merchant

taler-merchant-httpd_post-orders-ID-abort.c (29362B)

---

 /*
   This file is part of TALER
   (C) 2014-2021 Taler Systems SA
 
   TALER 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,
   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 taler-merchant-httpd_post-orders-ID-abort.c
  * @brief handling of POST /orders/$ID/abort requests
  * @author Marcello Stanisci
  * @author Christian Grothoff
  * @author Florian Dold
  */
 #include "platform.h"
 #include <taler/taler_json_lib.h>
 #include <taler/taler_exchange_service.h>
 #include "taler-merchant-httpd_exchanges.h"
 #include "taler-merchant-httpd_helper.h"
 #include "taler-merchant-httpd_post-orders-ID-abort.h"
 
 
 /**
  * How long to wait before giving up processing with the exchange?
  */
 #define ABORT_GENERIC_TIMEOUT (GNUNET_TIME_relative_multiply ( \
                                  GNUNET_TIME_UNIT_SECONDS, \
                                  30))
 
 /**
  * How often do we retry the (complex!) database transaction?
  */
 #define MAX_RETRIES 5
 
 /**
  * Information we keep for an individual call to the /abort handler.
  */
 struct AbortContext;
 
 /**
  * Information kept during a /abort request for each coin.
  */
 struct RefundDetails
 {
 
   /**
    * Public key of the coin.
    */
   struct TALER_CoinSpendPublicKeyP coin_pub;
 
   /**
    * Signature from the exchange confirming the refund.
    * Set if we were successful (status 200).
    */
   struct TALER_ExchangeSignatureP exchange_sig;
 
   /**
    * Public key used for @e exchange_sig.
    * Set if we were successful (status 200).
    */
   struct TALER_ExchangePublicKeyP exchange_pub;
 
   /**
    * Reference to the main AbortContext
    */
   struct AbortContext *ac;
 
   /**
    * Handle to the refund operation we are performing for
    * this coin, NULL after the operation is done.
    */
   struct TALER_EXCHANGE_RefundHandle *rh;
 
   /**
    * URL of the exchange that issued this coin.
    */
   char *exchange_url;
 
   /**
    * Body of the response from the exchange.  Note that the body returned MUST
    * be freed (if non-NULL).
    */
   json_t *exchange_reply;
 
   /**
    * Amount this coin contributes to the total purchase price.
    * This amount includes the deposit fee.
    */
   struct TALER_Amount amount_with_fee;
 
   /**
    * Offset of this coin into the `rd` array of all coins in the
    * @e ac.
    */
   unsigned int index;
 
   /**
    * HTTP status returned by the exchange (if any).
    */
   unsigned int http_status;
 
   /**
    * Did we try to process this refund yet?
    */
   bool processed;
 
   /**
    * Did we find the deposit in our own database?
    */
   bool found_deposit;
 };
 
 
 /**
  * Information we keep for an individual call to the /abort handler.
  */
 struct AbortContext
 {
 
   /**
    * Hashed contract terms (according to client).
    */
   struct TALER_PrivateContractHashP h_contract_terms;
 
   /**
    * Context for our operation.
    */
   struct TMH_HandlerContext *hc;
 
   /**
    * Stored in a DLL.
    */
   struct AbortContext *next;
 
   /**
    * Stored in a DLL.
    */
   struct AbortContext *prev;
 
   /**
    * Array with @e coins_cnt coins we are despositing.
    */
   struct RefundDetails *rd;
 
   /**
    * MHD connection to return to
    */
   struct MHD_Connection *connection;
 
   /**
    * Task called when the (suspended) processing for
    * the /abort request times out.
    * Happens when we don't get a response from the exchange.
    */
   struct GNUNET_SCHEDULER_Task *timeout_task;
 
   /**
    * Response to return, NULL if we don't have one yet.
    */
   struct MHD_Response *response;
 
   /**
    * Handle to the exchange that we are doing the abortment with.
    * (initially NULL while @e fo is trying to find a exchange).
    */
   struct TALER_EXCHANGE_Handle *mh;
 
   /**
    * Handle for operation to lookup /keys (and auditors) from
    * the exchange used for this transaction; NULL if no operation is
    * pending.
    */
   struct TMH_EXCHANGES_KeysOperation *fo;
 
   /**
    * URL of the exchange used for the last @e fo.
    */
   const char *current_exchange;
 
