sketching out refund API implementation

2 files changed, 337 insertions, 0 deletions

diff --git a/src/exchange-lib/exchange_api_refund.c b/src/exchange-lib/exchange_api_refund.c
new file mode 100644
index 000000000..ade070093
--- /dev/null
+++ b/src/exchange-lib/exchange_api_refund.c
@@ -0,0 +1,335 @@
+/*
+  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 exchange-lib/exchange_api_refund.c
+ * @brief Implementation of the /refund request of the exchange's HTTP API
+ * @author Sree Harsha Totakura <sreeharsha@totakura.in>
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include <curl/curl.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_json_lib.h"
+#include "taler_exchange_service.h"
+#include "exchange_api_common.h"
+#include "exchange_api_handle.h"
+#include "taler_signatures.h"
+
+
+/**
+ * @brief A Refund Handle
+ */
+struct TALER_EXCHANGE_RefundHandle
+{
+
+  /**
+   * The connection to exchange this request handle will use
+   */
+  struct TALER_EXCHANGE_Handle *exchange;
+
+  /**
+   * The url for this request.
+   */
+  char *url;
+
+  /**
+   * JSON encoding of the request to POST.
+   */
+  char *json_enc;
+
+  /**
+   * Handle for the request.
+   */
+  struct GNUNET_CURL_Job *job;
+
+  /**
+   * Function to call with the result.
+   */
+  TALER_EXCHANGE_RefundResultCallback cb;
+
+  /**
+   * Closure for @a cb.
+   */
+  void *cb_cls;
+
+  /**
+   * Information the exchange should sign in response.
+   */
+  struct TALER_RefundConfirmationPS depconf;
+
+};
+
+
+/**
+ * Verify that the signature on the "200 OK" response
+ * from the exchange is valid.
+ *
+ * @param rh refund handle
+ * @param json json reply with the signature
+ * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
+ */
+static int
+verify_refund_signature_ok (const struct TALER_EXCHANGE_RefundHandle *rh,
+                             const json_t *json)
+{
+  struct TALER_ExchangeSignatureP exchange_sig;
+  struct TALER_ExchangePublicKeyP exchange_pub;
+  const struct TALER_EXCHANGE_Keys *key_state;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_fixed_auto ("sig", &exchange_sig),
+    GNUNET_JSON_spec_fixed_auto ("pub", &exchange_pub),
+    GNUNET_JSON_spec_end()
+  };
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (json,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  key_state = TALER_EXCHANGE_get_keys (rh->exchange);
+  if (GNUNET_OK !=
+      TALER_EXCHANGE_test_signing_key (key_state,
+				       &exchange_pub))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND,
+                                  &rh->depconf.purpose,
+                                  &exchange_sig.eddsa_signature,
+                                  &exchange_pub.eddsa_pub))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Function called when we're done processing the
+ * HTTP /refund request.
+ *
+ * @param cls the `struct TALER_EXCHANGE_RefundHandle`
+ * @param response_code HTTP response code, 0 on error
+ * @param json parsed JSON result, NULL on error
+ */
+static void
+handle_refund_finished (void *cls,
+                         long response_code,
+                         const json_t *json)
+{
+  struct TALER_EXCHANGE_RefundHandle *rh = cls;
+
+  rh->job = NULL;
+  switch (response_code)
+  {
+  case 0:
+    break;
+  case MHD_HTTP_OK:
+    if (GNUNET_OK !=
+        verify_refund_signature_ok (rh,
+				    json))
+    {
+      GNUNET_break_op (0);
+      response_code = 0;
+    }
+    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 */
+    break;
+  case MHD_HTTP_UNAUTHORIZED:
+    /* Nothing really to verify, exchange says one of the signatures is
+       invalid; as we checked them, this should never happen, we
+       should pass the JSON reply to the application */
+    break;
+  case MHD_HTTP_NOT_FOUND:
+    /* Nothing really to verify, this should never
+       happen, we should pass the JSON reply to the application */
+    break;
+  case MHD_HTTP_INTERNAL_SERVER_ERROR:
+    /* Server had an internal issue; we should retry, but this API
+       leaves this to the application */
+    break;
+  default:
+    /* unexpected response code */
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Unexpected response code %u\n",
+                response_code);
+    GNUNET_break (0);
+    response_code = 0;
+    break;
+  }
+  rh->cb (rh->cb_cls,
+          response_code,
+          json);
+  TALER_EXCHANGE_refund_cancel (rh);
+}
+
+
+/**
+ * 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 refund_fee fee applicable to this coin for the refund
+ * @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 TALER_Amount *refund_fee,
