path: root/src/lib/exchange_api_refund.c

/*
  This file is part of TALER
  Copyright (C) 2014-2021 Taler Systems SA

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

  TALER 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 General Public License for more details.

  You should have received a copy of the GNU General Public License along with
  TALER; see the file COPYING.  If not, see
  <http://www.gnu.org/licenses/>
*/
/**
 * @file lib/exchange_api_refund.c
 * @brief Implementation of the /refund request of the exchange's HTTP API
 * @author Christian Grothoff
 */
#include "platform.h"
#include <jansson.h>
#include <microhttpd.h> /* just for HTTP status codes */
#include <gnunet/gnunet_util_lib.h>
#include <gnunet/gnunet_json_lib.h>
#include <gnunet/gnunet_curl_lib.h>
#include "taler_json_lib.h"
#include "taler_exchange_service.h"
#include "exchange_api_handle.h"
#include "taler_signatures.h"
#include "exchange_api_curl_defaults.h"


/**
 * @brief A Refund Handle
 */
struct TALER_EXCHANGE_RefundHandle
{

  /**
   * The connection to exchange this request handle will use
   */
  struct TALER_EXCHANGE_Handle *exchange;

  /**
   * The url for this request.
   */
  char *url;

  /**
   * Context for #TEH_curl_easy_post(). Keeps the data that must
   * persist for Curl to make the upload.
   */
  struct TALER_CURL_PostContext ctx;

  /**
   * Handle for the request.
   */
  struct GNUNET_CURL_Job *job;

  /**
   * Function to call with the result.
   */
  TALER_EXCHANGE_RefundCallback cb;

  /**
   * Closure for @a cb.
   */
  void *cb_cls;

  /**
   * Hash over the proposal data to identify the contract
   * which is being refunded.
   */
  struct TALER_PrivateContractHashP h_contract_terms;

  /**
   * The coin's public key.  This is the value that must have been
   * signed (blindly) by the Exchange.
   */
  struct TALER_CoinSpendPublicKeyP coin_pub;

  /**
   * The Merchant's public key.  Allows the merchant to later refund
   * the transaction or to inquire about the wire transfer identifier.
   */
  struct TALER_MerchantPublicKeyP merchant;

  /**
   * Merchant-generated transaction ID for the refund.
   */
  uint64_t rtransaction_id;

  /**
   * Amount to be refunded, including refund fee charged by the
   * exchange to the customer.
   */
  struct TALER_Amount refund_amount;

};


/**
 * Verify that the signature on the "200 OK" response
 * from the exchange is valid.
 *
 * @param[in,out] rh refund handle (refund fee added)
 * @param json json reply with the signature
 * @param[out] exchange_pub set to the exchange's public key
 * @param[out] exchange_sig set to the exchange's signature
 * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
 */
static enum GNUNET_GenericReturnValue
verify_refund_signature_ok (struct TALER_EXCHANGE_RefundHandle *rh,
                            const json_t *json,
                            struct TALER_ExchangePublicKeyP *exchange_pub,
                            struct TALER_ExchangeSignatureP *exchange_sig)
{
  const struct TALER_EXCHANGE_Keys *key_state;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_fixed_auto ("exchange_sig",
                                 exchange_sig),
    GNUNET_JSON_spec_fixed_auto ("exchange_pub",
                                 exchange_pub),
    GNUNET_JSON_spec_end ()
  };

  if (GNUNET_OK !=
      GNUNET_JSON_parse (json,
                         spec,
                         NULL, NULL))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  key_state = TALER_EXCHANGE_get_keys (rh->exchange);
  if (GNUNET_OK !=
      TALER_EXCHANGE_test_signing_key (key_state,
                                       exchange_pub))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (GNUNET_OK !=
      TALER_exchange_online_refund_confirmation_verify (
        &rh->h_contract_terms,
        &rh->coin_pub,
        &rh->merchant,
        rh->rtransaction_id,
        &rh->refund_amount,
        exchange_pub,
        exchange_sig))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Verify that the information in the "409 Conflict" response
 * from the exchange is valid and indeed shows that the refund
 * amount requested is too high.
 *
 * @param[in,out] rh refund handle (refund fee added)
 * @param json json reply with the coin transaction history
 * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
 */
static enum GNUNET_GenericReturnValue
verify_conflict_history_ok (struct TALER_EXCHANGE_RefundHandle *rh,
                            const json_t *json)
{
  json_t *history;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_json ("history",
                           &history),
    GNUNET_JSON_spec_end ()
  };
  size_t len;
  struct TALER_Amount dtotal;
  bool have_deposit;
  struct TALER_Amount rtotal;
  bool have_refund;

