/*
     This file is part of GNUnet
     Copyright (C) 2013, 2017 GNUnet e.V.

     GNUnet is free software: you can redistribute it and/or modify it
     under the terms of the GNU Affero General Public License as published
     by the Free Software Foundation, either version 3 of the License,
     or (at your option) any later version.

     GNUnet is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Affero General Public License for more details.

     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.

     SPDX-License-Identifier: AGPL3.0-or-later
 */

/**
 * @file dns/plugin_block_dns.c
 * @brief block plugin for advertising a DNS exit service
 * @author Christian Grothoff
 *
 * Note that this plugin might more belong with EXIT and PT
 * as those two are using this type of block.  Still, this
 * might be a natural enough place for people to find the code...
 */
#include "platform.h"
#include "gnunet_block_plugin.h"
#include "block_dns.h"
#include "gnunet_signatures.h"
#include "gnunet_block_group_lib.h"


/**
 * Number of bits we set per entry in the bloomfilter.
 * Do not change!
 */
#define BLOOMFILTER_K 16


/**
 * Create a new block group.
 *
 * @param ctx block context in which the block group is created
 * @param type type of the block for which we are creating the group
 * @param nonce random value used to seed the group creation
 * @param raw_data optional serialized prior state of the group, NULL if unavailable/fresh
 * @param raw_data_size number of bytes in @a raw_data, 0 if unavailable/fresh
 * @param va variable arguments specific to @a type
 * @return block group handle, NULL if block groups are not supported
 *         by this @a type of block (this is not an error)
 */
static struct GNUNET_BLOCK_Group *
block_plugin_dns_create_group (void *cls,
                               enum GNUNET_BLOCK_Type type,
                               uint32_t nonce,
                               const void *raw_data,
                               size_t raw_data_size,
                               va_list va)
{
  unsigned int bf_size;
  const char *guard;

  guard = va_arg (va, const char *);
  if (0 == strcmp (guard,
                   "seen-set-size"))
    bf_size = GNUNET_BLOCK_GROUP_compute_bloomfilter_size (va_arg (va, unsigned
                                                                   int),
                                                           BLOOMFILTER_K);
  else if (0 == strcmp (guard,
                        "filter-size"))
    bf_size = va_arg (va, unsigned int);
  else
  {
    GNUNET_break (0);
    bf_size = 8;
  }
  GNUNET_break (NULL == va_arg (va, const char *));
  return GNUNET_BLOCK_GROUP_bf_create (cls,
                                       bf_size,
                                       BLOOMFILTER_K,
                                       type,
                                       nonce,
                                       raw_data,
                                       raw_data_size);
}


/**
 * Function called to validate a reply or a request.  For
 * request evaluation, simply pass "NULL" for the reply_block.
 *
 * @param cls closure
 * @param ctx block context
 * @param type block type
 * @param bg group to evaluate against
 * @param eo control flags
 * @param query original query (hash)
 * @param xquery extended query data (can be NULL, depending on type)
 * @param xquery_size number of bytes in @a xquery
 * @param reply_block response to validate
 * @param reply_block_size number of bytes in @a reply_block
 * @return characterization of result
 */
static enum GNUNET_BLOCK_EvaluationResult
block_plugin_dns_evaluate (void *cls,
                           struct GNUNET_BLOCK_Context *ctx,
                           enum GNUNET_BLOCK_Type type,
                           struct GNUNET_BLOCK_Group *bg,
                           enum GNUNET_BLOCK_EvaluationOptions eo,
                           const struct GNUNET_HashCode *query,
                           const void *xquery,
                           size_t xquery_size,
                           const void *reply_block,
                           size_t reply_block_size)
{
  const struct GNUNET_DNS_Advertisement *ad;
  struct GNUNET_HashCode phash;

  switch (type)
  {
  case GNUNET_BLOCK_TYPE_DNS:
    if (0 != xquery_size)
      return GNUNET_BLOCK_EVALUATION_REQUEST_INVALID;

    if (NULL == reply_block)
      return GNUNET_BLOCK_EVALUATION_REQUEST_VALID;

    if (sizeof(struct GNUNET_DNS_Advertisement) != reply_block_size)
    {
      GNUNET_break_op (0);
      return GNUNET_BLOCK_EVALUATION_RESULT_INVALID;
    }
    ad = reply_block;

    if (ntohl (ad->purpose.size) !=
        sizeof(struct GNUNET_DNS_Advertisement)
        - sizeof(struct GNUNET_CRYPTO_EddsaSignature))
    {
      GNUNET_break_op (0);
      return GNUNET_BLOCK_EVALUATION_RESULT_INVALID;
    }
    if (0 ==
        GNUNET_TIME_absolute_get_remaining (GNUNET_TIME_absolute_ntoh
                                              (ad->expiration_time)).
        rel_value_us)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "DNS advertisement has expired\n");
      return GNUNET_BLOCK_EVALUATION_RESULT_INVALID;
    }
    if (GNUNET_OK !=
        GNUNET_CRYPTO_eddsa_verify_ (GNUNET_SIGNATURE_PURPOSE_DNS_RECORD,
                                     &ad->purpose,
                                     &ad->signature,
                                     &ad->peer.public_key))
    {
      GNUNET_break_op (0);
      return GNUNET_BLOCK_EVALUATION_RESULT_INVALID;
    }
    GNUNET_CRYPTO_hash (reply_block,
                        reply_block_size,
                        &phash);
    if (GNUNET_YES ==
        GNUNET_BLOCK_GROUP_bf_test_and_set (bg,
                                            &phash))
      return GNUNET_BLOCK_EVALUATION_OK_DUPLICATE;
    return GNUNET_BLOCK_EVALUATION_OK_MORE;

  default:
    return GNUNET_BLOCK_EVALUATION_TYPE_NOT_SUPPORTED;
  }
}


/**
 * Function called to obtain the key for a block.
 *
 * @param cls closure
 * @param type block type
 * @param block block to get the key for
 * @param block_size number of bytes in @a block
 * @param key set to the key (query) for the given block
 * @return #GNUNET_OK on success, #GNUNET_SYSERR if type not supported
 *         (or if extracting a key from a block of this type does not work)
 */
static int
block_plugin_dns_get_key (void *cls,
                          enum GNUNET_BLOCK_Type type,
                          const void *block,
                          size_t block_size,
                          struct GNUNET_HashCode *key)
{
  /* we cannot extract a key from a block of this type */
  return GNUNET_SYSERR;
}


/**
 * Entry point for the plugin.
 */
void *
libgnunet_plugin_block_dns_init (void *cls)
{
  static enum GNUNET_BLOCK_Type types[] = {
    GNUNET_BLOCK_TYPE_DNS,
    GNUNET_BLOCK_TYPE_ANY       /* end of list */
  };
  struct GNUNET_BLOCK_PluginFunctions *api;

  api = GNUNET_new (struct GNUNET_BLOCK_PluginFunctions);
  api->evaluate = &block_plugin_dns_evaluate;
  api->get_key = &block_plugin_dns_get_key;
  api->create_group = &block_plugin_dns_create_group;
  api->types = types;
  return api;
}


/**
 * Exit point from the plugin.
 */
void *
libgnunet_plugin_block_dns_done (void *cls)
{
  struct GNUNET_BLOCK_PluginFunctions *api = cls;

  GNUNET_free (api);
  return NULL;
}


/* end of plugin_block_dns.c */