   /**
    * Number of coins this abort is for.  Length of the @e rd array.
    */
   size_t coins_cnt;
 
   /**
    * How often have we retried the 'main' transaction?
    */
   unsigned int retry_counter;
 
   /**
    * Number of transactions still pending.  Initially set to
    * @e coins_cnt, decremented on each transaction that
    * successfully finished.
    */
   size_t pending;
 
   /**
    * Number of transactions still pending for the currently selected
    * exchange.  Initially set to the number of coins started at the
    * exchange, decremented on each transaction that successfully
    * finished.  Once it hits zero, we pick the next exchange.
    */
   size_t pending_at_ce;
 
   /**
    * HTTP status code to use for the reply, i.e 200 for "OK".
    * Special value UINT_MAX is used to indicate hard errors
    * (no reply, return #MHD_NO).
    */
   unsigned int response_code;
 
   /**
    * #GNUNET_NO if the @e connection was not suspended,
    * #GNUNET_YES if the @e connection was suspended,
    * #GNUNET_SYSERR if @e connection was resumed to as
    * part of #MH_force_ac_resume during shutdown.
    */
   int suspended;
 
 };
 
 
 /**
  * Head of active abort context DLL.
  */
 static struct AbortContext *ac_head;
 
 /**
  * Tail of active abort context DLL.
  */
 static struct AbortContext *ac_tail;
 
 
 /**
  * Abort all pending /deposit operations.
  *
  * @param ac abort context to abort
  */
 static void
 abort_refunds (struct AbortContext *ac)
 {
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
               "Aborting pending /deposit operations\n");
   for (size_t i = 0; i<ac->coins_cnt; i++)
   {
     struct RefundDetails *rdi = &ac->rd[i];
 
     if (NULL != rdi->rh)
     {
       TALER_EXCHANGE_refund_cancel (rdi->rh);
       rdi->rh = NULL;
     }
   }
 }
 
 
 void
 TMH_force_ac_resume ()
 {
   for (struct AbortContext *ac = ac_head;
        NULL != ac;
        ac = ac->next)
   {
     abort_refunds (ac);
     if (NULL != ac->timeout_task)
     {
       GNUNET_SCHEDULER_cancel (ac->timeout_task);
       ac->timeout_task = NULL;
     }
     if (GNUNET_YES == ac->suspended)
     {
       ac->suspended = GNUNET_SYSERR;
       MHD_resume_connection (ac->connection);
     }
   }
 }
 
 
 /**
  * Resume the given abort context and send the given response.
  * Stores the response in the @a ac and signals MHD to resume
  * the connection.  Also ensures MHD runs immediately.
  *
  * @param ac abortment context
  * @param response_code response code to use
  * @param response response data to send back
  */
 static void
 resume_abort_with_response (struct AbortContext *ac,
                             unsigned int response_code,
                             struct MHD_Response *response)
 {
   abort_refunds (ac);
   ac->response_code = response_code;
   ac->response = response;
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
               "Resuming /abort handling as exchange interaction is done (%u)\n",
               response_code);
   if (NULL != ac->timeout_task)
   {
     GNUNET_SCHEDULER_cancel (ac->timeout_task);
     ac->timeout_task = NULL;
   }
   GNUNET_assert (GNUNET_YES == ac->suspended);
   ac->suspended = GNUNET_NO;
   MHD_resume_connection (ac->connection);
   TALER_MHD_daemon_trigger (); /* we resumed, kick MHD */
 }
 
 
 /**
  * Resume abortment processing with an error.
  *
  * @param ac operation to resume
  * @param http_status http status code to return
  * @param ec taler error code to return
  * @param msg human readable error message
  */
 static void
 resume_abort_with_error (struct AbortContext *ac,
                          unsigned int http_status,
                          enum TALER_ErrorCode ec,
                          const char *msg)
 {
   resume_abort_with_response (ac,
                               http_status,
                               TALER_MHD_make_error (ec,
                                                     msg));
 }
 
