path: root/src/backend/taler-merchant-httpd_post-orders-ID-pay.c

/*
   This file is part of TALER
   (C) 2014-2023 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-pay.c
 * @brief handling of POST /orders/$ID/pay requests
 * @author Marcello Stanisci
 * @author Christian Grothoff
 * @author Florian Dold
 */
#include "platform.h"
#include <taler/taler_dbevents.h>
#include <taler/taler_signatures.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-pay.h"
#include "taler-merchant-httpd_private-get-orders.h"


/**
 * How often do we retry the (complex!) database transaction?
 */
#define MAX_RETRIES 5

/**
 * Maximum number of coins that we allow per transaction
 */
#define MAX_COIN_ALLOWED_COINS 1024

/**
 * How often do we ask the exchange again about our
 * KYC status? Very rarely, as if the user actively
 * changes it, we should usually notice anyway.
 */
#define KYC_RETRY_FREQUENCY GNUNET_TIME_UNIT_WEEKS

/**
 * Information we keep for an individual call to the pay handler.
 */
struct PayContext;


/**
 * Information kept during a pay request for each coin.
 */
struct DepositConfirmation
{

  /**
   * Reference to the main PayContext
   */
  struct PayContext *pc;

  /**
   * URL of the exchange that issued this coin.
   */
  char *exchange_url;

  /**
   * Details about the coin being deposited.
   */
  struct TALER_EXCHANGE_CoinDepositDetail cdd;

  /**
   * Fee charged by the exchange for the deposit operation of this coin.
   */
  struct TALER_Amount deposit_fee;

  /**
   * Fee charged by the exchange for the refund operation of this coin.
   */
  struct TALER_Amount refund_fee;

  /**
   * Wire fee charged by the exchange of this coin.
   */
  struct TALER_Amount wire_fee;

  /**
   * If a minimum age was required (i. e. pc->minimum_age is large enough),
   * this is the signature of the minimum age (as a single uint8_t), using the
   * private key to the corresponding age group.  Might be all zeroes for no
   * age attestation.
   */
  struct TALER_AgeAttestation minimum_age_sig;

  /**
   * If a minimum age was required (i. e. pc->minimum_age is large enough),
   * this is the age commitment (i. e. age mask and vector of EdDSA public
   * keys, one per age group) that went into the mining of the coin.  The
   * SHA256 hash of the mask and the vector of public keys was bound to the
   * key.
   */
  struct TALER_AgeCommitment age_commitment;

  /**
   * Age mask in the denomination that defines the age groups.  Only
   * applicable, if minimum age was required.
   */
  struct TALER_AgeMask age_mask;

  /**
   * Offset of this coin into the `dc` array of all coins in the
   * @e pc.
   */
  unsigned int index;

  /**
   * true, if no field "age_commitment" was found in the JSON blob
   */
  bool no_age_commitment;

  /**
   * True, if no field "minimum_age_sig" was found in the JSON blob
   */
  bool no_minimum_age_sig;

  /**
   * true, if no field "h_age_commitment" was found in the JSON blob
   */
  bool no_h_age_commitment;

  /**
   * true if we found this coin in the database.
   */
  bool found_in_db;

  /**
   * true if we #deposit_paid_check() matched this coin in the database.
   */
  bool matched_in_db;

};


/**
 * Information kept during a pay request for each exchange.
 */
struct ExchangeGroup
{

  /**
   * Payment context this group is part of.
   */
  struct PayContext *pc;

  /**
   * Handle to the batch deposit operation we are performing for this
   * exchange, NULL after the operation is done.
   */
  struct TALER_EXCHANGE_BatchDepositHandle *bdh;

  /**
   * 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;

  /**
   * Handle for operation to lookup /wire from
   * the exchange used for this transaction; NULL if no operation is
   * pending.
   */
  struct TMH_EXCHANGES_WireOperation *gwo;

  /**
   * URL of the exchange that issued this coin. Aliases
   * the exchange URL of one of the coins, do not free!
   */
  const char *exchange_url;

  /**
   * Wire fee that applies to this exchange for the
   * given payment context's wire method.
   */
  struct TALER_Amount wire_fee;

  /**
   * true if we already tried a forced /keys download.
   */
  bool tried_force_keys;
};


/**
 * Information we keep for an individual call to the /pay handler.
 */
struct PayContext
{

  /**
   * Stored in a DLL.
   */
  struct PayContext *next;

  /**
   * Stored in a DLL.
   */
  struct PayContext *prev;

  /**
   * Array with @e num_exchange exchanges we are depositing
   * coins into.
   */
  struct ExchangeGroup **egs;

  /**
   * Array with @e coins_cnt coins we are despositing.
   */
  struct DepositConfirmation *dc;

  /**
   * MHD connection to return to
   */
  struct MHD_Connection *connection;

  /**
   * Details about the client's request.
   */
  struct TMH_HandlerContext *hc;

  /**
   * What wire method (of the @e mi) was selected by the wallet?
   * Set in #parse_pay().
   */
  struct TMH_WireMethod *wm;

  /**
   * Task called when the (suspended) processing for
   * the /pay 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;

  /**
   * Our contract (or NULL if not available).
   */
  json_t *contract_terms;

  /**
   * Placeholder for #TALER_MHD_parse_post_json() to keep its internal state.
   */
  void *json_parse_context;

  /**
   * Optional session id given in @e root.
   * NULL if not given.
   */
  char *session_id;

  /**
   * Transaction ID given in @e root.
   */
  const char *order_id;

  /**
   * Fulfillment URL from the contract, or NULL if we don't have one.
   */
  char *fulfillment_url;

  /**
   * Serial number of this order in the database (set once we did the lookup).
   */
  uint64_t order_serial;

  /**
   * Hashed proposal.
   */
  struct TALER_PrivateContractHashP h_contract_terms;

  /**
   * "h_wire" from @e contract_terms.  Used to identify
   * the instance's wire transfer method.
   */
  struct TALER_MerchantWireHashP h_wire;

  /**
   * Maximum fee the merchant is willing to pay, from @e root.
   * Note that IF the total fee of the exchange is higher, that is
   * acceptable to the merchant if the customer is willing to
   * pay the difference
   * (i.e. amount - max_fee <= actual-amount - actual-fee).
   */
  struct TALER_Amount max_fee;

  /**
   * Maximum wire fee the merchant is willing to pay, from @e root.
   * Note that IF the total fee of the exchange is higher, that is
   * acceptable to the merchant if the customer is willing to
   * pay the amorized difference.  Wire fees are charged over an
   * aggregate of several translations, hence unlike the deposit
   * fees, they are amortized over several customer's transactions.
   * The contract specifies under @e wire_fee_amortization how many
   * customer's transactions he expects the wire fees to be amortized
   * over on average.  Thus, if the wire fees are larger than
   * @e max_wire_fee, each customer is expected to contribute
   * $\frac{actual-wire-fee - max_wire_fee}{wire_fee_amortization}$.
   * The customer's contribution may be further reduced by the
   * difference between @e max_fee and the sum of the deposit fees.
   *
   * Default is that the merchant is unwilling to pay any wire fees.
   */
  struct TALER_Amount max_wire_fee;

  /**
   * Amount from @e root.  This is the amount the merchant expects
   * to make, minus @e max_fee.
   */
  struct TALER_Amount amount;

  /**
   * Considering all the coins with the "found_in_db" flag
   * set, what is the total amount we were so far paid on
   * this contract?
   */
  struct TALER_Amount total_paid;

  /**
   * Considering all the coins with the "found_in_db" flag
   * set, what is the total amount we had to pay in deposit
   * fees so far on this contract?
   */
  struct TALER_Amount total_fees_paid;

  /**
   * Considering all the coins with the "found_in_db" flag
   * set, what is the total amount we already refunded?
   */
  struct TALER_Amount total_refunded;

  /**
   * Wire transfer deadline. How soon would the merchant like the
   * wire transfer to be executed?
   */
  struct GNUNET_TIME_Timestamp wire_transfer_deadline;

  /**
   * Timestamp from @e contract_terms.
   */
  struct GNUNET_TIME_Timestamp timestamp;

  /**
   * Refund deadline from @e contract_terms.
   */
  struct GNUNET_TIME_Timestamp refund_deadline;

  /**
   * Deadline for the customer to pay for this proposal.
   */
  struct GNUNET_TIME_Timestamp pay_deadline;

  /**
   * Set to the POS key, if applicable for this order.
   */
  char *pos_key;

  /**
   * Algorithm chosen for generating the confirmation code.
   */
  enum TALER_MerchantConfirmationAlgorithm pos_alg;

  /**
   * Number of transactions that the wire fees are expected to be
   * amortized over.  Never zero, defaults (conservateively) to 1.
   * May be higher if merchants expect many small transactions to
   * be aggregated and thus wire fees to be reasonably amortized
   * due to aggregation.
   */
  uint32_t wire_fee_amortization;

  /**
   * Minimum age required for this purchase.
   */
  unsigned int minimum_age;

  /**
   * Number of coins this payment is made of.  Length
   * of the @e dc array.
   */
  unsigned int coins_cnt;

  /**
   * Number of exchanges involved in the payment. Length
   * of the @e eg array.
   */
  unsigned int num_exchanges;

  /**
   * How often have we retried the 'main' transaction?
   */
  unsigned int retry_counter;

  /**
   * Number of batch transactions pending.
   */
  unsigned int pending_at_eg;

  /**
   * Number of coin deposits pending.
   */
  unsigned int pending;

  /**
   * 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_pc_resume during shutdown.
   */
  enum GNUNET_GenericReturnValue suspended;

};


/**
 * Active KYC operation with an exchange.
 */
struct KycContext
{
  /**
   * Kept in a DLL.
   */
  struct KycContext *next;

  /**
   * Kept in a DLL.
   */
  struct KycContext *prev;

  /**
   * Looking for the exchange.
   */
  struct TMH_EXCHANGES_KeysOperation *fo;

