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/*
  This file is part of GNUnet
  Copyright (C) 2014, 2015, 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
*/
/**
 * @file src/include/gnunet_curl_lib.h
 * @brief library to make it easy to download JSON replies over HTTP
 * @author Sree Harsha Totakura <sreeharsha@totakura.in>
 * @author Christian Grothoff
 *
 * @defgroup curl CURL integration library
 * Download JSON using libcurl.
 * @{
 */
#ifndef GNUNET_CURL_LIB_H
#define GNUNET_CURL_LIB_H
#if HAVE_LIBCURL
#include <curl/curl.h>
#elif HAVE_LIBGNURL
#include <gnurl/curl.h>
#else
#error "needs curl or gnurl"
#endif
#include <jansson.h>
#include "gnunet_util_lib.h"


/**
 * Function called by the context to ask for the event loop to be
 * rescheduled, that is the application should call
 * #GNUNET_CURL_get_select_info() as the set of sockets we care about
 * just changed.
 *
 * @param cls closure
 */
typedef void
(*GNUNET_CURL_RescheduleCallback)(void *cls);

/**
 * @brief Buffer data structure we use to buffer the HTTP download
 * before giving it to the JSON parser.
 */
struct GNUNET_CURL_DownloadBuffer
{

  /**
   * Download buffer
   */
  void *buf;

  /**
   * The size of the download buffer
   */
  size_t buf_size;

  /**
   * Error code (based on libc errno) if we failed to download
   * (i.e. response too large).
   */
  int eno;

};


/**
 * Parses the raw response we got from the Web server.
 *
 * @param db the raw data
 * @param eh handle
 * @param response_code HTTP response code
 * @return the parsed object
 */
typedef void *
(*GNUNET_CURL_RawParser) (struct GNUNET_CURL_DownloadBuffer *db,
                          CURL *eh,
                          long *response_code);

/**
 * Deallocate the response.
 * 
 * @param response object to clean
 */
typedef void
(*GNUNET_CURL_ResponseCleaner) (void *response);

/**
 * Initialise this library.  This function should be called before using any of
 * the following functions.
 *
 * @param cb function to call when rescheduling is required
 * @param cb_cls closure for @a cb
 * @return library context
 */
struct GNUNET_CURL_Context *
GNUNET_CURL_init (GNUNET_CURL_RescheduleCallback cb,
                  void *cb_cls);


/**
 * Obtain the information for a select() call to wait until
 * #GNUNET_CURL_perform() is ready again.
 *
 * Basically, a client should use this API to prepare for select(),
 * then block on select(), then call #GNUNET_CURL_perform() and then
 * start again until the work with the context is done.
 *
 * This function will NOT zero out the sets and assumes that @a max_fd
 * and @a timeout are already set to minimal applicable values.  It is
 * safe to give this API FD-sets and @a max_fd and @a timeout that are
 * already initialized to some other descriptors that need to go into
 * the select() call.
 *
 * @param ctx context to get the event loop information for
 * @param read_fd_set will be set for any pending read operations
 * @param write_fd_set will be set for any pending write operations
 * @param except_fd_set is here because curl_multi_fdset() has this argument
 * @param max_fd set to the highest FD included in any set;
 *        if the existing sets have no FDs in it, the initial
 *        value should be "-1". (Note that `max_fd + 1` will need
 *        to be passed to select().)
 * @param timeout set to the timeout in milliseconds (!); -1 means
 *        no timeout (NULL, blocking forever is OK), 0 means to
 *        proceed immediately with #GNUNET_CURL_perform().
 */
void
GNUNET_CURL_get_select_info (struct GNUNET_CURL_Context *ctx,
                             fd_set *read_fd_set,
                             fd_set *write_fd_set,
                             fd_set *except_fd_set,
                             int *max_fd,
                             long *timeout);


/**
 * Add custom request header.
 *
 * @param ctx cURL context.
 * @param header header string; will be given to the context AS IS.
 * @return #GNUNET_OK if no errors occurred, #GNUNET_SYSERR otherwise.
 */
int
GNUNET_CURL_append_header (struct GNUNET_CURL_Context *ctx,
                           const char *header);

/**
 * Run the main event loop for the CURL interaction.
 *
 * @param ctx the library context
 */
void
GNUNET_CURL_perform (struct GNUNET_CURL_Context *ctx);


/**
 * Run the main event loop for the Taler interaction.
 *
 * @param ctx the library context
 * @param rp parses the raw response returned from
 *        the Web server.
 * @param rc cleans/frees the response
 */
void
GNUNET_CURL_perform2 (struct GNUNET_CURL_Context *ctx,
                      GNUNET_CURL_RawParser rp,
                      GNUNET_CURL_ResponseCleaner rc);

