implement instances via one base URL per instance

Previously, instances were addressed in various ways depending on then
request (GET parameter, some instance_id in the POST body).  With this
commit, users of the merchant backend don't see the instance, they just
see another base URL.

26 files changed, 332 insertions, 367 deletions

diff --git a/src/backend/taler-merchant-httpd.c b/src/backend/taler-merchant-httpd.c
index 5269c4c4..0accbb85 100644
--- a/src/backend/taler-merchant-httpd.c
+++ b/src/backend/taler-merchant-httpd.c
@@ -301,6 +301,10 @@ url_handler (void *cls,
   struct TM_HandlerContext *hc;
   struct GNUNET_AsyncScopeId aid;
   const char *correlation_id = NULL;
+  char *instance_id;
+  char *effective_url;
+  int ret;
+
 
   hc = *con_cls;
 
@@ -338,23 +342,53 @@ url_handler (void *cls,
                 method,
                 url);
 
-  for (unsigned int i = 0; NULL != handlers[i].url; i++)
+  /* Find out the merchant backend instance for the request.
+   * If there is an instance, remove the instance specification
+   * from the beginning of the request URL. */
+  {
+    const char *instance_prefix = "/instances/";
+    if (0 == strncmp (url, instance_prefix, strlen (instance_prefix)))
+    {
+      // url starts with "/instance/"
+      instance_id = GNUNET_strdup (url + strlen (instance_prefix));
+      char *slash = strchr (instance_id, '/');
+      if (NULL == slash)
+      {
+        GNUNET_free (instance_id);
+        return TMH_MHD_handler_static_response (&h404,
+                                                connection,
+                                                con_cls,
+                                                upload_data,
+                                                upload_data_size,
+                                                NULL);
+      }
+      effective_url = GNUNET_strdup (slash);
+      *slash = '\0';
+    }
+    else
+    {
+      effective_url = GNUNET_strdup (url);
+      instance_id = NULL;
+    }
+  }
+
+
+  for (unsigned int i=0;NULL != handlers[i].url;i++)
   {
     struct TMH_RequestHandler *rh = &handlers[i];
 
-    if ( (0 == strcmp (url,
-                       rh->url)) &&
+    if ( (0 == strcasecmp (effective_url,
+                           rh->url)) &&
          ( (NULL == rh->method) ||
            (0 == strcasecmp (method,
                              rh->method)) ) )
     {
-      int ret;
-
       ret = rh->handler (rh,
-                         connection,
-                         con_cls,
-                         upload_data,
-                         upload_data_size);
+			 connection,
+			 con_cls,
+			 upload_data,
+			 upload_data_size,
+                         instance_id);
       hc = *con_cls;
       if (NULL != hc)
       {
@@ -363,14 +397,18 @@ url_handler (void *cls,
          * we get another callack for this request. */
         hc->async_scope_id = aid;
       }
+      GNUNET_free_non_null (instance_id);
       return ret;
     }
   }
-  return TMH_MHD_handler_static_response (&h404,
-                                          connection,
-                                          con_cls,
-                                          upload_data,
-                                          upload_data_size);
+  ret = TMH_MHD_handler_static_response (&h404,
+                                         connection,
+                                         con_cls,
+                                         upload_data,
+                                         upload_data_size,
+                                         instance_id);
+  GNUNET_free_non_null (instance_id);
+  return ret;
 }
 
 
@@ -1132,23 +1170,26 @@ instances_iterator_cb (void *cls,
 
 
 /**
- * Lookup a merchant instance by its name.
+ * Lookup a merchant instance by its instance ID.
  *
- * @param name name of the instance to resolve
+ * @param instance_id identifier of the instance to resolve
  * @return NULL if that instance is unknown to us
  */
 struct MerchantInstance *
-TMH_lookup_instance (const char *name)
+TMH_lookup_instance (const char *instance_id)
 {
   struct GNUNET_HashCode h_instance;
 
-  GNUNET_CRYPTO_hash (name,
-                      strlen (name),
+  if (NULL == instance_id)
+    instance_id = "default";
+
+  GNUNET_CRYPTO_hash (instance_id,
+                      strlen (instance_id),
                       &h_instance);
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
               "Looking for by-id key %s of '%s' in hashmap\n",
               GNUNET_h2s (&h_instance),
-              name);
+              instance_id);
   /* We're fine if that returns NULL, the calling routine knows how
      to handle that */
   return GNUNET_CONTAINER_multihashmap_get (by_id_map,
@@ -1157,35 +1198,6 @@ TMH_lookup_instance (const char *name)
 
 
 /**
- * Extract merchant instance from the given JSON; if not
- * 'instance' field was found, then "default" instance is
- * returned.
- *
- * @param json the JSON to inspect; it is not required to
- * comply with any particular format. It will only be checked
- * if the field "instance" is there.
- * @return a pointer to a `struct MerchantInstance`. This will be
- * the 'default' merchant if the frontend did not specify any
- * "instance" field. The user should not care to free the returned
- * value, as it is taken from a global array that will be freed
- * by the general shutdown routine. NULL if the frontend specified
- * a wrong instance
- */
-struct MerchantInstance *
-TMH_lookup_instance_json (struct json_t *json)
-{
-  struct json_t *instance;
-  const char *instance_str;
-
-  if (NULL == (instance = json_object_get (json, "instance")))
-    instance_str = "default";
-  else
-    instance_str = json_string_value (instance);
-  return TMH_lookup_instance (instance_str);
-}
-
-
-/**
  * Iterate over locations in config in order to populate
  * the location data.
  *
diff --git a/src/backend/taler-merchant-httpd.h b/src/backend/taler-merchant-httpd.h
index ee3d88fe..4e939b96 100644
--- a/src/backend/taler-merchant-httpd.h
+++ b/src/backend/taler-merchant-httpd.h
@@ -203,13 +203,16 @@ struct TMH_RequestHandler
    * @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
+   * @param instance_id mechant backend instance ID, or NULL if no explicit
+   *        instance has been specified
    * @return MHD result code
    */
   int (*handler)(struct TMH_RequestHandler *rh,
                  struct MHD_Connection *connection,
                  void **connection_cls,
                  const char *upload_data,
-                 size_t *upload_data_size);
+                 size_t *upload_data_size,
+                 const char *instance_id);
 
   /**
    * Default response code.
@@ -351,21 +354,4 @@ struct MerchantInstance *
 TMH_lookup_instance (const char *name);
 