  if (GNUNET_OK !=
      GNUNET_JSON_parse (json,
                         spec,
                         NULL, NULL))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  len = json_array_size (history);
  if (0 == len)
  {
    GNUNET_break_op (0);
    GNUNET_JSON_parse_free (spec);
    return GNUNET_SYSERR;
  }
  have_deposit = false;
  have_refund = false;
  for (size_t off = 0; off<len; off++)
  {
    json_t *transaction;
    struct TALER_Amount amount;
    const char *type;
    struct GNUNET_JSON_Specification spec_glob[] = {
      TALER_JSON_spec_amount_any ("amount",
                                  &amount),
      GNUNET_JSON_spec_string ("type",
                               &type),
      GNUNET_JSON_spec_end ()
    };

    transaction = json_array_get (history,
                                  off);
    if (GNUNET_OK !=
        GNUNET_JSON_parse (transaction,
                           spec_glob,
                           NULL, NULL))
    {
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
    if (0 == strcasecmp (type,
                         "DEPOSIT"))
    {
      struct TALER_Amount deposit_fee;
      struct TALER_MerchantWireHashP h_wire;
      struct TALER_PrivateContractHashP h_contract_terms;
      struct TALER_AgeCommitmentHash h_age_commitment;
      bool no_hac;
      // struct TALER_ExtensionContractHashP h_extensions; // FIXME!
      struct TALER_DenominationHashP h_denom_pub;
      struct GNUNET_TIME_Timestamp wallet_timestamp;
      struct TALER_MerchantPublicKeyP merchant_pub;
      struct GNUNET_TIME_Timestamp refund_deadline;
      struct TALER_CoinSpendSignatureP sig;
      struct GNUNET_JSON_Specification ispec[] = {
        GNUNET_JSON_spec_fixed_auto ("coin_sig",
                                     &sig),
        GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
                                     &h_contract_terms),
        GNUNET_JSON_spec_fixed_auto ("h_wire",
                                     &h_wire),
        GNUNET_JSON_spec_fixed_auto ("h_denom_pub",
                                     &h_denom_pub),
        GNUNET_JSON_spec_mark_optional (
          GNUNET_JSON_spec_fixed_auto ("h_age_commitment",
                                       &h_age_commitment),
          &no_hac),
        GNUNET_JSON_spec_timestamp ("timestamp",
                                    &wallet_timestamp),
        GNUNET_JSON_spec_timestamp ("refund_deadline",
                                    &refund_deadline),
        TALER_JSON_spec_amount_any ("deposit_fee",
                                    &deposit_fee),
        GNUNET_JSON_spec_fixed_auto ("merchant_pub",
                                     &merchant_pub),
        GNUNET_JSON_spec_end ()
      };

      if (GNUNET_OK !=
          GNUNET_JSON_parse (transaction,
                             ispec,
                             NULL, NULL))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (GNUNET_OK !=
          TALER_wallet_deposit_verify (&amount,
                                       &deposit_fee,
                                       &h_wire,
                                       &h_contract_terms,
                                       no_hac
                                       ? NULL
                                       : &h_age_commitment,
                                       NULL /* FIXME-OEC: h_extensions! */,
                                       &h_denom_pub,
                                       wallet_timestamp,
                                       &merchant_pub,
                                       refund_deadline,
                                       &rh->coin_pub,
                                       &sig))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if ( (0 != GNUNET_memcmp (&rh->h_contract_terms,
                                &h_contract_terms)) ||
           (0 != GNUNET_memcmp (&rh->merchant,
                                &merchant_pub)) )
      {
        /* deposit information is about a different merchant/contract */
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (have_deposit)
      {
        /* this cannot really happen, but we conservatively support it anyway */
        if (GNUNET_YES !=
            TALER_amount_cmp_currency (&amount,
                                       &dtotal))
        {
          GNUNET_break_op (0);
          GNUNET_JSON_parse_free (spec);
          return GNUNET_SYSERR;
        }
        GNUNET_break (0 <=
                      TALER_amount_add (&dtotal,
                                        &dtotal,
                                        &amount));
      }
      else
      {
        dtotal = amount;
        have_deposit = true;
      }
    }
    else if (0 == strcasecmp (type,
                              "REFUND"))
    {
      struct TALER_MerchantSignatureP sig;
      struct TALER_Amount refund_fee;
      struct TALER_Amount sig_amount;
      struct TALER_PrivateContractHashP h_contract_terms;
      uint64_t rtransaction_id;
      struct TALER_MerchantPublicKeyP merchant_pub;
      struct GNUNET_JSON_Specification ispec[] = {
        TALER_JSON_spec_amount_any ("refund_fee",
                                    &refund_fee),
        GNUNET_JSON_spec_fixed_auto ("merchant_sig",
                                     &sig),
        GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
                                     &h_contract_terms),
        GNUNET_JSON_spec_fixed_auto ("merchant_pub",
                                     &merchant_pub),
        GNUNET_JSON_spec_uint64 ("rtransaction_id",
                                 &rtransaction_id),
        GNUNET_JSON_spec_end ()
      };

