implementing parsing of /refund requests

src/exchange/Makefile.am

@@ -35,6 +35,7 @@ taler_exchange_httpd_SOURCES = \
   taler-exchange-httpd_mhd.c taler-exchange-httpd_mhd.h \
   taler-exchange-httpd_parsing.c taler-exchange-httpd_parsing.h \
   taler-exchange-httpd_refresh.c taler-exchange-httpd_refresh.h \
+  taler-exchange-httpd_refund.c taler-exchange-httpd_refund.h \
   taler-exchange-httpd_reserve.c taler-exchange-httpd_reserve.h \
   taler-exchange-httpd_responses.c taler-exchange-httpd_responses.h \
   taler-exchange-httpd_tracking.c taler-exchange-httpd_tracking.h \

src/exchange/taler-exchange-httpd.c

@@ -30,6 +30,7 @@
 #include "taler-exchange-httpd_mhd.h"
 #include "taler-exchange-httpd_admin.h"
 #include "taler-exchange-httpd_deposit.h"
+#include "taler-exchange-httpd_refund.h"
 #include "taler-exchange-httpd_reserve.h"
 #include "taler-exchange-httpd_wire.h"
 #include "taler-exchange-httpd_refresh.h"
@@ -200,6 +201,14 @@ handle_mhd_request (void *cls,
         "Only POST is allowed", 0,
         &TMH_MHD_handler_send_json_pack_error, MHD_HTTP_METHOD_NOT_ALLOWED },
 
+      /* Refunding coins */
+      { "/refund", MHD_HTTP_METHOD_POST, "application/json",
+        NULL, 0,
+        &TMH_REFUND_handler_refund, MHD_HTTP_OK },
+      { "/refund", NULL, "text/plain",
+        "Only POST is allowed", 0,
+        &TMH_MHD_handler_send_json_pack_error, MHD_HTTP_METHOD_NOT_ALLOWED },
+
       /* Dealing with change */
       { "/refresh/melt", MHD_HTTP_METHOD_POST, "application/json",
         NULL, 0,

src/exchange/taler-exchange-httpd_deposit.c

@@ -1,6 +1,6 @@
 /*
   This file is part of TALER
-  Copyright (C) 2014, 2015 GNUnet e.V.
+  Copyright (C) 2014, 2015, 2016 Inria and GNUnet e.V.
 
   TALER is free software; you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free Software
@@ -21,9 +21,6 @@
  * @author Florian Dold
  * @author Benedikt Mueller
  * @author Christian Grothoff
- *
- * TODO:
- * - ugly if-construction for deposit type
  */
 #include "platform.h"
 #include <gnunet/gnunet_util_lib.h>
@@ -119,28 +116,37 @@ verify_and_execute_deposit (struct MHD_Connection *connection,
 
 
 /**
- * Handle a "/deposit" request.  This function parses the
+ * Handle a "/deposit" request.  Parses the JSON, and, if successful,
- * JSON information and then calls #verify_and_execute_deposit()
+ * passes the JSON data to #verify_and_execute_deposit() to further
- * to verify the signatures and execute the deposit.
+ * check the details of the operation specified.  If everything checks
+ * out, this will ultimately lead to the "/deposit" being executed, or
+ * rejected.
  *
+ * @param rh context of the handler
  * @param connection the MHD connection to handle
- * @param root root of the posted JSON
+ * @param[in,out] connection_cls the connection's closure (can be updated)
- * @param amount how much should be deposited
+ * @param upload_data upload data
- * @param wire json describing the wire details (?)
+ * @param[in,out] upload_data_size number of bytes (left) in @a upload_data
  * @return MHD result code
   */
-static int
+int
-parse_and_handle_deposit_request (struct MHD_Connection *connection,
+TMH_DEPOSIT_handler_deposit (struct TMH_RequestHandler *rh,
-                                  const json_t *root,
+                             struct MHD_Connection *connection,
-                                  const struct TALER_Amount *amount,
+                             void **connection_cls,
-                                  json_t *wire)
+                             const char *upload_data,
+                             size_t *upload_data_size)
 {
+  json_t *json;
   int res;
+  json_t *wire;
   struct TALER_EXCHANGEDB_Deposit deposit;
   struct TALER_EXCHANGEDB_DenominationKeyIssueInformation *dki;
   struct TMH_KS_StateHandle *ks;
   struct GNUNET_HashCode my_h_wire;
+  struct TALER_Amount amount;
   struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_json ("wire", &wire),
+    TALER_JSON_spec_amount ("f", &amount),
     TALER_JSON_spec_denomination_public_key ("denom_pub", &deposit.coin.denom_pub),
     TALER_JSON_spec_denomination_signature ("ub_sig", &deposit.coin.denom_sig),
     GNUNET_JSON_spec_fixed_auto ("coin_pub", &deposit.coin.coin_pub),
@@ -155,10 +161,20 @@ parse_and_handle_deposit_request (struct MHD_Connection *connection,
     GNUNET_JSON_spec_end ()
   };
 
