/*
      This file is part of GNUnet
      Copyright (C) 2004-2013, 2016 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
 */

/**
 * @author Christian Grothoff
 *
 * @file
 * API to the DHT service
 *
 * @defgroup dht  DHT service
 * Distributed Hash Table
 *
 * @see [Documentation](https://gnunet.org/developer-handbook-dht)
 *
 * @{
 */

#ifndef GNUNET_DHT_SERVICE_H
#define GNUNET_DHT_SERVICE_H

#include "gnunet_util_lib.h"
#include "gnunet_block_lib.h"
#include "gnunet_hello_lib.h"

#ifdef __cplusplus
extern "C"
{
#if 0                           /* keep Emacsens' auto-indent happy */
}
#endif
#endif


/**
 * Default republication frequency for stored data in the DHT.
 */
#define GNUNET_DHT_DEFAULT_REPUBLISH_FREQUENCY GNUNET_TIME_relative_multiply ( \
    GNUNET_TIME_UNIT_MINUTES, 60)


/**
 * Connection to the DHT service.
 */
struct GNUNET_DHT_Handle;

/**
 * Handle to control a get operation.
 */
struct GNUNET_DHT_GetHandle;

/**
 * Handle to control a find peer operation.
 */
struct GNUNET_DHT_FindPeerHandle;


/**
 * Options for routing.
 */
enum GNUNET_DHT_RouteOption
{
  /**
   * Default.  Do nothing special.
   */
  GNUNET_DHT_RO_NONE = 0,

  /**
   * Each peer along the way should look at 'enc' (otherwise
   * only the k-peers closest to the key should look at it).
   */
  GNUNET_DHT_RO_DEMULTIPLEX_EVERYWHERE = 1,

  /**
   * We should keep track of the route that the message
   * took in the P2P network.
   */
  GNUNET_DHT_RO_RECORD_ROUTE = 2,

  /**
   * This is a 'FIND-PEER' request, so approximate results are fine.
   */
  GNUNET_DHT_RO_FIND_PEER = 4,

  /**
   * Possible message option for query key randomization.
   */
  GNUNET_DHT_RO_BART = 8,

  /**
   * Flag given to monitors if this was the last hop for a GET/PUT.
   */
  GNUNET_DHT_RO_LAST_HOP = 16
};


/**
 * Initialize the connection with the DHT service.
 *
 * @param cfg configuration to use
 * @param ht_len size of the internal hash table to use for
 *               processing multiple GET/FIND requests in parallel
 * @return NULL on error
 */
struct GNUNET_DHT_Handle *
GNUNET_DHT_connect (const struct GNUNET_CONFIGURATION_Handle *cfg,
                    unsigned int ht_len);


/**
 * Shutdown connection with the DHT service.
 *
 * @param handle connection to shut down
 */
void
GNUNET_DHT_disconnect (struct GNUNET_DHT_Handle *handle);


/* *************** Standard API: get and put ******************* */


/**
 * Opaque handle to cancel a PUT operation.
 */
struct GNUNET_DHT_PutHandle;


/**
 * Perform a PUT operation storing data in the DHT.
 *
 * @param handle handle to DHT service
 * @param key the key to store under
 * @param desired_replication_level estimate of how many
 *                nearest peers this request should reach
 * @param options routing options for this message
 * @param type type of the value
 * @param size number of bytes in @a data; must be less than 64k
 * @param data the data to store
 * @param exp desired expiration time for the value
 * @param cont continuation to call when done (transmitting request to service)
 *        You must not call #GNUNET_DHT_disconnect in this continuation
 * @param cont_cls closure for @a cont
 * @return handle to cancel the "PUT" operation, NULL on error
 *        (size too big)
 */
struct GNUNET_DHT_PutHandle *
GNUNET_DHT_put (struct GNUNET_DHT_Handle *handle,
                const struct GNUNET_HashCode *key,
                uint32_t desired_replication_level,
                enum GNUNET_DHT_RouteOption options,
                enum GNUNET_BLOCK_Type type,
                size_t size,
                const void *data,
                struct GNUNET_TIME_Absolute exp,
                GNUNET_SCHEDULER_TaskCallback cont,
                void *cont_cls);


