/*
 * This file is part of GNUnet
 * Copyright (C) 2009-2013, 2016-2018 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 namestore/plugin_namestore_postgres.c
 * @brief postgres-based namestore backend
 * @author Christian Grothoff
 */
#include "platform.h"
#include "gnunet_namestore_plugin.h"
#include "gnunet_namestore_service.h"
#include "gnunet_gnsrecord_lib.h"
#include "gnunet_pq_lib.h"
#include "namestore.h"


#define LOG(kind, ...) GNUNET_log_from (kind, "namestore-postgres", __VA_ARGS__)


/**
 * Context for all functions in this plugin.
 */
struct Plugin
{
  /**
   * Our configuration.
   */
  const struct GNUNET_CONFIGURATION_Handle *cfg;

  /**
   * Database is prepared and ready
   */
  int ready;

  /**
   * Postgres database handle.
   */
  struct GNUNET_PQ_Context *dbh;
};


/**
 * Initialize the database connections and associated
 * data structures (create tables and indices
 * as needed as well).
 *
 * @param plugin the plugin context (state for this module)
 * @return #GNUNET_OK on success
 */
static int
init_database (struct Plugin *plugin, char **emsg, int drop)
{
  struct GNUNET_PQ_ExecuteStatement es_temporary =
    GNUNET_PQ_make_execute (
      "CREATE TEMPORARY TABLE ns098records ("
      " seq BIGSERIAL PRIMARY KEY,"
      " zone_private_key BYTEA NOT NULL DEFAULT '',"
      " pkey BYTEA DEFAULT '',"
      " rvalue BYTEA NOT NULL DEFAULT '',"
      " record_count INTEGER NOT NULL DEFAULT 0,"
      " record_data BYTEA NOT NULL DEFAULT '',"
      " label TEXT NOT NULL DEFAULT '',"
      " CONSTRAINT zl UNIQUE (zone_private_key,label)"
      ")");
  struct GNUNET_PQ_ExecuteStatement es_default =
    GNUNET_PQ_make_execute ("CREATE TABLE ns098records ("
                            " seq BIGSERIAL PRIMARY KEY,"
                            " zone_private_key BYTEA NOT NULL DEFAULT '',"
                            " pkey BYTEA DEFAULT '',"
                            " rvalue BYTEA NOT NULL DEFAULT '',"
                            " record_count INTEGER NOT NULL DEFAULT 0,"
                            " record_data BYTEA NOT NULL DEFAULT '',"
                            " label TEXT NOT NULL DEFAULT '',"
                            " CONSTRAINT zl UNIQUE (zone_private_key,label)"
                            ")");
  const struct GNUNET_PQ_ExecuteStatement *cr;
  struct GNUNET_PQ_ExecuteStatement sc = GNUNET_PQ_EXECUTE_STATEMENT_END;
  struct GNUNET_PQ_ExecuteStatement es_drop =
    GNUNET_PQ_make_execute ("DROP TABLE IF EXISTS ns098records");
  if (GNUNET_YES ==
      GNUNET_CONFIGURATION_get_value_yesno (plugin->cfg,
                                            "namestore-postgres",
                                            "TEMPORARY_TABLE"))
    cr = &es_temporary;
  else
    cr = &es_default;

  if (GNUNET_YES ==
      GNUNET_CONFIGURATION_get_value_yesno (plugin->cfg,
                                            "namestore-postgres",
                                            "ASYNC_COMMIT"))
    sc = GNUNET_PQ_make_try_execute ("SET synchronous_commit TO off");

