[wip, #7267] more refined denomination conflict response during deposit

If a coin was known but with a different denomination, return to the
client an error response that contains the denomination's public key and
the corresponding signature of the provided coin.

8 files changed, 218 insertions, 21 deletions

diff --git a/src/exchange/taler-exchange-httpd_db.c b/src/exchange/taler-exchange-httpd_db.c
index 5be12a508..1c11a02fb 100644
--- a/src/exchange/taler-exchange-httpd_db.c
+++ b/src/exchange/taler-exchange-httpd_db.c
@@ -19,9 +19,11 @@
  * @author Christian Grothoff
  */
 #include "platform.h"
+#include <gnunet/gnunet_db_lib.h>
 #include <pthread.h>
 #include <jansson.h>
 #include <gnunet/gnunet_json_lib.h>
+#include "taler_error_codes.h"
 #include "taler_exchangedb_plugin.h"
 #include "taler_json_lib.h"
 #include "taler_mhd_lib.h"
@@ -62,14 +64,39 @@ TEH_make_coin_known (const struct TALER_CoinPublicInfo *coin,
                                     NULL);
     return GNUNET_DB_STATUS_HARD_ERROR;
   case TALER_EXCHANGEDB_CKS_DENOM_CONFLICT:
-    /* FIXME: insufficient_funds != denom conflict! See issue #7267, need new
-     * strategy for evidence gathering */
-    *mhd_ret = TEH_RESPONSE_reply_coin_insufficient_funds (
-      connection,
-      TALER_EC_EXCHANGE_GENERIC_COIN_CONFLICTING_DENOMINATION_KEY,
-      &h_denom_pub,
-      &coin->coin_pub);
-    return GNUNET_DB_STATUS_HARD_ERROR;
+    /* The exchange has a seen this coin before, but with a different denomination.
+     * Get the corresponding signature and sent it to the client as proof */
+    {
+      struct conflict
+      {
+        struct TALER_DenominationPublicKey pub;
+        struct TALER_DenominationSignature sig;
+      } conflict = {0};
+
+      if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT !=
+          TEH_plugin->get_signature_for_known_coin (TEH_plugin->cls,
+                                                    &coin->coin_pub,
+                                                    &conflict.pub,
+                                                    &conflict.sig))
+      {
+        /* There _should_ have been a result, because
+         * we ended here due to a conflict! */
+        *mhd_ret = TALER_MHD_reply_with_error (connection,
+                                               MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                               TALER_EC_GENERIC_DB_FETCH_FAILED,
+                                               NULL);
+        return GNUNET_DB_STATUS_HARD_ERROR;
+      }
+
+      *mhd_ret = TEH_RESPONSE_reply_coin_denomination_conflict (
+        connection,
+        TALER_EC_EXCHANGE_GENERIC_COIN_CONFLICTING_DENOMINATION_KEY,
+        &coin->coin_pub,
+        &conflict.pub,
+        &conflict.sig);
+
+      return GNUNET_DB_STATUS_HARD_ERROR;
+    }
   case TALER_EXCHANGEDB_CKS_AGE_CONFLICT_EXPECTED_NULL:
   case TALER_EXCHANGEDB_CKS_AGE_CONFLICT_EXPECTED_NON_NULL:
   case TALER_EXCHANGEDB_CKS_AGE_CONFLICT_VALUE_DIFFERS:
diff --git a/src/exchange/taler-exchange-httpd_responses.c b/src/exchange/taler-exchange-httpd_responses.c
index 2d8dede51..a6d2c7ffc 100644
--- a/src/exchange/taler-exchange-httpd_responses.c
+++ b/src/exchange/taler-exchange-httpd_responses.c
@@ -180,6 +180,29 @@ TEH_RESPONSE_reply_coin_insufficient_funds (
 