/**
 * Cleanup library initialisation resources.  This function should be called
 * after using this library to cleanup the resources occupied during library's
 * initialisation.
 *
 * @param ctx the library context
 */
void
GNUNET_CURL_fini (struct GNUNET_CURL_Context *ctx);


/**
 * Entry in the context's job queue.
 */
struct GNUNET_CURL_Job;

/**
 * Function to call upon completion of a job.
 *
 * @param cls closure
 * @param response_code HTTP response code from server, 0 on hard error
 * @param json response, NULL if response was not in JSON format
 */
typedef void
(*GNUNET_CURL_JobCompletionCallback)(void *cls,
                                     long response_code,
                                     const void *response);


/**
 * Schedule a CURL request to be executed and call the given @a jcc
 * upon its completion. Note that the context will make use of the
 * CURLOPT_PRIVATE facility of the CURL @a eh.
 *
 * This function modifies the CURL handle to add the
 * "Content-Type: application/json" header if @a add_json is set.
 *
 * @param ctx context to execute the job in
 * @param eh curl easy handle for the request, will
 *           be executed AND cleaned up
 * @param add_json add "application/json" content type header
 * @param jcc callback to invoke upon completion
 * @param jcc_cls closure for @a jcc
 * @return NULL on error (in this case, @eh is still released!)
 */
struct GNUNET_CURL_Job *
GNUNET_CURL_job_add (struct GNUNET_CURL_Context *ctx,
                     CURL *eh,
                     int add_json,
                     GNUNET_CURL_JobCompletionCallback jcc,
                     void *jcc_cls);


/**
 * Schedule a CURL request to be executed and call the given @a jcc
 * upon its completion.  Note that the context will make use of the
 * CURLOPT_PRIVATE facility of the CURL @a eh.
 *
 * This function modifies the CURL handle to add the
 * "Content-Type: application/json" header if @a add_json is set.
 *
 * @param ctx context to execute the job in
 * @param eh curl easy handle for the request, will
 *           be executed AND cleaned up
 * @param job_headers extra headers to add for this request
 * @param jcc callback to invoke upon completion
 * @param jcc_cls closure for @a jcc
 * @return NULL on error (in this case, @eh is still released!)
 */
struct GNUNET_CURL_Job *
GNUNET_CURL_job_add2 (struct GNUNET_CURL_Context *ctx,
                     CURL *eh,
                     const struct curl_slist *job_headers,
                     GNUNET_CURL_JobCompletionCallback jcc,
                     void *jcc_cls);


/**
 * Cancel a job.  Must only be called before the job completion
 * callback is called for the respective job.
 *
 * @param job job to cancel
 */
void
GNUNET_CURL_job_cancel (struct GNUNET_CURL_Job *job);


/* ******* GNUnet SCHEDULER integration ************ */


/**
 * Closure for #GNUNET_CURL_gnunet_scheduler_reschedule().
 */
struct GNUNET_CURL_RescheduleContext;


/**
 * Initialize reschedule context.
 *
 * @param ctx context to manage
 * @return closure for #GNUNET_CURL_gnunet_scheduler_reschedule().
 */
struct GNUNET_CURL_RescheduleContext *
GNUNET_CURL_gnunet_rc_create (struct GNUNET_CURL_Context *ctx);

/**
 * Initialize reschedule context; with custom response parser
 *
 * @param ctx context to manage
 * @return closure for #GNUNET_CURL_gnunet_scheduler_reschedule().
 */
struct GNUNET_CURL_RescheduleContext *
GNUNET_CURL_gnunet_rc_create_with_parser (struct GNUNET_CURL_Context *ctx,
                                          GNUNET_CURL_RawParser rp,
                                          GNUNET_CURL_ResponseCleaner rc);


/**
 * Destroy reschedule context.
 *
 * @param rc context to destroy
 */
void
GNUNET_CURL_gnunet_rc_destroy (struct GNUNET_CURL_RescheduleContext *rc);


/**
 * Implementation of the #GNUNET_CURL_RescheduleCallback for GNUnet's
 * scheduler.  Will run the CURL context using GNUnet's scheduler.
 * Note that you MUST immediately destroy the reschedule context after
 * calling #GNUNET_CURL_fini().
 *
 * @param cls must point to a `struct GNUNET_CURL_RescheduleContext *`
 *           (pointer to a pointer!)
 */
void
GNUNET_CURL_gnunet_scheduler_reschedule (void *cls);


/**
 * Enable sending the async scope ID as a header.
 *
 * @param ctx the context to enable this for
 * @param header_name name of the header to send.
 */
void
GNUNET_CURL_enable_async_scope_header (struct GNUNET_CURL_Context *ctx, const char *header_name);


#endif
/** @} */  /* end of group */

/* end of gnunet_curl_lib.h */