  {
    struct GNUNET_PQ_ExecuteStatement es[] = {
      *cr,
      GNUNET_PQ_make_try_execute ("CREATE INDEX IF NOT EXISTS ir_pkey_reverse "
                                  "ON ns098records (zone_private_key,pkey)"),
      GNUNET_PQ_make_try_execute ("CREATE INDEX IF NOT EXISTS ir_pkey_iter "
                                  "ON ns098records (zone_private_key,seq)"),
      GNUNET_PQ_make_try_execute ("CREATE INDEX IF NOT EXISTS ir_label "
                                  "ON ns098records (label)"),
      GNUNET_PQ_make_try_execute ("CREATE INDEX IF NOT EXISTS zone_label "
                                  "ON ns098records (zone_private_key,label)"),
      sc,
      GNUNET_PQ_EXECUTE_STATEMENT_END
    };
    struct GNUNET_PQ_ExecuteStatement es_alt[] = {
      es_drop,
      *cr,
      GNUNET_PQ_make_try_execute ("CREATE INDEX IF NOT EXISTS ir_pkey_reverse "
                                  "ON ns098records (zone_private_key,pkey)"),
      GNUNET_PQ_make_try_execute ("CREATE INDEX IF NOT EXISTS ir_pkey_iter "
                                  "ON ns098records (zone_private_key,seq)"),
      GNUNET_PQ_make_try_execute ("CREATE INDEX IF NOT EXISTS ir_label "
                                  "ON ns098records (label)"),
      GNUNET_PQ_make_try_execute ("CREATE INDEX IF NOT EXISTS zone_label "
                                  "ON ns098records (zone_private_key,label)"),
      sc,
      GNUNET_PQ_EXECUTE_STATEMENT_END
    };
    if (GNUNET_NO == drop)
    {
      plugin->dbh = GNUNET_PQ_connect_with_cfg (plugin->cfg,
                                                "namestore-postgres",
                                                NULL,
                                                es,
                                                NULL);
    }
    else
    {
      plugin->dbh = GNUNET_PQ_connect_with_cfg (plugin->cfg,
                                                "namestore-postgres",
                                                NULL,
                                                es_alt,
                                                NULL);
    }
  }
  if (NULL == plugin->dbh)
  {
    *emsg = GNUNET_strdup ("Failed to connect to PQ database");
    return GNUNET_SYSERR;
  }
  GNUNET_PQ_disconnect (plugin->dbh);
  plugin->dbh = NULL;
  return GNUNET_OK;
}


static int
database_prepare (struct Plugin *plugin)
{
  enum GNUNET_GenericReturnValue ret;
  if (GNUNET_YES == plugin->ready)
    return GNUNET_OK;
  struct GNUNET_PQ_PreparedStatement ps[] = {
    GNUNET_PQ_make_prepare ("store_records",
                            "INSERT INTO ns098records"
                            " (zone_private_key, pkey, rvalue, record_count, record_data, label)"
                            " VALUES ($1, $2, $3, $4, $5, $6)"
                            " ON CONFLICT ON CONSTRAINT zl"
                            " DO UPDATE"
                            "    SET pkey=$2,rvalue=$3,record_count=$4,record_data=$5"
                            "    WHERE ns098records.zone_private_key = $1"
                            "          AND ns098records.label = $6"),
    GNUNET_PQ_make_prepare ("delete_records",
                            "DELETE FROM ns098records "
                            "WHERE zone_private_key=$1 AND label=$2"),
    GNUNET_PQ_make_prepare ("zone_to_name",
                            "SELECT seq,record_count,record_data,label FROM ns098records"
                            " WHERE zone_private_key=$1 AND pkey=$2"),
    GNUNET_PQ_make_prepare ("iterate_zone",
                            "SELECT seq,record_count,record_data,label FROM ns098records "
                            "WHERE zone_private_key=$1 AND seq > $2 ORDER BY seq ASC LIMIT $3"),
    GNUNET_PQ_make_prepare ("iterate_all_zones",
                            "SELECT seq,record_count,record_data,label,zone_private_key"
                            " FROM ns098records WHERE seq > $1 ORDER BY seq ASC LIMIT $2"),
    GNUNET_PQ_make_prepare ("lookup_label",
                            "SELECT seq,record_count,record_data,label "
                            "FROM ns098records WHERE zone_private_key=$1 AND label=$2"),
    GNUNET_PQ_make_prepare ("edit_set",
                            "SELECT seq,record_count,record_data,label "
                            "FROM ns098records WHERE zone_private_key=$1 AND label=$2 FOR UPDATE NOWAIT"),
    GNUNET_PQ_PREPARED_STATEMENT_END
  };
  ret = GNUNET_PQ_prepare_statements (plugin->dbh, ps);
  if (GNUNET_OK != ret)
    return ret;
  plugin->ready = GNUNET_YES;
  return GNUNET_OK;
}


