Add Max Payload Size limit option (--max-payload-size)

This option excludes TCP packets with the data payload larger than
defined value from being copied by WinDivert driver to GoodbyeDPI.

As most of HTTP and TLS ClientHello packets are repatively small,
and file transfers are usually big and are sent/received using
the whole available MTU/MSS, we can just exclude them from
being processed by our userspace program to reduce unnecessary
CPU load.

README.md

@@ -58,6 +58,10 @@ Usage: goodbyedpi.exe [OPTION...]
  --reverse-frag           fragment (split) the packets just as --native-frag, but send them in the
                           reversed order. Works with the websites which could not handle segmented
                           HTTPS TLS ClientHello (because they receive the TCP flow "combined").
+ --max-payload [value]    packets with TCP payload data more than [value] won't be processed.
+                          Use this option to reduce CPU usage by skipping huge amount of data
+                          (like file transfers) in already established sessions.
+                          May skip some huge HTTP requests from being processed.
 
 
 LEGACY modesets:

src/goodbyedpi.c

@@ -61,8 +61,9 @@ WINSOCK_API_LINKAGE INT WSAAPI inet_pton(INT Family, LPCSTR pStringBuf, PVOID pA
 
 /* #IPID# is a template to find&replace */
 #define IPID_TEMPLATE "#IPID#"
+#define MAXPAYLOADSIZE_TEMPLATE "#MAXPAYLOADSIZE#"
 #define FILTER_STRING_TEMPLATE \
-        "(tcp and !impostor and !loopback and " \
+        "(tcp and !impostor and !loopback " MAXPAYLOADSIZE_TEMPLATE " and " \
         "((inbound and (" \
          "(" \
           "(" \
@@ -169,6 +170,7 @@ static struct option long_options[] = {
     {"wrong-seq",   no_argument,       0,  ')' },
     {"native-frag", no_argument,       0,  '*' },
     {"reverse-frag",no_argument,       0,  '(' },
+    {"max-payload", optional_argument, 0,  '|' },
     {0,             0,                 0,   0  }
 };
 
@@ -178,7 +180,7 @@ static char *filter_passive_string = NULL;
 static void add_filter_str(int proto, int port) {
     const char *udp = " or (udp and !impostor and !loopback and " \
                       "(udp.SrcPort == %d or udp.DstPort == %d))";
-    const char *tcp = " or (tcp and !impostor and !loopback and " \
+    const char *tcp = " or (tcp and !impostor and !loopback " MAXPAYLOADSIZE_TEMPLATE " and " \
                       "(tcp.SrcPort == %d or tcp.DstPort == %d))";
 
     char *current_filter = filter_string;
@@ -212,12 +214,26 @@ static void add_ip_id_str(int id) {
     filter_passive_string = newstr;
 }
 
-static void finalize_filter_strings() {
+static void add_maxpayloadsize_str(unsigned short maxpayload) {
     char *newstr;
+    const char *maxpayloadsize_str = "and (tcp.PayloadLength ? tcp.PayloadLength < %hu : true)";
+    char *addfilter = malloc(strlen(maxpayloadsize_str) + 16);
 
-    newstr = repl_str(filter_string, IPID_TEMPLATE, "");
+    sprintf(addfilter, maxpayloadsize_str, maxpayload);
+
+    newstr = repl_str(filter_string, MAXPAYLOADSIZE_TEMPLATE, addfilter);
     free(filter_string);
     filter_string = newstr;
+}
+
+static void finalize_filter_strings() {
+    char *newstr, *newstr2;
+
+    newstr2 = repl_str(filter_string, IPID_TEMPLATE, "");
+    newstr = repl_str(newstr2, MAXPAYLOADSIZE_TEMPLATE, "");
+    free(filter_string);
+    free(newstr2);
+    filter_string = newstr;
 
     newstr = repl_str(filter_passive_string, IPID_TEMPLATE, "");
     free(filter_passive_string);
@@ -558,6 +574,7 @@ int main(int argc, char *argv[]) {
     unsigned int http_fragment_size = 0;
     unsigned int https_fragment_size = 0;
     unsigned int current_fragment_size = 0;
+    unsigned short max_payload_size = 0;
     BYTE should_send_fake = 0;
     BYTE ttl_of_fake_packet = 0;
     BYTE ttl_min_nhops = 0;
@@ -845,6 +862,14 @@ int main(int argc, char *argv[]) {
                 do_fragment_http_persistent = 1;
                 do_fragment_http_persistent_nowait = 1;
                 break;
+            case '|': // --max-payload
+                if (!optarg && argv[optind] && argv[optind][0] != '-')
+                    optarg = argv[optind];
+                if (optarg)
+                    max_payload_size = atousi(optarg, "Max payload size parameter error!");
+                if (!max_payload_size)
+                    max_payload_size = 1200;
+                break;
             default:
                 puts("Usage: goodbyedpi.exe [OPTION...]\n"
                 " -p          block passive DPI\n"
@@ -888,9 +913,13 @@ int main(int argc, char *argv[]) {
                 " --reverse-frag           fragment (split) the packets just as --native-frag, but send them in the\n"
                 "                          reversed order. Works with the websites which could not handle segmented\n"
                 "                          HTTPS TLS ClientHello (because they receive the TCP flow \"combined\").\n"
-                "\n"
+                " --max-payload [value]    packets with TCP payload data more than [value] won't be processed.\n"
-                "\n"
+                "                          Use this option to reduce CPU usage by skipping huge amount of data\n"
-                "LEGACY modesets:\n"
+                "                          (like file transfers) in already established sessions.\n"
+                "                          May skip some huge HTTP requests from being processed.\n"
+                "                          Default (if set): --max-payload 1200.\n"
+                "\n");
+                puts("LEGACY modesets:\n"
                 " -1          -p -r -s -f 2 -k 2 -n -e 2 (most compatible mode)\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 (better speed for HTTP and HTTPS)\n"
@@ -935,7 +964,8 @@ int main(int argc, char *argv[]) {
            "Allow missing SNI: %d\n"                /* 15 */
            "Fake requests, TTL: %s (fixed: %hu, auto: %hu-%hu-%hu, min distance: %hu)\n"  /* 16 */
            "Fake requests, wrong checksum: %d\n"    /* 17 */
-           "Fake requests, wrong SEQ/ACK: %d\n",    /* 18 */
+           "Fake requests, wrong SEQ/ACK: %d\n"     /* 18 */
+           "Max payload size: %hu\n",               /* 19 */
            do_passivedpi,                                         /* 1 */
            (do_fragment_http ? http_fragment_size : 0),           /* 2 */
            (do_fragment_http_persistent ? http_fragment_size : 0),/* 3 */
@@ -955,7 +985,8 @@ int main(int argc, char *argv[]) {
                ttl_of_fake_packet, do_auto_ttl ? auto_ttl_1 : 0, do_auto_ttl ? auto_ttl_2 : 0,
                do_auto_ttl ? auto_ttl_max : 0, ttl_min_nhops,
            do_wrong_chksum, /* 17 */
-           do_wrong_seq     /* 18 */
+           do_wrong_seq,    /* 18 */
+           max_payload_size /* 19 */
           );
 
     if (do_fragment_http && http_fragment_size > 2 && !do_native_frag) {
@@ -970,8 +1001,10 @@ int main(int argc, char *argv[]) {
         exit(EXIT_FAILURE);
     }
 
-    puts("\nOpening filter");
+    if (max_payload_size)
+        add_maxpayloadsize_str(max_payload_size);
     finalize_filter_strings();
+    puts("\nOpening filter");
     filter_num = 0;
 
     if (do_passivedpi) {