Detect if pcap version defines pcap_set_immediate_mode.

cmake/Modules/FindPCAP.cmake

@@ -18,6 +18,7 @@
 #  PCAP_LIBRARY              The libpcap library (possibly includes a thread
 #                            library e.g. required by pf_ring's libpcap)
 #  HAVE_PF_RING              If a found version of libpcap supports PF_RING
+#  HAVE_PCAP_IMMEDIATE_MODE  If the version of libpcap found supports immediate mode
 
 find_path(PCAP_ROOT_DIR
     NAMES include/pcap.h
@@ -73,6 +74,7 @@ endif (NOT PCAP_LINKS_SOLO)
 include(CheckFunctionExists)
 set(CMAKE_REQUIRED_LIBRARIES ${PCAP_LIBRARY})
 check_function_exists(pcap_get_pfring_id HAVE_PF_RING)
+check_function_exists(pcap_set_immediate_mode HAVE_PCAP_IMMEDIATE_MODE)
 set(CMAKE_REQUIRED_LIBRARIES)
 
 mark_as_advanced(

src/CMakeLists.txt

@@ -1,5 +1,9 @@
 SET(LIBTINS_INCLUDE_DIR ../include/tins/)
 
+IF(HAVE_PCAP_IMMEDIATE_MODE)
+    ADD_DEFINITIONS("-DHAVE_PCAP_IMMEDIATE_MODE=1")
+ENDIF()
+
 INCLUDE_DIRECTORIES(
     ${LIBTINS_INCLUDE_DIR}
     ${OPENSSL_INCLUDE_DIR}

src/sniffer.cpp

@@ -343,9 +343,14 @@ void Sniffer::set_promisc_mode(bool promisc_enabled)
 
 void Sniffer::set_immediate_mode(bool enabled) 
 {
+    // As of libpcap version 1.5.0 this function exists. Before, it was
+    // technically always immediate mode since capture used TPACKET_V1/2
+    // which doesn't do packet buffering.
+    #ifdef HAVE_PCAP_IMMEDIATE_MODE
     if (pcap_set_immediate_mode(get_pcap_handle(), enabled)) {
         throw runtime_error(pcap_geterr(get_pcap_handle()));
     }
+    #endif // HAVE_PCAP_IMMEDIATE_MODE
 }
 
 void Sniffer::set_rfmon(bool rfmon_enabled)