 
 /**
  * Generate a response that indicates abortment success.
  *
  * @param ac abortment context
  */
 static void
 generate_success_response (struct AbortContext *ac)
 {
   json_t *refunds;
   unsigned int hc = MHD_HTTP_OK;
 
   refunds = json_array ();
   if (NULL == refunds)
   {
     GNUNET_break (0);
     resume_abort_with_error (ac,
                              MHD_HTTP_INTERNAL_SERVER_ERROR,
                              TALER_EC_GENERIC_JSON_ALLOCATION_FAILURE,
                              "could not create JSON array");
     return;
   }
   for (size_t i = 0; i<ac->coins_cnt; i++)
   {
     struct RefundDetails *rdi = &ac->rd[i];
     json_t *detail;
 
     if (rdi->found_deposit)
     {
       if ( ( (MHD_HTTP_BAD_REQUEST <= rdi->http_status) &&
              (MHD_HTTP_NOT_FOUND != rdi->http_status) &&
              (MHD_HTTP_GONE != rdi->http_status) ) ||
            (0 == rdi->http_status) ||
            (NULL == rdi->exchange_reply) )
       {
         hc = MHD_HTTP_BAD_GATEWAY;
       }
     }
     if (! rdi->found_deposit)
     {
       detail = GNUNET_JSON_PACK (
         GNUNET_JSON_pack_string ("type",
                                  "undeposited"));
     }
     else
     {
       if (MHD_HTTP_OK != rdi->http_status)
       {
         detail = GNUNET_JSON_PACK (
           GNUNET_JSON_pack_string ("type",
                                    "failure"),
           GNUNET_JSON_pack_uint64 ("exchange_status",
                                    rdi->http_status),
           GNUNET_JSON_pack_uint64 ("exchange_code",
                                    (NULL != rdi->exchange_reply)
                                    ? TALER_JSON_get_error_code (
                                      rdi->exchange_reply)
                                    : TALER_EC_GENERIC_INVALID_RESPONSE),
           GNUNET_JSON_pack_allow_null (
             GNUNET_JSON_pack_object_incref ("exchange_reply",
                                             rdi->exchange_reply)));
       }
       else
       {
         detail = GNUNET_JSON_PACK (
           GNUNET_JSON_pack_string ("type",
                                    "success"),
           GNUNET_JSON_pack_uint64 ("exchange_status",
                                    rdi->http_status),
           GNUNET_JSON_pack_data_auto ("exchange_sig",
                                       &rdi->exchange_sig),
           GNUNET_JSON_pack_data_auto ("exchange_pub",
                                       &rdi->exchange_pub));
       }
     }
     GNUNET_assert (0 ==
                    json_array_append_new (refunds,
                                           detail));
   }
 
   /* Resume and send back the response.  */
   resume_abort_with_response (
     ac,
     hc,
     TALER_MHD_MAKE_JSON_PACK (
       GNUNET_JSON_pack_array_steal ("refunds",
                                     refunds)));
 }
 
 
 /**
  * Custom cleanup routine for a `struct AbortContext`.
  *
  * @param cls the `struct AbortContext` to clean up.
  */
 static void
 abort_context_cleanup (void *cls)
 {
   struct AbortContext *ac = cls;
 
   if (NULL != ac->timeout_task)
   {
     GNUNET_SCHEDULER_cancel (ac->timeout_task);
     ac->timeout_task = NULL;
   }
   abort_refunds (ac);
   for (size_t i = 0; i<ac->coins_cnt; i++)
   {
     struct RefundDetails *rdi = &ac->rd[i];
 
     if (NULL != rdi->exchange_reply)
     {
       json_decref (rdi->exchange_reply);
       rdi->exchange_reply = NULL;
     }
     GNUNET_free (rdi->exchange_url);
   }
   GNUNET_free (ac->rd);
   if (NULL != ac->fo)
   {
     TMH_EXCHANGES_keys4exchange_cancel (ac->fo);
     ac->fo = NULL;
   }
   if (NULL != ac->response)
   {
     MHD_destroy_response (ac->response);
     ac->response = NULL;
   }
   GNUNET_CONTAINER_DLL_remove (ac_head,
                                ac_tail,
                                ac);
   GNUNET_free (ac);
 }
 
 
 /**
  * Find the exchange we need to talk to for the next
  * pending deposit permission.
  *
  * @param ac abortment context we are processing
  */
 static void
 find_next_exchange (struct AbortContext *ac);
 
