HTTP websites.
+
+Use `goodbyedpi.exe -4` if it works for your ISP's DPI. This is the fastest mode but not compatible with every DPI.
+
 # How does it work
 
 ### Passive DPI
 
-Most Passive DPI send HTTP 301 Redirect if you try to access blocked website over HTTP and TCP Reset in case of HTTPS, faster then destination website. Packets sent by DPI have always have IP Identification field equal to `0x0000` or `0x0001`, as seen with Russian providers. These packets are blocked by GoodbyeDPI.
+Most Passive DPI send HTTP 302 Redirect if you try to access blocked website over HTTP and TCP Reset in case of HTTPS, faster than destination website. Packets sent by DPI always have IP Identification field equal to `0x0000` or `0x0001`, as seen with Russian providers. These packets, if they redirect you to another website (censorship page), are blocked by GoodbyeDPI.
 
 ### Active DPI
 
-Active DPI is more tricky to fool. Currently the software uses 3 methods to circumvent Active DPI:
+Active DPI is more tricky to fool. Currently the software uses 4 methods to circumvent Active DPI:
 
 * TCP-level fragmentation for first data packet
 * 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
 
-These methods do not break any website as are fully compatible with TCP and HTTP standards, yet it's sufficient to prevent DPI data classification and to circumvent censorship.
+These methods should not break any website as they're fully compatible with TCP and HTTP standards, yet it's sufficient to prevent DPI data classification and to circumvent censorship. Additional space may break some websites, although it's acceptable by HTTP/1.1 specification (see 19.3 Tolerant Applications).
+
+The program loads WinDivert driver which uses Windows Filtering Platform to set filters and redirect packets to the userspace. It's running as long as console window is visible and terminates when you close the window.
+
+# How to build from source
+
+This project can be build using **GNU Make** and [**mingw**](https://mingw-w64.org). The only dependency is [WinDivert](https://github.com/basil00/Divert).
+
+To build x86 exe run:
+
+`make CPREFIX=i686-w64-mingw32 WINDIVERTHEADERS=/path/to/windivert/include WINDIVERTLIBS=/path/to/windivert/x86`
+
+And for x86_64:
+
+`make CPREFIX=x86_64-w64-mingw32 WINDIVERTHEADERS=/path/to/windivert/include WINDIVERTLIBS=/path/to/windivert/amd64`
+
+# How to install as Windows Service
+
+One way is using an [srvstart](http://www.rozanski.org.uk/software) program.  
+Unpack it to `goodbyedpi` directory and create 3 files:
+
+*goodbyedpi.ini*
+```INI
+[GoodByeDPI]
+startup=goodbyedpi.exe
+shutdown_method=winmessage
+auto_restart=n
+```
+*srvinstall.bat*
+```Batchfile
+srvstart install GoodByeDPI -c %CD%\goodbyedpi.ini
+```
+*srvremove.bat*
+```Batchfile
+srvstart remove GoodByeDPI
+```
+Run these batch files as Administrator to install/remove service.  
+Open Windows Services panel to run service or make it start automaticaly.
 
 # Similar projects
 

goodbyedpi.c

@@ -12,7 +12,7 @@
 
 #define die() do { printf("Something went wrong!\n" \
     "Make sure you're running this program with administrator privileges\n"); \
-    sleep(10); exit(1); } while (0)
+    sleep(10); exit(EXIT_FAILURE); } while (0)
 
 #define MAX_FILTERS 4
 #define MAX_PACKET_SIZE 1516
@@ -21,32 +21,62 @@
 #define IPV4_TOTALLEN_OFFSET 2
 #define TCP_WINDOWSIZE_OFFSET 14
 
