pcap-helper.cpp

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
#include "pcap-helper.hpp"

#include <pcap/pcap.h>
#include <unistd.h>

#if !defined(PCAP_NETMASK_UNKNOWN)
#define PCAP_NETMASK_UNKNOWN  0xffffffff
#endif

namespace nfd {
namespace face {

PcapHelper::PcapHelper(const std::string& interfaceName)
  : m_pcap(nullptr)
{
  char errbuf[PCAP_ERRBUF_SIZE] = {};
  m_pcap = pcap_create(interfaceName.data(), errbuf);
  if (!m_pcap)
    BOOST_THROW_EXCEPTION(Error("pcap_create: " + std::string(errbuf)));

#ifdef HAVE_PCAP_SET_IMMEDIATE_MODE
  // Enable "immediate mode", effectively disabling any read buffering in the kernel.
  // This corresponds to the BIOCIMMEDIATE ioctl on BSD-like systems (including macOS)
  // where libpcap uses a BPF device. On Linux this forces libpcap not to use TPACKET_V3,
  // even if the kernel supports it, thus preventing bug #1511.
  if (pcap_set_immediate_mode(m_pcap, 1) < 0)
    BOOST_THROW_EXCEPTION(Error("pcap_set_immediate_mode failed"));
#endif
}

PcapHelper::~PcapHelper()
{
  close();
}

void
PcapHelper::activate(int dlt)
{
  int ret = pcap_activate(m_pcap);
  if (ret < 0)
    BOOST_THROW_EXCEPTION(Error("pcap_activate: " + std::string(pcap_statustostr(ret))));

  if (pcap_set_datalink(m_pcap, dlt) < 0)
    BOOST_THROW_EXCEPTION(Error("pcap_set_datalink: " + getLastError()));

  if (pcap_setdirection(m_pcap, PCAP_D_IN) < 0)
    BOOST_THROW_EXCEPTION(Error("pcap_setdirection: " + getLastError()));
}

void
PcapHelper::close()
{
  if (m_pcap) {
    pcap_close(m_pcap);
    m_pcap = nullptr;
  }
}

int
PcapHelper::getFd() const
{
  int fd = pcap_get_selectable_fd(m_pcap);
  if (fd < 0)
    BOOST_THROW_EXCEPTION(Error("pcap_get_selectable_fd failed"));

  // we need to duplicate the fd, otherwise both pcap_close() and the
  // caller may attempt to close the same fd and one of them will fail
  return ::dup(fd);
}

std::string
PcapHelper::getLastError() const
{
  return pcap_geterr(m_pcap);
}

size_t
PcapHelper::getNDropped() const
{
  pcap_stat ps{};
  if (pcap_stats(m_pcap, &ps) < 0)
    BOOST_THROW_EXCEPTION(Error("pcap_stats: " + getLastError()));

  return ps.ps_drop;
}

void
PcapHelper::setPacketFilter(const char* filter) const
{
  bpf_program prog;
  if (pcap_compile(m_pcap, &prog, filter, 1, PCAP_NETMASK_UNKNOWN) < 0)
    BOOST_THROW_EXCEPTION(Error("pcap_compile: " + getLastError()));

  int ret = pcap_setfilter(m_pcap, &prog);
  pcap_freecode(&prog);
  if (ret < 0)
    BOOST_THROW_EXCEPTION(Error("pcap_setfilter: " + getLastError()));
}

std::tuple<const uint8_t*, size_t, std::string>
PcapHelper::readNextPacket() const
{
  pcap_pkthdr* header;
  const uint8_t* packet;

  int ret = pcap_next_ex(m_pcap, &header, &packet);
  if (ret < 0)
    return std::make_tuple(nullptr, 0, getLastError());
  else if (ret == 0)
    return std::make_tuple(nullptr, 0, "timed out");
  else
    return std::make_tuple(packet, header->caplen, "");
}

} // namespace face
} // namespace nfd