From 252ee3e82f99906523095f26c6442c6a20d66ed1 Mon Sep 17 00:00:00 2001
From: emanuele-f <black.silver@hotmail.it>
Date: Sat, 21 Sep 2019 17:02:24 +0200
Subject: [PATCH] Call pcap_set_immediate_mode if available

---
 CMakeLists.txt     |  7 +++++++
 configure.seed     |  6 ++++++
 tools/n2n_decode.c | 42 +++++++++++++++++++++++++++++++++---------
 3 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index deb6a3b..68d0097 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,6 @@
 project(n2n)
 cmake_minimum_required(VERSION 2.6)
+include(CheckFunctionExists)
 
 # N2n information
 set(N2N_VERSION 2.5.1)
@@ -98,6 +99,12 @@ if(PCAP_LIB)
   add_executable(n2n-decode tools/n2n_decode.c)
   target_link_libraries(n2n-decode n2n pcap)
   install(TARGETS n2n-decode RUNTIME DESTINATION bin)
+
+  set(CMAKE_REQUIRED_LIBRARIES ${PCAP_LIB})
+  check_function_exists(pcap_set_immediate_mode HAVE_PCAP_IMMEDIATE_MODE)
+  IF(HAVE_PCAP_IMMEDIATE_MODE)
+    ADD_DEFINITIONS("-DHAVE_PCAP_IMMEDIATE_MODE")
+  ENDIF()
 endif()
 
 install(TARGETS n2n-benchmark RUNTIME DESTINATION bin)
diff --git a/configure.seed b/configure.seed
index 432650a..0f8b596 100644
--- a/configure.seed
+++ b/configure.seed
@@ -31,6 +31,12 @@ if test x$pcap != x; then
   ADDITIONAL_TOOLS="$ADDITIONAL_TOOLS n2n-decode"
 fi
 
+AC_CHECK_LIB([pcap], [pcap_set_immediate_mode], pcap_immediate_mode=true)
+
+if test x$pcap_immediate_mode != x; then
+  AC_DEFINE([HAVE_PCAP_IMMEDIATE_MODE], [], [Have pcap_immediate_mode])
+fi
+
 MACHINE=`uname -m`
 SYSTEM=`uname -s`
 
diff --git a/tools/n2n_decode.c b/tools/n2n_decode.c
index bfe1156..6caf85c 100644
--- a/tools/n2n_decode.c
+++ b/tools/n2n_decode.c
@@ -20,11 +20,13 @@
 #include "n2n.h"
 
 #define SNAPLEN 1500
+#define TIMEOUT 200
 
 /* *************************************************** */
 
 static int aes_mode = 0;
 static int running = 1;
+static char *ifname = NULL;
 static n2n_edge_conf_t conf;
 static n2n_trans_op_t transop;
 static pcap_t *handle;
@@ -146,17 +148,22 @@ static int run_packet_loop() {
   struct pcap_pkthdr header;
   const u_char *packet;
 
-  traceEvent(TRACE_NORMAL, "Running loop");
+  traceEvent(TRACE_NORMAL, "Capturing packets on %s...", ifname);
 
-  // TODO handle timeout
   while(running) {
-    n2n_common_t common = {0};
-    n2n_PACKET_t pkt = {0};
+    n2n_common_t common;
+    n2n_PACKET_t pkt;
     uint ipsize, common_offset;
     size_t idx, rem;
 
+    memset(&common, 0, sizeof(common));
+    memset(&pkt, 0, sizeof(pkt));
+
     packet = pcap_next(handle, &header);
 
+    if(!packet)
+      continue;
+
     if(header.caplen < MIN_LEN) {
       traceEvent(TRACE_INFO, "Skipping packet too small: size=%d", header.caplen);
       continue;
@@ -219,7 +226,7 @@ static int run_packet_loop() {
 int main(int argc, char* argv[]) {
   u_char c;
   struct bpf_program fcode;
-  char *bpf_filter = NULL, *ifname = NULL, *out_fname = NULL;
+  char *bpf_filter = NULL, *out_fname = NULL;
   char errbuf[PCAP_ERRBUF_SIZE];
   int rv = 0;
   FILE *outf = stdout;
@@ -240,7 +247,7 @@ int main(int argc, char* argv[]) {
 
     switch(c) {
     case 'c':
-      strncpy((char*)conf.community_name, optarg, sizeof(conf.community_name));
+      strncpy((char*)conf.community_name, optarg, sizeof(conf.community_name)-1);
       break;
     case 'i':
       ifname = strdup(optarg);
@@ -278,13 +285,30 @@ int main(int argc, char* argv[]) {
 #endif
     n2n_transop_twofish_init(&conf, &transop);
 
-  handle = pcap_open_live(ifname, SNAPLEN, 1, 1000, errbuf);
-
-  if(handle == NULL) {
+  if((handle = pcap_create(ifname, errbuf)) == NULL) {
     traceEvent(TRACE_ERROR, "Cannot open device %s: %s", ifname, errbuf);
     return(1);
   }
 
+  if((pcap_set_timeout(handle, TIMEOUT) != 0) ||
+     (pcap_set_snaplen(handle, SNAPLEN) != 0)) {
+    traceEvent(TRACE_ERROR, "Error while setting timeout/snaplen");
+    return(1);
+  }
+
+#ifdef HAVE_PCAP_IMMEDIATE_MODE
+  /* The timeout is not honored unless immediate mode is set.
+   * See https://github.com/mfontanini/libtins/issues/180 */
+  if(pcap_set_immediate_mode(handle, 1) != 0) {
+    traceEvent(TRACE_ERROR, "Could not set PCAP immediate mode");
+    return(1);
+  }
+#endif
+
+  if(pcap_activate(handle) != 0) {
+    traceEvent(TRACE_ERROR, "pcap_activate failed: %s", pcap_geterr(handle));
+  }
+
   if(pcap_datalink(handle) != DLT_EN10MB) {
     traceEvent(TRACE_ERROR, "Device %s doesn't provide Ethernet headers - not supported", ifname);
     return(2);