  /**
   * Exchange this is about.
   */
  char *exchange_url;

  /**
   * Merchant instance this is for.
   */
  struct TMH_MerchantInstance *mi;

  /**
   * Wire method we are checking the status of.
   */
  struct TMH_WireMethod *wm;

  /**
   * Handle for the GET /deposits operation.
   */
  struct TALER_EXCHANGE_DepositGetHandle *dg;

  /**
   * Contract we are looking up.
   */
  struct TALER_PrivateContractHashP h_contract_terms;

  /**
   * Coin we are looking up.
   */
  struct TALER_CoinSpendPublicKeyP coin_pub;

  /**
   * Initial DB timestamp.
   */
  struct GNUNET_TIME_Timestamp kyc_timestamp;

  /**
   * Initial KYC status.
   */
  bool kyc_ok;

};


/**
 * Head of active pay context DLL.
 */
static struct PayContext *pc_head;

/**
 * Tail of active pay context DLL.
 */
static struct PayContext *pc_tail;

/**
 * Head of active KYC context DLL.
 */
static struct KycContext *kc_head;

/**
 * Tail of active KYC context DLL.
 */
static struct KycContext *kc_tail;


/**
 * Free resources used by @a kc.
 *
 * @param[in] kc object to free
 */
static void
destroy_kc (struct KycContext *kc)
{
  if (NULL != kc->fo)
  {
    TMH_EXCHANGES_keys4exchange_cancel (kc->fo);
    kc->fo = NULL;
  }
  if (NULL != kc->dg)
  {
    TALER_EXCHANGE_deposits_get_cancel (kc->dg);
    kc->dg = NULL;
  }
  TMH_instance_decref (kc->mi);
  kc->mi = NULL;
  GNUNET_free (kc->exchange_url);
  GNUNET_CONTAINER_DLL_remove (kc_head,
                               kc_tail,
                               kc);
  GNUNET_free (kc);
}


/**
 * Compute the timeout for a /pay request based on the number of coins
 * involved.
 *
 * @param num_coins number of coins
 * @returns timeout for the /pay request
 */
static struct GNUNET_TIME_Relative
get_pay_timeout (unsigned int num_coins)
{
  struct GNUNET_TIME_Relative t;

  /* FIXME:  Do some benchmarking to come up with a better timeout.
   * We've increased this value so the wallet integration test passes again
   * on my (Florian) machine.
   */
  t = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS,
                                     15 * (1 + (num_coins / 5)));

  return t;
}


void
TMH_force_pc_resume ()
{
  struct KycContext *kc;

  while (NULL != (kc = kc_head))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Aborting KYC check at %s\n",
                kc->exchange_url);
    destroy_kc (kc);
  }
  for (struct PayContext *pc = pc_head;
       NULL != pc;
       pc = pc->next)
  {
    if (NULL != pc->timeout_task)
    {
      GNUNET_SCHEDULER_cancel (pc->timeout_task);
      pc->timeout_task = NULL;
    }
    if (GNUNET_YES == pc->suspended)
    {
      pc->suspended = GNUNET_SYSERR;
      MHD_resume_connection (pc->connection);
    }
  }
}


/**
 * Resume the given pay context and send the given response.
 * Stores the response in the @a pc and signals MHD to resume
 * the connection.  Also ensures MHD runs immediately.
 *
 * @param pc payment context
 * @param response_code response code to use
 * @param response response data to send back
 */
static void
resume_pay_with_response (struct PayContext *pc,
                          unsigned int response_code,
                          struct MHD_Response *response)
{
  pc->response_code = response_code;
  pc->response = response;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Resuming /pay handling. HTTP status for our reply is %u.\n",
              response_code);
  if (NULL != pc->timeout_task)
  {
    GNUNET_SCHEDULER_cancel (pc->timeout_task);
    pc->timeout_task = NULL;
  }
  GNUNET_assert (GNUNET_YES == pc->suspended);
  pc->suspended = GNUNET_NO;
  MHD_resume_connection (pc->connection);
  TALER_MHD_daemon_trigger (); /* we resumed, kick MHD */
}


/**
 * Resume payment processing with an error.
 *
 * @param pc operation to resume
 * @param ec taler error code to return
 * @param msg human readable error message
 */
static void
resume_pay_with_error (struct PayContext *pc,
                       enum TALER_ErrorCode ec,
                       const char *msg)
{
  resume_pay_with_response (
    pc,
    TALER_ErrorCode_get_http_status_safe (ec),
    TALER_MHD_make_error (ec,
                          msg));
}


/**
 * Custom cleanup routine for a `struct PayContext`.
 *
 * @param cls the `struct PayContext` to clean up.
 */
static void
pay_context_cleanup (void *cls)
{
  struct PayContext *pc = cls;

  if (NULL != pc->timeout_task)
  {
    GNUNET_SCHEDULER_cancel (pc->timeout_task);
    pc->timeout_task = NULL;
  }
  if (NULL != pc->contract_terms)
  {
    json_decref (pc->contract_terms);
    pc->contract_terms = NULL;
  }
  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dc = &pc->dc[i];

    TALER_denom_sig_free (&dc->cdd.denom_sig);
    GNUNET_free (dc->exchange_url);
  }
  GNUNET_free (pc->dc);
  for (unsigned int i = 0; i<pc->num_exchanges; i++)
  {
    struct ExchangeGroup *eg = pc->egs[i];

    if (NULL != eg->fo)
      TMH_EXCHANGES_keys4exchange_cancel (eg->fo);
    if (NULL != eg->gwo)
      TMH_EXCHANGES_wire4exchange_cancel (eg->gwo);
    GNUNET_free (eg);
  }
  GNUNET_free (pc->egs);
  if (NULL != pc->response)
  {
    MHD_destroy_response (pc->response);
    pc->response = NULL;
  }
  GNUNET_free (pc->fulfillment_url);
  GNUNET_free (pc->session_id);
  GNUNET_CONTAINER_DLL_remove (pc_head,
                               pc_tail,
                               pc);
  GNUNET_free (pc->pos_key);
  GNUNET_free (pc);
}


/**
 * Execute the DB transaction.  If required (from
 * soft/serialization errors), the transaction can be
 * restarted here.
 *
 * @param pc payment context to transact
 */
static void
execute_pay_transaction (struct PayContext *pc);


/**
 * Function called with detailed wire transfer data.
 *
 * @param cls a `struct KycContext *`
 * @param dr HTTP response data
 */
static void
deposit_get_callback (
  void *cls,
  const struct TALER_EXCHANGE_GetDepositResponse *dr)
{
  struct KycContext *kc = cls;
  enum GNUNET_DB_QueryStatus qs;
  struct GNUNET_TIME_Timestamp now;

  kc->dg = NULL;
  now = GNUNET_TIME_timestamp_get ();
  switch (dr->hr.http_status)
  {
  case MHD_HTTP_OK:
    qs = TMH_db->account_kyc_set_status (
      TMH_db->cls,
      kc->mi->settings.id,
      &kc->wm->h_wire,
      kc->exchange_url,
      0LL,
      NULL, /* no signature */
      NULL, /* no signature */
      now,
      true,
      TALER_AML_NORMAL);
    GNUNET_break (qs > 0);
    break;
  case MHD_HTTP_ACCEPTED:
    qs = TMH_db->account_kyc_set_status (
      TMH_db->cls,
      kc->mi->settings.id,
      &kc->wm->h_wire,
      kc->exchange_url,
      dr->details.accepted.requirement_row,
      NULL, /* no signature */
      NULL, /* no signature */
      now,
      dr->details.accepted.kyc_ok,
      dr->details.accepted.aml_decision);
    GNUNET_break (qs > 0);
    break;
  default:
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "KYC check failed at %s with unexpected status %u\n",
                kc->exchange_url,
                dr->hr.http_status);
  }
  destroy_kc (kc);
}


/**
 * Function called with the result of our exchange lookup.
 *
 * @param cls the `struct KycContext`
 * @param keys NULL if exchange was not found to be acceptable
 */
static void
process_kyc_with_exchange (
  void *cls,
  struct TALER_EXCHANGE_Keys *keys)
{
  struct KycContext *kc = cls;

  kc->fo = NULL;
  if (NULL == keys)
  {
    destroy_kc (kc);
    return;
  }
  kc->dg = TALER_EXCHANGE_deposits_get (
    TMH_curl_ctx,
    kc->exchange_url,
    keys,
    &kc->mi->merchant_priv,
    &kc->wm->h_wire,
    &kc->h_contract_terms,
    &kc->coin_pub,
    GNUNET_TIME_UNIT_ZERO,
    &deposit_get_callback,
    kc);
  if (NULL == kc->dg)
  {
    GNUNET_break (0);
    destroy_kc (kc);
  }
}


/**
 * Function called from ``account_kyc_get_status``
 * with KYC status information for this merchant.
 *
 * @param cls a `struct KycContext *`
 * @param h_wire hash of the wire account
 * @param exchange_kyc_serial serial number for the KYC process at the exchange, 0 if unknown
 * @param payto_uri payto:// URI of the merchant's bank account
 * @param exchange_url base URL of the exchange for which this is a status
 * @param last_check when did we last get an update on our KYC status from the exchange
 * @param kyc_ok true if we satisfied the KYC requirements
 * @param aml_decision latest AML decision by the exchange
 */
static void
kyc_cb (
  void *cls,
  const struct TALER_MerchantWireHashP *h_wire,
  uint64_t exchange_kyc_serial,
  const char *payto_uri,
  const char *exchange_url,
  struct GNUNET_TIME_Timestamp last_check,
  bool kyc_ok,
  enum TALER_AmlDecisionState aml_decision)
{
  struct KycContext *kc = cls;

  (void) h_wire;
  (void) exchange_kyc_serial;
  (void) payto_uri;
  (void) exchange_url;
  kc->kyc_timestamp = last_check;
  kc->kyc_ok = kyc_ok;
  /* FIXME: act on aml_decision? */
}