+  res = TMH_PARSE_post_json (connection,
+                             connection_cls,
+                             upload_data,
+                             upload_data_size,
+                             &json);
+  if (GNUNET_SYSERR == res)
+    return MHD_NO;
+  if ( (GNUNET_NO == res) || (NULL == json) )
+    return MHD_YES;
   memset (&deposit, 0, sizeof (deposit));
   res = TMH_PARSE_json_data (connection,
-                             root,
+                             json,
                              spec);
+  json_decref (json);
   if (GNUNET_SYSERR == res)
     return MHD_NO; /* hard failure */
   if (GNUNET_NO == res)
@@ -205,12 +221,12 @@ parse_and_handle_deposit_request (struct MHD_Connection *connection,
                      &dki->issue.properties.fee_deposit);
   TMH_KS_release (ks);
   deposit.wire = wire;
-  deposit.amount_with_fee = *amount;
+  deposit.amount_with_fee = amount;
   if (-1 == TALER_amount_cmp (&deposit.amount_with_fee,
                               &deposit.deposit_fee))
   {
     /* Total amount smaller than fee, invalid */
-     GNUNET_JSON_parse_free (spec);
+    GNUNET_JSON_parse_free (spec);
     return TMH_RESPONSE_reply_arg_invalid (connection,
                                            "f");
   }
@@ -221,64 +237,4 @@ parse_and_handle_deposit_request (struct MHD_Connection *connection,
 }
 
 
-/**
- * Handle a "/deposit" request.  Parses the JSON in the post to find
- * the "type" (either DIRECT_DEPOSIT or INCREMENTAL_DEPOSIT), and, if
- * successful, passes the JSON data to
- * #parse_and_handle_deposit_request() to further check the details
- * of the operation specified in the "wire" field of the JSON data.
- * If everything checks out, this will ultimately lead to the
- * "/deposit" being executed, or rejected.
- *
- * @param rh context of the handler
- * @param connection the MHD connection to handle
- * @param[in,out] connection_cls the connection's closure (can be updated)
- * @param upload_data upload data
- * @param[in,out] upload_data_size number of bytes (left) in @a upload_data
- * @return MHD result code
-  */
-int
-TMH_DEPOSIT_handler_deposit (struct TMH_RequestHandler *rh,
-                             struct MHD_Connection *connection,
-                             void **connection_cls,
-                             const char *upload_data,
-                             size_t *upload_data_size)
-{
-  json_t *json;
-  json_t *wire;
-  int res;
-  struct TALER_Amount amount;
-  struct GNUNET_JSON_Specification spec[] = {
-    GNUNET_JSON_spec_json ("wire", &wire),
-    TALER_JSON_spec_amount ("f", &amount),
-    GNUNET_JSON_spec_end ()
-  };
-
-  res = TMH_PARSE_post_json (connection,
-                             connection_cls,
-                             upload_data,
-                             upload_data_size,
-                             &json);
-  if (GNUNET_SYSERR == res)
-    return MHD_NO;
-  if ( (GNUNET_NO == res) || (NULL == json) )
-    return MHD_YES;
-  res = TMH_PARSE_json_data (connection,
-                             json,
-                             spec);
-  if (GNUNET_OK != res)
-  {
-    json_decref (json);
-    return (GNUNET_NO == res) ? MHD_YES : MHD_NO;
-  }
-  res = parse_and_handle_deposit_request (connection,
-                                          json,
-                                          &amount,
-                                          wire);
-  GNUNET_JSON_parse_free (spec);
-  json_decref (json);
-  return res;
-}
-
-
 /* end of taler-exchange-httpd_deposit.c */

src/exchange/taler-exchange-httpd_deposit.h

@@ -29,13 +29,9 @@
 
 
 /**
- * Handle a "/deposit" request.  Parses the JSON in the post to find
+ * Handle a "/deposit" request.  Parses the JSON, and, if successful,
- * the "type" (either DIRECT_DEPOSIT or INCREMENTAL_DEPOSIT), and, if
+ * checks the signatures.  If everything checks out, this will
- * successful, passes the JSON data to
+ * ultimately lead to the "/deposit" being executed, or rejected.
- * #parse_and_handle_deposit_request() to further check the details
- * of the operation specified in the "wire" field of the JSON data.
- * If everything checks out, this will ultimately lead to the
- * "/deposit" being executed, or rejected.
  *
  * @param rh context of the handler
  * @param connection the MHD connection to handle

