/*
  This file is part of TALER
  Copyright (C) 2014-2017 GNUnet e.V.

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

  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with
  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
*/
/**
 * @file taler-exchange-httpd_db.c
 * @brief High-level (transactional-layer) database operations for the exchange.
 * @author Christian Grothoff
 */
#include "platform.h"
#include <pthread.h>
#include <jansson.h>
#include <gnunet/gnunet_json_lib.h>
#include "taler_json_lib.h"
#include "taler-exchange-httpd_responses.h"
#include "taler-exchange-httpd_keystate.h"

/**
 * How often should we retry a transaction before giving up
 * (for transactions resulting in serialization/dead locks only).
 */
#define MAX_TRANSACTION_COMMIT_RETRIES 3

/**
 * Code to begin a transaction, must be inline as we define a block
 * that ends with #COMMIT_TRANSACTION() within which we perform a number
 * of retries.  Note that this code may call "return" internally, so
 * it must be called within a function where any cleanup will be done
 * by the caller. Furthermore, the function's return value must
 * match that of a #TEH_RESPONSE_reply_internal_db_error() status code.
 *
 * @param session session handle
 * @param connection connection handle
 */
#define START_TRANSACTION(session,connection)                 \
{ /* start new scope, will be ended by COMMIT_TRANSACTION() */\
  unsigned int transaction_retries = 0;                       \
  enum GNUNET_DB_QueryStatus transaction_commit_result;       \
transaction_start_label: /* we will use goto for retries */   \
  if (GNUNET_OK !=                                            \
      TEH_plugin->start (TEH_plugin->cls,                     \
                         session))                            \
  {                                                           \
    GNUNET_break (0);                                         \
    return TEH_RESPONSE_reply_internal_db_error (connection, \
						 TALER_EC_DB_START_FAILED);	     \
  }

/**
 * Code to conclude a transaction, dual to #START_TRANSACTION().  Note
 * that this code may call "return" internally, so it must be called
 * within a function where any cleanup will be done by the caller.
 * Furthermore, the function's return value must match that of a
 * #TEH_RESPONSE_reply_internal_db_error() status code.
 *
 * @param session session handle
 * @param connection connection handle
 */
#define COMMIT_TRANSACTION(session,connection)                             \
  transaction_commit_result =                                              \
    TEH_plugin->commit (TEH_plugin->cls,                                   \
                        session);                                          \
  if (GNUNET_DB_STATUS_HARD_ERROR == transaction_commit_result)            \
  {                                                                        \
    TALER_LOG_WARNING ("Transaction commit failed in %s\n", __FUNCTION__); \
    return TEH_RESPONSE_reply_commit_error (connection, \
					    TALER_EC_DB_COMMIT_FAILED_HARD); \
  }                                                       \
  if (GNUNET_DB_STATUS_SOFT_ERROR == transaction_commit_result)            \
  {                                                                        \
    TALER_LOG_WARNING ("Transaction commit failed in %s\n", __FUNCTION__); \
    if (transaction_retries++ <= MAX_TRANSACTION_COMMIT_RETRIES)           \
      goto transaction_start_label;                                        \
    TALER_LOG_WARNING ("Transaction commit failed %u times in %s\n",       \
                       transaction_retries,                                \
                       __FUNCTION__);                                      \
    return TEH_RESPONSE_reply_commit_error (connection, \
					    TALER_EC_DB_COMMIT_FAILED_ON_RETRY);				\
  }                                                                        \
} /* end of scope opened by BEGIN_TRANSACTION */


/**
 * Code to include to retry a transaction, must only be used in between
 * #START_TRANSACTION and #COMMIT_TRANSACTION.
 *
 * @param session session handle
 * @param connection connection handle
 */
#define RETRY_TRANSACTION(session,connection)                                    \
  do {                                                                           \
    TEH_plugin->rollback (TEH_plugin->cls,                                       \
                          session);                                              \
    if (transaction_retries++ <= MAX_TRANSACTION_COMMIT_RETRIES)                 \
      goto transaction_start_label;                                              \
    TALER_LOG_WARNING ("Transaction commit failed %u times in %s\n",             \
                       transaction_retries,                                      \
                       __FUNCTION__);                                            \
    return TEH_RESPONSE_reply_commit_error (connection,                          \
					    TALER_EC_DB_COMMIT_FAILED_ON_RETRY); \
  } while (0)


/**
 * Run a database transaction for @a connection.
 * Starts a transaction and calls @a cb.  Upon success,
 * attempts to commit the transaction.  Upon soft failures,
 * retries @a cb a few times.  Upon hard or persistent soft
 * errors, generates an error message for @a connection.
 * 
 * @param connection MHD connection to run @a cb for
 * @param[out] set to MHD response code, if transaction failed
 * @param cb callback implementing transaction logic
 * @param cb_cls closure for @a cb, must be read-only!
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure
 */
int
TEH_DB_run_transaction (struct MHD_Connection *connection,
			int *mhd_ret,
			TEH_DB_TransactionCallback cb,
			void *cb_cls)
{
  struct TALER_EXCHANGEDB_Session *session;