+#define DIVERT_NO_LOCALNETS_DST "(" \
+                   "(ip.DstAddr < 127.0.0.1 or ip.DstAddr > 127.255.255.255) and " \
+                   "(ip.DstAddr < 10.0.0.0 or ip.DstAddr > 10.255.255.255) and " \
+                   "(ip.DstAddr < 192.168.0.0 or ip.DstAddr > 192.168.255.255) and " \
+                   "(ip.DstAddr < 172.16.0.0 or ip.DstAddr > 172.31.255.255) and " \
+                   "(ip.DstAddr < 169.254.0.0 or ip.DstAddr > 169.254.255.255)" \
+                   ")"
+#define DIVERT_NO_LOCALNETS_SRC "(" \
+                   "(ip.SrcAddr < 127.0.0.1 or ip.SrcAddr > 127.255.255.255) and " \
+                   "(ip.SrcAddr < 10.0.0.0 or ip.SrcAddr > 10.255.255.255) and " \
+                   "(ip.SrcAddr < 192.168.0.0 or ip.SrcAddr > 192.168.255.255) and " \
+                   "(ip.SrcAddr < 172.16.0.0 or ip.SrcAddr > 172.31.255.255) and " \
+                   "(ip.SrcAddr < 169.254.0.0 or ip.SrcAddr > 169.254.255.255)" \
+                   ")"
+    
 static HANDLE filters[MAX_FILTERS];
 static int filter_num = 0;
-static const char *http_redirect_10 = "HTTP/1.0 30";
+static const char *http10_redirect_302 = "HTTP/1.0 302 ";
-static const char *http_redirect_11 = "HTTP/1.1 30";
+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 *blocklist[] = {
+static const char *http_useragent_find = "\r\nUser-Agent: ";
-    "warning.rt.ru",
+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 ",
+};
 
-static char* dumb_memmem(char* haystack, int hlen, char* needle, int nlen) {
+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 haystack+i;
+            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;
 }
 
@@ -66,30 +96,63 @@ static void deinit_all() {
 
 static void sigint_handler(int sig) {
     deinit_all();
-    exit(0);
+    exit(EXIT_SUCCESS);
 }
 
-static int find_passivedpi_redirect(char *pktdata) {
+static int is_passivedpi_redirect(const char *pktdata, int pktlen) {
-    if (memcmp(pktdata, http_redirect_11, strlen(http_redirect_11)) == 0
+    /* First check if this is HTTP 302 redirect */
-        || memcmp(pktdata, http_redirect_10, strlen(http_redirect_10)) == 0) {
+    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(char *pktdata, int pktlen) {
+static PVOID find_host_header(const char *pktdata, int pktlen) {
     return dumb_memmem(pktdata, pktlen,
-                (char*)http_host_find, strlen(http_host_find));
+                http_host_find, strlen(http_host_find));
 }
 
-static void change_window_size(char *pkt) {
+/* Finds User-Agent header with \r\n before it */
-    *(pkt + IPV4_HDR_LEN + TCP_WINDOWSIZE_OFFSET) = 0x00;
+static PVOID find_useragent_header(const char *pktdata, int pktlen) {
-    *(pkt + IPV4_HDR_LEN + TCP_WINDOWSIZE_OFFSET + 1) = 0x02;
+    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 offset) {
+    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;
+        }
+        /* Try to find HTTP method in a second part of fragmented packet */
+        if ((offset == 1 || offset == 2) &&
+            memcmp(pkt, http_methods[i] + offset,
+                   strlen(http_methods[i]) - offset) == 0
+           )
+        {
+            return (char*)pkt + strlen(http_methods[i]) - offset - 1;
+        }
+    }
+    return NULL;
 }
 
 int main(int argc, char *argv[]) {
-    int i, should_reinject = 0;
+    static const char fragment_size_message[] =
+                "Fragment size should be in range [0 - 65535]\n";
+    int i, should_reinject, should_recalc_checksum = 0;
+    int opt;
     HANDLE w_filter = NULL;
     WINDIVERT_ADDRESS addr;
     char packet[MAX_PACKET_SIZE];
@@ -99,52 +162,125 @@ int main(int argc, char *argv[]) {
     PWINDIVERT_IPHDR ppIpHdr;
     PWINDIVERT_TCPHDR ppTcpHdr;
 
-    int do_passivedpi, do_fragment, do_host, do_host_removespace;
+    int do_passivedpi = 0, do_fragment_http = 0,
-    int temp;
+        do_fragment_https = 0, do_host = 0,
-    char *data_addr, *data_addr_rn, *host_addr = NULL;
+        do_host_removespace = 0, do_additional_space = 0;
-    int host_len, fromhost_uptoend_len;
+    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\n");
+    printf("GoodbyeDPI: Passive DPI blocker and Active DPI circumvention utility\n");
 
-    if (argc == 2) {
+    if (argc == 1) {
-        temp = atoi(argv[1]);
+        /* enable mode -1 by default */
-        do_passivedpi = !!(temp & 1);
+        do_passivedpi = do_host = do_host_removespace \
-        do_fragment = !!(temp & 2);
+            = do_fragment_http = do_fragment_https = 1;
-        do_host = !!(temp & 4);
-        do_host_removespace = !!(temp & 8);
-
-        printf("Block passive: %d, Fragment: %d, hoSt: %d, Host no space: %d\n",
-               do_passivedpi, do_fragment, do_host, do_host_removespace);
     }
-    else {
-        printf("goodbyedpi.exe [1: block passive DPI, 2: fragment outbound, "
-               "4: replace Host with hoSt, 8: remove space between host header and value]\n");
-        printf("Default: 15 (all enabled)\n");
 