 
 MHD_RESULT
+TEH_RESPONSE_reply_coin_denomination_conflict (
+  struct MHD_Connection *connection,
+  enum TALER_ErrorCode ec,
+  const struct TALER_CoinSpendPublicKeyP *coin_pub,
+  const struct TALER_DenominationPublicKey *prev_denom_pub,
+  const struct TALER_DenominationSignature *prev_denom_sig)
+{
+  return TALER_MHD_REPLY_JSON_PACK (
+    connection,
+    TALER_ErrorCode_get_http_status_safe (ec),
+    TALER_JSON_pack_ec (ec),
+    GNUNET_JSON_pack_data_auto ("coin_pub",
+                                coin_pub),
+    TALER_JSON_pack_denom_pub ("prev_denom_pub",
+                               prev_denom_pub),
+    TALER_JSON_pack_denom_sig ("prev_denom_sig",
+                               prev_denom_sig)
+    );
+
+}
+
+
+MHD_RESULT
 TEH_RESPONSE_reply_coin_age_commitment_conflict (
   struct MHD_Connection *connection,
   enum TALER_ErrorCode ec,
@@ -188,7 +211,6 @@ TEH_RESPONSE_reply_coin_age_commitment_conflict (
   const struct TALER_CoinSpendPublicKeyP *coin_pub,
   const struct TALER_AgeCommitmentHash *h_age_commitment)
 {
-  const struct TALER_AgeCommitmentHash *hac = h_age_commitment;
   const char *conflict_detail;
 
   switch (status)
@@ -196,10 +218,10 @@ TEH_RESPONSE_reply_coin_age_commitment_conflict (
 
   case TALER_EXCHANGEDB_CKS_AGE_CONFLICT_EXPECTED_NULL:
     conflict_detail = "expected NULL age commitment hash";
-    hac = NULL;
+    h_age_commitment = NULL;
     break;
   case TALER_EXCHANGEDB_CKS_AGE_CONFLICT_EXPECTED_NON_NULL:
-    conflict_detail = "unexpected NULL age commitment hash";
+    conflict_detail = "expected non-NULL age commitment hash";
     break;
   case TALER_EXCHANGEDB_CKS_AGE_CONFLICT_VALUE_DIFFERS:
     conflict_detail = "expected age commitment hash differs";
@@ -218,7 +240,7 @@ TEH_RESPONSE_reply_coin_age_commitment_conflict (
                                 h_denom_pub),
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_data_auto ("expected_age_commitment_hash",
-                                  hac)),
+                                  h_age_commitment)),
     GNUNET_JSON_pack_string ("conflict_detail",
                              conflict_detail)
     );
diff --git a/src/exchange/taler-exchange-httpd_responses.h b/src/exchange/taler-exchange-httpd_responses.h
index b10a72824..57aeefe42 100644
--- a/src/exchange/taler-exchange-httpd_responses.h
+++ b/src/exchange/taler-exchange-httpd_responses.h
@@ -162,6 +162,28 @@ TEH_RESPONSE_reply_coin_insufficient_funds (
 