  *mhd_ret = -1; /* invalid value */
  if (NULL == (session = TEH_plugin->get_session (TEH_plugin->cls)))
  {
    GNUNET_break (0);
    *mhd_ret = TEH_RESPONSE_reply_internal_db_error (connection,
						     TALER_EC_DB_SETUP_FAILED);
    return GNUNET_SYSERR;
  }
  for (unsigned int retries = 0;retries < MAX_TRANSACTION_COMMIT_RETRIES; retries++)
  {
    enum GNUNET_DB_QueryStatus qs;

    if (GNUNET_OK !=                                            
	TEH_plugin->start (TEH_plugin->cls,                     
			   session))                            
    {                                      
      GNUNET_break (0);                                         
      *mhd_ret = TEH_RESPONSE_reply_internal_db_error (connection, 
						       TALER_EC_DB_START_FAILED);
      return GNUNET_SYSERR;
    }
    qs = cb (cb_cls,
	     connection,
	     session,
	     mhd_ret);
    if (0 > qs)
      TEH_plugin->rollback (TEH_plugin->cls,
			    session);      
    if (GNUNET_DB_STATUS_HARD_ERROR == qs)
      return GNUNET_SYSERR;
    if (0 <= qs)
      qs = TEH_plugin->commit (TEH_plugin->cls,
			       session);                              
    if (GNUNET_DB_STATUS_HARD_ERROR == qs)
    {
      *mhd_ret = TEH_RESPONSE_reply_commit_error (connection,
						  TALER_EC_DB_COMMIT_FAILED_HARD);
      return GNUNET_SYSERR;
    }
    /* make sure callback did not violate invariants! */
    GNUNET_assert (-1 == *mhd_ret);
    if (0 <= qs)
      return GNUNET_OK;
  }
  TALER_LOG_WARNING ("Transaction commit failed %u times\n",
		     MAX_TRANSACTION_COMMIT_RETRIES);
  *mhd_ret = TEH_RESPONSE_reply_commit_error (connection,
					      TALER_EC_DB_COMMIT_FAILED_ON_RETRY);
  return GNUNET_SYSERR;
}


/**
 * Calculate the total value of all transactions performed.
 * Stores @a off plus the cost of all transactions in @a tl
 * in @a ret.
 *
 * @param tl transaction list to process
 * @param off offset to use as the starting value
 * @param[out] ret where the resulting total is to be stored
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on errors
 */
int
TEH_DB_calculate_transaction_list_totals (struct TALER_EXCHANGEDB_TransactionList *tl,
					  const struct TALER_Amount *off,
					  struct TALER_Amount *ret)
{
  struct TALER_Amount spent = *off;
  struct TALER_EXCHANGEDB_TransactionList *pos;
  struct TALER_Amount refunded;

  TALER_amount_get_zero (spent.currency,
                         &refunded);
  for (pos = tl; NULL != pos; pos = pos->next)
  {
    switch (pos->type)
    {
    case TALER_EXCHANGEDB_TT_DEPOSIT:
      /* spent += pos->amount_with_fee */
      if (GNUNET_OK !=
          TALER_amount_add (&spent,
                            &spent,
                            &pos->details.deposit->amount_with_fee))
      {
        GNUNET_break (0);
        return GNUNET_SYSERR;
      }
      break;
    case TALER_EXCHANGEDB_TT_REFRESH_MELT:
      /* spent += pos->amount_with_fee */
      if (GNUNET_OK !=
          TALER_amount_add (&spent,
                            &spent,
                            &pos->details.melt->amount_with_fee))
      {
        GNUNET_break (0);
        return GNUNET_SYSERR;
      }
      break;
    case TALER_EXCHANGEDB_TT_REFUND:
      /* refunded += pos->refund_amount - pos->refund_fee */
      if (GNUNET_OK !=
          TALER_amount_add (&refunded,
                            &refunded,
                            &pos->details.refund->refund_amount))
      {
        GNUNET_break (0);
        return GNUNET_SYSERR;
      }
      if (GNUNET_OK !=
          TALER_amount_subtract (&refunded,
                                 &refunded,
                                 &pos->details.refund->refund_fee))
      {
        GNUNET_break (0);
        return GNUNET_SYSERR;
      }
      break;
    case TALER_EXCHANGEDB_TT_PAYBACK:
      /* spent += pos->value */
      if (GNUNET_OK !=
          TALER_amount_add (&spent,
                            &spent,
                            &pos->details.payback->value))
      {
        GNUNET_break (0);
        return GNUNET_SYSERR;
      }
      break;
    }
  }
  /* spent = spent - refunded */
  if (GNUNET_SYSERR ==
      TALER_amount_subtract (&spent,
                             &spent,
                             &refunded))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }

  *ret = spent;
  return GNUNET_OK;
}


/**
 * Parse coin melt requests from a JSON object and write them to
 * the database.
 *
 * @param connection the connection to send errors to
 * @param session the database connection
 * @param key_state the exchange's key state
 * @param session_hash hash identifying the refresh session
 * @param coin_details details about the coin being melted
 * @param[out] meltp on success, set to melt details
 * @return #GNUNET_OK on success,
 *         #GNUNET_NO if an error message was generated,
 *         #GNUNET_SYSERR on internal errors (no response generated)
 */
static int
refresh_check_melt (struct MHD_Connection *connection,
                    struct TALER_EXCHANGEDB_Session *session,
                    const struct TEH_KS_StateHandle *key_state,
                    const struct GNUNET_HashCode *session_hash,
                    const struct TEH_DB_MeltDetails *coin_details,
                    struct TALER_EXCHANGEDB_RefreshMelt *meltp)
{
  struct TALER_EXCHANGEDB_DenominationKeyIssueInformation *dk;
  struct TALER_EXCHANGEDB_DenominationKeyInformationP *dki;
  struct TALER_EXCHANGEDB_TransactionList *tl;
  struct TALER_Amount coin_value;
  struct TALER_Amount coin_residual;
  struct TALER_Amount spent;
  int res;
  enum GNUNET_DB_QueryStatus qs;

