path: root/src/include/taler_exchangedb_plugin.h

/*
  This file is part of TALER
  Copyright (C) 2014, 2015, 2016 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, If not, see <http://www.gnu.org/licenses/>
*/
/**
 * @file include/taler_exchangedb_plugin.h
 * @brief Low-level (statement-level) database access for the exchange
 * @author Florian Dold
 * @author Christian Grothoff
 */
#ifndef TALER_EXCHANGEDB_PLUGIN_H
#define TALER_EXCHANGEDB_PLUGIN_H

#include <jansson.h>
#include <gnunet/gnunet_util_lib.h>
#include "taler_exchangedb_lib.h"


/**
 * @brief Information we keep on bank transfer(s) that established a reserve.
 */
struct TALER_EXCHANGEDB_BankTransfer
{

  /**
   * Public key of the reserve that was filled.
   */
  struct TALER_ReservePublicKeyP reserve_pub;

  /**
   * Amount that was transferred to the exchange.
   */
  struct TALER_Amount amount;

  /**
   * When did the exchange receive the incoming transaction?
   * (This is the execution date of the exchange's database,
   * the execution date of the bank should be in @e wire).
   */
  struct GNUNET_TIME_Absolute execution_date;

  /**
   * Detailed wire information about the sending account.
   */
  json_t *sender_account_details;

  /**
   * Detailed wire transfer information that uniquely identifies the
   * wire transfer.
   */
  json_t *transfer_details;

};


/**
 * @brief A summary of a Reserve
 */
struct TALER_EXCHANGEDB_Reserve
{
  /**
   * The reserve's public key.  This uniquely identifies the reserve
   */
  struct TALER_ReservePublicKeyP pub;

  /**
   * The balance amount existing in the reserve
   */
  struct TALER_Amount balance;

  /**
   * The expiration date of this reserve
   */
  struct GNUNET_TIME_Absolute expiry;
};


/**
 * @brief Information we keep for a withdrawn coin to reproduce
 * the /withdraw operation if needed, and to have proof
 * that a reserve was drained by this amount.
 */
struct TALER_EXCHANGEDB_CollectableBlindcoin
{

  /**
   * Our signature over the (blinded) coin.
   */
  struct TALER_DenominationSignature sig;

  /**
   * Denomination key (which coin was generated).
   */
  struct TALER_DenominationPublicKey denom_pub;

  /**
   * Value of the coin being exchangeed (matching the denomination key)
   * plus the transaction fee.  We include this in what is being
   * signed so that we can verify a reserve's remaining total balance
   * without needing to access the respective denomination key
   * information each time.
   */
  struct TALER_Amount amount_with_fee;

  /**
   * Withdrawl fee charged by the exchange.  This must match the Exchange's
   * denomination key's withdrawl fee.  If the client puts in an
   * invalid withdrawl fee (too high or too low) that does not match
   * the Exchange's denomination key, the withdraw operation is invalid
   * and will be rejected by the exchange.  The @e amount_with_fee minus
   * the @e withdraw_fee is must match the value of the generated
   * coin.  We include this in what is being signed so that we can
   * verify a exchange's accounting without needing to access the
   * respective denomination key information each time.
   */
  struct TALER_Amount withdraw_fee;

  /**
   * Public key of the reserve that was drained.
   */
  struct TALER_ReservePublicKeyP reserve_pub;

  /**
   * Hash over the blinded message, needed to verify
   * the @e reserve_sig.
   */
  struct GNUNET_HashCode h_coin_envelope;

  /**
   * Signature confirming the withdrawl, matching @e reserve_pub,
   * @e denom_pub and @e h_coin_envelope.
   */
  struct TALER_ReserveSignatureP reserve_sig;
};



/**
 * @brief Types of operations on a reserved.
 */
enum TALER_EXCHANGEDB_ReserveOperation
{
  /**
   * Money was deposited into the reserve via a bank transfer.
   */
  TALER_EXCHANGEDB_RO_BANK_TO_EXCHANGE = 0,

  /**
   * A Coin was withdrawn from the reserve using /withdraw.
   */
  TALER_EXCHANGEDB_RO_WITHDRAW_COIN = 1
};


/**
 * @brief Reserve history as a linked list.  Lists all of the transactions
 * associated with this reserve (such as the bank transfers that
 * established the reserve and all /withdraw operations we have done
 * since).
 */
struct TALER_EXCHANGEDB_ReserveHistory
{

  /**
   * Next entry in the reserve history.
   */
  struct TALER_EXCHANGEDB_ReserveHistory *next;

  /**
   * Type of the event, determins @e details.
   */
  enum TALER_EXCHANGEDB_ReserveOperation type;

  /**
   * Details of the operation, depending on @e type.
   */
  union
  {

    /**
     * Details about a bank transfer to the exchange.
     */
    struct TALER_EXCHANGEDB_BankTransfer *bank;

    /**
     * Details about a /withdraw operation.
     */
    struct TALER_EXCHANGEDB_CollectableBlindcoin *withdraw;

  } details;

};


/**
 * @brief Specification for a /deposit operation.  The combination of
 * the coin's public key, the merchant's public key and the
 * transaction ID must be unique.  While a coin can (theoretically) be
 * deposited at the same merchant twice (with partial spending), the
 * merchant must either use a different public key or a different
 * transaction ID for the two transactions.  The same coin must not
 * be used twice at the same merchant for the same transaction
 * (as determined by transaction ID).
 */
struct TALER_EXCHANGEDB_Deposit
{
  /**
   * Information about the coin that is being deposited.
   */
  struct TALER_CoinPublicInfo coin;