 
-/**
- * Extract merchant instance from the given JSON
- *
- * @param json the JSON to inspect; it is not required to
- * comply with any particular format. It will only be checked
- * if the field "instance" is there.
- * @return a pointer to a #struct MerchantInstance. This will be
- * the 'default' merchant if the frontend did not specif any
- * "instance" field. The user should not care to free the returned
- * value, as it is taken from a global array that will be freed
- * by the general shutdown routine. NULL if the frontend specified
- * a wrong instance
- */
-struct MerchantInstance *
-TMH_lookup_instance_json (struct json_t *json);
-
-
 #endif
diff --git a/src/backend/taler-merchant-httpd_check-payment.c b/src/backend/taler-merchant-httpd_check-payment.c
index 59ed60d1..2ba4cc4a 100644
--- a/src/backend/taler-merchant-httpd_check-payment.c
+++ b/src/backend/taler-merchant-httpd_check-payment.c
@@ -291,6 +291,8 @@ check_order_and_request_payment (struct MHD_Connection *connection,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -298,12 +300,12 @@ MH_handler_check_payment (struct TMH_RequestHandler *rh,
                           struct MHD_Connection *connection,
                           void **connection_cls,
                           const char *upload_data,
-                          size_t *upload_data_size)
+                          size_t *upload_data_size,
+                          const char *instance_id)
 {
   const char *order_id;
   const char *contract_url;
   const char *session_id;
-  const char *instance_str;
   const char *fulfillment_url;
   char *final_contract_url;
   char *h_contract_terms_str;
@@ -315,12 +317,7 @@ MH_handler_check_payment (struct TMH_RequestHandler *rh,
   int ret;
   int refunded;
 
-  instance_str = MHD_lookup_connection_value (connection,
-                                              MHD_GET_ARGUMENT_KIND,
-                                              "instance");
-  if (NULL == instance_str)
-    instance_str = "default";
-  mi = TMH_lookup_instance (instance_str);
+  mi = TMH_lookup_instance (instance_id);
   if (NULL == mi)
     return TMH_RESPONSE_reply_bad_request (connection,
                                            TALER_EC_CHECK_PAYMENT_INSTANCE_UNKNOWN,
@@ -343,7 +340,7 @@ MH_handler_check_payment (struct TMH_RequestHandler *rh,
   {
     final_contract_url = TALER_url_absolute_mhd (connection,
                                                  "/public/proposal",
-                                                 "instance", instance_str,
+                                                 "instance", instance_id,
                                                  "order_id", order_id,
                                                  NULL);
     GNUNET_assert (NULL != final_contract_url);
diff --git a/src/backend/taler-merchant-httpd_check-payment.h b/src/backend/taler-merchant-httpd_check-payment.h
index 14c2a67b..98fa3a11 100644
--- a/src/backend/taler-merchant-httpd_check-payment.h
+++ b/src/backend/taler-merchant-httpd_check-payment.h
@@ -34,6 +34,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -41,6 +43,7 @@ MH_handler_check_payment (struct TMH_RequestHandler *rh,
                           struct MHD_Connection *connection,
                           void **connection_cls,
                           const char *upload_data,
-                          size_t *upload_data_size);
+                          size_t *upload_data_size,
+                          const char *instance_id);
 
 #endif
diff --git a/src/backend/taler-merchant-httpd_config.c b/src/backend/taler-merchant-httpd_config.c
index 51d44729..3e7b7b39 100644
--- a/src/backend/taler-merchant-httpd_config.c
+++ b/src/backend/taler-merchant-httpd_config.c
@@ -39,6 +39,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -46,19 +48,13 @@ MH_handler_config (struct TMH_RequestHandler *rh,
                    struct MHD_Connection *connection,
                    void **connection_cls,
                    const char *upload_data,
-                   size_t *upload_data_size)
+                   size_t *upload_data_size,
+                   const char *instance_id)
 {
   int ret;
-  const char *instance_str;
   struct MerchantInstance *mi;
 
-  instance_str = MHD_lookup_connection_value (connection,
-                                              MHD_GET_ARGUMENT_KIND,
-                                              "instance");
-  if (NULL == instance_str)
-    instance_str = "default";
-
-  mi = TMH_lookup_instance (instance_str);
+  mi = TMH_lookup_instance (instance_id);
 
   if (NULL == mi)
     return TMH_RESPONSE_reply_bad_request (connection,
diff --git a/src/backend/taler-merchant-httpd_config.h b/src/backend/taler-merchant-httpd_config.h
index cff766eb..08594a5f 100644
--- a/src/backend/taler-merchant-httpd_config.h
+++ b/src/backend/taler-merchant-httpd_config.h
@@ -31,6 +31,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -38,6 +40,7 @@ MH_handler_config (struct TMH_RequestHandler *rh,
                    struct MHD_Connection *connection,
                    void **connection_cls,
                    const char *upload_data,
-                   size_t *upload_data_size);
+                   size_t *upload_data_size,
+                   const char *instance_id);
 
 #endif
diff --git a/src/backend/taler-merchant-httpd_history.c b/src/backend/taler-merchant-httpd_history.c
index 2d620890..36ca7290 100644
--- a/src/backend/taler-merchant-httpd_history.c
+++ b/src/backend/taler-merchant-httpd_history.c
@@ -122,6 +122,8 @@ pd_cb (void *cls,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -129,7 +131,8 @@ MH_handler_history (struct TMH_RequestHandler *rh,
                     struct MHD_Connection *connection,
                     void **connection_cls,
                     const char *upload_data,
-                    size_t *upload_data_size)
+                    size_t *upload_data_size,
+                    const char *instance_id)
 {
   #define LOG_INFO(...) GNUNET_log (GNUNET_ERROR_TYPE_INFO, __VA_ARGS__)
   const char *str;
@@ -172,10 +175,7 @@ MH_handler_history (struct TMH_RequestHandler *rh,
     }
   }
 
-  str = MHD_lookup_connection_value (connection,
-                                     MHD_GET_ARGUMENT_KIND,
-                                     "instance");
-  mi = TMH_lookup_instance (NULL != str ? str : "default");
+  mi = TMH_lookup_instance (instance_id);
 
   if (NULL == mi)
   {
diff --git a/src/backend/taler-merchant-httpd_history.h b/src/backend/taler-merchant-httpd_history.h
index a06e926f..5ea2ed23 100644
--- a/src/backend/taler-merchant-httpd_history.h
+++ b/src/backend/taler-merchant-httpd_history.h
@@ -34,6 +34,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -41,7 +43,8 @@ MH_handler_history (struct TMH_RequestHandler *rh,
                     struct MHD_Connection *connection,
                     void **connection_cls,
                     const char *upload_data,
-                    size_t *upload_data_size);
+                    size_t *upload_data_size,
+                    const char *instance_id);
 