src/exchange/taler-exchange-httpd_refund.c

@@ -0,0 +1,146 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2014, 2015, 2016 Inria and GNUnet e.V.
+
+  TALER is free software; you can redistribute it and/or modify it under the
+  terms of the GNU Affero General Public License as published by the Free Software
+  Foundation; either version 3, or (at your option) any later version.
+
+  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more details.
+
+  You should have received a copy of the GNU Affero General Public License along with
+  TALER; see the file COPYING.  If not, If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file taler-exchange-httpd_refund.c
+ * @brief Handle /refund requests; parses the POST and JSON and
+ *        verifies the coin signature before handing things off
+ *        to the database.
+ * @author Florian Dold
+ * @author Benedikt Mueller
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include <gnunet/gnunet_util_lib.h>
+#include <gnunet/gnunet_json_lib.h>
+#include <jansson.h>
+#include <microhttpd.h>
+#include <pthread.h>
+#include "taler_json_lib.h"
+#include "taler-exchange-httpd_parsing.h"
+#include "taler-exchange-httpd_refund.h"
+#include "taler-exchange-httpd_responses.h"
+#include "taler-exchange-httpd_keystate.h"
+#include "taler-exchange-httpd_validation.h"
+
+
+/**
+ * We have parsed the JSON information about the refund, do some basic
+ * sanity checks (especially that the signature on the coin is valid)
+ * and then execute the refund.  Note that we need the DB to check
+ * the fee structure, so this is not done here.
+ *
+ * @param connection the MHD connection to handle
+ * @param refund information about the refund
+ * @return MHD result code
+ */
+static int
+verify_and_execute_refund (struct MHD_Connection *connection,
+			   const struct TALER_EXCHANGEDB_Refund *refund)
+{
+  struct TALER_RefundRequestPS dr;
+
+  dr.purpose.purpose = htonl (TALER_SIGNATURE_MERCHANT_REFUND);
+  dr.purpose.size = htonl (sizeof (struct TALER_RefundRequestPS));
+  dr.h_contract = refund->h_contract;
+  dr.transaction_id = GNUNET_htonll (refund->transaction_id);
+  dr.rtransaction_id = GNUNET_htonll (refund->rtransaction_id);
+  TALER_amount_hton (&dr.refund_amount,
+                     &refund->refund_amount);
+  TALER_amount_hton (&dr.refund_fee,
+                     &refund->refund_fee);
+  dr.merchant = refund->merchant_pub;
+  dr.coin_pub = refund->coin.coin_pub;
+  if (GNUNET_OK !=
+      GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_MERCHANT_REFUND,
+                                  &dr.purpose,
+                                  &refund->merchant_sig.eddsa_sig,
+                                  &refund->merchant_pub.eddsa_pub))
+  {
+    TALER_LOG_WARNING ("Invalid signature on /refund request\n");
+    return TMH_RESPONSE_reply_signature_invalid (connection,
+                                                 "merchant_sig");
+  }
+#if 1
+  GNUNET_break (0); // FIXME: not implemented
+  return MHD_NO;
+#else
+  return TMH_DB_execute_refund (connection,
+				refund);
+#endif
+}
+
+
+/**
+ * Handle a "/refund" request.  Parses the JSON, and, if successful,
+ * passes the JSON data to #parse_and_handle_refund_request() to
+ * further check the details of the operation specified.  If
+ * everything checks out, this will ultimately lead to the "/refund"
+ * being executed, or rejected.
+ *
+ * @param rh context of the handler
+ * @param connection the MHD connection to handle
+ * @param[in,out] connection_cls the connection's closure (can be updated)
+ * @param upload_data upload data
+ * @param[in,out] upload_data_size number of bytes (left) in @a upload_data
+ * @return MHD result code
+  */
+int
+TMH_REFUND_handler_refund (struct TMH_RequestHandler *rh,
+			   struct MHD_Connection *connection,
+			   void **connection_cls,
+			   const char *upload_data,
+			   size_t *upload_data_size)
+{
+  json_t *json;
+  int res;
+  struct TALER_EXCHANGEDB_Refund refund;
+  struct GNUNET_JSON_Specification spec[] = {
+    TALER_JSON_spec_amount ("refund_amount", &refund.refund_amount),
+    TALER_JSON_spec_amount ("refund_fee", &refund.refund_fee),
+    GNUNET_JSON_spec_fixed_auto ("H_contract", &refund.h_contract),
+    GNUNET_JSON_spec_uint64 ("transaction_id", &refund.transaction_id),
+    GNUNET_JSON_spec_fixed_auto ("coin_pub", &refund.coin.coin_pub),
+    GNUNET_JSON_spec_fixed_auto ("merchant_pub", &refund.merchant_pub),
+    GNUNET_JSON_spec_uint64 ("rtransaction_id", &refund.rtransaction_id),
+    GNUNET_JSON_spec_fixed_auto ("merchant_sig", &refund.merchant_sig),
+    GNUNET_JSON_spec_end ()
+  };
+
+  res = TMH_PARSE_post_json (connection,
+                             connection_cls,
+                             upload_data,
+                             upload_data_size,
+                             &json);
+  if (GNUNET_SYSERR == res)
+    return MHD_NO;
+  if ( (GNUNET_NO == res) || (NULL == json) )
+    return MHD_YES;
+  res = TMH_PARSE_json_data (connection,
+                             json,
+                             spec);
+  json_decref (json);
+  if (GNUNET_SYSERR == res)
+    return MHD_NO; /* hard failure */
+  if (GNUNET_NO == res)
+    return MHD_YES; /* failure */
+  res = verify_and_execute_refund (connection,
+				   &refund);
+  GNUNET_JSON_parse_free (spec);
+  return res;
+}
+
+
+/* end of taler-exchange-httpd_refund.c */

