[taler-exchange] 01/08: towards age-withdraw and -reveal API

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oec pushed a commit to branch master
in repository exchange.

commit fde760aef037d14c84c49f500c0db91d7e95ae98
Author: Özgür Kesim <oec-taler@kesim.org>
AuthorDate: Thu Jul 13 08:45:05 2023 +0200

    towards age-withdraw and -reveal API
---
 src/include/taler_exchange_service.h       | 108 ++++++-
 src/lib/Makefile.am                        |   1 +
 src/lib/exchange_api_age_withdraw.c        |  31 +-
 src/lib/exchange_api_age_withdraw_reveal.c | 435 +++++++++++++++++++++++++++++
 4 files changed, 556 insertions(+), 19 deletions(-)

diff --git a/src/include/taler_exchange_service.h 
b/src/include/taler_exchange_service.h
index ac4bc6c3..13a238ba 100644
--- a/src/include/taler_exchange_service.h
+++ b/src/include/taler_exchange_service.h
@@ -2745,7 +2745,7 @@ TALER_EXCHANGE_batch_withdraw2_cancel (
 /* ********************* /reserve/$RESERVE_PUB/age-withdraw *************** */
 
 /**
- * @brief Information needed to withdraw age restricted coins.
+ * @brief Information needed to withdraw (and reveal) age restricted coins.
  */
 struct TALER_EXCHANGE_AgeWithdrawCoinInput
 {
@@ -2753,7 +2753,7 @@ struct TALER_EXCHANGE_AgeWithdrawCoinInput
    * The master secret from which we derive all other relevant values for
    * the coin: private key, nonces (if applicable) and age restriction
    */
-  const struct TALER_PlanchetMasterSecretP secret[TALER_CNC_KAPPA];
+  const struct TALER_PlanchetMasterSecretP secrets[TALER_CNC_KAPPA];
 
   /**
    * The denomination of the coin.  Must support age restriction, i.e
@@ -2794,6 +2794,11 @@ struct TALER_EXCHANGE_AgeWithdrawResponse
        */
       uint8_t noreveal_index;
 
+      /**
+       * The commitment of the call to /age-withdraw
+       */
+      struct TALER_AgeWithdrawCommitmentHashP h_commitment;
+
       /**
        * Signature of the exchange over the origina TALER_AgeWithdrawRequestPS
        */
@@ -2842,7 +2847,7 @@ TALER_EXCHANGE_age_withdraw (
   struct TALER_EXCHANGE_Keys *keys,
   const struct TALER_ReservePrivateKeyP *reserve_priv,
   size_t num_coins,
-  const struct TALER_EXCHANGE_AgeWithdrawCoinInput coin_inputs[const static
+  const struct TALER_EXCHANGE_AgeWithdrawCoinInput coin_inputs[static
                                                                num_coins],
   uint8_t max_age,
   TALER_EXCHANGE_AgeWithdrawCallback res_cb,
@@ -2859,6 +2864,103 @@ TALER_EXCHANGE_age_withdraw_cancel (
   struct TALER_EXCHANGE_AgeWithdrawHandle *awh);
 
