implement caching/persisting of exchange /refund responses

2 files changed, 71 insertions, 31 deletions

diff --git a/ChangeLog b/ChangeLog
index d34b96fb..4a61c55e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri 10 Apr 2020 09:01:22 PM CEST
+    Changing refund API to have the merchant backend make the /refund
+    request to the exchange instead of having the wallet do it (#5299). -CG
+
 Tue 31 Mar 2020 04:17:58 PM CEST
  	Releasing taler-merchant 0.7.0. -CG
 
@@ -30,16 +34,16 @@ Wed Oct 18 15:33:23 CEST 2017
 	Releasing taler-merchant 0.4.0. -CG
 
 Thu Jun 22 15:12:37 CEST 2017
-        Implementing /refund
+    Implementing /refund
 
 Tue Jun  6 14:30:43 CEST 2017
-        Abstracting the response gotten from the exchange's tracking
-        API and relying it to the frontend.
-        A payment generator has been implemented so that the db can
-        easily be populated for testing purposes.
-        /history API now has the way to query from a starting base date
-        ahead into the future.
-        Memory leak fixes. -CG/MS
+    Abstracting the response gotten from the exchange's tracking
+    API and relying it to the frontend.
+    A payment generator has been implemented so that the db can
+    easily be populated for testing purposes.
+    /history API now has the way to query from a starting base date
+    ahead into the future.
+    Memory leak fixes. -CG/MS
 	Releasing taler-merchant 0.3.0. -CG
 
 Mon Mar  6 17:57:51 CET 2017
@@ -52,24 +56,22 @@ Mon Mar  6 00:59:25 CET 2017
 	IP address (#4752).  Enabling use of dual-stack by default. -CG
 
 Thu Dec 15 10:37:08 CET 2016
-        Implementing:
-        - /map/in, /map/out API, to allow frontends to store
-        plain text contracts in database and retrieving them
-        by looking for their hashcodes.
-
+    Implementing:
+    - /map/in, /map/out API, to allow frontends to store
+    plain text contracts in database and retrieving them
+    by looking for their hashcodes.
 
 Fri Nov 18 18:54:07 CET 2016
 	Misc. minor updates to match API changes from exchange 0.2.
 	Releasing taler-merchant 0.2.0. -CG
 
 Mon Oct 10 16:27:57 CEST 2016
-        Implementing:
-        - /track API, to map transactions to wire transfers and
-        viceversa.
-        - /history API, to get the list of transactions in DB.
-        - merchant "instances", to run make multiple shops on the
-        same backend.
-        -MS
+    Implementing:
+    - /track API, to map transactions to wire transfers and
+    viceversa.
+    - /history API, to get the list of transactions in DB.
+    - merchant "instances", to run make multiple shops on the
+    same backend. -MS
 
 Tue Jun  7 15:17:45 CEST 2016
 	Store signing key used by exchange in DB.  Might be useful
diff --git a/src/backend/taler-merchant-httpd_refund_lookup.c b/src/backend/taler-merchant-httpd_refund_lookup.c
index e80241b7..0fd83ad3 100644
--- a/src/backend/taler-merchant-httpd_refund_lookup.c
+++ b/src/backend/taler-merchant-httpd_refund_lookup.c
@@ -64,6 +64,11 @@ struct CoinRefund
   struct ProcessRefundData *prd;
 
   /**
+   * URL of the exchange for this @e coin_pub.
+   */
+  char *exchange_url;
+
+  /**
    * Coin to refund.
    */
   struct TALER_CoinSpendPublicKeyP coin_pub;
@@ -213,6 +218,7 @@ cleanup_prd (struct TM_HandlerContext *cls)
       json_decref (cr->exchange_reply);
       cr->exchange_reply = NULL;
     }
+    GNUNET_free (cr->exchange_url);
     GNUNET_free (cr);
   }
   GNUNET_free (prd);
@@ -295,12 +301,25 @@ refund_cb (void *cls,
   }
   else
   {
+    enum GNUNET_DB_QueryStatus qs;
+
     cr->exchange_pub = *exchange_pub;
     cr->exchange_sig = *exchange_sig;
-    /* FIXME: store in our database,
-       1) as evidence for us that the refund happened, and
-       2) to possibly avoid doing another exchange iteration
-       the next time around. */
+    qs = db->put_refund_proof (db->cls,
+                               &cr->prd->merchant->pubkey,
+                               &cr->prd->h_contract_terms,
+                               &cr->coin_pub,
+                               cr->rtransaction_id,
+                               exchange_pub,
+                               exchange_sig);
+    if (0 >= qs)
+    {
+      /* generally, this is relatively harmless for the merchant, but let's at
+         least log this. */
+      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                  "Failed to persist exchange response to /refund in database: %d\n",
+                  qs);
+    }
   }
   check_resume_prd (cr->prd);
 }
@@ -381,6 +400,7 @@ process_refunds_cb (void *cls,
               TALER_amount2s (refund_amount),
               reason);
   cr = GNUNET_new (struct CoinRefund);
+  cr->exchange_url = GNUNET_strdup (exchange_url);
   cr->prd = prd;
   cr->coin_pub = *coin_pub;
   cr->rtransaction_id = rtransaction_id;
@@ -389,13 +409,6 @@ process_refunds_cb (void *cls,
   GNUNET_CONTAINER_DLL_insert (prd->cr_head,
                                prd->cr_tail,
                                cr);
-  /* FIXME: check in database if we already got the
-     results from #refund_cb() from an earlier request,
-     if so, avoid this step: */
-  cr->fo = TMH_EXCHANGES_find_exchange (exchange_url,
-                                        NULL,
-                                        &exchange_found_cb,
-                                        cr);
 }
 
 
@@ -529,6 +542,31 @@ MH_handler_refund_lookup (struct TMH_RequestHandler *rh,
                                          TALER_EC_REFUND_LOOKUP_DB_ERROR,
                                          "Failed to lookup refunds for contract");
     }
+
+    /* Now launch exchange interactions, unless we already have the
+       response in the database! */
+    for (struct CoinRefund *cr = prd->cr_head;
+         NULL != cr;
+         cr = cr->next)
+    {
+      enum GNUNET_DB_QueryStatus qs;
+
+      qs = db->get_refund_proof (db->cls,
+                                 &cr->prd->merchant->pubkey,
+                                 &cr->prd->h_contract_terms,
+                                 &cr->coin_pub,
+                                 cr->rtransaction_id,
+                                 &cr->exchange_pub,
+                                 &cr->exchange_sig);
+      if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT != qs)
+      {
+        /* We need to talk to the exchange */
+        cr->fo = TMH_EXCHANGES_find_exchange (cr->exchange_url,
+                                              NULL,
+                                              &exchange_found_cb,
+                                              cr);
+      }
+    }
   }
 
   /* Check if there are still exchange operations pending */