 
 /**
  * Function called with the result from the exchange (to be
  * passed back to the wallet).
  *
  * @param cls closure
  * @param rr response data
  */
 static void
 refund_cb (void *cls,
            const struct TALER_EXCHANGE_RefundResponse *rr)
 {
   struct RefundDetails *rd = cls;
   const struct TALER_EXCHANGE_HttpResponse *hr = &rr->hr;
   struct AbortContext *ac = rd->ac;
 
   rd->rh = NULL;
   rd->http_status = hr->http_status;
   rd->exchange_reply = json_incref ((json_t*) hr->reply);
   if (MHD_HTTP_OK == hr->http_status)
   {
     rd->exchange_pub = rr->details.ok.exchange_pub;
     rd->exchange_sig = rr->details.ok.exchange_sig;
   }
   ac->pending_at_ce--;
   if (0 == ac->pending_at_ce)
     find_next_exchange (ac);
 }
 
 
 /**
  * Function called with the result of our exchange lookup.
  *
  * @param cls the `struct AbortContext`
  * @param keys keys of the exchange
  * @param exchange representation of the exchange
  */
 static void
 process_abort_with_exchange (void *cls,
                              struct TALER_EXCHANGE_Keys *keys,
                              struct TMH_Exchange *exchange)
 {
   struct AbortContext *ac = cls;
 
   (void) exchange;
   ac->fo = NULL;
   GNUNET_assert (GNUNET_YES == ac->suspended);
   if (NULL == keys)
   {
     resume_abort_with_response (
       ac,
       MHD_HTTP_GATEWAY_TIMEOUT,
       TALER_MHD_make_error (
         TALER_EC_MERCHANT_GENERIC_EXCHANGE_TIMEOUT,
         NULL));
     return;
   }
   /* Initiate refund operation for all coins of
      the current exchange (!) */
   GNUNET_assert (0 == ac->pending_at_ce);
   for (size_t i = 0; i<ac->coins_cnt; i++)
   {
     struct RefundDetails *rdi = &ac->rd[i];
 
     if (rdi->processed)
       continue;
     GNUNET_assert (NULL == rdi->rh);
     if (0 != strcmp (rdi->exchange_url,
                      ac->current_exchange))
       continue;
     rdi->processed = true;
     ac->pending--;
     if (! rdi->found_deposit)
     {
       /* Coin wasn't even deposited yet, we do not need to refund it. */
       continue;
     }
     rdi->rh = TALER_EXCHANGE_refund (
       TMH_curl_ctx,
       ac->current_exchange,
       keys,
       &rdi->amount_with_fee,
       &ac->h_contract_terms,
       &rdi->coin_pub,
       0,                                /* rtransaction_id */
       &ac->hc->instance->merchant_priv,
       &refund_cb,
       rdi);
     if (NULL == rdi->rh)
     {
       GNUNET_break_op (0);
       resume_abort_with_error (ac,
                                MHD_HTTP_INTERNAL_SERVER_ERROR,
                                TALER_EC_MERCHANT_POST_ORDERS_ID_ABORT_EXCHANGE_REFUND_FAILED,
                                "Failed to start refund with exchange");
       return;
     }
     ac->pending_at_ce++;
   }
   /* Still continue if no coins for this exchange were deposited. */
   if (0 == ac->pending_at_ce)
     find_next_exchange (ac);
 }
 
 
 /**
  * Begin of the DB transaction.  If required (from
  * soft/serialization errors), the transaction can be
  * restarted here.
  *
  * @param ac abortment context to transact
  */
 static void
 begin_transaction (struct AbortContext *ac);
 
 
 /**
  * Find the exchange we need to talk to for the next
  * pending deposit permission.
  *
  * @param ac abortment context we are processing
  */
 static void
 find_next_exchange (struct AbortContext *ac)
 {
   for (size_t i = 0; i<ac->coins_cnt; i++)
   {
     struct RefundDetails *rdi = &ac->rd[i];
 
     if (! rdi->processed)
     {
       ac->current_exchange = rdi->exchange_url;
       ac->fo = TMH_EXCHANGES_keys4exchange (ac->current_exchange,
                                             false,
                                             &process_abort_with_exchange,
                                             ac);
       if (NULL == ac->fo)
       {
         /* strange, should have happened on pay! */
         GNUNET_break (0);
         resume_abort_with_error (ac,
                                  MHD_HTTP_INTERNAL_SERVER_ERROR,
                                  TALER_EC_MERCHANT_GENERIC_EXCHANGE_UNTRUSTED,
                                  ac->current_exchange);
         return;
       }
       return;
     }
   }
   ac->current_exchange = NULL;
   GNUNET_assert (0 == ac->pending);
   /* We are done with all the HTTP requests, go back and try
      the 'big' database transaction! (It should work now!) */
   begin_transaction (ac);
 }
 