src/exchange/taler-exchange-httpd_refund.h

@@ -0,0 +1,52 @@
+/*
+  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 Affero General Public License as published by the Free Software
+  Foundation; either version 3, or (at your option) any later version.
+
+  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more details.
+
+  You should have received a copy of the GNU Affero General Public License along with
+  TALER; see the file COPYING.  If not, If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file taler-exchange-httpd_refund.h
+ * @brief Handle /refund requests
+ * @author Florian Dold
+ * @author Benedikt Mueller
+ * @author Christian Grothoff
+ */
+#ifndef TALER_EXCHANGE_HTTPD_REFUND_H
+#define TALER_EXCHANGE_HTTPD_REFUND_H
+
+#include <gnunet/gnunet_util_lib.h>
+#include <microhttpd.h>
+#include "taler-exchange-httpd.h"
+
+
+/**
+ * Handle a "/refund" request.  Parses the JSON, and, if successful,
+ * passes the JSON data to #parse_and_handle_refund_request() to
+ * further check the details of the operation specified.  If
+ * everything checks out, this will ultimately lead to the "/refund"
+ * being executed, or rejected.
+ *
+ * @param rh context of the handler
+ * @param connection the MHD connection to handle
+ * @param[in,out] connection_cls the connection's closure (can be updated)
+ * @param upload_data upload data
+ * @param[in,out] upload_data_size number of bytes (left) in @a upload_data
+ * @return MHD result code
+  */
+int
+TMH_REFUND_handler_refund (struct TMH_RequestHandler *rh,
+			   struct MHD_Connection *connection,
+			   void **connection_cls,
+			   const char *upload_data,
+			   size_t *upload_data_size);
+
+#endif

src/include/taler_exchange_service.h

@@ -465,6 +465,83 @@ void
 TALER_EXCHANGE_deposit_cancel (struct TALER_EXCHANGE_DepositHandle *deposit);
 