  /**
   * ECDSA signature affirming that the customer intends
   * this coin to be deposited at the merchant identified
   * by @e h_wire in relation to the contract identified
   * by @e h_contract.
   */
  struct TALER_CoinSpendSignatureP csig;

  /**
   * Public key of the merchant.  Enables later identification
   * of the merchant in case of a need to rollback transactions.
   */
  struct TALER_MerchantPublicKeyP merchant_pub;

  /**
   * Hash over the contract between merchant and customer
   * (remains unknown to the Exchange).
   */
  struct GNUNET_HashCode h_contract;

  /**
   * Hash of the (canonical) representation of @e wire, used
   * to check the signature on the request.  Generated by
   * the exchange from the detailed wire data provided by the
   * merchant.
   */
  struct GNUNET_HashCode h_wire;

  /**
   * Detailed information about the receiver for executing the transaction.
   */
  json_t *receiver_wire_account;

  /**
   * Merchant-generated transaction ID to detect duplicate
   * transactions.
   */
  uint64_t transaction_id;

  /**
   * Time when this request was generated.  Used, for example, to
   * assess when (roughly) the income was achieved for tax purposes.
   * Note that the Exchange will only check that the timestamp is not "too
   * far" into the future (i.e. several days).  The fact that the
   * timestamp falls within the validity period of the coin's
   * denomination key is irrelevant for the validity of the deposit
   * request, as obviously the customer and merchant could conspire to
   * set any timestamp.  Also, the Exchange must accept very old deposit
   * requests, as the merchant might have been unable to transmit the
   * deposit request in a timely fashion (so back-dating is not
   * prevented).
   */
  struct GNUNET_TIME_Absolute timestamp;

  /**
   * How much time does the merchant have to issue a refund request?
   * Zero if refunds are not allowed.  After this time, the coin
   * cannot be refunded.
   */
  struct GNUNET_TIME_Absolute refund_deadline;

  /**
   * How much time does the merchant have to execute the wire transfer?
   * This time is advisory for aggregating transactions, not a hard
   * constraint (as the merchant can theoretically pick any time,
   * including one in the past).
   */
  struct GNUNET_TIME_Absolute wire_deadline;

  /**
   * Fraction of the coin's remaining value to be deposited, including
   * depositing fee (if any).  The coin is identified by @e coin_pub.
   */
  struct TALER_Amount amount_with_fee;

  /**
   * Depositing fee.
   */
  struct TALER_Amount deposit_fee;

};


/**
 * @brief Specification for a /refund operation.  The combination of
 * the coin's public key, the merchant's public key and the
 * transaction ID must be unique.  While a coin can (theoretically) be
 * deposited at the same merchant twice (with partial spending), the
 * merchant must either use a different public key or a different
 * transaction ID for the two transactions.  The same goes for
 * refunds, hence we also have a "rtransaction" ID which is disjoint
 * from the transaction ID.  The same coin must not be used twice at
 * the same merchant for the same transaction or rtransaction ID.
 */
struct TALER_EXCHANGEDB_Refund
{
  /**
   * Information about the coin that is being refunded.
   */
  struct TALER_CoinPublicInfo coin;

  /**
   * Public key of the merchant.
   */
  struct TALER_MerchantPublicKeyP merchant_pub;

  /**
   * Signature from the merchant affirming the refund.
   */
  struct TALER_MerchantSignatureP merchant_sig;

  /**
   * Hash over the contract between merchant and customer
   * (remains unknown to the Exchange).
   */
  struct GNUNET_HashCode h_contract;

  /**
   * Merchant-generated transaction ID to detect duplicate
   * transactions, of the original transaction that is being
   * refunded.
   */
  uint64_t transaction_id;

  /**
   * Merchant-generated REFUND transaction ID to detect duplicate
   * refunds.
   */
  uint64_t rtransaction_id;

  /**
   * Fraction of the original deposit's value to be refunded, including
   * refund fee (if any).  The coin is identified by @e coin_pub.
   */
  struct TALER_Amount refund_amount;

  /**
   * Refund fee to be covered by the customer.
   */
  struct TALER_Amount refund_fee;

};


/**
 * @brief Specification for coin in a /refresh/melt operation.
 */
struct TALER_EXCHANGEDB_RefreshMelt
{
  /**
   * Information about the coin that is being melted.
   */
  struct TALER_CoinPublicInfo coin;

  /**
   * Signature over the melting operation.
   */
  struct TALER_CoinSpendSignatureP coin_sig;

  /**
   * Hash of the refresh session this coin is melted into.
   */
  struct GNUNET_HashCode session_hash;

  /**
   * How much value is being melted?  This amount includes the fees,
   * so the final amount contributed to the melt is this value minus
   * the fee for melting the coin.  We include the fee in what is
   * being signed so that we can verify a reserve's remaining total
   * balance without needing to access the respective denomination key
   * information each time.
   */
  struct TALER_Amount amount_with_fee;

  /**
   * Melting fee charged by the exchange.  This must match the Exchange's
   * denomination key's melting fee.  If the client puts in an invalid
   * melting fee (too high or too low) that does not match the Exchange's
   * denomination key, the melting operation is invalid and will be
   * rejected by the exchange.  The @e amount_with_fee minus the @e
   * melt_fee is the amount that will be credited to the melting
   * session.
   */
  struct TALER_Amount melt_fee;

};