+    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;
-        do_fragment = 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("Opening filter\n");
+    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);
+
+    if (do_fragment_http && http_fragment_size > 2) {
+        printf("WARNING: HTTP fragmentation values > 2 are not fully compatible "
+               "with other options. Please use values <= 2 or disable HTTP fragmentation "
+               "completely.\n");
+    }
+
+    printf("\nOpening filter\n");
     filter_num = 0;
 
     if (do_passivedpi) {
-        /* Filter for inbound RST packets with ID = 0 or 1 */
+        /* IPv4 filter for inbound RST packets with ID = 0 or 1 */
-        filters[filter_num] = init("inbound and (ip.Id == 0x0001 or ip.Id == 0x0000) and "
+        filters[filter_num] = init(
-                        "(tcp.SrcPort == 443 or tcp.SrcPort == 80) and tcp.Rst",
+            "inbound and ip and tcp and "
+            "(ip.Id == 0x0001 or ip.Id == 0x0000) and "
+            "(tcp.SrcPort == 443 or tcp.SrcPort == 80) and tcp.Rst and "
+            DIVERT_NO_LOCALNETS_SRC,
             WINDIVERT_FLAG_DROP);
         filter_num++;
     }
 
     /* 
-     * Filter for inbound HTTP redirection packets and
+     * IPv4 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) "
+    filters[filter_num] = init("ip and tcp and "
-                      "or (inbound and (tcp.SrcPort == 80 or tcp.SrcPort == 443) and tcp.Ack and tcp.Syn) "
+        "(inbound and (("
-                      "or (outbound and (tcp.DstPort == 80 or tcp.DstPort == 443) and tcp.Ack)",
+         "((ip.Id == 0x0001 or ip.Id == 0x0000) and tcp.SrcPort == 80 and tcp.Ack) or "
+         "((tcp.SrcPort == 80 or tcp.SrcPort == 443) and tcp.Ack and tcp.Syn)"
+         ") and " DIVERT_NO_LOCALNETS_SRC ") or "
+        "(outbound and "
+         "(tcp.DstPort == 80 or tcp.DstPort == 443) and tcp.Ack and "
+         DIVERT_NO_LOCALNETS_DST ")"
+        ")",
         0);
 
     w_filter = filters[filter_num];
@@ -163,6 +299,7 @@ int main(int argc, char *argv[]) {
             //printf("Got %s packet, len=%d!\n", addr.Direction ? "inbound" : "outbound",
             //       packetLen);
             should_reinject = 1;
+            should_recalc_checksum = 0;
 
             if (WinDivertHelperParsePacket(packet, packetLen, &ppIpHdr,
                 NULL, NULL, NULL, &ppTcpHdr, NULL, &packet_data, &packet_dataLen)) {
@@ -173,77 +310,128 @@ int main(int argc, char *argv[]) {
                 if (addr.Direction == WINDIVERT_DIRECTION_INBOUND && packet_dataLen > 16) {
                     /* If INBOUND packet with DATA (tcp.Ack) */
 
-                    /* Drop packets from blocklist */
-                    /* for (i = 0; i < sizeof(blocklist) / sizeof(*blocklist); i++) {
-                        if (dumb_memmem(packet_data, packet_dataLen, (char*)blocklist[i],
-                            strlen(blocklist[i])) != NULL) {
-                                printf("Dropping packet!\n");
-                                dropped = 1;
-                                break;
-                        }
-                    } */
-
                     /* Drop packets from filter with HTTP 30x Redirect */
-                    if (do_passivedpi && find_passivedpi_redirect(packet_data)) {
+                    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)) {
+                        packet_dataLen > 16 && ppTcpHdr->DstPort == htons(80) &&
-                    if (do_host || do_host_removespace) {
+                        find_http_method_end(packet_data,
-                        data_addr = find_host_header(packet_data, packet_dataLen);
+                                             (do_fragment_http ? http_fragment_size : 0)) &&
-                    }
+                        (do_host || do_host_removespace))
+                {
 
-                    if (do_host && data_addr) {
+                    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));
+                            should_recalc_checksum = 1;
                             //printf("Replaced Host header!\n");
                         }
 