/**
 * Check for our KYC status at @a exchange_url for the
 * payment of @a pc. First checks if we already have a
 * positive result from the exchange, and if not checks
 * with the exchange.
 *
 * @param pc payment context to use as starting point
 * @param eg exchange group of the exchange we are triggering on
 */
static void
check_kyc (struct PayContext *pc,
           const struct ExchangeGroup *eg)
{
  enum GNUNET_DB_QueryStatus qs;
  struct KycContext *kc;

  kc = GNUNET_new (struct KycContext);
  qs = TMH_db->account_kyc_get_status (TMH_db->cls,
                                       pc->hc->instance->settings.id,
                                       &pc->wm->h_wire,
                                       eg->exchange_url,
                                       &kyc_cb,
                                       kc);
  if (qs < 0)
  {
    GNUNET_break (0);
    GNUNET_free (kc);
    return;
  }
  if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs)
  {
    if (kc->kyc_ok)
    {
      GNUNET_free (kc);
      return; /* we are done */
    }
    if (GNUNET_TIME_relative_cmp (
          GNUNET_TIME_absolute_get_duration (
            kc->kyc_timestamp.abs_time),
          <,
          KYC_RETRY_FREQUENCY))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  "Not re-checking KYC status at `%s', as we already recently asked\n",
                  eg->exchange_url);
      GNUNET_free (kc);
      return;
    }
  }
  kc->mi = pc->hc->instance;
  kc->mi->rc++;
  kc->wm = pc->wm;
  kc->exchange_url = GNUNET_strdup (eg->exchange_url);
  kc->h_contract_terms = pc->h_contract_terms;
  /* find one of the coins of the batch */
  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dc = &pc->dc[i];

    if (0 != strcmp (eg->exchange_url,
                     pc->dc[i].exchange_url))
      continue;
    kc->coin_pub = dc->cdd.coin_pub;
    break;
  }
  GNUNET_CONTAINER_DLL_insert (kc_head,
                               kc_tail,
                               kc);
  kc->fo = TMH_EXCHANGES_keys4exchange (kc->exchange_url,
                                        &process_kyc_with_exchange,
                                        kc);
  if (NULL == kc->fo)
  {
    GNUNET_break (0);
    destroy_kc (kc);
  }
}


/**
 * Handle case where the batch deposit completed
 * with a status of #MHD_HTTP_OK.
 *
 * @param eg group that completed
 * @param dr response from the server
 */
static void
handle_batch_deposit_ok (struct ExchangeGroup *eg,
                         const struct TALER_EXCHANGE_BatchDepositResult *dr)
{
  struct PayContext *pc = eg->pc;
  enum GNUNET_DB_QueryStatus qs
    = GNUNET_DB_STATUS_SUCCESS_NO_RESULTS;

  /* store result to DB */
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Storing successful payment %s (%s) at instance `%s'\n",
              pc->hc->infix,
              GNUNET_h2s (&pc->h_contract_terms.hash),
              pc->hc->instance->settings.id);
  for (unsigned int r = 0; r<MAX_RETRIES; r++)
  {
    unsigned int j = 0;

    TMH_db->preflight (TMH_db->cls);
    if (GNUNET_OK !=
        TMH_db->start (TMH_db->cls,
                       "batch-deposit-insert-confirmation"))
    {
      resume_pay_with_response (
        pc,
        MHD_HTTP_INTERNAL_SERVER_ERROR,
        TALER_MHD_MAKE_JSON_PACK (
          TALER_JSON_pack_ec (
            TALER_EC_GENERIC_DB_START_FAILED),
          TMH_pack_exchange_reply (&dr->hr)));
      return;
    }
    for (unsigned int i = 0; i<pc->coins_cnt; i++)
    {
      struct DepositConfirmation *dc = &pc->dc[i];

      if (0 != strcmp (eg->exchange_url,
                       pc->dc[i].exchange_url))
        continue;
      if (dc->found_in_db)
        continue;
      /* NOTE: We might want to check if the order was fully paid concurrently
         by some other wallet here, and if so, issue an auto-refund. Right now,
         it is possible to over-pay if two wallets literally make a concurrent
         payment, as the earlier check for 'paid' is not in the same transaction
         scope as this 'insert' operation. */
      GNUNET_assert (j < dr->details.ok.num_signatures);
      qs = TMH_db->insert_deposit (
        TMH_db->cls,
        pc->hc->instance->settings.id,
        dr->details.ok.deposit_timestamp,
        &pc->h_contract_terms,
        &dc->cdd.coin_pub,
        dc->exchange_url,
        &dc->cdd.amount,
        &dc->deposit_fee,
        &dc->refund_fee,
        &dc->wire_fee,
        &pc->wm->h_wire,
        &dr->details.ok.exchange_sigs[j++],
        dr->details.ok.exchange_pub);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      {
        TMH_db->rollback (TMH_db->cls);
        break;
      }
      if (0 > qs)
      {
        /* Always report on hard error as well to enable diagnostics */
        GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
        /* Forward error including 'proof' for the body */
        resume_pay_with_error (pc,
                               TALER_EC_GENERIC_DB_STORE_FAILED,
                               "insert_deposit");
        return;
      }
    }
    qs = TMH_db->commit (TMH_db->cls);
    if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
    {
      TMH_db->rollback (TMH_db->cls);
      continue;
    }
    if (GNUNET_DB_STATUS_HARD_ERROR == qs)
    {
      GNUNET_break (0);
      resume_pay_with_error (pc,
                             TALER_EC_GENERIC_DB_COMMIT_FAILED,
                             "insert_deposit");
    }
    break; /* DB transaction succeeded */
  } /* FOR DB retries */
  if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
  {
    resume_pay_with_error (pc,
                           TALER_EC_GENERIC_DB_SOFT_FAILURE,
                           "insert_deposit");
    return;
  }

  /* Transaction is done, mark affected coins as complete as well. */
  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dc = &pc->dc[i];

    if (0 != strcmp (eg->exchange_url,
                     pc->dc[i].exchange_url))
      continue;
    if (dc->found_in_db)
      continue;
    dc->found_in_db = true;     /* well, at least NOW it'd be true ;-) */
    pc->pending--;
  }
  check_kyc (pc,
             eg);
}


/**
 * Callback to handle a batch deposit permission's response.
 *
 * @param cls a `struct ExchangeGroup`
 * @param dr HTTP response code details
 */
static void
batch_deposit_cb (
  void *cls,
  const struct TALER_EXCHANGE_BatchDepositResult *dr)
{
  struct ExchangeGroup *eg = cls;
  struct PayContext *pc = eg->pc;

  eg->bdh = NULL;
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Batch deposit completed with status %u\n",
              dr->hr.http_status);
  GNUNET_assert (GNUNET_YES == pc->suspended);
  pc->pending_at_eg--;
  switch (dr->hr.http_status)
  {
  case MHD_HTTP_OK:
    handle_batch_deposit_ok (eg,
                             dr);
    if (0 == pc->pending_at_eg)
      execute_pay_transaction (eg->pc);
    return;
  default:
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Deposit operation failed with HTTP code %u/%d\n",
                dr->hr.http_status,
                (int) dr->hr.ec);
    /* Transaction failed */
    if (5 == dr->hr.http_status / 100)
    {
      /* internal server error at exchange */
      resume_pay_with_response (pc,
                                MHD_HTTP_BAD_GATEWAY,
                                TALER_MHD_MAKE_JSON_PACK (
                                  TALER_JSON_pack_ec (
                                    TALER_EC_MERCHANT_GENERIC_EXCHANGE_UNEXPECTED_STATUS),
                                  TMH_pack_exchange_reply (&dr->hr)));
      return;
    }
    if (NULL == dr->hr.reply)
    {
      /* We can't do anything meaningful here, the exchange did something wrong */
      resume_pay_with_response (
        pc,
        MHD_HTTP_BAD_GATEWAY,
        TALER_MHD_MAKE_JSON_PACK (
          TALER_JSON_pack_ec (
            TALER_EC_MERCHANT_GENERIC_EXCHANGE_REPLY_MALFORMED),
          TMH_pack_exchange_reply (&dr->hr)));
      return;
    }

    /* Forward error, adding the "exchange_url" for which the
       error was being generated */
    if (TALER_EC_EXCHANGE_GENERIC_INSUFFICIENT_FUNDS == dr->hr.ec)
    {
      resume_pay_with_response (
        pc,
        MHD_HTTP_CONFLICT,
        TALER_MHD_MAKE_JSON_PACK (
          TALER_JSON_pack_ec (
            TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_INSUFFICIENT_FUNDS),
          TMH_pack_exchange_reply (&dr->hr),
          GNUNET_JSON_pack_data_auto ("exchange_url",
                                      &eg->exchange_url)));
      return;
    }
    resume_pay_with_response (
      pc,
      MHD_HTTP_BAD_GATEWAY,
      TALER_MHD_MAKE_JSON_PACK (
        TALER_JSON_pack_ec (
          TALER_EC_MERCHANT_GENERIC_EXCHANGE_UNEXPECTED_STATUS),
        TMH_pack_exchange_reply (&dr->hr),
        GNUNET_JSON_pack_data_auto ("exchange_url",
                                    &eg->exchange_url)));
    return;
  } /* end switch */
}


/**
 * Function called with the result of our exchange keys lookup.
 *
 * @param cls the `struct ExchangeGroup`
 * @param keys the keys of the exchange
 */
static void
process_pay_with_keys (
  void *cls,
  struct TALER_EXCHANGE_Keys *keys)
{
  struct ExchangeGroup *eg = cls;
  struct PayContext *pc = eg->pc;
  struct TMH_HandlerContext *hc = pc->hc;
  unsigned int group_size;

  eg->fo = NULL;
  GNUNET_SCHEDULER_begin_async_scope (&hc->async_scope_id);
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Processing payment with exchange %s\n",
              eg->exchange_url);
  GNUNET_assert (GNUNET_YES == pc->suspended);
  if (NULL == keys)
  {
    GNUNET_break_op (0);
    pc->pending_at_eg--;
    resume_pay_with_error (
      pc,
      TALER_EC_MERCHANT_GENERIC_EXCHANGE_TIMEOUT,
      NULL);
    return;
  }