      if (GNUNET_OK !=
          GNUNET_JSON_parse (transaction,
                             ispec,
                             NULL, NULL))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (0 >
          TALER_amount_add (&sig_amount,
                            &refund_fee,
                            &amount))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (GNUNET_OK !=
          TALER_merchant_refund_verify (&rh->coin_pub,
                                        &h_contract_terms,
                                        rtransaction_id,
                                        &sig_amount,
                                        &merchant_pub,
                                        &sig))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if ( (0 != GNUNET_memcmp (&rh->h_contract_terms,
                                &h_contract_terms)) ||
           (0 != GNUNET_memcmp (&rh->merchant,
                                &merchant_pub)) )
      {
        /* refund is about a different merchant/contract */
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (rtransaction_id == rh->rtransaction_id)
      {
        /* Eh, this shows either a dependency failure or idempotency,
           but must not happen in a conflict reply. Fail! */
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }

      if (have_refund)
      {
        if (GNUNET_YES !=
            TALER_amount_cmp_currency (&amount,
                                       &rtotal))
        {
          GNUNET_break_op (0);
          GNUNET_JSON_parse_free (spec);
          return GNUNET_SYSERR;
        }
        GNUNET_break (0 <=
                      TALER_amount_add (&rtotal,
                                        &rtotal,
                                        &amount));
      }
      else
      {
        rtotal = amount;
        have_refund = true;
      }
    }
    else
    {
      /* unexpected type, new version on server? */
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "Unexpected type `%s' in response for exchange refund\n",
                  type);
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
  }

  {
    if (have_refund)
    {
      if (0 >
          TALER_amount_add (&rtotal,
                            &rtotal,
                            &rh->refund_amount))
      {
        GNUNET_break (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
    }
    else
    {
      rtotal = rh->refund_amount;
    }
  }
  if (-1 == TALER_amount_cmp (&dtotal,
                              &rtotal))
  {
    /* dtotal < rtotal: good! */
    GNUNET_JSON_parse_free (spec);
    return GNUNET_OK;
  }
  /* this fails to prove a conflict */
  GNUNET_break_op (0);
  GNUNET_JSON_parse_free (spec);
  return GNUNET_SYSERR;
}


/**
 * Verify that the information on the "412 Dependency Failed" response
 * from the exchange is valid and indeed shows that there is a refund
 * transaction ID reuse going on.
 *
 * @param[in,out] rh refund handle (refund fee added)
 * @param json json reply with the signature
 * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
 */
static enum GNUNET_GenericReturnValue
verify_failed_dependency_ok (struct TALER_EXCHANGE_RefundHandle *rh,
                             const json_t *json)
{
  json_t *h;
  json_t *e;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_json ("history",
                           &h),
    GNUNET_JSON_spec_end ()
  };

  if (GNUNET_OK !=
      GNUNET_JSON_parse (json,
                         spec,
                         NULL, NULL))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if ( (! json_is_array (h)) ||
       (1 != json_array_size (h) ) )
  {
    GNUNET_break_op (0);
    GNUNET_JSON_parse_free (spec);
    return GNUNET_SYSERR;
  }
  e = json_array_get (h, 0);
  {
    struct TALER_Amount amount;
    const char *type;
    struct TALER_MerchantSignatureP sig;
    struct TALER_Amount refund_fee;
    struct TALER_PrivateContractHashP h_contract_terms;
    uint64_t rtransaction_id;
    struct TALER_MerchantPublicKeyP merchant_pub;
    struct GNUNET_JSON_Specification ispec[] = {
      TALER_JSON_spec_amount_any ("amount",
                                  &amount),
      GNUNET_JSON_spec_string ("type",
                               &type),
      TALER_JSON_spec_amount_any ("refund_fee",
                                  &refund_fee),
      GNUNET_JSON_spec_fixed_auto ("merchant_sig",
                                   &sig),
      GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
                                   &h_contract_terms),
      GNUNET_JSON_spec_fixed_auto ("merchant_pub",
                                   &merchant_pub),
      GNUNET_JSON_spec_uint64 ("rtransaction_id",
                               &rtransaction_id),
      GNUNET_JSON_spec_end ()
    };

