track double spending in the txpool

Transactions in the txpool are marked when another transaction
is seen double spending one or more of its inputs.
This is then exposed wherever appropriate.

Note that being marked with this "double spend seen" flag does
NOT mean this transaction IS a double spend and will never be
mined: it just means that the network has seen at least another
transaction spending at least one of the same inputs, so care
should be taken to wait for a few confirmations before acting
upon that transaction (ie, mostly of use for merchants wanting
to accept unconfirmed transactions).

1 files changed, 9 insertions, 1 deletions

diff --git a/src/cryptonote_core/tx_pool.h b/src/cryptonote_core/tx_pool.h
index 3e4ccb338..8a0106638 100644
--- a/src/cryptonote_core/tx_pool.h
+++ b/src/cryptonote_core/tx_pool.h
@@ -137,10 +137,11 @@ namespace cryptonote
      * @param fee the transaction fee
      * @param relayed return-by-reference was transaction relayed to us by the network?
      * @param do_not_relay return-by-reference is transaction not to be relayed to the network?
+     * @param double_spend_seen return-by-reference was a double spend seen for that transaction?
      *
      * @return true unless the transaction cannot be found in the pool
      */
-    bool take_tx(const crypto::hash &id, transaction &tx, size_t& blob_size, uint64_t& fee, bool &relayed, bool &do_not_relay);
+    bool take_tx(const crypto::hash &id, transaction &tx, size_t& blob_size, uint64_t& fee, bool &relayed, bool &do_not_relay, bool &double_spend_seen);
 
     /**
      * @brief checks if the pool has a transaction with the given hash
@@ -391,6 +392,8 @@ namespace cryptonote
       time_t last_relayed_time;  //!< the last time the transaction was relayed to the network
       bool relayed;  //!< whether or not the transaction has been relayed to the network
       bool do_not_relay; //!< to avoid relay this transaction to the network
+
+      bool double_spend_seen; //!< true iff another tx was seen double spending this one
     };
 
   private:
@@ -478,6 +481,11 @@ namespace cryptonote
      */
     bool is_transaction_ready_to_go(txpool_tx_meta_t& txd, transaction &tx) const;
 
+    /**
+     * @brief mark all transactions double spending the one passed
+     */
+    void mark_double_spend(const transaction &tx);
+
     //TODO: confirm the below comments and investigate whether or not this
     //      is the desired behavior
     //! map key images to transactions which spent them