/**
 * Initialize the database connections and associated
 * data structures (create tables and indices
 * as needed as well).
 *
 * @param plugin the plugin context (state for this module)
 * @return #GNUNET_OK on success
 */
static enum GNUNET_GenericReturnValue
database_connect (struct Plugin *plugin)
{
  char *emsg;

  if (GNUNET_YES ==
      GNUNET_CONFIGURATION_get_value_yesno (plugin->cfg,
                                            "namestore-postgres",
                                            "INIT_ON_CONNECT"))
  {
    /**
     * Gracefully fail as this should not be a critical error if the
     * database is already created
     */
    if (GNUNET_OK !=
        init_database (plugin,
                       &emsg,
                       GNUNET_NO))
    {
      LOG (GNUNET_ERROR_TYPE_WARNING,
           "Failed to initialize database on connect: `%s'\n",
           emsg);
      GNUNET_free (emsg);
    }
  }
  plugin->dbh = GNUNET_PQ_connect_with_cfg (plugin->cfg,
                                            "namestore-postgres",
                                            NULL,
                                            NULL,
                                            NULL);
  if (NULL == plugin->dbh)
    return GNUNET_SYSERR;
  return GNUNET_OK;
}


/**
 * Store a record in the datastore.  Removes any existing record in the
 * same zone with the same name.
 *
 * @param cls closure (internal context for the plugin)
 * @param zone_key private key of the zone
 * @param label name that is being mapped (at most 255 characters long)
 * @param rd_count number of entries in @a rd array
 * @param rd array of records with data to store
 * @return #GNUNET_OK on success, else #GNUNET_SYSERR
 */
static int
namestore_postgres_store_records (void *cls,
                                  const struct
                                  GNUNET_IDENTITY_PrivateKey *zone_key,
                                  const char *label,
                                  unsigned int rd_count,
                                  const struct GNUNET_GNSRECORD_Data *rd)
{
  struct Plugin *plugin = cls;
  struct GNUNET_IDENTITY_PublicKey pkey;
  uint64_t rvalue;
  uint32_t rd_count32 = (uint32_t) rd_count;
  ssize_t data_size;

  GNUNET_assert (GNUNET_OK == database_prepare (plugin));
  memset (&pkey,
          0,
          sizeof(pkey));
  for (unsigned int i = 0; i < rd_count; i++)
    if (GNUNET_YES ==
        GNUNET_GNSRECORD_is_zonekey_type (rd[i].record_type))
    {
      GNUNET_break (GNUNET_OK ==
                    GNUNET_GNSRECORD_identity_from_data (rd[i].data,
                                                         rd[i].data_size,
                                                         rd[i].record_type,
                                                         &pkey));
      break;
    }
  rvalue = GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_WEAK,
                                     UINT64_MAX);
  data_size = GNUNET_GNSRECORD_records_get_size (rd_count,
                                                 rd);
  if (data_size < 0)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  if (data_size >= UINT16_MAX)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  /* if record set is empty, delete existing records */
  if (0 == rd_count)
  {
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (zone_key),
      GNUNET_PQ_query_param_string (label),
      GNUNET_PQ_query_param_end
    };
    enum GNUNET_DB_QueryStatus res;

    res = GNUNET_PQ_eval_prepared_non_select (plugin->dbh,
                                              "delete_records",
                                              params);
    if ((GNUNET_DB_STATUS_SUCCESS_ONE_RESULT != res) &&
        (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS != res))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
    GNUNET_log_from (GNUNET_ERROR_TYPE_DEBUG,
                     "postgres",
                     "Record deleted\n");
    return GNUNET_OK;
  }
  /* otherwise, UPSERT (i.e. UPDATE if exists, otherwise INSERT) */
  {
    char data[data_size];
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (zone_key),
      GNUNET_PQ_query_param_auto_from_type (&pkey),
      GNUNET_PQ_query_param_uint64 (&rvalue),
      GNUNET_PQ_query_param_uint32 (&rd_count32),
      GNUNET_PQ_query_param_fixed_size (data, data_size),
      GNUNET_PQ_query_param_string (label),
      GNUNET_PQ_query_param_end
    };
    enum GNUNET_DB_QueryStatus res;
    ssize_t ret;