    if (GNUNET_OK !=
        GNUNET_JSON_parse (e,
                           ispec,
                           NULL, NULL))
    {
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
    if (GNUNET_OK !=
        TALER_merchant_refund_verify (&rh->coin_pub,
                                      &h_contract_terms,
                                      rtransaction_id,
                                      &amount,
                                      &merchant_pub,
                                      &sig))
    {
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
    if ( (rtransaction_id != rh->rtransaction_id) ||
         (0 != GNUNET_memcmp (&rh->h_contract_terms,
                              &h_contract_terms)) ||
         (0 != GNUNET_memcmp (&rh->merchant,
                              &merchant_pub)) ||
         (0 == TALER_amount_cmp (&rh->refund_amount,
                                 &amount)) )
    {
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
  }
  GNUNET_JSON_parse_free (spec);
  return GNUNET_OK;
}


/**
 * Function called when we're done processing the
 * HTTP /refund request.
 *
 * @param cls the `struct TALER_EXCHANGE_RefundHandle`
 * @param response_code HTTP response code, 0 on error
 * @param response parsed JSON result, NULL on error
 */
static void
handle_refund_finished (void *cls,
                        long response_code,
                        const void *response)
{
  struct TALER_EXCHANGE_RefundHandle *rh = cls;
  struct TALER_ExchangePublicKeyP exchange_pub;
  struct TALER_ExchangeSignatureP exchange_sig;
  struct TALER_ExchangePublicKeyP *ep = NULL;
  struct TALER_ExchangeSignatureP *es = NULL;
  const json_t *j = response;
  struct TALER_EXCHANGE_HttpResponse hr = {
    .reply = j,
    .http_status = (unsigned int) response_code
  };

  rh->job = NULL;
  switch (response_code)
  {
  case 0:
    hr.ec = TALER_EC_GENERIC_INVALID_RESPONSE;
    break;
  case MHD_HTTP_OK:
    if (GNUNET_OK !=
        verify_refund_signature_ok (rh,
                                    j,
                                    &exchange_pub,
                                    &exchange_sig))
    {
      GNUNET_break_op (0);
      hr.http_status = 0;
      hr.ec = TALER_EC_EXCHANGE_REFUND_INVALID_SIGNATURE_BY_EXCHANGE;
    }
    else
    {
      ep = &exchange_pub;
      es = &exchange_sig;
    }
    break;
  case MHD_HTTP_BAD_REQUEST:
    /* This should never happen, either us or the exchange is buggy
       (or API version conflict); also can happen if the currency
       differs (which we should obviously never support).
       Just pass JSON reply to the application */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_FORBIDDEN:
    /* Nothing really to verify, exchange says one of the signatures is
       invalid; as we checked them, this should never happen, we
       should pass the JSON reply to the application */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_NOT_FOUND:
    /* Nothing really to verify, this should never
       happen, we should pass the JSON reply to the application */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_CONFLICT:
    /* Requested total refunds exceed deposited amount */
    if (GNUNET_OK !=
        verify_conflict_history_ok (rh,
                                    j))
    {
      GNUNET_break (0);
      hr.http_status = 0;
      hr.ec = TALER_EC_EXCHANGE_REFUND_INVALID_FAILURE_PROOF_BY_EXCHANGE;
      hr.hint = "conflict information provided by exchange is invalid";
      break;
    }
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_GONE:
    /* Kind of normal: the money was already sent to the merchant
       (it was too late for the refund). */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_PRECONDITION_FAILED:
    if (GNUNET_OK !=
        verify_failed_dependency_ok (rh,
                                     j))
    {
      GNUNET_break (0);
      hr.http_status = 0;
      hr.ec = TALER_EC_EXCHANGE_REFUND_INVALID_FAILURE_PROOF_BY_EXCHANGE;
      hr.hint = "failed precondition proof returned by exchange is invalid";
      break;
    }
    /* Two different refund requests were made about the same deposit, but
       carrying identical refund transaction ids.  */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_INTERNAL_SERVER_ERROR:
    /* Server had an internal issue; we should retry, but this API
       leaves this to the application */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  default:
    /* unexpected response code */
    GNUNET_break_op (0);
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Unexpected response code %u/%d for exchange refund\n",
                (unsigned int) response_code,
                hr.ec);
    break;
  }
  rh->cb (rh->cb_cls,
          &hr,
          ep,
          es);
  TALER_EXCHANGE_refund_cancel (rh);
}