 /**
  * Send proof that a request is invalid to client because of
+ * an conflict with the provided denomination (the exchange had seen
+ * this coin before, signed by a different denomination).
+ * This function will create a message with the denomination's public key
+ * that was seen before.
+ *
+ * @param connection connection to the client
+ * @param ec error code to return
+ * @param coin_pub the public key of the coin
+ * @param prev_denom_pub the denomination of the coin, as seen previously
+ * @param prev_denom_sig the signature with the denomination key over the coin
+ * @return MHD result code
+ */
+MHD_RESULT
+TEH_RESPONSE_reply_coin_denomination_conflict (
+  struct MHD_Connection *connection,
+  enum TALER_ErrorCode ec,
+  const struct TALER_CoinSpendPublicKeyP *coin_pub,
+  const struct TALER_DenominationPublicKey *prev_denom_pub,
+  const struct TALER_DenominationSignature *prev_denom_sig);
+
+/**
+ * Send proof that a request is invalid to client because of
  * a conflicting value for the age commitment hash of a coin.
  * This function will create a message with the conflicting
  * hash value for the age commitment of the given coin.
diff --git a/src/exchangedb/Makefile.am b/src/exchangedb/Makefile.am
index 84bd53018..847f2d880 100644
--- a/src/exchangedb/Makefile.am
+++ b/src/exchangedb/Makefile.am
@@ -126,6 +126,7 @@ libtaler_plugin_exchangedb_postgres_la_SOURCES = \
   pg_count_known_coins.h pg_count_known_coins.c \
   pg_ensure_coin_known.h pg_ensure_coin_known.c \
   pg_get_known_coin.h pg_get_known_coin.c \
+  pg_get_signature_for_known_coin.h pg_get_signature_for_known_coin.c \
   pg_get_coin_denomination.h pg_get_coin_denomination.c \
   pg_have_deposit2.h pg_have_deposit2.c \
   pg_aggregate.h pg_aggregate.c \
diff --git a/src/exchangedb/pg_get_signature_for_known_coin.c b/src/exchangedb/pg_get_signature_for_known_coin.c
new file mode 100644
index 000000000..06074312f
--- /dev/null
+++ b/src/exchangedb/pg_get_signature_for_known_coin.c
@@ -0,0 +1,63 @@
+/*
+   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 exchangedb/pg_get_signature_for_known_coin.c
+ * @brief Implementation of the get_signature_for_known_coin function for Postgres
+ * @author Özgür Kesim
+ */
+#include "platform.h"
+#include "taler_error_codes.h"
+#include "taler_dbevents.h"
+#include "taler_pq_lib.h"
+#include "pg_get_signature_for_known_coin.h"
+#include "pg_helper.h"
+
+enum GNUNET_DB_QueryStatus
+TEH_PG_get_signature_for_known_coin (
+  void *cls,
+  const struct TALER_CoinSpendPublicKeyP *coin_pub,
+  struct TALER_DenominationPublicKey *denom_pub,
+  struct TALER_DenominationSignature *denom_sig)
+{
+  struct PostgresClosure *pg = cls;
+  struct GNUNET_PQ_QueryParam params[] = {
+    GNUNET_PQ_query_param_auto_from_type (coin_pub),
+    GNUNET_PQ_query_param_end
+  };
+  struct GNUNET_PQ_ResultSpec rs[] = {
+    TALER_PQ_result_spec_denom_pub ("denom_pub",
+                                    denom_pub),
+    TALER_PQ_result_spec_denom_sig ("denom_sig",
+                                    denom_sig),
+    GNUNET_PQ_result_spec_end
+  };
+
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Getting denomination and signature for (potentially) known coin %s\n",
+              TALER_B2S (coin_pub));
+  PREPARE (pg,
+           "get_signature_for_known_coin",
+           "SELECT"
+           " denominations.denom_pub"
+           ",denom_sig"
+           " FROM known_coins"
+           " JOIN denominations USING (denominations_serial)"
+           " WHERE coin_pub=$1;");
+  return GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
+                                                   "get_signature_for_known_coin",
+                                                   params,
+                                                   rs);
+}
diff --git a/src/exchangedb/pg_get_signature_for_known_coin.h b/src/exchangedb/pg_get_signature_for_known_coin.h
new file mode 100644
index 000000000..ec389176b
--- /dev/null
+++ b/src/exchangedb/pg_get_signature_for_known_coin.h
@@ -0,0 +1,43 @@
+/*
+   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 exchangedb/pg_get_signature_for_known_coin.h
+ * @brief implementation of the get_signature_for_known_coin function for Postgres
+ * @author Özgür Kesim
+ */
+#ifndef PG_GET_SIGNATURE_FOR_KNOWN_COIN_H
+#define PG_GET_SIGNATURE_FOR_KNOWN_COIN_H
+
+#include "taler_util.h"
+#include "taler_json_lib.h"
+#include "taler_exchangedb_plugin.h"
+/**
+ * Retrieve the denomination and the corresponding signature for a known coin.
+ *
+ * @param cls the plugin closure
+ * @param coin_pub the public key of the coin to search for
+ * @param[out] denom_pub the denomination of the public key, if coin was present
+ * @param[out] denom_sig the signature with the denomination key of the coin, if coin was present
+ * @return transaction status code
+ */
+enum GNUNET_DB_QueryStatus
+TEH_PG_get_signature_for_known_coin (
+  void *cls,
+  const struct TALER_CoinSpendPublicKeyP *coin_pub,
+  struct TALER_DenominationPublicKey *denom_pub,
+  struct TALER_DenominationSignature *denom_sig);
+
+#endif
diff --git a/src/exchangedb/plugin_exchangedb_postgres.c b/src/exchangedb/plugin_exchangedb_postgres.c
index 51dbea659..7d9044a1e 100644
--- a/src/exchangedb/plugin_exchangedb_postgres.c
+++ b/src/exchangedb/plugin_exchangedb_postgres.c
@@ -130,6 +130,7 @@
 #include "pg_count_known_coins.h"
 #include "pg_ensure_coin_known.h"
 #include "pg_get_known_coin.h"
+#include "pg_get_signature_for_known_coin.h"
 #include "pg_get_coin_denomination.h"
 #include "pg_have_deposit2.h"
 #include "pg_aggregate.h"
@@ -232,14 +233,14 @@
  * @param conn SQL connection that was used
  */
 #define BREAK_DB_ERR(result,conn) do {                                  \
-    GNUNET_break (0);                                                   \
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,                                \
-                "Database failure: %s/%s/%s/%s/%s",                     \
-                PQresultErrorField (result, PG_DIAG_MESSAGE_PRIMARY),   \
-                PQresultErrorField (result, PG_DIAG_MESSAGE_DETAIL),    \
-                PQresultErrorMessage (result),                          \
-                PQresStatus (PQresultStatus (result)),                  \
-                PQerrorMessage (conn));                                 \
+          GNUNET_break (0);                                                   \
+          GNUNET_log (GNUNET_ERROR_TYPE_ERROR,                                \
+                      "Database failure: %s/%s/%s/%s/%s",                     \
+                      PQresultErrorField (result, PG_DIAG_MESSAGE_PRIMARY),   \
+                      PQresultErrorField (result, PG_DIAG_MESSAGE_DETAIL),    \
+                      PQresultErrorMessage (result),                          \
+                      PQresStatus (PQresultStatus (result)),                  \
+                      PQerrorMessage (conn));                                 \
 } while (0)
 