 
+/* ********************* /age-withdraw/$ACH/reveal ************************ */
+
+/**
+ * @brief A handle to a /age-withdraw/$ACH/reveal request
+ */
+struct TALER_EXCHANGE_AgeWithdrawRevealHandle;
+
+
+/**
+ *
+ */
+
+struct TALER_EXCHANGE_AgeWithdrawRevealResponse
+{
+  /**
+   * HTTP response data.
+   */
+  struct TALER_EXCHANGE_HttpResponse hr;
+
+  /**
+   * Details about the response
+   */
+  union
+  {
+    /**
+     * Details if the status is #MHD_HTTP_OK.
+     */
+    struct
+    {
+      /**
+       * Number of coins returned.
+       */
+      unsigned int num_coins;
+
+      /**
+       * Array of @e num_coins values about the coins obtained via the reveal
+       * operation.  The array give thes coins in the same order (and should
+       * have the same length) in which the original age-withdraw request
+       * specified the respective denomination keys.
+       */
+      const struct TALER_EXCHANGE_RevealedCoinInfo *coins;
+
+    } ok;
+    /* FIXME[oec]: error cases */
+  } details;
+
+};
+
+typedef void
+(*TALER_EXCHANGE_AgeWithdrawRevealCallback)(
+  void *cls,
+  const struct TALER_EXCHANGE_AgeWithdrawRevealResponse *awr);
+
+/**
+ * Submit an age-withdraw-reveal request to the exchange and get the exchange's
+ * response.
+ *
+ * This API is typically used by a wallet.  Note that to ensure that
+ * no money is lost in case of hardware failures, the provided
+ * argument @a rd should be committed to persistent storage
+ * prior to calling this function.
+ *
+ * @param curl_ctx The curl context
+ * @param exchange_url The base url of the exchange
+ * @param reserve_priv The pivate key to the reserve
+ * @param num_coins The number of elements in @e coin_inputs
+ * @param coins_input The input for the coins to withdraw
+ * @param noreveal_index The index into each of the kappa coin candidates, 
that should not be revealed to the exchange
+ * @param h_commitment The commmitment from the previous call to /age-withdraw
+ * @param res_cb A callback for the result, maybe NULL
+ * @param res_cb_cls A closure for @e res_cb, maybe NULL
+ * @return a handle for this request; NULL if the argument was invalid.
+ *         In this case, the callback will not be called.
+ */
+struct TALER_EXCHANGE_AgeWithdrawRevealHandle *
+TALER_EXCHANGE_age_withdraw_reveal (
+  struct GNUNET_CURL_Context *curl_ctx,
+  const char *exchange_url,
+  size_t num_coins,
+  const struct TALER_EXCHANGE_AgeWithdrawCoinInput coins_input[static
+                                                               num_coins],
+  uint8_t noreveal_index,
+  const struct TALER_AgeWithdrawCommitmentHashP *h_commitment,
+  TALER_EXCHANGE_AgeWithdrawRevealCallback res_cb,
+  void *res_cb_cls);
+
+
+/**
+ * @brief Cancel an age-withdraw-reveal request
+ *
+ * @param awrh Handle to an age-withdraw-reqveal request
+ */
+void
+TALER_EXCHANGE_age_withdraw_reveal_cancel (
+  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh);
+
+
 /* ********************* /refresh/melt+reveal ***************************** */
 
 
diff --git a/src/lib/Makefile.am b/src/lib/Makefile.am
index 762a3f80..7a4febdd 100644
--- a/src/lib/Makefile.am
+++ b/src/lib/Makefile.am
@@ -23,6 +23,7 @@ libtalerexchange_la_LDFLAGS = \
 libtalerexchange_la_SOURCES = \
   exchange_api_add_aml_decision.c \
   exchange_api_age_withdraw.c \
+  exchange_api_age_withdraw_reveal.c \
   exchange_api_auditor_add_denomination.c \
   exchange_api_batch_deposit.c \
   exchange_api_batch_withdraw.c \
diff --git a/src/lib/exchange_api_age_withdraw.c 
b/src/lib/exchange_api_age_withdraw.c
index 7bad025b..f1d26c3c 100644
--- a/src/lib/exchange_api_age_withdraw.c
+++ b/src/lib/exchange_api_age_withdraw.c
@@ -235,7 +235,8 @@ reserve_age_withdraw_ok (
 {
   struct TALER_EXCHANGE_AgeWithdrawResponse response = {
     .hr.reply = j_response,
-    .hr.http_status = MHD_HTTP_OK
+    .hr.http_status = MHD_HTTP_OK,
+    .details.ok.h_commitment = awh->h_commitment
   };
   struct GNUNET_JSON_Specification spec[] = {
     GNUNET_JSON_spec_uint8 ("noreaveal_index",
@@ -568,12 +569,13 @@ perform_protocol (
 