 /* end of taler-merchant-httpd_history.c */
 #endif
diff --git a/src/backend/taler-merchant-httpd_mhd.c b/src/backend/taler-merchant-httpd_mhd.c
index e4e5329c..a17485cc 100644
--- a/src/backend/taler-merchant-httpd_mhd.c
+++ b/src/backend/taler-merchant-httpd_mhd.c
@@ -37,6 +37,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -44,7 +46,8 @@ TMH_MHD_handler_static_response (struct TMH_RequestHandler *rh,
                                  struct MHD_Connection *connection,
                                  void **connection_cls,
                                  const char *upload_data,
-                                 size_t *upload_data_size)
+                                 size_t *upload_data_size,
+                                 const char *instance_id)
 {
   struct MHD_Response *response;
   int ret;
@@ -81,6 +84,8 @@ TMH_MHD_handler_static_response (struct TMH_RequestHandler *rh,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -88,7 +93,8 @@ TMH_MHD_handler_agpl_redirect (struct TMH_RequestHandler *rh,
                                   struct MHD_Connection *connection,
                                   void **connection_cls,
                                   const char *upload_data,
-                                  size_t *upload_data_size)
+                                  size_t *upload_data_size,
+                                  const char *instance_id)
 {
   const char *agpl =
     "This server is licensed under the Affero GPL. You will now be redirected to the source code.";
@@ -136,6 +142,8 @@ TMH_MHD_handler_agpl_redirect (struct TMH_RequestHandler *rh,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -143,7 +151,8 @@ TMH_MHD_handler_send_json_pack_error (struct TMH_RequestHandler *rh,
                                          struct MHD_Connection *connection,
                                          void **connection_cls,
                                          const char *upload_data,
-                                         size_t *upload_data_size)
+                                         size_t *upload_data_size,
+                                         const char *instance_id)
 {
   return TMH_RESPONSE_reply_json_pack (connection,
                                        rh->response_code,
diff --git a/src/backend/taler-merchant-httpd_mhd.h b/src/backend/taler-merchant-httpd_mhd.h
index 5f0e69be..0ec9830b 100644
--- a/src/backend/taler-merchant-httpd_mhd.h
+++ b/src/backend/taler-merchant-httpd_mhd.h
@@ -37,6 +37,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -44,7 +46,8 @@ TMH_MHD_handler_static_response (struct TMH_RequestHandler *rh,
                                  struct MHD_Connection *connection,
                                  void **connection_cls,
                                  const char *upload_data,
-                                 size_t *upload_data_size);
+                                 size_t *upload_data_size,
+                                 const char *instance_id);
 
 
 /**
@@ -56,6 +59,8 @@ TMH_MHD_handler_static_response (struct TMH_RequestHandler *rh,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -63,7 +68,8 @@ TMH_MHD_handler_agpl_redirect (struct TMH_RequestHandler *rh,
                                struct MHD_Connection *connection,
                                void **connection_cls,
                                const char *upload_data,
-                               size_t *upload_data_size);
+                               size_t *upload_data_size,
+                               const char *instance_id);
 
 
 /**
@@ -98,6 +104,8 @@ TMH_MHD_helper_send_json_pack (struct TMH_RequestHandler *rh,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -105,7 +113,8 @@ TMH_MHD_handler_send_json_pack_error (struct TMH_RequestHandler *rh,
                                       struct MHD_Connection *connection,
                                       void **connection_cls,
                                       const char *upload_data,
-                                      size_t *upload_data_size);
+                                      size_t *upload_data_size,
+                                      const char *instance_id);
 
 
 #endif
diff --git a/src/backend/taler-merchant-httpd_pay.c b/src/backend/taler-merchant-httpd_pay.c
index d381c7ee..e72a8e25 100644
--- a/src/backend/taler-merchant-httpd_pay.c
+++ b/src/backend/taler-merchant-httpd_pay.c
@@ -1471,27 +1471,6 @@ parse_pay (struct MHD_Connection *connection,
     pc->mode = PC_MODE_PAY;
   else
     pc->mode = PC_MODE_ABORT_REFUND;
-  pc->mi = TMH_lookup_instance_json (merchant);
-  if (NULL == pc->mi)
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "Unable to find the specified instance\n");
-    GNUNET_JSON_parse_free (spec);
-    if (MHD_NO ==
-	TMH_RESPONSE_reply_not_found (connection,
-                                  TALER_EC_PAY_INSTANCE_UNKNOWN,
-                                  "Unknown instance given"))
-    {
-      GNUNET_break (0);
-      return GNUNET_SYSERR;
-    }
-    return GNUNET_NO;
-  }
-
-  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-              "/pay: picked instance %s\n",
-              pc->mi->id);
-
   {
     const char *fulfillment_url;
     struct GNUNET_JSON_Specification espec[] = {
@@ -2136,6 +2115,8 @@ handler_pay_json (struct MHD_Connection *connection,
  * @param upload_data upload data
  * @param[in,out] upload_data_size number of bytes (left) in @a
  *       upload_data
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -2143,7 +2124,8 @@ MH_handler_pay (struct TMH_RequestHandler *rh,
                 struct MHD_Connection *connection,
                 void **connection_cls,
                 const char *upload_data,
-                size_t *upload_data_size)
+                size_t *upload_data_size,
+                const char *instance_id)
 {
   struct PayContext *pc;
   int res;
@@ -2160,6 +2142,25 @@ MH_handler_pay (struct TMH_RequestHandler *rh,
     pc->hc.cc = &pay_context_cleanup;
     pc->connection = connection;
     *connection_cls = pc;
+    pc->mi = TMH_lookup_instance (instance_id);
+    if (NULL == pc->mi)
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                  "Unable to find the specified instance\n");
+      if (MHD_NO ==
+          TMH_RESPONSE_reply_not_found (connection,
+                                    TALER_EC_PAY_INSTANCE_UNKNOWN,
+                                    "Unknown instance given"))
+      {
+        GNUNET_break (0);
+        return GNUNET_SYSERR;
+      }
+      return GNUNET_NO;
+    }
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "/pay: picked instance %s\n",
+                pc->mi->id);
+
   }
   else
   {
diff --git a/src/backend/taler-merchant-httpd_pay.h b/src/backend/taler-merchant-httpd_pay.h
index d4f4958a..cffb13bb 100644
--- a/src/backend/taler-merchant-httpd_pay.h
+++ b/src/backend/taler-merchant-httpd_pay.h
@@ -40,6 +40,8 @@ MH_force_pc_resume (void);
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -47,6 +49,7 @@ MH_handler_pay (struct TMH_RequestHandler *rh,
                 struct MHD_Connection *connection,
                 void **connection_cls,
                 const char *upload_data,
-                size_t *upload_data_size);
+                size_t *upload_data_size,
+                const char *instance_id);
 