/**
 * @brief Global information for a refreshing session.  Includes
 * dimensions of the operation, security parameters and
 * client signatures from "/refresh/melt" and "/refresh/commit".
 */
struct TALER_EXCHANGEDB_RefreshSession
{

  /**
   * Melt operation details.
   */
  struct TALER_EXCHANGEDB_RefreshMelt melt;

  /**
   * Number of new coins we are creating.
   */
  uint16_t num_newcoins;

  /**
   * Index (smaller #TALER_CNC_KAPPA) which the exchange has chosen to not
   * have revealed during cut and choose.
   */
  uint16_t noreveal_index;

};


/**
 * @brief We have as many `struct TALER_EXCHANGEDB_RefreshCommitCoin` as there are new
 * coins being created by the refresh (for each of the #TALER_CNC_KAPPA
 * sets).  These are the coins we ask the exchange to sign if the
 * respective set is selected.
 */
struct TALER_EXCHANGEDB_RefreshCommitCoin
{

  /**
   * Encrypted data allowing those able to decrypt it to derive
   * the private keys of the new coins created by the refresh.
   */
  struct TALER_RefreshLinkEncryptedP refresh_link;

  /**
   * Blinded message to be signed (in envelope), with @e coin_env_size bytes.
   */
  char *coin_ev;

  /**
   * Number of bytes in @e coin_ev.
   */
  size_t coin_ev_size;

};


/**
 * @brief Linked list of refresh information linked to a coin.
 */
struct TALER_EXCHANGEDB_LinkDataList
{
  /**
   * Information is stored in a NULL-terminated linked list.
   */
  struct TALER_EXCHANGEDB_LinkDataList *next;

  /**
   * Link data, used to recover the private key of the coin
   * by the owner of the old coin.
   */
  struct TALER_RefreshLinkEncryptedP link_data_enc;

  /**
   * Denomination public key, determines the value of the coin.
   */
  struct TALER_DenominationPublicKey denom_pub;

  /**
   * Signature over the blinded envelope.
   */
  struct TALER_DenominationSignature ev_sig;
};


/**
 * @brief Enumeration to classify the different types of transactions
 * that can be done with a coin.
 */
enum TALER_EXCHANGEDB_TransactionType
{
  /**
   * /deposit operation.
   */
  TALER_EXCHANGEDB_TT_DEPOSIT = 0,

  /**
   * /refresh/melt operation.
   */
  TALER_EXCHANGEDB_TT_REFRESH_MELT = 1,

  /**
   * /refund operation.
   */
  TALER_EXCHANGEDB_TT_REFUND = 2

};


/**
 * @brief List of transactions we performed for a particular coin.
 */
struct TALER_EXCHANGEDB_TransactionList
{

  /**
   * Next pointer in the NULL-terminated linked list.
   */
  struct TALER_EXCHANGEDB_TransactionList *next;

  /**
   * Type of the transaction, determines what is stored in @e details.
   */
  enum TALER_EXCHANGEDB_TransactionType type;

  /**
   * Details about the transaction, depending on @e type.
   */
  union
  {

    /**
     * Details if transaction was a /deposit operation.
     */
    struct TALER_EXCHANGEDB_Deposit *deposit;

    /**
     * Details if transaction was a /refresh/melt operation.
     */
    struct TALER_EXCHANGEDB_RefreshMelt *melt;

    /**
     * Details if transaction was a /refund operation.
     */
    struct TALER_EXCHANGEDB_Refund *refund;

  } details;

};


/**
 * @brief All of the information from a /refresh/melt commitment.
 */
struct TALER_EXCHANGEDB_MeltCommitment
{

  /**
   * Number of new coins we are creating.
   */
  uint16_t num_newcoins;

  /**
   * Array of @e num_newcoins denomination keys
   */
  struct TALER_DenominationPublicKey *denom_pubs;

  /**
   * 2D-Array of #TALER_CNC_KAPPA and @e num_newcoins commitments.
   */
  struct TALER_EXCHANGEDB_RefreshCommitCoin *commit_coins[TALER_CNC_KAPPA];

  /**
   * Array of #TALER_CNC_KAPPA links.
   */
  struct TALER_RefreshCommitLinkP commit_links[TALER_CNC_KAPPA];
};


/**
 * @brief Handle for a database session (per-thread, for transactions).
 */
struct TALER_EXCHANGEDB_Session;


/**
 * Function called with details about deposits that
 * have been made, with the goal of executing the
 * corresponding wire transaction.
 *
 * @param cls closure
 * @param rowid unique ID for the deposit in our DB, used for marking
 *              it as 'tiny' or 'done'
 * @param merchant_pub public key of the merchant
 * @param coin_pub public key of the coin
 * @param amount_with_fee amount that was deposited including fee
 * @param deposit_fee amount the exchange gets to keep as transaction fees
 * @param transaction_id unique transaction ID chosen by the merchant
 * @param h_contract hash of the contract between merchant and customer
 * @param wire_deadline by which the merchant adviced that he would like the
 *        wire transfer to be executed
 * @param receiver_wire_account wire details for the merchant, NULL from iterate_matching_deposits()
 * @return #GNUNET_OK to continue to iterate, #GNUNET_SYSERR to stop
 */
typedef int
(*TALER_EXCHANGEDB_DepositIterator)(void *cls,
                                    unsigned long long rowid,
                                    const struct TALER_MerchantPublicKeyP *merchant_pub,
                                    const struct TALER_CoinSpendPublicKeyP *coin_pub,
                                    const struct TALER_Amount *amount_with_fee,
                                    const struct TALER_Amount *deposit_fee,
                                    uint64_t transaction_id,
                                    const struct GNUNET_HashCode *h_contract,
                                    struct GNUNET_TIME_Absolute wire_deadline,
                                    const json_t *receiver_wire_account);