 
 /**
  * Function called with information about a coin that was deposited.
  *
  * @param cls closure
  * @param exchange_url exchange where @a coin_pub was deposited
  * @param coin_pub public key of the coin
  * @param amount_with_fee amount the exchange will deposit for this coin
  * @param deposit_fee fee the exchange will charge for this coin
  * @param refund_fee fee the exchange will charge for refunding this coin
  */
 static void
 refund_coins (void *cls,
               const char *exchange_url,
               const struct TALER_CoinSpendPublicKeyP *coin_pub,
               const struct TALER_Amount *amount_with_fee,
               const struct TALER_Amount *deposit_fee,
               const struct TALER_Amount *refund_fee)
 {
   struct AbortContext *ac = cls;
   struct GNUNET_TIME_Timestamp now;
 
   (void) deposit_fee;
   (void) refund_fee;
   now = GNUNET_TIME_timestamp_get ();
   for (size_t i = 0; i<ac->coins_cnt; i++)
   {
     struct RefundDetails *rdi = &ac->rd[i];
     enum GNUNET_DB_QueryStatus qs;
 
     if ( (0 !=
           GNUNET_memcmp (coin_pub,
                          &rdi->coin_pub)) ||
          (0 !=
           strcmp (exchange_url,
                   rdi->exchange_url)) )
       continue; /* not in request */
     rdi->found_deposit = true;
     rdi->amount_with_fee = *amount_with_fee;
     /* Store refund in DB */
     qs = TMH_db->refund_coin (TMH_db->cls,
                               ac->hc->instance->settings.id,
                               &ac->h_contract_terms,
                               now,
                               coin_pub,
                               /* justification */
                               "incomplete abortment aborted");
     if (0 > qs)
     {
       TMH_db->rollback (TMH_db->cls);
       if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
       {
         begin_transaction (ac);
         return;
       }
       /* Always report on hard error as well to enable diagnostics */
       GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
       resume_abort_with_error (ac,
                                MHD_HTTP_INTERNAL_SERVER_ERROR,
                                TALER_EC_GENERIC_DB_STORE_FAILED,
                                "refund_coin");
       return;
     }
   } /* for all coins */
 }
 
 
 /**
  * Begin of the DB transaction.  If required (from soft/serialization errors),
  * the transaction can be restarted here.
  *
  * @param ac abortment context to transact
  */
 static void
 begin_transaction (struct AbortContext *ac)
 {
   enum GNUNET_DB_QueryStatus qs;
 
   /* Avoid re-trying transactions on soft errors forever! */
   if (ac->retry_counter++ > MAX_RETRIES)
   {
     GNUNET_break (0);
     resume_abort_with_error (ac,
                              MHD_HTTP_INTERNAL_SERVER_ERROR,
                              TALER_EC_GENERIC_DB_SOFT_FAILURE,
                              NULL);
     return;
   }
   GNUNET_assert (GNUNET_YES == ac->suspended);
 
   /* First, try to see if we have all we need already done */
   TMH_db->preflight (TMH_db->cls);
   if (GNUNET_OK !=
       TMH_db->start (TMH_db->cls,
                      "run abort"))
   {
     GNUNET_break (0);
     resume_abort_with_error (ac,
                              MHD_HTTP_INTERNAL_SERVER_ERROR,
                              TALER_EC_GENERIC_DB_START_FAILED,
                              NULL);
     return;
   }
 
   /* check payment was indeed incomplete
      (now that we are in the transaction scope!) */
   {
     struct TALER_PrivateContractHashP h_contract_terms;
     bool paid;
 