 #endif
diff --git a/src/backend/taler-merchant-httpd_proposal.c b/src/backend/taler-merchant-httpd_proposal.c
index a93d6f17..7f61d215 100644
--- a/src/backend/taler-merchant-httpd_proposal.c
+++ b/src/backend/taler-merchant-httpd_proposal.c
@@ -149,10 +149,10 @@ json_parse_cleanup (struct TM_HandlerContext *hc)
  */
 static int
 proposal_put (struct MHD_Connection *connection,
-              json_t *order)
+              json_t *order,
+              const struct MerchantInstance *mi)
 {
   int res;
-  struct MerchantInstance *mi;
   struct TALER_Amount total;
   const char *order_id;
   const char *summary;
@@ -182,7 +182,6 @@ proposal_put (struct MHD_Connection *connection,
     GNUNET_JSON_spec_end ()
   };
   enum GNUNET_DB_QueryStatus qs;
-  const char *instance;
   struct WireMethod *wm;
 
   /* Add order_id if it doesn't exist. */
@@ -309,111 +308,81 @@ proposal_put (struct MHD_Connection *connection,
                          json_array ());
   }
 
-  instance = json_string_value (json_object_get (order,
-                                                 "instance"));
-  if (NULL == instance)
-  {
-    TALER_LOG_DEBUG ("Giving 'default' instance\n");
-    instance = "default";
-  }
-
   /* Fill in merchant information if necessary */
+  if (NULL == json_object_get (order, "merchant"))
   {
-    /* The frontend either fully specifieds the "merchant" field,
-     * or just gives the backend the "instance" name and lets it
-     * fill out. */
-    struct MerchantInstance *my_mi = TMH_lookup_instance (instance);
-
-    if (NULL == my_mi)
+    const char *mj = NULL;
+    const char *ma = NULL;
+    json_t *locations;
+    char *label;
+    json_t *jmerchant;
+
+    jmerchant = json_object ();
+    json_object_set_new (jmerchant,
+                         "name",
+                         json_string (mi->name));
+    json_object_set_new (jmerchant,
+                         "instance",
+                         json_string (mi->id));
+    locations = json_object_get (order,
+                                 "locations");
+    if (NULL != locations)
     {
-      TALER_LOG_WARNING ("Does 'default' instance exist?\n");
-      return TMH_RESPONSE_reply_not_found
-        (connection,
-         TALER_EC_CONTRACT_INSTANCE_UNKNOWN,
-         "merchant instance (order:instance) not found");
-    }
-
-    /**
-     * Potential bug: if the outer 'instance' field is not
-     * given and the 'merchant' object is also missing, then
-     * is not possible to extract the instance!
-     */
-    if (NULL == json_object_get (order,
-                                 "merchant"))
-    {
-      const char *mj = NULL;
-      const char *ma = NULL;
-      json_t *locations;
-      char *label;
-      json_t *jmerchant;
-
-      jmerchant = json_object ();
-      json_object_set_new (jmerchant,
-                           "name",
-                           json_string (my_mi->name));
-      json_object_set_new (jmerchant,
-                           "instance",
-                           json_string (instance));
-      locations = json_object_get (order,
-                                   "locations");
-      if (NULL != locations)
+      json_t *loca;
+      json_t *locj;
+
+      /* Handle merchant address */
+      GNUNET_assert (0 < GNUNET_asprintf (&label,
+                                          "%s-address",
+                                          mi->id));
+      loca = json_object_get (default_locations,
+                              label);
+      if (NULL != loca)
+      {
+        loca = json_deep_copy (loca);
+        ma = STANDARD_LABEL_MERCHANT_ADDRESS;
+        json_object_set_new (locations,
+                             ma,
+                             loca);
+        json_object_set_new (jmerchant,
+                             "address",
+                             json_string (ma));
+      }
+      GNUNET_free (label);
+
+      /* Handle merchant jurisdiction */
+      GNUNET_assert (0 < GNUNET_asprintf (&label,
+                                          "%s-jurisdiction",
+                                          mi->id));
+      locj = json_object_get (default_locations,
+                              label);
+      if (NULL != locj)
       {
-        json_t *loca;
-        json_t *locj;
-
-        /* Handle merchant address */
-        GNUNET_assert (0 < GNUNET_asprintf (&label,
-                                            "%s-address",
-                                            my_mi->id));
-        loca = json_object_get (default_locations,
-                                label);
-        if (NULL != loca)
+        if ( (NULL != loca) &&
+             (1 == json_equal (locj,
+                               loca)) )
         {
-          loca = json_deep_copy (loca);
-          ma = STANDARD_LABEL_MERCHANT_ADDRESS;
-          json_object_set_new (locations,
-                               ma,
-                               loca);
-          json_object_set_new (jmerchant,
-                               "address",
-                               json_string (ma));
+          /* addresses equal, re-use */
+          mj = ma;
         }
-        GNUNET_free (label);
-
-        /* Handle merchant jurisdiction */
-        GNUNET_assert (0 < GNUNET_asprintf (&label,
-                                            "%s-jurisdiction",
-                                            my_mi->id));
-        locj = json_object_get (default_locations,
-                                label);
-        if (NULL != locj)
+        else
         {
-          if ( (NULL != loca) &&
-               (1 == json_equal (locj,
-                                 loca)) )
-          {
-            /* addresses equal, re-use */
-            mj = ma;
-          }
-          else
-          {
-            locj = json_deep_copy (locj);
-            mj = STANDARD_LABEL_MERCHANT_JURISDICTION;
-            json_object_set_new (locations,
-                                 mj,
-                                 locj);
-          }
-          json_object_set_new (merchant,
-                               "jurisdiction",
-                               json_string (mj));
+          locj = json_deep_copy (locj);
+          mj = STANDARD_LABEL_MERCHANT_JURISDICTION;
+          json_object_set_new (locations,
+                               mj,
+                               locj);
         }
-        GNUNET_free (label);
-      } /* have locations */
-      json_object_set_new (order,
-                           "merchant",
-                           jmerchant);
-    } /* needed to synthesize merchant info */
-  } /* scope of 'my_mi' */
+        json_object_set_new (merchant,
+                             "jurisdiction",
+                             json_string (mj));
+      }
+      GNUNET_free (label);
+    } /* have locations */
+    json_object_set_new (order,
+                         "merchant",
+                         jmerchant);
+  } /* needed to synthesize merchant info */
 