  dk = TEH_KS_denomination_key_lookup (key_state,
                                       &coin_details->coin_info.denom_pub,
                                       TEH_KS_DKU_DEPOSIT);
  if (NULL == dk)
    return (MHD_YES ==
            TEH_RESPONSE_reply_internal_error (connection,
					       TALER_EC_REFRESH_MELT_DB_DENOMINATION_KEY_NOT_FOUND,
					       "denomination key no longer available while executing transaction"))
        ? GNUNET_NO : GNUNET_SYSERR;
  dki = &dk->issue;
  TALER_amount_ntoh (&coin_value,
                     &dki->properties.value);
  /* fee for THIS transaction; the melt amount includes the fee! */
  spent = coin_details->melt_amount_with_fee;
  /* add historic transaction costs of this coin */
  qs = TEH_plugin->get_coin_transactions (TEH_plugin->cls,
                                          session,
                                          &coin_details->coin_info.coin_pub,
					  &tl);
  (void) qs; /* FIXME #5010 */
  if (GNUNET_OK !=
      TEH_DB_calculate_transaction_list_totals (tl,
						&spent,
						&spent))
  {
    GNUNET_break (0);
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    return (MHD_YES ==
            TEH_RESPONSE_reply_internal_db_error (connection,
						  TALER_EC_REFRESH_MELT_COIN_HISTORY_COMPUTATION_FAILED))
      ? GNUNET_NO : GNUNET_SYSERR;
  }
  /* Refuse to refresh when the coin's value is insufficient
     for the cost of all transactions. */
  if (TALER_amount_cmp (&coin_value,
                        &spent) < 0)
  {
    GNUNET_assert (GNUNET_SYSERR !=
                   TALER_amount_subtract (&coin_residual,
                                          &spent,
                                          &coin_details->melt_amount_with_fee));
    res = (MHD_YES ==
           TEH_RESPONSE_reply_refresh_melt_insufficient_funds (connection,
                                                               &coin_details->coin_info.coin_pub,
                                                               coin_value,
                                                               tl,
                                                               coin_details->melt_amount_with_fee,
                                                               coin_residual))
        ? GNUNET_NO : GNUNET_SYSERR;
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    return res;
  }
  TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                          tl);

  meltp->coin = coin_details->coin_info;
  meltp->coin_sig = coin_details->melt_sig;
  meltp->session_hash = *session_hash;
  meltp->amount_with_fee = coin_details->melt_amount_with_fee;
  meltp->melt_fee = coin_details->melt_fee;
  return GNUNET_OK;
}


/**
 * Execute a "/refresh/melt".  We have been given a list of valid
 * coins and a request to melt them into the given
 * @a refresh_session_pub.  Check that the coins all have the
 * required value left and if so, store that they have been
 * melted and confirm the melting operation to the client.
 *
 * @param connection the MHD connection to handle
 * @param session_hash hash code of the session the coins are melted into
 * @param num_new_denoms number of entries in @a denom_pubs, size of y-dimension of @a commit_coin array
 * @param denom_pubs public keys of the coins we want to withdraw in the end
 * @param coin_melt_detail signature and (residual) value of the respective coin should be melted
 * @param commit_coin 2d array of coin commitments (what the exchange is to sign
 *                    once the "/refres/reveal" of cut and choose is done),
 *                    x-dimension must be #TALER_CNC_KAPPA
 * @param transfer_pubs array of transfer public keys (what the exchange is
 *                    to return via "/refresh/link" to enable linkage in the
 *                    future) of length #TALER_CNC_KAPPA
 * @return MHD result code
 */
int
TEH_DB_execute_refresh_melt (struct MHD_Connection *connection,
                             const struct GNUNET_HashCode *session_hash,
                             unsigned int num_new_denoms,
                             const struct TALER_DenominationPublicKey *denom_pubs,
                             const struct TEH_DB_MeltDetails *coin_melt_detail,
                             struct TALER_EXCHANGEDB_RefreshCommitCoin *const* commit_coin,
                             const struct TALER_TransferPublicKeyP *transfer_pubs)
{
  struct TEH_KS_StateHandle *key_state;
  struct TALER_EXCHANGEDB_RefreshSession refresh_session;
  struct TALER_EXCHANGEDB_Session *session;
  int res;

  if (NULL == (session = TEH_plugin->get_session (TEH_plugin->cls)))
  {
    GNUNET_break (0);
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_DB_SETUP_FAILED);
  }
  START_TRANSACTION (session, connection);
  res = TEH_plugin->get_refresh_session (TEH_plugin->cls,
                                         session,
                                         session_hash,
                                         &refresh_session);
  if (GNUNET_YES == res)
  {
    TEH_plugin->rollback (TEH_plugin->cls,
                          session);
    res = TEH_RESPONSE_reply_refresh_melt_success (connection,
                                                   session_hash,
                                                   refresh_session.noreveal_index);
    return (GNUNET_SYSERR == res) ? MHD_NO : MHD_YES;
  }
  if (GNUNET_SYSERR == res)
  {
    TEH_plugin->rollback (TEH_plugin->cls,
                          session);
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_REFRESH_MELT_DB_FETCH_ERROR);
  }