+		       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)
+{
+  struct TALER_EXCHANGE_RefundHandle *rh;
+  struct GNUNET_CURL_Context *ctx;
+  struct TALER_MerchantSignatureP merchant_sig;
+  struct TALER_MerchantPublicKeyP merchant_pub;
+  json_t *refund_obj;
+  CURL *eh;
+
+  if (GNUNET_YES !=
+      MAH_handle_is_ready (exchange))
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  /* FIXME: create signature! */
+
+  refund_obj = json_pack ("{s:o, s:o," /* amount/fee */
+			  " s:o, s:o," /* H_contract, coin_pub */
+			  " s:I, s:I," /* transaction id, rtransaction id */
+			  " s:o, s:o}", /* merchant_pub, merchant_sig */
+			  "amount", TALER_JSON_from_amount (amount),
+			  "fee", TALER_JSON_from_amount (amount),
+			  "H_contract", GNUNET_JSON_from_data (h_contract,
+                                                               sizeof (struct GNUNET_HashCode)),
+			  "coin_pub", GNUNET_JSON_from_data (coin_pub,
+                                                             sizeof (*coin_pub)),
+			  "transaction_id", (json_int_t) transaction_id,
+			  "rtransaction_id", (json_int_t) rtransaction_id,
+			  "merchant_pub", GNUNET_JSON_from_data (&merchant_pub,
+                                                                 sizeof (merchant_pub)),
+			  "merchant_sig", GNUNET_JSON_from_data (&merchant_sig,
+                                                                 sizeof (merchant_sig))
+			  );
+
+  rh = GNUNET_new (struct TALER_EXCHANGE_RefundHandle);
+  rh->exchange = exchange;
+  rh->cb = cb;
+  rh->cb_cls = cb_cls;
+  rh->url = MAH_path_to_url (exchange, "/refund");
+  rh->depconf.purpose.size = htonl (sizeof (struct TALER_RefundConfirmationPS));
+  rh->depconf.purpose.purpose = htonl (TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND);
+  rh->depconf.h_contract = *h_contract;
+  rh->depconf.transaction_id = GNUNET_htonll (transaction_id);
+  rh->depconf.rtransaction_id = GNUNET_htonll (rtransaction_id);
+  TALER_amount_hton (&rh->depconf.refund_amount,
+                     amount);
+  TALER_amount_hton (&rh->depconf.refund_fee,
+                     refund_fee);
+  rh->depconf.coin_pub = *coin_pub;
+  rh->depconf.merchant = *merchant_pub;
+
+  eh = curl_easy_init ();
+  GNUNET_assert (NULL != (rh->json_enc =
+                          json_dumps (refund_obj,
+                                      JSON_COMPACT)));
+  json_decref (refund_obj);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "URL for refund: `%s'\n",
+              rh->url);
+  GNUNET_assert (CURLE_OK ==
+                 curl_easy_setopt (eh,
+                                   CURLOPT_URL,
+                                   rh->url));
+  GNUNET_assert (CURLE_OK ==
+                 curl_easy_setopt (eh,
+                                   CURLOPT_POSTFIELDS,
+                                   rh->json_enc));
+  GNUNET_assert (CURLE_OK ==
+                 curl_easy_setopt (eh,
+                                   CURLOPT_POSTFIELDSIZE,
+                                   strlen (rh->json_enc)));
+  ctx = MAH_handle_to_context (exchange);
+  rh->job = GNUNET_CURL_job_add (ctx,
+				 eh,
+				 GNUNET_YES,
+				 &handle_refund_finished,
+				 rh);
+  return rh;
+}
+
+
+/**
+ * Cancel a refund permission request.  This function cannot be used
+ * on a request handle if a response is already served for it.
+ *
+ * @param refund the refund permission request handle
+ */
+void
+TALER_EXCHANGE_refund_cancel (struct TALER_EXCHANGE_RefundHandle *refund)
+{
+  if (NULL != refund->job)
+  {
+    GNUNET_CURL_job_cancel (refund->job);
+    refund->job = NULL;
+  }
+  GNUNET_free (refund->url);
+  GNUNET_free (refund->json_enc);
+  GNUNET_free (refund);
+}
+
+
+/* end of exchange_api_refund.c */
diff --git a/src/include/taler_exchange_service.h b/src/include/taler_exchange_service.h
index 2f9a1932c..04f94e570 100644
--- a/src/include/taler_exchange_service.h
+++ b/src/include/taler_exchange_service.h
@@ -506,6 +506,7 @@ typedef void
  * @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 refund_fee fee applicable to this coin for the refund
  * @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
@@ -522,6 +523,7 @@ typedef void
 struct TALER_EXCHANGE_RefundHandle *
 TALER_EXCHANGE_refund (struct TALER_EXCHANGE_Handle *exchange,
 		       const struct TALER_Amount *amount,
+		       const struct TALER_Amount *refund_fee,
 		       const struct GNUNET_HashCode *h_contract,
 		       const struct TALER_CoinSpendPublicKeyP *coin_pub,
 		       uint64_t rtransaction_id,