       /* Build the candidate array */
       {
-        const struct CoinCandidate *can = awh->coin_data[i].coin_candidates;
         json_t *j_can = json_array ();
         FAIL_IF (NULL == j_can);
 
         for (size_t k = 0; k < TALER_CNC_KAPPA; k++)
         {
+          const struct CoinCandidate *can =
+            &awh->coin_data[i].coin_candidates[k];
           json_t *jc = GNUNET_JSON_PACK (
             TALER_JSON_pack_blinded_planchet (
               NULL,
@@ -591,20 +593,17 @@ perform_protocol (
     }
   }
 
-  /* Sign the request */
-  {
-    struct TALER_AgeWithdrawCommitmentHashP coins_commitment_h;
-
-    GNUNET_CRYPTO_hash_context_finish (coins_hctx,
-                                       &coins_commitment_h.hash);
+  /* Build the hash of the commitment */
+  GNUNET_CRYPTO_hash_context_finish (coins_hctx,
+                                     &awh->h_commitment.hash);
 
-    TALER_wallet_age_withdraw_sign (&coins_commitment_h,
-                                    &awh->amount_with_fee,
-                                    &awh->age_mask,
-                                    awh->max_age,
-                                    awh->reserve_priv,
-                                    &awh->reserve_sig);
-  }
+  /* Sign the request */
+  TALER_wallet_age_withdraw_sign (&awh->h_commitment,
+                                  &awh->amount_with_fee,
+                                  &awh->age_mask,
+                                  awh->max_age,
+                                  awh->reserve_priv,
+                                  &awh->reserve_sig);
 
   /* Initiate the POST-request */
   j_request_body = GNUNET_JSON_PACK (
@@ -833,7 +832,7 @@ prepare_coins (
     {
       struct CoinCandidate *can = &cd->coin_candidates[k];
 
-      can->secret = input->secret[k];
+      can->secret = input->secrets[k];
 