  /* store 'global' session data */
  refresh_session.num_newcoins = num_new_denoms;
  refresh_session.noreveal_index
    = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
				TALER_CNC_KAPPA);
  key_state = TEH_KS_acquire ();
  if (GNUNET_OK !=
      (res = refresh_check_melt (connection,
                                 session,
                                 key_state,
                                 session_hash,
                                 coin_melt_detail,
                                 &refresh_session.melt)))
  {
    TEH_KS_release (key_state);
    TEH_plugin->rollback (TEH_plugin->cls,
                          session);
    return (GNUNET_SYSERR == res) ? MHD_NO : MHD_YES;
  }
  TEH_KS_release (key_state);

  if (GNUNET_OK !=
      (res = TEH_plugin->create_refresh_session (TEH_plugin->cls,
                                                 session,
                                                 session_hash,
                                                 &refresh_session)))
  {
    TEH_plugin->rollback (TEH_plugin->cls,
                          session);
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_REFRESH_MELT_DB_STORE_SESSION_ERROR);
  }

  /* store requested new denominations */
  if (GNUNET_OK !=
      TEH_plugin->insert_refresh_order (TEH_plugin->cls,
                                        session,
                                        session_hash,
                                        num_new_denoms,
                                        denom_pubs))
  {
    TEH_plugin->rollback (TEH_plugin->cls,
                          session);
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_REFRESH_MELT_DB_STORE_ORDER_ERROR);
  }

  if (GNUNET_OK !=
      TEH_plugin->insert_refresh_commit_coins (TEH_plugin->cls,
                                               session,
                                               session_hash,
                                               num_new_denoms,
                                               commit_coin[refresh_session.noreveal_index]))
  {
    TEH_plugin->rollback (TEH_plugin->cls,
                          session);
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_REFRESH_MELT_DB_STORE_ORDER_ERROR);
  }
  if (GNUNET_OK !=
      TEH_plugin->insert_refresh_transfer_public_key (TEH_plugin->cls,
                                                      session,
                                                      session_hash,
                                                      &transfer_pubs[refresh_session.noreveal_index]))
  {
    TEH_plugin->rollback (TEH_plugin->cls,
                          session);
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_REFRESH_MELT_DB_STORE_TRANSFER_ERROR);
  }

  COMMIT_TRANSACTION (session, connection);
  return TEH_RESPONSE_reply_refresh_melt_success (connection,
                                                  session_hash,
                                                  refresh_session.noreveal_index);
}


/**
 * Check if the given @a transfer_privs correspond to an honest
 * commitment for the given session.
 * Checks that the transfer private keys match their commitments.
 * Then derives the shared secret for each #TALER_CNC_KAPPA, and check that they match.
 *
 * @param connection the MHD connection to handle
 * @param session database connection to use
 * @param session_hash hash of session to query
 * @param off commitment offset to check
 * @param transfer_priv private transfer key
 * @param melt information about the melted coin
 * @param num_newcoins number of newcoins being generated
 * @param denom_pubs array of @a num_newcoins keys for the new coins
 * @param hash_context hash context to update by hashing in the data
 *                     from this offset
 * @return #GNUNET_OK if the committment was honest,
 *         #GNUNET_NO if there was a problem and we generated an error message
 *         #GNUNET_SYSERR if we could not even generate an error message
 */
static int
check_commitment (struct MHD_Connection *connection,
                  struct TALER_EXCHANGEDB_Session *session,
                  const struct GNUNET_HashCode *session_hash,
                  unsigned int off,
                  const struct TALER_TransferPrivateKeyP *transfer_priv,
                  const struct TALER_EXCHANGEDB_RefreshMelt *melt,
                  unsigned int num_newcoins,
                  const struct TALER_DenominationPublicKey *denom_pubs,
                  struct GNUNET_HashContext *hash_context)
{
  struct TALER_TransferSecretP transfer_secret;
  unsigned int j;

  TALER_link_reveal_transfer_secret (transfer_priv,
                                     &melt->coin.coin_pub,
                                     &transfer_secret);

  /* Check that the commitments for all new coins were correct */
  for (j = 0; j < num_newcoins; j++)
  {
    struct TALER_FreshCoinP fc;
    struct TALER_CoinSpendPublicKeyP coin_pub;
    struct GNUNET_HashCode h_msg;
    char *buf;
    size_t buf_len;

    TALER_setup_fresh_coin (&transfer_secret,
                            j,
                            &fc);
    GNUNET_CRYPTO_eddsa_key_get_public (&fc.coin_priv.eddsa_priv,
                                        &coin_pub.eddsa_pub);
    GNUNET_CRYPTO_hash (&coin_pub,
                        sizeof (struct TALER_CoinSpendPublicKeyP),
                        &h_msg);
    if (GNUNET_YES !=
        GNUNET_CRYPTO_rsa_blind (&h_msg,
                                 &fc.blinding_key.bks,
                                 denom_pubs[j].rsa_public_key,
                                 &buf,
                                 &buf_len))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "Blind failed (bad denomination key!?)\n");
      return (MHD_YES ==
	      TEH_RESPONSE_reply_internal_error (connection,
						 TALER_EC_REFRESH_REVEAL_BLINDING_ERROR,
						 "Blinding error"))
        ? GNUNET_NO : GNUNET_SYSERR;
    }
    GNUNET_CRYPTO_hash_context_read (hash_context,
                                     buf,
                                     buf_len);
    GNUNET_free (buf);
  }
  return GNUNET_OK;
}