/**
 * Function called with the session hashes and transfer secret
 * information for a given coin.
 *
 * @param cls closure
 * @param session_hash a session the coin was melted in
 * @param transfer_pub public transfer key for the session
 * @param shared_secret_enc set to shared secret for the session
 */
typedef void
(*TALER_EXCHANGEDB_TransferDataCallback)(void *cls,
                                         const struct GNUNET_HashCode *session_hash,
                                         const struct TALER_TransferPublicKeyP *transfer_pub,
                                         const struct TALER_EncryptedLinkSecretP *shared_secret_enc);


/**
 * Function called with the results of the lookup of the
 * wire transfer identifier information.  Only called if
 * we are at least aware of the transaction existing.
 *
 * @param cls closure
 * @param wtid wire transfer identifier, NULL
 *         if the transaction was not yet done
 * @param coin_contribution how much did the coin we asked about
 *        contribute to the total transfer value? (deposit value including fee)
 * @param coin_fee how much did the exchange charge for the deposit fee
 * @param execution_time when was the transaction done, or
 *         when we expect it to be done (if @a wtid was NULL)
 */
typedef void
(*TALER_EXCHANGEDB_TrackTransactionCallback)(void *cls,
                                        const struct TALER_WireTransferIdentifierRawP *wtid,
                                        const struct TALER_Amount *coin_contribution,
                                        const struct TALER_Amount *coin_fee,
                                        struct GNUNET_TIME_Absolute execution_time);


/**
 * Function called with the results of the lookup of the
 * transaction data associated with a wire transfer identifier.
 *
 * @param cls closure
 * @param merchant_pub public key of the merchant (should be same for all callbacks with the same @e cls)
 * @param h_wire hash of wire transfer details of the merchant (should be same for all callbacks with the same @e cls)
 * @param h_contract which contract was this payment about
 * @param transaction_id merchant's transaction ID for the payment
 * @param coin_pub which public key was this payment about
 * @param coin_value amount contributed by this coin in total (with fee)
 * @param coin_fee applicable fee for this coin
 */
typedef void
(*TALER_EXCHANGEDB_WireTransferDataCallback)(void *cls,
                                             const struct TALER_MerchantPublicKeyP *merchant_pub,
                                             const struct GNUNET_HashCode *h_wire,
                                             const struct GNUNET_HashCode *h_contract,
                                             uint64_t transaction_id,
                                             const struct TALER_CoinSpendPublicKeyP *coin_pub,
                                             const struct TALER_Amount *coin_value,
                                             const struct TALER_Amount *coin_fee);


/**
 * Callback with data about a prepared transaction.
 *
 * @param cls closure
 * @param rowid row identifier used to mark prepared transaction as done
 * @param wire_method which wire method is this preparation data for
 * @param buf transaction data that was persisted, NULL on error
 * @param buf_size number of bytes in @a buf, 0 on error
 */
typedef void
(*TALER_EXCHANGEDB_WirePreparationCallback) (void *cls,
                                             unsigned long long rowid,
                                             const char *wire_method,
                                             const char *buf,
                                             size_t buf_size);


/**
 * @brief The plugin API, returned from the plugin's "init" function.
 * The argument given to "init" is simply a configuration handle.
 */
struct TALER_EXCHANGEDB_Plugin
{

  /**
   * Closure for all callbacks.
   */
  void *cls;

  /**
   * Name of the library which generated this plugin.  Set by the
   * plugin loader.
   */
  char *library_name;

  /**
   * Get the thread-local database-handle.
   * Connect to the db if the connection does not exist yet.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param the database connection, or NULL on error
   */
  struct TALER_EXCHANGEDB_Session *
  (*get_session) (void *cls);


  /**
   * Drop the Taler tables.  This should only be used in testcases.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @return #GNUNET_OK upon success; #GNUNET_SYSERR upon failure
   */
  int
  (*drop_tables) (void *cls);


  /**
   * Create the necessary tables if they are not present
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @return #GNUNET_OK upon success; #GNUNET_SYSERR upon failure
   */
  int
  (*create_tables) (void *cls);


  /**
   * Start a transaction.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to use
   * @return #GNUNET_OK on success
   */
  int
  (*start) (void *cls,
            struct TALER_EXCHANGEDB_Session *session);


  /**
   * Commit a transaction.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to use
   * @return #GNUNET_OK on success, #GNUNET_NO if the transaction
   *         can be retried, #GNUNET_SYSERR on hard failures
   */
  int
  (*commit) (void *cls,
             struct TALER_EXCHANGEDB_Session *session);


  /**
   * Abort/rollback a transaction.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to use
   */
  void
  (*rollback) (void *cls,
               struct TALER_EXCHANGEDB_Session *session);


  /**
   * Insert information about a denomination key and in particular
   * the properties (value, fees, expiration times) the coins signed
   * with this key have.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to use
   * @param denom_pub the public key used for signing coins of this denomination
   * @param issue issuing information with value, fees and other info about the coin
   * @return #GNUNET_OK on success; #GNUNET_SYSERR on failure
   */
  int
  (*insert_denomination_info) (void *cls,
                               struct TALER_EXCHANGEDB_Session *session,
                               const struct TALER_DenominationPublicKey *denom_pub,
                               const struct TALER_EXCHANGEDB_DenominationKeyInformationP *issue);