       /* Derive the age restriction from the given secret and
        * the maximum age */
diff --git a/src/lib/exchange_api_age_withdraw_reveal.c 
b/src/lib/exchange_api_age_withdraw_reveal.c
new file mode 100644
index 00000000..fdca3d6e
--- /dev/null
+++ b/src/lib/exchange_api_age_withdraw_reveal.c
@@ -0,0 +1,435 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2023 Taler Systems SA
+
+  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 lib/exchange_api_age_withdraw_reveal.c
+ * @brief Implementation of /age-withdraw/$ACH/reveal requests
+ * @author Özgür Kesim
+ */
+
+#include "platform.h"
+#include <gnunet/gnunet_common.h>
+#include <jansson.h>
+#include <microhttpd.h> /* just for HTTP status codes */
+#include <gnunet/gnunet_util_lib.h>
+#include <gnunet/gnunet_json_lib.h>
+#include <gnunet/gnunet_curl_lib.h>
+#include "taler_curl_lib.h"
+#include "taler_json_lib.h"
+#include "taler_exchange_service.h"
+#include "exchange_api_common.h"
+#include "exchange_api_handle.h"
+#include "taler_signatures.h"
+#include "exchange_api_curl_defaults.h"
+
+/**
+ * Handler for a running age-withdraw-reveal  request
+ */
+struct TALER_EXCHANGE_AgeWithdrawRevealHandle
+{
+
+  /* The index not to be disclosed */
+  uint8_t noreveal_index;
+
+  /* The age-withdraw commitment */
+  struct TALER_AgeWithdrawCommitmentHashP h_commitment;
+
+  /* Number of coins */
+  size_t num_coins;
+
+  /* The n*kappa coin secrets from the age-withdraw commitment */
+  const struct TALER_EXCHANGE_AgeWithdrawCoinInput *coins_input;
+
+  /* The curl context for the request */
+  struct GNUNET_CURL_Context *curl_ctx;
+
+  /* The url for the reveal request */
+  const char *request_url;
+
+  /**
+   * CURL handle for the request job.
+   */
+  struct GNUNET_CURL_Job *job;
+
+  /**
+   * Post Context
+   */
+  struct TALER_CURL_PostContext post_ctx;
+
+  /* Callback */
+  TALER_EXCHANGE_AgeWithdrawRevealCallback callback;
+
+  /* Reveal */
+  void *callback_cls;
+};
+
+
+/**
+ * We got a 200 OK response for the /age-withdraw/$ACH/reveal operation.
+ * Extract the signed blindedcoins and return it to the caller.
+ *
+ * @param awrh operation handle
+ * @param j_response reply from the exchange
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR on errors
+ */
+static enum GNUNET_GenericReturnValue
+age_withdraw_reveal_ok (
+  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh,
+  const json_t *j_response)
+{
+  struct TALER_EXCHANGE_AgeWithdrawRevealResponse response = {
+    .hr.reply = j_response,
+    .hr.http_status = MHD_HTTP_OK,
+    .details.ok.num_coins = awrh->num_coins
+  };
+  const json_t *j_sigs;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_array_const ("ev_sigs",
+                                  &j_sigs),
+    GNUNET_JSON_spec_end ()
+  };
+
+  if (GNUNET_OK!=
+      GNUNET_JSON_parse (j_response,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
+  if (awrh->num_coins != json_array_size (j_sigs))
+  {
+    /* Number of coins generated does not match our expectation */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
+  for (size_t n = 0; n < awrh->num_coins; n++)
+  {
+    // TODO[oec] extract the individual coins.
+  }
+
+  awrh->callback (awrh->callback_cls,
+                  &response);
+  /* make sure the callback isn't called again */
+  awrh->callback = NULL;
+
+  return GNUNET_OK;
+}
+
+
+/**
+ * Function called when we're done processing the
+ * HTTP /age-withdraw/$ACH/reveal request.
+ *
+ * @param cls the `struct TALER_EXCHANGE_AgeWithdrawRevealHandle`
+ * @param response_code The HTTP response code
+ * @param response response data
+ */
+static void
+handle_age_withdraw_reveal_finished (
+  void *cls,
+  long response_code,
+  const void *response)
+{
+  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh = cls;
+  const json_t *j_response = response;
+  struct TALER_EXCHANGE_AgeWithdrawRevealResponse awr = {
+    .hr.reply = j_response,
+    .hr.http_status = (unsigned int) response_code
+  };
+
+  awrh->job = NULL;
+  switch (response_code)
+  {
+  case 0:
+    awr.hr.ec = TALER_EC_GENERIC_INVALID_RESPONSE;
+    break;
+  case MHD_HTTP_OK:
+    if (GNUNET_OK !=
+        age_withdraw_reveal_ok (awrh,
+                                j_response))