   /* extract fields we need to sign separately */
   res = TMH_PARSE_json_data (connection,
@@ -444,45 +413,6 @@ proposal_put (struct MHD_Connection *connection,
        "order:products");
   }
 
-  mi = TMH_lookup_instance_json (merchant);
-
-  if (NULL == mi)
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "Not able to find the specified instance\n");
-    GNUNET_JSON_parse_free (spec);
-    return TMH_RESPONSE_reply_not_found
-      (connection,
-       TALER_EC_CONTRACT_INSTANCE_UNKNOWN,
-       "Unknown instance (order:merchant:instance) given");
-  }
-
-  /* The outer instance field, and the one included
-   * in the merchant object are different */
-  if (0 != strcmp (mi->id,
-                   instance))
-  {
-    TALER_LOG_ERROR
-      ("Inconsistent instance specified"
-       " by merchant ('%s' vs '%s')\n",
-       instance,
-       mi->id);
-
-    TALER_LOG_DEBUG ("Dump wrong order: %s\n",
-                     json_dumps (order,
-                                 JSON_INDENT (1)));
-
-    return TMH_RESPONSE_reply_not_found
-      (connection,
-       TALER_EC_CONTRACT_INSTANCE_INCONSISTENT,
-       "Inconsistent instance given");
-  }
-
-  /* Setting the instance on the order directly is just a shortcut,
-     the wallet shouldn't see that. */
-  json_object_del (order, "instance");
-  instance = NULL;
-
   /* add fields to the contract that the backend should provide */
   json_object_set (order,
                    "exchanges",
@@ -499,7 +429,7 @@ proposal_put (struct MHD_Connection *connection,
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                 "No wire method available for"
-                " specified instance\n");
+                " instance '%s'\n", mi->id);
     GNUNET_JSON_parse_free (spec);
     return TMH_RESPONSE_reply_not_found
       (connection,
@@ -618,10 +548,12 @@ proposal_put (struct MHD_Connection *connection,
  *
  * @param connection the MHD connection to handle
  * @param[in,out] connection_cls the connection's closure
- * (can be updated)
+ *                (can be updated)
  * @param upload_data upload data
  * @param[in,out] upload_data_size number of bytes (left) in
- * @a upload_data
+ *                @a upload_data
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -629,10 +561,12 @@ MH_handler_proposal_put (struct TMH_RequestHandler *rh,
                          struct MHD_Connection *connection,
                          void **connection_cls,
                          const char *upload_data,
-                         size_t *upload_data_size)
+                         size_t *upload_data_size,
+                         const char *instance_id)
 {
   int res;
   struct TMH_JsonParseContext *ctx;
+  struct MerchantInstance *mi;
   json_t *root;
   json_t *order;
 
@@ -662,6 +596,12 @@ MH_handler_proposal_put (struct TMH_RequestHandler *rh,
        (NULL == root) )
     return MHD_YES;
 
+  mi = TMH_lookup_instance (instance_id);
+  if (NULL == mi)
+    return TMH_RESPONSE_reply_not_found (connection,
+                                         TALER_EC_CONTRACT_INSTANCE_UNKNOWN,
+                                         "instance");
+
   order = json_object_get (root,
                            "order");
   if (NULL == order)
@@ -672,8 +612,7 @@ MH_handler_proposal_put (struct TMH_RequestHandler *rh,
        "order");
   }
   else
-    res = proposal_put (connection,
-                        order);
+    res = proposal_put (connection, order, mi);
   json_decref (root);
   return res;
 }
@@ -691,6 +630,8 @@ MH_handler_proposal_put (struct TMH_RequestHandler *rh,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -698,10 +639,10 @@ MH_handler_proposal_lookup (struct TMH_RequestHandler *rh,
                             struct MHD_Connection *connection,
                             void **connection_cls,
                             const char *upload_data,
-                            size_t *upload_data_size)
+                            size_t *upload_data_size,
+                            const char *instance_id)
 {
   const char *order_id;
-  const char *instance;
   const char *nonce;
   int res;
   enum GNUNET_DB_QueryStatus qs;
@@ -710,14 +651,7 @@ MH_handler_proposal_lookup (struct TMH_RequestHandler *rh,
   struct GNUNET_CRYPTO_EddsaSignature merchant_sig;
   const char *stored_nonce;
 
-  instance = MHD_lookup_connection_value (connection,
-                                          MHD_GET_ARGUMENT_KIND,
-                                          "instance");
-  if (NULL == instance)
-    return TMH_RESPONSE_reply_arg_missing (connection,
-					   TALER_EC_PARAMETER_MISSING,
-                                           "instance");
-  mi = TMH_lookup_instance (instance);
+  mi = TMH_lookup_instance (instance_id);
   if (NULL == mi)
     return TMH_RESPONSE_reply_not_found (connection,
                                          TALER_EC_CONTRACT_INSTANCE_UNKNOWN,
diff --git a/src/backend/taler-merchant-httpd_proposal.h b/src/backend/taler-merchant-httpd_proposal.h
index fe5b319a..137c32a6 100644
--- a/src/backend/taler-merchant-httpd_proposal.h
+++ b/src/backend/taler-merchant-httpd_proposal.h
@@ -33,6 +33,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -40,7 +42,8 @@ MH_handler_proposal_put (struct TMH_RequestHandler *rh,
                          struct MHD_Connection *connection,
                          void **connection_cls,
                          const char *upload_data,
-                         size_t *upload_data_size);
+                         size_t *upload_data_size,
+                         const char *instance_id);
 