 
@@ -601,6 +602,8 @@ libtaler_plugin_exchangedb_postgres_init (void *cls)
     = &TEH_PG_ensure_coin_known;
   plugin->get_known_coin
     = &TEH_PG_get_known_coin;
+  plugin->get_signature_for_known_coin
+    = &TEH_PG_get_signature_for_known_coin;
   plugin->get_coin_denomination
     = &TEH_PG_get_coin_denomination;
   plugin->have_deposit2
diff --git a/src/include/taler_exchangedb_plugin.h b/src/include/taler_exchangedb_plugin.h
index 596764b1c..25d3b17f9 100644
--- a/src/include/taler_exchangedb_plugin.h
+++ b/src/include/taler_exchangedb_plugin.h
@@ -4358,7 +4358,8 @@ struct TALER_EXCHANGEDB_Plugin
    * Retrieve information about the given @a coin from the database.
    *
    * @param cls database connection plugin state
-   * @param coin the coin that must be made known
+   * @param coin_pub the coin that must be made known
+   * @param[out] coin_info detailed information about the coin
    * @return database transaction status, non-negative on success
    */
   enum GNUNET_DB_QueryStatus
@@ -4366,6 +4367,21 @@ struct TALER_EXCHANGEDB_Plugin
                       const struct TALER_CoinSpendPublicKeyP *coin_pub,
                       struct TALER_CoinPublicInfo *coin_info);
 
+  /**
+   * Retrieve the signature and corresponding denomination for a given @a coin
+   * from the database
+   *
+   * @param cls database connection plugin state
+   * @param coin_pub the public key of the coin we search for
+   * @param[out] denom_pub the public key of the denomination that the coin was signed with
+   * @param[out] denom_sig the signature with the denomination's private key over the coin_pub
+   */
+  enum GNUNET_DB_QueryStatus
+    (*get_signature_for_known_coin) (
+    void *cls,
+    const struct TALER_CoinSpendPublicKeyP *coin_pub,
+    struct TALER_DenominationPublicKey *denom_pub,
+    struct TALER_DenominationSignature *denom_sig);
 
   /**
    * Retrieve the denomination of a known coin.