  /**
   * Fetch information about a denomination key.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to use
   * @param denom_pub the public key used for signing coins of this denomination
   * @param[out] issue set to issue information with value, fees and other info about the coin, can be NULL
   * @return #GNUNET_OK on success; #GNUNET_NO if no record was found, #GNUNET_SYSERR on failure
   */
  int
  (*get_denomination_info) (void *cls,
                            struct TALER_EXCHANGEDB_Session *session,
                            const struct TALER_DenominationPublicKey *denom_pub,
                            struct TALER_EXCHANGEDB_DenominationKeyInformationP *issue);


  /**
   * Get the summary of a reserve.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param db the database connection handle
   * @param[in,out] reserve the reserve data.  The public key of the reserve should be set
   *          in this structure; it is used to query the database.  The balance
   *          and expiration are then filled accordingly.
   * @return #GNUNET_OK upon success; #GNUNET_SYSERR upon failure
   */
  int
  (*reserve_get) (void *cls,
                  struct TALER_EXCHANGEDB_Session *db,
                  struct TALER_EXCHANGEDB_Reserve *reserve);


  /**
   * Insert a incoming transaction into reserves.  New reserves are
   * also created through this function.  Note that this API call
   * starts (and stops) its own transaction scope (so the application
   * must not do so).
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param db the database connection handle
   * @param reserve_pub public key of the reserve
   * @param balance the amount that has to be added to the reserve
   * @param execution_time when was the amount added
   * @param sender_account_details information about the sender
   * @param transfer_details information that uniquely identifies the wire transfer
   * @return #GNUNET_OK upon success; #GNUNET_NO if the given
   *         @a details are already known for this @a reserve_pub,
   *         #GNUNET_SYSERR upon failures (DB error, incompatible currency)
   */
  int
  (*reserves_in_insert) (void *cls,
                         struct TALER_EXCHANGEDB_Session *db,
                         const struct TALER_ReservePublicKeyP *reserve_pub,
                         const struct TALER_Amount *balance,
                         struct GNUNET_TIME_Absolute execution_time,
                         const json_t *sender_account_details,
                         const json_t *transfer_details);


  /**
   * Locate the response for a /withdraw request under the
   * key of the hash of the blinded message.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection to use
   * @param h_blind hash of the blinded coin to be signed (will match
   *                `h_coin_envelope` in the @a collectable to be returned)
   * @param collectable corresponding collectable coin (blind signature)
   *                    if a coin is found
   * @return #GNUNET_SYSERR on internal error
   *         #GNUNET_NO if the collectable was not found
   *         #GNUNET_YES on success
   */
  int
  (*get_withdraw_info) (void *cls,
                        struct TALER_EXCHANGEDB_Session *session,
                        const struct GNUNET_HashCode *h_blind,
                        struct TALER_EXCHANGEDB_CollectableBlindcoin *collectable);


  /**
   * Store collectable bit coin under the corresponding
   * hash of the blinded message.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection to use
   * @param collectable corresponding collectable coin (blind signature)
   *                    if a coin is found
   * @return #GNUNET_SYSERR on internal error
   *         #GNUNET_NO if the collectable was not found
   *         #GNUNET_YES on success
   */
  int
  (*insert_withdraw_info) (void *cls,
                           struct TALER_EXCHANGEDB_Session *session,
                           const struct TALER_EXCHANGEDB_CollectableBlindcoin *collectable);


  /**
   * Get all of the transaction history associated with the specified
   * reserve.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to use
   * @param reserve_pub public key of the reserve
   * @return known transaction history (NULL if reserve is unknown)
   */
  struct TALER_EXCHANGEDB_ReserveHistory *
  (*get_reserve_history) (void *cls,
                          struct TALER_EXCHANGEDB_Session *session,
                          const struct TALER_ReservePublicKeyP *reserve_pub);


  /**
   * Free memory associated with the given reserve history.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param rh history to free.
   */
  void
  (*free_reserve_history) (void *cls,
                           struct TALER_EXCHANGEDB_ReserveHistory *rh);


  /**
   * Check if we have the specified deposit already in the database.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection
   * @param deposit deposit to search for
   * @return #GNUNET_YES if we know this operation,
   *         #GNUNET_NO if this exact deposit is unknown to us,
   *         #GNUNET_SYSERR on DB error
   */
  int
  (*have_deposit) (void *cls,
                   struct TALER_EXCHANGEDB_Session *session,
                   const struct TALER_EXCHANGEDB_Deposit *deposit);


  /**
   * Insert information about deposited coin into the database.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to the database
   * @param deposit deposit information to store
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
   */
  int
  (*insert_deposit) (void *cls,
                     struct TALER_EXCHANGEDB_Session *session,
                     const struct TALER_EXCHANGEDB_Deposit *deposit);


  /**
   * Insert information about refunded coin into the database.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to the database
   * @param refund refund information to store
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
   */
  int
  (*insert_refund) (void *cls,
                    struct TALER_EXCHANGEDB_Session *session,
                    const struct TALER_EXCHANGEDB_Refund *refund);


  /**
   * Mark a deposit as tiny, thereby declaring that it cannot be
   * executed by itself and should no longer be returned by
   * @e iterate_ready_deposits()
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to the database
   * @param deposit_rowid identifies the deposit row to modify
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
   */
  int
  (*mark_deposit_tiny) (void *cls,
                        struct TALER_EXCHANGEDB_Session *session,
                        unsigned long long rowid);