-                    if (do_host_removespace && data_addr) {
+                        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,
+                                                            (do_fragment_http ? http_fragment_size : 0));
+
+                            if (method_addr) {
+                                memmove(method_addr + 1, method_addr, (PVOID)host_addr - (PVOID)method_addr);
+                                should_recalc_checksum = 1;
+                            }
+                        }
+                        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;
-                            fromhost_uptoend_len = packet_dataLen - ((PVOID)host_addr - packet_data);
+                                useragent_addr = find_useragent_header(packet_data, packet_dataLen);
-                            if (host_len <= 64) {
+                                if (host_len <= 253 && useragent_addr) {
-                                /* Move memory left by 1 byte and reduce packet size for 1 byte */
+                                    useragent_addr += strlen(http_useragent_find);
-                                memmove(host_addr - 1, host_addr, fromhost_uptoend_len);
+                                    /* useragent_addr is in the beginning of User-Agent value */
-                                /* Reduce "Total Length" in IP header by 1 byte */
+
-                                *(uint16_t*)(packet + IPV4_TOTALLEN_OFFSET) = ntohs(
+                                    data_len = packet_dataLen - ((PVOID)useragent_addr - packet_data);
-                                     htons(*(uint16_t*)(packet + IPV4_TOTALLEN_OFFSET)) - 1);
+                                    data_addr_rn = dumb_memmem(useragent_addr,
-                                /* Reduce packetLen by 1 byte */
+                                                            data_len, "\r\n", 2);
-                                packetLen--;
+                                    /* data_addr_rn is in the end of User-Agent value */
+
+                                    if (data_addr_rn) {
+                                        if (useragent_addr > host_addr) {
+                                            /* User-Agent goes AFTER Host header */
+                                            data_len = (PVOID)data_addr_rn - (PVOID)host_addr;
+
+                                            /* Move one byte to the LEFT from "Host:"
+                                            * to the end of User-Agent
+                                            */
+                                            memmove(host_addr - 1, host_addr, data_len);
+                                            /* Put space in the end of User-Agent header */
+                                            *(char*)(data_addr_rn - 1) = ' ';
+                                            should_recalc_checksum = 1;
                                             //printf("Replaced Host header!\n");
                                         }
+                                        else {
+                                            /* User-Agent goes BEFORE Host header */
+                                            data_len = (PVOID)host_addr - (PVOID)data_addr_rn - 1;
+
+                                            /* Move one byte to the RIGHT from the end of User-Agent
+                                            * to the "Host:"
+                                            */
+                                            memmove(data_addr_rn + 1, data_addr_rn, data_len);
+                                            /* Put space in the end of User-Agent header */
+                                            *(char*)(data_addr_rn) = ' ';
+                                            should_recalc_checksum = 1;
+                                            //printf("Replaced Host header!\n");
                                         }
-                    }
+                                    } /* if (dara_addr_rn) */
-                    if (do_host || do_host_removespace) {
+                                } /* if (host_len <= 253 && useragent_addr) */
-                        WinDivertHelperCalcChecksums(packet, packetLen, 0);
+                            } /* if (data_addr_rn) */
-                    }
+                        } /* else if (do_host_removespace) */
-                }
+                    } /* if (data_addr) */
-            }
+                } /* Handle OUTBOUND packet with data */
+            } /* Handle packet with data */
+
             /* 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) {
-                    if (do_fragment) {
                     //printf("Changing Window Size!\n");
-                        change_window_size(packet);
+                    if (do_fragment_http && ppTcpHdr->SrcPort == htons(80)) {
-                        WinDivertHelperCalcChecksums(packet, packetLen, 0);
+                        change_window_size(packet, http_fragment_size);
+                        should_recalc_checksum = 1;
+                    }
+                    else if (do_fragment_https && ppTcpHdr->SrcPort != htons(80)) {
+                        change_window_size(packet, https_fragment_size);
+                        should_recalc_checksum = 1;
                     }
                 }
             }
 
             if (should_reinject) {
                 //printf("Re-injecting!\n");
+                if (should_recalc_checksum) {
+                    WinDivertHelperCalcChecksums(packet, packetLen, 0);
+                }
+                else {
+                    WinDivertHelperCalcChecksums(packet, packetLen,
+                                                 WINDIVERT_HELPER_NO_REPLACE);
+                }
                 WinDivertSend(w_filter, packet, packetLen, &addr, NULL);
             }
         }