    ret = GNUNET_GNSRECORD_records_serialize (rd_count,
                                              rd,
                                              data_size,
                                              data);
    if ((ret < 0) ||
        (data_size != ret))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }

    res = GNUNET_PQ_eval_prepared_non_select (plugin->dbh,
                                              "store_records",
                                              params);
    if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT != res)
      return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Closure for #parse_result_call_iterator.
 */
struct ParserContext
{
  /**
   * Function to call for each result.
   */
  GNUNET_NAMESTORE_RecordIterator iter;

  /**
   * Closure for @e iter.
   */
  void *iter_cls;

  /**
   * Zone key, NULL if part of record.
   */
  const struct GNUNET_IDENTITY_PrivateKey *zone_key;

  /**
   * Number of results still to return (counted down by
   * number of results given to iterator).
   */
  uint64_t limit;
};


/**
 * A statement has been run.  We should evaluate the result, and if possible
 * call the @a iter in @a cls with the result.
 *
 * @param cls closure of type `struct ParserContext *`
 * @param res the postgres result
 * @param num_results the number of results in @a result
 */
static void
parse_result_call_iterator (void *cls,
                            PGresult *res,
                            unsigned int num_results)
{
  struct ParserContext *pc = cls;

  if (NULL == pc->iter)
    return;   /* no need to do more work */
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Got %d results from PQ.\n", num_results);
  for (unsigned int i = 0; i < num_results; i++)
  {
    uint64_t serial;
    void *data;
    size_t data_size;
    uint32_t record_count;
    char *label;
    struct GNUNET_IDENTITY_PrivateKey zk;
    struct GNUNET_PQ_ResultSpec rs_with_zone[] = {
      GNUNET_PQ_result_spec_uint64 ("seq", &serial),
      GNUNET_PQ_result_spec_uint32 ("record_count", &record_count),
      GNUNET_PQ_result_spec_variable_size ("record_data", &data, &data_size),
      GNUNET_PQ_result_spec_string ("label", &label),
      GNUNET_PQ_result_spec_auto_from_type ("zone_private_key", &zk),
      GNUNET_PQ_result_spec_end
    };
    struct GNUNET_PQ_ResultSpec rs_without_zone[] = {
      GNUNET_PQ_result_spec_uint64 ("seq", &serial),
      GNUNET_PQ_result_spec_uint32 ("record_count", &record_count),
      GNUNET_PQ_result_spec_variable_size ("record_data", &data, &data_size),
      GNUNET_PQ_result_spec_string ("label", &label),
      GNUNET_PQ_result_spec_end
    };
    struct GNUNET_PQ_ResultSpec *rs;

    rs = (NULL == pc->zone_key) ? rs_with_zone : rs_without_zone;
    if (GNUNET_YES !=
        GNUNET_PQ_extract_result (res,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      return;
    }

    if (record_count > 64 * 1024)
    {
      /* sanity check, don't stack allocate far too much just
         because database might contain a large value here */
      GNUNET_break (0);
      GNUNET_PQ_cleanup_result (rs);
      return;
    }

    {
      struct GNUNET_GNSRECORD_Data rd[GNUNET_NZL (record_count)];

      GNUNET_assert (0 != serial);
      if (GNUNET_OK !=
          GNUNET_GNSRECORD_records_deserialize (data_size,
                                                data,
                                                record_count,
                                                rd))
      {
        GNUNET_break (0);
        GNUNET_PQ_cleanup_result (rs);
        return;
      }
      pc->iter (pc->iter_cls,
                serial,
                (NULL == pc->zone_key) ? &zk : pc->zone_key,
                label,
                record_count,
                rd);
    }
    GNUNET_PQ_cleanup_result (rs);
  }
  pc->limit -= num_results;
}