+    {
+      GNUNET_break_op (0);
+      awr.hr.http_status = 0;
+      awr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+      break;
+    }
+    GNUNET_assert (NULL == awrh->callback);
+    TALER_EXCHANGE_age_withdraw_reveal_cancel (awrh);
+    return;
+  case MHD_HTTP_UNAVAILABLE_FOR_LEGAL_REASONS:
+    /* only validate reply is well-formed */
+    {
+      uint64_t ptu;
+      struct GNUNET_JSON_Specification spec[] = {
+        GNUNET_JSON_spec_uint64 ("legitimization_uuid",
+                                 &ptu),
+        GNUNET_JSON_spec_end ()
+      };
+
+      if (GNUNET_OK !=
+          GNUNET_JSON_parse (j_response,
+                             spec,
+                             NULL, NULL))
+      {
+        GNUNET_break_op (0);
+        awr.hr.http_status = 0;
+        awr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+        break;
+      }
+    }
+  case MHD_HTTP_BAD_REQUEST:
+    /* This should never happen, either us or the exchange is buggy
+       (or API version conflict); just pass JSON reply to the application */
+    awr.hr.ec = TALER_JSON_get_error_code (j_response);
+    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
+    break;
+  case MHD_HTTP_FORBIDDEN:
+    GNUNET_break_op (0);
+    /**
+     * This should never happen, as we don't sent any signatures
+     * to the exchange to verify.  We should simply pass the JSON reply
+     * to the application
+     **/
+    awr.hr.ec = TALER_JSON_get_error_code (j_response);
+    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
+    break;
+  case MHD_HTTP_NOT_FOUND:
+    /* Nothing really to verify, the exchange basically just says
+       that it doesn't know this age-withraw commitment. */
+    awr.hr.ec = TALER_JSON_get_error_code (j_response);
+    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
+    break;
+  case MHD_HTTP_CONFLICT:
+    /* An age commitment for one of the coins did not fulfill
+     * the required maximum age requirement of the corresponding
+     * reserve.
+     * Error code: TALER_EC_EXCHANGE_GENERIC_COIN_AGE_REQUIREMENT_FAILURE.
+     */
+    awr.hr.ec = TALER_JSON_get_error_code (j_response);
+    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
+    break;
+  case MHD_HTTP_GONE:
+    /* could happen if denomination was revoked */
+    /* Note: one might want to check /keys for revocation
+       signature here, alas tricky in case our /keys
+       is outdated => left to clients */
+    awr.hr.ec = TALER_JSON_get_error_code (j_response);
+    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
+    break;
+  case MHD_HTTP_INTERNAL_SERVER_ERROR:
+    /* Server had an internal issue; we should retry, but this API
+       leaves this to the application */
+    awr.hr.ec = TALER_JSON_get_error_code (j_response);
+    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
+    break;
+  default:
+    /* unexpected response code */
+    GNUNET_break_op (0);
+    awr.hr.ec = TALER_JSON_get_error_code (j_response);
+    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Unexpected response code %u/%d for exchange age-withdraw\n",
+                (unsigned int) response_code,
+                (int) awr.hr.ec);
+    break;
+  }
+  awrh->callback (awrh->callback_cls,
+                  &awr);
+  TALER_EXCHANGE_age_withdraw_reveal_cancel (awrh);
+}
+
+
+/**
+ * Prepares the request URL for the age-withdraw-reveal request
+ *
+ * @param exchange_url The base-URL to the exchange
+ * @param[in,out] awrh The handler
+ * @return GNUNET_OK on success, GNUNET_SYSERR otherwise
+ */
+static
+enum GNUNET_GenericReturnValue
+prepare_url (
+  const char *exchange_url,
+  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh)
+{
+  char arg_str[sizeof (struct TALER_AgeWithdrawCommitmentHashP) * 2 + 32];
+  char pub_str[sizeof (struct TALER_AgeWithdrawCommitmentHashP) * 2];
+  char *end;
+
+  end = GNUNET_STRINGS_data_to_string (&awrh->h_commitment,
+                                       sizeof (awrh->h_commitment),
+                                       pub_str,
+                                       sizeof (pub_str));
+  *end = '\0';
+  GNUNET_snprintf (arg_str,
+                   sizeof (arg_str),
+                   "age-withraw/%s/reveal",