  /* Initiate /batch-deposit operation for all coins of
     the current exchange (!) */
  group_size = 0;
  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dc = &pc->dc[i];
    const struct TALER_EXCHANGE_DenomPublicKey *denom_details;
    bool is_age_restricted_denom = false;

    if (0 != strcmp (eg->exchange_url,
                     pc->dc[i].exchange_url))
      continue;
    if (dc->found_in_db)
      continue;

    denom_details
      = TALER_EXCHANGE_get_denomination_key_by_hash (keys,
                                                     &dc->cdd.h_denom_pub);
    if (NULL == denom_details)
    {
      pc->pending_at_eg--;
      resume_pay_with_response (
        pc,
        MHD_HTTP_BAD_REQUEST,
        TALER_MHD_MAKE_JSON_PACK (
          TALER_JSON_pack_ec (
            TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_DENOMINATION_KEY_NOT_FOUND),
          GNUNET_JSON_pack_data_auto ("h_denom_pub",
                                      &dc->cdd.h_denom_pub),
          GNUNET_JSON_pack_allow_null (
            GNUNET_JSON_pack_object_steal (
              "exchange_keys",
              TALER_EXCHANGE_keys_to_json (keys)))));
      return;
    }
    dc->deposit_fee = denom_details->fees.deposit;
    dc->refund_fee = denom_details->fees.refund;

    if (GNUNET_TIME_absolute_is_past (
          denom_details->expire_deposit.abs_time))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "Denomination key offered by client has expired for deposits\n");
      pc->pending_at_eg--;
      resume_pay_with_response (
        pc,
        MHD_HTTP_GONE,
        TALER_MHD_MAKE_JSON_PACK (
          TALER_JSON_pack_ec (
            TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_DENOMINATION_DEPOSIT_EXPIRED),
          GNUNET_JSON_pack_data_auto ("h_denom_pub",
                                      &denom_details->h_key)));
      return;
    }


    /* Now that we have the details about the denomination, we can verify age
     * restriction requirements, if applicable. Note that denominations with an
     * age_mask equal to zero always pass the age verification.  */
    is_age_restricted_denom = (0 != denom_details->key.age_mask.bits);

    if (is_age_restricted_denom &&
        (0 < pc->minimum_age))
    {
      /* Minimum age given and restricted coin provided: We need to verify the
       * minimum age */
      unsigned int code = 0;

      if (dc->no_age_commitment)
      {
        GNUNET_break_op (0);
        code = TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_AGE_COMMITMENT_MISSING;
        goto AGE_FAIL;
      }
      dc->age_commitment.mask = denom_details->key.age_mask;
      if (((int) (dc->age_commitment.num + 1)) !=
          __builtin_popcount (dc->age_commitment.mask.bits))
      {
        GNUNET_break_op (0);
        code =
          TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_AGE_COMMITMENT_SIZE_MISMATCH;
        goto AGE_FAIL;
      }
      if (GNUNET_OK !=
          TALER_age_commitment_verify (
            &dc->age_commitment,
            pc->minimum_age,
            &dc->minimum_age_sig))
        code = TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_AGE_VERIFICATION_FAILED;
AGE_FAIL:
      if (0 < code)
      {
        pc->pending_at_eg--;
        GNUNET_free (dc->age_commitment.keys);
        resume_pay_with_response (
          pc,
          MHD_HTTP_BAD_REQUEST,
          TALER_MHD_MAKE_JSON_PACK (
            TALER_JSON_pack_ec (code),
            GNUNET_JSON_pack_data_auto ("h_denom_pub",
                                        &denom_details->h_key)));
        return;
      }

      /* Age restriction successfully verified!
       * Calculate the hash of the age commitment. */
      TALER_age_commitment_hash (&dc->age_commitment,
                                 &dc->cdd.h_age_commitment);
      GNUNET_free (dc->age_commitment.keys);
    }
    else if (is_age_restricted_denom &&
             dc->no_h_age_commitment)
    {
      /* The contract did not ask for a minimum_age but the client paid
       * with a coin that has age restriction enabled.  We lack the hash
       * of the age commitment in this case in order to verify the coin
       * and to deposit it with the exchange. */
      pc->pending_at_eg--;
      GNUNET_break_op (0);
      resume_pay_with_response (
        pc,
        MHD_HTTP_BAD_REQUEST,
        TALER_MHD_MAKE_JSON_PACK (
          TALER_JSON_pack_ec (
            TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_AGE_COMMITMENT_HASH_MISSING),
          GNUNET_JSON_pack_data_auto ("h_denom_pub",
                                      &denom_details->h_key)));
      return;
    }
    group_size++;
  }

  if (0 == group_size)
  {
    GNUNET_break (0);
    pc->pending_at_eg--;
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Group size zero, %u batch transactions remain pending\n",
                pc->pending_at_eg);
    if (0 == pc->pending_at_eg)
      execute_pay_transaction (pc);
    return;
  }

  {
    struct TALER_EXCHANGE_CoinDepositDetail cdds[group_size];
    struct TALER_EXCHANGE_DepositContractDetail dcd = {
      .wire_deadline = pc->wire_transfer_deadline,
      .merchant_payto_uri = pc->wm->payto_uri,
      .wire_salt = pc->wm->wire_salt,
      .h_contract_terms = pc->h_contract_terms,
      .policy_details = NULL, /* FIXME-oec #7270 */
      .timestamp = pc->timestamp,
      .merchant_pub = hc->instance->merchant_pub,
      .refund_deadline = pc->refund_deadline
    };
    enum TALER_ErrorCode ec;

    for (unsigned int i = 0; i<pc->coins_cnt; i++)
    {
      struct DepositConfirmation *dc = &pc->dc[i];

      if (dc->found_in_db)
        continue;
      if (0 != strcmp (dc->exchange_url,
                       eg->exchange_url))
        continue;
      cdds[i] = dc->cdd;
      dc->wire_fee = eg->wire_fee;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Initiating batch deposit with %u coins\n",
                group_size);
    eg->bdh = TALER_EXCHANGE_batch_deposit (
      TMH_curl_ctx,
      eg->exchange_url,
      keys,
      &dcd,
      group_size,
      cdds,
      &batch_deposit_cb,
      eg,
      &ec);
    if (NULL == eg->bdh)
    {
      /* Signature was invalid or some other constraint was not satisfied.  If
         the exchange was unavailable, we'd get that information in the
         callback. */
      pc->pending_at_eg--;
      GNUNET_break_op (0);
      resume_pay_with_response (
        pc,
        TALER_ErrorCode_get_http_status_safe (ec),
        TALER_MHD_MAKE_JSON_PACK (
          TALER_JSON_pack_ec (ec),
          GNUNET_JSON_pack_string ("exchange_url",
                                   eg->exchange_url)));
      return;
    }
    if (TMH_force_audit)
      TALER_EXCHANGE_batch_deposit_force_dc (eg->bdh);
  }
}


/**
 * Function called with the result of our exchange lookup.
 *
 * @param cls the `struct ExchangeGroup`
 * @param keys the keys of the exchange
 */
static void
process_pay_with_wire (
  void *cls,
  const struct TMH_ExchangeWireDetails *wire)
{
  struct ExchangeGroup *eg = cls;
  struct PayContext *pc = eg->pc;
  struct TMH_HandlerContext *hc = pc->hc;
  enum GNUNET_GenericReturnValue ret;

  eg->gwo = NULL;
  GNUNET_SCHEDULER_begin_async_scope (&hc->async_scope_id);
  if (NULL == wire)
  {
    GNUNET_break_op (0);
    pc->pending_at_eg--;
    /* FIXME: define more specific error code... */
    resume_pay_with_error (
      pc,
      TALER_EC_MERCHANT_GENERIC_EXCHANGE_CONNECT_FAILURE,
      NULL);
    return;
  }
  if (GNUNET_OK !=
      TMH_exchange_check_debit (wire,
                                pc->wm))
  {
    GNUNET_break_op (0);
    pc->pending_at_eg--;
    resume_pay_with_error (
      pc,
      TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_WIRE_METHOD_UNSUPPORTED,
      NULL);
    return;
  }
  ret = TMH_EXCHANGES_lookup_wire_fee (wire,
                                       pc->wm->wire_method,
                                       &eg->wire_fee);
  if (GNUNET_OK != ret)
  {
    enum TALER_ErrorCode ec;

    ec = (GNUNET_NO == ret)
      ? TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_WIRE_METHOD_UNSUPPORTED
      : TALER_EC_MERCHANT_GENERIC_EXCHANGE_WIRE_REQUEST_FAILED;
    pc->pending_at_eg--;
    GNUNET_break_op (0);
    resume_pay_with_error (
      pc,
      ec,
      pc->wm->wire_method);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Got /wire for %s, now going for /keys\n",
              eg->exchange_url);
  eg->fo = TMH_EXCHANGES_keys4exchange (eg->exchange_url,
                                        &process_pay_with_keys,
                                        eg);
  if (NULL == eg->fo)
  {
    GNUNET_break (0);
    pc->pending_at_eg--;
    resume_pay_with_error (pc,
                           TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_EXCHANGE_LOOKUP_FAILED,
                           "Failed to lookup exchange by URL");
    return;
  }
}