/**
 * Cancels a DHT PUT operation.  Note that the PUT request may still
 * go out over the network (we can't stop that); However, if the PUT
 * has not yet been sent to the service, cancelling the PUT will stop
 * this from happening (but there is no way for the user of this API
 * to tell if that is the case).  The only use for this API is to
 * prevent a later call to 'cont' from #GNUNET_DHT_put (i.e. because
 * the system is shutting down).
 *
 * @param ph put operation to cancel ('cont' will no longer be called)
 */
void
GNUNET_DHT_put_cancel (struct GNUNET_DHT_PutHandle *ph);


/**
 * Iterator called on each result obtained for a DHT
 * operation that expects a reply
 *
 * @param cls closure
 * @param exp when will this value expire
 * @param key key of the result
 * @param get_path peers on reply path (or NULL if not recorded)
 *                 [0] = datastore's first neighbor, [length - 1] = local peer
 * @param get_path_length number of entries in @a get_path
 * @param put_path peers on the PUT path (or NULL if not recorded)
 *                 [0] = origin, [length - 1] = datastore
 * @param put_path_length number of entries in @a put_path
 * @param type type of the result
 * @param size number of bytes in @a data
 * @param data pointer to the result data
 */
typedef void
(*GNUNET_DHT_GetIterator) (void *cls,
                           struct GNUNET_TIME_Absolute exp,
                           const struct GNUNET_HashCode *key,
                           const struct GNUNET_PeerIdentity *get_path,
                           unsigned int get_path_length,
                           const struct GNUNET_PeerIdentity *put_path,
                           unsigned int put_path_length,
                           enum GNUNET_BLOCK_Type type,
                           size_t size,
                           const void *data);


/**
 * Perform an asynchronous GET operation on the DHT identified. See
 * also #GNUNET_BLOCK_evaluate.
 *
 * @param handle handle to the DHT service
 * @param type expected type of the response object
 * @param key the key to look up
 * @param desired_replication_level estimate of how many
                  nearest peers this request should reach
 * @param options routing options for this message
 * @param xquery extended query data (can be NULL, depending on type)
 * @param xquery_size number of bytes in @a xquery
 * @param iter function to call on each result
 * @param iter_cls closure for @a iter
 * @return handle to stop the async get
 */
struct GNUNET_DHT_GetHandle *
GNUNET_DHT_get_start (struct GNUNET_DHT_Handle *handle,
                      enum GNUNET_BLOCK_Type type,
                      const struct GNUNET_HashCode *key,
                      uint32_t desired_replication_level,
                      enum GNUNET_DHT_RouteOption options,
                      const void *xquery,
                      size_t xquery_size,
                      GNUNET_DHT_GetIterator iter,
                      void *iter_cls);


/**
 * Tell the DHT not to return any of the following known results
 * to this client.
 *
 * @param get_handle get operation for which results should be filtered
 * @param num_results number of results to be blocked that are
 *        provided in this call (size of the @a results array)
 * @param results array of hash codes over the `data` of the results
 *        to be blocked
 */
void
GNUNET_DHT_get_filter_known_results (struct GNUNET_DHT_GetHandle *get_handle,
                                     unsigned int num_results,
                                     const struct GNUNET_HashCode *results);

/**
 * Stop async DHT-get.  Frees associated resources.
 *
 * @param get_handle GET operation to stop.
 */
void
GNUNET_DHT_get_stop (struct GNUNET_DHT_GetHandle *get_handle);


/* *************** Extended API: monitor ******************* */

/**
 * Handle to monitor requests
 */
struct GNUNET_DHT_MonitorHandle;