+                   pub_str);
+
+  awrh->request_url = TALER_url_join (exchange_url,
+                                      arg_str,
+                                      NULL);
+  if (NULL == awrh->request_url)
+  {
+    GNUNET_break (0);
+    TALER_EXCHANGE_age_withdraw_reveal_cancel (awrh);
+    return GNUNET_SYSERR;
+  }
+
+  return GNUNET_OK;
+}
+
+
+/**
+ * Call /age-withdraw/$ACH/reveal
+ *
+ * @param awrh The handler
+ * @param num_coins Number of coin candidates in reveal_inputs
+ * @param reveal_inputs The secrets of the coin candidates
+ */
+static
+void
+perform_protocol (
+  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh)
+{
+  CURL *curlh = NULL;
+  json_t *j_request_body = NULL;
+  json_t *j_array_of_secrets = NULL;
+  json_t *j_secrets = NULL;
+  json_t *j_sec = NULL;
+
+#define FAIL_IF(cond) \
+  do { \
+    if ((cond)) \
+    { \
+      GNUNET_break (! (cond)); \
+      goto ERROR; \
+    } \
+  } while(0)
+
+  for (size_t n = 0; n < awrh->num_coins; n++)
+  {
+    const struct TALER_PlanchetMasterSecretP *secrets =
+      awrh->coins_input[n].secrets;
+
+    j_secrets = json_array ();
+    FAIL_IF (NULL == j_secrets);
+
+    for (uint8_t k = 0; k < TALER_CNC_KAPPA; k++)
+    {
+      const struct TALER_PlanchetMasterSecretP *secret = &secrets[k];
+      if (awrh->noreveal_index == k)
+        continue;
+
+      j_sec = GNUNET_JSON_PACK (
+        GNUNET_JSON_pack_data_auto (NULL, secret));
+
+      FAIL_IF (NULL == j_sec);
+      FAIL_IF (0 < json_array_append_new (j_secrets,
+                                          j_sec));
+    }
+
+    FAIL_IF (0 < json_array_append_new (j_array_of_secrets,
+                                        j_secrets));
+  }
+  j_request_body = GNUNET_JSON_PACK (
+    GNUNET_JSON_pack_array_steal ("disclosed_coin_secrets",
+                                  j_array_of_secrets));
+  FAIL_IF (NULL == j_request_body);
+
+  curlh = TALER_EXCHANGE_curl_easy_get_ (awrh->request_url);
+  FAIL_IF (NULL == curlh);
+  FAIL_IF (GNUNET_OK !=
+           TALER_curl_easy_post (&awrh->post_ctx,
+                                 curlh,
+                                 j_request_body));
+  json_decref (j_request_body);
+  j_request_body = NULL;
+
+  awrh->job = GNUNET_CURL_job_add2 (awrh->curl_ctx,
+                                    curlh,
+                                    awrh->post_ctx.headers,
+                                    &handle_age_withdraw_reveal_finished,
+                                    awrh);
+  FAIL_IF (NULL == awrh->job);
+
+  /* No error, return */
+  return;
+
+ERROR:
+  if (NULL != j_sec)
+    json_decref (j_sec);
+  if (NULL != j_secrets)
+    json_decref (j_secrets);
+  if (NULL != j_array_of_secrets)
+    json_decref (j_array_of_secrets);
+  if (NULL != j_request_body)
+    json_decref (j_request_body);
+  if (NULL != curlh)
+    curl_easy_cleanup (curlh);
+  TALER_EXCHANGE_age_withdraw_reveal_cancel (awrh);
+  return;
+#undef FAIL_IF
+}
+
+
+struct TALER_EXCHANGE_AgeWithdrawRevealHandle *
+TALER_EXCHANGE_age_withdraw_reveal (
+  struct GNUNET_CURL_Context *curl_ctx,
+  const char *exchange_url,
+  size_t num_coins,
+  const struct TALER_EXCHANGE_AgeWithdrawCoinInput coins_input[static
+                                                               num_coins],
+  uint8_t noreveal_index,
+  const struct TALER_AgeWithdrawCommitmentHashP *h_commitment,
+  TALER_EXCHANGE_AgeWithdrawRevealCallback reveal_cb,
+  void *reveal_cb_cls)
+{
+  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh =
+    GNUNET_new (struct TALER_EXCHANGE_AgeWithdrawRevealHandle);
+  awrh->curl_ctx = curl_ctx;
+  awrh->noreveal_index = noreveal_index;
+  awrh->callback = reveal_cb;
+  awrh->callback_cls = reveal_cb_cls;
+  awrh->h_commitment = *h_commitment;
+  awrh->num_coins = num_coins;
+  awrh->coins_input = coins_input;
+
+
+  if (GNUNET_OK !=
+      prepare_url (exchange_url,
+                   awrh))
+    return NULL;
+
+  perform_protocol (awrh);
+
+  return awrh;
+}
+
+
+void
+TALER_EXCHANGE_age_withdraw_reveal_cancel (
+  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh)
+{
+  /* FIXME[oec] */
+  (void) awrh;
+}
+
+
+/* exchange_api_age_withdraw_reveal.c */

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