/**
 * Start batch deposits for all exchanges involved
 * in this payment.
 *
 * @param pc payment context we are processing
 */
static void
start_batch_deposits (struct PayContext *pc)
{
  for (unsigned int i = 0; i<pc->num_exchanges; i++)
  {
    struct ExchangeGroup *eg = pc->egs[i];
    bool have_coins = false;

    for (unsigned int j = 0; j<pc->coins_cnt; j++)
    {
      struct DepositConfirmation *dc = &pc->dc[j];

      if (0 != strcmp (eg->exchange_url,
                       pc->dc[j].exchange_url))
        continue;
      if (dc->found_in_db)
        continue;
      have_coins = true;
      break;
    }
    if (! have_coins)
      continue; /* no coins left to deposit at this exchange */
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Getting /wire details for %s\n",
                eg->exchange_url);
    eg->gwo = TMH_EXCHANGES_wire4exchange (eg->exchange_url,
                                           &process_pay_with_wire,
                                           eg);
    if (NULL == eg->gwo)
    {
      GNUNET_break (0);
      resume_pay_with_error (pc,
                             TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_EXCHANGE_LOOKUP_FAILED,
                             "Failed to lookup exchange by URL");
      return;
    }
    pc->pending_at_eg++;
  }
  if (0 == pc->pending_at_eg)
    execute_pay_transaction (pc);
}


/**
 * 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
 * @param wire_fee wire fee the exchange of this coin charges
 */
static void
check_coin_paid (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,
                 const struct TALER_Amount *wire_fee)
{
  struct PayContext *pc = cls;

  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dc = &pc->dc[i];

    if (dc->found_in_db)
      continue; /* processed earlier, skip "expensive" memcmp() */
    /* Get matching coin from results*/
    if ( (0 != GNUNET_memcmp (coin_pub,
                              &dc->cdd.coin_pub)) ||
         (0 !=
          strcmp (exchange_url,
                  dc->exchange_url)) ||
         (0 != TALER_amount_cmp (amount_with_fee,
                                 &dc->cdd.amount)) )
      continue; /* does not match, skip */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Deposit of coin `%s' already in our DB.\n",
                TALER_B2S (coin_pub));

    GNUNET_assert (0 <=
                   TALER_amount_add (&pc->total_paid,
                                     &pc->total_paid,
                                     amount_with_fee));
    GNUNET_assert (0 <=
                   TALER_amount_add (&pc->total_fees_paid,
                                     &pc->total_fees_paid,
                                     deposit_fee));
    dc->deposit_fee = *deposit_fee;
    dc->refund_fee = *refund_fee;
    dc->wire_fee = *wire_fee;
    dc->cdd.amount = *amount_with_fee;
    dc->found_in_db = true;
    pc->pending--;
  }
}


/**
 * Function called with information about a refund.  Check if this coin was
 * claimed by the wallet for the transaction, and if so add the refunded
 * amount to the pc's "total_refunded" amount.
 *
 * @param cls closure with a `struct PayContext`
 * @param coin_pub public coin from which the refund comes from
 * @param refund_amount refund amount which is being taken from @a coin_pub
 */
static void
check_coin_refunded (void *cls,
                     const struct TALER_CoinSpendPublicKeyP *coin_pub,
                     const struct TALER_Amount *refund_amount)
{
  struct PayContext *pc = cls;

  /* We look at refunds here that apply to the coins
     that the customer is currently trying to pay us with.

     Such refunds are not "normal" refunds, but abort-pay refunds, which are
     given in the case that the wallet aborts the payment.
     In the case the wallet then decides to complete the payment *after* doing
     an abort-pay refund (an unusual but possible case), we need
     to make sure that existing refunds are accounted for. */

  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dc = &pc->dc[i];

    /* Get matching coins from results.  */
    if (0 != GNUNET_memcmp (coin_pub,
                            &dc->cdd.coin_pub))
      continue;
    GNUNET_assert (0 <=
                   TALER_amount_add (&pc->total_refunded,
                                     &pc->total_refunded,
                                     refund_amount));
    break;
  }
}


/**
 * Check whether the amount paid is sufficient to cover the price.
 *
 * @param pc payment context to check
 * @return true if the payment is sufficient, false if it is
 *         insufficient
 */
static bool
check_payment_sufficient (struct PayContext *pc)
{
  struct TALER_Amount acc_fee;
  struct TALER_Amount acc_amount;
  struct TALER_Amount final_amount;
  struct TALER_Amount wire_fee_delta;
  struct TALER_Amount wire_fee_customer_contribution;
  struct TALER_Amount total_wire_fee;
  struct TALER_Amount total_needed;

  if (0 == pc->coins_cnt)
  {
    return ((0 == pc->amount.value) &&
            (0 == pc->amount.fraction));
  }

  acc_fee = pc->dc[0].deposit_fee;
  total_wire_fee = pc->dc[0].wire_fee;
  acc_amount = pc->dc[0].cdd.amount;

  /**
   * This loops calculates what are the deposit fee / total
   * amount with fee / and wire fee, for all the coins.
   */
  for (unsigned int i = 1; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dc = &pc->dc[i];

    GNUNET_assert (dc->found_in_db);
    if ( (0 >
          TALER_amount_add (&acc_fee,
                            &dc->deposit_fee,
                            &acc_fee)) ||
         (0 >
          TALER_amount_add (&acc_amount,
                            &dc->cdd.amount,
                            &acc_amount)) )
    {
      GNUNET_break (0);
      /* Overflow in these amounts? Very strange. */
      resume_pay_with_error (pc,
                             TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_AMOUNT_OVERFLOW,
                             "Overflow adding up amounts");
      return false;
    }
    if (1 ==
        TALER_amount_cmp (&dc->deposit_fee,
                          &dc->cdd.amount))
    {
      GNUNET_break_op (0);
      resume_pay_with_error (pc,
                             TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_FEES_EXCEED_PAYMENT,
                             "Deposit fees exceed coin's contribution");
      return false;
    }

    /* If exchange differs, add wire fee */
    {
      bool new_exchange = true;

      for (unsigned int j = 0; j<i; j++)
        if (0 == strcasecmp (dc->exchange_url,
                             pc->dc[j].exchange_url))
        {
          new_exchange = false;
          break;
        }

      if (! new_exchange)
        continue;

      if (GNUNET_OK !=
          TALER_amount_cmp_currency (&total_wire_fee,
                                     &dc->wire_fee))
      {
        GNUNET_break_op (0);
        resume_pay_with_error (pc,
                               TALER_EC_GENERIC_CURRENCY_MISMATCH,
                               total_wire_fee.currency);
        return false;
      }
      if (0 >
          TALER_amount_add (&total_wire_fee,
                            &total_wire_fee,
                            &dc->wire_fee))
      {
        GNUNET_break (0);
        resume_pay_with_error (pc,
                               TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_EXCHANGE_WIRE_FEE_ADDITION_FAILED,
                               "could not add exchange wire fee to total");
        return false;
      }
    }
  } /* deposit loop */

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Amount received from wallet: %s\n",
              TALER_amount2s (&acc_amount));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Deposit fee for all coins: %s\n",
              TALER_amount2s (&acc_fee));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Total wire fee: %s\n",
              TALER_amount2s (&total_wire_fee));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Max wire fee: %s\n",
              TALER_amount2s (&pc->max_wire_fee));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Deposit fee limit for merchant: %s\n",
              TALER_amount2s (&pc->max_fee));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Total refunded amount: %s\n",
              TALER_amount2s (&pc->total_refunded));

  /* Now compare exchange wire fee compared to
   * what we are willing to pay */
  if (GNUNET_YES !=
      TALER_amount_cmp_currency (&total_wire_fee,
                                 &pc->max_wire_fee))
  {
    GNUNET_break (0);
    resume_pay_with_error (pc,
                           TALER_EC_GENERIC_CURRENCY_MISMATCH,
                           total_wire_fee.currency);
    return false;
  }

  switch (TALER_amount_subtract (&wire_fee_delta,
                                 &total_wire_fee,
                                 &pc->max_wire_fee))
  {
  case TALER_AAR_RESULT_POSITIVE:
    /* Actual wire fee is indeed higher than our maximum,
       compute how much the customer is expected to cover!  */
    TALER_amount_divide (&wire_fee_customer_contribution,
                         &wire_fee_delta,
                         pc->wire_fee_amortization);
    break;
  case TALER_AAR_RESULT_ZERO:
  case TALER_AAR_INVALID_NEGATIVE_RESULT:
    /* Wire fee threshold is still above the wire fee amount.
       Customer is not going to contribute on this.  */
    GNUNET_assert (GNUNET_OK ==
                   TALER_amount_set_zero (total_wire_fee.currency,
                                          &wire_fee_customer_contribution));
    break;
  default:
    GNUNET_assert (0);
  }

  /* add wire fee contribution to the total fees */
  if (0 >
      TALER_amount_add (&acc_fee,
                        &acc_fee,
                        &wire_fee_customer_contribution))
  {
    GNUNET_break (0);
    resume_pay_with_error (pc,
                           TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_AMOUNT_OVERFLOW,
                           "Overflow adding up amounts");
    return false;
  }
  if (-1 == TALER_amount_cmp (&pc->max_fee,
                              &acc_fee))
  {
    /**
     * Sum of fees of *all* the different exchanges of all the coins are
     * higher than the fixed limit that the merchant is willing to pay.  The
     * difference must be paid by the customer.
     */
    struct TALER_Amount excess_fee;

    /* compute fee amount to be covered by customer */
    GNUNET_assert (TALER_AAR_RESULT_POSITIVE ==
                   TALER_amount_subtract (&excess_fee,
                                          &acc_fee,
                                          &pc->max_fee));
    /* add that to the total */
    if (0 >
        TALER_amount_add (&total_needed,
                          &excess_fee,
                          &pc->amount))
    {
      GNUNET_break (0);
      resume_pay_with_error (pc,
                             TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_AMOUNT_OVERFLOW,
                             "Overflow adding up amounts");
      return false;
    }
  }
  else
  {
    /* Fees are fully covered by the merchant, all we require
       is that the total payment is not below the contract's amount */
    total_needed = pc->amount;
  }