     qs = TMH_db->lookup_order_status (TMH_db->cls,
                                       ac->hc->instance->settings.id,
                                       ac->hc->infix,
                                       &h_contract_terms,
                                       &paid);
     switch (qs)
     {
     case GNUNET_DB_STATUS_SOFT_ERROR:
     case GNUNET_DB_STATUS_HARD_ERROR:
       /* Always report on hard error to enable diagnostics */
       GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
       TMH_db->rollback (TMH_db->cls);
       if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
       {
         begin_transaction (ac);
         return;
       }
       /* Always report on hard error as well to enable diagnostics */
       GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
       resume_abort_with_error (ac,
                                MHD_HTTP_INTERNAL_SERVER_ERROR,
                                TALER_EC_GENERIC_DB_FETCH_FAILED,
                                "order status");
       return;
     case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
       TMH_db->rollback (TMH_db->cls);
       resume_abort_with_error (ac,
                                MHD_HTTP_NOT_FOUND,
                                TALER_EC_MERCHANT_POST_ORDERS_ID_ABORT_CONTRACT_NOT_FOUND,
                                "Could not find contract");
       return;
     case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
       if (paid)
       {
         /* Payment is complete, refuse to abort. */
         TMH_db->rollback (TMH_db->cls);
         resume_abort_with_error (ac,
                                  MHD_HTTP_PRECONDITION_FAILED,
                                  TALER_EC_MERCHANT_POST_ORDERS_ID_ABORT_REFUND_REFUSED_PAYMENT_COMPLETE,
                                  "Payment was complete, refusing to abort");
         return;
       }
     }
     if (0 !=
         GNUNET_memcmp (&ac->h_contract_terms,
                        &h_contract_terms))
     {
       GNUNET_break_op (0);
       TMH_db->rollback (TMH_db->cls);
       resume_abort_with_error (ac,
                                MHD_HTTP_FORBIDDEN,
                                TALER_EC_MERCHANT_POST_ORDERS_ID_ABORT_CONTRACT_HASH_MISSMATCH,
                                "Provided hash does not match order on file");
       return;
     }
   }
 
   /* Mark all deposits we have in our database for the order as refunded. */
   qs = TMH_db->lookup_deposits (TMH_db->cls,
                                 ac->hc->instance->settings.id,
                                 &ac->h_contract_terms,
                                 &refund_coins,
                                 ac);
   if (0 > qs)
   {
     TMH_db->rollback (TMH_db->cls);
     if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
     {
       begin_transaction (ac);
       return;
     }
     /* Always report on hard error as well to enable diagnostics */
     GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
     resume_abort_with_error (ac,
                              MHD_HTTP_INTERNAL_SERVER_ERROR,
                              TALER_EC_GENERIC_DB_FETCH_FAILED,
                              "deposits");
     return;
   }
 
   qs = TMH_db->commit (TMH_db->cls);
   if (0 > qs)
   {
     TMH_db->rollback (TMH_db->cls);
     if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
     {
       begin_transaction (ac);
       return;
     }
     resume_abort_with_error (ac,
                              MHD_HTTP_INTERNAL_SERVER_ERROR,
                              TALER_EC_GENERIC_DB_COMMIT_FAILED,
                              NULL);
     return;
   }
 
   /* At this point, the refund got correctly committed
      into the database. Tell exchange about abort/refund. */
   if (ac->pending > 0)
   {
     find_next_exchange (ac);
     return;
   }
   generate_success_response (ac);
 }
 
 
 /**
  * Try to parse the abort request into the given abort context.
  * Schedules an error response in the connection on failure.
  *
  * @param connection HTTP connection we are receiving abortment on
  * @param hc context we use to handle the abortment
  * @param ac state of the /abort call
  * @return #GNUNET_OK on success,
  *         #GNUNET_NO on failure (response was queued with MHD)
  *         #GNUNET_SYSERR on hard error (MHD connection must be dropped)
  */
 static enum GNUNET_GenericReturnValue
 parse_abort (struct MHD_Connection *connection,
              struct TMH_HandlerContext *hc,
              struct AbortContext *ac)
 {
   const json_t *coins;
   struct GNUNET_JSON_Specification spec[] = {
     GNUNET_JSON_spec_array_const ("coins",
                                   &coins),
     GNUNET_JSON_spec_fixed_auto ("h_contract",
                                  &ac->h_contract_terms),
 
     GNUNET_JSON_spec_end ()
   };
   enum GNUNET_GenericReturnValue res;
 