/**
 * Exchange a coin as part of a refresh operation.  Obtains the
 * envelope from the database and performs the signing operation.
 *
 * @param connection the MHD connection to handle
 * @param session database connection to use
 * @param session_hash hash of session to query
 * @param key_state key state to lookup denomination pubs
 * @param denom_pub denomination key for the coin to create
 * @param commit_coin the coin that was committed
 * @param coin_off number of the coin
 * @return NULL on error, otherwise signature over the coin
 */
static struct TALER_DenominationSignature
refresh_exchange_coin (struct MHD_Connection *connection,
                       struct TALER_EXCHANGEDB_Session *session,
                       const struct GNUNET_HashCode *session_hash,
                       struct TEH_KS_StateHandle *key_state,
                       const struct TALER_DenominationPublicKey *denom_pub,
                       const struct TALER_EXCHANGEDB_RefreshCommitCoin *commit_coin,
                       unsigned int coin_off)
{
  struct TALER_EXCHANGEDB_DenominationKeyIssueInformation *dki;
  struct TALER_DenominationSignature ev_sig;

  dki = TEH_KS_denomination_key_lookup (key_state,
                                        denom_pub,
					TEH_KS_DKU_WITHDRAW);
  if (NULL == dki)
  {
    GNUNET_break (0);
    ev_sig.rsa_signature = NULL;
    return ev_sig;
  }
  if (GNUNET_OK ==
      TEH_plugin->get_refresh_out (TEH_plugin->cls,
                                   session,
                                   session_hash,
                                   coin_off,
                                   &ev_sig))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Returning cached reply for /refresh/reveal signature\n");
    return ev_sig;
  }

  ev_sig.rsa_signature
    = GNUNET_CRYPTO_rsa_sign_blinded (dki->denom_priv.rsa_private_key,
                                      commit_coin->coin_ev,
                                      commit_coin->coin_ev_size);
  if (NULL == ev_sig.rsa_signature)
  {
    GNUNET_break (0);
    return ev_sig;
  }
  if (GNUNET_SYSERR ==
      TEH_plugin->insert_refresh_out (TEH_plugin->cls,
                                      session,
                                      session_hash,
                                      coin_off,
                                      &ev_sig))
  {
    GNUNET_break (0);
    GNUNET_CRYPTO_rsa_signature_free (ev_sig.rsa_signature);
    ev_sig.rsa_signature = NULL;
  }

  return ev_sig;
}


/**
 * The client request was well-formed, now execute the DB transaction
 * of a "/refresh/reveal" operation.  We use the @a ev_sigs and
 * @a commit_coins to clean up resources after this function returns
 * as we might experience retries of the database transaction.
 *
 * @param connection the MHD connection to handle
 * @param session database session
 * @param session_hash hash identifying the refresh session
 * @param refresh_session information about the refresh operation we are doing
 * @param denom_pubs array of "num_newcoins" denomination keys for the new coins
 * @param[out] ev_sigs where to store generated signatures for the new coins,
 *                     array of length "num_newcoins", memory released by the
 *                     caller
 * @param[out] commit_coins array of length "num_newcoins" to be used for
 *                     information about the new coins from the commitment.
 * @return MHD result code
 */
static int
execute_refresh_reveal_transaction (struct MHD_Connection *connection,
                                    struct TALER_EXCHANGEDB_Session *session,
                                    const struct GNUNET_HashCode *session_hash,
                                    const struct TALER_EXCHANGEDB_RefreshSession *refresh_session,
                                    const struct TALER_DenominationPublicKey *denom_pubs,
                                    struct TALER_DenominationSignature *ev_sigs,
                                    struct TALER_EXCHANGEDB_RefreshCommitCoin *commit_coins)
{
  unsigned int j;
  struct TEH_KS_StateHandle *key_state;
  int ret;

  START_TRANSACTION (session, connection);
  key_state = TEH_KS_acquire ();
  for (j=0;j<refresh_session->num_newcoins;j++)
  {
    if (NULL == ev_sigs[j].rsa_signature) /* could be non-NULL during retries */
      ev_sigs[j] = refresh_exchange_coin (connection,
                                          session,
                                          session_hash,
                                          key_state,
                                          &denom_pubs[j],
                                          &commit_coins[j],
                                          j);
    if (NULL == ev_sigs[j].rsa_signature)
    {
      TEH_plugin->rollback (TEH_plugin->cls,
                            session);
      ret = TEH_RESPONSE_reply_internal_db_error (connection,
						  TALER_EC_REFRESH_REVEAL_SIGNING_ERROR);
      goto cleanup;
    }
  }
  COMMIT_TRANSACTION (session, connection);
  ret = TEH_RESPONSE_reply_refresh_reveal_success (connection,
                                                   refresh_session->num_newcoins,
                                                   ev_sigs);
 cleanup:
  TEH_KS_release (key_state);
  return ret;
}