  /* Do not count refunds towards the payment */
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Subtracting total refunds from paid amount: %s\n",
              TALER_amount2s (&pc->total_refunded));
  if (0 >
      TALER_amount_subtract (&final_amount,
                             &acc_amount,
                             &pc->total_refunded))
  {
    GNUNET_break (0);
    resume_pay_with_error (pc,
                           TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_REFUNDS_EXCEED_PAYMENTS,
                           "refunded amount exceeds total payments");
    return false;
  }

  if (-1 == TALER_amount_cmp (&final_amount,
                              &total_needed))
  {
    /* acc_amount < total_needed */
    if (-1 < TALER_amount_cmp (&acc_amount,
                               &total_needed))
    {
      GNUNET_break_op (0);
      resume_pay_with_error (pc,
                             TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_REFUNDED,
                             "contract not paid up due to refunds");
    }
    else if (-1 < TALER_amount_cmp (&acc_amount,
                                    &pc->amount))
    {
      GNUNET_break_op (0);
      resume_pay_with_error (pc,
                             TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_INSUFFICIENT_DUE_TO_FEES,
                             "contract not paid up due to fees (client may have calculated them badly)");
    }
    else
    {
      GNUNET_break_op (0);
      resume_pay_with_error (pc,
                             TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_PAYMENT_INSUFFICIENT,
                             "payment insufficient");
    }
    return false;
  }
  return true;
}


/**
 * Use database to notify other clients about the
 * payment being completed.
 *
 * @param pc context to trigger notification for
 */
static void
trigger_payment_notification (struct PayContext *pc)
{
  {
    struct TMH_OrderPayEventP pay_eh = {
      .header.size = htons (sizeof (pay_eh)),
      .header.type = htons (TALER_DBEVENT_MERCHANT_ORDER_PAID),
      .merchant_pub = pc->hc->instance->merchant_pub
    };

    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Notifying clients about payment of order %s\n",
                pc->order_id);
    GNUNET_CRYPTO_hash (pc->order_id,
                        strlen (pc->order_id),
                        &pay_eh.h_order_id);
    TMH_db->event_notify (TMH_db->cls,
                          &pay_eh.header,
                          NULL,
                          0);
  }
  if ( (NULL != pc->session_id) &&
       (NULL != pc->fulfillment_url) )
  {
    struct TMH_SessionEventP session_eh = {
      .header.size = htons (sizeof (session_eh)),
      .header.type = htons (TALER_DBEVENT_MERCHANT_SESSION_CAPTURED),
      .merchant_pub = pc->hc->instance->merchant_pub
    };

    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Notifying clients about session change to %s for %s\n",
                pc->session_id,
                pc->fulfillment_url);
    GNUNET_CRYPTO_hash (pc->session_id,
                        strlen (pc->session_id),
                        &session_eh.h_session_id);
    GNUNET_CRYPTO_hash (pc->fulfillment_url,
                        strlen (pc->fulfillment_url),
                        &session_eh.h_fulfillment_url);
    TMH_db->event_notify (TMH_db->cls,
                          &session_eh.header,
                          NULL,
                          0);
  }
}


/**
 * Generate response (payment successful)
 *
 * @param[in,out] pc payment context where the payment was successful
 */
static void
generate_success_response (struct PayContext *pc)
{
  struct GNUNET_CRYPTO_EddsaSignature sig;
  char *pos_confirmation;

  /* Sign on our end (as the payment did go through, even if it may
     have been refunded already) */
  TALER_merchant_pay_sign (&pc->h_contract_terms,
                           &pc->hc->instance->merchant_priv,
                           &sig);
  /* Build the response */
  pos_confirmation = (NULL == pc->pos_key)
    ? NULL
    : TALER_build_pos_confirmation (pc->pos_key,
                                    pc->pos_alg,
                                    &pc->amount,
                                    pc->timestamp);
  resume_pay_with_response (
    pc,
    MHD_HTTP_OK,
    TALER_MHD_MAKE_JSON_PACK (
      GNUNET_JSON_pack_allow_null (
        GNUNET_JSON_pack_string ("pos_confirmation",
                                 pos_confirmation)),
      GNUNET_JSON_pack_data_auto ("sig",
                                  &sig)));
  GNUNET_free (pos_confirmation);
}


static void
execute_pay_transaction (struct PayContext *pc)
{
  struct TMH_HandlerContext *hc = pc->hc;
  const char *instance_id = hc->instance->settings.id;

  /* Avoid re-trying transactions on soft errors forever! */
  if (pc->retry_counter++ > MAX_RETRIES)
  {
    GNUNET_break (0);
    resume_pay_with_error (pc,
                           TALER_EC_GENERIC_DB_SOFT_FAILURE,
                           NULL);
    return;
  }
  GNUNET_assert (GNUNET_YES == pc->suspended);

  /* Initialize some amount accumulators
     (used in check_coin_paid(), check_coin_refunded()
     and check_payment_sufficient()). */
  GNUNET_break (GNUNET_OK ==
                TALER_amount_set_zero (pc->amount.currency,
                                       &pc->total_paid));
  GNUNET_break (GNUNET_OK ==
                TALER_amount_set_zero (pc->amount.currency,
                                       &pc->total_fees_paid));
  GNUNET_break (GNUNET_OK ==
                TALER_amount_set_zero (pc->amount.currency,
                                       &pc->total_refunded));
  for (unsigned int i = 0; i<pc->coins_cnt; i++)
    pc->dc[i].found_in_db = false;
  pc->pending = pc->coins_cnt;

  /* 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 pay"))
  {
    GNUNET_break (0);
    resume_pay_with_error (pc,
                           TALER_EC_GENERIC_DB_START_FAILED,
                           NULL);
    return;
  }

  {
    enum GNUNET_DB_QueryStatus qs;

    /* Check if some of these coins already succeeded for _this_ contract.  */
    qs = TMH_db->lookup_deposits (TMH_db->cls,
                                  instance_id,
                                  &pc->h_contract_terms,
                                  &check_coin_paid,
                                  pc);
    if (0 > qs)
    {
      TMH_db->rollback (TMH_db->cls);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      {
        execute_pay_transaction (pc);
        return;
      }
      /* Always report on hard error as well to enable diagnostics */
      GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
      resume_pay_with_error (pc,
                             TALER_EC_GENERIC_DB_FETCH_FAILED,
                             "lookup deposits");
      return;
    }
  }


  {
    enum GNUNET_DB_QueryStatus qs;

    /* Check if we refunded some of the coins */
    qs = TMH_db->lookup_refunds (TMH_db->cls,
                                 instance_id,
                                 &pc->h_contract_terms,
                                 &check_coin_refunded,
                                 pc);
    if (0 > qs)
    {
      TMH_db->rollback (TMH_db->cls);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      {
        execute_pay_transaction (pc);
        return;
      }
      /* Always report on hard error as well to enable diagnostics */
      GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
      resume_pay_with_error (pc,
                             TALER_EC_GENERIC_DB_FETCH_FAILED,
                             "lookup refunds");
      return;
    }
  }

  /* Check if there are coins that still need to be processed */
  if (0 != pc->pending)
  {
    /* we made no DB changes, so we can just rollback */
    TMH_db->rollback (TMH_db->cls);

    /* Ok, we need to first go to the network to process more coins.
       We that interaction in *tiny* transactions (hence the rollback
       above). */
    start_batch_deposits (pc);
    return;
  }

  /* 0 == pc->pending: all coins processed, let's see if that was enough */
  if (! check_payment_sufficient (pc))
  {
    /* check_payment_sufficient() will have queued an error already.
       We need to still abort the transaction. */
    TMH_db->rollback (TMH_db->cls);
    return;
  }
  /* Payment succeeded, save in database */
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Order `%s' (%s) was fully paid\n",
              pc->order_id,
              GNUNET_h2s (&pc->h_contract_terms.hash));
  {
    enum GNUNET_DB_QueryStatus qs;

    qs = TMH_db->mark_contract_paid (TMH_db->cls,
                                     instance_id,
                                     &pc->h_contract_terms,
                                     pc->session_id);
    if (qs < 0)
    {
      TMH_db->rollback (TMH_db->cls);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      {
        execute_pay_transaction (pc);
        return;
      }
      GNUNET_break (0);
      resume_pay_with_error (pc,
                             TALER_EC_GENERIC_DB_STORE_FAILED,
                             "mark contract paid");
      return;
    }
  }

  TMH_notify_order_change (hc->instance,
                           TMH_OSF_CLAIMED | TMH_OSF_PAID,
                           pc->timestamp,
                           pc->order_serial);
  {
    enum GNUNET_DB_QueryStatus qs;
    json_t *jhook;

    jhook = GNUNET_JSON_PACK (
      GNUNET_JSON_pack_object_incref ("contract_terms",
                                      pc->contract_terms),
      GNUNET_JSON_pack_string ("order_id",
                               pc->order_id)
      );
    GNUNET_assert (NULL != jhook);
    qs = TMH_trigger_webhook (pc->hc->instance->settings.id,
                              "pay",
                              jhook);
    json_decref (jhook);
    if (qs < 0)
    {
      TMH_db->rollback (TMH_db->cls);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      {
        execute_pay_transaction (pc);
        return;
      }
      GNUNET_break (0);
      resume_pay_with_error (pc,
                             TALER_EC_GENERIC_DB_STORE_FAILED,
                             "failed to trigger webhooks");
      return;
    }
  }
  {
    enum GNUNET_DB_QueryStatus qs;

    /* Now commit! */
    qs = TMH_db->commit (TMH_db->cls);
    if (0 > qs)
    {
      /* commit failed */
      TMH_db->rollback (TMH_db->cls);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      {
        execute_pay_transaction (pc);
        return;
      }
      GNUNET_break (0);
      resume_pay_with_error (pc,
                             TALER_EC_GENERIC_DB_COMMIT_FAILED,
                             NULL);
      return;
    }
    trigger_payment_notification (pc);
  }
  generate_success_response (pc);
}