 
+/* *********************  /refund *********************** */
+
+/**
+ * @brief A Refund Handle
+ */
+struct TALER_EXCHANGE_RefundHandle;
+
+
+/**
+ * Callbacks of this type are used to serve the result of submitting a
+ * deposit permission request to a exchange.
+ *
+ * @param cls closure
+ * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful deposit;
+ *                    0 if the exchange's reply is bogus (fails to follow the protocol)
+ * @param obj the received JSON reply, should be kept as proof (and, in particular,
+ *            be forwarded to the customer)
+ */
+typedef void
+(*TALER_EXCHANGE_RefundResultCallback) (void *cls,
+					unsigned int http_status,
+					const json_t *obj);
+
+
+/**
+ * Submit a refund request to the exchange and get the exchange's
+ * response.  This API is used by a merchant.  Note that
+ * while we return the response verbatim to the caller for further
+ * processing, we do already verify that the response is well-formed
+ * (i.e. that signatures included in the response are all valid).  If
+ * the exchange's reply is not well-formed, we return an HTTP status code
+ * of zero to @a cb.
+ *
+ * The @a exchange must be ready to operate (i.e.  have
+ * finished processing the /keys reply).  If this check fails, we do
+ * NOT initiate the transaction with the exchange and instead return NULL.
+ *
+ * @param exchange the exchange handle; the exchange must be ready to operate
+ * @param amount the amount to be refunded; must be larger than the refund fee
+ *        (as that fee is still being subtracted), and smaller than the amount 
+ *        (with deposit fee) of the original deposit contribution of this coin
+ * @param h_contract hash of the contact of the merchant with the customer that is being refunded
+ * @param transaction_id transaction id for the transaction being refunded, must match @a h_contract
+ * @param coin_pub coin’s public key of the coin from the original deposit operation
+ * @param rtransaction_id transaction id for the transaction between merchant and customer (of refunding operation);
+ *                        this is needed as we may first do a partial refund and later a full refund.  If both
+ *                        refunds are also over the same amount, we need the @a rtransaction_id to make the disjoint
+ *                        refund requests different (as requests are idempotent and otherwise the 2nd refund might not work).
+ * @param merchant_priv the private key of the merchant, used to generate signature for refund request
+ * @param cb the callback to call when a reply for this request is available
+ * @param cb_cls closure for the above callback
+ * @return a handle for this request; NULL if the inputs are invalid (i.e.
+ *         signatures fail to verify).  In this case, the callback is not called.
+ */
+struct TALER_EXCHANGE_RefundHandle *
+TALER_EXCHANGE_refund (struct TALER_EXCHANGE_Handle *exchange,
+		       const struct TALER_Amount *amount,
+		       const struct GNUNET_HashCode *h_contract,
+		       const struct TALER_CoinSpendPublicKeyP *coin_pub,
+		       uint64_t rtransaction_id,
+		       const struct TALER_MerchantPrivateKeyP *merchant_priv,
+		       TALER_EXCHANGE_RefundResultCallback cb,
+		       void *cb_cls);
+
+
+/**
+ * Cancel a refund permission request.  This function cannot be used
+ * on a request handle if a response is already served for it.  If 
+ * this function is called, the refund may or may not have happened.
+ * However, it is fine to try to refund the coin a second time.
+ *
+ * @param refund the refund request handle
+ */
+void
+TALER_EXCHANGE_refund_cancel (struct TALER_EXCHANGE_RefundHandle *refund);
+
+
 /* ********************* /reserve/status *********************** */
 
 

src/include/taler_exchangedb_plugin.h

@@ -298,6 +298,67 @@ struct TALER_EXCHANGEDB_Deposit
 };
 
 
+/**
+ * @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 Global information for a refreshing session.  Includes
  * dimensions of the operation, security parameters and

src/include/taler_signatures.h

@@ -395,6 +395,64 @@ struct TALER_DepositConfirmationPS
 };
 
 
+/**
+ * @brief Format used to generate the signature on a request to refund
+ * a coin into the account of the customer.
+ */
+struct TALER_RefundRequestPS
+{
+  /**
+   * Purpose must be #TALER_SIGNATURE_MERCHANT_REFUND.
+   */
+  struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
+
+  /**
+   * Hash over the contract which is being refunded.
+   */
+  struct GNUNET_HashCode h_contract GNUNET_PACKED;
+
+  /**
+   * Merchant-generated transaction ID of the orginal transaction.
+   */
+  uint64_t transaction_id GNUNET_PACKED;
+
+  /**
+   * The coin's public key.  This is the value that must have been
+   * signed (blindly) by the Exchange.  
+   */
+  struct TALER_CoinSpendPublicKeyP coin_pub;
+
+  /**
+   * The Merchant's public key.  Allows the merchant to later refund
+   * the transaction or to inquire about the wire transfer identifier.
+   */
+  struct TALER_MerchantPublicKeyP merchant;
+
+  /**
+   * Merchant-generated transaction ID for the refund.
+   */
+  uint64_t rtransaction_id GNUNET_PACKED;
+
+  /**
+   * Amount to be refunded, including refund fee charged by the
+   * exchange to the customer.
+   */
+  struct TALER_AmountNBO refund_amount;
+
+  /**
+   * Refund fee charged by the exchange.  This must match the
+   * Exchange's denomination key's refund fee.  If the client puts in
+   * an invalid refund fee (too high or too low) that does not match
+   * the Exchange's denomination key, the refund operation is invalid
+   * and will be rejected by the exchange.  The @e amount_with_fee
+   * minus the @e refund_fee is the amount that will be credited to
+   * the original coin.
+   */
+  struct TALER_AmountNBO refund_fee;
+
+};
+
+
 /**
  * @brief Message signed by a coin to indicate that the coin should be
  * melted.