 
 /**
@@ -60,5 +63,6 @@ MH_handler_proposal_lookup (struct TMH_RequestHandler *rh,
                             struct MHD_Connection *connection,
                             void **connection_cls,
                             const char *upload_data,
-                            size_t *upload_data_size);
+                            size_t *upload_data_size,
+                            const char *instance_id);
 #endif
diff --git a/src/backend/taler-merchant-httpd_refund.c b/src/backend/taler-merchant-httpd_refund.c
index 1f80491c..a20149a1 100644
--- a/src/backend/taler-merchant-httpd_refund.c
+++ b/src/backend/taler-merchant-httpd_refund.c
@@ -155,6 +155,8 @@ json_parse_cleanup (struct TM_HandlerContext *hc)
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -162,7 +164,8 @@ MH_handler_refund_increase (struct TMH_RequestHandler *rh,
                             struct MHD_Connection *connection,
                             void **connection_cls,
                             const char *upload_data,
-                            size_t *upload_data_size)
+                            size_t *upload_data_size,
+                            const char *instance_id)
 {
   int res;
   struct TMH_JsonParseContext *ctx;
@@ -171,7 +174,6 @@ MH_handler_refund_increase (struct TMH_RequestHandler *rh,
   json_t *contract_terms;
   const char *order_id;
   const char *reason;
-  const char *merchant;
   struct MerchantInstance *mi;
   struct GNUNET_HashCode h_contract_terms;
   struct TALER_MerchantRefundConfirmationPS confirmation;
@@ -180,7 +182,6 @@ MH_handler_refund_increase (struct TMH_RequestHandler *rh,
     TALER_JSON_spec_amount ("refund", &refund),
     GNUNET_JSON_spec_string ("order_id", &order_id),
     GNUNET_JSON_spec_string ("reason", &reason),
-    GNUNET_JSON_spec_string ("instance", &merchant),
     GNUNET_JSON_spec_end ()
   };
   enum GNUNET_DB_QueryStatus qs;
@@ -226,11 +227,12 @@ MH_handler_refund_increase (struct TMH_RequestHandler *rh,
     return MHD_NO;
   }
 
-  mi = TMH_lookup_instance (merchant);
+  mi = TMH_lookup_instance (instance_id);
   if (NULL == mi)
   {
+    GNUNET_assert (NULL != instance_id);
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No instance found\n");
+                "Instance '%s' not found\n", instance_id);
     GNUNET_JSON_parse_free (spec);
     json_decref (root);
     return TMH_RESPONSE_reply_not_found (connection,
@@ -491,6 +493,8 @@ process_refunds_cb (void *cls,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -498,34 +502,23 @@ MH_handler_refund_lookup (struct TMH_RequestHandler *rh,
                           struct MHD_Connection *connection,
                           void **connection_cls,
                           const char *upload_data,
-                          size_t *upload_data_size)
+                          size_t *upload_data_size,
+                          const char *instance_id)
 {
   const char *order_id;
-  const char *instance;
   struct GNUNET_HashCode h_contract_terms;
   json_t *contract_terms;
   struct MerchantInstance *mi;
   enum GNUNET_DB_QueryStatus qs;
 
-  instance = MHD_lookup_connection_value (connection,
-                                          MHD_GET_ARGUMENT_KIND,
-                                          "instance");
-  if (NULL == instance)
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "Argument 'instance' not given\n");
-    return TMH_RESPONSE_reply_arg_missing (connection,
-					   TALER_EC_PARAMETER_MISSING,
-                                           "instance");
-  }
-
-  mi = TMH_lookup_instance (instance);
+  mi = TMH_lookup_instance (instance_id);
 
   if (NULL == mi)
   {
+    GNUNET_assert (NULL != instance_id);
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                 "Unknown instance given: %s\n",
-                instance);
+                instance_id);
     return TMH_RESPONSE_reply_not_found (connection,
                                          TALER_EC_REFUND_INSTANCE_UNKNOWN,
                                          "Unknown instance given");
diff --git a/src/backend/taler-merchant-httpd_refund.h b/src/backend/taler-merchant-httpd_refund.h
index 32083273..eadd24a9 100644
--- a/src/backend/taler-merchant-httpd_refund.h
+++ b/src/backend/taler-merchant-httpd_refund.h
@@ -34,6 +34,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -41,7 +43,8 @@ MH_handler_refund_increase (struct TMH_RequestHandler *rh,
                             struct MHD_Connection *connection,
                             void **connection_cls,
                             const char *upload_data,
-                            size_t *upload_data_size);
+                            size_t *upload_data_size,
+                            const char *instance_id);
 
 
 /**
@@ -52,6 +55,8 @@ MH_handler_refund_increase (struct TMH_RequestHandler *rh,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -59,7 +64,8 @@ MH_handler_refund_lookup (struct TMH_RequestHandler *rh,
                           struct MHD_Connection *connection,
                           void **connection_cls,
                           const char *upload_data,
-                          size_t *upload_data_size);
+                          size_t *upload_data_size,
+                          const char *instance_id);
 
 /**
  * Get the JSON representation of a refund.
diff --git a/src/backend/taler-merchant-httpd_tip-authorize.c b/src/backend/taler-merchant-httpd_tip-authorize.c
index 4c2451e8..1a79d772 100644
--- a/src/backend/taler-merchant-httpd_tip-authorize.c
+++ b/src/backend/taler-merchant-httpd_tip-authorize.c
@@ -45,11 +45,6 @@ struct TipAuthContext
   void *json_parse_context;
 
   /**
-   * Merchant instance to use.
-   */
-  const char *instance;
-
-  /**
    * Justification to use.
    */
   const char *justification;
@@ -112,6 +107,8 @@ cleanup_tac (struct TM_HandlerContext *hc)
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -119,7 +116,8 @@ MH_handler_tip_authorize (struct TMH_RequestHandler *rh,
                           struct MHD_Connection *connection,
                           void **connection_cls,
                           const char *upload_data,
-                          size_t *upload_data_size)
+                          size_t *upload_data_size,
+                          const char *instance_id)
 {
   struct TipAuthContext *tac;
   int res;
@@ -153,7 +151,6 @@ MH_handler_tip_authorize (struct TMH_RequestHandler *rh,
   {
     struct GNUNET_JSON_Specification spec[] = {
       TALER_JSON_spec_amount ("amount", &tac->amount),
-      GNUNET_JSON_spec_string ("instance", &tac->instance),
       GNUNET_JSON_spec_string ("justification", &tac->justification),
       GNUNET_JSON_spec_end()
     };
@@ -181,12 +178,13 @@ MH_handler_tip_authorize (struct TMH_RequestHandler *rh,
     tac->parsed_json = GNUNET_YES;
   }
 
-  mi = TMH_lookup_instance (tac->instance);
+  mi = TMH_lookup_instance (instance_id);
   if (NULL == mi)
   {
+    GNUNET_assert (NULL != instance_id);
     GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                 "Instance `%s' not configured\n",
-                tac->instance);
+                instance_id);
     return TMH_RESPONSE_reply_not_found (connection,
                                          TALER_EC_TIP_AUTHORIZE_INSTANCE_UNKNOWN,
                                          "unknown instance");
@@ -195,7 +193,7 @@ MH_handler_tip_authorize (struct TMH_RequestHandler *rh,
   {
     GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                 "Instance `%s' not configured for tipping\n",
-                tac->instance);
+                (NULL != instance_id) ? instance_id : "default");
     return TMH_RESPONSE_reply_not_found (connection,
                                          TALER_EC_TIP_AUTHORIZE_INSTANCE_DOES_NOT_TIP,
                                          "exchange for tipping not configured for the instance");
diff --git a/src/backend/taler-merchant-httpd_tip-authorize.h b/src/backend/taler-merchant-httpd_tip-authorize.h
index b7c3b9a1..025b9580 100644
--- a/src/backend/taler-merchant-httpd_tip-authorize.h
+++ b/src/backend/taler-merchant-httpd_tip-authorize.h
@@ -32,6 +32,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -39,6 +41,7 @@ MH_handler_tip_authorize (struct TMH_RequestHandler *rh,
                           struct MHD_Connection *connection,
                           void **connection_cls,
                           const char *upload_data,
-                          size_t *upload_data_size);
+                          size_t *upload_data_size,
+                          const char *instance_id);
 