/**
 * Try to parse the pay request into the given pay context.
 * Schedules an error response in the connection on failure.
 *
 * @param[in,out] pc context we use to handle the payment
 * @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_pay (struct PayContext *pc)
{
  const char *session_id = NULL;
  const json_t *coins;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_array_const ("coins",
                                  &coins),
    GNUNET_JSON_spec_mark_optional (
      GNUNET_JSON_spec_string ("session_id",
                               &session_id),
      NULL),
    GNUNET_JSON_spec_end ()
  };

  {
    enum GNUNET_GenericReturnValue res;

    res = TALER_MHD_parse_json_data (pc->connection,
                                     pc->hc->request_body,
                                     spec);
    if (GNUNET_YES != res)
    {
      GNUNET_break_op (0);
      return res;
    }
  }

  /* copy session ID (if set) */
  if (NULL != session_id)
  {
    pc->session_id = GNUNET_strdup (session_id);
  }
  else
  {
    /* use empty string as default if client didn't specify it */
    pc->session_id = GNUNET_strdup ("");
  }
  pc->coins_cnt = json_array_size (coins);
  if (pc->coins_cnt > MAX_COIN_ALLOWED_COINS)
  {
    GNUNET_break_op (0);
    return (MHD_YES ==
            TALER_MHD_reply_with_error (
              pc->connection,
              MHD_HTTP_BAD_REQUEST,
              TALER_EC_GENERIC_PARAMETER_MALFORMED,
              "'coins' array too long"))
        ? GNUNET_NO
        : GNUNET_SYSERR;
  }

  /* note: 1 coin = 1 deposit confirmation expected */
  pc->dc = GNUNET_new_array (pc->coins_cnt,
                             struct DepositConfirmation);

  /* This loop populates the array 'dc' in 'pc' */
  {
    unsigned int coins_index;
    json_t *coin;

    json_array_foreach (coins, coins_index, coin)
    {
      struct DepositConfirmation *dc = &pc->dc[coins_index];
      const char *exchange_url;
      struct GNUNET_JSON_Specification ispec[] = {
        GNUNET_JSON_spec_fixed_auto ("coin_sig",
                                     &dc->cdd.coin_sig),
        GNUNET_JSON_spec_fixed_auto ("coin_pub",
                                     &dc->cdd.coin_pub),
        TALER_JSON_spec_denom_sig ("ub_sig",
                                   &dc->cdd.denom_sig),
        GNUNET_JSON_spec_fixed_auto ("h_denom",
                                     &dc->cdd.h_denom_pub),
        TALER_JSON_spec_amount ("contribution",
                                TMH_currency,
                                &dc->cdd.amount),
        GNUNET_JSON_spec_string ("exchange_url",
                                 &exchange_url),
        /* if a minimum age was required, the minimum_age_sig and
         * age_commitment must be provided */
        GNUNET_JSON_spec_mark_optional (
          GNUNET_JSON_spec_fixed_auto ("minimum_age_sig",
                                       &dc->minimum_age_sig),
          &dc->no_minimum_age_sig),
        GNUNET_JSON_spec_mark_optional (
          TALER_JSON_spec_age_commitment ("age_commitment",
                                          &dc->age_commitment),
          &dc->no_age_commitment),
        /* if minimum age was not required, but coin with age restriction set
         * was used, h_age_commitment must be provided. */
        GNUNET_JSON_spec_mark_optional (
          GNUNET_JSON_spec_fixed_auto ("h_age_commitment",
                                       &dc->cdd.h_age_commitment),
          &dc->no_h_age_commitment),
        GNUNET_JSON_spec_end ()
      };
      enum GNUNET_GenericReturnValue res;
      bool have_eg = false;

      res = TALER_MHD_parse_json_data (pc->connection,
                                       coin,
                                       ispec);
      if (GNUNET_YES != res)
      {
        GNUNET_break_op (0);
        return res;
      }

      for (unsigned int j = 0; j<coins_index; j++)
      {
        if (0 ==
            GNUNET_memcmp (&dc->cdd.coin_pub,
                           &pc->dc[j].cdd.coin_pub))
        {
          GNUNET_break_op (0);
          return (MHD_YES ==
                  TALER_MHD_reply_with_error (pc->connection,
                                              MHD_HTTP_BAD_REQUEST,
                                              TALER_EC_GENERIC_PARAMETER_MALFORMED,
                                              "duplicate coin in list"))
                ? GNUNET_NO
                : GNUNET_SYSERR;
        }
      }

      dc->exchange_url = GNUNET_strdup (exchange_url);
      dc->index = coins_index;
      dc->pc = pc;

      if (0 !=
          strcasecmp (dc->cdd.amount.currency,
                      TMH_currency))
      {
        GNUNET_break_op (0);
        return (MHD_YES ==
                TALER_MHD_reply_with_error (pc->connection,
                                            MHD_HTTP_CONFLICT,
                                            TALER_EC_GENERIC_CURRENCY_MISMATCH,
                                            TMH_currency))
              ? GNUNET_NO
              : GNUNET_SYSERR;
      }

      /* Check the consistency of the (potential) age restriction
       * information. */
      if (dc->no_age_commitment != dc->no_minimum_age_sig)
      {
        GNUNET_break_op (0);
        return (MHD_YES ==
                TALER_MHD_reply_with_error (
                  pc->connection,
                  MHD_HTTP_BAD_REQUEST,
                  TALER_EC_GENERIC_PARAMETER_MALFORMED,
                  "inconsistent: 'age_commitment' vs. 'minimum_age_sig'"
                  )
                )
              ? GNUNET_NO
              : GNUNET_SYSERR;
      }

      /* Setup exchange group */
      for (unsigned int i = 0; i<pc->num_exchanges; i++)
      {
        if (0 ==
            strcmp (pc->egs[i]->exchange_url,
                    exchange_url))
        {
          have_eg = true;
          break;
        }
      }
      if (! have_eg)
      {
        struct ExchangeGroup *eg;

        eg = GNUNET_new (struct ExchangeGroup);
        eg->pc = pc;
        eg->exchange_url = dc->exchange_url;
        GNUNET_array_append (pc->egs,
                             pc->num_exchanges,
                             eg);
      }
    }
  }
  return GNUNET_OK;
}


/**
 * Function called with information about a coin that was deposited.
 * Checks if this coin is in our list of deposits as well.
 *
 * @param cls closure with our `struct PayContext *`
 * @param deposit_serial which deposit operation is this about
 * @param exchange_url URL of the exchange that issued 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 h_wire hash of merchant's wire details
 * @param coin_pub public key of the coin
 */
static void
deposit_paid_check (
  void *cls,
  uint64_t deposit_serial,
  const char *exchange_url,
  const struct TALER_MerchantWireHashP *h_wire,
  const struct TALER_Amount *amount_with_fee,
  const struct TALER_Amount *deposit_fee,
  const struct TALER_CoinSpendPublicKeyP *coin_pub)
{
  struct PayContext *pc = cls;

  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dci = &pc->dc[i];

    if ( (0 ==
          GNUNET_memcmp (&dci->cdd.coin_pub,
                         coin_pub)) &&
         (0 ==
          strcmp (dci->exchange_url,
                  exchange_url)) &&
         (0 ==
          TALER_amount_cmp (&dci->cdd.amount,
                            amount_with_fee)) )
    {
      dci->matched_in_db = true;
      break;
    }
  }
}


/**
 * Handle case where contract was already paid. Either decides
 * the payment is idempotent, or refunds the excess payment.
 *
 * @param[in,out] pc context we use to handle the payment
 * @return #GNUNET_NO if response was queued with MHD
 *         #GNUNET_SYSERR on hard error (MHD connection must be dropped)
 */
static enum GNUNET_GenericReturnValue
handle_contract_paid (struct PayContext *pc)
{
  enum GNUNET_DB_QueryStatus qs;
  bool unmatched = false;
  json_t *refunds;

  qs = TMH_db->lookup_deposits_by_order (TMH_db->cls,
                                         pc->order_serial,
                                         &deposit_paid_check,
                                         pc);
  if (qs <= 0)
  {
    GNUNET_break (0);
    return (MHD_YES ==
            TALER_MHD_reply_with_error (pc->connection,
                                        MHD_HTTP_INTERNAL_SERVER_ERROR,
                                        TALER_EC_GENERIC_DB_FETCH_FAILED,
                                        "lookup_deposits_by_order"))
       ? GNUNET_NO
       : GNUNET_SYSERR;
  }
  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dci = &pc->dc[i];

    if (! dci->matched_in_db)
      unmatched = true;
  }
  if (! unmatched)
  {
    /* Everything fine, idempotent request */
    struct GNUNET_CRYPTO_EddsaSignature sig;

    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Idempotent pay request for order `%s', signing again\n",
                pc->order_id);
    TALER_merchant_pay_sign (&pc->h_contract_terms,
                             &pc->hc->instance->merchant_priv,
                             &sig);
    return (MHD_YES ==
            TALER_MHD_REPLY_JSON_PACK (
              pc->connection,
              MHD_HTTP_OK,
              GNUNET_JSON_pack_data_auto ("sig",
                                          &sig)))
       ? GNUNET_NO
       : GNUNET_SYSERR;
  }
  /* Conflict, double-payment detected! */
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Client attempted to pay extra for already paid order `%s'\n",
              pc->order_id);
  refunds = json_array ();
  GNUNET_assert (NULL != refunds);
  for (unsigned int i = 0; i<pc->coins_cnt; i++)
  {
    struct DepositConfirmation *dci = &pc->dc[i];
    struct TALER_MerchantSignatureP merchant_sig;

    if (dci->matched_in_db)
      continue;
    TALER_merchant_refund_sign (&dci->cdd.coin_pub,
                                &pc->h_contract_terms,
                                0, /* rtransaction id */
                                &dci->cdd.amount,
                                &pc->hc->instance->merchant_priv,
                                &merchant_sig);
    GNUNET_assert (
      0 ==
      json_array_append_new (
        refunds,
        GNUNET_JSON_PACK (
          GNUNET_JSON_pack_data_auto (
            "coin_pub",
            &dci->cdd.coin_pub),
          GNUNET_JSON_pack_data_auto (
            "merchant_sig",
            &merchant_sig),
          TALER_JSON_pack_amount ("amount",
                                  &dci->cdd.amount),
          GNUNET_JSON_pack_uint64 ("rtransaction_id",
                                   0))));
  }
  return (MHD_YES ==
          TALER_MHD_REPLY_JSON_PACK (
            pc->connection,
            MHD_HTTP_CONFLICT,
            TALER_MHD_PACK_EC (
              TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_ALREADY_PAID),
            GNUNET_JSON_pack_array_steal ("refunds",
                                          refunds)))
       ? GNUNET_NO
       : GNUNET_SYSERR;
}