/**
 * Lookup records in the datastore for which we are the authority.
 *
 * @param cls closure (internal context for the plugin)
 * @param zone private key of the zone
 * @param label name of the record in the zone
 * @param iter function to call with the result
 * @param iter_cls closure for @a iter
 * @param method the method to use "lookup_record" or "edit_set"
 * @return #GNUNET_OK on success, #GNUNET_NO for no results, else #GNUNET_SYSERR
 */
static int
lookup_records (void *cls,
                const struct
                GNUNET_IDENTITY_PrivateKey *zone,
                const char *label,
                GNUNET_NAMESTORE_RecordIterator iter,
                void *iter_cls,
                const char*method)
{
  struct Plugin *plugin = cls;
  GNUNET_assert (GNUNET_OK == database_prepare (plugin));
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (zone),
    GNUNET_PQ_query_param_string (label),
    GNUNET_PQ_query_param_end
  };
  struct ParserContext pc;
  enum GNUNET_DB_QueryStatus res;

  if (NULL == zone)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  pc.iter = iter;
  pc.iter_cls = iter_cls;
  pc.zone_key = zone;
  res = GNUNET_PQ_eval_prepared_multi_select (plugin->dbh,
                                              method,
                                              params,
                                              &parse_result_call_iterator,
                                              &pc);
  if (res < 0)
    return GNUNET_SYSERR;
  if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == res)
    return GNUNET_NO;
  return GNUNET_OK;
}


/**
 * Lookup records in the datastore for which we are the authority.
 *
 * @param cls closure (internal context for the plugin)
 * @param zone private key of the zone
 * @param label name of the record in the zone
 * @param iter function to call with the result
 * @param iter_cls closure for @a iter
 * @return #GNUNET_OK on success, #GNUNET_NO for no results, else #GNUNET_SYSERR
 */
static int
namestore_postgres_lookup_records (void *cls,
                                   const struct
                                   GNUNET_IDENTITY_PrivateKey *zone,
                                   const char *label,
                                   GNUNET_NAMESTORE_RecordIterator iter,
                                   void *iter_cls)
{
  return lookup_records (cls, zone, label, iter, iter_cls, "lookup_label");
}


/**
 * Edit records in the datastore for which we are the authority.
 *
 * @param cls closure (internal context for the plugin)
 * @param zone private key of the zone
 * @param label name of the record in the zone
 * @param iter function to call with the result
 * @param iter_cls closure for @a iter
 * @return #GNUNET_OK on success, #GNUNET_NO for no results, else #GNUNET_SYSERR
 */
static int
namestore_postgres_edit_records (void *cls,
                                 const struct
                                 GNUNET_IDENTITY_PrivateKey *zone,
                                 const char *label,
                                 GNUNET_NAMESTORE_RecordIterator iter,
                                 void *iter_cls)
{
  return lookup_records (cls, zone, label, iter, iter_cls, "edit_set");
}


/**
 * Iterate over the results for a particular key and zone in the
 * datastore.  Will return at most one result to the iterator.
 *
 * @param cls closure (internal context for the plugin)
 * @param zone hash of public key of the zone, NULL to iterate over all zones
 * @param serial serial number to exclude in the list of all matching records
 * @param limit maximum number of results to fetch
 * @param iter function to call with the result
 * @param iter_cls closure for @a iter
 * @return #GNUNET_OK on success, #GNUNET_NO if there were no more results, #GNUNET_SYSERR on error
 */
static int
namestore_postgres_iterate_records (void *cls,
                                    const struct
                                    GNUNET_IDENTITY_PrivateKey *zone,
                                    uint64_t serial,
                                    uint64_t limit,
                                    GNUNET_NAMESTORE_RecordIterator iter,
                                    void *iter_cls)
{
  struct Plugin *plugin = cls;
  enum GNUNET_DB_QueryStatus res;
  struct ParserContext pc;