 #endif
diff --git a/src/backend/taler-merchant-httpd_tip-pickup.c b/src/backend/taler-merchant-httpd_tip-pickup.c
index eba99e38..6232c4b8 100644
--- a/src/backend/taler-merchant-httpd_tip-pickup.c
+++ b/src/backend/taler-merchant-httpd_tip-pickup.c
@@ -494,6 +494,8 @@ parse_planchet (struct MHD_Connection *connection,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -501,7 +503,8 @@ MH_handler_tip_pickup (struct TMH_RequestHandler *rh,
                        struct MHD_Connection *connection,
                        void **connection_cls,
                        const char *upload_data,
-                       size_t *upload_data_size)
+                       size_t *upload_data_size,
+                       const char *instance_id)
 {
   int res;
   struct GNUNET_HashCode tip_id;
@@ -608,6 +611,8 @@ MH_handler_tip_pickup (struct TMH_RequestHandler *rh,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -615,10 +620,10 @@ MH_handler_tip_pickup_get (struct TMH_RequestHandler *rh,
                            struct MHD_Connection *connection,
                            void **connection_cls,
                            const char *upload_data,
-                           size_t *upload_data_size)
+                           size_t *upload_data_size,
+                           const char *instance_id)
 {
   struct MerchantInstance *mi;
-  const char *instance_str;
   const char *tip_id_str;
   char *exchange_url;
   json_t *extra;
@@ -630,12 +635,7 @@ MH_handler_tip_pickup_get (struct TMH_RequestHandler *rh,
   int ret;
   int qs;
 
-  instance_str = MHD_lookup_connection_value (connection,
-                                              MHD_GET_ARGUMENT_KIND,
-                                              "instance");
-  if (NULL == instance_str)
-    instance_str = "default";
-  mi = TMH_lookup_instance (instance_str);
+  mi = TMH_lookup_instance (instance_id);
   if (NULL == mi)
     return TMH_RESPONSE_reply_bad_request (connection,
                                            TALER_EC_TIP_INSTANCE_UNKNOWN,
diff --git a/src/backend/taler-merchant-httpd_tip-pickup.h b/src/backend/taler-merchant-httpd_tip-pickup.h
index 181725a7..f0e9733d 100644
--- a/src/backend/taler-merchant-httpd_tip-pickup.h
+++ b/src/backend/taler-merchant-httpd_tip-pickup.h
@@ -32,6 +32,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -39,7 +41,8 @@ MH_handler_tip_pickup (struct TMH_RequestHandler *rh,
                        struct MHD_Connection *connection,
                        void **connection_cls,
                        const char *upload_data,
-                       size_t *upload_data_size);
+                       size_t *upload_data_size,
+                       const char *instance_id);
 
 /**
  * Manages a GET /tip-pickup call.
@@ -49,6 +52,8 @@ MH_handler_tip_pickup (struct TMH_RequestHandler *rh,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -56,7 +61,8 @@ MH_handler_tip_pickup_get (struct TMH_RequestHandler *rh,
                            struct MHD_Connection *connection,
                            void **connection_cls,
                            const char *upload_data,
-                           size_t *upload_data_size);
+                           size_t *upload_data_size,
+                           const char *instance_id);
 
 
 #endif
diff --git a/src/backend/taler-merchant-httpd_tip-query.c b/src/backend/taler-merchant-httpd_tip-query.c
index 2b90b795..bd61a3e6 100644
--- a/src/backend/taler-merchant-httpd_tip-query.c
+++ b/src/backend/taler-merchant-httpd_tip-query.c
@@ -52,6 +52,12 @@ struct TipQueryContext
   const char *instance;
 
   /**
+   * GNUNET_YES if the tip query has already been processed
+   * and we can queue the response.
+   */
+  int processed;
+
+  /**
    * Context for checking the tipping reserve's status.
    */
   struct CheckTipReserve ctr;
@@ -126,6 +132,8 @@ generate_final_response (struct TipQueryContext *tqc)
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -133,7 +141,8 @@ MH_handler_tip_query (struct TMH_RequestHandler *rh,
                       struct MHD_Connection *connection,
                       void **connection_cls,
                       const char *upload_data,
-                      size_t *upload_data_size)
+                      size_t *upload_data_size,
+                      const char *instance_id)
 {
   struct TipQueryContext *tqc;
   struct MerchantInstance *mi;
@@ -172,28 +181,21 @@ MH_handler_tip_query (struct TMH_RequestHandler *rh,
     return res;
   }
 
-  if (NULL != tqc->instance)
+  if (GNUNET_YES == tqc->processed)
   {
     /* We've been here before, so TMH_check_tip_reserve() must have
        finished and left the result for us. Finish processing. */
     return generate_final_response (tqc);
   }
 
-  /* No error yet, so first time here, let's query the exchange */
-  tqc->instance = MHD_lookup_connection_value (connection,
-                                               MHD_GET_ARGUMENT_KIND,
-                                               "instance");
-  if (NULL == tqc->instance)
-    return TMH_RESPONSE_reply_arg_missing (connection,
-                                           TALER_EC_PARAMETER_MISSING,
-                                           "instance");
 
-  mi = TMH_lookup_instance (tqc->instance);
+  mi = TMH_lookup_instance (instance_id);
   if (NULL == mi)
   {
+    GNUNET_assert (NULL != instance_id);
     GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                 "Instance `%s' not configured\n",
-                tqc->instance);
+                instance_id);
     return TMH_RESPONSE_reply_not_found (connection,
                                          TALER_EC_TIP_AUTHORIZE_INSTANCE_UNKNOWN,
                                          "unknown instance");
@@ -202,7 +204,7 @@ MH_handler_tip_query (struct TMH_RequestHandler *rh,
   {
     GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                 "Instance `%s' not configured for tipping\n",
-                tqc->instance);
+                instance_id);
     return TMH_RESPONSE_reply_not_found (connection,
                                          TALER_EC_TIP_AUTHORIZE_INSTANCE_DOES_NOT_TIP,
                                          "exchange for tipping not configured for the instance");
@@ -236,6 +238,7 @@ MH_handler_tip_query (struct TMH_RequestHandler *rh,
     }
   }
 