   res = TALER_MHD_parse_json_data (connection,
                                    hc->request_body,
                                    spec);
   if (GNUNET_YES != res)
   {
     GNUNET_break_op (0);
     return res;
   }
   ac->coins_cnt = json_array_size (coins);
   if (0 == ac->coins_cnt)
   {
     GNUNET_break_op (0);
     return (MHD_YES ==
             TALER_MHD_reply_with_error (connection,
                                         MHD_HTTP_BAD_REQUEST,
                                         TALER_EC_MERCHANT_POST_ORDERS_ID_ABORT_COINS_ARRAY_EMPTY,
                                         "coins"))
       ? GNUNET_NO
       : GNUNET_SYSERR;
   }
   /* note: 1 coin = 1 deposit confirmation expected */
   ac->pending = ac->coins_cnt;
   ac->rd = GNUNET_new_array (ac->coins_cnt,
                              struct RefundDetails);
   /* This loop populates the array 'rd' in 'ac' */
   {
     unsigned int coins_index;
     json_t *coin;
     json_array_foreach (coins, coins_index, coin)
     {
       struct RefundDetails *rd = &ac->rd[coins_index];
       const char *exchange_url;
       struct GNUNET_JSON_Specification ispec[] = {
         TALER_JSON_spec_web_url ("exchange_url",
                                  &exchange_url),
         GNUNET_JSON_spec_fixed_auto ("coin_pub",
                                      &rd->coin_pub),
         GNUNET_JSON_spec_end ()
       };
 
       res = TALER_MHD_parse_json_data (connection,
                                        coin,
                                        ispec);
       if (GNUNET_YES != res)
       {
         GNUNET_break_op (0);
         return res;
       }
       rd->exchange_url = GNUNET_strdup (exchange_url);
       rd->index = coins_index;
       rd->ac = ac;
     }
   }
   GNUNET_log (GNUNET_ERROR_TYPE_INFO,
               "Handling /abort for order `%s' with contract hash `%s'\n",
               ac->hc->infix,
               GNUNET_h2s (&ac->h_contract_terms.hash));
   return GNUNET_OK;
 }
 
 
 /**
  * Handle a timeout for the processing of the abort request.
  *
  * @param cls our `struct AbortContext`
  */
 static void
 handle_abort_timeout (void *cls)
 {
   struct AbortContext *ac = cls;
 
   ac->timeout_task = NULL;
   GNUNET_assert (GNUNET_YES == ac->suspended);
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
               "Resuming abort with error after timeout\n");
   if (NULL != ac->fo)
   {
     TMH_EXCHANGES_keys4exchange_cancel (ac->fo);
     ac->fo = NULL;
   }
   resume_abort_with_error (ac,
                            MHD_HTTP_GATEWAY_TIMEOUT,
                            TALER_EC_MERCHANT_GENERIC_EXCHANGE_TIMEOUT,
                            NULL);
 }
 
 
 MHD_RESULT
 TMH_post_orders_ID_abort (const struct TMH_RequestHandler *rh,
                           struct MHD_Connection *connection,
                           struct TMH_HandlerContext *hc)
 {
   struct AbortContext *ac = hc->ctx;
 
   if (NULL == ac)
   {
     ac = GNUNET_new (struct AbortContext);
     GNUNET_CONTAINER_DLL_insert (ac_head,
                                  ac_tail,
                                  ac);
     ac->connection = connection;
     ac->hc = hc;
     hc->ctx = ac;
     hc->cc = &abort_context_cleanup;
   }
   if (GNUNET_SYSERR == ac->suspended)
     return MHD_NO; /* during shutdown, we don't generate any more replies */
   if (0 != ac->response_code)
   {
     MHD_RESULT res;
 
     /* We are *done* processing the request,
        just queue the response (!) */
     if (UINT_MAX == ac->response_code)
     {
       GNUNET_break (0);
       return MHD_NO; /* hard error */
     }
     res = MHD_queue_response (connection,
                               ac->response_code,
                               ac->response);
     MHD_destroy_response (ac->response);
     ac->response = NULL;
     GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                 "Queueing response (%u) for /abort (%s).\n",
                 (unsigned int) ac->response_code,
                 res ? "OK" : "FAILED");
     return res;
   }
   {
     enum GNUNET_GenericReturnValue ret;
 
     ret = parse_abort (connection,
                        hc,
                        ac);
     if (GNUNET_OK != ret)
       return (GNUNET_NO == ret)
              ? MHD_YES
              : MHD_NO;
   }
 
   /* Abort not finished, suspend while we interact with the exchange */
   GNUNET_assert (GNUNET_NO == ac->suspended);
   MHD_suspend_connection (connection);
   ac->suspended = GNUNET_YES;
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
               "Suspending abort handling while working with the exchange\n");
   ac->timeout_task = GNUNET_SCHEDULER_add_delayed (ABORT_GENERIC_TIMEOUT,
                                                    &handle_abort_timeout,
                                                    ac);
   begin_transaction (ac);
   return MHD_YES;
 }
 
 
 /* end of taler-merchant-httpd_post-orders-ID-abort.c */