/**
 * Execute a "/refresh/reveal".  The client is revealing to us the
 * transfer keys for @a #TALER_CNC_KAPPA-1 sets of coins.  Verify that the
 * revealed transfer keys would allow linkage to the blinded coins,
 * and if so, return the signed coins for corresponding to the set of
 * coins that was not chosen.
 *
 * @param connection the MHD connection to handle
 * @param session_hash hash identifying the refresh session
 * @param transfer_privs array with the revealed transfer keys,
 *                      length must be #TALER_CNC_KAPPA - 1
 * @return MHD result code
 */
int
TEH_DB_execute_refresh_reveal (struct MHD_Connection *connection,
                               const struct GNUNET_HashCode *session_hash,
                               struct TALER_TransferPrivateKeyP *transfer_privs)
{
  int res;
  struct TALER_EXCHANGEDB_Session *session;
  struct TALER_EXCHANGEDB_RefreshSession refresh_session;
  struct TALER_DenominationPublicKey *denom_pubs;
  struct TALER_DenominationSignature *ev_sigs;
  struct TALER_EXCHANGEDB_RefreshCommitCoin *commit_coins;
  unsigned int i;
  unsigned int j;
  unsigned int off;
  struct GNUNET_HashContext *hash_context;
  struct GNUNET_HashCode sh_check;
  int ret;
  struct TALER_TransferPublicKeyP gamma_tp;

  if (NULL == (session = TEH_plugin->get_session (TEH_plugin->cls)))
  {
    GNUNET_break (0);
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_DB_SETUP_FAILED);
  }

  res = TEH_plugin->get_refresh_session (TEH_plugin->cls,
                                         session,
                                         session_hash,
                                         &refresh_session);
  if (GNUNET_NO == res)
    return TEH_RESPONSE_reply_arg_invalid (connection,
					   TALER_EC_REFRESH_REVEAL_SESSION_UNKNOWN,
                                           "session_hash");
  if ( (GNUNET_SYSERR == res) ||
       (refresh_session.noreveal_index >= TALER_CNC_KAPPA) )
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_REFRESH_REVEAL_DB_FETCH_SESSION_ERROR);
  denom_pubs = GNUNET_new_array (refresh_session.num_newcoins,
                                 struct TALER_DenominationPublicKey);
  if (GNUNET_OK !=
      TEH_plugin->get_refresh_order (TEH_plugin->cls,
                                     session,
                                     session_hash,
                                     refresh_session.num_newcoins,
                                     denom_pubs))
  {
    GNUNET_break (0);
    GNUNET_free (denom_pubs);
    GNUNET_CRYPTO_rsa_signature_free (refresh_session.melt.coin.denom_sig.rsa_signature);
    GNUNET_CRYPTO_rsa_public_key_free (refresh_session.melt.coin.denom_pub.rsa_public_key);
    return (MHD_YES == TEH_RESPONSE_reply_internal_db_error (connection,
							     TALER_EC_REFRESH_REVEAL_DB_FETCH_ORDER_ERROR))
        ? GNUNET_NO : GNUNET_SYSERR;
  }

  hash_context = GNUNET_CRYPTO_hash_context_start ();
  /* first, iterate over transfer public keys for hash_context */
  off = 0;
  for (i=0;i<TALER_CNC_KAPPA;i++)
  {
    if (i == refresh_session.noreveal_index)
    {
      off = 1;
      /* obtain gamma_tp from db */
      if (GNUNET_OK !=
          TEH_plugin->get_refresh_transfer_public_key (TEH_plugin->cls,
                                                       session,
                                                       session_hash,
                                                       &gamma_tp))
      {
        GNUNET_break (0);
        GNUNET_free (denom_pubs);
        GNUNET_CRYPTO_rsa_signature_free (refresh_session.melt.coin.denom_sig.rsa_signature);
        GNUNET_CRYPTO_rsa_public_key_free (refresh_session.melt.coin.denom_pub.rsa_public_key);
        GNUNET_CRYPTO_hash_context_abort (hash_context);
        return (MHD_YES == TEH_RESPONSE_reply_internal_db_error (connection,
								 TALER_EC_REFRESH_REVEAL_DB_FETCH_TRANSFER_ERROR))
          ? GNUNET_NO : GNUNET_SYSERR;
      }
      GNUNET_CRYPTO_hash_context_read (hash_context,
                                       &gamma_tp,
                                       sizeof (struct TALER_TransferPublicKeyP));
    }
    else
    {
      /* compute tp from private key */
      struct TALER_TransferPublicKeyP tp;

      GNUNET_CRYPTO_ecdhe_key_get_public (&transfer_privs[i - off].ecdhe_priv,
                                          &tp.ecdhe_pub);
      GNUNET_CRYPTO_hash_context_read (hash_context,
                                       &tp,
                                       sizeof (struct TALER_TransferPublicKeyP));
    }
  }

  /* next, add all of the hashes from the denomination keys to the
     hash_context */
  {
    struct TALER_DenominationPublicKey denom_pubs[refresh_session.num_newcoins];

    if (GNUNET_OK !=
        TEH_plugin->get_refresh_order (TEH_plugin->cls,
                                       session,
                                       session_hash,
                                       refresh_session.num_newcoins,
                                       denom_pubs))
    {
      GNUNET_break (0);
      GNUNET_free (denom_pubs);
      GNUNET_CRYPTO_rsa_signature_free (refresh_session.melt.coin.denom_sig.rsa_signature);
      GNUNET_CRYPTO_rsa_public_key_free (refresh_session.melt.coin.denom_pub.rsa_public_key);
      GNUNET_CRYPTO_hash_context_abort (hash_context);
      return (MHD_YES == TEH_RESPONSE_reply_internal_db_error (connection,
							       TALER_EC_REFRESH_REVEAL_DB_FETCH_ORDER_ERROR))
        ? GNUNET_NO : GNUNET_SYSERR;
    }
    for (i=0;i<refresh_session.num_newcoins;i++)
    {
      char *buf;
      size_t buf_size;

      buf_size = GNUNET_CRYPTO_rsa_public_key_encode (denom_pubs[i].rsa_public_key,
                                                      &buf);
      GNUNET_CRYPTO_hash_context_read (hash_context,
                                       buf,
                                       buf_size);
      GNUNET_free (buf);
      GNUNET_CRYPTO_rsa_public_key_free (denom_pubs[i].rsa_public_key);
    }
  }

