epcap_compile

/* Copyright (c) 2012-2021, Michael Santos <michael.santos@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *
 * Neither the name of the author nor the names of its contributors
 * may be used to endorse or promote products derived from this software
 * without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
#include "epcap_compile.h"
#include "erl_nif.h"

static ERL_NIF_TERM atom_ok;
static ERL_NIF_TERM atom_error;
static ERL_NIF_TERM atom_enomem;

typedef struct {
  ErlNifMutex *lock;
} epcap_compile_priv_t;

static int load(ErlNifEnv *env, void **priv_data, ERL_NIF_TERM load_info) {
  epcap_compile_priv_t *priv;

  atom_ok = enif_make_atom(env, "ok");
  atom_error = enif_make_atom(env, "error");
  atom_enomem = enif_make_atom(env, "enomem");

  priv = enif_alloc(sizeof(epcap_compile_priv_t));
  if (priv == NULL)
    goto EPCAP_COMPILE_ERROR;

  priv->lock = enif_mutex_create("epcap_compile_lock");
  if (priv->lock == NULL)
    goto EPCAP_COMPILE_ERROR;

  *priv_data = priv;

  return 0;

EPCAP_COMPILE_ERROR:
  if (priv) {
    if (priv->lock)
      enif_mutex_destroy(priv->lock);

    enif_free(priv);
  }

  return -1;
}

static int reload(ErlNifEnv *env, void **priv_data, ERL_NIF_TERM load_info) {
  return 0;
}

static int upgrade(ErlNifEnv *env, void **priv_data, void **old_priv_data,
                   ERL_NIF_TERM load_info) {
  return 0;
}

static void unload(ErlNifEnv *env, void *priv_data) {
  epcap_compile_priv_t *priv = priv_data;
  if (priv) {
    if (priv->lock)
      enif_mutex_destroy(priv->lock);

    enif_free(priv);
  }
}

static ERL_NIF_TERM nif_pcap_compile(ErlNifEnv *env, int argc,
                                     const ERL_NIF_TERM argv[]) {
  epcap_compile_priv_t *priv;
  ErlNifBinary filter = {0};
  int optimize;
  u_int32_t netmask;
  int linktype;
  int snaplen;

  pcap_t *p;
  struct bpf_program fp = {0};

  unsigned int i;
  ERL_NIF_TERM insns = {0};
  ERL_NIF_TERM res = {0};
  int rv;

  priv = enif_priv_data(env);

  if (!enif_inspect_iolist_as_binary(env, argv[0], &filter))
    return enif_make_badarg(env);

  if (!enif_get_int(env, argv[1], &optimize))
    return enif_make_badarg(env);

  if (!enif_get_uint(env, argv[2], &netmask))
    return enif_make_badarg(env);

  if (!enif_get_int(env, argv[3], &linktype))
    return enif_make_badarg(env);

  if (!enif_get_int(env, argv[4], &snaplen))
    return enif_make_badarg(env);

  /* NULL terminate the filter */
  if (!enif_realloc_binary(&filter, filter.size + 1))
    return enif_make_tuple2(env, atom_error, atom_enomem);

  filter.data[filter.size - 1] = '\0';

  p = pcap_open_dead(linktype, snaplen);

  if (p == NULL)
    return enif_make_tuple2(env, atom_error, atom_enomem);

  enif_mutex_lock(priv->lock);

  rv = pcap_compile(p, &fp, (const char *)filter.data, optimize, netmask);

  enif_mutex_unlock(priv->lock);

  if (rv != 0) {
    res = enif_make_tuple2(
        env, atom_error, enif_make_string(env, pcap_geterr(p), ERL_NIF_LATIN1));
    goto ERR;
  }

  insns = enif_make_list(env, 0);

  /* Build the list from the end of the buffer, so the list does
   * not need to be reversed. */
  i = fp.bf_len;
  while (i--) {
    ErlNifBinary fcode = {0};

    if (!enif_alloc_binary(sizeof(struct bpf_insn), &fcode)) {
      res = enif_make_tuple2(env, atom_error, atom_enomem);
      pcap_freecode(&fp);
      goto ERR;
    }

    (void)memcpy(fcode.data, fp.bf_insns + i, fcode.size);
    insns = enif_make_list_cell(env, enif_make_binary(env, &fcode), insns);
  }

  res = enif_make_tuple2(env, atom_ok, insns);
  pcap_freecode(&fp);

ERR:
  pcap_close(p);

  return res;
}

static ErlNifFunc nif_funcs[] = {
    {"pcap_compile", 5, nif_pcap_compile},
};

ERL_NIF_INIT(epcap_compile, nif_funcs, load, reload, upgrade, unload)