  /**
   * Test if a deposit was marked as done, thereby declaring that it cannot be
   * refunded anymore.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to the database
   * @param deposit the deposit to check
   * @return #GNUNET_YES if is is marked done done, #GNUNET_NO if not,
   *         #GNUNET_SYSERR on error (deposit unknown)
   */
  int
  (*test_deposit_done) (void *cls,
                        struct TALER_EXCHANGEDB_Session *session,
                        const struct TALER_EXCHANGEDB_Deposit *deposit);


  /**
   * Mark a deposit as done, thereby declaring that it cannot be
   * executed at all anymore, and should no longer be returned by
   * @e iterate_ready_deposits() or @e iterate_matching_deposits().
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to the database
   * @param deposit_rowid identifies the deposit row to modify
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
   */
  int
  (*mark_deposit_done) (void *cls,
                        struct TALER_EXCHANGEDB_Session *session,
                        unsigned long long rowid);


  /**
   * Obtain information about deposits that are ready to be executed.
   * Such deposits must not be marked as "tiny" or "done", and the
   * execution time and refund deadlines must both be in the past.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to the database
   * @param deposit_cb function to call for ONE such deposit
   * @param deposit_cb_cls closure for @a deposit_cb
   * @return number of rows processed, 0 if none exist,
   *         #GNUNET_SYSERR on error
   */
  int
  (*get_ready_deposit) (void *cls,
                        struct TALER_EXCHANGEDB_Session *session,
                        TALER_EXCHANGEDB_DepositIterator deposit_cb,
                        void *deposit_cb_cls);


/**
 * Maximum number of results we return from iterate_matching_deposits().
 *
 * Limit on the number of transactions we aggregate at once.  Note
 * that the limit must be big enough to ensure that when transactions
 * of the smallest possible unit are aggregated, they do surpass the
 * "tiny" threshold beyond which we never trigger a wire transaction!
 */
#define TALER_EXCHANGEDB_MATCHING_DEPOSITS_LIMIT 10000
#define TALER_EXCHANGEDB_MATCHING_DEPOSITS_LIMIT_STR "10000"

  /**
   * Obtain information about other pending deposits for the same
   * destination.  Those deposits must not already be "done".
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session connection to the database
   * @param h_wire destination of the wire transfer
   * @param merchant_pub public key of the merchant
   * @param deposit_cb function to call for each deposit
   * @param deposit_cb_cls closure for @a deposit_cb
   * @param limit maximum number of matching deposits to return; should
   *        be #TALER_EXCHANGEDB_MATCHING_DEPOSITS_LIMIT, larger values
   *        are not supported, smaller values would be inefficient.
   * @return number of rows processed, 0 if none exist,
   *         #GNUNET_SYSERR on error
   */
  int
  (*iterate_matching_deposits) (void *cls,
                                struct TALER_EXCHANGEDB_Session *session,
                                const struct GNUNET_HashCode *h_wire,
                                const struct TALER_MerchantPublicKeyP *merchant_pub,
                                TALER_EXCHANGEDB_DepositIterator deposit_cb,
                                void *deposit_cb_cls,
                                uint32_t limit);


  /**
   * Lookup refresh session data under the given @a session_hash.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database handle to use
   * @param session_hash hash over the melt to use for the lookup
   * @param[out] refresh_session where to store the result
   * @return #GNUNET_YES on success,
   *         #GNUNET_NO if not found,
   *         #GNUNET_SYSERR on DB failure
   */
  int
  (*get_refresh_session) (void *cls,
                          struct TALER_EXCHANGEDB_Session *session,
                          const struct GNUNET_HashCode *session_hash,
                          struct TALER_EXCHANGEDB_RefreshSession *refresh_session);


  /**
   * Store new refresh session data under the given @a session_hash.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database handle to use
   * @param session_hash hash over the melt to use to locate the session
   * @param refresh_session session data to store
   * @return #GNUNET_YES on success,
   *         #GNUNET_SYSERR on DB failure
   */
  int
  (*create_refresh_session) (void *cls,
                             struct TALER_EXCHANGEDB_Session *session,
                             const struct GNUNET_HashCode *session_hash,
                             const struct TALER_EXCHANGEDB_RefreshSession *refresh_session);


  /**
   * Store in the database which coin(s) we want to create
   * in a given refresh operation.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection
   * @param session_hash hash to identify refresh session
   * @param num_newcoins number of coins to generate, size of the @a denom_pubs array
   * @param denom_pubs array denominations of the coins to create
   * @return #GNUNET_OK on success
   *         #GNUNET_SYSERR on internal error
   */
  int
  (*insert_refresh_order) (void *cls,
                           struct TALER_EXCHANGEDB_Session *session,
                           const struct GNUNET_HashCode *session_hash,
                           uint16_t num_newcoins,
                           const struct TALER_DenominationPublicKey *denom_pubs);


  /**
   * Lookup in the database for the @a num_newcoins coins that we want to
   * create in the given refresh operation.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection
   * @param session_hash hash to identify refresh session
   * @param num_newcoins size of the @a denom_pubs array
   * @param[out] denom_pubs where to write @a num_newcoins denomination keys
   * @return #GNUNET_OK on success
   *         #GNUNET_SYSERR on internal error
   */
  int
  (*get_refresh_order) (void *cls,
                        struct TALER_EXCHANGEDB_Session *session,
                        const struct GNUNET_HashCode *session_hash,
                        uint16_t num_newcoins,
                        struct TALER_DenominationPublicKey *denom_pubs);