  /* next, add public key of coin and amount being refreshed */
  {
    struct TALER_AmountNBO melt_amountn;

    GNUNET_CRYPTO_hash_context_read (hash_context,
                                     &refresh_session.melt.coin.coin_pub,
                                     sizeof (struct TALER_CoinSpendPublicKeyP));
    TALER_amount_hton (&melt_amountn,
                       &refresh_session.melt.amount_with_fee);
    GNUNET_CRYPTO_hash_context_read (hash_context,
                                     &melt_amountn,
                                     sizeof (struct TALER_AmountNBO));
  }

  commit_coins = GNUNET_new_array (refresh_session.num_newcoins,
                                   struct TALER_EXCHANGEDB_RefreshCommitCoin);
  off = 0;
  for (i=0;i<TALER_CNC_KAPPA;i++)
  {
    if (i == refresh_session.noreveal_index)
    {
      off = 1;
      /* obtain commit_coins for the selected gamma value from DB */
      if (GNUNET_OK !=
          TEH_plugin->get_refresh_commit_coins (TEH_plugin->cls,
                                                session,
                                                session_hash,
                                                refresh_session.num_newcoins,
                                                commit_coins))
      {
        GNUNET_break (0);
        GNUNET_free (denom_pubs);
        GNUNET_CRYPTO_rsa_signature_free (refresh_session.melt.coin.denom_sig.rsa_signature);
        GNUNET_CRYPTO_rsa_public_key_free (refresh_session.melt.coin.denom_pub.rsa_public_key);
        GNUNET_CRYPTO_hash_context_abort (hash_context);
        return TEH_RESPONSE_reply_internal_db_error (connection,
						     TALER_EC_REFRESH_REVEAL_DB_FETCH_COMMIT_ERROR);
      }
      /* add envelopes to hash_context */
      for (j=0;j<refresh_session.num_newcoins;j++)
      {
        GNUNET_CRYPTO_hash_context_read (hash_context,
                                         commit_coins[j].coin_ev,
                                         commit_coins[j].coin_ev_size);
      }
      continue;
    }
    if (GNUNET_OK !=
        (res = check_commitment (connection,
                                 session,
                                 session_hash,
                                 i,
                                 &transfer_privs[i - off],
                                 &refresh_session.melt,
                                 refresh_session.num_newcoins,
                                 denom_pubs,
                                 hash_context)))
    {
      GNUNET_break_op (0);
      for (j=0;j<refresh_session.num_newcoins;j++)
      {
        GNUNET_CRYPTO_rsa_public_key_free (denom_pubs[j].rsa_public_key);
        GNUNET_free (commit_coins[j].coin_ev);
      }
      GNUNET_free (commit_coins);
      GNUNET_free (denom_pubs);
      GNUNET_CRYPTO_rsa_signature_free (refresh_session.melt.coin.denom_sig.rsa_signature);
      GNUNET_CRYPTO_rsa_public_key_free (refresh_session.melt.coin.denom_pub.rsa_public_key);
      GNUNET_CRYPTO_hash_context_abort (hash_context);
      return (GNUNET_NO == res) ? MHD_YES : MHD_NO;
    }
  }

  /* Check session hash matches */
  GNUNET_CRYPTO_hash_context_finish (hash_context,
                                     &sh_check);
  if (0 != memcmp (&sh_check,
                   session_hash,
                   sizeof (struct GNUNET_HashCode)))
  {
    GNUNET_break_op (0);
    ret = TEH_RESPONSE_reply_refresh_reveal_missmatch (connection,
                                                       &refresh_session,
                                                       commit_coins,
                                                       denom_pubs,
                                                       &gamma_tp);
    for (j=0;j<refresh_session.num_newcoins;j++)
    {
      GNUNET_free (commit_coins[j].coin_ev);
      GNUNET_CRYPTO_rsa_public_key_free (denom_pubs[j].rsa_public_key);
    }
    GNUNET_free (commit_coins);
    GNUNET_free (denom_pubs);
    GNUNET_CRYPTO_rsa_signature_free (refresh_session.melt.coin.denom_sig.rsa_signature);
    GNUNET_CRYPTO_rsa_public_key_free (refresh_session.melt.coin.denom_pub.rsa_public_key);

    return ret;
  }

  /* Client request OK, start transaction */
  ev_sigs = GNUNET_new_array (refresh_session.num_newcoins,
                              struct TALER_DenominationSignature);