/**
 * Check the database state for the given order. * Schedules an error response in the connection on failure.
 *
 * @param pc context we use to handle the payment
 * @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
check_contract (struct PayContext *pc)
{
  /* obtain contract terms */
  enum GNUNET_DB_QueryStatus qs;
  bool paid = false;

  if (NULL != pc->contract_terms)
  {
    json_decref (pc->contract_terms);
    pc->contract_terms = NULL;
  }
  qs = TMH_db->lookup_contract_terms2 (TMH_db->cls,
                                       pc->hc->instance->settings.id,
                                       pc->order_id,
                                       &pc->contract_terms,
                                       &pc->order_serial,
                                       &paid,
                                       NULL,
                                       &pc->pos_key,
                                       &pc->pos_alg);
  if (0 > qs)
  {
    /* single, read-only SQL statements should never cause
       serialization problems */
    GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR != qs);
    /* Always report on hard error to enable diagnostics */
    GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
    return (MHD_YES ==
            TALER_MHD_reply_with_error (pc->connection,
                                        MHD_HTTP_INTERNAL_SERVER_ERROR,
                                        TALER_EC_GENERIC_DB_FETCH_FAILED,
                                        "contract terms"))
       ? GNUNET_NO
       : GNUNET_SYSERR;
  }
  if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
  {
    return (MHD_YES ==
            TALER_MHD_reply_with_error (pc->connection,
                                        MHD_HTTP_NOT_FOUND,
                                        TALER_EC_MERCHANT_GENERIC_ORDER_UNKNOWN,
                                        pc->order_id))
       ? GNUNET_NO
       : GNUNET_SYSERR;
  }
  /* hash contract (needed later) */
  if (GNUNET_OK !=
      TALER_JSON_contract_hash (pc->contract_terms,
                                &pc->h_contract_terms))
  {
    GNUNET_break (0);
    return (MHD_YES ==
            TALER_MHD_reply_with_error (pc->connection,
                                        MHD_HTTP_INTERNAL_SERVER_ERROR,
                                        TALER_EC_GENERIC_FAILED_COMPUTE_JSON_HASH,
                                        NULL))
       ? GNUNET_NO
       : GNUNET_SYSERR;
  }
  if (paid)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Order `%s' paid, checking for double-payment\n",
                pc->order_id);
    return handle_contract_paid (pc);
  }
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Handling payment for order `%s' with contract hash `%s'\n",
              pc->order_id,
              GNUNET_h2s (&pc->h_contract_terms.hash));

  /* basic sanity check on the contract */
  if (NULL == json_object_get (pc->contract_terms,
                               "merchant"))
  {
    /* invalid contract */
    GNUNET_break (0);
    return (MHD_YES ==
            TALER_MHD_reply_with_error (pc->connection,
                                        MHD_HTTP_INTERNAL_SERVER_ERROR,
                                        TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_MERCHANT_FIELD_MISSING,
                                        NULL))
       ? GNUNET_NO
       : GNUNET_SYSERR;
  }

  /* Get details from contract and check fundamentals */
  {
    const char *fulfillment_url = NULL;
    struct GNUNET_JSON_Specification espec[] = {
      TALER_JSON_spec_amount ("amount",
                              TMH_currency,
                              &pc->amount),
      GNUNET_JSON_spec_mark_optional (
        GNUNET_JSON_spec_string ("fulfillment_url",
                                 &fulfillment_url),
        NULL),
      TALER_JSON_spec_amount ("max_fee",
                              TMH_currency,
                              &pc->max_fee),
      TALER_JSON_spec_amount ("max_wire_fee",
                              TMH_currency,
                              &pc->max_wire_fee),
      GNUNET_JSON_spec_uint32 ("wire_fee_amortization",
                               &pc->wire_fee_amortization),
      GNUNET_JSON_spec_timestamp ("timestamp",
                                  &pc->timestamp),
      GNUNET_JSON_spec_timestamp ("refund_deadline",
                                  &pc->refund_deadline),
      GNUNET_JSON_spec_timestamp ("pay_deadline",
                                  &pc->pay_deadline),
      GNUNET_JSON_spec_timestamp ("wire_transfer_deadline",
                                  &pc->wire_transfer_deadline),
      GNUNET_JSON_spec_fixed_auto ("h_wire",
                                   &pc->h_wire),
      GNUNET_JSON_spec_mark_optional (
        GNUNET_JSON_spec_uint32 ("minimum_age",
                                 &pc->minimum_age),
        NULL),
      GNUNET_JSON_spec_end ()
    };
    enum GNUNET_GenericReturnValue res;

    pc->minimum_age = 0;
    res = TALER_MHD_parse_internal_json_data (pc->connection,
                                              pc->contract_terms,
                                              espec);
    if (NULL != fulfillment_url)
      pc->fulfillment_url = GNUNET_strdup (fulfillment_url);
    if (GNUNET_YES != res)
    {
      GNUNET_break (0);
      return res;
    }
  }

  if (GNUNET_TIME_timestamp_cmp (pc->wire_transfer_deadline,
                                 <,
                                 pc->refund_deadline))
  {
    /* This should already have been checked when creating the order! */
    GNUNET_break (0);
    return TALER_MHD_reply_with_error (pc->connection,
                                       MHD_HTTP_INTERNAL_SERVER_ERROR,
                                       TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_REFUND_DEADLINE_PAST_WIRE_TRANSFER_DEADLINE,
                                       NULL);
  }
  if (GNUNET_TIME_absolute_is_past (pc->pay_deadline.abs_time))
  {
    /* too late */
    return (MHD_YES ==
            TALER_MHD_reply_with_error (pc->connection,
                                        MHD_HTTP_GONE,
                                        TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_OFFER_EXPIRED,
                                        NULL))
       ? GNUNET_NO
       : GNUNET_SYSERR;
  }

  /* Make sure wire method (still) exists for this instance */
  {
    struct TMH_WireMethod *wm;

    wm = pc->hc->instance->wm_head;
    while (0 != GNUNET_memcmp (&pc->h_wire,
                               &wm->h_wire))
      wm = wm->next;
    if (NULL == wm)
    {
      GNUNET_break (0);
      return TALER_MHD_reply_with_error (pc->connection,
                                         MHD_HTTP_INTERNAL_SERVER_ERROR,
                                         TALER_EC_MERCHANT_POST_ORDERS_ID_PAY_WIRE_HASH_UNKNOWN,
                                         NULL);
    }
    pc->wm = wm;
  }

  return GNUNET_OK;
}


/**
 * Handle a timeout for the processing of the pay request.
 *
 * @param cls our `struct PayContext`
 */
static void
handle_pay_timeout (void *cls)
{
  struct PayContext *pc = cls;

  pc->timeout_task = NULL;
  GNUNET_assert (GNUNET_YES == pc->suspended);
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Resuming pay with error after timeout\n");
  resume_pay_with_error (pc,
                         TALER_EC_MERCHANT_GENERIC_EXCHANGE_TIMEOUT,
                         NULL);
}


MHD_RESULT
TMH_post_orders_ID_pay (const struct TMH_RequestHandler *rh,
                        struct MHD_Connection *connection,
                        struct TMH_HandlerContext *hc)
{
  struct PayContext *pc = hc->ctx;
  enum GNUNET_GenericReturnValue ret;

  GNUNET_assert (NULL != hc->infix);
  if (NULL == pc)
  {
    pc = GNUNET_new (struct PayContext);
    GNUNET_CONTAINER_DLL_insert (pc_head,
                                 pc_tail,
                                 pc);
    pc->connection = connection;
    pc->hc = hc;
    pc->order_id = hc->infix;
    hc->ctx = pc;
    hc->cc = &pay_context_cleanup;
    ret = parse_pay (pc);
    if (GNUNET_OK != ret)
      return (GNUNET_NO == ret)
       ? MHD_YES
       : MHD_NO;
  }
  if (GNUNET_SYSERR == pc->suspended)
    return MHD_NO; /* during shutdown, we don't generate any more replies */
  GNUNET_assert (GNUNET_NO == pc->suspended);
  if (0 != pc->response_code)
  {
    /* We are *done* processing the request, just queue the response (!) */
    if (UINT_MAX == pc->response_code)
    {
      GNUNET_break (0);
      return MHD_NO; /* hard error */
    }
    return MHD_queue_response (connection,
                               pc->response_code,
                               pc->response);
  }
  ret = check_contract (pc);
  if (GNUNET_OK != ret)
    return (GNUNET_NO == ret)
      ? MHD_YES
      : MHD_NO;

  /* Payment not finished, suspend while we interact with the exchange */
  MHD_suspend_connection (connection);
  pc->suspended = GNUNET_YES;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Suspending pay handling while working with the exchange\n");
  GNUNET_assert (NULL == pc->timeout_task);
  pc->timeout_task
    = GNUNET_SCHEDULER_add_delayed (get_pay_timeout (pc->coins_cnt),
                                    &handle_pay_timeout,
                                    pc);
  GNUNET_assert (NULL != pc->wm);
  execute_pay_transaction (pc);
  return MHD_YES;
}


/* end of taler-merchant-httpd_post-orders-ID-pay.c */