/**
 * Callback called on each GET request going through the DHT.
 *
 * @param cls Closure.
 * @param options Options, for instance RecordRoute, DemultiplexEverywhere.
 * @param type The type of data in the request.
 * @param hop_count Hop count so far.
 * @param path_length number of entries in @a path (or 0 if not recorded).
 * @param path peers on the GET path (or NULL if not recorded).
 * @param desired_replication_level Desired replication level.
 * @param key Key of the requested data.
 */
typedef void
(*GNUNET_DHT_MonitorGetCB) (void *cls,
                            enum GNUNET_DHT_RouteOption options,
                            enum GNUNET_BLOCK_Type type,
                            uint32_t hop_count,
                            uint32_t desired_replication_level,
                            unsigned int path_length,
                            const struct GNUNET_PeerIdentity *path,
                            const struct GNUNET_HashCode *key);


/**
 * Callback called on each GET reply going through the DHT.
 *
 * @param cls Closure.
 * @param type The type of data in the result.
 * @param get_path Peers on GET path (or NULL if not recorded).
 * @param get_path_length number of entries in @a get_path.
 * @param put_path peers on the PUT path (or NULL if not recorded).
 * @param put_path_length number of entries in @a get_path.
 * @param exp Expiration time of the data.
 * @param key Key of the data.
 * @param data Pointer to the result data.
 * @param size Number of bytes in @a data.
 */
typedef void
(*GNUNET_DHT_MonitorGetRespCB) (void *cls,
                                enum GNUNET_BLOCK_Type type,
                                const struct GNUNET_PeerIdentity *get_path,
                                unsigned int get_path_length,
                                const struct GNUNET_PeerIdentity *put_path,
                                unsigned int put_path_length,
                                struct GNUNET_TIME_Absolute exp,
                                const struct GNUNET_HashCode *key,
                                const void *data,
                                size_t size);


/**
 * Callback called on each PUT request going through the DHT.
 *
 * @param cls Closure.
 * @param options Options, for instance RecordRoute, DemultiplexEverywhere.
 * @param type The type of data in the request.
 * @param hop_count Hop count so far.
 * @param path_length number of entries in @a path (or 0 if not recorded).
 * @param path peers on the PUT path (or NULL if not recorded).
 * @param desired_replication_level Desired replication level.
 * @param exp Expiration time of the data.
 * @param key Key under which data is to be stored.
 * @param data Pointer to the data carried.
 * @param size Number of bytes in @a data.
 */
typedef void
(*GNUNET_DHT_MonitorPutCB) (void *cls,
                            enum GNUNET_DHT_RouteOption options,
                            enum GNUNET_BLOCK_Type type,
                            uint32_t hop_count,
                            uint32_t desired_replication_level,
                            unsigned int path_length,
                            const struct GNUNET_PeerIdentity *path,
                            struct GNUNET_TIME_Absolute exp,
                            const struct GNUNET_HashCode *key,
                            const void *data,
                            size_t size);


/**
 * Start monitoring the local DHT service.
 *
 * @param handle Handle to the DHT service.
 * @param type Type of blocks that are of interest.
 * @param key Key of data of interest, NULL for all.
 * @param get_cb Callback to process monitored get messages.
 * @param get_resp_cb Callback to process monitored get response messages.
 * @param put_cb Callback to process monitored put messages.
 * @param cb_cls Closure for callbacks
 * @return Handle to stop monitoring.
 */
struct GNUNET_DHT_MonitorHandle *
GNUNET_DHT_monitor_start (struct GNUNET_DHT_Handle *handle,
                          enum GNUNET_BLOCK_Type type,
                          const struct GNUNET_HashCode *key,
                          GNUNET_DHT_MonitorGetCB get_cb,
                          GNUNET_DHT_MonitorGetRespCB get_resp_cb,
                          GNUNET_DHT_MonitorPutCB put_cb,
                          void *cb_cls);


/**
 * Stop monitoring.
 * On return handle will no longer be valid, caller must not use it anymore.
 *
 * @param handle The handle to the monitor request returned by
 *         #GNUNET_DHT_monitor_start().
 */
void
GNUNET_DHT_monitor_stop (struct GNUNET_DHT_MonitorHandle *handle);


#if 0                           /* keep Emacsens' auto-indent happy */
{
#endif
#ifdef __cplusplus
}
#endif

#endif

/** @} */  /* end of group dht */