  GNUNET_assert (GNUNET_OK == database_prepare (plugin));
  pc.iter = iter;
  pc.iter_cls = iter_cls;
  pc.zone_key = zone;
  pc.limit = limit;
  if (NULL == zone)
  {
    struct GNUNET_PQ_QueryParam params_without_zone[] = {
      GNUNET_PQ_query_param_uint64 (&serial),
      GNUNET_PQ_query_param_uint64 (&limit),
      GNUNET_PQ_query_param_end
    };

    res = GNUNET_PQ_eval_prepared_multi_select (plugin->dbh,
                                                "iterate_all_zones",
                                                params_without_zone,
                                                &parse_result_call_iterator,
                                                &pc);
  }
  else
  {
    struct GNUNET_PQ_QueryParam params_with_zone[] = {
      GNUNET_PQ_query_param_auto_from_type (zone),
      GNUNET_PQ_query_param_uint64 (&serial),
      GNUNET_PQ_query_param_uint64 (&limit),
      GNUNET_PQ_query_param_end
    };

    res = GNUNET_PQ_eval_prepared_multi_select (plugin->dbh,
                                                "iterate_zone",
                                                params_with_zone,
                                                &parse_result_call_iterator,
                                                &pc);
  }
  if (res < 0)
    return GNUNET_SYSERR;

  if ((GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == res) ||
      (pc.limit > 0))
    return GNUNET_NO;
  return GNUNET_OK;
}


/**
 * Look for an existing PKEY delegation record for a given public key.
 * Returns at most one result to the iterator.
 *
 * @param cls closure (internal context for the plugin)
 * @param zone private key of the zone to look up in, never NULL
 * @param value_zone public key of the target zone (value), never NULL
 * @param iter function to call with the result
 * @param iter_cls closure for @a iter
 * @return #GNUNET_OK on success, #GNUNET_NO if there were no results, #GNUNET_SYSERR on error
 */
static int
namestore_postgres_zone_to_name (void *cls,
                                 const struct
                                 GNUNET_IDENTITY_PrivateKey *zone,
                                 const struct
                                 GNUNET_IDENTITY_PublicKey *value_zone,
                                 GNUNET_NAMESTORE_RecordIterator iter,
                                 void *iter_cls)
{
  struct Plugin *plugin = cls;
  GNUNET_assert (GNUNET_OK == database_prepare (plugin));
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (zone),
    GNUNET_PQ_query_param_auto_from_type (value_zone),
    GNUNET_PQ_query_param_end
  };
  enum GNUNET_DB_QueryStatus res;
  struct ParserContext pc;

  pc.iter = iter;
  pc.iter_cls = iter_cls;
  pc.zone_key = zone;
  res = GNUNET_PQ_eval_prepared_multi_select (plugin->dbh,
                                              "zone_to_name",
                                              params,
                                              &parse_result_call_iterator,
                                              &pc);
  if (res < 0)
    return GNUNET_SYSERR;
  return GNUNET_OK;
}


/**
 * Begin a transaction for a client.
 *
 * @param cls closure (internal context for the plugin)
 * @param emsg error message set of return code is #GNUNET_SYSERR
 * @return #GNUNET_YES on success, #GNUNET_SYSERR if transaction cannot be started.
 */
static enum GNUNET_GenericReturnValue
namestore_postgres_transaction_begin (void *cls,
                                      char **emsg)
{
  struct Plugin *plugin = cls;
  GNUNET_assert (GNUNET_OK == database_prepare (plugin));
  struct GNUNET_PQ_ExecuteStatement es[] = {
    GNUNET_PQ_make_execute ("BEGIN"),
    GNUNET_PQ_EXECUTE_STATEMENT_END
  };

  return GNUNET_PQ_exec_statements (plugin->dbh, es);
}


/**
 * Commit a transaction for a client.
 * This releases the lock on the database.
 *
 * @param cls closure (internal context for the plugin)
 * @param emsg error message set of return code is #GNUNET_SYSERR
 * @return #GNUNET_YES on success, #GNUNET_SYSERR if transaction cannot be started.
 */
static enum GNUNET_GenericReturnValue
namestore_postgres_transaction_rollback (void *cls,
                                         char **emsg)
{
  struct Plugin *plugin = cls;
  GNUNET_assert (GNUNET_OK == database_prepare (plugin));
  struct GNUNET_PQ_ExecuteStatement es[] = {
    GNUNET_PQ_make_execute ("ROLLBACK"),
    GNUNET_PQ_EXECUTE_STATEMENT_END
  };