  /* FIXME: might need to store revealed transfer private keys for
     the auditor for later; should pass them as arguments here! #4792*/
  res = execute_refresh_reveal_transaction (connection,
                                            session,
                                            session_hash,
                                            &refresh_session,
                                            denom_pubs,
                                            ev_sigs,
                                            commit_coins);
  for (i=0;i<refresh_session.num_newcoins;i++)
  {
    if (NULL != ev_sigs[i].rsa_signature)
      GNUNET_CRYPTO_rsa_signature_free (ev_sigs[i].rsa_signature);
    GNUNET_free (commit_coins[i].coin_ev);
  }
  for (j=0;j<refresh_session.num_newcoins;j++)
    if (NULL != denom_pubs[j].rsa_public_key)
      GNUNET_CRYPTO_rsa_public_key_free (denom_pubs[j].rsa_public_key);
  GNUNET_CRYPTO_rsa_signature_free (refresh_session.melt.coin.denom_sig.rsa_signature);
  GNUNET_CRYPTO_rsa_public_key_free (refresh_session.melt.coin.denom_pub.rsa_public_key);
  GNUNET_free (ev_sigs);
  GNUNET_free (denom_pubs);
  GNUNET_free (commit_coins);
  return res;
}


/**
 * Closure for #handle_transfer_data().
 */
struct HTD_Context
{

  /**
   * Session link data we collect.
   */
  struct TEH_RESPONSE_LinkSessionInfo *sessions;

  /**
   * Database session. Nothing to do with @a sessions.
   */
  struct TALER_EXCHANGEDB_Session *session;

  /**
   * MHD connection, for queueing replies.
   */
  struct MHD_Connection *connection;

  /**
   * Number of sessions the coin was melted into.
   */
  unsigned int num_sessions;

  /**
   * How are we expected to proceed. #GNUNET_SYSERR if we
   * failed to return an error (should return #MHD_NO).
   * #GNUNET_NO if we succeeded in queueing an MHD error
   * (should return #MHD_YES from #TEH_execute_refresh_link),
   * #GNUNET_OK if we should call #TEH_RESPONSE_reply_refresh_link_success().
   */
  int status;
};


/**
 * Function called with the session hashes and transfer secret
 * information for a given coin.  Gets the linkage data and
 * builds the reply for the client.
 *
 *
 * @param cls closure, a `struct HTD_Context`
 * @param session_hash a session the coin was melted in
 * @param transfer_pub public transfer key for the session
 */
static void
handle_transfer_data (void *cls,
                      const struct GNUNET_HashCode *session_hash,
                      const struct TALER_TransferPublicKeyP *transfer_pub)
{
  struct HTD_Context *ctx = cls;
  struct TALER_EXCHANGEDB_LinkDataList *ldl;
  struct TEH_RESPONSE_LinkSessionInfo *lsi;

  if (GNUNET_OK != ctx->status)
    return;
  ldl = TEH_plugin->get_link_data_list (TEH_plugin->cls,
                                        ctx->session,
                                        session_hash);
  if (NULL == ldl)
  {
    ctx->status = GNUNET_NO;
    if (MHD_NO ==
        TEH_RESPONSE_reply_json_pack (ctx->connection,
                                      MHD_HTTP_NOT_FOUND,
                                      "{s:s}",
                                      "error",
                                      "link data not found (link)"))
      ctx->status = GNUNET_SYSERR;
    return;
  }
  GNUNET_array_grow (ctx->sessions,
                     ctx->num_sessions,
                     ctx->num_sessions + 1);
  lsi = &ctx->sessions[ctx->num_sessions - 1];
  lsi->transfer_pub = *transfer_pub;
  lsi->ldl = ldl;
}


/**
 * Execute a "/refresh/link".  Returns the linkage information that
 * will allow the owner of a coin to follow the refresh trail to
 * the refreshed coin.
 *
 * @param connection the MHD connection to handle
 * @param coin_pub public key of the coin to link
 * @return MHD result code
 */
int
TEH_DB_execute_refresh_link (struct MHD_Connection *connection,
                             const struct TALER_CoinSpendPublicKeyP *coin_pub)
{
  struct HTD_Context ctx;
  int res;
  unsigned int i;

  if (NULL == (ctx.session = TEH_plugin->get_session (TEH_plugin->cls)))
  {
    GNUNET_break (0);
    return TEH_RESPONSE_reply_internal_db_error (connection,
						 TALER_EC_DB_SETUP_FAILED);
  }
  ctx.connection = connection;
  ctx.num_sessions = 0;
  ctx.sessions = NULL;
  ctx.status = GNUNET_OK;
  res = TEH_plugin->get_transfer (TEH_plugin->cls,
                                  ctx.session,
                                  coin_pub,
                                  &handle_transfer_data,
                                  &ctx);
  if (GNUNET_SYSERR == ctx.status)
  {
    res = MHD_NO;
    goto cleanup;
  }
  if (GNUNET_NO == ctx.status)
  {
    res = MHD_YES;
    goto cleanup;
  }
  GNUNET_assert (GNUNET_OK == ctx.status);
  if (0 == ctx.num_sessions)
    return TEH_RESPONSE_reply_arg_unknown (connection,
					   TALER_EC_REFRESH_LINK_COIN_UNKNOWN,
                                           "coin_pub");
  res = TEH_RESPONSE_reply_refresh_link_success (connection,
                                                 ctx.num_sessions,
                                                 ctx.sessions);
 cleanup:
  for (i=0;i<ctx.num_sessions;i++)
    TEH_plugin->free_link_data_list (TEH_plugin->cls,
                                     ctx.sessions[i].ldl);
  GNUNET_free_non_null (ctx.sessions);
  return res;
}


/* end of taler-exchange-httpd_db.c */