struct TALER_EXCHANGE_RefundHandle *
TALER_EXCHANGE_refund (
  struct TALER_EXCHANGE_Handle *exchange,
  const struct TALER_Amount *amount,
  const struct TALER_PrivateContractHashP *h_contract_terms,
  const struct TALER_CoinSpendPublicKeyP *coin_pub,
  uint64_t rtransaction_id,
  const struct TALER_MerchantPrivateKeyP *merchant_priv,
  TALER_EXCHANGE_RefundCallback cb,
  void *cb_cls)
{
  struct TALER_MerchantPublicKeyP merchant_pub;
  struct TALER_MerchantSignatureP merchant_sig;
  struct TALER_EXCHANGE_RefundHandle *rh;
  struct GNUNET_CURL_Context *ctx;
  json_t *refund_obj;
  CURL *eh;
  char arg_str[sizeof (struct TALER_CoinSpendPublicKeyP) * 2 + 32];

  GNUNET_assert (GNUNET_YES ==
                 TEAH_handle_is_ready (exchange));
  GNUNET_CRYPTO_eddsa_key_get_public (&merchant_priv->eddsa_priv,
                                      &merchant_pub.eddsa_pub);
  TALER_merchant_refund_sign (coin_pub,
                              h_contract_terms,
                              rtransaction_id,
                              amount,
                              merchant_priv,
                              &merchant_sig);
  {
    char pub_str[sizeof (struct TALER_CoinSpendPublicKeyP) * 2];
    char *end;

    end = GNUNET_STRINGS_data_to_string (
      coin_pub,
      sizeof (struct TALER_CoinSpendPublicKeyP),
      pub_str,
      sizeof (pub_str));
    *end = '\0';
    GNUNET_snprintf (arg_str,
                     sizeof (arg_str),
                     "/coins/%s/refund",
                     pub_str);
  }
  refund_obj = GNUNET_JSON_PACK (
    TALER_JSON_pack_amount ("refund_amount",
                            amount),
    GNUNET_JSON_pack_data_auto ("h_contract_terms",
                                h_contract_terms),
    GNUNET_JSON_pack_uint64 ("rtransaction_id",
                             rtransaction_id),
    GNUNET_JSON_pack_data_auto ("merchant_pub",
                                &merchant_pub),
    GNUNET_JSON_pack_data_auto ("merchant_sig",
                                &merchant_sig));
  rh = GNUNET_new (struct TALER_EXCHANGE_RefundHandle);
  rh->exchange = exchange;
  rh->cb = cb;
  rh->cb_cls = cb_cls;
  rh->url = TEAH_path_to_url (exchange,
                              arg_str);
  if (NULL == rh->url)
  {
    json_decref (refund_obj);
    GNUNET_free (rh);
    return NULL;
  }
  rh->h_contract_terms = *h_contract_terms;
  rh->coin_pub = *coin_pub;
  rh->merchant = merchant_pub;
  rh->rtransaction_id = rtransaction_id;
  rh->refund_amount = *amount;
  eh = TALER_EXCHANGE_curl_easy_get_ (rh->url);
  if ( (NULL == eh) ||
       (GNUNET_OK !=
        TALER_curl_easy_post (&rh->ctx,
                              eh,
                              refund_obj)) )
  {
    GNUNET_break (0);
    if (NULL != eh)
      curl_easy_cleanup (eh);
    json_decref (refund_obj);
    GNUNET_free (rh->url);
    GNUNET_free (rh);
    return NULL;
  }
  json_decref (refund_obj);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "URL for refund: `%s'\n",
              rh->url);
  ctx = TEAH_handle_to_context (exchange);
  rh->job = GNUNET_CURL_job_add2 (ctx,
                                  eh,
                                  rh->ctx.headers,
                                  &handle_refund_finished,
                                  rh);
  return rh;
}


void
TALER_EXCHANGE_refund_cancel (struct TALER_EXCHANGE_RefundHandle *refund)
{
  if (NULL != refund->job)
  {
    GNUNET_CURL_job_cancel (refund->job);
    refund->job = NULL;
  }
  GNUNET_free (refund->url);
  TALER_curl_easy_post_finished (&refund->ctx);
  GNUNET_free (refund);
}


/* end of exchange_api_refund.c */