+  tqc->processed = GNUNET_YES;
   TMH_check_tip_reserve (&tqc->ctr,
                          mi->tip_exchange);
   return MHD_YES;
diff --git a/src/backend/taler-merchant-httpd_tip-query.h b/src/backend/taler-merchant-httpd_tip-query.h
index f3a9ebff..10b1e1be 100644
--- a/src/backend/taler-merchant-httpd_tip-query.h
+++ b/src/backend/taler-merchant-httpd_tip-query.h
@@ -31,6 +31,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -38,6 +40,7 @@ MH_handler_tip_query (struct TMH_RequestHandler *rh,
                       struct MHD_Connection *connection,
                       void **connection_cls,
                       const char *upload_data,
-                      size_t *upload_data_size);
+                      size_t *upload_data_size,
+                      const char *instance_id);
 
 #endif
diff --git a/src/backend/taler-merchant-httpd_track-transaction.c b/src/backend/taler-merchant-httpd_track-transaction.c
index 6879612d..1376aa9a 100644
--- a/src/backend/taler-merchant-httpd_track-transaction.c
+++ b/src/backend/taler-merchant-httpd_track-transaction.c
@@ -1037,6 +1037,8 @@ find_exchange (struct TrackTransactionContext *tctx)
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -1044,13 +1046,12 @@ MH_handler_track_transaction (struct TMH_RequestHandler *rh,
                               struct MHD_Connection *connection,
                               void **connection_cls,
                               const char *upload_data,
-                              size_t *upload_data_size)
+                              size_t *upload_data_size,
+                              const char *instance_id)
 {
   struct TrackTransactionContext *tctx;
   const char *order_id;
-  const char *instance;
   enum GNUNET_DB_QueryStatus qs;
-  struct GNUNET_HashCode h_instance;
   struct json_t *contract_terms;
 
   if (NULL == *connection_cls)
@@ -1105,26 +1106,16 @@ MH_handler_track_transaction (struct TMH_RequestHandler *rh,
     return TMH_RESPONSE_reply_arg_missing (connection,
                                            TALER_EC_PARAMETER_MISSING,
                                            "order_id");
-  instance = MHD_lookup_connection_value (connection,
-                                          MHD_GET_ARGUMENT_KIND,
-                                          "instance");
-  if (NULL == instance)
-    instance = "default";
-
-  GNUNET_CRYPTO_hash (instance,
-                      strlen (instance),
-                      &h_instance);
-
-  tctx->mi = GNUNET_CONTAINER_multihashmap_get (by_id_map,
-                                                &h_instance);
-  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-              "Tracking on behalf of instance '%s'\n",
-              instance);
 
+  tctx->mi = TMH_lookup_instance (instance_id);
   if (NULL == tctx->mi)
     return TMH_RESPONSE_reply_not_found (connection,
                                          TALER_EC_TRACK_TRANSACTION_INSTANCE_UNKNOWN,
                                          "unknown instance");
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Tracking on behalf of instance '%s'\n",
+              instance_id);
+
 
   /* Map order id to contract terms; the objective is to get
      the contract term's hashcode so as to retrieve all the
diff --git a/src/backend/taler-merchant-httpd_track-transaction.h b/src/backend/taler-merchant-httpd_track-transaction.h
index 30896bf3..7efecaa9 100644
--- a/src/backend/taler-merchant-httpd_track-transaction.h
+++ b/src/backend/taler-merchant-httpd_track-transaction.h
@@ -32,6 +32,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -39,7 +41,8 @@ MH_handler_track_transaction (struct TMH_RequestHandler *rh,
                               struct MHD_Connection *connection,
                               void **connection_cls,
                               const char *upload_data,
-                              size_t *upload_data_size);
+                              size_t *upload_data_size,
+                              const char *instance_id);
 
 
 #endif
diff --git a/src/backend/taler-merchant-httpd_track-transfer.c b/src/backend/taler-merchant-httpd_track-transfer.c
index 54810037..f833c7e9 100644
--- a/src/backend/taler-merchant-httpd_track-transfer.c
+++ b/src/backend/taler-merchant-httpd_track-transfer.c
@@ -881,6 +881,8 @@ proof_cb (void *cls,
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -888,12 +890,12 @@ MH_handler_track_transfer (struct TMH_RequestHandler *rh,
                            struct MHD_Connection *connection,
                            void **connection_cls,
                            const char *upload_data,
-                           size_t *upload_data_size)
+                           size_t *upload_data_size,
+                           const char *instance_id)
 {
   struct TrackTransferContext *rctx;
   const char *str;
   const char *url;
-  const char *instance_str;
   const char *wire_method;
   int ret;
   enum GNUNET_DB_QueryStatus qs;
@@ -973,13 +975,7 @@ MH_handler_track_transfer (struct TMH_RequestHandler *rh,
   }
   rctx->wire_method = GNUNET_strdup (wire_method);
 
-  instance_str = MHD_lookup_connection_value (connection,
-                                              MHD_GET_ARGUMENT_KIND,
-                                              "instance");
-  if (NULL == instance_str)
-    instance_str = "default";
-
-  rctx->mi = TMH_lookup_instance (instance_str);
+  rctx->mi = TMH_lookup_instance (instance_id);
   if (NULL == rctx->mi)
     return TMH_RESPONSE_reply_not_found (connection,
                                          TALER_EC_TRACK_TRANSFER_INSTANCE_UNKNOWN,
diff --git a/src/backend/taler-merchant-httpd_track-transfer.h b/src/backend/taler-merchant-httpd_track-transfer.h
index 13a173c9..8da998dc 100644
--- a/src/backend/taler-merchant-httpd_track-transfer.h
+++ b/src/backend/taler-merchant-httpd_track-transfer.h
@@ -34,6 +34,8 @@
  * @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
+ * @param instance_id merchant backend instance ID or NULL is no instance
+ *        has been explicitly specified
  * @return MHD result code
  */
 int
@@ -41,7 +43,8 @@ MH_handler_track_transfer (struct TMH_RequestHandler *rh,
                            struct MHD_Connection *connection,
                            void **connection_cls,
                            const char *upload_data,
-                           size_t *upload_data_size);
+                           size_t *upload_data_size,
+                           const char *instance_id);
 
 
 #endif