  /**
   * Store information about the commitments of the given index @a i
   * for the given refresh session in the database.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection to use
   * @param session_hash hash to identify refresh session
   * @param cnc_index cut and choose index (1st dimension), relating to #TALER_CNC_KAPPA
   * @param num_newcoins coin index size of the @a commit_coins array
   * @param commit_coin array of coin commitments to store
   * @return #GNUNET_OK on success
   *         #GNUNET_SYSERR on error
   */
  int
  (*insert_refresh_commit_coins) (void *cls,
                                  struct TALER_EXCHANGEDB_Session *session,
                                  const struct GNUNET_HashCode *session_hash,
                                  uint16_t cnc_index,
                                  uint16_t num_newcoins,
                                  const struct TALER_EXCHANGEDB_RefreshCommitCoin *commit_coins);


  /**
   * Obtain information about the commitment of the
   * given coin of the given refresh session from the database.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection to use
   * @param session_hash hash to identify refresh session
   * @param cnc_index cut and choose set index (1st dimension)
   * @param num_coins size of the @a commit_coins array
   * @param[out] commit_coins array of coin commitments to return
   * @return #GNUNET_OK on success
   *         #GNUNET_NO if not found
   *         #GNUNET_SYSERR on error
   */
  int
  (*get_refresh_commit_coins) (void *cls,
                               struct TALER_EXCHANGEDB_Session *session,
                               const struct GNUNET_HashCode *session_hash,
                               uint16_t cnc_index,
                               uint16_t num_coins,
                               struct TALER_EXCHANGEDB_RefreshCommitCoin *commit_coins);

  /**
   * Free refresh @a commit_coins data obtained via @e get_refresh_commit_coins.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param num_coins size of the @a commit_coins array
   * @param commit_coins array of coin commitments to free
   */
  void
  (*free_refresh_commit_coins) (void *cls,
                                unsigned int num_coins,
                                struct TALER_EXCHANGEDB_RefreshCommitCoin *commit_coins);


  /**
   * Store the commitment to the given (encrypted) refresh link data
   * for the given refresh session.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection to use
   * @param session_hash hash to identify refresh session
   * @param cnc_index cut and choose index, relating to #TALER_CNC_KAPPA
   * @param link link information to store
   * @return #GNUNET_SYSERR on internal error, #GNUNET_OK on success
   */
  int
  (*insert_refresh_commit_link) (void *cls,
                                 struct TALER_EXCHANGEDB_Session *session,
                                 const struct GNUNET_HashCode *session_hash,
                                 uint16_t cnc_index,
                                 const struct TALER_RefreshCommitLinkP *link);

  /**
   * Obtain the commited (encrypted) refresh link data
   * for the given refresh session.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection to use
   * @param session_hash hash to identify refresh session
   * @param cnc_index cut and choose index (1st dimension)
   * @param[out] link information to return
   * @return #GNUNET_SYSERR on internal error,
   *         #GNUNET_NO if commitment was not found
   *         #GNUNET_OK on success
   */
  int
  (*get_refresh_commit_link) (void *cls,
                              struct TALER_EXCHANGEDB_Session *session,
                              const struct GNUNET_HashCode *session_hash,
                              uint16_t cnc_index,
                              struct TALER_RefreshCommitLinkP *link);


  /**
   * Get all of the information from the given melt commit operation.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection to use
   * @param session_hash hash to identify refresh session
   * @return NULL if the @a session_hash does not correspond to any known melt
   *         operation
   */
  struct TALER_EXCHANGEDB_MeltCommitment *
  (*get_melt_commitment) (void *cls,
                          struct TALER_EXCHANGEDB_Session *session,
                          const struct GNUNET_HashCode *session_hash);


  /**
   * Free information about a melt commitment.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param mc melt commitment data to free
   */
  void
  (*free_melt_commitment) (void *cls,
                           struct TALER_EXCHANGEDB_MeltCommitment *mc);


  /**
   * Insert signature of a new coin generated during refresh into
   * the database indexed by the refresh session and the index
   * of the coin.  This data is later used should an old coin
   * be used to try to obtain the private keys during "/refresh/link".
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection
   * @param session_hash hash to identify refresh session
   * @param newcoin_index coin index
   * @param ev_sig coin signature
   * @return #GNUNET_OK on success
   */
  int
  (*insert_refresh_out) (void *cls,
                         struct TALER_EXCHANGEDB_Session *session,
                         const struct GNUNET_HashCode *session_hash,
                         uint16_t newcoin_index,
                         const struct TALER_DenominationSignature *ev_sig);


  /**
   * Obtain the link data of a coin, that is the encrypted link
   * information, the denomination keys and the signatures.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection
   * @param session_hash session to get linkage data for
   * @return all known link data for the session
   */
  struct TALER_EXCHANGEDB_LinkDataList *
  (*get_link_data_list) (void *cls,
                         struct TALER_EXCHANGEDB_Session *session,
                         const struct GNUNET_HashCode *session_hash);


  /**
   * Free memory of the link data list.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param ldl link data list to release
   */
  void
  (*free_link_data_list) (void *cls,
                          struct TALER_EXCHANGEDB_LinkDataList *ldl);