  return GNUNET_PQ_exec_statements (plugin->dbh, es);
}


/**
 * Roll back a transaction for a client.
 * This releases the lock on the database.
 *
 * @param cls closure (internal context for the plugin)
 * @param emsg error message set of return code is #GNUNET_SYSERR
 * @return #GNUNET_YES on success, #GNUNET_SYSERR if transaction cannot be started.
 */
static enum GNUNET_GenericReturnValue
namestore_postgres_transaction_commit (void *cls,
                                       char **emsg)
{
  struct Plugin *plugin = cls;
  GNUNET_assert (GNUNET_OK == database_prepare (plugin));
  struct GNUNET_PQ_ExecuteStatement es[] = {
    GNUNET_PQ_make_execute ("COMMIT"),
    GNUNET_PQ_EXECUTE_STATEMENT_END
  };

  return GNUNET_PQ_exec_statements (plugin->dbh, es);
}


static enum GNUNET_GenericReturnValue
namestore_postgres_initialize_database (void *cls,
                                        char **emsg)
{
  int ret;
  ret = init_database (cls, emsg, GNUNET_NO);
  if (GNUNET_SYSERR == ret)
    return ret;
  return database_connect (cls);
}


static enum GNUNET_GenericReturnValue
namestore_postgres_reset_database (void *cls,
                                   char **emsg)
{
  int ret;
  ret = init_database (cls, emsg, GNUNET_YES);
  if (GNUNET_SYSERR == ret)
    return ret;
  return database_connect (cls);
}


/**
 * Shutdown database connection and associate data
 * structures.
 *
 * @param plugin the plugin context (state for this module)
 */
static void
database_shutdown (struct Plugin *plugin)
{
  GNUNET_PQ_disconnect (plugin->dbh);
  plugin->dbh = NULL;
}


/**
 * Entry point for the plugin.
 *
 * @param cls the `struct GNUNET_NAMESTORE_PluginEnvironment*`
 * @return NULL on error, othrewise the plugin context
 */
void *
libgnunet_plugin_namestore_postgres_init (void *cls)
{
  struct Plugin *plugin;
  const struct GNUNET_CONFIGURATION_Handle *cfg = cls;
  struct GNUNET_NAMESTORE_PluginFunctions *api;

  plugin = GNUNET_new (struct Plugin);
  plugin->cfg = cfg;
  if (GNUNET_OK != database_connect (plugin))
  {
    database_shutdown (plugin);
    GNUNET_free (plugin);
    return NULL;
  }
  api = GNUNET_new (struct GNUNET_NAMESTORE_PluginFunctions);
  api->cls = plugin;
  api->store_records = &namestore_postgres_store_records;
  api->iterate_records = &namestore_postgres_iterate_records;
  api->zone_to_name = &namestore_postgres_zone_to_name;
  api->lookup_records = &namestore_postgres_lookup_records;
  api->transaction_begin = &namestore_postgres_transaction_begin;
  api->transaction_commit = &namestore_postgres_transaction_commit;
  api->transaction_rollback = &namestore_postgres_transaction_rollback;
  api->initialize_database = &namestore_postgres_initialize_database;
  api->reset_database = &namestore_postgres_reset_database;
  api->edit_records = &namestore_postgres_edit_records;
  LOG (GNUNET_ERROR_TYPE_INFO,
       "Postgres namestore plugin running\n");
  return api;
}


/**
 * Exit point from the plugin.
 *
 * @param cls the plugin context (as returned by "init")
 * @return always NULL
 */
void *
libgnunet_plugin_namestore_postgres_done (void *cls)
{
  struct GNUNET_NAMESTORE_PluginFunctions *api = cls;
  struct Plugin *plugin = api->cls;

  database_shutdown (plugin);
  plugin->cfg = NULL;
  GNUNET_free (plugin);
  GNUNET_free (api);
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Postgres namestore plugin is finished\n");
  return NULL;
}


/* end of plugin_namestore_postgres.c */