  /**
   * Obtain shared secret and transfer public key from the public key of
   * the coin.  This information and the link information returned by
   * @e get_link_data_list() enable the owner of an old coin to determine
   * the private keys of the new coins after the melt.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection
   * @param coin_pub public key of the coin
   * @param tdc function to call for each session the coin was melted into
   * @param tdc_cls closure for @a tdc
   * @return #GNUNET_OK on success,
   *         #GNUNET_NO on failure (not found)
   *         #GNUNET_SYSERR on internal failure (database issue)
   */
  int
  (*get_transfer) (void *cls,
                   struct TALER_EXCHANGEDB_Session *session,
                   const struct TALER_CoinSpendPublicKeyP *coin_pub,
                   TALER_EXCHANGEDB_TransferDataCallback tdc,
                   void *tdc_cls);


  /**
   * Compile a list of all (historic) transactions performed
   * with the given coin (/refresh/melt and /deposit operations).
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection
   * @param coin_pub coin to investigate
   * @return list of transactions, NULL if coin is fresh
   */
  struct TALER_EXCHANGEDB_TransactionList *
  (*get_coin_transactions) (void *cls,
                            struct TALER_EXCHANGEDB_Session *session,
                            const struct TALER_CoinSpendPublicKeyP *coin_pub);


  /**
   * Free linked list of transactions.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param list list to free
   */
  void
  (*free_coin_transaction_list) (void *cls,
                                 struct TALER_EXCHANGEDB_TransactionList *list);


  /**
   * Lookup the list of Taler transactions that was aggregated
   * into a wire transfer by the respective @a raw_wtid.
   *
   * @param cls the @e cls of this struct with the plugin-specific state
   * @param session database connection
   * @param wtid the raw wire transfer identifier we used
   * @param cb function to call on each transaction found
   * @param cb_cls closure for @a cb
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on database errors,
   *         #GNUNET_NO if we found no results
   */
  int
  (*lookup_wire_transfer) (void *cls,
                           struct TALER_EXCHANGEDB_Session *session,
                           const struct TALER_WireTransferIdentifierRawP *wtid,
                           TALER_EXCHANGEDB_WireTransferDataCallback cb,
                           void *cb_cls);


  /**
   * Try to find the wire transfer details for a deposit operation.
   * If we did not execute the deposit yet, return when it is supposed
   * to be executed.
   *
   * @param cls closure
   * @param session database connection
   * @param h_contract hash of the contract
   * @param h_wire hash of merchant wire details
   * @param coin_pub public key of deposited coin
   * @param merchant_pub merchant public key
   * @param transaction_id transaction identifier
   * @param cb function to call with the result
   * @param cb_cls closure to pass to @a cb
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on DB errors,
   *         #GNUNET_NO if nothing was found
   */
  int
  (*wire_lookup_deposit_wtid)(void *cls,
                              struct TALER_EXCHANGEDB_Session *session,
			      const struct GNUNET_HashCode *h_contract,
			      const struct GNUNET_HashCode *h_wire,
			      const struct TALER_CoinSpendPublicKeyP *coin_pub,
			      const struct TALER_MerchantPublicKeyP *merchant_pub,
			      uint64_t transaction_id,
			      TALER_EXCHANGEDB_TrackTransactionCallback cb,
			      void *cb_cls);


  /**
   * Function called to insert aggregation information into the DB.
   *
   * @param cls closure
   * @param session database connection
   * @param wtid the raw wire transfer identifier we used
   * @param deposit_serial_id row in the deposits table for which this is aggregation data
   * @param execution_time when did we execute the transaction
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on DB errors
   */
  int
  (*insert_aggregation_tracking)(void *cls,
                                 struct TALER_EXCHANGEDB_Session *session,
                                 const struct TALER_WireTransferIdentifierRawP *wtid,
                                 unsigned long long deposit_serial_id,
                                 struct GNUNET_TIME_Absolute execution_time);


  /**
   * Function called to insert wire transfer commit data into the DB.
   *
   * @param cls closure
   * @param session database connection
   * @param type type of the wire transfer (i.e. "sepa")
   * @param buf buffer with wire transfer preparation data
   * @param buf_size number of bytes in @a buf
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on DB errors
   */
  int
  (*wire_prepare_data_insert)(void *cls,
                              struct TALER_EXCHANGEDB_Session *session,
                              const char *type,
                              const char *buf,
                              size_t buf_size);


  /**
   * Function called to mark wire transfer commit data as finished.
   *
   * @param cls closure
   * @param session database connection
   * @param rowid which entry to mark as finished
   * @return #GNUNET_OK on success, #GNUNET_SYSERR on DB errors
   */
  int
  (*wire_prepare_data_mark_finished)(void *cls,
                                     struct TALER_EXCHANGEDB_Session *session,
                                     unsigned long long rowid);


  /**
   * Function called to get an unfinished wire transfer
   * preparation data. Fetches at most one item.
   *
   * @param cls closure
   * @param session database connection
   * @param cb function to call for ONE unfinished item
   * @param cb_cls closure for @a cb
   * @return #GNUNET_OK on success,
   *         #GNUNET_NO if there are no entries,
   *         #GNUNET_SYSERR on DB errors
   */
  int
  (*wire_prepare_data_get)(void *cls,
                           struct TALER_EXCHANGEDB_Session *session,
                           TALER_EXCHANGEDB_WirePreparationCallback cb,
                           void *cb_cls);


  /**
   * Function called to perform "garbage collection" on the
   * database, expiring records we no longer require.
   *
   * @param cls closure
   * @return #GNUNET_OK on success,
   *         #GNUNET_SYSERR on DB errors
   */
  int
  (*gc) (void *cls);

};


#endif /* _TALER_EXCHANGE_DB_H */